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LOCAL REGULATION OF INTESTINAL BLOOD FLOW

DURING DIGESTION

BY

Siu PO Sit

A DISSERTATION

Submitted to
Michigan State University
in partial fulfillment of the requirements
for the degree of

DOCTOR OF PHILOSOPHY

Department of Physiology

1980

ABSTRACT

LOCAL REGULATION OF INTESTINAL BLOOD FLOW
DURING DIGESTION

BY

Siu Po Sit

In order to examine the relationship between post-
prandial intestinal hyperemia and the increase in local
metabolism, various constituents of chyme were placed in
the canine small intestine and their effects on venous
outflow and oxygen consumption were monitored.

The results indicate that in the jejunum, digested
food plus bile has a greater hyperemic and metabolic effect
than digested food alone or undigested food plus bile.
While both digested food and undigested food plus bile
increased flow, only the former increased oxygen consump—
tion. Bile in the jejunum did not.have any effect on blood
flow or oxidative metabolism. Bile in the ileum increased
flow but not oxygen consumption. There was a significant
correlation between the changes in blood flow and oxygen
consumption during the placement of digested food.

Although digested food plus bile produced a greater
increase in both blood flow and oxygen consumption, there

was no significant correlation between the changes in these

Siu Po Sit

two variables. These findings indicate that postprandial
intestinal hyperemia may involve both metabolically and
nonmetabolically linked factors. The food solutions used
in the above study contained many nutrients and each of
them may have different mechanisms in causing an increase
in flow. Thus, in subsequent experiments, the mechanisms
by which a major nutrient, glucose, causes an increase in
blood flow in the intestine were examined.

In the first two series of experiments, the vas-
cular and metabolic effects as well as absorption rates of
glucose, 3-0-methyl glucose and 2-deoxy glucose were com-
pared because they have different absorptive and metabolic
characteristics in the small intestine. The results show
that glucose and 3-O-methyl glucose are absorbed and
increase blood flow. 2-deoxy glucose was not absorbed
and did not increase flow. Thus, absorption of glucose
may play a role in the glucose-induced hyperemia. Of the
three glucoses, only glucose increased oxygen consumption
and its hyperemic effect was significantly greater than
3-0-methyl glucose. This suggests that an increase in
oxidative metabolism may play a role in the hyperemia.
Bile did not alter jejunal blood flow when placed into the
lumen but it markedly enhanced the hyperemic effect of
glucose and not 3-0-methyl glucose or 2-deoxy glucose.
This indicates that the influence of bile on the glucose-

induced hyperemia has chemical structural specificity.

Siu Po Sit

In the third series of experiments, the effects of
luminal placement of glucose and glucose plus bile on blood
flow, glucose absorption and oxygen consumption were com-
pared in the proximal jejunum.

During the placement of glucose, there was a sig-
nificant correlation between the changes in blood flow and
oxygen consumption as well as blood flow and glucose absorp—
tion. However, the addition of bile into the glucose solu-
tion altered the relationship between the changes in blood
flow and oxygen consumption. The changes in these vari-
ables were no longer significantly correlated during the
placement of glucose plus bile. In contrast, the relation-
ship between the changes in blood flow and glucose absorp-
tion remained the same and was significantly correlated
with or without bile.

It is concluded that the local regulation of blood
flow during postprandial intestinal hyperemia may involve
metabolic and nonmetabolic factors. Various constituents
of chyme can elicit different responses in blood flow and
oxygen consumption in the small intestine. The hyperemic
effect of glucose in the jejunal lumen is, at least in
part, related to glucose absorption and an increase in
oxidative metabolism. Bile enhances both the hyperemic
as well as the metabolic effects of glucose and digested
food. Bile also alters the positive relationship between
the changes in blood flow and oxygen consumption produced

by glucose and digested food.

To Jean, Ling Ling, Kristofer
and
my parents
Whose unwavering support and

sacrifices made this possible

ii

ACKNOWLEDGMENTS

My sincere appreciation is extended to Dr. C. C.
Chou for his invaluable advice and support throughout the
course of this study. I would also like to express my
gratitude to Dr. Tai Akera, Dr. R. K. Ringer, Dr. J. B.
Scott and Dr. L. F. Wolterink for their services on the
advisory committee.

I am greatly indebted to my fellow students, the
staff and the faculty in the Department of Physiology
for without whose assistance and much needed advice this

study would never have been possible.

iii

TABLE OF CONTENTS

LIST OF FIGURES . . . . . . . . . . . . . .
CHAPTER

I. INTRODUCTION . . . . . . . . . . .

II. LITERATURE REVIEW . . . . . . . . .

Splanchnic Circulation . . . .

Gastrointestinal Circulation .

Circulatory Adjustments to Food

Postprandial Intestinal Hyperemi

Neural Mechanisms . . . . .
Humoral Mechanisms . . . .

Intake
a . . .

Local Regulation of Intestinal Blood

Flow, Absorption and Oxidative
Metabolism . . . . . . . . .

III. METHODS . . . . . . . . . . . . . .

Surgical Procedures . . . . . .

Preparation of the Solutions Studied .

Food Solutions . . . . . .
Glucose Solutions . . . . .

Experimental Procedures . . .

Food Studies . . . . . . .
Glucose Studies . . . . . .

Series 1 . . . . . . .
Series 2 . . . . . . .
Series 3 . . . . . . .

Statistical Analysis of the Resu

iv

lts .

Page

vi

26
33

33
34

34
35

36

36
38

38
39

40

CHAPTER Page
IV. RESULTS . . . . . . . . . . . . . . . . . . . 42
Food Studies . . . . . . . . . . . . . . 42

Series 1 . . . . . . . . . . . . . . 42
Series 2 . . . . . . . . . . . . . . 56

Glucose Studies . . . . . . . . . . . . . 67

Series 1 . . . . . . . . . . . . . . 67

Series 2 . . . . . . . . . . . . . . 68

series 3 O O O O O O O O O O O O O O 76

V. DISCUSSION . . . . . . . . . . . . . . . . . 92

VI. SUMMARY AND CONCLUSIONS . . . . . . . . . . . 108
BIBLIOGRAPHY . . . . . . . . . . . . . . . . . . . . 112

APPENDIX . . . . . . . . . . . . . . . . . . . . . . 124

LIST OF FIGURES
Figure

1. Effects of luminal placement of digested
food alone on jejunal A-V O differ-
ence, blood flow, oxygen cogsumption
and luminal pressure . . . . . . . . . . .

2. Effects of luminal placement of digested
food plus bile on jejunal A-V O dif-
ference, blood flow, oxygen congumption
and luminal pressure . . . . . . . . . . . .

3. Effects of luminal placement of undigested
food plus bile on jejunal A-V O differ-
ence, blood flow, oxygen consumption and
luminal pressure . . . . . . . . . . . . .

4. Effects of luminal placement of bile on
jejunal A-V 0 difference, blood flow,
oxygen consumption and luminal pressure . . .

5. Effects of luminal placement of bile on
ileal A-V 0 difference, blood flow,
oxygen consumption and luminal pressure . . .

6. The temporal relationships between blood
flow, A-V 0 difference, oxygen con-
sumption, a rtic pressure and luminal
pressure during placement of digested
food alone in the jejunum . . . . . . .

7. Relationship between the percent changes
in blood flow and oxygen consumption
during placement of digested food in
the jejunum . . . . . . . . . . .

8. The temporal relationships between blood
flow, A-V 0 difference, oxygen con-
sumption, aortic pressure and luminal
pressure during placement of digested
food plus bile in the jejunum . . . . . .

vi

Page

44

47

50

52

54

58

6O

63

Figure

9.

10.

11.

12.

13.

14.

15.

16.

17.

18.

Relationship between the percent changes
in blood flow and oxygen consumption
during the placement of digested food
plus bile in the jejunum . . . . . . . . . .

Comparison of vascular effects of glucose
(G) and 3-O-methyl glucose (3-MG) with
or without bile, in double jejunal seg—
ments . . . . . . . . . . . . . . . . . . . .

Comparison of the vascular effects of
glucose (G) and 2-deoxy glucose (2-DG)
with or without bile, in the double
jejunal segments . . . . . . . . . . . . . .

Percent changes in blood flow and oxygen
consumption from precontrol after luminal
placement of glucose (G), 3-O-methyl
glucose (3-MG), 2-deoxy glucose (2-DG),
with bile, and bile alone . . . . . . . . . .

Effects of luminal placement of 200 mM
glucose in saline on jejunal blood flow,
A-V 0 difference, oxygen consumption,
glucose absorption, and luminal pressure .

Relationship between the percent changes
in blood flow and oxygen consumption
during the placement of 200 mM glucose
in saline in the jejunum . . . . . . . .

Relationship between the percent changes
in blood flow and the rates of glucose
absorption during the placement of 200
mM glucose in saline in the jejunum . . . . .

Effects of 200 mM glucose plus bile on
jejunal blood flow, A-V 0 difference,
oxygen consumption, glucose absorption,
and luminal pressure . . . . . . . . . . .

Relationship between the percent changes
in blood flow and oxygen consumption
during the placement of 200 mM glucose
plus bile in the jejunum . . . . . .

Relationship between the percent changes
in blood flow and glucose absorption
during the placement of 200 mM glucose
plus bile in the jejunum . . . . .

vii

Page

65

7O

72

74

78

81

83

85

87

9O

CHAPTER I

INTRODUCTION

Postprandial intestinal hyperemia is characterized
by an increase in blood flow through the digestive organs
with little or no change in flow to other vascular beds
(25, 120-122). Recently it has been demonstrated that
the intestinal hyperemia is a local phenomenon and is con-
fined only to that region of the small intestine which is
exposed to food (25). In addition, it was observed that
the constituents of chyme responsible for the hyperemia
were the digested products of food (26). The mechanisms
by which these digested products cause an increase in local
blood flow however, are still not clear.

Many studies have shown that the hemodynamic changes
after a meal are associated with an enhancement of splanch-
nic oxidative metabolism (29, 30). In addition, the pres-
ence of various digested products in the gut lumen have
been shown to increase both blood flow and oxygen consump-
tion of the small intestine (118, 119). The results from
these studies have led to a hypothesis suggesting that the
local regulation of postprandial intestinal hyperemia is

linked to the heightened metabolic activities during

digestion and absorption (34, 118). However, unlike the
heart or the skeletal muscle where many classical studies
have been performed to evaluate the relationship between
the rate of oxidative metabolism and functional hyperemia
(69), there is virtually no similar study performed on the
small intestine during digestion and absorption. Thus the
purpose of this study was to examine the relationship
between the intestinal hyperemia and the increase in oxi-
dative metabolism during digestion. In addition, the study
also examined the relationships between blood flow, oxida-
tive metabolism and glucose absorption during glucose

induced intestinal hyperemia.

CHAPTER II

LITERATURE REVIEW

Splanchnic Circulation

 

The Splanchnic viscera receives up to 28% of the
total cardiac output. This constitutes a greater share
than any other organ in the body. The stomach, pancreas,
duodenum, and gallbladder receive a supply of blood from
the celiac artery; while the inferior mesenteric artery
supplies blood to the transverse, descending, and pelvic
colon as well as the rectum. In addition, the superior
mesenteric artery supplies blood to the pancreas, duodenum,
small intestine, cecum, ascending colon, and transverse
colon. In contrast to the rest of the organs in the body,
venous outflow from the stomach, small and large intestine,
pancreas, and spleen is not drained by the central venous
system. Rather it is drained by the portal vein which,
together with the hepatic artery, supplies blood to the
liver. This review will focus on the mesenteric circula-
tion and its relationship with some of the functions of

the intestine that are pertinent to this study.

Gastrointestinal Circulation

 

Blood supply to the gastrointestinal tract is best
characterized by its complex system of vascular arcades.
These extend even into the intramural layers of the intes-
tine as well as the stomach (82, 113, 115). In 1958, Grim
and Lindseth (51) using 24Na-labeled glass microspheres
first described the flow distribution in the wall of the
small intestine. They suggested that the supply of blood
to the three layers (mucosa, submucosa and muscularis) of
the intestine may be separate entities in parallel to each
other. However, it has become increasingly clear that the
mucosa-submucosa layers are coupled in series and, as a
whole, are in parallel with the muscularis layer (82, 113).
The bulk of evidence (9, 25, 47, 51, 73, 82, 113, 126) thus
far indicates that the mucosa-submucosa receives a major
portion (82 to 88%) of total wall flow as compared with
the muscularis layer (12 to 18%). In addition, blood flow
to these two layers as expressed by volume per unit weight
of tissue, is much greater than the muscularis (9, 25, 47,
51, 73, 82, 113, 126). Svanvik and Lundgren (113) attrib-
uted this phenomenon to the higher metabolic demands of
these two layers due to active transport as well as secre-
tion.

While the distribution of flow to the intramural
layers has been well recognized, the blood supply to the
intestinal villus has, until recently, been controversial

(6, 8, 12, 64, 65, 82, 86, 87, 111, 113). Levitt and Levitt

(86) first proposed that there are two sets of blood ves-
sels within the villus possessing distinct anatomical and
functional characteristics. One set of these blood sup—
plies runs close to the tip of the villus while the other
is at the crypt or the submucosa. They cited as evidence
that there seemed to be two distinct components in the
absorptive patterns of various substances, one being flow
dependent while the other diffusion dependent. As such,
materials entering the villus could be readily carried away
by the circulation close to the tip and thus the rate was
directly proportional to blood flow. Substances that
entered the crypt or submucosa circulation were limited
by the longer distance between the lumen and the vessels
and thus were diffusion dependent. This is in contrast
to the hypothesis of Lundgren et al. (64, 65, 87, 111) and
Jacobson and Noer (62). They suggested that each villus
is supplied by a single arterial vessel (around 20 um in
diameter) emerging from the submucosa. It runs "in the
central core without branching" and the direction of flow
is opposite to the venous vessel draining the villus (64,
65, 87, 111). These vessels are about 15 to 20 u apart
and appear to be permeable to a variety of substances,
especially those that are lipid-soluble.

An obvious implication of this anatomical arrange-
ment is the possibility of a countercurrent exchanger
mechanism analogous to the one observed in the kidney.

Thus, materials (especially those that are lipid-soluble)

absorbed from the lumen of the gut should be trapped at

the tip of villus since what entered the capillaries and
vein could diffuse back into the arterial vessel. On the
other hand, blood borne, diffusable materials could be
accumulated at the base of the villus due to shunting of
the substances among the two vessels. This has been proven
to be the case (6, 8, 64, 65). For example, Jodal and Lund-
gren (64, 65) observed that during absorption there was

a tip to base concentration gradient of 5:1 for the lipid
soluble palmitic acid and only a 2:1 concentration gradient
for the water soluble short chain butyric acid. Jodal and
Lundgren (63) have also demonstrated that during intestinal
absorption of sodium chloride, there was a four-fold tip

to base gradient in the villus with the interstitial fluid
osmolality reaching 1,200 mOsm/kg at the tip. Regarding
the second possibility, Kemp et a1. (74) has shown that
there was indeed extravascular shunting of oxygen from the
arterial to the venous vessel, resulting in a gradient of
the gas from the base to the tip of the villus. It has
also been observed (1, 74) that this shunting of oxygen

was more pronounced during hypovolumic shock, due to a pro-
longed transit time of blood in the villus as would have
been predicted by the countercurrent exchanger model. It
is apparent that the dual circulation hypothesis proposed
by Levitt and Levitt (86) can not explain the osmotic gradi-
ent as observed by so many investigators (6, 8, 63, 64,

74). However, the countercurrent exchanger mechanism theory

is not without its share of criticisms (ll, 85). As sug-
gested by Levitt et a1. (85), diffusion of lipid-soluble
materials from the lumen to the artery in the villus would
effectively destroy the concentration gradient between the
two vessels and render the exchanger theory inoperative.
In addition, these investigators (11, 85) failed to find
any evidence that may indicate there was a delay in the
luminal absorption of diffusable gases in the rabbit small
intestine as observed earlier in cats (85). However, in

a recent finding this same group (12) did find a signifi-
cant delay in the absorption of these gases in dogs and
they conceded that there may be a species difference in
the efficiency of the countercurrent exchanger mechanism.
Although it now appears that the countercurrent exchanger
theory of the villus is gaining acceptance, definite proof
of its existence is still lacking and further testing is
necessary (113).

Capillary perfusion in the intestinal vascular bed
is mainly determined by the arterioles and precapillary
sphincters (69, 82, 113). It has been observed that at
rest, only about 20 to 40% of the capillaries in the villi
are opened for perfusion (69, 113). The arterioles and
precapillary sphincters are arranged in series and con-
trolled by both extrinsic and intrinsic mechanisms (113).
Since there is no known parasympathetic vasodilator outflow
to the mesenteric bed, it is believed that the sympathetic

vasoconstrictor fibers, circulating hormones and gases

constitute the major extrinsic controlling mechanisms of
blood flow in this area (82). In contrast, the local con-
trolling factors of blood flow to the intestine have not
been identified (69, 82, 113). There is no doubt that the
intestine is capable of autoregulation and autoregulatory
escape as demonstrated so convincingly by P. C. Johnson

et a1. (67, 68, 69) as well as Folkow et a1. (38, 39).

The precise mechanism(s) for this phenomenon however,
remains elusive. Two major functions of the intestine are
the digestion and absorption of nutrients (30). Since food
intake is known to increase gut blood flow, postprandial
intestinal hyperemia has been "loosely" referred to as a
functional hyperemia of the mesenteric bed (46). The rest
of this review will be devoted to examining the control

of blood flow during this mesenteric hyperemia.

Circulatory Adjustments to Food Intake

The cardiovascular responses of the body to food
intake have long been a subject of interest to many inves-
tigators. Grollman (52) as well as Gladstone (44) studied
the effect of eating on cardiac output of human subjects
and found it increased after food ingestion. Herrick et
a1. (56) found in dogs that blood flow through the femoral,
carotid and superior mesenteric arteries increased follow-
ing a meal. Dagenais et a1. (29) studied the demodynamic
effects of carbohydrate and protein meals in man. A pro-

tein rich meal brought a greater increment of cardiac output

than did a carbohydrate rich diet. Brandt and associates
(14) found in humans that protein feeding induced a 35%
increase in splanchnic blood flow while glucose feeding
did not elicit any response.

With the advent of research in chronic conscious
animals, the ability to study the hemodynamic responses
of the body to food intake in intact, awake animals became
possible. Fronek and Stahlgren (43) performed feeding
experiments on conscious dogs with implanted electromagnetic
flow transducers around the ascending aorta, brachio-
cephalic, superior mesenteric and iliac arteries. During
the anticipation and ingestion periods, cardiac output was
observed to increase by 142% with a concomitant rise in
both blood pressure and heart rate. The changes in these
parameters reached a maximum in the first minute after the
beginning of ingestion and gradually declined back to con-
trol level 1 hour after feeding. Total peripheral resis-
tance tended to drop during anticipation of food but
increased modestly (5%) during ingestion. This slight
increase persisted even after the completion of food
intake. Brachiocephalic flow increased during ingestion
by 196% while the iliac flow dropped to 75.4% of control
level. Although there was a slight increase in superior
mesenteric blood flow at this time, mesenteric regional
resistance was found to increase by 28%. The authors sug-
gested that there was a general sympathetic response to

anticipation and actual ingestion of food. During

10

digestion (l and 3 hours after ingestion), blood pressure,
cardiac output, heart rate and total peripheral resistance
were not significantly different from respective Control
values. Superior mesenteric blood flow increased by as
much as 133% of control while the brachiocephalic and iliac
arterial flows decreased to 86.5% and 74% of control,
respectively. The authors concluded that there seemed to
be a redistribution of cardiac output to the splanchnic
bed during digestion. Indeed the ratio of flow in the
superior mesenteric artery to cardiac output was found to
have increased from 9% at control to 13% three hours after
food intake.

Since the introduction of the redistribution hypoth-
esis by Fronek and Stahlgren (43), many new studies have
been performed to investigate this phenomenon. Burns and
Schenk (16) in 1969 measured cardiac output and blood flow
through the superior mesenteric artery of conscious dogs
following a meal. Electromagnetic flow meters were planted
on the ascending aorta and the superior mesenteric artery
to monitor blood flow. After consuming a standard meal
of 15 oz. of horsemeat, mesenteric blood flow began to rise
within 5 minutes and reached a plateau approximately 50
minutes later. The mean flow was still 50% above the con-
trol level 3 hours after feeding. Although there were
occasional changes in cardiac output during ingestion, no
detectable increment was observed during digestion. Vatner

et al. (121) found in conscious dogs that anticipation and

11

ingestion of a meal caused increases in cardiac output,
heart rate and aortic blood pressure. These parameters
returned to the control level within 10 to 30 minutes after
food presentation and remained stable throughout the diges-
tive period. Although mesenteric blood flow decreased
(10%) transiently during anticipation, it began to increase
during actual ingestion and reached maximal values (115% to
300% of control) within an hour. The increase in blood
flow to the viscera has been reported to last up to 7 hours
postprandially. The same group of investigators (120)
found in a subsequent study that in addition to the above
mentioned vascular changes, renal resistance increased by
24%, iliac and coronary resistances decreased by 33% and
62% respectively during the anticipation and ingestion
period. During digestion, the increase in mesenteric flow
was accompanied by a slight decrease (10%) in iliac flow
while cardiac output, heart rate, renal and coronary vas-
cular resistances returned to their control levels. This
suggested that there was vasoconstriction in the skin and
skeletal muscle to compensate for the increase in flow to
the mesenteric vascular bed during digestion.

In 1974, Vatner et al. (122) studied the regional
circulatory adjustments to eating and digestion in con-
scious primates. During ingestion of a meal consisting
of different fruits, baboons experienced an increase in
both heart rate (82%) and atrial pressure (25%). Likewise,

iliac and coronary flows were observed to increase by 84%

12

and 152% respectively. There was a transient but signifi-
cant decrease in both mesenteric (12%) and renal (4%) blood
flow during this time. During digestion, mesenteric blood
flow rose and reached a maximum in an hour. This increase
in flow was reported to last up to 4 hours and was accom-
panied by a significant decrease in iliac flow (31%).
Heart rate, arterial pressure, coronary and renal blood
flow remained at control levels throughout digestion.

These recent studies have therefore shown that
although cardiac output, heart rate and systemic pressure
increase during the anticipation and ingestion of food,
the changes are transient and decline to control levels
30 minutes after ingestion (16, 43, 120, 121, 122).
Mesenteric blood flow begins to increase from 5 to 30 min-
utes after completion of food intake and the hyperemia may
last up to 7 hours. This increase in mesenteric blood flow
during digestion is accompanied by increased resistance
in the brachiocephalic and iliac arteries (43, 120, 122).
There is a postprandial redistribution of cardiac output
favoring the mesenteric vascular bed at the expense of the
muscle and skin.

These studies, however, have not determined the
specific localization of the hyperemia within the mesen-

teric circulation.

13

Postprandial Intestinal Hyperemia

 

Fara et a1. (34) observed that intraduodenal instilla-

tion of corn oil in cats caused increases of blood flow

through the superior mesenteric, pancreatic and jejunal
arteries while flow through the stomach and colon were

not altered. Chou et a1. (25) found in anesthetized dogs
that the hyperemia through the various organs within the
gastrointestinal tract seemed to follow the pattern of
chyme movement. The flow through the celiac artery was
observed to increase when food was introduced into the
stomach but did not change when instilled into the
duodenum. Superior mesenteric blood flow on the other
hand, fell transiently but not significantly during intra-
gastric placement of food; started to rise 30 minutes after
the placement and remained increased for 3 hours. This

was significant since the celiac artery supplies the stomach
whereas the superior mesenteric artery supplies the small
intestine. These findings were interpreted to indicate
that blood flow may increase only in that region exposed

to food and not indiscriminantly throughout the gastro-
intestinal tract.

This possibility was further explored by these
investigators when they infused food intraduodenally. In
addition to monitoring the superior mesenteric arterial
flow, they measured venous outflow from an isolated in
sitg jejunal segment. As before, superior mesenteric blood

flow was found to increase during the intraduodenal food

14

infusion but venous outflow from the isolated jejunal seg-
ment which had no contact with food was not altered. When
the same food was placed only into the isolated jejunal
segment, the blood flow through the segment increased but
that through the superior mesenteric artery did not. Sub-
sequently venous outflows from two isolated adjacent in gigg
jejunal segments were measured simultaneously; one segment
contained 10 m1 of food and the other, the same amount of
saline. The segment with food increased its flow while

no change was observed in the control segment with saline.
These findings suggested that the intestinal hyperemia that
occurs during digestion was a local phenomenon. Radio-
active microspheres were also used by these authors (25)

to study the compartmental blood flow in the jejunum.

Three isolated in situ jejunal segments were used, one was
left empty and the other two contained either 10 m1 of non-
absorbable polyethylene glycol solution or the same amount
of food. It was found that only the segment containing
food showed an increase in blood flow. The increase in

the total wall flow was the result of an increase in mucosal-
submucosal flow; while flow to the muscularis was not
altered. Yu et al. (126) in a similar study using radio-
active microspheres observed that placement of 50% glucose
solution in an isolated jejunal segment in dogs induced

an increase in blood flow in the mucosa-submucosa but did
not affect flow to the muscularis. Thus the increase in

the superior mesenteric blood flow during digestion may

15

well be due to an increased flow to that segment of the
small intestine that contains chyme. Furthermore, the
increased flow appears to be localized to the mucosal-
submucosal layer of the intestinal wall (25, 126).
Although some information has surfaced in recent
years concerning the mechanisms involving the cardiovas-
cular responses to food intake, the overall picture is not
entirely clear. Opinions are not always unanimous as to
what mediates the local intestinal hyperemia during diges-
tion. Nor is there any concensus as to what initiates the
increase in flow to the part of the intestine that is in
contact with food. Nonetheless, investigations have been
done to elucidate the mechanisms of the postprandial
responses. Among the mediators that have been implicated
are: (1) local neural pathways and (2) various humoral sub-
stances that are released into the blood stream during

digestion.

Neural Mechanisms

 

There are two major intrinsic nerve plexuses within
the gastrointestinal tract: the submucosal plexus of Meiss-
ner and the myenteric plexus of Auerbach. The former is
situated between the muscularis mucosa and the circular
muscles of the intestinal wall. The latter plexus is
located between the longitudinal and circular muscle coats.
The sensory endings of the visceral afferent fibers are

dendrites from the submucosal plexus that may be situated

16

in the mucosal epithelium, in the muscle layers or in the
plexuses. They are chemical and mechanical receptors that
are activated by changes in the intestinal contents (pep-
tides, amino acids, fats, pH and osmolality) and by stretch
and distention of the gut wall (30, 97, 115). The afferent
impulses may be conducted centrally via the vagal and sym-
pathetic fibers or be transmitted locally via the submucosal
plexus to the myenteric plexus (30, 97, 115).

Zamiatina (127) found that the presence of food
or its digestive products in the lumen of the gut can stimu-
late the receptors in the intestinal wall. During diges-
tion in cats that were fed meat, especially high neural
activity was seen from the afferent nerves of the jejunum,
mesentery and pancreas but not of the colon. This is also
true with glucose and amino acid solutions infused into
the gut. Glucose (4 to 10%) solutions have a stimulating
effect on the upper part of the jejunum whereas amino acid
mixtures intensify the neural activities in the jejunum,
mesentery and pancreas. In a similar experiment Sharma
and Nasset (102) have also been able to demonstrate that
when glucose and amino acid solutions were perfused through
the lumen of the small intestine, the frequency of firing
from mesenteric nerves increased by as much as 400% from
control.

Fronek and Stahlgren (43) characterized the
increases in heart rate, blood pressure and cardiac output

during anticipation and ingestion of food as a generalized

17

sympathetic response. They cited as evidence the findings
of Ehrlich et a1. (32) that there was no increase in mean
arterial blood pressure during ingestion in catecholamine-
depleted dogs.

The roles played by the autonomic nervous system
during anticipation, ingestion and digestion of food were
examined in detail by Vatner et al. (121). The effects
of food presentation, actual ingestion and digestion on
cardiac output, heart rate, aortic pressure and mesenteric
blood flow before and after adrenergic and cholinergic
blockade in conscious dogs were investigated. Alpha and
beta adrenergic blockade by phenoxybenzamine and propranolol
attenuated the increases in heart rate, blood pressure and
mesenteric resistance during the anticipation and ingestion
periods. No effect was observed on the mesenteric hyperemia
during the digestion period. Cholinergic blockade prevented
the mesenteric vasodilation during digestion but bilateral
thoracic vagotomy had no effect on the response. Fara et
a1. (34) also observed in cats that atropine blocked the
increase in superior mesenteric blood flow seen after the
intraduodenal instillation of milk, corn oil (fat),
L-phenylalanine or hydrochloric acid. Bilateral
splanchnicectomy or combined alpha and beta adrenergic
blockades have no effect on the vasodilation. Vatner et
al. (122) have shown in primates that the mesenteric vaso-

dilation could be attenuated by prior cholinergic blockage

18

with atropine. Again the blockade had no effect on the
vascular responses seen in the early ingestion phase of
a meal.

Thus, these findings seem to suggest that the sym-
pathetic nervous system is involved in the anticipation
and ingestion responses to food. The fact that bilateral
thoracic vagotomy had no effect on the postprandial vas-
cular response indicates that cholinergic influence is at
the local level; most likely involving the intramural nerve
plexus.

Chen et al. (20) have demonstrated that dibucaine
can attenuate the vascular effects of intraluminally placed
hypertonic salt solutions. Before applying the local anes—
thetic, 1500 mOsm of NaCl, KCl, MgCl2 or CaCl2 salt solu-
tions all increased blood flow in an in EEEE jejunal loop.
However, after the mucosa of the segment had been exposed
to dibucaine, only MgCl2 increased blood flow. Other solu-
tions either lowered blood flow or had no effect on the
jejunal vasculature. Chou et a1. (21) showed that
dibucaine can also attenuate the increase in blood flow
evoked by a hypertonic glucose solution in the lumen of
the gut. Yu et al. (126) observed that the inhibitory
effect of the local anaesthetic on the vasocilation is
limited to the mucosal layer of the luminal wall. They
observed that dibucaine attenuated the mucosal hyperemic

response to hypertonic glucose solution in the lumen.

19

Blood flow to the other two layers was not affected by the
anaesthetic.

As discussed above, the cardiovascular responses
seen during the anticipation and ingestion of food may in
part, be mediated by the sympathetic fibers. Local
cholinergic plexuses have been suggested to play a role
in mediating the mesenteric hyperemia during digestion.
Precisely what neural mechanisms are involved in the vas-
cular adjustments during digestion is not clear. It is
possible that receptors on the mucosa continuously monitor
the content of the chyme and provide vital information for
a local reflex arc during the presence of food in the lumen.
In turn, the intraluminal cholinergic plexus may either
act on the blood vessels or release local vasoactive agents

to produce the vascular responses to food intake.

Humoral Mechanisms

 

Among the many substances that are released into
the blood stream during digestion are the GI hormones. The
specific actions of these hormones, i.e., gastrin, secretin
and cholecystokinin (CCK) on secretion, absorption, motility
and metabolism of the gastrointestinal tract have long been
under intense scrutiny. It was not until recently that
attention has been given to their possible vascular effects.
All three of these hormones are released from the upper
gastrointestinal tract during digestion. They have been

shown to have specific vascular effects on different organs.

20

The antrum of the stomach is the main source of
gastrin. The release of the hormone can be stimulated by
vagal stimulation, gastric distention or various chemicals
(e.g., meat extracts, amino acids, histamine and alcohol)
in the stomach. Inhibition of the release of the hormone
occurs when the antral pH drops below 3.5 (66).

Chou et a1. (22) observed in dogs that infusions
of gastrin extracted from porcine antrum into the superior
mesenteric artery decrease the resistance of the intestine
by 10% to 12%. Laureta et a1. (83) found local intra-
arterial infusion of the hormone to have a similar effect
on the canine stomach. It was concluded that gastrin may
very well be vasoactive in both the gastric and mesenteric
vascular beds. Swan and Jacobson (114) on the other hand,
found that gastrin had no effect on the total blood flow
to a gastric pouch but did increase its mucosal blood flow.
The effects of subcutaneous injection of gastrin extracted
from porcine antrum were examined by Burns and Schenk in
dogs (16). Injection of the extract subcutaneously
increased mesenteric blood flow within 5 minutes, flow
reached a peak (45% above control) in l to 2 hours and
remained elevated for up to 3 hours. In addition to its
effects on the gastric and mesenteric vasculature, gastrin
has also been shown to increase pancreatic secretion and
blood flow (45) as well as decrease hepatic vascular resis-
tance (91). Whether the hormone has a direct influence

on the blood vessels or acts indirectly through the release

21

of intermediary agents is still not clear. Fasth et a1.
(36) observed in cat small intestine that atropine can
attenuate the increase in intestinal motility but not the
increase in blood flow induced by the intra-arterial infu-
sion of gastrin. Bowen et a1. (13) recently found that
cholinergic blockade by atropine abolished the vasodilat-
ing effect of pentagastrin in the canine distal ileum.
Thus, depending on the species, the hormone's actions on
both motility and blood flow may well be mediated through
cholinergic receptors.

Secretin was first isolated by Mutt and Jorpes
(89) and synthesized by Bodansky et a1. (7). It is
believed that secretin is produced by villus epithelial
cells in the duodenum (30, 66). Hydrogen ions in the duod-
enum are the most effective stimulant for the release of
the hormone. Intraduodenal installation of fatty acids
and amino acids have also been shown to cause the release
of the peptide (66). Secretin is most effective in stimu-
lating the secretion of bicarbonate and fluid in the pan-
creas and pepsin in the stomach (30, 66, 95).

The vascular effects of secretin in the gastro-
intestinal vasculature have been studied in cats (34, 95),
dogs (13, 22, 45, 83) and humans (117). Chou et a1. (22)
and Laureta et a1. (83) did not observe any change in vas-
cular resistance when they infused the hormone intra-
arterially into the canine superior mesenteric artery and

the stomach. Goodhead et a1. (45) found that intravenous

22

infusion of secretin increases blood flow to the pancreas
and duodenum but does not affect blood flow to the other
parts of the alimentary tract. Recently Bowen et a1. (13)
observed in dogs that synthetic secretin administered intra-
arterially into a loop of distal ileum did not elicit any
response. Burns and Schenk (16) on the other hand, found

in dogs that intravenous injection of an impure extract

of secretin increased mesenteric blood flow within 5 minutes.
This increment reached a maximum (38% above control) in

2 hours. Ross (95) examined the effects of a natural secre-
tin extract on flow rates in the femoral, hepatic and
superior mesenteric arteries in cats. Rapid injection
decreased resistance in the superior mesenteric and femoral
arteries but not the hepatic artery. These changes were
accompanied by a prolonged increase in blood pressure.

Fara et a1. (34) observed that intravenous administration

of a pure, natural secretin into cats increased the superior
mesenteric, pancreatic and jejunal arterial blood flow.

Uden (117) observed in humans that secretin injection
increased mesenteric blood flow. Thus, substantial dis-
agreement exists as to the vascular effects of secretin

in the stomach and the small intestine. This may stem from
the fact that most studies were conducted with purified
secretin rather than the synthetic one. Naturally obtained
extracts of the hormone are known to contain various other
vasoactive substances such as CCK or plasma kinin. These

contaminants may have contributed to many of the

23

vasodilating effects of secretin. Only Bowen and associ-
ates (13) have used synthetic secretin in their studies.

Unfortunately, they did not examine the vascular effects

of the hormone in the entire gastrointestinal tract.

Ivy and Oldberg's cholecystokinin (CCK) (60) and
Harper and Raper's pancreozymin (55) have been proven to
be one single hormone (72). CCK is a strong stimulant of
gallbladder contraction and a weak stimulant of gastric
secretion. Presence of amino acids, fatty acids and hydro-
gen ions in the duodenum stimulates the release of the hor-
mone from the upper small intestine.

Fara et al. (35) was able to mimic the vascular
effects of intraduodenal fat by intravenous infusion of
CCK. In cats, infusion of the partially purified hormone
increased both superior mesenteric blood flow and duodenal
motility. It was postulated that CCK may be the mediator
of fat-induced vasodilation in the duodenum. Fasth et a1.
(36) found that local intra-arterial infusion of the hormone
into the cat's small intestine caused an immediate but short
lasting increase of blood flow. Both the vascular and
metabolic effects of CCK were examined by Fara et a1. (34)
in cats. CCK increased blood flow and O2 consumption in
the jejunum and pancreas. These effects were not blocked
by atropine or vagotomy. Bowen et a1. (13) however,
observed in the canine ileum that the increases in superior

mesenteric blood flow and 0 consumption after infusion

2
of CCK could be blocked by atropine. Route of infusion

24

and dosage of the hormone as well as Species difference
may account for the contrasting results.

Fara et a1. (34) suggested that the mesenteric
vasodilation caused by CCK may have been the consequence
of the release of local vasoactive substances triggered
by the hormone. Their in yitrg studies have shown that
CCK does not affect the active tension of a superior mesen-
teric arterial strip. Thus, it is unlikely that the hor-
mone has any direct effect on the mesenteric vasculature.
Biber et a1. (7) observed in cats that blocking the vas-
cular effects of 5-hydroxytryptamine (5-HT) by an a-receptor
antagonist (dihydroergotamine) can abolish the intestinal
vascular responses to CCK infusion. It was suggested that
5-HT, may be the intermediary vasoactive agent for the
mesenteric vasodilation elicited by CCK. Hilton and Jones
(58) perfused the cat's pancreas with CCK and found
increases in pancreatic blood flow and secretion. In addi-
tion, they observed that the activity of the active kinin-
forming enzyme "kallikrein" in the perfusate had increased
about fourfold. This led them to speculate that plasma
kinin may play a prominent role in the functional vasodila-
tion of the pancreas during CCK infusion.

In summary, all three gastrointestinal hormones
have been shown to be vasoactive in the gastrointestinal
vasculature. Infusion (both i.a. and i.v.) of gastrin in
dogs and cats produced vasodilation in the superior mesen-

teric, pancreatic and hepatic arterial blood flows (16,

25

22, 45, 83, 91). Whether this hormone acts directly or
through other vasoactive agents is not known. Findings
concerning the vascular effects of secretin are contro-
versial. There is conflicting evidence as to whether or
not the hormone is vasoactive in the small intestine (l3,
16, 22, 34, 83, 95). Its vasodilating effect on the pan-
creas however, has been well established (41, 45, 90, 117).
CCK is known to decrease vascular resistance in the small
intestine (7, 13, 22, 34, 35, 116), stomach (83), pancreas
(45, 58, 90) and in the portal vein (91, 116). It was sug-
gested that the hormone's action may be mediated by 5-
hydroxytryptamine (7) and kallikrein (58).

It must be emphasized that much of the vascular
effects of the hormones described above were obtained from
pharmacological doses. Thus, any extrapolation from these
data must be treated with caution. Chou et a1. (24)
recently found that of the 3 hormones, only CCK was able
to exert its vascular effects at physiological doses (2
to 8 u units/ml). This was compatible with the observation
by Fara et a1. (34) in cats that infusion of low doses of
CCK mimicked the vascular response induced by intraduodenal
fat. Furthermore, atropine, which prevents the release
of CCK (123), has been shown to prevent postprandial mesen-
teric vasodilation (34, 120, 122). What these findings
seem to suggest then, is that the mesenteric vasodilation
could be a consequence of the release of CCK. It is

unlikely, however, that CCK was the sole vasoactive agent

26

involved since mesenteric blood flow has been shown to
increase by as much as 300% of control postprandially (120,
122). The average increase of flow in the superior mesen-
teric artery after CCK infusion (even at pharmacological
doses) is less than 100% (7, 13, 34).

Many other substances have been shown to be vaso-
active in the mesenteric vasculature. Unfortunately, their
exact role in postprandial hyperemia has not been deter-
mined. As mentioned earlier both 5-hydroxytryptamine (7)
and kallikrein (58) have been suggested as possible medi-
ators for the vascular effects of CCK in the small intes-
tine and the pancreas (7, 58). Local hypoxia and hyper-
capnia (78, 107) as well as the intra-arterial infusion
of magnesium, ATP, ADP, AMP, bradykinin, prostaglandins,
acetylcholine or histamine in the dog cause intestinal
vasodilation (30, 48, 54, 99, 115). What role these sub-
stances play in postprandial hemodynamics, however, has
not been determined. Thus, besides the three gastro-
intestinal hormones, little is known concerning the pos-
sible role of other endogenous humoral substances in elicit-
ing the local increase of mesenteric blood flow.

Local Regulation of Intestinal Blood

Flow, Absorption and
Oxidative Metabolism

 

 

 

Chou and co-workers (26) recently observed that
the constituents of chyme responsible for the hyperemia

are the digested products of food. Existing evidence seems

27

to agree with this view. For example, many elementary
digested products of proteins, carbohydrates and lipids
have been shown to decrease vascular resistance when placed
inside the lumen of the intestine (21, 26, 34, 118, 119,
126). Studies by Fara et a1. (34) as well as others (25)
have also shown that the time of the onset of postprandial
hyperemia occurs more rapidly with digested food than with
undigested food. Thus, it is very likely that digestion
plays a vital role in postprandial hyperemia and is
probably a prerequisite to the increase in intestinal blood
flow caused by the presence of food.

The question of how the processes of absorption
trigger postprandial hyperemia has never been fully eluci-
dated. It is well known however that the absorption of
some nutrients (amino acids and glucose) is an energy
requiring process (30) and addition of exogenous substrates
into the intestinal lumen accelerates local metabolism
(84). For example, glucose is absorbed by an active trans-
port mechanism against a concentration gradient (5, 18,

28, 30, 125). The transport of glucose into the mucosal
epithelial cell is made possible by a mobile sodium carrier
located in the brush border plasma membrane (18, 28, 30,
125). Crane (28) postulated that there are two binding
sites on the carrier molecule, one for sodium and the other
for glucose. It was further suggested that the glucose
molecule cannot attach to the carrier unless sodium is

already occupying its site on the carrier molecule. Once

28

the carrier has bound sodium and glucose, the entire com-
plex is driven (by the concentration gradient of sodium)
from the luminal to the cytoplasmic side of the brush
border plasma membrane, where both molecules are then dis-
charged (5, 28, 30). Accumulation of the sugar inside the
cell allows it to diffuse into the circulation. The sodium
concentration gradient, i.e., 100 to 140 mEq/kg in the
lumen and 50 mEq/kg or less inside the cell, is maintained
by the active extrusion of the ion at the expense of ATP
by a Na-pump located on the serosal side of the cell (5,
28, 30).

Thus, the absorption of glucose is an energy-
requiring process and indeed, the absorption of the sugar
has consistently been shown to increase intestinal oxygen
consumption and blood flow (118, 119). But unlike the
heart and the skeletal muscle where many classical studies
have been performed to correlate the rate of metabolism
and functional hyperemia (2, 4, 15, 31, 40, 75, 76, 79,
80), there is virtually no data available to clearly estab-
lish that the regulation of the glucose-induced hyperemia
is related to factors that are linked to oxidative metab-
olism.

It is without a doubt that all cells in the body
require an adequate supply of oxygen to maintain their
function. Since blood is the only means of oxygen trans-
port to the cells, it is vital that blood flow to the

tissue is closely monitored and regulated by cellular oxygen

29

demand. This in fact is the rationale behind the metabolic
hypothesis of the local regulation of blood flow (99).

The hypothesis suggests that the flow adjustments of an
organ in response to changes in metabolism are caused by
the alterations in the concentrations of oxygen or other
metabolites in the tissue fluids surrounding the arterioles
and precapillary sphincters (99). For example, an increase
in oxidative metabolism (as during increased work load of
the heart or skeletal muscle) increases the production of
metabolites and decreases P02 in the tissue fluids, result-
ing in the relaxation of the vascular smooth muscles (vaso-
dilation) and thus, oxygen delivery is augmented in response
to an elevated metabolic demand. Alternatively, a sudden
increase in blood supply causes an increase in oxygen
delivery above and beyond that which is needed by the tis-
sues, resulting in an increase in the concentration of tis-
sue oxygen which leads to an active contraction of the vas-
cular smooth muscles (vasoconstriction) and returns oxygen
delivery to normal.

The causal relationship between metabolic activity
and blood flow is best illustrated by studies done on the
heart and skeletal muscle (2, 4, 15, 31, 40, 75, 76, 79,

80, 105). For example, Shipley and Gregg (105) first demon-
strated that the increase in myocardial contractility during
stimulation of the canine stellate ganglia was accompanied
by increases in both coronary blood flow and oxygen con-

sumption. They suggested that the increase in coronary

30

flow was in part related to the augmented cardiac metab-
olism. Eckenhoff et a1. (31) measured coronary blood flow
and oxygen consumption at rest, during hemorrhage and after
epinephrine injection in anesthetized dogs. Arterial and
venous oxygen samples were taken from the carotid artery
and greater cardiac vein. Oxygen content in whole blood
was analyzed by the method of Van Slyke and Neil (31).

Left descending coronary arterial flow was monitored by

a bubble flowmeter. Oxygen consumption was calculated as

the products of A-V 0 difference and coronary blood flow.

2
It was observed that there was a good correlation (r =
0.85) between coronary blood flow and cardiac oxygen con-
sumption. Foltz et al. (40) and Alella et al. (2) also
observed that there was a significant correlation between
coronary flow and myocardial oxygen consumption. Braunwald
et a1. (15) in a subsequent study, observed that this rela-
tionship between the two variables remains unchanged over
a wide range of arterial blood pressure and cardiac output.
Kramer et a1. (79, 80) as well as Barger et a1. (4) have
also demonstrated a similar relationship between flow and
oxygen consumption in the canine skeletal muscle during
exercise. They observed that during steady state, work
done by the muscle, blood flow and oxygen consumption were
linearly correlated.

Certainly, the intestine must regulate its blood

flow to meet its metabolic demands. The question is

whether this is the only factor that determines the control

31

of blood flow by the gut. The problem is complex in that
unlike the heart or skeletal muscle, the intestine has to
perform various functions during digestion besides mus-
cular contraction (30). These include secretion and
absorption (30). It is the last function in particular
that makes the gut unique among the major organs in the
body.

In addition to relying on its blood supply for
chemical energy to maintain cellular integrity, the intes-
tine must also depend on its circulation to perform absorp-
tion (30, 82). Blood vessels and lymphatics are the only
means by which nutrients can be transported from the intes-
tine to the rest of the body for use or storage. Teleo-
logically, it is certainly most advantageous for the gut
to increase its blood flow during the height of absorption
(postprandial) to transport the nutrients. Thus, in addi-
tion to meeting its metabolic demands, the gut probably
also regulates its blood flow to accomplish its absorptive
function. The mechanisms by which the intestine regulates
its blood flow to serve these two functions is not clear.
Whether the functional hyperemia during digestion corre-
lates with the increase in metabolism is not known. Since
the rate of metabolism increases during intestinal absorp-
tion (30), the possibility exists that the regulation of
the hyperemia is linked to factors that are closely related
to oxidative metabolism. On the other hand, it is not

inconceivable that different mechanisms are involved, since

32

the two functions (providing chemical energy and nutrient
transport) do not serve the same purpose.

The purpose of this study, therefore, is to examine
the relationship between the metabolic activity of the gut
and its local regulation of blood flow during postprandial
intestinal hyperemia.

There are two specific aims: (1) To examine the
relationship between the intestinal hyperemia and the
increase in oxygen consumption during digestion, and (2)
To study the relationship between the increase in blood
flow, oxygen consumption and glucose absorption during the
luminal placement of glucose and its synthetic analogs,
2—deoxy glucose and 3-0-methyl glucose in the small intes-

tine.

CHAPTER III

METHODS

Surgical Procedures

Mongrel dogs of either sex (15-25 kg) were fasted
for 24 hours, anesthetized with sodium pentobarbital (30
mg/kg, i.v.) and ventilated with a positive pressure Harvard
respiration pump (Model #607, Dover, Mass.) to achieve
normal arterial blood pH. Systemic arterial blood pressure
(mm Hg) was monitored by a Statham pressure transducer
(Model #P23Gb, Hato Ray, Puerto Rico) via a catheter (PE
280) inserted into the femoral artery, and continuously
recorded on a four channel Hewlett Packard oscillograph
(7700 series, Waltham, Mass.).

The abdominal cavity was exposed through a midline
incision and a loop of the proximal jejunum or distal ileum
supplied by a single artery and vein was exteriorized.
After administration of heparin sodium (6 mg/kg), the vein
was cannulated for measurement of venous outflow. The
outflow was directed to a reservoir and was returned to
the animal through a femoral vein at a rate equal to the
venous outflow. A rubber tube was placed into the lumen
of the segment for the introduction and withdrawal of

33

34

solutions to be tested. At all other times, the tube was
connected to a Statham pressure transducer (P23Gb) to
monitor intraluminal pressure. Both ends of the segment
were cut to exclude collateral blood flow and were tied

to prevent bleeding. The segment was covered with a plastic
sheet to prevent desiccation and kept at 37°C with a heat
lamp. In the double jejunal segment preparation, two seg-
ments of equal length were prepared from the jejunal loop

as described above (21-26).

Preparation of the Solutions Studied

Food Solutions

 

The solutions studied were: (1) digested food,

(2) undigested food plus bile, (3) digested food plus bile,
and (4) bile alone.

The food solutions were made from a commercially
available dog food (protein 12%, fat 7%, fiber 1.5%, ash
3%, linoleic acid 0.4%, moisture 78%, Alpo Beef, Allen
Products Co., Allentown, Pa.). A can of this dog food was
homogenized in an electric blender, then the pH of the
homogenate was adjusted to 7.0 by adding sodium bicarbonate.
A part of the homogenate was retained to be used in the
experiments as undigested food. To the other part of the
homogenate a pancreatic enzyme preparation (187.5 mg/lOO
cc; Viokase R, Viobin Co., Monticello, I11.) was added and
the whole was gently mixed with a magnetic stirrer at room

temperature for 5 hours to permit digestion. The digested

35

food was then made near isotonic by adding 2 parts of dis-
tilled water to 1 part of the digested food. The mean 1
SEM osmolality of the diluted digested food made from 6
cans of the dog food was 278 i 29 mOsm/kg.

Prior to each experiment, bile was aspirated from
the animal's gallbladder with a needle and syringe. The
volume of bile obtained from each dog varied from 15 to
30 ml. The digested food plus bile solution was prepared
by mixing equal parts of undiluted digested food, distilled
water and gallbladder bile together. The whole was then
gently mixed with a magnetic stirrer for approximately 15
minutes. The undigested food plus bile solution was pre-
pared in a similar fashion. The pH and osmolality of this
solution was 7.0 i 0.47 and 317 i 8 mOsm/kg, respectively.
The bile to be placed in the lumen was diluted with 2 parts
normal saline to 1 part bile. The diluted gallbladder bile
had a pH of 7.0 i 0.37 and an osmolality of 284 i 7.4

mOsm/kg.

Glucose Solutions

 

The solutions studied were: 3-0-methyl glucose,
2-deoxy glucose and glucose (Sigma Chem. Co.). In addition,
the effects of these glucoses plus bile were also studied.
The solutions were made as follows: One part of normal
saline or gallbladder bile was added to 2 parts of a solu-

tion containing 300 mM of each of these glucoses. These

36

solutions were isotonic, at pH 6.8-7.2, and were kept at

37°C.

Experimental Procedures

 

Food Studies

 

The purpose of these studies was to examine the
relationship between postprandial intestinal hyperemia and
local oxygen consumption. In the first series of experi-
ments, various food solutions were placed into the lumen
of a single jejunal segment and their effects on blood flow,
oxygen consumption, luminal pressure, as well as systemic
arterial pressure were measured. The solutions studied
were digested food, digested food plus bile, undigested
food plus bile, and bile alone. In addition, the effects
of bile in the ileum were also examined. Each of these
solutions was individually placed inside the lumen of the
jejunal or ileal segment for a 30 minute period during which
the changes in local blood flow, oxygen consumption, luminal
pressure and systemic arterial pressure were monitored.
Blood flow was determined by timed collection of venous
outflow by graduated cylinders. Oxygen consumption was
calculated as the product of blood flow times arteriovenous

(A-V 02) difference. Arterial 0 samples were taken from

2

the femoral artery and venous samples from the venous out-
flow of the intestinal segment under study. The 02 content
in mg% of whole blood was determined by the Lex-OZ-Con

(Lexington Instrument Corp., Waltham, MA.). These variables

37

were measured before and at 5, 10, 15, 20, 25, and 30
minutes after placement of each solution.

In the second series of experiments, the temporal
relationship between the increase in blood flow and oxygen
consumption during placement of digested food and digested
food and bile was studied. Blood flow was continuously
monitored by an electromagnetic blood flow probe (Model
BL 2024 F17, Biotronex Lab. Inc., Silver Spring, MA.) and
Biotronex flow meter (BL-610). The vein draining the
intestinal segment was cannulated with the in-line flow
probe through which blood flowed to a reservoir. The out-
flow was then returned to the animal through a femoral vein
at a rate equal to venous outflow. Prior to and during
each experiment, the flow meter was calibrated with the
timed collection of venous outflow by graduated cylinders.
A-V 02 difference was determined continuously by perfusing
the femoral arterial blood and a portion of the jejunal
venous outflow through an A-V 02 difference analyzer
(#1020, A-Vox Systems, San Antonio, TX.) at a constant rate
(6.0 to 6.8 ml/min). These variables, along with luminal
pressure and systemic arterial pressure were continuously
recorded on a Hewlett-Packard oscillograph (7700 series,
Waltham, MA.). The protocol for this series of experiments
was the same as the first one. The percent changes from
control of blood flow and oxygen consumption were then

correlated using the least squares regression analysis.

38

Glucose Studies

 

Three series of experiments were performed. In
the first two series, the effects of glucose, 3-0-methyl
glucose and 2-deoxy glucose on blood flow, absorption and
local metabolism were compared. It has been shown that
glucose is both actively absorbed and metabolized, 3-0-
methyl glucose is actively absorbed but not metabolized
(18, 28, 125), and 2-deoxy glucose is neither absorbed nor
metabolized by the small intestine (28). Thus, by compar-
ing the vascular and metabolic effects as well as the
absorption of these glucoses, one can determine whether
the glucose induced hyperemia is related to its metabolism
and/or absorption. In addition, the effects of bile on

these parameters were also examined.

Series 1. The vascular effects of glucose and its
synthetic analogs, 3-0-methyl glucose (3-MG) and 2-deoxy
glucose (2-DG) with or without bile, were compared in the
double jejunal segment preparation (21-26). The protocol
for the experiments consisted of three 15 minute periods:
control, test, and post-experimental control. In the pre-
and post-experimental periods, both segments contained 10
m1 normal saline while in the test period one segment con-
tained 10 ml of glucose solution and the other contained
10 ml of either 3-MG or 2-DG solution so that their vaso-

activities could be compared.

39

In each 15 minute period, venous outflow from both
segments were simultaneously collected in graduated cylin-
ders in 3 minute samples with 1 minute intervals in between
collections. The volume of blood was determined and the
blood poured into the reservoir. After each period, the
luminal contents were withdrawn and the lumen was gently

and thoroughly washed with normal saline.

Series 2. Only one jejunal segment was prepared
for this series of experiments. In addition to venous out-
flow, oxygen consumption and glucose absorption were
measured during luminal placement of glucose + bile, 3-

MG + bile, 2-DG + bile, or bile alone. A-V 02 difference

was continuously monitored by the A-V O analyzer as

2
described above. Arterial and venous samples were obtained
before and at 5, 10, and 15 minutes after the placement

of test solutions for the determinations of plasma glucose
and 2-DG (glucose oxidase method) or 3-MG concentration
(Somogyi and Nelson method, see appendix). Oxygen consump-
tion of the jejunal segment was calculated as the product
of A-V 02 difference and venous outflow. The protocol for

the experiments in this series was similar to that of the

first series.

Series 3. In this series of experiments, the
temporal relationship between the increase in blood flow,
oxygen consumption, and glucose absorption was examined.

A single segment of the proximal jejunum was used. Blood

40

flow was determined by an in-line electromagnetic flow
probe (Model BL 2024 F17) and a Biotronex flowmeter
(BL-610). A-V 02 difference was continuously monitored

by the A-Vox analyzer as described above. Blood samples
were obtained from a femoral artery and the venous outflow
of the jejunal segment for the determination of the plasma
glucose concentration by the oxidase method by a glucose
analyzer (Model 23 A, Yellow Springs Instr. Co. Inc.,
Yellow Spring, OH.). Isotonic glucose (300 mM) diluted
with either normal saline or gallbladder bile was placed
inside the jejunal lumen for a 20 minute period. Blood
flow, glucose absorption (blood flow x A-V glucose differ-

ence) and oxygen consumption (blood flow x A-V O differ-

2
ence) were determined at control and at 15 second intervals
during the first five minutes of glucose placement and at

1 minute intervals thereafter. The percent changes from

control in these three variables were then correlated.

Statistical Analysis of the Results
The Student's t-test modified for paired comparisons

was used to evaluate the changes from control in the vari-
ables produced by the test solutions. The Student's group
t-test for equal variance with unpaired observations was
used to compare the changes in the monitored variables
between groups of animals. In addition, the data from the
studies on glucose and its synthetic analogs were analyzed

by a two-way analysis of variance. The least squares

41

regression analysis was used to correlate the changes in
two variables. The statistical significance was set at

p values less than 0.05.

CHAPTER IV

RESULTS

The mean i SEM systemic arterial blood pressure

was 122 i 2 mmHg (N = 102) and was not altered by the

placement of various test and control solutions into the

intestinal lumen.

Food Studies

 

Series 1

The effects of luminal placement of digested food,
undigested food plus bile, and digested food plus bile on
venous outflow, oxygen consumption, and luminal pressure
were examined in the single jejunal segment. In addition,
the effect of bile alone on these variables in both the
jejunum and ileum were also studied. The purpose was to
determine whether the increase in local blood flow in
response to the presence of food (or bile) in the gut lumen
is accompanied by an enhancement of local oxidative metab-
olism. As shown in Figure 1, placement of digested food
significantly increased blood flow as well as oxygen con-
sumption. Blood flow increased from a control value of
48.1 i 4.2 to 54.1 i 4.4 ml/min/lOO gm at 5 minutes after

42

43

Fig. 1.--Effects of luminal placement of digested food
alone on jejunal A-V 0 difference, blood flow,
oxygen consumption and luminal pressure.
Asterisks indicate values significantly differ-
ent from control (time = 0) at p < 0.05; n = 7.

44

A-v 0
2 3 '-
(ml/IOOm') [fl El 0 fl
2 -

so _ 1 /1‘\(‘ DEPI

(ml/min/lOOgm)

 

 

 

40'

21) -
OXYGEN 1" F F I
CONSUMPTION 15 "
l/

(ml/min/IOOQm)

 

 

 

1.0'

6 .-
LuMINAL

PRESSURE 3 '

 

 

I\I__ {/1 I I T}:

(mm Hg)

 

L i I . I
o 10 20 30

45

the introduction of the food solution. A steady state of
blood flow was reached within 5 to 10 minutes after the
food placement and this lasted for approximately 20 minutes.
Blood flow at this state was 52.8 i 4.5 ml/min/lOO gm.
The mean t SEM percent increase in flow from precontrol
during the steady state was approximately 10 i 1.9%. There
was a concomitant increase in oxygen consumption from 1.36
i 0.08 m1/min/100 gm at control to 1.58 i 0.1 ml/min/lOO
gm at 20 minutes after food placement. This represents
a 16.4 i 4.1% increase from precontrol. This increase in
oxygen consumption was met by an increase in blood flow
since A-V 02 difference was not altered. There was no sig-
nificant change in luminal pressure throughout the entire
30 minute period.

Figure 2 shows the effect of digested food plus

bile on blood flow, oxygen consumption, A-V 0 difference,

2
and luminal pressure. Within 5 minutes after placement

of the food solution, blood flow increased from 46.8 i 4.3
ml/min/lOO gm at control to 65.9 i 6.7 ml/min/lOO gm, a

37.7 i 8.1% increase. The increase is significantly greater
than the 10% increase in blood flow observed when digested
food markedly enhanced its hyperemic effect. Furthermore,
the hyperemia was maintained throughout the 30 minute
experimental period. The blood flow remained at 55.5 i

6.4 ml/min/lOO gm at 30 minutes after food placement.

Along with the increase in flow, there was also an increase

in oxygen consumption, which peaked at 15 minutes and

46

Fig. 2.--Effects of luminal placement of digested food
plus bile on jejunal A-V 0 difference, blood
flow, oxygen consumption and luminal pressure.
Asterisks indicate values significantly differ—
ent from control (time = 0) at p < 0.05, n = 6.

47

Digesied Food + Bile N = 6

 

 

6 —
A'V A02 3 )—
(mVKmmD
05
70
BLOOD FLOW
50
(ml/min/lOOgn)
30
3_.
OXYGEN
COMSUNPTION 2 )-
mwmmmpqm
l h-
8 .—
UMMML

PRESSURE 4 -
(mmHg)

 

 

 

 

 

 

 

 

 

 

& & rr m;
_ F] Li L L.
,/H7 HR

TIME (min)

48

gradually returned to control at 30 minutes. The peak
increase in oxygen consumption was about 29.8 i 7.9% above
control (from the control of 2.18 i 0.28 to 2.91 t 0.46
ml/min/lOO gm at 15 minutes after the placement) which,
like the increase in flow, was greater (p < 0.05) than the
effect of digested food alone in the lumen (+16.4%). Since
A—V 02 was not significantly altered, the increase in oxygen
consumption was provided by an increase in oxygen delivery
rather than by an increase in extraction by the intestine.
Luminal pressure was slightly but significantly elevated
only at 5 minutes after.food placement.

Figure 3 shows the effect of undigested food plus
bile on flow and local metabolism. There was a slight but
significant increase in blood flow (12.7 i 1.4%) beginning
5 minutes after placement of the food solution. The hyper-
emia persisted for almost 30 minutes. However, in contrast
to the digested food and digested food plus bile solution,
there were no significant changes in oxygen consumption.
Also, both A-V 02 difference and luminal pressure were un-
changed. Luminal placement of bile (three fold diluted gall-
bladder bile with normal saline) in the jejunum had no effect
on any of the variables that were monitored (Figure 4).

Since bile salts are absorbed in the ileum and bile
produces an increase in local blood flow when placed into
the ileal lumen (23), the effects of bile on blood flow,
oxygen consumption and luminal pressure in the terminal

ileum were also studied. As shown in Figure 5, blood flow

49

Fig. 3.—-Effects of luminal placement of undigested food
plus bile on jejunal A-V 0 difference, blood
flow, oxygen consumption and luminal pressure.
Asterisks indicate values significantly different
from control (time = 0) at p < 0.05; n = 7.

50

Undigested Food+ Bile N ‘ 7

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

a P< 0.05
5 r
M A02 * )1 i i i
3 r-
(ml/IOOml)
o L _ _ .J .1 _.
so r
BLOOD FLOW {Liv {LP/{K
40- I/
( mI/min/IOOgm)
30 L
3 .-

OXYGEN I 1‘
CONSUMPTION 2 - I/ I *1
(ml/min/IOOgm)

1 .-
3 -
LUMINAL T
PRESSURE 2 - ——
/I I _________.4)
(mm Hg) 1 I \I/{ \I
— J.
L I I J
0 10 20 30

TIME (min)

51

Fig. 4.--Effects of luminal placement of bile on jejunal
A-V 0 difference, blood flow, oxygen consumption
and luminal pressure. N = 6.

52
Bile N=6

 

 

 

 

 

 

 

 

 

 

 

 

6- I I I I I
A-V A02
(mvamU -
0L. L ._ r. _ .I
50-
BLOODFLOW
405 ______,}___‘,,..“-’,,
(ml/min/lOOgm)
30-
3!—

OXYGEN
CONSLMPTION 2 P- }\I/ \1/
(ml/min/IOan)

 

 

 

1 I.
3 -
LUMINAL
PRESSURE 2- \/\/\/
(mmHg) 1 L
L 1 l 1
0 10 20 30

TIME (min)

53

Fig. S.--Effects of luminal placement of bile on ileal
A-V 0 difference, blood flow, oxygen consump-
tion and luminal pressure. Asterisks indicate
values significantly different from control
(time = 0) at p < 0.05; n = 6.

54

.2 i

( I/IQO I)
L L—

70 - [>13/13/1¥\ S I.

 

 

 

8o

 

BLOOD FLOW

 

 

 

 

 

 

60 -
(mI/mIn/IOOgm)
5O -
40 I-
2.0 r
OXYGEN .
CONSUMPTION 1.5 ..
(mI/min/IOOgm) I\£‘ ~1\£# #I
1.0 -
4 .—
LU M INAL f/}:\},{‘ {/f\
PRESSURE 3 ' j
l l l l
O 10 20 30

TIME (min)

55

increased within 5 minutes after the placement and
remained at a steady level for 30 minutes. The control
flow was 42.1 i 3 ml/min/lOO gm which rose to 68.0 i 8.2
ml/min/lOO gm 20 minutes after the placement, a 61.5%
increase in local blood flow. Oxygen consumption
decreased slightly but not significantly throughout the
30 minute placement period.

The results from this series of experiments indi-
cate that digested food plus bile, has a greater hyperemic
as well as metabolic effect than digested food alone and
undigested food plus bile. Addition of bile to digested
food, which contained pancreatic enzymes could promote
digestion and absorption of lipids in the food thereby
enhancing the hyperemia. While both digested food alone and
undigested food plus bile increased flow by approximately
10%, only the former increased oxygen consumption. Bile
in the jejunal lumen did not have any effect on blood flow
or oxygen consumption, but bile in the ileum increased
flow by 60% and did not alter oxygen consumption (Figure 5).
These results thus indicate that postprandial intestinal
hyperemia is a complex phenomenon and different constitu-
ents of chyme can elicit different responses in blood flow
and oxygen consumption. In the case of digested food and
digested food plus bile, the increase in blood flow was
accompanied by an increase in local metabolism (Figures
1 and 2). The possibility thus exists that the heightened

oxidative metabolism may contribute to the hyperemia induced

56

by these food solutions. Accordingly, the temporal rela-
tionship between these two variables during food placement
was examined more closely in the next series of experi-

ments.

Series 2

In this series of experiments, digested food and
digested food plus bile were individually placed into the
lumen of the proximal jejunum for 30 minutes during which
blood flow and oxygen consumption as well as luminal pres-
sure were monitored continuously. Figure 6 shows the
hyperemic and metabolic responses of the jejunal segment
to the placement of digested food. Flow increased within
15 seconds (8.7 i 1.7%) after the introduction of this food
solution and was accompanied by an increase in oxygen con-
sumption (12.5 i 2.0%). Flow remained significantly ele-
vated until 20 minutes after placement and then declined
back to control level. In contrast, oxygen consumption
remained significantly increased throughout the entire 30
minutes placement. These changes were not accompanied by
any alterations in blood pressure, luminal pressure or
A-V 02 difference.

Figure 7 shows the relationship between the per-
cent changes from controls of blood flow and oxygen con-
sumption. These data were taken at 15 second intervals
for the first 5 minutes after food placement and at l min-

ute intervals thereafter. There was a significant

Fig.

57

6.--The temporal relationships between blood flow,

A-V 0 difference, oxygen consumption, aortic
pressure and luminal pressure during placement

of digested food alone in the jejunum. The

food solution was placed into the lumen at time
0. Both blood flow and oxygen consumption
increased significantly (p < 0.05) 15 seconds
after the placement. Flow remained significantly
elevated until 20 minutes after placement and
declined gradually back to control level (p

> 0.05 as compared to 0 time 20 minutes after

the placement). In contrast, oxygen consumption
remained significantly (p < 0.05) increased
throughout the entire 30 minute placement period.
Aortic pressure, luminal pressure and A-V 0
difference were not significantly altered (% = 7).

58

 

‘IIIIIIIIIYRTILI

I

”\fl‘“ -1- -------- I__
IIII+IIIHIIIIIIII IWIIN

J

I

 

 

L l

I l I I
0 60 120 180 240 300 6 1O 15 20 25 3O

 

 

 

 

 

(mI/IOOmI)
CONS‘JMPT'ON
(mI/mIrI/ZOC-gm} -

OXYGEN
LUMINAL

4..

PRESSURE

(mm “9)

2-

0».

TIME (min)

(sec)

59

Fig. 7.--Relationship between the percent changes in blood
flow and oxygen consumption during placement of
digested food in the jejunum. The variables
were recorded at 15 second intervals for the first
5 minutes after food placement and at 1 minute
intervals thereafter.

% CHANGE BLOOD FLOW

60

25

20 .
15 .. . . , . . .
. .0 o... . . . . . sI0pe=Ol7
10 . . a. 2. .. . . . . r = 0.30
g . . : .0 ° . o ' p<0.00|
5 o ..' . . o . 3.: o. .
o u . o . .

%CHANGE 02 CONSUMPTION

61

correlation between the percent change in blood flow and
oxygen consumption (r = 0.3, p < 0.001). The equation for
the regression line is: y = 6.7 + 0.17 x, where y = %
changes in flow and x = % changes in oxygen consumption.
Figure 8 shows the temporal relationship between
blood flow, oxygen consumption, and luminal pressure when
digested food plus bile was placed into the jejunal lumen.
Blood flow increased almost immediately and peaked
at 5 minutes (51.6 i 15.5%) after the introduction of the
food solution. It remained elevated throughout the entire

30 minute placement period. A-V 0 difference, on the

2
other hand, fell transiently for 10 minutes (p < 0.05)
but returned back to control level during the rest of the
experimental period. Oxygen consumption increased sig-
nificantly 15 seconds after the placement of food. This
increase reached a peak 10 minutes after placement (+33.3
t 8.5%) and remained elevated throughout the entire 30
minutes of food placement. Motility was elevated during
the initial 10 minutes after food placement but returned
to control level during the final 15 minutes. As shown
in Figure 9, there was no significant correlation between
the percent change in flow and oxygen consumption during
the presence of digested food plus bile in the jejunum

(r = 0.03, p > 0.5). The equation for the line is:

y = 44.7 - 0.66 x.

This series of experiments shows that both

digested food alone and digested food plus bile produce

62

Fig. 8.--The temporal relationships between blood flow,
A-V 0 difference, oxygen consumption, aortic
pressure and luminal pressure during placement
of digested food plus bile in the jejunum. The
food solution was placed into the lumen at time 0.
Both blood flow and oxygen consumption increased
significantly (p < 0.05) 15 seconds after the
placement. They remain elevated throughout the
entire 30 minute placement period. There was a
significant decrease (p < 0.05) in A-V O dif-
ference during the initial 5 minutes after food
placement. Luminal pressure was elevated sig-
nificantly (p < 0.05) during the first 10 min-
utes of placement. Aortic pressure was not sig—
nificantly altered (n = 6).

OOOOOOOOOOO

RRRRRRRR

 

‘r

 

 

 

 

iii/Hi"I

- H

5 IHHH i M HHH HW'H "

Lk-i-z-iiiiriiiimii-H HMiHIHWHHHHM
Hiiii—HHHHii
iiHHi-HH HHHHH iHiHH-HHHH i HHH

 

g ,H HHHHHHHHH HHHiHii H i HHH iii

L l

 

I
O“!201U2:03U6110 1.5 210 530

64

Fig. 9.--Relationship between the percent changes in
blood flow and oxygen consumption during the
placement of digested food plus bile in the
jejunum. The variables were recorded at 15
second intervals for the first 5 minutes after

food placement and at 1 minute intervals there-
after.

65

2052828 No uoquox

 

o—

 

o
C 0 C
o
o o o o o o o o
o o. o oo
o o o
C O C O C . O C. .
o 0' O 000 o. 0 fl 0 0 0
O O O O O O
o . o. 3 o
o o 00 o o
O O O 000 O 00 0 O O O. O
o o
0 ll Ilb'! o
o 00 o o o o o o
no. .- 000 o o o
o o
o
o
o o o o
o o
o
o
O O O
o o
0000 o
ndAa
o coo .0 o o
”0.0... e o o. 0
8.0.1.8: . . . . .. .
o on
o o o o o
o o o
o o
o o o o.

00

on

8—

MO'H 00018 39NVHO %

66

a prompt and simultaneous increase in blood flow and oxygen
consumption. In both cases, the increases in flow were
maintained at a steady level for 20 minutes and then gradu-
ally returned toward control level but the increase in
oxygen consumption was maintained at a steady level
throughout the 30 minute placement period (Figures 6 and
8). The A-V 02 difference (oxygen extraction) was either
decreased or unchanged during the first 5 minutes and
tended to increase during the last 10 minute placement
period. Thus, it appears that during the early part the
increase in oxygen consumption is primarily met by an
increase in blood flow but during the last 10 minutes, an
increase in tissue oxygen extraction plays a role in the
increase in oxygen consumption since blood flow returned‘
toward control level.

There was a significant correlation between the
changes in oxygen consumption and blood flow when digested
food alone was in the lumen (r = 0.30, p < 0.001).
Although digested food plus bile produced a much greater
increase in both blood flow and oxygen consumption, the
correlation between the changes in these variables were
not significant. Furthermore, while the y intercept of
the regression line of digested food was 6.7% and was not
significantly different from the origin (Figure 7), that
of digested food plus bile was 44.7% and was significantly
different from the origin (Figure 9). This seems to indi-

cate that the presence of bile in the digested food

67

produces a 44.7% increase in flow even in the absence of
any apparent change in oxygen consumption. Moreover, the
slope of the line (-0.06, Figure 9) indicates that this
increase in flow remained virtually constant over a wide
range of increases in oxygen consumption.

The food solutions in the above study contain many
nutrients and each of them may have different mechanisms
in causing an increase in flow. Thus, in the second part
of this study, the mechanisms by which a major nutrient,
glucose, causes an increase in local blood flow in the

jejunum was examined.

Glucose Studies

Series 1

In this series of experiments, the vascular effects
of glucose and its synthetic analogs, 3-0-methyl glucose
and 2-deoxy glucose, with or without bile, were compared
in a double jejunal segment preparation. During the test
period, one segment contained 10 ml of glucose solution
and the other contained 10 ml of either 3-O-methyl glucose
or 2-deoxy glucose solution so that their vasoactivities
could be compared.

After the introduction of the test solutions, blood
flow often reaches a steady state within 5 to 10 minutes
which lasts for about 20 minutes. Thus, the flow values
taken at the 12 to 15 minute period were used for express-

ing and analyzing the data.

68

As shown in Figure 10, glucose and 3-0-methyl glu-
cose in the absence of bile significantly increased venous
outflow by 8.9% and 4% of precontrol respectively; the
difference in their hyperemic effect of 5.0% was statis-
tically significant (p < 0.05) the hyperemic effect of
glucose (17.2% above control) but not 3-0-methyl glucose
(4.3%). The difference in their hyperemic effect thus
increased to 13.3%. Figure 11 shows that while glucose
significantly increased blood flow, 2-deoxy glucose did
not alter flow either with or without bile. Thus, of the
three glucoses, only glucose and 3—0~methyl glucose were
capable of increasing blood flow with the hyperemic effect
of glucose being greater than that of 3—0-methyl glucose.
The addition of bile enhanced the hyperemic effect of glu-

cose and not 3-0-methyl glucose or 2—deoxy glucose.

Series 2

The purpose of this series of experiments was to
determine whether the differences in the vascular effect
of the three glucoses were related to its absorption and/or
an increase in local metabolism. A single segment of the
proximal jejunum was used in these experiments. Each glu-
cose plus bile was individually placed into the jejunal
lumen for 20 minutes. As shown in Figure 12, in the
presence of bile, both glucose and 3-0-methyl glucose
increased blood flow but only glucose significantly

increased oxygen consumption. The placement of glucose

Fig.

69

lO.--Comparison of vascular effects of glucose (G)

and 3-0-methyl glucose (3-MG) with or without
bile, in double jejunal segments (n = 6).

Values above bars indicate percent changes from
precontrol. A - B = Difference in changes
produced by the two paired solutions. Aster-
isks indicate that the values are significant

at p < 0.05. Addition of bile markedly enhanced
the hyperemic effect of glucose (p < 0.05, two-
way analysis of variance) but not 3-0-methyl
glucose.

70

U45 Wfim
+

 

 

 

 

 

 

 

  

 

 

 

 

 

 

 

 

ooz os...0-m .92 .22 o .002 0

V V 3s V V V V «EV V V.V
\ A A .8
- ow

\ i \

, \t s
«$m.¢.m.m_ 1,404.36 fix. ZEN: L om
602 92-0% 602 602 o 602 o

.. V V V V VVVS V V.V
1 i 1 A 1 r i r :0.
L \ -ov
fix. 5.0m he???» .xowgww L om

 

mid. m Hzmiomm < Hzmfiowm

(fioOI/in/iw)
MO‘ldan snONaA

(boOI/U!w/Iw)
MO'Han SOONEA

Fig.

71

ll.--Comparison of the vascular effects of glucose

(G) and 2-deoxy glucose (2-DG) with or without
bile, in the double jejunal segments (n = 7).
Values above bars indicate percent change from
precontrol. A - B = Difference in changes
produced by two paired solutions. Asterisks
indicate that the values are significant at

p < 0.05. Addition of bile markedly enhanced
the hyperemic effect of glucose (p < 0.05,
two-way analysis of variance) but not 2-deoxy
glucose.

72

«o\o m.m«m.~..

xxomfims

mid—m
+
OQuN

 

 

 

 

.002 502
V V VVVVVV M M
.[IL

o\o_._«m.m-

_ooz oo-m .002
V V VSV V V
xmwfim

m Hzmzomm

 

 

 

 

 

35
602 o 602 o
V V VVVVVVV V Vw
A .18
\ 40¢
il-L,
s é
1...\..N.m.m.i now
502 o 63. 0
V V VVVVVV V Qw
C C. a
low
.xvmfiwm -Om
L om

 

< Hzmfiomm

(boOI/in/iw)
MO'Han snONBA

(500l/U!'-U/IUJ)
MOI-1100 snONaA

Fig.

73

12.--Percent changes in blood flow and oxygen con-

sumption from precontrol after luminal place-
ment of glucose (G), 3-0-methyl glucose (3-MG),
2-deoxy glucose (2-DG), with bile, and bile
alone. Control blood flow was 42.5 i 2.1 ml/
min/100 g and V0 was 1.50 i 0.05 ml/min/lOO g.
HEXOSE ABS. denoées the rate of absorption of
the hexose placed into the lumen. During the
placement of Saline + bile, the rate of glucose
absorption was determined. Asterisks indicate
that the values are significant at p < 0.05.

% CHANGE
01 o 01 o

 

2 MOI-J
0A 00018_

'SBV
0|.3rSOX3H

H
i

HEXOSE CZBschB.
(mg/min/ lOOg)

 
 

 

MO'IJ
GOO-IQ

 

80A

39v
3__sox3H
o .211

HEXOSE ABSORB.

(mg/min/ lOOg)

G
—l

—l\)04
O

(9=N) 37l|8+ 902

31l8 + BNI‘IVS

(§=N)

74

%CHANG
- N

o 01 o o
I fl

I
m
,1»-
08 ,,
SD

 

E
Z;

 

 

 

HEXOSE ABSORB.
(mg/min/ lOOg)

E
G
I

 

 

MO'L-l
(10018

 

20A

 

it

1 n 4
N 04 A
O O 0

'38V
BSOXHH

O —i—-T

 

5
HEXOSE ABSORB.
(mg /min/IOO g)

3'IIB+ 9

(2=N)

(9=N) 31l8 + 9W 9

75

plus bile increased local oxygen consumption by 17.8 i
5.9%. The hyperemic effect of glucose (18.2 i 4.8%) was
significantly greater than that of the 3-0-methyl glucose
(7.4 i 2.3%). There was however no significant difference
between the absorption rates of glucose and 3-0—methyl glu-
cose (p > 0.05, unpaired t-test). Bile alone or 2-deoxy
glucose plus bile did not alter blood flow or oxygen con-
sumption. There was no hexose absorbed when saline
(during control periods), bile, or 2-deoxy glucose plus
bile were in the lumen.

The results from these two series of experiments
show that of the three glucoses, only those that are
absorbed (glucose and 3-0-methyl glucose) caused an
increase in blood flow and that glucose, which increased
oxygen consumption, caused a greater hyperemic effect than
3-0-methy1 glucose, which did not increase oxygen consump-
tion. This seems to indicate that both the absorption of
glucose and the increase in oxidative metabolism may con-
tribute to the glucose induced hyperemia. The results also
indicate that bile only enhanced the hyperemic effect of
glucose but not that of 3-O-methyl glucose or Z-deoxy glu-
cose. This enhancing effect of bile does not appear to
be due to the vascular effect of bile since bile alone in
the jejunal lumen does not increase local blood flow. The
enhancing effect of bile may be related to glucose absorp-
tion and/or oxygen consumption. Thus, in the next series

of experiments, the effects on blood flow, glucose

76

absorption and oxygen consumption of luminal placement of
glucose alone and glucose plus bile were compared in the

proximal jejunum.

Series 3

Glucose alone or glucose plus bile was placed in
the lumen of a jejunal segment for 20 minutes during which
blood flow, oxygen consumption and luminal pressure were
continuously monitored.

Figure 13 shows the effect of luminal placement
of 200 mM glucose in saline. Blood flow increased immedi-
ately after glucose was introduced into the lumen. Flow
increased from a control value of 49.3 i 3.6 to 52.6 i 4.1
ml/min/lOO gm at 15 minutes. This represented a 6.1 i 1.4%
increase from control. Oxygen consumption increased gradu-
ally from 1.60 i 0.16 at control to 1.72 1 0.17 m1/min/100
gm at 15 minutes. This was a 9.1% increase from control.
The increase in oxygen consumption was not through an
enhanced extraction of oxygen since A-V 02 difference was
not significantly altered. Thus the increase in oxygen
consumption was met by an increase in blood flow. Glucose
absorption increased from 0 at control to 24.0 f 3.2 mg/min/
100 gm at 15 minutes after placement of the solution.
Luminal pressure on the other hand, was not significantly
altered. Thus, all three monitored variables (blood flow,
oxygen consumption and glucose absorption) increased during

the 20 minute period when glucose was present in the lumen.

77

Fig. l3.--Effects of luminal placement of 200 mM glucose
in saline on jejunal blood flow, A-V O differ-
ence, oxygen consumption, glucose absorption,
and luminal pressure. Asterisks indicate values
significantly different from control (time = 0)
at p < 0.05, n = 6.

78

55 .. 6 200 mM GLUCOSE IN SALINE

 

 

 

 

 

 

 

 

 

 

 

 

 

BLOOD FLOW 55 I- g * * * *
(mi/min/lOqu) I/ \{ I. I. I I‘ll—I. 1c
45L
4.5 r
A'V A02
(ml/ IOO ml) 3‘5 '- [\I/{f{/1\}Efii‘]: /l I
2.5 -
21 :—

OXYGEN ' . * . t '
,SONSUMPTION 1.8 P / * I [ T {\[kIL’F—fl
(mi/min/lOOgm) _ {/1 .

1.4 '-
30 H-

GLUCOSE 2” ' I/III#I—I‘I/I~{—I*H

 

 

 

ABSQRPTION
(mg/mun/lOOgm) 10 .-
o — o
4 .
LUMINAL I I I I T I
PRESSURE K ——- \ _
(mm Hg) 1/ I \I/ l l l I I
l
L l L l I
0 10 20

TIME (min)

79

Figure 14 shows the relationship between the per-
cent changes in blood flow and oxygen consumption. There
was a significant correlation between the changes in the
two variables (r = 0.25, p < 0.01). The equation for the
line is: y = 5.9 + 0.19 x. There was also a significant
correlation between the change in blood flow and glucose
absorption as shown in Figure 15 (r = 0.27, p < 0.001).
The equation for the regression line is y = 4.9 + 0.12 x.

Figure 16 shows the effects of luminal placement
of glucose plus bile on local blood flow, A-V O2 differ-
ence, oxygen consumption, glucose absorption and luminal
pressure. Blood flow increased immediately following
introduction of glucose plus bile and the hyperemia (25.0
i 4.3% at 10 minutes) persisted for the entire 20 minute
placement period. Oxygen consumption increased gradually
from 1.58 i 0.14 at control to 2.00 i 0.19 ml/min/lOO gm
at 15 minutes. This represented a 21.9 i 4.5% increase
from control. The increase in oxygen consumption was not
through an enhanced extraction of oxygen since A-V O2 dif-
ference was not significantly altered. Glucose absorption
increased from 0 at control to 26.7 i 4.7 mg/min/lOO gm
at 15 minutes after placement of the solution. Luminal
pressure was not significantly altered.

Figure 17 shows the relationship between the per-
cent changes in blood flow and oxygen consumption. There

was no significant correlation between the changes in these

variables (r = 0.05, p > 0.5). The equation for the line

80

Fig. l4.-—Relationship between the percent changes in
blood flow and oxygen consumption during the
placement of 200 mM glucose in saline in the
jejunum. The data included were the values
recorded at 15 second intervals for the first
5 minutes after glucose placement and at 1
minute intervals thereafter. The data was
linearly correlated using the least squares
regression analysis.

% CHANGE BLOOD FLOW

25

20

15

IO

81

o o
O z .
' slope=O.l9
r = 0.25
o
p< OOI
o .0 0
o o 0
o. ...O o. '
. . Q . .
o 0.: .. 5'0.... fl. .
. O
... I O .0
. o
o o
o o 0' o
. o
. o
o
. .0 . .0- . .
o
0

IO 20

%CHANGE O2 CONSUMPTION

3O

82

Fig. lS.—-Relationship between the percent changes in
blood flow and the rates of glucose absorption
during the placement of 200 mM glucose in saline
in the jejunum. The data included the values
recorded at 15 second intervals for the first 3
minutes after glucose placement and at 1 minute
intervals thereafter. The data was linearly
correlated using the least squares regression
analysis.

% CHANGE BLOOD FLOW

83

25 "

slope=0.l2
o
‘5 r= 0.27
p< 0.00|
o ' o
o ...
O . O Q
10 . '. o .00. ' ..: “'0
. o. o o. O . . z ..
. o o o.
o . .
. . . . ..:oo. .. . o
o '0‘ . . o
o
5 ' , ..
.0 ‘. O
’ £0 0' a...
. o

GLUCOSE ABSORPTION (mg/min/IOOgm)

84

Fig. l6.--Effects of 200 mM glucose plus bile on jejunal
blood flow, A-V 0 difference, oxygen consump-
tion, glucose absorption, and luminal pressure.
Asterisks indicate values significantly differ-
ent from control (time = 0) at p < 0.05; n = 6.

 

IO
BLOOD FLOW

(ml/min/lOOgm) 65

P

 

 

 

50
4
A'V A02
(ml/IOOmI)
2
2.2
OXYGEN
CONSUMPTION 1,8
(ml/min/IOOgm)
1.4
30
2
GLUCOSE o
ABSORPTION

(mg/min/IOOgm) lo

 

0
5
LUMINAL
PRESSURE
(mmHg) 2

85

I 200 mM GLUCOSE IN BILE

(I HI H II *I

 

 

 

 

TIME (min)

Fig.

86

l7.—-Relationship between the percent changes
blood flow and oxygen consumption during
placement of 200 mM glucose plus bile in
jejunum. The variables were recorded at

in
the
the
15

second intervals for the first three minutes

after glucose placement and at 1 minute inter-
vals thereafter. The data was linearly corre—
lated using the least squares regression analy-

sis.

% CHANGE BLOOD FLOW

87

7O

60

4O , .

20 0.0 .0 o.:. . o o o co slope= 0'06
o o g .0 o _
. . u... 3.: . r- 0.05
0": 0 * P >05

10 -

0 IO 20 30 4O 50

%CHANGE 02 CONSUMPTION

88

is y = 23.6 + 0.06 x. In contrast, there was a significant
correlation between the percent change in blood flow and
glucose absorption (r = 0.36, p < 0.001; Figure 18). The
equation for the line is: y = 17.9 + 0.35 x.

Thus the results from this series of experiments
indicate that the hyperemic effect of glucose plus bile
was significantly greater than that of the glucose plus
saline solution. This greater increase in blood flow was
accompanied by a greater increase in oxygen consumption
(p < 0.05) but not glucose absorption. The increase in
oxygen consumption during the placement of glucose plus
saline was 14.0 i 3.4% above control and during glucose
plus bile placement was 22.7 i 5.6% above control.
Although the changes in blood flow and oxygen consumption
produced by glucose plus saline were significantly corre-
lated (Figure 14), changes in these two variables caused
by glucose plus bile were not significantly correlated
(Figure 17). Also, while the y intercept of the regression
line of glucose plus saline was 5.9% which was not signifi-
cantly different from the origin (Figure 14), that of glu-
cose plus bile was 23.6% which was significantly different
from the origin (Figure 17). This indicates that glucose
plus bile could produce a 23.6% increase in flow even in
the absence of any apparent change in oxygen consumption.
Furthermore, the slope of the line, i.e., 0.06, seems to
suggest that the hyperemia could occur over a wide range

of increases in oxygen consumption. Thus, the influence

89

Fig. 18.--Relationship between the percent changes in
blood flow and glucose absorption during the
placement of 200 mM glucose plus bile in the
jejunum. The variables were recorded at 15
second intervals for the first three minutes
after glucose placement and at 1 minute inter-
vals thereafter. The data was linearly corre-

lated using the least squares regression
analysis.

 

 

 

 

% CHANGE BLOOD FLOW

70

50

4O

20

IO

10

90

20

O
00 00
O O.
O
O
O
O .00
O. O O
O 0
O O O.
O
O
O... 0.
000
O .000
a... 0-... O .0.
O O
O O O
O O O O O
.0
O .0
O O
.. .17.. " ' '
"" ° slope=O.35
... .
r = 0.36
O
p< 0.00!

30 40 5O

GLUCOSE ABSORPTION (mg/min/ | 00 gm)

91

of bile on the relationship between glucose induced

increases in flow and oxygen consumption is essentially
similar to its influence on digested food induced

increases in flow and oxygen consumption, i.e., addition

of bile to digested food altered the significant relationship
between the two variables and the slope of the regression
line (Figure 9).

The addition of bile into the glucose solution
however did not change the rate of glucose absorption
(Figures 13 and 16). Moreover, the relationship between
the changes in blood flow and glucose absorption remained
the same, i.e., significantly correlated, with or without
bile (Figures 15 and 18). Thus, while bile abolished the
significant correlation between glucose induced increases
in blood flow and oxygen consumption, it did not alter the
relationship between changes in blood flow and glucose

absorption.

CHAPTER V

DISCUSSION

Postprandial intestinal hyperemia is characterized
by an increase in blood flow through the digestive organs
with little or no changes in cardiac output, systemic pres-
sure, or flows to other peripheral vascular beds (16, 25,
43, 120-122). In an extensive series of studies, Chou and
co-workers (7, 13) demonstrated that this mesenteric hyper-
emia is a local phenomenon and is confined only to that
region of the small intestine which is exposed to food.
Brandt et a1. (14) and Dagenais et al. (29) observed that
the hemodynamic changes after a meal in humans are associ-
ated with an enhancement of splanchnic oxidative metabolism.
In addition, the presence of glucose and amino acids in
the gut lumen has consistently been shown to increase both
blood flow and oxygen consumption of the small intestine
(118, 119).

The results from these studies have led to a hypoth-
esis suggesting that the postprandial increase in gut blood
flow is linked to the heightened metabolic activities
during digestion and absorption (34, 118). However, unlike

the heart or the skeletal muscle where many classical

92

93

studies have been performed to correlate the rate of
metabolism and functional hyperemia (69), there are vir-
tually no data available to clearly establish that local
regulation of intestinal blood flow during digestion is
related to factors that are linked to oxidative metabolism.
The purpose of this study was to examine the rela-
tionship between the intestinal hyperemia and the increase
in oxidative metabolism during digestion. In the first
series of experiments, various food solutions were placed
in the small intestine and their effects on blood flow and
oxygen consumption were studied. The food solutions used
were: digested food plus bile, which is a completely
digested food solution that has been shown to cause a maxi-
mal hyperemic response; digested food alone and undigested
food plus bile, which are partially digested food solutions
that cause a slight increase in flow (26); and bile alone,
which has no vascular effects in the jejunum but increases
flOw in the ileum (26). The aim was to examine the rela-
tionship between the changes in blood flow and oxygen con-
sumption at different levels of the intestinal hyperemic
response to food. Each of these food solutions was
individually placed inside the lumen of the intestinal
segment for a 30 minute period during which the changes
in blood flow, oxygen consumption, luminal pressure and

systemic pressure were monitored.

94

The results show that completely digested food
solution, i.e., digested food plus bile, has a greater
hyperemic (+50%) as well as metabolic (+30%) effect than
the other two solutions--digested food and undigested food
plus bile (Figures 1, 2 and 3). While digested food alone
and undigested food plus bile increased flow by approxi-
mately 10%, only the former increased oxygen consumption
(+16%). Luminal placement of bile in the jejunum did not
have any effect on blood flow or oxygen consumption. In
contrast, bile in the ileum increased flow by 60% but did
not alter oxygen consumption (Figure 5). These results
indicate that the local regulation of blood flow during
postprandial intestinal hyperemia is a complex phenomenon
and different constituents of chyme can elicit different
responses in blood flow as well as oxygen consumption.
Indeed, as illustrated by the effects of undigested food
plus bile in the jejunum and bile in the ileum (Figures
3 and 5), the hyperemic response of the small intestine
to the postprandial lumen contents is not always accom-
panied by an enhancement of oxygen consumption.

Thus, the overall local control of intestinal
blood flow after a meal may involve both metabolically
and nonmetabolically linked factors. This conclusion is
supported by the results from the series of experiments
in which the temporal relationship between the increases
in blood flow and oxygen consumption during the placement

of digested food and digested food plus bile was examined

95

in detail. As shown in Figure 7, when digested food alone
was in the jejunal lumen, there was a significant corre-
lation between the changes in blood flow and oxygen con-
sumption. On the other hand, the changes in these two
variables were not significantly correlated when digested
food plus bile was placed in the jejunum (Figure 9). What
this data suggests is that the hyperemic effect of
digested food alone but not digested food plus bile may
in part be related to factors that are linked to oxida-
tive metabolism. As shown in Figure 7, the y intercept
during digested food placement was 6.7% and was not dif-
ferent from the origin. However, the addition of bile into
the food solution increased the y intercept to 44.7%
(Figure 9). Thus the presence of bile in the digested
food produced a 44.7% increase in flow even in the absence
of any apparent change in oxygen consumption. Moreover,
the slope of the line (-0.06, Figure 9) indicates that this
increase in flow remained virtually constant over a wide
range of increases in oxygen consumption. Thus, although
bile enhanced both the hyperemic and metabolic effect of
digested food, the greater increases in these two vari-
ables were not significantly correlated. That is, the
increase in flow was not accompanied by a proportional
increase in oxygen consumption.

It is not clear how the presence of bile can alter
the relationship between blood flow and oxygen consumption.

One possibility is that bile causes a redistribution of

96

blood flow as well as oxygen consumption within the three
layers of the intestinal wall and total wall measurement
is not representative of these changes. Chou et a1. (25)
as well as others (126), using the radioactive microsphere
technique, observed that blood flow increased preferenti—
ally to the mucosa-submucosa layer of the intestine when
food or hypertonic glucose was present in the gut. There
is no evidence that this increase in the mucosa-submucosa
flow is accompanied by a decrease in muscularis flow.
Ideally, mucosal flow and oxygen consumption should be
correlated rather than total wall flow and total wall oxygen
consumption as was done in this present study. However,
as of this writing, there is no method available to simul-
taneously monitor the rate of changes in these two vari-
ables in the different layers of the intestinal wall. The
mucosa-submucosa layer receives a major portion of total
wall flow (up to 88%) and the flow per unit tissue weight
in this layer is much greater than the muscularis layer
(25, 113, 126). The total wall flow as measured in this
present study is, therefore, a close approximation (albeit
not exact) of the changes in mucosa-submucosa flow in
response to the placement of food.

In contrast to blood flow, the rates of oxygen
consumption in the different layers of the intestinal wall
at rest and during the presence of nutrients is largely
unknown. However, because of the fact that major func-

tions of the intestine such as active transport and

97

secretion are performed by the mucosa and submucosa layers,
it is expected that these layers have a much greater
metabolic demand than the muscularis (113), and the
increase in oxygen consumption during luminal placement
of food is mainly due to an increase in mucosal-submucosal
oxidative metabolism. If these assumptions are correct,
the total wall oxygen consumption as measured in this
present study is a close approximation of the mucosal-
submucosal oxygen consumption. Thus, the conclusion that
the hyperemic effect of digested food plus bile is not
related to local metabolism is a valid one. Conversely,
if these assumptions are incorrect, this would indicate
that: (1) At rest, there is a disparity between the meta-
bolic demands of the intestinal intramural layers and their
distribution of blood flow. An unlikely event that is in
sharp disaccord with most experimental evidence (46, 67-
71, 82, 103, 104, 113, 115, 118). (2) The increase in
oxidative metabolism during digested food plus bile place-
ment occurs in all compartments of the intestinal wall,
or the mucosa-submucosa layer actually has decreased oxygen
consumption; the fact that the hyperemic response of the
whole wall to the presence of food is a result of the
increase in mucosa-submucosa flow (25, 126) would certainly
indicate that blood flow is not exclusively controlled by
metabolic factors.

A second possibility of how the addition of bile

to digested food alters the relationship between the

98

increases in blood flow and oxygen consumption is related
to bile's effect on motility. In addition to absorption
and secretion, another major function of the intestine is
motor activity. The motility is often stimulated by the
presence of foodstuffs inside the lumen of the gut (30).
It has been shown in experimental settings that the
motility of the intestine can affect its blood flow

(61, 101, 106). For example, Sidky and Bean (106),

Semba et al. (101) and Chou and Grassmick (23) have shown
that rhythmic contraction may cause rhythmic changes in
flow with an increase in mean flow while tonic contraction
is accompanied by a decrease in flow. Thus, depending on
the type of motility, intestinal blood flow can be altered
in different directions. In the present study, placement
of digested food plus bile often caused an initial increase
in motility of a rhythmic nature (Figure 2). Could this
transient increase in motility affect blood flow enough

to render a poor correlation between flow and consumption?
Kewenter (77) found that when graded doses of acetylcholine
were given intra-arterially into the intestine, blood flow
was affected only at extremely high doses, that produced
an intense motor activity. This led Svanvik and Lundgren
(113) to conclude that gut motility does not affect intes-
tinal blood flow to any great extent under physiological
conditions. In this present study, the increase in rhyth-
mic contraction was small and usually stopped after the

first 5 to 10 minutes during placement (Figure 2). Thus

99

it is not likely that flow was affected to an extent that
would alter the temporal relationship between the changes
in blood flow and oxygen consumption. This conclusion is
supported by a recent finding from our laboratory (Sit and
Chou, unpublished observation) that total abolishment of
intestinal motility during digested food plus bile place-
ment in the jejunum and bile in the ileum still resulted
in an increase in local blood flow which is poorly corre-
lated with the increase in oxygen consumption. Thus the
fact that during digested food plus bile placement there
is no significant correlation between the increase in flow
and oxygen consumption cannot be attributed to the increase
in motility.

A third possibility of how bile alters the relation-
ship between the changes in the two variables monitored
may be related to the effect of bile on food digestion.
Chou and co-workers (21, 25, 26, 81, 126) have demon-
strated that the constituents of chyme responsible for
postprandial intestinal hyperemia are the digested pro-
ducts of food. Of the three major sources of nutrients,
both carbohydrates and proteins can be digested to their
final digestive products (glucose and amino acids) by the
pancreatic enzymes used in this study (30). On the other
hand, complete digestion of lipids requires the presence
of both the pancreatic enzymes and gallbladder bile (30).
Thus, the digested food used in this study probably con-

tained less fatty acids than the digested food plus bile

100

solution. A recent study performed in our laboratory
(Nyhof and Chou, unpublished observation) has indicated
that the increase in flow related well with the increase

in oxygen consumption during the placement of a long

chain fatty acid (oleic) with bile. Thus, the difference
in the correlation between the hyperemia and oxygen con-
sumption during the placement of the two food solutions

was not due to their difference in fatty acids concentra-
tion, i.e., the action of bile in facilitating the diges-
tion of lipids. The two solutions also contained amino
acids and glucose. The amino acids have been shown to have
no effect on blood flow when placed into the jejunal lumen
at physiological concentrations (26). On the other hand,
glucose at physiological concentrations increases both flow
and oxygen consumption upon placement in the lumen of the
small intestine (21, 26, 118, 119).

The mechanism by which glucose induces an increase
in flow in the intestine has never been elucidated. More-
over, what effect bile has on the glucose induced hyperemia
is largely unknown. This possibility must be explored
because in addition to its action on lipid digestion and
absorption bile may alter the hyperemic effect of glucose
and may cause an alteration in the relationship between
the hyperemia and the increase in oxygen consumption.

Thus, in the second part of this study, three series of
experiments were performed to examine the possible

mechanisms by which glucose increases local blood flow in

101

the intestine. In addition, the effect of bile on the
glucose induced hyperemia was also studied.

In the first two series of experiments, glucose
and its synthetic analogs, 3-0-methyl glucose and Z-deoxy
glucose were used for the study; the rationale being that
these glucoses have different absorption and metabolic
characteristics. There are structural requirements for
the active absorption and metabolism of glucose by the
small intestine (18, 28, 125). Eliminating the hydroxyl
group at the C-2 position of the molecule (2-deoxy glucose)
can prevent its absorption by the intestine, while substi-
tuting a methyl group at the C-3 position (3-0-methy1 glu-
cose) inhibits its metabolism but not absorption (18, 28,
125). Thus, by comparing the vascular and metabolic effects
as well as the absorption of these glucoses, one can iden—
tify some of the mechanisms involved in the hyperemia.

In the third series of experiments, the temporal relation-
ship between the increase in blood flow, oxygen consump-
tion and glucose absorption during placement of a 200 mM
glucose solution, with or without bile, were also examined.

The results indicate that both glucose and 3-0-
methyl glucose, which were absorbed from the lumen, sig-
nificantly increased local blood flow but the non-
absorbable glucose, 2-deoxy glucose, did not (Figure 12).
This indicates that the glucose induced hyperemia is at
least in part, related to its absorption. Other studies

also support this hypothesis (21, 25, 126). It has been

102

shown that a 20% glucose solution (1,200 mOsm/liter) in .
the jejunum increases local blood flow but a solution of

a nonabsorbable substance (polyethylene glycol) with the
same osmolality, does not (21). Furthermore, the

increased jejunal blood flow during the presence of food
and hypertonic glucose in the lumen is confined to the
mucosal layer (25, 126). The mucosa is the site for trans-
membrane transport of water, electrolytes and other nutri-
ents. Thus, the postprandial intestinal hyperemia seems

to be a functional hyperemia related to the absorption of
nutrients. Indeed, in the present study, there was a
significant correlation between the increase in blood flow
and gluCose absorption during the luminal placement of
glucose (Figure 15). Although the absorption rate of 3-
O—methyl glucose is similar to that of glucose, the hyper-
emic effect of 3-0-methyl glucose is less than that of glu-
cose (Figures 10 and 11). This appears to indicate that
absorption may not be the only contributing factor of the
hyperemia. This present study shows that glucose

increases local oxygen consumption while 3-0-methyl glucose
does not cause a significant increase (Figure 12). An
increase in local metabolism therefore, may be another
contributing factor for the glucose induced hyperemia.

As shown in Figure 13, the increase in blood flow during
the placement of the glucose solution was accompanied by
an increase in oxygen consumption. The relationship

between the changes in these two variables was

103

significantly correlated (Figure 14). A recent study has
also suggested that the increased local metabolism is a
factor modulating local blood flow during absorption of
fluid from the ileum containing a glucose and Tyrode solu-
tion (118).

As discussed earlier, luminal placement of digested
food increased blood flow and oxygen consumption (Figure 6).
These increases are significantly correlated (Figure 7).
Similarly, luminal placement of glucose increased both
blood flow and oxygen consumption and these increases are
also correlated (Figures 13 and 14). In addition, both
glucose and digested food have quantitatively similar
hyperemic as well as metabolic effects upon placement in
the intestine (Figures 6 and 13) and , as shown in Figures
7 and 14, the relationship between the changes in blood
flow and oxygen consumption during the placement of digested
food is almost identical to the placement of glucose. The
slope of the line for glucose was 0.19; and for digested
food alone was 0.17. The digested food used in this study
contained predominantly amino acids and glucose and only
the latter is believed to be vasoactive at physiological
concentrations in the lumen of the small intestine (26).
The effect of luminal placement of digested food therefore,
may well be due to its glucose content.

As mentioned earlier, the addition of bile to the
digested food altered the relationship between the changes

in blood flow and oxygen consumption (Figure 9). The

104

mechanism by which the presence of bile alters this rela-

tionship is not clear. This effect of bile is not due to

its digestive action which increases the concentration of

fatty acids in the solution containing both digested food

and bile (Nyhof and Chou, unpublished observation). Since
the effect of bile on digested food may be mediated by its
action on glucose in the digested food, its effect on the

glucose induced hyperemia was then determined.

As shown in Figures 10 and 11, the addition of bile
to the glucose solution markedly enhanced the hyperemic
effect of glucose. More importantly, while the increase
in blood flow and oxygen consumption were significantly
correlated during the placement of glucose alone
(Figure 14), the addition of bile altered this relation-
ship and rendered it insignificant (Figure 18). What this
finding seems to suggest is that the effect of bile in
altering the relationship between the changes in blood flow
and oxygen consumption during digested food placement may
be due to its action on glucose contained in the food
solution. This conclusion is supported by the correlation
analyses shown in Figures 9 and 18. Comparison of these
figures indicate that the relationship between the changes
in blood flow and oxygen consumption during digested food
plus bile placement is virtually identical to that of glu-
cose plus bile. The slope for digested food plus bile is
-0.06 and the slope for glucose plus bile is 0.06. The

increases in flow and oxygen consumption were not

105

significantly correlated during the placement of either
of these two solutions.

Bile is an important constituent of chyme and is
secreted into the small intestine after every meal.
While the important role of bile in facilitating the diges-
tion and absorption of lipids is well established (19, 30,
66, 108, 109) its contribution in postprandial intestinal
hyperemia has until recently been largely unknown (26).
The fact that it can enhance the hyperemic effect of
digested food has been assumed to be due to its action on
lipid digestion and absorption (26). The finding from this
present study that bile enhances the hyperemic effect of
glucose (Figures 10 and 11) further underscores the impor-
tance of bile in the overall regulation of blood flow during
the mesenteric hyperemic response to food. It points out
that the influence of bile goes beyond its role in the
lipid induced hyperemia and that it plays a significant
part in the hyperemic effect of at least one other nutrient
as well. Another contribution of bile to postprandial
intestinal hyperemia is likely its hyperemic effect in the
ileum (Figure 5). Luminal placement of bile in the ileum
increased flow markedly but the hyperemia was not accom-
panied by an enhancement of oxygen consumption.

The fact that the bile enhanced hyperemic effect
of glucose and digested food in the jejunum as well as
bile's own hyperemic effect in the ileum are not correlated

with an increase in oxygen consumption strongly suggests

106

that the local regulation of intestinal blood flow during
postprandial hyperemia is not exclusively linked to factors
that are related to oxidative metabolism. This is in con-
trast to what was observed in the myocardium and skeletal
muscle. The preponderance of evidence indicates that there
is a close correlation between the functional hyperemia

in these organs and their metabolic rate (2, 4, 15, 31,

40, 75, 76, 79, 80, 105). In the heart, oxygen consumption
is considered a major determinant of blood flow under a

wide range of conditions (99). This includes enhancement

in work load due to either positive inotropism or increases
in blood pressure. In the skeletal muscle increaSes in
oxidative metabolism have been identified as a causal factor
in the active hyperemia during exercise (99). In this study,
there is little evidence that such a close relationship
exists between the two variables during postprandial intes—
tinal hyperemia.

It is not clear why the regulatory mechanism during
the functional hyperemia in the gut is different from the
heart and skeletal muscle. One possibility may be that
during digestion, the functions performed by the intes-
tinal circulare are more complex than the other two organs
and thus require flow regulatory mechanisms that are not
necessarily linked to oxidative metabolism. For example,
whereas the basic function of the heart and skeletal muscle
is to perform muscular contraction, the functions of the

intestine include secretion, absorption in addition to

107

chyme propulsion by the visceral smooth muscles (30).
While it is true that active absorption by the gut
accelerates cellular oxygen consumption, it also entails
the washout of nutrients from the gut lumen to other

parts of the body for use or storage. Thus, the hyper-
emia in the intestine during digestion serves at least two
distinct purposes: (1) To maintain adequate delivery of
oxygen in response to the heightened demand, and (2) To
transport the absorbed nutrients elsewhere. Teleologic-
ally, it is conceivable that the intestine employs differ-
ent mechanisms to control its blood supply to serve these
functions. Indeed, as mentioned in the literature review
of this study, both local nerves and GI hormones have been
proposed as mediators of postprandial intestinal hyperemia
and may constitute the nonmetabolically linked controlling
factors. The data from this study support this thesis and
the precise role of these factors in the local regulation
of intestinal blood flow during digestion warrants further

investigation.

CHAPTER VI

SUMMARY AND CONCLUSIONS

Postprandial
an increase in blood
tract after a meal.
the observation that
splanchnic oxidative

esis suggesting that

intestinal hyperemia is defined as
flow through the gastrointestinal
Associated with this phenomenon is
there is also an enhancement in
metabolism. This has led to a hypoth-

the cause of the postprandial increase

in mesenteric blood flow is probably linked to the height-

ened metabolic activities during digestion and absorption.

However, there is virtually no data available to clearly

establish that these

two events are related to each other.

The purpose of this study was to examine the relationship

between the increase

in blood flow and oxygen consumption

during postprandial intestinal hyperemia. In addition,

some mechanisms by which a major nutrient, glucose, may

induce an increase in local blood flow in the jejunum were

also studied. The results indicate that:

(l) Luminal placement of digested food and digested

food plus bile in the jejunum increased local

blood flow as well as oxygen consumption. The

latter produced a greater increase in flow and

108

(2)

(3)

109

oxygen consumption than the former. Undigested
food plus bile increased jejunal flow but did not
have any effect on oxidative metabolism. Bile

in the jejunum did not have any effect on blood
flow or oxygen consumption. In contrast, bile in
the ileum increased flow but did not alter oxygen
consumption.

There was a significant correlation between the
increase in blood flow and oxygen consumption
during the luminal placement of digested food.
Digested food plus bile increased blood flow and
oxygen consumption more than digested food alone
did. But the greater increases in these two vari-
ables by digested food plus bile were not signifi-
cantly correlated. Thus bile enhanced the
digested food-induced hyperemia and the increase
in oxygen consumption but altered the positive
relationship between these two variables.

Both glucose and 3-0-methyl glucose were absorbed
and increased local blood flow when placed into
the jejunum. Glucose increased, but 3-0-methyl
glucose did not alter, oxygen consumption and the
former produced a greater hyperemia than the
latter. 2-deoxy glucose was not absorbed and did
not alter local blood flow or oxygen consumption.
These findings indicate that the glucose induced

hyperemia is related to absorption and an increase

110

in oxidative metabolism. Of the three glucoses,

only the vascular effect of glucose was enhanced

by bile. Thus, the potentiating effect of bile

on the glucose-induced hyperemia seems to have

chemical structural specificity.

(4) During the luminal placement of glucose, there

was a significant correlation between the changes

in blood flow and oxygen consumption as well as

blood flow and glucose absorption. Glucose plus
bile increased blood flow and oxygen consumption
more than glucose alone did. But the greater
increases in these two variables were not signifi-
cantly correlated. Thus, the influence of bile

on the vascular and metabolic effect of luminal

placement of glucose is similar to that of digested

food. The relationship between blood flow and glu—
cose absorption remained the same and was signifi-
cantly correlated with or without bile.

In conclusion, the local regulation of blood flow
during postprandial intestinal hyperemia is a complex
phenomenon that may involve both metabolically and non-
metabolically linked factors. Various constituents of
chyme can elicit different responses in blood flow and oxy-
gen consumption in the small intestine. The hyperemic
effect of glucose in the jejunum is, at least in part,
related to glucose absorption and an increase in oxidative

metabolism. Bile enhances both the hyperemic as well as

111

the metabolic effects of glucose and digested food. Bile
also alters the positive correlation between the changes
in blood flow and oxygen consumption produced by glucose
as well as digested food. These findings thus indicate
that the contribution of bile to postprandial intestinal
hyperemia goes beyond its actions in facilitating the

digestion and absorption of lipids.

BIBLIOGRAPHY

BIBLIOGRAPHY

Ahren, C., and U. Hagland. Mucosal lesions in the
small intestine of the cat during low flow. Acta
Physiol. Scand. 88: 541, 1973.

 

Alella, A.; F. L. Williams; C. Bolene-Williams; and
L. N. Katz. Interrelationship between cardiac
oxygen consumption and coronary blood flow. Am.
J. Physiol. 183: 570, 1955.

 

Alpers, D. H., and J. L. Kinzie. Regulation of
small intestinal protein metabolism. Gastroenter—
ology 64: 471, 1973.

 

Barger, A. C.; V. Richards; J. Metcalfe; and B.
Gunther. Regulation of the circulation during
exercise. Am. J. Physiol. 184: 613, 1956.

 

Barnett, J. E., and K. A. Munday. Structural
requirements for active intestinal sugar trans-
port in the hamster. Transport Across the
Intestine, 99 (W. L. Burland and P. D. Samuels,
Eds.), Edinburgh and London: Churchill Living-
stone, 1972.

 

 

Biber, B. The effects of intestinal vasodilator
mechanisms on the rate of 85Kr absorption in
the cat. Acta Physiol. Scand. 90: 578, 1974.

 

Biber, B.; J. Fara; and O. Lundgren. 5-
hydroxytryptamine and intestinal blood flow.
Acta Physiol. Scand. 84: 9A, 1972.

 

Biber, B.; O. Lundgren; and J. Svanvik. The influ-
ence of blood flow on the rate of absorption of
5Kr from the small intestine of the cat. Acta
Physiol. Scand. 89: 227, 1973.

 

Biber, B.; O. Lundgren; and J. Svanvik. Intramural
blood flow and blood volume in the small intestine
of the cat as analyzed by an indicator dilution
technique. Acta Physiol. Scand. 87: 391, 1973.

 

112

10.

11.

12.

13.

14.

15.

16.

17.

18.

113

Bodanszky, M.; M. A. Ondetti; and S. D. Levine.
Synthesis of a heptacosa peptide amide with the
hormonal activity of secretin. Chem. Industr. 42:
1757, 1966.

 

Bond, J. B.; D. G. Levitt; and M. D. Levitt. Use
of inert gas and carbon monoxide to study the pos-
sible influence of countercurrent exchange on
passive absorption from the small bowel. J;
Clin. Invest. 54: 1259, 1974.

 

Bond, J. H.; D. G. Levitt; and M. D. Levitt. Quanti-
tation of countercurrent exchange during passive
absorption from the dog small intestine. J.

Clin. Invest. 59: 308, 1977.

 

Bowen, J. C.; W. Powlik; W. F. Fang; and E. D.
Jacobson. Pharmacologic effects of gastro-
intestinal hormones on intestinal oxygen con-
sumption and blood flow. Surgery 78: 515, 1975.

Brandt, J. L.; L. Castleman; H. D. Ruskin; J.
Greenwald; and J. J. Kelly, Jr. The effect of
oral protein and glucose feeding on splanchnic
blood flow and oxygen utilization in normal and
cirrhotic subjects. J. Clin. Invest. 34: 1017,
1955.

 

Braunwald, E.; S. J. Sarnoff; R. B. Case; W. N.
Stainsby; and G. H. Welch, Jr. Hemodynamic
determinants of coronary flow: Effect of changes
in aortic pressure and cardiac output on the
relationship between myocardial oxygen consump-
tion and coronary flow. Am. J. Physiol. 192:
157, 1958.

 

Burns, G. P., and W. G. Schenk. Effects of diges-
tion and exercise on intestinal blood flow and
cardiac output. Arch. Surg. 98: 790, 1969.

 

Butterfield, W. J.; B. M. Sargeant; and M. J.
Whichelow. The metabolism of human forearm
tissues after ingestion of glucose, fructose,
sucrose, or liquid glucose. A study by con-

tinuous in-vivo autoanalysis. Lancet I: 574,
1964.

Campbell, P. N., and F. G. Young. Metabolic studies
with 3-methy1 glucose. 1. Its fate in the animal
body. Biochem. J. 52: 439, 1952.

 

19.

20.

21.

22.

23.

24.

25.

26.

27.

28.

29.

30.

114

Carey, M. C., and D. M. Small. The characteristics
of mixed micellar solutions with particular refer-
ence to bile. Am. J. Med. 49: 590, 1970.

 

Chen, W. T.; J. M. Dabney; and C. C. Chou. Mucosal
nerves as a mediator of local intestinal blood
flow. Clin. Res. 17: 525, 1969.

 

Chou, C. C.; T. D. Burns; C. P. Hsieh; and J. M.
Dabney. Mechanisms of local vasodilation with
hypertonic glucose in the jejunum. Surgery 71:
380, 1972.

Chou, C. C.; E. C. Frohlich; and E. C. Texter, Jr.
Effects of gastrointestinal hormones on the seg-
mental mesenteric resistances. Fed. Proc. 23:
407, 1964.

 

Chou, C. C., and B. Grassmick. Motility and blood
flow distribution within the wall of the gastro-
intestinal tract. Am. J. Physiol. 235: H34, 1978.

 

Chou, C. C.; C. P. Hsieh; and J. M. Dabney. Com-
parison of vascular effects of gastrointestinal

hormones on various organs. Am. J. Physiol. 232:
H103, 1977.

 

Chou, C. C.; C. P. Hsieh; Y. M. Yu; P. Kvietys;
L. C. Yu; R. Pittman; and J. M. Dabney. Locali-
zation of mesenteric hyperemia during digestion
in dogs. Am. J. Physiol. 230: 583, 1976.

 

Chou, C. C.; P. Kvietys; J. Post; and S. P. Sit.
Constituents of chyme responsible for post-
prandial intestinal hyperemia. Am. J. Physiol.
235: H677, 1978.

 

Crane, C. W., and A. Neuberger. The digestion and
absorption of protein by normal man. Biochem. J.
74: 313, 1960.

 

Crane, R. K. Intestinal absorption of sugars.
Physiol. Rev. 40: 789, 1960.

 

Dagenais, G. R.; A. Oriol; and M. McGregor. Hemo-
dynamic effects of carbohydrate and protein
meals in man: rest and exercise. J. App .
Physiol. 21(4): 1157, 1966.

Davenport, H. W. Physiology of the Digestive Tract.
Chicago, Year Book Medical Publishers Incorporated,
1968.

 

31.

32.

33.

34.

35.

36.

37.

38.

39.

40.

115

Eckenhoff, J. E.; J. H. Hafkenschiel; C. M. Land-
messer; and M. Harmel. Cardiac oxygen metabolism
and control of the coronary circulation. Am. J.
Physiol. 149: 634, 1947.

Ehrlich, V.; K. Fronek; and L. Slegr. Die WirKung
des Reserpins auf die Speichel-Sekretion und den
Kreislauf wahrend des unbedingten und bedingten
Nahrungs-reflexes und wahrend der Differenzierung-
schemmung beim Hunde. Arch. Intern. Pharmacodyn.
115: 373, 1958.

 

Fara, J. W. Escape from tension induced by
noradrenaline or electrical stimulation in iso-
lated mesenteric arteries. Br. J. Pharmacol. 43:
865, 1971.

 

Fara, J. W.; E. H. Rubinstein; and R. R. Sonnenschein.
Intestinal hormones in mesenteric vasodilation
after intraduodenal agents. Am. J. Physiol. 223:
1058, 1972.

 

Fara, J. W.; E. H. Rubinstein; and R. R. Sonnenschein.
Vasceral and behavioral responses to intraduodenal
fat. Science 166: 110, 1969.

Fasth, S.; S. Filipsson; L. Hulten; and J. Martinson.
The effect of the gastrointestinal hormones on
small intestinal motility and blood flow.
Experientia 29: 982, 1973.

 

Folkow, B. Regional adjustments of intestinal blood
flow. Gastroenterology 65: 423, 1967.

 

Folkow, B.; D. H. Lewis; 0. Lundgren; S. Mellander;
and I. Wallentin. The effect of graded vasocon—
stricter fiber stimulation on the intestinal resis-
tance and capacitance vessels. Acta Physiol. Scand.
61: 455, 1964.

 

Folkow, B.; D. H. Lewis; 0. Lundgren; S. Mellander;
and I. Wallentin. The effect of the sympathetic
vasoconstrictor fibers on the distribution of
capillary blood flow in the intestine. Acta
Physiol. Scand. 61: 458, 1964.

 

Foltz, E. L.; R. G. Page; W. F. Sheldon; S. K. Wong;
W. J. Tuddenham; and A. J. Weiss. Factors in vari-
ation and regulation of coronary blood flow in
intact anesthetized dogs. Am. J. Physiol. 162:
521, 1950.

 

41.

42.

43.

44.

45.

46.

47.

48.

49.

50.

51.

116

Frogge, J. D.; A. S. Hermreck; and A. P. Thal.
Metabolic and hemodynamic effects of secretin

and pancreozymin on the pancreas. Surgery 68:
498, 1970.

Fronek, K., and A. Fronek. Combined effect of exer-
cise and digestion on hemodynamics in conscious
dogs. Am. J. Physiol. 218: 555, 1970.

 

Fronek, K., and L. H. Stahlgren. Systemic and
regional hemodynamic changes during food intake
and digestion in non-anesthetized dogs. Circ.
Res. 23: 687, 1968.

Gladstone, S. A. Cardiac output and related func-
tions under basal and postprandial conditions.
Arch. Inter. Med. 55: 533, 1935.

 

Goodhead, B.; H. S. Himal; and J. Zanbilowcz.
Relationship between pancreatic secretion and
pancreatic blood flow. Gut ll: 62, 1970.

Granger, D. N.; J. D. Valleau; R. B. Parker; R. S.
Lane; and A. E. Taylor. Effects of adenosine on
intestinal hemodynamics, oxygen delivery, and
capillary fluid exchange. Am. J. Physiol. 235:
H707, 1978.

 

Greenway, C. V., and V. S. Murthy. Effects of vaso-
pressin and isoprenaline infusions on the dis-
tribution of blood flow in the intestine: criteria
for the validity of microsphere studies. Br. J.
Pharmacol. 46: 177, 1972.

 

Greenway, C. V., and R. D. Stark. Hepatic vascular
bed. Physiol. Rev. 51: 23, 1971.

 

Gregg, D. E.; W. H. Pritchard; R. W. Eckstein; R. E.
Shipley; A. Rotta; J. Dingle; T. W. Steegle; and
J. T. Wearn. Observations on the accuracy of the
Thermostromuhr. Am. J. Physiol. 136: 250, 1942.

 

Gregory, R. A., and H. J. Tracy. The constitution
and properties of two gastrins extracted from hog
central mucosa. Gut 5: 103, 1964.

Grim, E., and E. O. Lindseth. Distribution of blood
flow to the tissues of the small intestine of the
dog. Univ. Minn. Med. Bull. 30: 138, 1958.

 

52.

53.

54.

55.

56.

57.

58.

59.

60.

61.

62.

117

Grollman, A. Physiological variation in the cardiac
output of man. Part III. The effect of the inges-
tion of food on the cardiac output, pulse rate,
blood pressure and oxygen consumption of man.

Am. J. Physiol. 89: 366, 1929.

 

Grossman, M. I.; C. R. Robertson; and A. C. Ivy.
Proof of a hormonal mechanism for gastric secre-
tion--the humoral transmission of the distention
stimulus. Am. J. Physiol. 153: 1, 1948.

 

Haddy, F. J.; C. C. Chou; J. B. Scott; and J. M.
Dabney. Intestinal vascular responses to naturally

occurring vasoactive substances. Gastroenterology
52: 2, 1967.

 

Harper, A. A., and H. S. Raper. Pancreozymin, a
stimulant of the secretion of pancreatic enzymes
in extracts of the small intestine. J. Physiol.
102: 115, 1943.

 

Herrick, J. B.; H. E. Essex; F. C. Mann; and E. J.
Baldes. The effect of digestion on the blood flow
in certain blood vessels of the dog. Am. J.
Physiol. 108: 621, 1934.

Henrich, H. Adjustment behavior of adrenergic-induced
vasoconstrictors in the intestinal circulation of
the cat. Angiologica 10: 233, 1973.

 

Hilton, S. M., and M. Jones. The role of plasma kinin
in functional vasocilation in the pancreas. J.
Physiol. 195: 521, 1968.

Hulten, L.; J. Lindhagen; and O. Lundgren. Sympa—
thetic nervous control of intramural blood flow
in the feline and human intestine. Gastro-
enterology 72: 41, 1977.

 

Ivy, A. C., and E. Oldberg. A hormone mechanism for
gallbladder contraction and evacution. Am. J.
Physiol. 86: 599, 1928.

Jacobson, E. D.; G. F. Brobmann; and G. A. Brecher.
Intestinal motor activity and blood flow.
Gastroenterology 58: 575, 1970.

 

Jacobson, L. F., and R. J. Noer. The vascular pat-
tern of the intestinal villi in various laboratory
animals and man. Anat. Rec. 114: 85, 1952.

 

63.

64.

65.

66.

67.

68.

69.

70.

71.

72.

73.

74.

118

Jodal, M., and O. Lundgren. Demonstration of tissue
hyperosmolality in the tips of intestinal villi
during sodium chloride absorption. Acta Physiol.
Scand. 95: 47A, 1975.

 

Jodal, M., and O. Lundgren. The distribution of
absorbed 3H-palmitic acid in the intestinal villi
of the cat during various circulating conditions.
Acta Physiol. Scand. 89: 318, 1973.

 

Jodal, M., and O. Lundgren. Studies on the in vivo
absorption of butyric acid in the small intestine
of the cat. Acta Physiol. Scand. 89: 327, 1973.

 

Johnson, L. R. Gastrointestinal hormones. In
E. D. Jacobson and L. L. Shanbour (Eds.), M.T.P.
Int. Rev. of Sci. 1:4, Gastrointestinal Physiology,
Baltimore, University Park Press, 1972.

 

Johnson, P. C. Autoregulation of blood flow in the
intestine. Gastroenterolggy 52: 435, 1967.

Johnson, P. C. Autoregulatory response of cat mesen-
teric arterioles measured in vivo. Circ. Res. 22:
199, 1968.

 

Johnson, P. C. The microcirculation, and local and
humoral control of the circulation. In A. C. Guyton
and C. E. Jones (Eds.), M.T.P. Int. Rev. of Sci.
1:1, Cardiovascular Physiology, Baltimore,
University Park Press, 1975.

 

Johnson, P. C. Origin, localization, and homeostatic
significance of autoregulation in the intestine.
Circ. Res. 14 (Suppl. 1): 225, 1964.

 

Jones, W. B.; H. D. Thomas; and T. J. Reeves.
Circulatory and ventilatory responses to post-
prandial exercise. Am. Heart J. 69: 668, 1965.

 

Jorpes, J. E., and V. Mutt. Cholecystokinin and
pancreozymin, one single hormone. Acta Physiol.
Scand. 66: 196, 1966.

 

Kampp, M., and O. Lundgren. Blood flow and flow
distribution in tbs small intestine of the cat as
analyzed by the Kr 5 wash-out technique. Acta
Physiol. Scand. 72: 282, 1968.

Kampp, M.; O. Lundgren; and N. J. Nilsson. Extra-
vascular shunting of oxygen in the small intestine
of the cat. Acta Physiol. Scand. 72: 396, 1968.

 

75.

76.

77.

78.

79.

80.

81.

82.

83.

84.

85.

119

Katz, A. M.; L. N. Katz; and F. L. Williams. Regu-
lation of coronary blood flow. Am. J. Physiol.
180: 392, 1955.

 

Katz, L. N., and H. Feinberg. The relation of cardiac
effort to myocardial oxygen consumption and coronary
flow. Circ. Res. 6: 656, 1958.

 

Kewenter, J. Effect of graded acetycholine infusions
on intestinal motility, volume and blood flow.
Scand. J. Gastroenterol. 6: 435, 1971.

 

Korner, P. I.; Y. P. Chalmers; and S. W. White. Some
mechanisms of reflex control of the circulation by
the sympatho-adrenal system. Circ. Res. 20: 21 III,
157, 1967.

 

Kramer, K., and W. Quensal. Untersuchungen fiber den
Muskelstoffwechsel des Warmeblfiters. I. Mitteilung.
Der Verlauf der Muskeldurchblutung wahrend tetan—
ischen Kontraktion. Pflfigers Arch. ges. Physiol.
239: 621, 1937.

 

Kramer, K.; F. Obal; and W. Quensel. Untersuchungen
fiber den Muskelstoffwechsel des Warmeblfiters. III.
Mitteilung. Die Sauresoffaufnahme des Muskels
wahrend rythmischer Tatigkeit. Pflfigers Arch. ges.
Physiol. 241: 717, 1939.

 

Kvietys, P.; R. Pittman; and C. C. Chou. Contribution
of luminal concentration of nutrients and osmolality
to postprandial intestinal hyperemia in dogs.

Proc. Soc. Exptl. Biol. Med. 152: 659, 1976.

 

Lanciault, G., and E. D. Jacobson. The gastrointes-
tinal circulation. Gastroenterology 71: 851, 1976.

 

Laureta, H. C.; C. C. Chou; and E. C. Texter, Jr.
Effects of gastrointestinal hormones on total
resistance of gastric circulation. Clin. Res. 13:

256, 1965.

 

Lester, R. G., and E. Grim. Substrate utilization
and oxygen consumption by canine jejunal mucosa in
vitro. Am. J. Physiol. 229: 139, 1975.

 

Levitt, M. D.; J. H. Bond; and D. G. Levitt. Does
countercurrent exchange influence small bowel
function? Am. J. Dig. Dis. 19: 771, 1974.

 

86.

87.

88.

89.

90.

91.

92.

93.

94.

95.

96.

97.

120

Levitt, M. D., and D. G. Levitt. Use of inert gases
to study the interaction of blood flow and diffusion
during passive absorption from the gastrointestinal
tract of the rat. J. Clin. Invest. 52: 1852, 1973.

 

Lundgren, 0. Studies on blood flow distribution and
countercurrent exchange in the small intestine.
Acta Physiol. Scand. 303 (Suppl.): 1, 1967.

 

Mutt, V., and J. E. Jorpes. Chemistry and physiology
of cholecystokinin-pancreozymin. Proc. XXIV.
Int. Cong. Physiol. Sci. 6: 193, 1968.

 

Mutt, V., and J. E. Jorpes. Secretin: isolation and
determination of structure. Proceeding of the
Fourth International Symposium on the Chemistry of
Natural Products. Stockholm, Sweden, 1966.

 

 

 

Papp, M.; B. Varga; and G. Folly. Effects of
secretin, pancreozymin, histamine and decholin on

canine pancreatic blood flow. Pfugers Arch. 340:
349, 1973.

 

Post, J. A., and K. M. Hanson. Hepatic, vascular and
biliary responses to infusion of gastrointestinal
hormones and bile salts. Digestion 12: 65, 1975.

 

Reininger, E. J., and S. Nutik. Determination of
cardiac output following a meal in the unanesthe-
tized dog. Fed. Proc. 19: 118, 1960.

 

Reininger, E. J., and L. A. Sapirstein. Effect of
digestion on distribution of blood flow in the
rat. Science 126: 1176, 1957.

Richardson, D. R., and P. C. Johnson. Comparison of
autoregulatory escape and autoregulation in the
intestinal vascular bed. Am. J. Physiol. 217: 586,
1969.

 

Ross, G. Cardiovascular effects of secretin.
Am. J. Physiol. 218: 1166, 1970.

 

Ross, G. Norepinephrine vasoconstrictor escape in
isolated mesenteric arteries. Am. J. Physiol. 228:
1652, 1975.

 

Ruch, T. C.; H. D. Patton; J. W. Woodbury; and A. L.
Towe. Neurophysiology. Philadelphia, W. B.
Saunders Co., 1965, pp. 226-237.

 

121

98. Schedel, H. P.

Water and electrolytes transport.
Clinical aspects. Med. Clin. of N. Am. 58:
1974.

1429,

99. Scott, J. B.,

and J. M. Dabney. Relation of gut
motility to blood flow in the ileum of the dog.
Circ. Res. 14 (Suppl. 1): 234, 1964.

100. Scott, J. B.,

and F. J. Haddy. Metabolically linked
vasoactive chemicals in local regulation of blood
flow. Physiol. Rev. 48: 688, 1968.

101. Semba, T

.; F. Kazumoto; and K. Fujii. The influence
of rhythmic and tonic contraction of the small
intestine on the blood flow through the intestinal
segment. Japan J. Physiol. 21: l, 1971.

102. Sharma, K. N.,

and E. S. Nasset. Electrical activity

in mesenteric nerves after perfusion of gut lumen.

Am. J. Physiol. 202: 725, 1962.

103. Shepherd, A. P.; D. Mailman; T. F. Burks; and H. J.
Granger. Effects of norepinephrine and sympathetic
stimulation on extraction of oxygen and 3 Rb in
perfused canine small bowel. Circ. Res. 33: 166,
1973.

104. Shepherd, A. P., and H. J. Granger.
escape in the gut:

Autoregulatory
ology 65: 77,

a system analysis. Gastroenter-

1973.

105. Shipley, R. E., and D. E. Gregg. The cardiac response
to stimulation of the stellate ganglia and cardiac
nerves. Am. J. Physiol. 143: 396, 1945.

106. Sidky, M., and J. W. Bean.

Influence of rhythmic
and tonic contraction of intestinal muscle on blood

flow and blood reservoir capacity in dog intestine.
Am. J. Physiol. 193: 386, 1958.

Sidky, M. N., and J. W. Bean.
ations of blood CO

107.

Local and general alter-
and influence of intestinal

motility in regula ion of intestinal blood flow.
Am. J. Physiol. 167: 413, 1951.

 

 

 

108. Simmonds, W. J. Absorption of lipids. In E. D.
Jacobson and L. L. Shanbour (Eds.), M.T.P. Int. Rev.
of Sci. 1:4, Gastrointestinal Physiology, Baltimore,
University Park Press, 1972.

109.

Simmonds, W. J.

The role of micellar solubilization
in lipid absorption. Aust. J. Exp. Biol. Med. Sci.
50: 403, 1972.

110.

111.

112.

113.

114.

115.

116.

117.

118.

119.

120.

122

Sit, S. P.; P. Kvietys; R. Gallavan; C. C. Chou; and
D. Collings. Vascular effects of local i.a. infu-
sion of micellar fatty acids and taurocholate in
the canine small intestine. The Physiologist 20:
28, 1977.

 

Svanvik, J. Mucosal blood circulation and its influ-
ence on passive absorption in the small intestine,
an experimental study in the cat. Acta Physiol.
Scand. 385 (Suppl.): 1, 1973.

 

Svanvik, J. Mucosal hemodynamics in the small intes-
tine of the cat during regional sympathetic vaso-
constrictor activation. Acta Physiol. Scand. 89:
19, 1973.

 

Svanvik, J., and O. Lundgren. Gastrointestinal circu-
lation. In R. Crane (Ed.), M.T.P. Int. Rev. of Sci.
2:12, Gastrointestinal Physiology, Baltimore,
University Park Press, 1977.

 

 

Swan, K. G., and E. D. Jacobson. Gastric blood flow
and secretion in conscious dogs. Am. J. Physiol.
212: 891, 1967.

 

Texter, E. D.; C. C. Chou; H. C. Laureta; and G. R.
Van Trappen. Physiology of the Gastrointestinal
Tract. St. Louis, The C. V. Mosby Co., 1968.

 

Thulin, L. Effects of gastrointestinal polypeptides
on hepatic bile flow and splanchnic circulation.
Acta Chir. Scand. 441 (Suppl): 1, 1973.

 

Uden, R. Effect of secretin in celiac and superior
mesenteric angiography. Acta Radiol. 8: 497, 1969.

 

Valleau, J. D.; D. N. Granger; and A. E. Taylor.
Effect of solute-coupled volume absorption on oxygen
consumption in the cat ileum. Am. J. Physiol. 236:
E198, 1979.

 

Varro, V.; L. Cserney; F. Szarvas; and G. Blaho.
Effects of glucose and glycine solution on the
circulation of the isolated jejunal loop in the
dog. Am. J. Digest. Diseases 12: 60, 1967.

 

Vatner, S. F.; D. Franklin; and R. L. Van Citters.
Coronary visceral vasoactivity associated with

eating and digestion in the conscious dog.
Am. J. Physiol. 219: 1380, 1970.

 

121.

122.

123.

124.

125.

126.

127.

123

Vatner, S. F.; D. Franklin; and R. L. Van Citters.
Mesenteric vasoactivity associated with eating and
digestion in the conscious dog. Am. J. Physiol.
219: 170, 1970.

 

Vatner, S. F.; T. A. Patrick; C. B. Higgens; and D.
Franklin. Regional circulatory adjustments to
eating and digestion in conscious unrestrained
primates. J. Appl. Physiol. 36: 524, 1974.

 

Wang, C. C., and M. I. Grossman. Physiological deter-
mination of the release of secretin and pancreozymin
from intestine of dogs with transplanted pancreas.
Am. J. Physiol. 164: 527, 1951.

 

William, J. H., Jr.; M. Mager; and E. D. Jacobson.
Relationship of mesenteric blood flow to intestinal
absorption of carbohydrates. J. Lab. Clin. Med. 63:
853, 1964.

 

Wilson, T. H., and B. R. Landau. Specificity of sugar
transport by the intestine of the hamster. Am. J.
Physiol. 198: 99, 1960.

Yu, Y. M.; Luke C. C. Yu; and C. C. Chou. Distribu-
tion of blood flow in the intestine with hypertonic
glucose in the lumen. Surgery 78: 520, 1975.

Zamiatina, O. N. Electrophysiological investigation
of the afferent impulsation in intestinal nerves.
Schenov. Physiol. J. USSR. English Transl. 43: 412,
1957.

 

APPENDIX

APPENDIX

Method of Somogyi-Nelson

 

Reagents:

1.

Alkaline copper tartrate. 24 gm anhydrous sodium car-
bonate and 12 gm sodium potassium tartrate were dis-
solved in 200 ml distilled water. 40 ml of a 10% copper
sulfate solution was then added to the solution. When
dissolved, 16 gm sodium bicarbonate was added and
stirred. 180 gm anhydrous sodium sulfate was dissolved
in 600 ml water. The solution was heated to boil,
cooled and added to the copper solution. The mixture
was then transferred to a 1000 ml volumetric flask and
diluted to volume.

Acid arsenomolybdate solution. 50 gm ammonium molyb-
date was dissolved in 900 ml distilled water. 42 ml
concentrated sulfuric acid was added to the solution
and the whole was stirred gently. 6 gm disodium 0-
arsenate dissolved in 50 ml water was then added to the
mixture and placed in an incubator at 37°C for 48 hours.
Standards.

A. Stock standard. 1 gm glucose was dissolved in a

0.2% benzoic acid solution and diluted to 100 ml

124

125

in a volumetric flask. This solution contained
10 mg glucose/m1.
B. Working standard. The stock standard solution was
diluted 1:100 and 2:100 with 0.2% benzoic acid.
The standard solutions thus contained 0.1 and 0.2
mg glucose/ml.
4. Zinc sulfate solution, 5.0%, 0.175M. 50 gm zinc sulfate
was dissolved in distilled water and diluted to 1 L.
5. Barium hydroxide, 0.3 N. 95 gm barium hydroxide was
dissolved in distilled water and diluted to 2 L.

Procedure: 1 volume of plasma sample was diluted with 5

 

volume water, 2 volume barium hydroxide and 2 volume zinc
sulfate. This produced a 1:10 dilution of the plasma sample.
It was added to a Folin-Wu sugar tube. To three other tubes,
1 ml of water was added (blank) to the first, 1 m1 standard
containing 0.1 mg glucose to the second, and 1 ml standard
containing 0.2 mg glucose to the third. 1 m1 alkaline
copper tartrate was added to each tube. These tubes were
then heated in a boiling water bath for 15 minutes. After
cooling, 1 m1 of the arsenomolybdate solution was added to
each tube. The tubes were diluted to 25 ml each with dis-
tilled water and mixed by inversion. The samples were read
against the blank in a photometer at 500 nm.

Calculation: Since 1 ml of a 1:10 plasma sample was treated

 

the same as 1 m1 of standard containing 0.1 mg/ml (10 mg/
100 m1) of glucose or 012 mg/ml (20 mg/100 ml), the calcu-

lation was:

126

Absorbance of sample

 

Absorbance of standard

x 10 x 10 (or 20) =

mg of glucose/100 m1 sample

Glucose Oxidase Method

 

Reagents:

1.

Phosphate buffer, 0.1 M, pH 7.0. 8.7 gm NaZHPO4 and

5.3 gm KH2P04 were dissolved in 950 ml water. pH of

the solution was adjusted to 7.0 and then diluted to

1 L.

Buffered peroxidase solution. 125 ml phosphate buffer,

175 ml water and 200 m1 glycerin were added to a volu-

metric flask and mixed. 10 mg peroxidase and 100 mg

O-dianisidine dissolved in 10 ml methanol were than

added to the mixutre.

Glucose oxidase solution. 500 mg glucose oxidase was

dissolved in 50 m1 of 40% glycerin.

Zinc sulfate and barium hydroxide as used for the

preparation of the Somogyi reagents.

Standards.

A. Stock standard. 10 mg/ml. Same as given for the
Somogyi-Nelson method.

B. Working standards. 1, 2 and 3 m1 of the stock
standard were diluted to 10 ml with 0.1% benzoic
acid. These were equivalent to 100, 200, and 300

mg glucose/100 m1 of the solution.

Procedure: 4.5 ml buffered peroxidase was pipetted to a

 

test tube. After warming to 37°C, 0.02 ml of the plasma

127

sample was added to the solution. 0.5 ml glucose oxidase
solution was added to the mixture and the whole was incu-
bated at 37°C for 30 minutes. After incubation, 3 m1 of
30% sulfuric acid was added to the solution and mixed.
The standards and samples were read against the blank at
530 nm.

Calculation: Since the standards and samples were treated

 

similarly:

Absorbance of sample
Absorbance of standard

 

x Conc. of standard =

Cone. of sample

   

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