VASCULAR RESPONSES 0F . SKIN AND SKELETAL MUSCLE DURING PROSTAGLANDIN A1 INFUSIONS Thesis for the Degree of M. S. ' MTCHIGAN STATE UNIVERSITY JANET L. PARKER .1972 ‘ M? amomc or ‘4’ x ‘ MOM; & SUNS' 300K BINDERY INC. ‘IBRARY amoms 'RTIISPORT.-IICIIIGA__I ‘i—‘_" ABSTRACT VASCULAR RESPONSES OF SKIN AND SKELETAL MUSCLE DURING PROSTAGLANDIN Al INFUSIONS BY Janet L. Parker Collateral-free, innervated canine forelimbs were used to study blood flows, vascular resistances, and transcapil- lary fluid flux changes in skin and skeletal muscle vascular beds during prostaglandin Al infusions. Large and small artery and vein pressures were measured and total and seg- mental vascular resistances were calculated in both skin and muscle during natural and constant (pump-perfused) arterial inflow. Steady-state muscle (brachial) and skin (cephalic) vein outflows were measured, and limb weight was monitored continually. During natural perfusion (N=16), intra-arterial PGA1 infusions (0.2-10.0 HQ/min) decreased skin and muscle small artery pressures at each level of infusion. Initially (0.2-1.0 ug/min) skin and muscle flows increased 20%, skin, muscle, and total resistances decreased, and muscle and skin small vessels resistances decreased. Limb weight also in- creased. When the systemic pressure began to fall (l.0-l0.0 ug/min) these values returned toward control levels. During Janet L. Parker constant flow (N=9), intra-arterial infusions (O.2-l0.0 ug/ min), brachial (perfusion) and small artery pressures and‘ total resistances decreased due to active vasodilation in small vessel segments of both skin and muscle. No redistri- bution of blood flow between skin and muscle vascular beds occurred. Venous resistances remained unchanged. A lower dose range of infusions (0.02-0.20) in another group of animals (N=5) produced changes qualitatively similar to those seen in the previous constant flow group over the lower infusion rates. Limb weight measurements suggest little effect upon transcapillary fluid movement. Ten minute intra— venous infusions (6 Ug/min) during natural arterial perfusion (N=5) showed a slight increase in flow during the first minute followed by large decreases in flow during the re- mainder of infusion. Total outflow decreased 50%. Initially, total and small vessel resistances were decreased, although the systemic blood pressure was well below control and tend- ing to cause reflex vasoconstruction. The data demonstrates that PGA1 causes active vasodilation in the skin and muscle beds of the dog forelimb, that this vasodilation is dose related, and that the major site of action is at the small vessel (arteriolar) level. VASCULAR RESPONSES OF SKIN AND SKELETAL MUSCLE DURING PROSTAGLANDIN Al INFUSIONS By A: (N' Janet L. Parker A THESIS Submitted to Michigan State University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Department of Physiology 1972 .\‘\1 A DEDICATION to my husband to my father to the loving memory of my mother ii ACKNOWLEDGEMENTS The author wishes to express her sincere appreciation to her advisor, T. E. Emerson, Jr., Ph. D., for his invalu— able instruction and encouragement during the course of the graduate program. The author is also indebted to Drs. J. B. Scott and R. M. Daugherty for their advice and consultation. The author's gratitude is also extended to Mr. R. S. Underwood and Mr. W. M. Wynne for their technical assistance. iii CHAPTER TABLE OF CONTENTS I 0 INTRODUCTION. 0 I O O O O O O O O O O O O O O Q I I 0 REVIEW OF LI TERATURE O O O I O O O O O C O O O . Systemic Circulatory Effects. . . . . . . Effect Upon Myocardial Contractility. . . Peripheral Vascular Effects . . . . . . . Effect Upon Coronary Vasculature. . . . . Renal Vascular Effects. . . . . . . . . . Pulmonary Vascular Effects. . . . . . . . Skin and Skeletal Muscle Circulation. . . Microcirculatory Effects. . . . . . . . . III. MATERIALS AND METHODS . . . . . . . . . . . . . IV 0 RESULTS 0 0 O O 0 O O O O O O O O O O O O C O O I. II. III. Intra-arterial Infusion-Natural Brachial Artery Inflow O O O O O O O I O O O O O O Intra-arterial Infusion-Constant Brachial Artery Flow 0 O O O O O O I O I O O O O O Intravenous Infusion-Natural Brachial Artery Flow . . . . . . . . . . . . . . . V. DISCUSSION. 0 O O O O O O O I O O O O O O O O 0 Flow Effects. 0 O O O O O O O O O O O O 0 Resistance. . . . . . . . . . . . . . . . Weight and Transcapillary Fluid Fluxes. . VI. SUMMARY AND CONCLUSIONS . . . . . . . . . . . . REFERENCES CITED 0 O O O O O O O O O O I O 0 C O O O 0 iv Page 10 ll 12 l3 13 15 17 21 21 29 32 43 43 45 48 52 54 LIST OF FIGURES FIGURE 1. Average responses of forelimb blood flows, pres- sures, and weight to progressively increasing rates of intrabrachial infusion of prosta— glandin A1 at natural arterial inflow. . . . . . Total forelimb, total muscle and total skin resistance reSponses to progressively increasing rates of intrabrachial infusion of PGAl. Data from experiments illustrated in Figure l . . . . Segmental resistance responses to progressively increasing rates of intrabrachial infusion of PGA . Data from experiments illustrated in Figure l . . . . . . . . . . . . . . . . . . . . Average responses of forelimb blood flows, pres- sures and weight to progressively increasing rates of intrabrachial infusion of prosta- glandin A1 at constant arterial inflow . . . . . Average responses of forelimb blood flows, pres- sures and weight to progressively increasing rates of a low dose of intrabrachial infusion of prostaglandin A1 at constant arterial inflow . . Average responses of forelimb blood flows, pres- sures and weight to intravenous infusion (6 ug/ min) of prostaglandin A1 at natural arterial in- f 10W 0 O O C O I O I O O O O O O O O O I I O O D Total forelimb, total muscle and total skin re- sistance responses to intravenous infusion (6 ug/min) of prostaglandin A1. Data from ex- periments illustrated in Figure 6. . . . . . . . Segmental resistance responses to intravenous infusion (6 ug/min) of_prostaglandin A1. Data from the experiments illustrated in Figure 6 . . Page 24 26 28 31 34 36 39 41 CHAPTER I INTRODUCTION The presence of a vasodilator with smooth muscle stimu- lating activity was first demonstrated by von Euler, nearly forty years ago, in the seminal fluid of man and sheep. Since that time the prostaglandins have been found to be widely distributed in mammalian tissues, and shown, in many bio— logical systems, to be among the most potent substances known (Bergstrom EE.EA" 1968). In the past decade, they have been ascribed a myriad of biological activities and chemical puri- fication techniques have enabled their use in many clinical situations ranging from induction of labor to bronchodila- tion. The effects of the prostaglandin A (PGA) compounds, in contrast to the numerous actions of the prostaglandin E and prostaglandin F compounds, are relatively specific for the cardiovascular system. Furthermore, they are not substantial- ly metabolized in the lungs, as are the other prostaglandins, and have therefore been postulated as humoral factors in the regulation of arterial pressure and regional blood flow (Higgins 33 $1., 1971). In addition, the PGA compounds have been recently studied with regard to possible therapeutic uses in circulatory shock, congestive heart failure, and hypertension (Higgins 32 31., 1971). However, the intracies of the cardiovascular actions of the PGA compounds have not been completely elucidated. Although they have been shown to have potent peripheral dilatory activity, little is known about their effects upon segmental resistances and transvascular fluid fluxes. The aim of the present study was to determine the local and remote effects of PGA1 on canine forelimb 1) skin and muscle blood flow, 2) parallel and series coupled vascular resistances, and 3) transcapillary fluid movement. CHAPTER II REVIEW OF LITERATURE The prostaglandins are a unique family of unsaturated fatty acids, grouped chemically into four series, named E, F, A, and B. They are widely distributed in mammalian tissues and body fluids, and are attributed widely varying and sometimes opposing biological actions. Although they appear to have potential value in many clinical conditions, a physiological role for any of the prostaglandins remains to be demonstrated. Chemically, the prostaglandins are all derived from the hypothetical parent compound, prostanoic acid, and consist of a five membered ring in a twenty carbon skeleton. The fourteen known prostaglandins (PGs), have common structure and differ only in the degree of unsaturation or substitution in the cyc10pentane ring or aliphatic side chains (Bergstrom et 31., 1968). The E group (PGE) contains characteristic ll a-hydroxy and 9—keto groups, and is easily dehydrated by weak alkali to the 10:11 unsaturated ketone, prostaglandin A (PGA). PGA can isomerize to form the double conjugated ketone, PGB. The F prostaglandins are analogous to the E compounds but the 9-keto group is reduced to a hydroxyl (Bergstrom et_al., 1962a; Bergstrom 32 31., 1962b). The groups are further defined by a subscript number, referring to the number of double bonds present in the aliphatic side chain. Thus, PGA has only the 13:14 trans double bond, 1 whereas PGE2 and PGF3 have two and three bonds, respectively. //A\\///\\V///COOH (14) (13) OH PGA Prostaglandin research was initiated with the clinical observation that the human uterus responds to semen with contraction or relaxation (Kurzok and Lieb, 1930). Later, the presence of this biologically active substance in the seminal fluid of man.and sheep was independelty demonstrated by Goldblatt (1933) and von Euler (1934). Von Euler showed that this substance caused a prolonged fall in blood pressure after intravenous injection in the rabbit and cat, and termed this active principlekprostaglandin (von Euler, 1936). Due to the lack of isolation and purification techniques, little definitive work was done with prostaglandin until nearly thirty years later. In 1957, Sune Bergstrom undertook to isolate this substance and found not one, but thirteen naturally occurring prostaglandins in sheep vescicular glands (Bergstrom gt a1., 1960). Bergstrom and his co-workers succeeded in elucidating the structure of the PGE and PGE compounds in 1960, and a phenomenal expansion of prosta— glandin literature followed. Recently, some of the prosta- glandins have been totally synthesized in the laboratory (Beal et a1., 1967). Soon after their identification, the prostaglandins were demonstrated in most mammalian tissues, including lung (Samuelsson, 1964), brain (Coceani and Wolfe, 1965), Spinal cord (Horton and Main, 1967), and kidney (Daniels gt 31., 1967; Lee 23 a1., 1966), and were found to be released from the stomach (Coceani et al., 1967), adrenals (Ramwell 2E.3l" 19660, diaphragm (Ramwell gt 31., 1965), and other organs (Bergstrom gt_al., 1968). They have been shown to possess a myriad of biological activities involving the cardiovascular system (vasodilation, constriction, cardiac effects), renal system (water and electrolyte excretion), the female and male reproductive systems (labor induction, therapeutic abortion, fertility), the pulmonary system (bronchodilation), the upper respiratory system (nasal patency), and the gastrointestinal system (antisecretory activity). Thus, due to their ability to affect many physiological functions, the prostaglandins appear to have potential value in a wide variety of clinical conditions. The PGA compounds are particularly interesting with regard to their specificity upon the cardiovascular and renal systems. This group was first distinguished from the other prostaglandins because of its potent vasodepressor activity and lack of non-vascular smooth muscle stimulating activity (Daniels 3E_31., 1965). In addition, the PGA compounds are not substantially metabolized in the lungs (McGiff 33 31., 1969) as are the other prostaglandins. These compounds have therefore been postulated as hormonal factors in the regula- tion of blood pressure and regional blood flow (Higgins 31 313, 1970), and their cardiovascular actions have been recently evaluated in basic and clinical studies. Most current studies are being carried out with PGA because it is more readily 1 available as a pure crystalline entity than PGA2 and the bio- logical properties of the two appear to be equivalent (Hinman, 1970). Systemic Circulatory Effects PGAl, similar to PGE has highly potent hypotensive 1' properties in the dog (Nakano, 1967; Nakano and McCurdy, 1967); Nakano and McCurdy, 1968; Horton and Jones, 1969), cat (Horton and Jones, 1969), rat (Weeks 31 31., 1969), rabbit (Horton and Jones, 1969), and human (Carlson 3E_31,, 1970; Carr gt 31., 1970; Westura 33 31., 1970). Intravenous injec- tions of graded doses of PGA in dogs (0.25-4.0 ug/kg) l significantly reduce mean blood pressure and total peripheral resistance and increase heart rate and cardiac output essen- tially in prOportion to the dose given (Nakano, 1967; Nakano and McCurdy, 1968). As has recently been shown for PGEl (Emerson et al., 1971) intravenous injections of PGAl trans- iently increase the venous return to the heart (Nakano and McCurdy, 1967). Effects of PGAl on systemic hemodynamics have been studied in intact conscious dogs after implantation of Doppler ultrasonic flow probes (Higgins 33 31., 1971). Intravenous influsions of 1.0 u9/min reduce arterial blood pressure and systemic resistance by averages of 30% and 51% respectively, and increase heart rate and cardiac output 64% and 47%, reSpectively. Since blood pressure falls while cardiac output rises, the primary mechanism of the blood pressure fall with PGA is decreased peripheral resistance. 1 Weeks 31 31. (1967) determined that the depressor activity of the two PGA forms is about 2.5 times as great as the PGE forms in dogs. However, studies indicate that PGA is less effective than PGE in lowering blood pressure in rats and man (Carlson, 1970; Weeks, 31 31., 1969). Recently, studies have been completed on the anti- hypertensive effects of PGA in patients with essential hyper- l tension. Intravenous infusions of rates from 0.3 to 1.2 ug/kg/min for 30-60 min lowered blood pressure, but the magni- tude of the response varied with the individual (Christlieb, 1969). Carr (1970) reported that similar infusions of PGA1 increased cardiac output, reduced blood pressure, and decreased peripheral resistance in five patients. In addition, the renal fraction of the cardiac output increased dramatical— ly. Lee 33 31. (1971) infused PGAl i.v. for one hour into six patients and noted a decrease in blood pressure from 200/112 mm Hg to 140/85 mm Hg at infusion rates of 2.1-ll.2 ug/kg/min. In addition, none of the side effects reported to occur during PGE administration (headache, facial flushing, 1 visual symptoms, abdominal cramps)(Bergstrom 3E 31., 1965) were found to occur during PGA infusion, and these authors 1 suggested that PGA may function as an "ideal" antihyper- l tensive agent. Westura (1970) also infused PGA at two dose 1 levels in patients. At the first level (1.0 ug/kg/min) he found a progressive fall in systemic blood pressure, a rise in stroke volume and cardiac index, and an increase in heart rate. At the higher dose (2.0 ug/kg/min) a further small decrease in systolic blood pressure was recorded, but no further lowering of diastolic blood pressure occurred. Heart rate continued to increase while the cardiac index decreased slightly. He concluded that the antihypertensive action of PGAl is direct peripheral dilation leading to a fall in peripheral resistance and a decline in blood pressure accom- panied by a compensatory increase in heart rate which is almost entirely reflex in nature. However, the study did not permit the authors to rule out the possibility that PGAl had a direct stimulatory effect on the heart to increase rate. In this regard, Carlson 3E_31. (1970) infused lower doses of PGA1 into three healthy subjects and noted that the heart rate tended to increase without significant change in blood pressure. Recently, Higgins 3E_31. (1971) demonstrated total pre— vention of cardiac acceleration with PGAl after combined beta receptor and cholinergic nerve fiber blockade in the conscious dog. These data are consistent with findings in the isolated heart (Lee EE.§A°' 1965) and anesthetized dog (Carlson and Oro, 1966; Nakano and McCurdy, 1968) which suggest that prostaglandins are devoid of direct positive chronotropic activity. Effect Upon Myocardial Contractility It is still unclear if PGAl has a direct effect upon myocardial contractility. Intravenous injections of PGAl in vagotomized, propanolol treated dogs decreased left ventricular end diastolic pressure and increased dp/dt, accompanied by a fall in systemic blood pressure (Nakano and McCurdy, 1968). Also, the df/dt and peak tension values of myocardial contractile force (measured with a Walton-Brodie strain gauge) increased 44%. In this study, another deter— minant of dp/dt, heart rate, was changing during this period and may have contributed to the increased dp/dt and force. However, when injected into the left coronary artery during perfusion at constant flow, PGA augmented left ventricular 1 10 contractile force, without increasing heart rate (Nutter and Crumly, 1970). On the other hand, in a more complete study, Higgins 33 a1. (1971) found PGA to be devoid of significant inotropic -- 1 activity when alterations in heart rate and reflex sympa- thetic tone were controlled by atrial pacing and beta adren— ergic blockade, and left ventricular pressure was held constant. In a recent publication (1972), he uses three para- meters to characterize the contractile state of the left ventricle (LV):LV isolength velocity, maximum dp/dt, and the quotient of dp/dt/developed LV pressure. These parameters increased 29, 24, and 25%, reSpectively, during PGAl infusion in conscious dogs. Following beta blockade, the increases were 10, 10, and 12%, and when changes in afterload (via intra- aortic balloon) and heart rate were prevented in addition, minimal changes of 4, 8, and 6% occurred. Thus, a direct inotropic action of PGA appears unlikely, and augmentation l of the contractile state which results from PGAl infusion is apparently due to indirect reflex effects. In this regard, studies on the isolated, perfused, rabbit heart have shown no direct effect of PGA1 on heart rate or contractility (Lee and Covino, 1965). Peripheral Vascular Effects The local effect of a substance on specific vascular beds is frequently evaluated through changes in blood flow or resistance after close i.a. injection or infusion. In such 11 experiments, i.a. administration of PGA1 increased blood flow and decreased vascular resistance in the iliac (Higgins et al., 1970), superior mesenteric (Nakano gt al., 1968), mesenteric (Higgins gt al., 1970), subclavian and pOpliteal (Barner gt al., 1971), brachial and carotid (Nakano, 1968; Nakano 92 al., 1968), femoral (Nakano, 1968; Barner et al., 1971), renal (Nakano, 1968) and coronary (Nakano, 1968; Christlieb gt al., 1969; Barner gt al., 1971; Higgins et al., 1971) arteries. This effect is not blocked by atrOpine, propanolol, methysergide, or diphenhydramine (Nakano, 1968; Smith g£_al., 1967). When regional blood flows were measured by a DOppler flowmeter, i.v. injections (1 ug/kg) decreased mean aortic pressure while increasing flows and decreasing resistances in the coronary, mesenteric, renal, and iliac arteries (Bloor and Sobel, 1970). In addition, studies from isolated vascular smooth muscle have shown that partially contracted helical strips from small renal, skeletal muscle, and mesenteric arteries are contracted further by high con- centrations and relaxed by low concentrations of PGAl, demonstrating a biphasic response (Strong and Bohr, 1967). Effect Upon Coronary Vasculature I.a. injections of PGA into the coronary circulation l have been shown to increase coronary blood flow and decrease coronary resistance in the dog (Nakano, 1968). Barner gt 3l° (1971) reported that 25 ug i.v. injections in dogs decreased 12 mean aortic pressure, and decreased flow in the internal carotid and popliteal arteries, concommitant with an increase and then a decrease to 12.5% below control in coronary blood flow. To ascertain a possible direct dilatory effect upon the coronary bed, Bloor £2 31. (1970) infused PGAl via an intracoronary tube and noted a 74% increase in coronary blood flow prior to any change in arterial pressure or heart rate. In addition, myocardial reactive hypermia following a 10 to 30 second occlusion of the left circumflex artery was di- minished or abolished during PGA infusion. When heart rate was maintained constant by atrial overdrive (Higgins, 1970) PGAl still caused a marked decrease in coronary resistance which was not diminished by beta bloCkade. However, in con- trast to the above, isolated coronary smooth muscle has been shown to contract in response to the prostaglandins (Strong and Bohr, 1967). Renal Vascular Effects The renal vascular bed has been shown in animal studies to be particularly sensitive to PGA infusion (Lee, 1968; Lee 1., 1971), the typical response being an increase in renal 21:. blood flow, GFR, and sodium and water excretion. Lee 32 il' reported that very low infusion rates of PGA into patients 1 with essential hypertension were not associated with a change in blood pressure but resulted in a significant increase in effective renal plasma flow (ERPF), GFR, and urinary flow. 13 At the higher infusion rates, blood pressure fell, and ERPF, GFR, and urinary flow fell towards preinfusion control levels. Thus, decreased renal perfusion pressure secondary to a re- duction in systemic arterial pressure and increase in sympa- thetic activity offsets the direct renal vasodilating and natriuretic action of PGAl. PGAl also apparently causes a shift of renal blood flow to cortical regions, as a result of decreased afferent glomerular resistance (Schoones et_§1,, 1970). Pulmonary Vascular Effects Pulmonary arterial pressure (PAP) increases (Nakano and McCurdy, 1967, 1968) and pulmonary vascular resistance de- creases (Nakano, 1968) following i.v. injection of PGA1 in dogs. However, when right cardiac input was held constant PGAl injection did not change or decrease pulmonary arterial pressure. Thus, the mechanism of the increased PAP appears to be via increased pulmonary blood flow rather than a direct effect upon the pulmonary vessels. Skin and Skeletal Muscle Circulation Locally, PGA is a potent dilator of the resistance 1 vessels in the hindlimb and forelimb of the dog, although PGEl's effect is apparently greater and more prolonged (Nakano 23 al., 1968). PGA2 causes a significant decrease in total peripheral resistance and increase in femoral arterial blood flow in the dog (Lee et 31., 1965). In contrast to the 14 above, Covino EE.E$° (1968) found no significant change in femoral arterial blood flow during i.v. infusion in dogs, although the local effects were not separated from compensa— tory effects due to decreased systemic pressure. In the isolated canine hindlimb, i.a. infusions of PGAl caused a decreased vascular resistance and increased vascular capacity (Greenburg and Sparks, 1969). In addition, these authors reported a dilatory effect of PGA upon the venous segment of l the hindlimb vasculature when perfused at constant flow. They also reported that PGAl causes relaxation of isolated veins, although supportive data was presented only for PGEl. Femoral arterial blood flow is distributed mainly to skin, subcutaneous tissues, and skeletal muscle. Little work has been done to separate the effects of PGAl on these vascular beds. The effects of i.a. PGA upon the isolated 1 denervated hindpaw, primarily a cutaneous vascular bed, have demonstrated decreased vascular resistance in the face of decreased systemic pressure (Kadowitz et al., 1971). Daugherty §E_a1. (1968) used the method of Haddy gt_§l. (1961) to separate skin and muscle blood flow in the forelimb during i.a. and i.v. infusion of PGE1, a dilator similar to PGAl. These authors found PGEl to produce prOportional increases in flows and decreases in resistance in skin and muscle. In addition, they reported a tendency for reduction in venous resistance. 15 Horton 22 31. (1969) report decreases in both systemic arterial blood pressure and perfusion pressure of a constant flow perfused hindlimb with i.v. infusions of PGAl in the cat and dog. The mechanism of the hindlimb vasodilation was fur- ther investigated using a cross-perfusion technique. The innervated hindlimb of a cat (recipient) was perfused at constant flow with blood from a donor cat. Intravenous in- fusions of PGAl into the recipient cat caused a fall in systemic pressure and a rise in perfusion pressure, although close i.a. injections into the limb resulted in a fall in perfusion pressure. Thus, although it is clear that PGAl decreases total resistance in the hindlimb, the effect on the parallel and series coupled resistances in skin and muscle vascular beds has not been shown. The effect of PGA upon peripheral veins 1 also needs further attention. Microcirculatornyffects Few studies have been done on the effects of PGAl on capillary flow and pressure, and possible effects upon capil- lary permeability. Kaley and Weiner (1967) observed the microcirculation of the rat mesocecal bed under the microsc0pe and noted that the similar compound, PGEl, increased capillary flow by dilating metarterioles and venules and by Opening precapillary sphincters. They also reported an increase in Vascular permeability with PGE comparable to that produced 16 by bradykinin. However, Daugherty 33.31} were not able to demonstrate changes in fluid filtration or capillary perme- ability in the isolated forelimb during PGEl infusion. Using both PGEl and PGAl in the isolated hindlimb, Greenburg and Sparks (1969) found an increased K capillary filtration fl coefficient, which they attributed solely to decreased pre- capillary sphincter tone. CHAPTER III MATERIALS AND METHODS Mongrel dogs of either sex were anesthetized with sodium pentobarbital (30 mg/kg) and artificially ventilated via a cuffed endotracheal tube. The skin of the right forelimb was circumferentially sectioned 3-5 cm above the elbow. The right brachial artery, forelimb nerves, and brachial and cephalic veins were isolated and the muscles and remaining connective tissue were sectioned by electrocautery. The humerus was cut and the ends of the marrow cavity were packed with bone wax. Thus, all blood entered limb only through the brachial artery and left via the brachial and cephalic veins. The forelimb nerves (median, ulnar, radial, and musculocu- taneous) were left intact and were coated with an inert sili- cone spray to prevent drying. Heparin was administered in a dose of approximately 10 mg/kg. Small bore polyethylene tubing was used to measure intra- vascular pressures as previously described by Daugherty gt gt. (1968) at the following sites: 1) brachial artery via a side branch (PE 60), 2) skin small artery from the third super- ficial volar metacarpal artery on the undersurface of the paw (PE 60), 30 muscle small artery from a vessel supplying a 17 l8 flexor muscle in the middle portion of the forelimb (PE 50), 4) skin small vein from the second superficial dorsal meta— carpal vein on the upper surface of the paw (PE 60), 5) muscle small vein from a deep vessel draining a flexor muscle in the middle portion of the forelimb (PE 10), 6) skin large vein from the cephalic vein via a side branch (PE 60), 7) muscle large vein from the brachial vein via a side branch (PE 60). The systemic pressure of the animal was monitored by plac— ing a catheter (PE 240) into the aorta via a femoral artery. Pressures were measured with low-volume displacement trans- ducers (Statham Laboratories, Model P23Gb, Hato Rey, Puerto Rico) and recorded on a direct writing oscillograph (Sanborn Co., Model 60-1300, Boston, Mass.). The brachial and cephalic veins were partially transected 3-5 cm downstream from the sites of the large vein pressure measurement and the vessels cannulated with a short section of large bore polyethylene tubing, usually PE320 or PE380. Outflow from both veins flowed by gravity into a graduated cylinder blood reservoir maintained at constant volume by a Sigmamotor pump (Sigmamotor, Model T-6SH, Middleport, N. Y.) connected to a cannulated jugular vein. Blood flows were determined by timed collec- tions of the two outflows with a graduated cylinder and stop— watch. The median cubital vein represents the major connec- tion between the skin and muscle vascular beds in this . preparation. Following ligation of this vessel, the brachial l9 venous outflow is predominately from muscle, and the cephalic venous outflow is predomnately from the skin vascular bed. This preparation thus presents fairly complete separation of the two parallel coupled vascular beds, and has been shown to accurately represent them in previous studies (Daugherty gt_gt., 1967; Abboud, 1968; Daugherty gt gt., 1968). After cannulation, the forelimb was placed on a wire mesh platform attached to a strain gauge torsion balance. In each experi— ment, the balance was calibrated by the addition of a 29 weight which produced a deflection of 8-15 mm pen deflection on the oscilloscope. Limb weight was monitored continually during all of the experiments. In 21 animals, limbs were perfused naturally through the uninterrupted brachial artery. PGAl was infused intra- arterially (Harvard Apparatus, Model 901, Dover, Mass.) via a side branch of the brachial artery, whereas the intravenous infusions were made into the cannulated jugular vein° In the remaining fourteen animals, a finger type blood pump (Sigma- motor, Inc., Model T,10, Middleport, N. Y.) was interposed between the femoral and brachial arteries, and the limbs per- fused at constant flow. PGAl was then infused into the tubing upstream to the pump. PGAl was stored at 0°C in stock solutions containing 0.1 ml of 95% ethanol for each milligram PGAl and diluted to the appropriate concentrations with normal saline at the start of each experiment. In all intra-arterial infusions, PGAl was 20 infused at sequentially increasing rates, and steady state values of each parameter were obtained at each infusion level. When perfused naturally (N=16), the rates of infusion employed were from 0.2-10 ug/min, and in the constant flow preparations, PGAl was infused at two dose ranges, 0.2-10 ug/min (N=9) and 0.02—2.0 ug/min (N=5). The intravenous infusions were all made at a single infusion rate of 6.0 Hg/min for ten minutes in five animals, and all of the fore- limbs were perfused naturally. Normal saline was infused intra-arterially at the rates listed above to serve as the corresponding control series for each of the groups. Total forelimb resistance was calculated by dividing the pressure gradient across the limb (mean venous pressure subtracted from arterial pressure) by the total venous out- flow. Total skin and muscle resistances were calculated by dividing the appropriate pressure gradients by the cephalic and brachial venous outflows, respectively. Skin and muscle arterial, small vessel, and venous resistances were calcu- lated by dividing their respective arterial, small vessel, and venous pressure gradients by the appropriate cephalic or brachial venous outflow. Statistical analysis was completed using the student t test modified for paired replicates. A P value less than 0.05 was considered significant. CHAPTER IV RESULTS I. Intra-arterial Infusion-Natural Brachial Artery Inflow The effect of intra—arterial administration of PGAl on forelimb weight, blood flows, and aortic, arterial, and venous pressures are shown in Figure 1. Note that total venous out- flow increased progressively over the lower dose range due to a rise in both cephalic (P< 0.05) and brachial (P< 0.05) vein outflows. At the infusion rate of 1.0 ug/min the flows began to progressively decrease to levels below control. Forelimb weight increased to 7.2 grams above control (P< 0.05) and then began to decrease to a level not significantly different than control. The change in weight appears to reflect the increases in flows and venous pressures. Aortic pressure re- mained constant at the low infusion rates and began to decline at 1.0 ug/min (P<:0.05). Throughout all infusion rates muscle and skin small artery pressures decreased, the decrease becoming significant (P<<0.05) in both muscle and skin at 0.5 ug/min. Skin small vein pressure rose and began to fall again at 1.0 ug/min (P<<0.05); muscle small vein pressure rose slightly (P<<0.05) before decreasing. Both large vein 21 22 pressures rose (P< 0.05 at 0.5 ug/min) and fell (P‘<0.05 at 10 ug/min) proportionately throughout infusion. All para— meters were monitored for several minutes after stopping the infusion. During this period arterial pressures tended to return to preinfusion values. Saline control infusions were without significant effect upon any of these parameters. Figure 2 illustrates total resistances in the natural flow preparation calculated from the data shown in Figure 1. Total forelimb resistance during infusion of PGAl fell from 1.6 to 1.3, the decrease becoming significant at 2.0 ug/min. Total skin resistance fell to 2.7 (P<:0.05) before rising again, and total muscle resistance fell from 4.1 to 3.2 (P<<0.05) before increasing. After stopping the infusion, the resistances increased to or above control levels. Figure 3 shows the segmental resistance components of Figure 2. Resistance decreased significantly in muscle and skin small vessel segments at the lower doses of infusion, becom- ing significant at 0.5 ug/min. At the higher doses, resistance increased to control levels in muscle small vessels and near control levels in skin small vessels. When PGAl infusion was stopped, both resistances increased. On the average, skin arterial and skin venous resistances both fell, although neither of these changed significantly. Muscle arterial re- sistance remained unchanged at the lower doses of infusion, and rose as the infusion rate was increased (P«‘0.05 at 10 ug/ min); muscle venous resistance remained unchanged throughout infusion. ‘ \k. N h t\\ ‘ | Aver m \ \L 'e responses of forelimb blood flows, ressively hial infusion l arterial pressures, and weight to pro increasing rates of intrabra of prostaglandin A at natur inflow. l I“ rv V J F 'v ,1: 54 .AWL Flow anmm PRESSURE gm. mmHg 24 IOO 50" l25 " lOO " 75" 50 o 1 1 A l 1 1 . 2 .5 to 2.0 5.0 I00 0 PGA. fig/mn Figure 1 Total outflow Cephalic vein Brachial vein Aorta M uscle small artery Skin small artery Skin small vein Mu ecle small vein Brachi al vein Cephalic vein 25 .H madman cfi poumuo lmoHHH mucmeflnomxo Eouw mono .Hflmwoumon ou momcommoy mocmumflmmu cflxm HMHOD cam oHomsE Hmuou .QEHHmHOM amuoe .m ousmflm 26 £5.23 .28 E... .o.oh 23:6 .30... m musmwm :E\o<\.Ho>flmmoumoum ou momcommon mocmumflmmn Hancofimom .m madman 28 Soc 2. 20 as! 23:: 5.3 3.3:. 2032 3:23 aim 3:: ..o E. 5.5 3:: =2:- 292.! n.0 N.O 0.. ON on 0.? mwnumnww SDNVJ. SISBS 29 II. Intra-arterial Infusion-Constant Brachial Artery Flow Figure 4 illustrates the pressure, flow, and weight changes in the forelimbs perfused at constant arterial inflow and receiving the same dose of PGA as the limbs perfused at 1 natural flow. During the control period, the limbs gained an average of 0.9 gram, apparently due to the dependent posi— tion of the limb relative to the right atrium. At 0.2 and 0.5 ug/min rates the steady state weight gain was 3.8 and 5.6 grams, respectively (P<10.05). Weight then stabilized at a level significantly above control as the rate was further increased. The significant changes in the pressure parameters of these limbs occurred in l) the decreasing aortic pressure, and 2) the proportionate decrease and then increase in the brachial artery, muscle small artery, and skin small artery pressures. The increase in pressure of large and small arteries occurring from 1.0 to 10 ug/min coincides with the decrease in aortic pressure. All pressures rose during the post infusion period. As skin and muscle blood flows remained unchanged in this series, the decreases in pressure reflect decreases in resistances. Calculated resistances show de- creases in total skin and muscle resistances which are due to decreases in the small vessel segment of both vascular beds. Neither muscle or skin arterial resistances changed signifi- cantly, although skin arterial resistances decreased on the average (P> 0.05). 30 Figure 4. Average responses of forelimb blood flows, pressures and weight to progressively increas- ing rates of intrabrachial infusion of prostaglandin A1 at constant arterial inflow. 23Wt gm. FLOWS lm/mm PRENMRE mmHg I0 A L A _____—-. 5 v v fl 0 MG IOO F- 75 i- ISO I25- IOO .- 75- 0 l l s 1 0.2 O .5 LO 2.0 5.0 PGAifw/mm Figure 4 Total outflow Brachial vein Cephalic vein 8r ac hial artery Muscle small artery Aorta Skin small artery Skin small vein Muscle small vein Brachial vein Cephalic vein 32 Because of the extreme potency demonstrated in the previous two studies, another series of constant flow perfused limbs was performed while exploring a lower dose range. This series demonstrates purely local effects of PGAl and is illustrated in Figure 5. Forelimb weight did not change sig- nificantly during the entire infusion of PGA There was no 1' shift of blood flow between the muscle and skin vascular beds, as indicated by the brachial and cephalic vein outflows. Brachial artery pressure decreased progressively during the entire infusion, indicating a corresponding decrease in total forelimb resistance. The proportionate decreases in the muscle and skin small artery pressures indicate similar changes in their respective resistances. Calculated resist- ances show that the only significant changes in the segmental resistances occurred in the small vessel segment. All venous pressures remained constant throughout the entire infusion period, indicating a constant resistance to blood flow through this segment. III. Intravenous Infusion-Natural Brachial Artety Flow Limb weight, pressure, and flow changes during intra- venous infusion of PGA are shown in Figure 6. Forelimb 1 weight gained 3 grams during the first minute of infusion (P<<0.02) and then fell progressively to below control levels at minute 10 (P>-0.05). At twenty minutes post-infusion, Figure 5. 33 Average responses of forelimb blood flows, pressures and weight to progressively increasing rates of a low dose of intra- brachial infusion of prostaglandin A1 at constant arterial inflow. AMn FLOW mem PRESSURE gm. mmHg 34 *5 -5 K30 b N'S 75l- 50 —= 45, :47 :7 ej 25 'ZSF : 5 NA 20 4. 7* = :______‘ l5 - ' 3 c # fi l0- 5 3 A . L 4 o s l l I a .02 .05 D .20 0 PGA. flglmn Total outflow Brachial vein Ceph alic vein AoNa Brachial artery Muscle small artery Skin small artery Skin small vein Muscle small vein Brachial vein Cephalic vein 35 Figure 6. Average responses of forelimb blood flows, pressures and weight to intravenous infusion (6 ug/min) of prostaglandin A1 at natural forelimb arterial inflow. 36 PGA S/ig/min Total Outflow ’ ‘Cephallc Vein ‘syv’ 25 . Brachial Vein l25 Aorta lOO Muscle Small Artery Sllln Small Artery 75 O a: ”J I E I E . ..f t '0 ' Skin Small Vein 1 Muscle Small Vein 5 Cephalic Vein .. . . , L ._ -1 n g Brachial Vein '5 O 2 4 6 8 IO 30 Time (min) Figure 6 37 limb weight had continued to fall and was 4 grams below the control value (P<<0.05). On the average, total outflow increased during the first minute (P >0.05) due to increases in both the cephalic and brachial vein outflows; both flows decreased during the rest of the infusion period to levels well below control. Although outflows remained below control levels at 20 min. post-infusion (P<:0.005), they had begun to return to control values. All arterial pressures were well below control during the entire infusion period of PGAl. Skin and muscle small vein pressures transiently rose (P<:0.05) and then decreased to below control values by min. 10 (P<:0.025). On the average, large vein pressures rose at min. 1 (P>>0.05) and both skin (P‘<0.01) and muscle (P«:0.005) large vein pressures were reduced to levels below control by minute 10. Total resistances of these limbs are illustrated in Figure 7. Total forelimb resistance fell initially (P¢<0.005), due to decreases in skin (Pi<0.05) and muscle (P«<0.025) total re- sistances. At min. 2, all resistances began to steadily in- crease toward control levels, and total muscle resistance exceeded control levels by minute 10 (P<:0.05). These in- creases correspond with the period of decreased flow illus- trated in Figure 6. The segmental resistances, shown in Figure 8, indicate that the greatest initial fall in resist- ance is located in the small vessel segments of both muscle (P<:0.005) and skin (P< 0.025). Following infusion, both small vessel resistances rose to values well above control. 38 .m musmflm CH popmuumoaafl mucmEHHomxo Eoum mama .Hm catamammumoum mo AaflE\mn my coamomcfl mooco>muucH on mmmcommon oocmumflmmu cfixm Hauou paw oHUmSE Hmuou .QEHHmHOM Hmuoe .n ousmflm 39 h onsmwm 3:5 25... on o. o o c N o r... l . . . . . . . l . 1...] 0.. 95.20.... .22. . ON .56 .20... on . Qv 23:2 .20... r . 1 J L as}... m .42 alumna/bum eauoisgsea 40 .o ousmHm CH omumuumsHHH mquEHHomxm EOHH cyan .Hd CHUCMHmmumOHm Ho ACHE\mn ov ConCHCH mDOCo>muuCH ou momCommoH moCmumHmoH HmaCoEmom .m OHDmHm 41 m onsmHm 3:5 25». On O. O 0 V N 0 0. 1"! q a d u e a a a 1 J I i 2.8.5 .56 ll l\.e\ 1/ ll aaoce> 0.322 \\ I: \\.e. .e. -iiieell... \ in... o. / . 0.. 3:23 23:! \\\ .otet.< 5.5 e\ QN . O.n :33 :25 can .euue> Exam 2032 m i loe saxoi o .«aa ulul/lul/buulul aoua isgseu 42 On the average, skin arterial resistance was decreased by minute 2 (P<<0.05) and then gradually increased to levels above control. Muscle arterial resistance gradually rose and at minute 10 was significantly above control levels (P<<0.05). Both skin (P:>0.05) and muscle (P‘<0.05) venous resistances demonstrated a gradual, steady rise during PGAl infusion. Both arterial and venous resistances rose following infusion. CHAPTER V DISCUSSION Flow Effects Locally increasing plasma PGAl concentration increases flow in muscle and skin vascular beds of the dog forelimb. In the natural flow preparations, PGA1 caused an initial increase in blood flow in both skin and muscle, which began to wane concommitantly with the decrease in aortic pressure. This suggests that the local effect of PGAl is to dilate the two vascular beds and thereby increase blood flow, and the following decrease in blood flow is most likely due to the decreased systemic pressure initiating the baroreceptor reflex and increasing peripheral resistance. Part of the decrease in flow is also due to the decreased pressure grad- ient across the limb caused by the decreased aortic pressure. In this regard, when PGAl infusion was discontinued, aortic pressure rose, but limb outflow continued to fall, indicating that some degree of the dilatory action of PGAl had been occurring at the higher dose levels, compromising the reflex vasoconstriction. The large increases in the brachial and cephalic vein outflows suggest similar effects on resistance in the 43 44 parallel coupled skin and muscle vascular beds. This is supported by observations at constant flow where dispropor- tionate changes in skin and muscle resistances would have been reflected by opposite changes in cephalic and brachial venous outflows. Both doses at constant arterial inflow (0.2-10.0 ug/min and 0.02-0.20 ug/min) reduced brachial artery pressure but did not change flow in the two veins. This vasodilator action of PGAl is similar to that previously reported of PGE1 (Daugherty, 1971) and acetylcholine and bradykinin (Daugherty gt gt., 1968) which have been shown to produce proportionate decreases in skin and muscle resistances. In addition, Daugherty (1971) reports that when infused intravenously (1-20 Ug/min) in the same preparation, PGEl increases both skin and muscle blood flow. In the present study, intravenous PGA1 infusions (6 ug/min) increased both skin and muscle blood flows very transiently, and then flows began to decrease to values well below control. The dif- ference between these two observations may result from the dose level administered, or the time period, or the relative potence of the two prostaglandins. The systemic pressure decreased further and more quickly during the PGA infusion, 1 thereby inhibiting any longer lasting increase in flow such as that seen with PGEl. It appears that the primary mechan- ism causing the decrease in flows was the decreased driving pressure gradient, as the flows began to decrease while the vascular resistances were still below control. 45 Resistance In the naturally perfused limbs, local infusion of low doses of PGAl increased blood flows concommitantly with decreasing arterial pressure, suggesting an active increase in vessel calibre and decrease in resistance. These find— ings were confirmed in the constant flow preparations, where, in the absence of flow shifts, passive changes in vessel calibre do not mask active changes. In these limbs, low dose PGAl infusions (0.02—0.20 ug/min) proportionately de- creased the arterial pressures (perfusion and small artery) of the limb without altering any of the other parameters. This represents an active decrease in total forelimb re- sistance due to proportionate decreases in skin and muscle small vessel resistances. Thus the major site of the dila- tory action of PGAl is at the small vessel level in both of the parallel and series coupled vascular beds of the forelimb. As the arterioles are the major site of the resistance in the small vessel segment, the probable site of activity is at the arteriolar level. In addition, these studies indicate some degree of activity of PGA upon the arterial segment. 1 This was shown most clearly in the constant flow low dose series (Figure 5) in which the mean transmural pressure (distending-pressure) across the arterial segment decreased continually during the infusion period. This would tend to passively increase resistance in this segment, when in fact, no significant arterial resistance change was observed. 46 Thus, a dilatory action of PGAl upon the arteries prevented the expected passive decrease in vessel calibre. At the higher dose rates (1.0-10.0 pg/min) in both constant and natural flow, arterial resistances began to rise again, concommitantly with the significant decrease in arterial pressure. During natural inflow, this response coincides with the decreases in flows seen during the same time period, and is apparently the combined result of a barostatic reflex and a passive vasoconstriction due to the decreasing transmural pressure. Several authors have reported an effect of the prosta- glandins upon the venous segment of the forelimb or hind- limb. Daugherty (1971) reports that at constant arterial inflow, PGE produced a tendency for a decrease in muscle 1 small vein pressures, indicating a possible active relaxa— tion, but having no effect upon the skin small vein pressures. The decrease, however, was small in muscle, occurring in seven out of ten experiments, and in six out of eleven in skin. Greenburg and Sparks (1969) report that in addition to their action upon resistance vessels, both PGEl and PGAl cause active relaxation of venous smooth muscle, in both isolated muscle venous strips and in the isolated perfused hindlimb. Although data was shown for PGE none was illus- ll trated for the effect of PGAl upon the venous segment of the hindlimb. In their study, both PGEl and PGAl at natural arterial inflow increased the vascular capacity of the 47 perfused hindlimb, but this may have been due to the passive distension of the venous segment by the increased flow, rather than by actual relaxation of the smooth muscle of the capacitance vessels. In contrast to the above, none of the present experiments performed at either dose of PGA during 1 constant flow perfusion demonstrated any effect upon the venous segment of the vasculature. All the small and large vein pressures remained constant during the entire period of infusion. The failure to observe this venous effect may theoretically be due to l) subthreshold doses or 2) maximally dilated veins prior to drug administration. However, initial venous resistances in this study were comparable to or greater than those reported in the study by Daugherty (1971) in which he reported an active decrease in venous resistance. In ad— dition, the dose level administered was slightly greater. Thus, it appears that the veins show little responsiveness to infusions of PGAl, at least at these dose levels. Strong and Bohr (1967) found a biphasic reSponse of skeletal muscle artery strips to prostaglandins, relaxing upon exposure to low concentrations, and contracting in response to high concentrations. PGA1 was the most potent in producing both relaxation and contraction. The current study did not demonstrate this response, perhaps because of the differences in the dose levels administered, or differences in experimental procedure, that is, in vitro versus in vivo preparations. 48 Thus, a pronounced dilatory effect upon the resistance vessels was observed, although the data fail to provide evidence for an effect of PGA upon the smooth muscle of l capacitance vessels. Weight and Transcapillary Fluid Fluxes Weight increases seen in the lower rates of infusion at natural flow may theoretically be due to increased vascular volume, interstitial fluid volume, intracellular fluid volume or some combination of the three. In this study, the initial weight gain was associated with increased flows, increased venous pressures, and decreased segmental resistances. The decreased resistances suggest that much, if not all of the weight gain may be attributed to increased vessel calibre and hence increased vascular volume. However, it is possible that a small increase in interstitial fluid volume occurred, due to filtration caused by an increase in the transmural hydro- static pressure gradient in the capillaries. Indeed, the small vein pressures, which represents a minimum for capillary pressure, are increased during this period. A rise in the capillary pressure would occur if the decreased arterial pressure and trend toward a decrease in venous (post-capillary) resistances were overcome by the decrease in precapillary resistance. Thus, although it is clear that the increased vascular volume could have contributed the majority of the weight gain during the period when the flows were increased, 49 it is possible that some degree of pressure dependent fil- tration may have occurred. Indeed, at natural inflow, upon cessation of infusion, vascular resistances in the forelimb were either at or above control levels (Figures 2 and 3), although the limb weight was significantly above control levels. The constant or increased vascular resistances sug- gest that the mean vessel calibres were either constant or decreased, and thus that an increased intravascular volume could not have accounted for the maintenance of the increased weight following infusion. These data provide no direct evidence that prostaglandin A1 infusions change the microvascular permeability to protein. Other vasodilators such as acetylcholine and histamine have been shown to cause edema and increase lymph protein concen- trations when administered locally (Haddy gt gt., 1972; Grega gt_gt., 1972), via microvascular pressure dependent mechanisms. These workers showed that, in addition, histamine apparently increases protein permeability by a pressure inde- pendent mechanism. In the current study, the natural flow data show a possible slight pressure dependent increase in filtration, although effects upon permeability cannot be directly concluded from this. At constant inflow, unlike histamine, low dose PGAl infusions did not change limb weight at all, indicating no probable pressure independent effect of PGA upon net fluid filtration. It is theoretically pos- l sible that the lymph vessels may have carried off some or all 50 of any fluid filtered, although this seems unlikely consider- ing the complete lack of weight gain in the low dose infu- sions. The picture is complicated somewhat by the 5.4 gram weight increase in the high dose infusions. However, as seen in Figure 4, these limbs were not completely isogravimetric during the control period. Perhaps this explains the weight gain and the disparity between the two groups. Thus, although this experiment provides no evidence for an effect of PGAl upon permeability to protein, if an increase did occur, it was not apparently sufficient to cause an increase in inter- stitial volume during constant arterial inflow at the lower local dose. When PGAl was infused intravenously, the limb weight increased during the first minute and then gradually fell to below control values. The initial weight gain occurred simultaneously with the increased flows and large vein pres- sures, indicating that the primary cause of the weight gain is increased intravascular volume. From minutes 2-20, total forelimb resistances and resistances in the capicitance ves- sels was increasing. These reSponses suggest that forelimb mean vessel calibre and consequently, intravascular blood volume was decreasing and could explain the loss of weight which occurred during this period. Other investigators have reported that prostaglandins have no effect upon fluid filtration. Daugherty (1971) re- ported no evidence for alterations in transcapillary fluid 51 fluxes with PGEl in a similar preparation. He reported a possible proportional dilation of both arteries and veins, resulting in no significant change in precapillary and post- capillary resistance ratios. Thus it is possible that the capillary hydrostatic pressure would not increase with PGEl. 1 may be unlike PGE1 as no evidence was demon- strated for dilation of the postcapillary vessels. Greenburg However, PGA and Sparks (1969) reported a large increase in vascular capacity but no net filtration associated with close arterial infusions of either PGEl or PGAl in the isolated hindlimb. In summary, locally increasing plasma PGA concentrations 1 causes active vasodilation in skin and skeletal muscle beds of the dog forelimb. The vasodilation is dose related over the range 0.02 ug/min-2.0 ug/min, and appears to affect both vascular beds about equally. The primary site of action is apparently at the small vessel (arteriolar) segment, with an additional affect upon the large arteries. Intravenous infu- sions caused a very small transientory increase in blood flow followed by a gradual decrease in levels well below control concommitant with the decrease in systemic blood pressure. The data provide no evidence for a significant pressure- independent effect of prostaglandin A upon transcapillary 1 fluid fluxes or permeability. This assumption necessitates further experiments such as analysis of lymph protein concen- trations during PGA infusion to fully clarify an effect upon 1 protein permeability. CHAPTER VI SUMMARY AND CONCLUSIONS Locally increasing plasma PGAl concentrations in the naturally perfused dog forelimb initially increased total limb blood flow 25% due to increases in both skin and muscle blood flows. When the PGAl concentrations reached levels sufficient to cause a decrease in systemic blood pressure, the blood flows in both beds began to fall. The decrease in blood flows is apparently due to the combined effects of the decreased driving pressure gradient and the barostatic reflex although, at least initially, the decrease is due to the decreased pressure gradient across the limb. Intravenous in- fusions of PGAl caused a slight transient rise in flow fol- lowed by prominent decreases in both skin and muscle. Thus, PGAl infusions increased flows at lower doses (local effect) and decreased both flows concommitantly with the decreasing systemic pressure. PGA infusions actively decreased resistance in the parallel coupled skin and skeletal muscle vascular beds of the forelimb. The primary site of activity is at the small vessel (arteriolar) level, although the large arteries are also apparently affected to a lesser degree. The vasodilation 52 53 is dose related and affects both beds about equally. Thus the local effects of PGAl infusion are to decrease resistance and increase blood flows in skin and skeletal muscle, whereas the remote effects tend to decrease systemic blood pressure and thereby decrease flows and increase resistances in the forelimb. 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Antihypertensive effects of prostaglandin A1 in essential hypertension. Circulation Res. Supplement III, 41 and 42:III—123, 1970. LIBR RIE lllllllllllllllllllllllllliIllillllillllll|||i||1||l|IIIHIIH s 64