EFFECTS OF CHANGING BLOOD FLOW, VENOUS PRESSURE AND PLASMA CATIONS ON THE VASCULAR RES!STA.NCE AND CAPACITY OF THE CANINE SPLEEN Thesis for the Degree of M. S. MICHIGAN STATE UNIVERSITY. LAWRENCE RAYMOND FINE 1973 ' LIBRAR y Michigan State University “‘- 1’1:an E: Benzene av ‘3‘ ”DAB 8: SUNS” BOOK BINDERY INC. LlB"‘ .rv amosns (F7 ‘-.flian|fll 5:" was (I) .Iv" ‘4“ ABSTRACT EFFECTS OF CHANGING BLOOD FLOW, VENOUS PRESSURE AND PLASMA CATIONS ON THE VASCULAR RESISTANCE AND CAPACITY OF THE CANINE SPLEEN BY Lawrence Raymond Fine Changes in blood flow through the canine spleen are caused by many factors, both remote and local. The purpose of this study was to investigate the local factors. Considered in this study were the effects of changing flow on perfusion pressure (autoregulation), increasing venous pres- sure (venous-arteriolar response), transient occlusion of arterial inflow (reactive dilation) and local intra-arterial infusions of naturally occurring cations, on the splenic vas- cular resistance. This was accomplished by measuring perfu- sion pressure, changes in weight, venous outflow and venous pressure in isolated, in situ, pump-perfused canine spleens while performing experimental maneuvers. Stepwise increases in arterial blood flow to the spleen caused an increase in perfusion pressure. The vascular re- sistance was decreased over low flow rates (9 to 60 ml/min) but was not significantly changed over high flow rates (3‘ IA‘R i“: j p A0 ‘ V- F H I“! ( D ‘,F“‘ ‘4... - 3'!!! ~43“ II] n,“ r,“ (J; (I’ (I, Lawrence Raymond Fine (60 to 204 ml/min). Increased blood flow increased splenic weight over the entire range of flows. The elevation of venous pressure above 9 mm Hg caused an increase in resistance in 7 of 10 animals studied. Three of the ten dogs showed little or no change to elevated venous pressure. In all ten animals, however, the splenic weight increased as a function of the rise in venous pressure. Stopping arterial inflow decreased perfusion pressure and upon resumption of arterial inflow perfusion pressure rose to a level lower than control. After about 16 seconds at this lower level, perfusion pressure began to oscillate, rising above and falling below control values. 2, CaCl2 and KCl at sequentially increasing rates into the splenic artery Infusing isotonic solutions of NaCl, MgCl caused varied responses. Sodium chloride was used as a volume control and did not significantly affect splenic weight or venous outflow. Calculated resistance did, however, decrease significantly at the highest infusion rates (3.38 and 7.75 ml/min). Infusion of MgCl resulted in a signifi- 2 cant increase in resistance, a decrease in splenic weight and an increase in venous outflow. Following the termination of the infusion, resistance rapidly and markedly increased while splenic weight and venous outflow gradually returned to con- trol values. Infusion of isotonic KCl was associated with a significant increase in calculated resistance, a decrease in :. Av< O‘:J* ”my; b.V Lawrence Raymond Fine weight and an increase in venous outflow. The infusion also caused a significant increase in systemic arterial pressure at high infusion rates. These studies thus indicate that the vascular bed of the spleen responds passively to an increasing flow over flow ranges 9 to 60 ml/min but exhibits autoregulation over flow ranges from 60 to 204 ml/min. The spleen also exhibits a venous-arteriolar response and reactive dilation. The major naturally occurring cations, i.e., Mg++, Ca++, and + . . K can not only affect the splenic re31stance but also can affect the reservoir capacity of the canine spleen. EFFECTS OF CHANGING BLOOD FLOW, VENOUS PRESSURE AND PLASMA CATIONS ON THE VASCULAR RESISTANCE AND CAPACITY OF THE CANINE SPLEEN BY Lawrence Raymond Fine A THESIS Submitted to Michigan State University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Department of Physiology 1973 ACKNOWLEDGEMENT S The author wishes to express his sincere appreciation to Dr. C. C. Chou for his invaluable encouragement and guidance and supreme patience through the course of this study. Sincere appreciation is also extended to Dr. J. M. Dabney whose sterling ideas and sparkling wit contributed in many ways toward the completion of this study. The author also wishes to express his special thanks to Dr. G. J. Grega for his service on the examination committee. A special thank you should be directed to my colleague Mr. C. P. Hsieh for his assistance throughout this study and to my dear sister Manette for her help in preparing the figures found within. ii TABLE OF CONTENTS CHAPTER LIST OF TABLES . . . . . . . . . LIST OF FIGURES O O O O O O O C O I 0 INTRODUCTION 0 O O O O C O O O 0 II. METHODS AND MATERIALS. . . . . . Surgical Procedure. . . . . . Flow-Pressure Relationship. . Venous-arteriolar Response. . Reactive Dilation . . . . . . Local Effects of Cations. . . Analysis of Results . . . . . III. RESULTS. 0 O O O O O C O I O O O Flow-Pressure Relationship. . Venous-arteriolar Response. . Reactive Dilation . . . . . . Local Effects of Cations. . . IV. DISCUSSION . . . . . . . . . . . V. SUMMARY AND CONCLUSIONS. . . . . BIBLIOGRAPHY O O O O O O O O O O O . C 0 iii Page iv l4 19 25 28 41 54 57 LIST OF TABLES TABLE Page 1. Vascular resistance as a function of perfusion pressure in the splenic artery. . . . . . . . . . 22 iv FIGURE 1. 10. LIST OF FIGURES Preparation of the isolated, in situ, canine Spleen. o o o o o o o o o o o o o o o o o o 0 O Venous outflow control apparatus. . . . . . . . Relationship of perfusion pressure (mm Hg) to arterial blood flow (ml/min) in the spleen. . . Changes in calculated resistance (upper panel) and splenic weight (lower panel) in relation- ship to changes in splenic arterial blood flow rate. 0 I O O O O O O O O O O O O O O O O O O 0 Calculated resistance (mm Hg/ml/min/lOO g) as a function of perfusion pressure (mm Hg). . . . . Relationship of calculated resistance and in- creases in weight to venous pressure. . . . . . Changes in splenic arterial perfusion pressure (mm Hg) as a result of a one minute cessation of arterial blood flow. . . . . . . . . . . . . Effects of local intrararterial infusion of iso- tonic solutions of NaCl (left) and MgCl (right) on the splenic vascular resistance, change of weight and venous flow. . . . . . . . Effects of local intra-arterial infusion of iso- tonic solutions of CaClz on the splenic vascu- lar resistance, changes in weight and venous flOWO O O O O O O O O O O O O O O O O O O O O 0 An actual recording showing effects of local intra-arterial infusion of an isotonic solution of CaClz into the spleen of a dog at sequential- ly increasing rates . . . . . . . . . . . . . . Page 11 16 18 21 24 27 30 33 35 O. LIST OF FIGURES--continued FIGURE 11. 12. Page Effects of local intra-arterial infusions of isotonic solutions of KCl on the splenic vas- cular resistance, changes in weight, venous outflow (V.F.) and systemic arterial pressure (S.P.). . . . . . . . . . . . . . . . . . . . . 37 An actual recording showing the effects of in- fusion an isotonic KCl solution into the splenic artery at increasing rates. . . . . . . 39 vi -§ § NV CHAPTER I INTRODUCTION The investigation of both anatomists and physiologists on the splenic vascular bed has been extensive and, thus, it has long been known that the spleen has several normal and important functions. The spleen has the ability to phagocy- tize and destroy blood cells, can initiate antibody formation and possesses the capability for erythropoeisis. The spleen of the dog also has the capacity to act as a major blood reservoir. Changes in blood flow into and out of the canine spleen are affected by both remote and local factors (21, 45, 55). Although many studies have been reported in regards to the remote control few studies have been done on the local control of blood flow through the spleen. This present study was, therefore, designed to investigate some of the local factors which may be involved in regulation of splenic blood flow and reservoir capacity. The factors considered in this study were the effects of changing arterial inflow (autoregulation), increasing venous pressure (venous-arteriolar response), transient occlusion of arterial inflow (reactive dilation) and increases in local blood concentration of the magnesium, calcium, or potassium ion. CHAPTER II METHODS AND MATERIALS Surgical Procedure Mongrel dogs (15-18 Kg) of either sex, which had been fasted for 24 hours, were used for this study. They were anesthetized with an intravenous injection of sodium pento- barbital (30 mg/Kg) and intubated with a cuffed endotracheal tube. All of the animals were artificially reSpirated with a positive pressure respiration pump (model #607, Harvard Apparatus Co. Inc., Harvard, Massachusetts). Both femoral arteries and one femoral vein were isolated and cleared of fascia for later cannulation. After an abdominal midline incision, the spleen was then exteriorized and wrapped immediately in a saline soaked towel to prevent cooling and drying. Taking care not to disturb the splenic artery, vein and nerve, the spleen was made free of collateral flow by ligation and section of the following vessels: those lying within the gastrosplenic and gastrocolic ligaments, the pancreatic arterial vessels originating from the splenic artery, and the collaterals joining the spleen and greater omentum. A branch of the splenic vein near the spleen was f!- y k. “'«C isolated, cleared of fascia and cannulated for the measure- ment of venous pressure. This cannula tubing (PE 90) was initially filled with heparinized saline and equippedeith a three-way stopcock at its end. Taking care not to disturb the splenic nerve, the splenic artery and vein were then iso- lated and cleared of extraneous tissue. After intravenous administration of sodium heparin (6 mg/kg, 120 units/mg) (Wolins Pharmaceutical Corp., Melville, New York) a polyethyline tube was introduced into the left femoral artery and attached to a pressure trans- ducer (Statham model #PZBGb, Hato Rey, Puerto Rico) for measuring systemic arterial pressure. As shown in Figure l, the splenic vein was cannulated (PE 320) and its blood allowed to flow freely into a reservoir filled initially with 250 ml 6% dextran in saline. The blood in the reservoir was returned to animal through a femor- al vein by means of a pump (Sigmamotor model T6SH, Middleport, New York). The volume of the venous reservoir was kept at a constant level throughout the experiment by adjusting the flow rate of the return pump to equal the venous outflow. The splenic artery was cannulated (PE 280) to allow perfusion of the spleen at a constant rate via a Sigmamotor pump with blood from the right femoral artery. The spleen was placed on a wire mesh platform which was suspended on one arm of a strain gauge weighing device. .musmmmnm cwm> mmHmH n >Hm .musmmmum scamsmumm H mm .aOHuomuflp 3on vocab mumoHUcH m30u~< .ammamm deflcmo .suflm.mm .meMHOmH may mo cOADMHMQmum .H musmflm e o I _|i._.aE':.._i 50> [Eiil .22.: 19.0.30“— 1 £53... Ir..— :33“...- 0:21:2 >._ I nowhnuoc The weighing device was connected to a direct writing oscil- lograph (Sanborn, model 7714A, Waltham, Massachusetts). The splenic venous pressure, systemic arterial pressure, and perfusion pressure of the spleen were all measured through pressure transducers (Statham, model P23Gb, Hato Rey, Puerto Rico) and continuously monitored with the direct writing oscillograph. The venous outflow of the spleen was measured periodically with a stopwatch and graduated cylinder. Blood flow to the splenic artery was adjusted initially by altering the rate of the perfusing pump so that l) the splenic arterial perfusion pressure approximately equalled the systemic arterial pressure, 2) venous outflow reached a constant level, and 3) there was no change in splenic weight, i.e., the splenic weight was isogravimetric. The spleen was covered with a plastic sheet to retard evaporative water loss and temperature was maintained near 37°C with a heat lamp. Four different experiments were performed in this study in 25 dogs, i.e., the relationship of pressure to flow through the spleen (autoregulation), the effects of raising splenic venous pressure on the local vascular resistance (venous- arteriolar response), the effects of stopping the arterial inflow and its resumption on the resistance (reactive dila- tion), and the effects of local infusion of major cation solutions, sodium chloride, magnesium chloride, calcium chloride and potassium chloride on the splenic vascular resis- tance and weight. Flow-Pressure Relationship The examination of the relationship of flow to pressure (autoregulation) in the spleen was performed by altering the rate of the pump perfusing the splenic artery while measuring the perfusion pressure. Initially, the rate of blood flow was adjusted to a value which provided a perfusion pressure approximately equal to systemic arterial pressure. When per- fusion pressure, venous outflow and pressure and weight of the spleen reached a steady state, the rate of flow was de- creased to about 10 ml/min. The flow was then increased step- wise causing the perfusion pressure to raise by approximately 20 mm Hg with each change until perfusion pressure reached about 180-200 mm Hg. Each flow was maintained until all the parameters measured became steady. Finally, the flow was returned to the control value. In seven of nine animals the experiment was performed as described above, however, in the other two dogs the flow was first increased to allow a perfusion pressure of around 200 mm Hg and then decreased in a stepwise fashion to a low perfusion pressure. Venous-arteriolar Response For this experiment, the venous outflow cannula was con- nected to a vertical graduated cylinder which was then connected to a cannula equipped with a stopcock as seen in Figure 2. When perfusion pressure, venous outflow and the weight of the spleen reached a steady state, the venous pres— sure was increased stepwise by turning the stopcock. With each stepwise increase in occlusion of venous outflow, the level of blood rose within the graduated column, to 5 cm, 10 gm, 20 cm, 30 cm, 35 cm and 40 cm. Each level of occlusion was maintained until the splenic venous and perfusion pres- sures reached a constant level, then the column of the blood was raised to the next higher level. After the column of the blood was raised to 40 cm, the partial occlusion of the venous outflow was released. Reactive Dilation Initially, the rate of blood flow was adjusted to a value which provided a perfusion pressure similar to systemic arterial pressure. When perfusion pressure, venous outflow and pressure and weight of the spleen reached a steady state the blood flow to the spleen was stopped by turning off the perfusion pump. After one minute of stop-flow the pump was turned on. One of two procedures was used during the stop-flow lO .pwmmmuocH mm3 whammmum msocm> can popsaooo haamflpumm was Bonuso msosm> Mooomoum msu mcflcusu mm .msumummmm Houucoo BonDso msocw> .m mssmflm 11 EM) 4mwmum xoooaOkm z_w> 0.2u4mm 3E mmmhwghzuo 12 period. As the pump was stOpped, the venous outflow was either allowed to flow freely or it was completely occluded. The occlusion of the venous outflow was released concurrently with the resumption of pump flow. Local Effects of Cations The isotonic solution of sodium chloride (161.7 mEq/ liter), magnesium chloride (231.2 mEq/liter), calcium chloride (239.6 mEq/liter) or potassium chloride (163.8 mEq/liter) was infused in random order upstream to the splenic arterial per- fusion pump. The solution was infused at sequentially increas— ing rates at 0.2, 0.38, 1.00, 1.94, 3.88 and 7.75 ml/min. (Harvard Infusion Pump, model 600-000, Harvard Apparatus Co., Dover, Massachusetts). Each infusion was continued for l to 2 min until perfusion pressure, venous outflow and splenic weight was constant. The infusion rate was then increased to the next higher rate. Since blood concentration of Na+ is not altered significantly by the infusion of isotonic NaCl solu- tion (5, 22) the vascular response to an infusion of NaCl served as a volume control for the other solutions. Analysis of Results In each experiment concerning the flow-pressure relation- ship, venous-arteriolar response and reactive dilation, resistance was calculated by dividing the arterial-venous 13 pressure difference by the blood flow. The quotient was then divided by the splenic weight (mm Hg/ml/min/lOO g). Splenic weight was measured post-mortem after allowing blood to drain freely from the organ. In the study of the effects of local infusions of cations, the splenic weight was not in- cluded in the calculation of resistance. In all experiments, the significance of change from control of perfusion pressure, resistance, splenic weight, venous flow and systemic arterial pressure was tested with the Student's t test modified for paired comparisons (41). CHAPTER III RESULTS Flow-Pressure Relationship The flow-pressure relationships for the individual ani— mals are presented in Figure 3. It may be seen that the responses of perfusion pressure to changing flow were similar for all of the animals; whether the flow was increased step- wise or decreased stepwise (dog 9 and 12) in the experiment. Perfusion pressures increased as a function of flow over the range 9 to 204 ml/min. Venous pressure also showed an increase as a function of flow, on the average 10 ml/min increase in flow increased venous pressure 0.26 mm Hg. Systemic arterial pressure was not significantly altered during changing of pump blood flow. Figure 4 shows the changes in calculated resistance (mm Hg/ml/min/lOO g) and in weight as the splenic blood flow was altered. The calculated resistance almost always decreased as flow was raised from 9 to about 60 ml/min. However, when flow was increased over the range 60 to 204 ml/min, resistance only slightly decreased or increased. The splenic weight showed an increase in most dogs as the blood flow was increased 14 15 .ucmfiflummxm may mpocwp mmcfla map mo unmflu map um mumnasz .cmmamm may CH ACHE\HEV open 30am UOOHQ Hafiumunm ou Amm EEC mudmmmum cOflmsmHmm mo mflsmcoflpmHom .m musmfim 16 :2 SN 3— m onsmflm 252$ 26.: 80.5 s. s. BHOSSBHd NOISHJHBd Figure 4. 17 Changes in calculated resistance (mm Hg/ml/min/ 100 9) (upper panel) and splenic weight (lower panel) in relationship to changes in splenic arterial blood flow rate. Numbers to the right of the lines identify the experiments. 18 p ‘8 R E SIS TA N C E (mm Hg/ml/min/IOOg) as ’— I 12 o E] 2; 4| -Z- E m 9 2‘ Lu 0 Z a <[ :1: L) - - . _ _ . _ l - 40 80 |20 160 200 BLOOD FLOW (ml/min) Figure 4 19 from 9 to 204 ml/min. On the average, each 10 ml/min in— crease in flow caused about a 3 gm increase in weight. Increased pump flow did not produce a corresponding increase in venous outflow, i.e., for each 10 ml/min increase in pump flow, venous flow increased on the average only 2.5 ml/min. Therefore, blood was being accumulated in the spleen and splenic weight thus increased as pump flow was increased. Figure 5 shows the relationship of calculated resistance to the splenic arterial perfusion pressure. In six of the nine animals resistance markedly decreased as the perfusion pressure was raised from 35 to 85 mm Hg. The resistance of the three other dogs either increased or fell slightly. In all the dogs, further increases in perfusion pressure, from 85 to about 210 mm Hg, did not substantially change resistance (Table l). Venous-arteriolar Response The effect of stepwise increases in venous pressure on the vascular resistance of the spleens of 10 dogs is presented in Figure 6. The average change in weight is also shown. It can be seen that little or no change occurred in the ten doqs When the venous pressure was increased from a control of 4-6 mm Hg to about 9 mm Hg. Seven of the ten dogs showed an in- crease in resistance as the venous pressure was increased above 9 mm Hg. Three of the ten dogs, however, showed little 20 .mucmfifluwmxm msu >maucwpfl mwcfla map mo unmflu may ou mumnfisz .Amm EEC mHSmmmHm cosmswumm mo COHDUGSM m mm Am ooa\cflE\HE\mm EEC museumflmmu owumHsonu .m musmflm 21 m musmflm a: 5.5 $885 zoaimwa a: a. 8. 8 a: 8." Moon/unuxlw/GH ww) BONVISISBH 22 mm.ow vo.H H©.m H m.mmH Am OOH mm.OH mN.OH mN.OH mm.OH om.OH mm.OH \He\mm see Ho.H mH.H mo.H MH.H Hm.H mm.a mocmHmHmmm Hm.~ H He.m H ms.m H mv.m H m~.m H me.m H Amm say H.0mH m.eHH o.HNH «.mm o.me o.ev musmmmHm GOHmDMHOm oaamamm Aoa u 2v A.m.m H :mmEv .humuum may ca whammmum QOHmsmnmm mo coauoasw H mm mocmumflmmu Hmasomm> .H magma .cHE\HE m.mm mm3 30am HMflHmuHm oaamamm mmmuw>< .mnz .mcfla Umnmmp .huz .wcwa pflaom .csonm ma mHmEHam mo mmsoum 03» mmmau CH usmflmz cw mmcmno mmmnm>m wnu .Hmsmm usmflu may sH .mocmumflmmu :fl mmcmno m 303m no: Uflp QOHQS mamfiflcm may mum mmCHH pmsmmp mHH£3 mosmumflmmu mcfl Immwuocfl ADHB musmmmum msocm> msfimmmuocfl ou mcflpcommmu mamaflcm 23 mo muasmmu on» mum mmcfla pHHOm .ucofiflummxm Hmeflcm cm mo DHSm now can ma mafia some .chmm puma esp sH .musmmmum msocm> on unmflmz CH mommmuosfl can mocmumflmmu Umwmasoamo mo mangOHpmamm .m musmflm 24 0' (J15) .LH 9 | EM NI ESVBHDNI 1 (AN) (515 05 I/uuil/Iw/ESH win) EONVISISHH 20 30 40 10 20 30 4o VENOUS PRESSURE 10 (mmHm Figure 6 25 change in resistance over control values as venous pressures were increased above 9 mm Hg. In all ten animals the weight increased as a function of the rise in venous pressure. The weight increased at a rate of about 7 grams/mm Hg venous pressure until the venous pres- sure reached approximately 26 mm Hg. Above this level the weight showed an increase of about 20 grams/mm Hg venous pres- sure. The rate of venous outflow diminished as the venous pressure was raised even though arterial inflow was constant. On the average, venous outflow decreased from a control of 76 ml/min to 27 ml/min when the venous pressure was increased to 25-30 mm Hg. When venous pressure was lowered to control »1evels the splenic weight decreased rapidly the venous outflow markedly increased. The systemic arterial pressure did not change signifi- cantly in eight of the ten dogs, however, two animals showed a decrease of about 17 mm Hg as the venous pressure was in- creased. In these two animals there was a large increase in splenic weight and a large decrease in venous outflow. A sub- stantial blood volume thus was pooled in the spleen which decreased the venous return and the systemic arterial pressure. Reactive Dilation The average effects of stOpping arterial inflow and its release on perfusion pressure in nine dogs are presented in Figure 7. The upper panel shows the results of the experiments Figure 7. 26 Changes in splenic arterial perfusion pressure (mm Hg) as a result of a one minute cessation of arterial blood flow. While the blood flow was stopped, the venous outflow was either occluded (top panel) or allowed to flow freely (lower panel). N=9. 27 \IEflVCiLHB (ILPTFHJDHAII3LIDEHEEI 120 80 m a: :> 40 a) w i—H. [LI 0: A 0 0- a? z E 9 V venous OUTFLOW OPEN (I) D u. E: 120 a. ' T Puma OFF Pump ON I— l min -| Figure 7 28 in which venous outflow was occluded when stopping arterial inflow was stOpped. The lower panel shows the results of the experiments in which venous outflow was left open when arterial inflow was stopped. Although the splenic weight did not change in the former but decreased in the latter experi- ments (during the stopping of flow), the effects of stopping arterial inflow on resistance in these two experiments were similar. StOpping arterial flow decreased perfusion pressure and upon resumption of arterial flow, perfusion pressure remained at this level for about 16 seconds then began to oscillate, rising above and falling below control values. This oscillation lasted for about two and one-half minutes and has three to four waves. The oscillation of perfusion pressure was not associated with changes in splenic weight. Since blood flow was held constant, the changes in perfusion pressure indicate changes in splenic vascular resistance. Splenic arterial occlusion did not cause any significant change in systemic arterial pressure or splenic venous pressure. Local Effects of Cations The effects of infusing isotonic solutions of NaCl and MgCl at sequentially increasing rates into the splenic 2 artery are shown in Figure 8. Infusion of NaCl caused a sig- nificant decrease in calculated resistance only at high infu- sion rates but splenic weight and venous outflow were not 29 .Houusoo Eoum mmcmco HCMOHMHGmHm m mumoflpcfl mxmflnmum¢ .GHE\HE ca 30am UOOHQ mmmum>m u m .mucmEflummxm HMEHsm mo menses n 2 .30am msocm> can unmme mo wmcmso .mocmumflmmn N smasomm> oaswamm may :0 Aunmfiuv Hum: cam Aumwav Humz mo mCOHu.5HOm UMGOHOmH MO COHmDMflH HMHHOUvalMHHCH HMUOH MO muhumwwm .m musmflm 30 ON m musmfim c_E\UmE £5. 20322. 3 o._ n6 0 7 ma NA 0.0 u - - - N“ N a - oo m_uZ «dung m0 Nam"; 2 ON T N A5 .vw 9 No M Z mVI «an .I o 0 0— an N— 0— T ON VN mu .0 02 an 00 we 05 Va «0 av... uni cpl o—+ an... 0.0 N.— 0.— ON VN ad (ugw/lm) MO‘H SOONQA (w 5) lHDIBMV (ugw/|w/6wa) SDNVISISSU 31 significantly affected at any infusion rate. Magnesium chloride caused a significant decrease in splenic resistance and splenic weight. Associated with these changes was a sig- nificant increase in venous flows. Figure 9 presents the average results of infusing iso- tonic solutions of calcium chloride into the splenic artery of ten dogs. Resistance increased significantly over the intermediate to high rates of infusion and this increase was accompanied by a significant decrease in splenic weight and an increase in venous flow. Immediately after stopping the infusion of calcium chloride, the resistance suddenly and markedly increased. The resistance then gradually returned to control values. Splenic weight and venous outflow, how- ever, gradually returned to control levels following termina— tion of the infusion. Figure 10 is an actual recording during infusion of the calcium chloride at various rates into a spleen. The increase in perfusion pressure at high infusion rates, the decrease in splenic weight and the rapid increase of perfusion pressure upon termination of the infusion can be seen clearly. The average results of the infusion of isotonic solutions of potassium chloride is shown in Figure 11. Calculated re- sistance increased significantly as a function of the infusion rate. Splenic weight decreased significantly and venous flow was increased. The systemic arterial pressure was significantly raised at high infusion rates. Figure 12 shows an actual Figure 9. 32 Effects of local intra-arterial infusion of isotonic solutions of CaCl2 on the splenic vascular resistance, changes in weight and venous flow. F = average blood flow in ml/min. Asterisks indicate a significant change from control. Dotted lines indicate changes follow- ing termination of the infusion. VENOUS FLOW 'RESISTANCE (mm H'g/ml/min) 7"?" 7".” .N 9° C) bu‘D’FO C> (3 (ml/min) 108 33 <:O<:l2 o 0.5 1.0 INFUSION RATE (mEq/min) Figure 9 1.5 1.8 on "3min." 34 Amm EEC musmmmum scamsmuwm HMHHmDHm owamamm H mm Asmv unmflm3 GH mmqmno u #2 < ACHE\HEV Boamuso msocm> m> Amm EEC wnsmmmum HMflumunm oaamumwm mm .mmumu msflmmwuocw haamwucmsqmm um moo M NO cmwamm ms» ODQH maumu mo COHDSHOm OAGOHOmfl no mo cOHmSMGH HMHHQHHMIMHucH Hmooa mo muommmm mcflsonm mcflpnoomu HMSDUM cfi .OH mHsmHm 35 OH musmHm :_E\_E an. 30—“— QE: AfifixumEv «.000 538 :5 30.3 n: o ._ V. a. 3.. a n. awn “.1“. . .H...,.m...uj..... .. oo— ._ o: .. _ .. w. , ; _ 8H SOON nun Avo— num— nzuu .:< I m> Rom EEC musmmwum HMflumuNm anmumwm H mm .mmpmu mCflmmmNOCfl um wumuum oanHmm may ouCfl CONDCHOm HUM UNCou 38 Iowa Cm mCflmsmCH mo mpommmm map mCH30Cm mCHUNoomN Hmsuom CC .NH musmflm 39 NH musmdm 5:55: 307. n.5,; Actions; By. 532 .3 Exam t we: On OO— On— OON . ...... _ . 8 3 A g .8. S— N. _, OO— Om.— OON SEN 31.55 .— a .34 31.55 a u 40 recording during the infusion of potassium chloride into the splenic artery. The increase in systemic arterial pressure and decrease in splenic weight as well as the increase of perfusion pressure during infusion of KCl are shown. CHAPTER IV DISCUSSION This study examined some of the local factors which may be involved in regulation of splenic blood flow and reser- voir capacity. The factors examined were the flow-pressure relationship, venous-arteriolar response, reactive dilation, and the effects of local intra-arterial infusion of isotonic solutions of sodium chloride, magnesium chloride, calcium chloride and potassium chloride. In in situ, constantly pump-perfused canine spleens, we measured splenic arterial perfusion pressure, changes in splenic weight, large vein pressure and venous outflow of the spleen. The systemic arterial pressure was also measured. Blood flow through an organ is determined by the pres- sure gradient across the vascular bed and the resistance to flow exerted by the vascular bed. Since the inflow to the spleen was kept constant at any given time in the present study, changes in splenic arterial perfusion pressure indi- cated changes in vascular resistance. Therefore, in this . study a decrease of perfusion pressure indicated a decrease in vascular resistance and an increase in perfusion pressure a rise in resistance. 41 42 The canine spleen can serve as a blood reservoir chang- ing its volume in response to a wide variety of stimuli (19, 21, 32, 55). The weight of the spleen were continuously recorded in this present study. Appreciable decrease or in- crease in splenic weight regularly followed an increase or decrease in venous outflow. Since arterial inflow was held constant by the pump, changes in venous outflow and thus splenic weight indicated changes in blood volume within the spleen. In the canine spleen, changes in its volume result primarily from changes in the contractile state of the splenic capsule and trabeculae (19, 21, 32, 55). Thus, changes in weight served as an indicator of changes in blood volume and changes in the contractile state of the splenic capsule and trabeculae. Autoregulation has been defined frequently as the ability of an organ to regulate its blood supply in accordance with its needs. More often, however, the term has been applied in a less general sense to the intrinsic tendency of an organ to maintain constant blood flow despite changes in arterial per- fusion pressure (39). Autoregulation or the relationship of blood flow rate to the difference in perfusion pressure has been examined in most of the vascular beds available for research. These in- clude the kidney (28, 31, 49, 58, 59), brain (42, 47), lung (18, 25, 58), skeletal muscle (2, 25, 43, 49, 58) and coronary (8, 49, 52, 57) vascular beds. The relationship of blood flow 43 rate to perfusion pressure has also been studied in splanch- nic vascular beds such as the spleen (13, 17), the stomach (35), the intestine (19, 36, 53, 58) and the portal venous (3, 30) and hepatic arterial (3, 30) systems of the liver. Autoregulation has been demonstrated in the intestine (36, 53, 58), the heart (8, 52), the brain (42, 47), the kidney (28, 31), skeletal muscle (43, 49), and the hepatic arterial circuit (3, 30). The portal venous system (30), the stomach (35) and lungs (18, 58) do not exhibit autoregulation. This present study shows that over the blood flow range of about 9 ml/min to 204 ml/min, the perfusion pressure rose as a function of the flow (Figure 3). A given increment in flow rate, however, produced a proportionally smaller incre- ment in perfusion pressure over the lower range of flow rate (9 to 60 ml/min) but a proportional increase in perfusion pressure over the higher range of flow rate (60 to 204 ml/min). Thus, the calculated resistance of the spleen appreciably decreased as the blood flow was increased from 9 to 60 ml/min but showed little change as the flow was increased further over the range 60 to 204 ml/min (Figure 4 and Table 1). Increasing the rate of blood flow to the splenic artery should increase the intravascular pressure thereby distending the vasculature and causing the resistance of the vessels to decrease. The fall in resistance over the blood flow range of 9 to 60 ml/min appears to be due to this phenomenon, i.e., passive distension of the vasculature. As flow was increased 44 from 60 to 204 ml/min, changes in resistance were minor, either increasing or decreasing slightly. On the average these changes were not statistically significant (Table 1). This indicates that the splenic vascular bed has a local mechanism which antagonizes the passive distending effect of raising flow or pressure over the flow ranges 60 to 204 ml/ min and pressure ranges 70-80 to 210 mm Hg (Figures 4 and 5). These results are in contrast to those reported by Frohlich and Gillenwater (13). They found, in constantly perfused canine spleens, that the vascular resistance de- creased as the perfusion pressure gradient increased over a wide range (67 to 313 mm Hg). Greenway and Stark, using naturally perfused cat spleens, reported a near linear rela- tionship between pressure and flow over the natural range of blood flow changes (4 to 88 ml/min) (17). Since they did not express their data as calculated resistance it is not known if autoregulation is present in their study. The responses of the splenic vasculature to changing flow and pressure seen in this present study are similar to those observed in the heart (52) and stomach (35). In these organs, resistance decreased over a low blood flow range but only slightly decreased or increased over the higher blood flow levels. Venous-arteriolar response has been defined as the active increase in precapillary resistance as venous pressure through an organ is elevated (25). The effects of increasing 45 venous pressure on local vascular resistance has been studied in several organs. These include both the portal venous and hepatic arterial systems of the liver (3, 30), the brain (10), the kidney (23, 28, 59, 60) and also the skeletal muscle (25, 26, 43) and intestine (36, 37, 38). Elevated venous pressure of the liver caused an increase in hepatic artery resistance while, in contrast, it decreased portal venous resistance in a graded fashion (30). In the brain, increasing the venous pressure over a wide range (2.5 to 27.9 mm Hg) was associated with progressive increases in cerebral vascular resistance (10). Early studies on the renal vascular bed suggested that increasing venous pressure did not cause the venous-arteriolar response (25, 59), however, more recent experiments show that elevation of venous pressure elicits an immediate increase in renal vascular resistance (23). Elevation of venous pressure in the fore- limb of the dog has also been shown to increase resistance across the bed, demonstrating the venous—arteriolar response (25, 26). Studies using the intestinal vasculature also show that a venous—arteriolar response does occur in the intestine (37, 38). This present study examines the effect of elevated venous pressure on the vascular resistance and weight of canine spleens. Little cnrrm> change in the calculated resistance occurred as venous pressure was increased from control (4-6 mm Hg) to about 9 mm Hg. When venous pressure was raised 46 above 9 mm Hg, seven of ten dogs showed an increase in re- sistance (Figure 6). Elevation of resistance was graded with the increase in venous pressure and remained elevated for as long as the increase in venous pressure was maintained. The spleen thus exhibits a venous-arteriolar response. In all ten animals, the weight increased as a function of the rise in venous pressure. This increase in weight was accompanied by a decrease in venous outflow. Because the arterial inflow was held constant, the association of decreased venous outflow with increased weight indicated that the in- creased splenic weight was due to pooling of blood in the spleen. This study provided results which are similar to those presented in studies of the venous-arteriolar response in skeletal muscle (24), intestine (34) and hepatic arterial system (28). In these organs, the calculated resistance was not changed when venous pressures were increased slightly but was elevated when venous pressures were increased further. Another example of local regulation is the change in blood flow across a vascular bed after temporary occlusion of its blood supply. Upon releasing the occlusion, blood flow increases far beyond the control level. This phenomenon is called reactive hyperemia. For short periods of occlusion, the extra blood flow lasts long enough to repay almost exact- ly the tissue oxygen deficit that has occurred during the period of occlusion (22). If the experiments were conducted 47 under a constant inflow, the post—occlusive period would result in a reactive dilation. The effects of temporary occlusion of the blood flow have been studied in many vascular beds. These include the heart (22, 44, 49), lungs (l8), kidney (33, 34, 49), liver (hepatic artery) (30), intestine (48, 53) and skeletal muscle (15, 16, 26, 33, 49). With the exception of the lung, all of these vascular beds exhibit, upon releasing temporary occlusion of flow, significant increases in blood flow in naturally perfused organs or decreases in resistance in those constantly perfused. Some vascular beds are more sensitive to occlusion and demonstrate greater reactive hyperemia than others. Guyton (22) reports that if the coronary flow to the heart is completely occluded for a few seconds to a few minutes and then suddenly released the blood flow increases to as high as three to six times normal. In other beds like the liver (30) and the intestine (48) the blood flow in- crease is not as marked after the occlusion is released. The results of our study showed that, following a one minute period of complete occlusion of the splenic artery, the perfusion pressure returned to a point about 26 mm Hg lower than control (Figure 7). The perfusion pressure re- mained at this decreased level for, on the average, 16 sec- onds and then began to oscillate rhythmically reaching levels above and falling to below control values. Since blood flow to the spleen was held constant, the decrease in perfusion .7? 48 pressure and its oscillation indicated a decrease and oscil- lation of splenic vascular resistance. Reactive dilation and the excursions of perfusion pressure were seen whether the venous outflow was occluded or left open during the stop- flow. The occlusion of the venous outflow kept splenic e weight constant while opening the venous outflow lowered q splenic weight during the stop-flow period. Thus, reactive dilation and excursions of vascular resistance in the spleen following temporary complete ischemia are not related to the 3' splenic weight and volume. The results of this study are in agreement with the findings in other vascular beds. The heart (22), kidney (34), skeletal muscle (15), intestine (53) and hepatic artery system of the liver (30) all demonstrate a reactive dilation or hyperemia following release of occlusion of the arterial blood supply. Only the spleen, however, shows the rhythmic oscillations in vascular resistance following the initial reactive dilation. Grandlay §£.§L- (20) mentions a rhythmic- ity in the natural flow of blood but is unable to assign a cause for it. Our findings do not suggest to us a possible reason for the oscillations. The effects of local intra—arterial infusion of the major cations, Na+, Mg++, Ca++, and K+ have been studied in several vascular beds. The results of increasing cation con- centrations have been examined in skeletal muscle (9, 14, 27, 29, 50), heart (29, 50, 51), kidney (14, 27, 50), intestine 49 (6, 27, 50, 56), stomach (27, 56), liver (5, 50) and superior mesentery circulation (56). Infusions of the sodium ion in isotonic solutions do not appear to affect the vascular resistance of skeletal muscle (14), heart (51), kidney (14), intestine (56), liver (5) and stomach (56). The effect of a slight to moderate increase in magnesium content of blood perfusing a vascular bed is dila- tion (5, 6, 14, 51, 56). The renal, forelimb, and coronary vascular beds respond to a local excess of calcium with con- strictions (9, 14, 29, 46, 51) whereas the intestinal and hepatic vascular beds appear to be little or irregularly affected (5, 6). Gastric vascular resistance decreases with elevation of blood calcium levels (56). Local intra-arterial infusions, at low rates, of potassium result in a decrease in resistance in most of the vascular beds studied, while in- creasing the blood potassium to higher levels produces increases in resistance (9, 14, 27, 50, 51, 56). Potassium has little effect on the hepatic arterial vasculature at lower infusion rates, whereas it increases its resistance at the higher infusion rates (56). In this study we have observed the effects of increas- ing the concentrations of the major cations in splenic arteri- al blood on the resistance to blood flow through the vascular bed of the spleen. The study shows that the major cations, i.e., magnesium, calcium, and potassium can not only affect 50 the splenic resistance but they are also able to influence the reservoir capacity of the canine spleen. The results obtained in this study show that infusion of sodium chloride in isotonic solution does not signifi- cantly change splenic weight or venous outflow. Calculated resistance did. fall at the high infusion rates. This de- crease in total resistance was most likely due to a decrease in blood viscosity as the infusion rate reached 7.75 ml/min while average blood flow was only 81.2 ml/min. These find- ings are in agreement with studies reported by workers in other vascular beds (5, 14, 51, 56). Increasing the levels of magnesium in the perfusing blood to the spleen caused a decrease in resistance, a fall in splenic weight and an increase in venous outflow. The effect of Mg++ on resistance is similar to those found in other vascular beds; increases in magnesium caused dilation of the vasculature (5, 6, 14, 51, 56). Dilation of the splenic vasculature is probably the mechanism behind the drop in the resistance of the spleen while preferential relaxation of the post-sinusoid sphincters may be the cause of an in- creased venous flow and a corresponding loss of weight. An increased venous outflow during a constant inflow means a decreased intrasplenic vascular volume. Perfusing isotonic solutions of calcium chloride into the splenic artery did not significantly alter the measured parameters at low infusion rates. Increasing the infusion 51 rate to 0.98 mEq/min and above resulted in a significant rise in resistance with a marked fall in splenic weight and increase in venous outflow (Figures 9 and 10). Upon termin- ation of the infusion, splenic resistance showed a transient and marked increase (Figure 10). Splenic weight and venous flow, however, were unaffected and they continued their return to control levels. The reSponse of the splenic vascu- lar resistance to Ca++ at high infusion rates is therefore similar to that seen in renal, forelimb, superior mesenteric and coronary vascular beds (9, 14, 29, 51, 56). It has been proposed that the mechanism of raising vascu- lar resistance during calcium infusion, involves an active mechanism (46, 50). The increase in Splenic resistance could be brought about by a constriction of the splenic vas- culature and by contraction of the splenic capsule and trabeculae. Both mechanisms would tend to increase venous outflow and decrease splenic weight. In the splenic vascu- lature, however, the greatest increase in calculated resis- tance occurs following the termination of the infusion. Whether this is a direct effect of Ca++, i.e., a sudden de- crease in Ca++ concentration, or an indirect effect, e.g., mediated by nerves, is not clear. The response of the vas- cular resistance upon termination of infusion of Ca++ ob- served in this present study has not been reported in the other vascular beds. 52 Potassium chloride infused at increasing rates caused a steady increase in resistance, a decrease in weight and an increase in venous outflow (Figures 11 and 12). The results of changes in resistance are in contrast with those found in other vascular beds. In the other vascular beds, infusion of K+ causes a fall in resistance as potassium was increased P} slightly. Increasing the infusion rate to higher levels caused an increase in resistance in the renal, coronary, and forelimb vascular beds (9, 14, 27, 50, 51, 56). h, II The effects of potassium ion on the splenic resistance ' and weight are similar to those reported during infusions of KCl into the hepatic artery (5). Infusion of potassium chloride into the hepatic artery caused no change in hepatic arterial resistance until the infusion rate was increased to 7.75 ml/min at which time hepatic arterial resistance increased and the liver weight decreased. There was no change in resistance of the portal venous system at any infusion rate. This present study also shows that local intra-arterial infusion of isotonic KCl solution increased systemic arterial pressure (Figure 11). The infusions of the sodium, magnesium or calcium ion into the splenic artery did not significantly alter the systemic pressure. Thus, this systemic effect is unique to the potassium ion. An increased systemic arterial pressure has also been found during local infusion of potas- sium chloride into the intestine or forelimb (4, ll). 53 This effect of KCl appears to be mediated by a neural reflex because the increase in systemic pressure was seen even when the splenic venous outflow was prevented from returning to the animal. The present study was designed to investigate the ef- fects of changing arterial blood flow, raising venous pressure, and intra-arterial infusions of naturally occurring cations, on the vasculature of the canine spleen. This was CHAPTER V SUMMARY AND CONCLUSIONS accomplished by measuring the arterial perfusion pressure, changes in weight, venous outflow and venous pressure in isolated, in situ, pump-perfused, canine spleens. 1. Increasing the rate of arterial blood flow in a step- wise manner caused an increase in perfusion pressure but a decrease in calculated resistance over low flow ranges (9 to 60 ml/min). The resistance only slightly increased or decreased when flow was increased between 60 and 204 ml/min. Elevation in venous pressure to levels over 9 mm Hg usually caused increases in calculated resistance (7 of 10 animals). Splenic weight increased during any elevation of venous pressure. Resumption of blood flow following one minute of com- plete ischemia resulted in a perfusion pressure which 54 55 was, on the average, 26 mm Hg less than the initial control levels. Perfusion pressure then underwent rhythmical oscillations above and below control levels for three to four minutes. The infusion of an isotonic solution of NaCl, which was used as a volume control, caused a decrease in .3 resistance only at high infusion rates (3.38 and 7.75 ml/min). This was probably due to a dilution effect. Infusions of MgCl caused a significant decrease in bi 2 resistance as well as splenic weight. The venous outflow increase was possibly caused by a relaxation of post-sinusoid sphincters. Infusion of CaCl2 resulted in an increase in resist- ance, at high infusion rates, and a decrease in splenic weight. Immediately following termination of the infusion, resistance rapidly and markedly in- creased while splenic weight and venous outflow re- turned to control values. Infusion of KCl resulted in a significant increase in resistance and venous outflow and a decrease in splenic weight. KCl infusion also resulted in a significant increase in systemic arterial pressure, something not seen with the other cations. The in- crease in systemic pressure may be mediated by neural reflex. 56 In conclusion, the present study shows that the spleen does exhibit autoregulation over pressure ranges from 85 to 210 mm Hg. The spleen increases its resistance in response to elevation of venous pressure (venous-arteriolar response). In addition, temporary complete ischemia results in a A definite reactive dilation. It is also concluded that + . . . + ++ + naturally occurring cations, i.e., Mg , Ca , and K can not only affect vascular resistance but also can affect the '10.-- . reservoir capacity of the canine spleen. BIBLIOGRAPHY 10. 11. BIBLIOGRAPHY Baker, C. H. and J. W. Remington. Role of the spleen in determining total body hematocrit. Am. J. Physiol. 198:906—910, 1960. Barcroft, H. Circulation in skeletal muscle. I2_Hand- book of Physiology, Edited by Hamilton, W. F. and P. Dow, Sec. 2, Vol. 2, Am. Physiol. Soc., Washington, D. C., 1963. Brauer, R. W. Autoregulation of blood flow in the liver. Circ. Res. 14:213-221, 1964. Chen, W. T., C. P. Hsieh, C. C. Chou, and J. M. Dabney. Effect of local stimulation of dog jejunum on intestinal motility and aortic pressure. The Physiol. 13:166, 1970. Chou, C. C. and T. E. Emerson. Local effects of Na+, K , Mg++, and Ca++ on vascular resistance in the dog liver. Am. J. Physiol. 215:1102-1106, 1968. Dabney, J. M., J. B. Scott, and C. C. Chou. Effects of cations on ileal compliance and blood flow. Am. J. Physiol. 212:835-839, 1967. Dawes, G. S. The vaso-dilator action of potassium. J. Physiol. 99:224-238, 1941. Day, S. B. and J. A. Johnson. Pressure-flow relationships in the isolated perfused rabbit heart. Am. J. Physiol. 196:1289-1291, 1959. Emanuel, D. A., J. B. Scott and F. J. Haddy. Effect of potassium on small and large blood vessels of the dog forelimb. Am. J. Physiol. 197:637-642, 1959. Emerson, T. E. and J. L. Parker. Effects of local in- creases of venous pressure on canine cerebral hemo- dynamics. Unpublished. Fine, L. R. and C. C. Chou. Unpublished findings. 57 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 58 Friedman, S. M. and C. L. Friedman. Effects of ions on vascular smooth muscle. In Handbook of Physiology, Edited by W. F. Hamilton and P. Dow, Sec. 2, Vol. 2, Am. Physiol. Soc., 1963. Frohlich, E. D. and J. Y. Gillenwater. Pressure-flow relationships in the perfused dog Spleen. Am. J. Physiol. 204:645-648, 1963. Frohlich, E. D., J. B. Scott, and F. J. Haddy. Effect of cations on resistance and responsiveness of renal and forelimb vascular beds. Am. J. Physiol. 203: 583-587, 1962. Geber, W. F. and J. M. Schwinghamer. Evaluation of local ischemia, general anoxia, and vasodilators in reactive hyperemia. Angiology 16:256-266, 1965. Green, H. D. and C. E. Rapela. Blood flow in passive vascular beds. Circ. Res. 14:11-16, 1964. Greenway, C. V., and R. D. Stark. Vascular responses of the spleen to rapid hemorrhage in the anesthetized cat. J. Physiol. 204:169-179, 1969. Grega, G. J., R. M. Daugherty, Jr., J. B. Scott, D. P. Radawski, and F. J. Haddy. Effect of pressure, flow, and vasoactive agents on vascular resistance and capil- lary filtration in canine fetal, newborn, and adult lung. Microvasc. Res. 3:297-307, 1971. Grim, Eugene. The flow of blood in the mesenteric ves- sels. In Handbook of Physiology, Sec. 2, Vol. 2, Edited by W. F. Hamilton and P. Dow, Amer. Physiol. Soc., Washington, D. C., 1963. Grindlay, J. H., J. F. Herrick, and E. J. Baldes. Rhythmicity of the spleen in relation to blood flow. Am. J. Physiol. 127:119-126, 1939. Grindlay, J. H., J. F. Herrick, and F. C. Mann. Measure- ment of the blood flow of the spleen. Am. J. Physiol. 127:106-118, 1939. Guyton, A. C. Textbook of Medical Physiology. W. B. Saunders, Philadelphia, Pa., 1971. Haddy, F. J. Effect of elevation of intraluminal pressure on renal vascular resistance. Circ. Res. 4:659-663, 1956. 24. 25. 26. 27. 28. 29. 30. 31. 32. 33. 34. 59 Haddy, F. J. and G. A. Camobell. Pulmonary vascular resistance in anesthetized dogs. Am.'J.‘Physiol. 172:747-751, 1953. Haddy, F. J. and R. P. Gilbert. The relation of a venous- arteriolar reflex to transmural pressure and resistance in small and large systemic vessels. Circ. Res. 4:25- 32, 1956. Haddy, F. J. and J. B. Scott. Effects of flow rate, venous pressure, metabolites, and oxygen upon resist- ance to blood flow through the dog forelimb. Circ. Res. 15:49-59, 1964. Haddy, F. J. and J. B. Scott. Metabolically linked vaso- active chemicals in local regulation of blood flow. Physiol. Rev. 48:688-707, 1968. Haddy, F. J., J. Scott, M. Fleischman, and D. Emanuel. Effect of change in flow rate upon renal vascular re- sistance. Am. J. Physiol. 195:111-119, 1958. Haddy, F. J., J. B. Scott, M. A. Florio, R. M. Daugherty, Jr., and J. N. Huizenga. Local vascular effects of hypokalemia, alkalosis, hypercalcemia and hypomagnesemia. Am. J. Physiol. 204:202-212, 1963. Hanson, K. M. and P. C. Johnson. Local control of hepatic arterial and portal venous flow in the dog. Am. J. Physiol. 211:712-720, 1966. Hardin, R. A., J. B. Scott, and F. J. Haddy. Relation- ship of pressure to blood flow in the dog kidney. Am. J. Physiol. 199:1192-1194, 1960. Hausner, E., E. E. Hiram, and F. C. Mann. Roentgenologic observations of the spleen of the dog under ether, sodium amytol, pentobarbital sodium, and pentothal sodium anesthesia. Am. J. Physiol. 121:387-391, 1938. Hinshaw, L. B., B. B. Page, C. M. Brake, and T. E. Emerson. Mechanisms of intrarenal hemodynamic changes following acute arterial occlusion. Am. J. Physiol. 205:1033-1041, 1963. Honda, N., C. Aizawa, and Y. Yoshitoshi. Post occlusive reactive hyperemia in the rabbit kidney. Am. J. Physiol. 215:190-196, 1968. 35. 36. 37. 38. 39. 40. 41. 42. 43. 44. 45. 46. 47. 48. 6O Jacobson, E. D. Gastric blood flow. Am. J. Digest. Dis. 8:577-586, 1963. Johnson, P. C. Autoregulation of intestinal blood flow. Am. J. Physiol. 199:311-318, 1960. Johnson, P. C. Effect of venous pressure on mean capil- lary pressure and vascular resistance in the intestine. Circ. Res. 16:294-300, 1965. Johnson, P. C. Myogenic nature of increase in intestinal vascular resistance with venous pressure elevation. Circ. Res. 7:992-999, 1959. Johnson, P. C. Review of previous studies and current theories of autoregulation. Circ. Res. 14:2-9, Supp. 1, 1964. Jones, R. D. and R. M. Berne. Local regulation of blood flow in skeletal muscle. Circ. Res. 14:30-38, 1964. Lacey, O. L. Statistical methods in experimentation. The Macmillan Co., New York. 1953. Lassen, N. A. Autoregulation of cerebral blood flow. Circ. Res. 14:201-204, 1964. Nagle, F. J., J. B. Scott, B. T. Swindall, and F. J. Haddy. Venous reSistance in skeletal muscle and skin during local blood flow regulation. Am. J. Physiol. 214:885- 891, 1968. Olsson, R. A., and M. C. Major. Kinetics of myocardial reactive hyperemia blood flow in the unanesthetized dog. Circ. Res. 14:81-85, 1964. Opdyke, D. F. Hemodynamics of blood flow through the spleen. Am. J. Physiol. 219:102-106, 1970. Overbeck, H. W., J. I, Molnar, and F. J. Haddy. Resist- ance to blood flow through the vascular bed of the dog forelimb. Am. J. Cardiol. 8:533-541, 1961. Rapela, C. E. and H. D. Green. Autoregulation of canine cerebral blood flow. Circ. Res. 15:205-211, 1964. Scott, J. B. and J. M. Dabney. Relation of gut motility to blood flow in the ileum of the dog. Circ. Res. 15:234-239, 1964. 49. 50. 51. 52. 53. 54. 55. 56. 57. 58. 59. 60. 61 Scott, J. B., R. M. Daugherty, Jr., J. M. Dabney, and F. J. Haddy. Role of chemical factors in regulation of flow through kidney, hindlimb, and heart. Am. J. Physiol. 208:813-824, 1965. Scott, J. B., R. M. Daugherty, Jr., H. W. Overbeck, and F. J. Haddy. Vascular effects of ions. Fed. Proc. 27: 1403-1407, 1968. Scott, J. E., E. D. Frohlich, R. A. Hardin, and F. J. Haddy. Na , K+, Ca++, and Mg++ action on coronary vascular resistance in the dog heart. Am. J. Physiol. 201:1095-1100, 1961. Scott, J. B., R. A. Hardin, and F. J. Haddy. Pressure- flow relationships in the coronary vascular bed of the dog. Am. J. Physiol. 199:765-769, 1960. Selkurt, E. E., M. P. Scibetta, and T. E. Cull. Hemo- dynamics of intestinal circulation. Circ. Res. 6:92-99, 1958. Stainsby, W. N. Autoregulation in skeletal muscle. Circ. Res. 14:39-45, 1964. Texter, E. C., Jr., C. C. Chou, H. C. Laureta, and G. R. Vantrappen. Physiology of the Gastrointestinal Tract. C. V. Mosby Co., St. Louis, 1968. Texter, E. C., H. C. Laureta, E. D. Frohlich, and C. C. Chou. Effects of major cations 0n gastric and mesenteric vascular resistances. Am. J. Physiol. 212:569-573, Texter, E. C., Jr., S. Merril, M. Schwartz, G. VanDer- strappen, and F. J. Haddy. Relationship of blood flow to pressure in the intestinal vascular bed of the dog. Am. J. Physiol. 202:253-256, 1962. Williams, M. H., Jr., Relationships between pulmonary artery pressure and blood flow in the dog lung. Am. J. Physiol. 179:243-245, 1954. Winton, F. R. Arterial, venous, intrarenal, and extra- renal pressure effects on renal blood flow. Circ. Res. 14:103-109, Supl. l, 1964. Winton, F. R. Influence of venous pressure on isOlated mammalian kidney. J. Physiol. 72:49, 1931. TAT IIIIII 12 93 UNIVERSITY LIBRARIES gun nun II 3056 4641 MICH N MI 3