ESTMTICN 0F RENAL VENOIB RESISTANCE AND ITS SIGNIFICANCE T0 AUTCBEGUIATIG‘I IN THE DCB KIDNEY BY CHARIES HENRY NELIS II AN ABSTRACT Submitted to the College of'Soienoe and.Arts Michigan.3tate university of.Agriculture and Applied Science in partial fulfillment of the requirements for the degree of MASTER OF SOME Department of Physiology and Pharmacology 1960 2/ i C; Q “ , Approved j/C / L: c 6 ' CtC;Z/J ii EE§TRAC£ It has been suggested that the degree of functional distention of the kidney may be related to the severity of experimentally produced hypertension GSwann gt a;., 1959). The mechanisms controlling this distention have not been described. Although pressure to distention and flow to distention relationships have not been adequately studied, much work has been done on renal pressure to flow relationships, is the per- fusing pressure increases, renal blood flow increases. The rise in flow rate is rapid at first and then progressively slower. This indicates a rise in renal resistance to blood flow at high perfusion pressures. The mechanism responsible for this resistance rise has not been described with certainty, although numerous theories have been proposed. In an attempt to locate the site of this resistance change, a method was developed which allows separation of renal resistance into two components, that coming before, and that after the peritubular capillary bed. Pressure, distention relationships for the organ were simultaneously determined. Isolated dog kidneys were perfused with the animald own blood under varying arterial and venous pressures. The ' flow rate was measured directly, and the distention determined by recording the organs weight changes. The mean peritubular capil- lary pressure was estimated by an indirect method, .111 When the renal artery is clamped and the venous pressure is set at some desired level, this pressure is transmitted equally throughout the kidney. The distention which results from each of a number of "distending pressures” can be recorded and thus the distending pressure to distention relationship established for the organ. This distending pressure is the interstitial pressure, and is developed at the site of interstitial fluid formation. This is the peritubular capillary bed. Studies have shown that the peritubular capillary pressure and interstitial pressures are essentially the same during perfusion (Gottschalk gt 2;., 1956). The peritubular capillary pressure can now be computed from the observed distention of the kidney under any set of perfusion con- ditions. Blood flow, arterial and venous pressures were measured directly. Using data obtained by these methods, the post- peritubular capillary resistance was calculated and it was found that this was linearly proportional to the distending pressure. A study of the relative contributions of the pre- and post-peritubular capillary resistances to the total renal resistance revealed that the resistance rise in autoregulation was located in the post-peritubular capillary segment of the vascular system. All theories thus far offered as explanations of autoregulation have assumed the resistance rise to be in the pre-peritubular capillary segment of the organ. The findings of this study seem incompatable with such theories and suggest that the resistance rise of autoregulation is due to venous constriction, perhaps by interstitial pressure. iv REFERENCES Gottschalk, C. w. and Mylle, M. (1956) 'Micropuncture Study of Pressures in Proximal Tubules and Peritubular Capil- laries of the Rat Kidney and Their Relation to Ureteral and Renal Venous Pressures." .Amer. J. Physiol., 185, 430‘439 o / Swann, H. G., Rainey, M. J. and Carmignani, A. E. (1959) "Functional Distention of the Kidney in Perinephric Hypertension.” American Heart Journal, 58, 608-622. ACKNOWIEDGMENTS The author wishes to express his gratitude to Dr. W. D. Collings for his liberal assistance in the prepara- tion of this document, and for his assistance in the experi— mental work. The contributions of E. J. McCoy and C. R. Replogle, both in terms of laboratory assistance and stimulating ideas, are also deeply appreciated. REVIEW OF LITERATURE vi TABIE OF C ONTENTS THEORETICAL PRINC IPIFS IETHCDS........ RESULTS........ DISCIBSIQI SUMMARY AND CONCLUSIONS APPENDIX 1 APPENDIX 2 APPENDIX 3 APPENDIX 4 REFERENCES 0 O O 0 O O. 0 O O O O O 0 0 0 0 O flflflflfl 1 5 31 35 37 39 [.1 43 1+8 ESTIMATION OF RENAL VENOUS RESISTANCE AND ITS SIGNIFICANCE TO AUTOREGUIATION IN THE DCI} KIDNEY BI" CHARIES HENRY WELIS II A THESIS Submitted to the College of Science and Arts Michigan State Uhivers ity of Agriculture and Applied Science in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Department of Physiology and Pharmacology 1960 -1... REVIEW OF lgTERATURE Although it has long been recognized that there was some relationship between renal contraction as seen in chronic pyelonephritis, and elevated levels of systemic arterial pres- sure (Tyson, 1883), only recently has it been realized that the kidney is distended in its functional state. This property was examined by Swann gt g1. (1958a) in a study in which they froze mouse kidneys in EAEE: then removed and sectioned them. The cortices of these organs, exclusive of glomeruli and vessels were found to be 45% interstitial fluid. Another method of measuring distending fluid was de- ' scribed by Swann.gt al. (1955a). Simultaneous clamping of the renal blood vessels was followed by removal and drainage of the organ. The quantity of drainage fluid, and its hematocrit, allowed estimation of the volume of the drained vascular bed and of the draining, cell-free fluid when the systemic hemato- crit was known. For dogs it was found that functionally dis- tended kidneys will drain 13 to 30% of their distended volume CSwann.§t §;., 1956a). The hematocrit of the drained fluid was about half that of blood. From these data the relative proportion of blood and 'diluting fluid" in the draining fluid was calculated. Studies of the electrolyte and protein contents of draining fluid, renal lymph, urine and blood, led Swann and co-workers (1956a, b, 1958b) to suggest that this distending 121 fluid was a mixture of capillary filtrate and tubular resorbate, and that it occupies the interstitial space in the distended organ. Overbaugh gt filo (1957) repeated this for several other mammals and found that all those tested had a sizeable degree of renal distention. Experimental renal hypertension has been produced by a variety of methods. One of these involves incarceration of one kidney in a relatively nonadistensible cast and removing the contralateral organ (Soskin and Saphir, 1932, Page, 1939, Corcoran and Page, 1942). It can also be produced by placing a constrictive clamp on the renal artery (Goldblatt gt gl., 1934). This results in a reduction of arterial pressure at the kidney (Mason gt al., 1940). Inasmuch as it has been shown that, in the normal subject, renal distention increases with increased arterial pressure (Swann.gtlgl., 1955b), we may logically con- clude that distention of the kidney in Goldblatt hypertension is reduced. It has been suggested that the reduction in renal distention may be the critical factor in these forms of experi- mental hypertension (Swann gt 31., 1959). .Arguments that the arterial clamping experiment caused an elevation of blood pressure initiated by reduced renal blood flow have been contested (Schroeder and Steele, 1940, Corcoran and Page, 1941, Friedmanqgt‘g;., 1941). Corcoran and Page (1941) were unable to detect persistant diodrast, phenol red, inulin clearance changes in animals rendered hypertensive by renal arterial constriction. .Also, in renal incarceration with silk crepe, hypertension persists without changes in renal plasma flow (Corcoran and Page, 1942). If on the basis of the above studies of Corcoran and Page, Friedman gt g;., and Schroeder and Steele, we reject the hypothesis that the level of a circulating pressor substance is dependent upon the degree of renal ischemia, then we must explore the possibility of the level of pressor substance being dependent in some manner on the degree of renal distention. In view of this the renal pressure-flowadistention relationships and mechanisms would seem to be fruitful areas to explore. Although little is known about the distention-pressure or distentionaflow relationships, there is a wealth of knowledge about pressure-flow relations in the kidney. As arterial pres- sure increases in the intact normal kidney, the flow increases, rapidly at first and then progressively more slowly (Selkurt 1946, Weiss gt gl., 1959, Hinshaw gt gl., 1959). As may be seen from.Figure 1 there is no flow with pressures of 14 mm Hg or less. Burton (1951) proposed the concept of critical closing of the renal vessels as a possible explanation of this phenomenon. The cause of the resistance rise at high flows has been the subject of much controversy. Perhaps the oldest and most generally favored theory is that the rise in resistance is due to constriction of renal arterioles (Thompson.gt‘g;., 1957, Haddy'gt‘g;., 1958, Forster and Mass, 1947, Shipley and Study, 1951). This concept is remenforced by the finding that cyanide produces irreversible vasodilation and abolishes auto- regulation while procaine will reversibly abolish it (Lochner and Ochwadt, 1954). On the basis of rising resistance with elevations in venous pressure, at a constant perfusion rate, Lochner and Ochwadt (1954) postulated the presence of pressure-sensitive structures in the renal vessels. Such sensing devices were thought to initiate a feedback mechanism leading to vasocon- striction in other renal vessels. thdy' t g}. (1958) too, felt that autoregulation must be due to an intrarenal reflex. Extrinsic denervation, inactivation of circulating catechol- amines,and the use of ganglion blocking agents failed to abolish it (Haddy, gt gl., 1958). It has been demonstrated, however, that the abolition of autoregulation is accompanied by a rise, not a fall, in renal resistance. When the renal resistance approaches twice that of the normal, autoregulation disappears, but the organ still responds to Levophed (nor-epinephrine) (Weiss, gt gl., 1959). These findings suggest that the vasodilation which re- sults from treatment with cyanide is not the factor which is directly responsible for the loss of autoregulation in these experiments. Conversely, the inability of the kidney to autoregulate when renal resistance is high can hardly be inter- preted as vasospasm if levophed will cause further resistance rises, as reported by'Weiss. The inability of the active vasoconstriction theory to explain the lack of autoregulation on the basis of vasomotor paralysis, or as an inability of the vessels to reSpond further because of maximal contraction of the vessel musculature, raises some doubts as to validity of the theory. In contrast to theories of autoregulation which are based on active vessel constriction, there are theories which attempt to explain it on the basis of physical changes in the system. Hinton (1951) discussed the possibility that the rise in resistance could be due to increase in viscosity of the blood following concentration during filtration. He challenged the idea, however, by referring to work by Whittaker and him, self (1933) in which they added red cells to blood perfusing the isolated hindlimb of a dog. From this work he concluded that viscosity changes which one could expect could cause only a small fraction of the resistance rise normally seen. Pappenheimer and Kinter (1956) recognized that blood flowing through a tube tended to concentrate its formed elements in the center and leave the periphery relatively cell free. The degree of concentration of the cells depends upon the velocity of flow. They felt that the relatively cell poor plasma would be progressively skimmed off delivering cell rich blood to the terminal arterioles. This blood was thought to be shunted past the peritubular capillaries to the renal vein. Since the effective viscosity varies directly with the third power of the red cell concentration, relatively small changes in cell concentration in the terminal arterioles will result in rather large increases in apparent resistance. The concomitant fall in hematocrit in medullary vessels will contribute relatively small decreases in total impedence to flow. Weiss, Passow and Rothstein (1959), on the other hand, were able to show autoregulation in kidneys perfused with cell free fluid. If autoregulation is not due to arteriolar constriction or plasma skimming, the structures responsible for this pheno- menon have not been determined. In view of this, the review of older literature by Koester gt g}. (1955) on intrarenal venous sinusoidal structures is particularly interesting. These struc- tures, which appear to be erectile tissue, protrude into the vascular lumina at the junctions of the arcuate and interlobar veins. Interest in these sinusoidal cushions was renewed by the observation of Swann gt gt. (1952) that the pressure in the arcuate veins was much higher than in the interlobars. These findings led us to undertake the measurement of the resistance to blood flow developed in the venous seg- ment of the renal circulation. -3- T__§§ETICAI.PRINCIPIE§ understanding the rationale employed in measuring the venous resistance requires consideration of the anatomy of the kidney. Its capsule is a firm fibrous structure and the attain- ment of functional distention of the organ involves filling and/or stretching of this capsule. The pressure necessary to accomplish this is the interstitial pressure and is derived from the peri- tubular capillary bed. In view of the discovery that albumins pass freely through these capillaries (Collings and Swann, 1958), one can assume that there is little difference between the colloid osmotic pressure within these vessels and that within the inter- stitial space. Moreover, Gottschalk (1956) has shown that the mean peritubular capillary hydrostatic pressure very closely approximates that of the interstitial space. The mean peritubular capillary pressure (PD) is related to venous pressure (RV), the resistance of vascular bed (RT) between the points of measurement of mean peritubular pressure and venous pressure, and blood flow (Q) as follows: PD The resistance of the vascular bed (HT) is related to the ==RTQ + P.V Equation 1 capillary pressure (PD ), flow and venous pressure by the following equation: 3T = “—— Equation 2 If the renal artery is clamped and renal vein pressure increased, this pressure is transmitted throughout the kidney as in any liquid-filled system. In this way the distention which results from any given peritubular capillary pressure can be determined. Once the relationships of peritubular capillary pressure and renal distention are determined for a given kidney by this method, one can infer the mean peritubular capillary pres— sure from the observed distention, when blood is flowing through the kidney. The sum of the resistances distal to the peritubular capillaries can be determined by dividing the pressure drop from the peritubular capillaries to the renal vein by the renal blood flow. (Equation 2) This method does not measure the resistance imposed by the sinusoidal cushions alone but rather the sum of all resis- tances distal to the point of mean peritubular capillary pressure. Similarly, it is possible to determine the sum of the serial resistances between the renal artery and the point of mean peritubular capillary pressure. -10- METHOUS Isolated kidneys were obtained by a left flank approach from 6 mongrel dogs of approximately 20 kilograms body weight. These organs were freed from the body wall by doubly ligating and severing small segments of perirenal fat, fascia and peri- toneum. This procedure was used to avoid the severe bleeding which would result from stripping the peritoneum from the capsule. When the kidney and its vessels had been dissected free, the ureter was cannulated with polyethylene tubing. The kidney was returned to its normal position and allowed to perfuse for 20 minutes in order to recover as nearly as possible from the effects of the.manipu1ation. Meanwhile the animal was heparinized and both femoral veins and one femoral artery was cannulated. The femoral vein cannulae were attached to a bubble-trapping reservoir to be used for return of blood to the animal (Appendix 2). The femoral artery cannula was next filled with blood. The distal end of this cannula opened on the inside of the perfusion chamber for eventual attachment of the renal artery. At the end of the period of it £122 perfusion both renal vessels were doubly clamped with mosquito forceps and sectioned between the clamps. The vessels of the excised organ were then cannulated with polished stainless steel cannulae which had -11- previously been filled with blood to avoid air emboli. The renal arterial cannula was now carefully attached to the distal end of the femoral cannula in the perfusion chamber so as to exclude all bubbles and the renal venous cannula was attached by Tygon tubing to a reservoir of adjustable height. (Appendix 3). As soon as the renal vessel cannulae were securely attached to perfusing system, blood flow was established. The average duration of ischemia was 4% minutes. The renal outflow drained into a reservoir, the height of which determined the renal venous pressure. This could be set for any value from -20 to +100 mm Hg. Overflow from the reservoir passed through a modified polyethylene graduated cylinder, the outflow of which could be stopped at will. Volume flow was monitored by timing the filling rate of the graduate. Blood was returned to the femoral veins of the dog by a Sigma- motor pump through the bubble-trapping apparatus previously mentioned. Arterial and venous pressures were measured at the perfusion chamber by Statham strain gauges, models Pe23A and P-23VV respectively, located at the same level as the kidney. The weight of the organ was determined by placing it in a wire basket suspended from.a Statham strain gauge, model 01-32-450, mounted in the roof of the perfusing chamber (see Appendix 3). Recordings of pressure and weight were made by a ..1 2.. Sanborn polygraph with the output of the pressure transducers amplified by Sanborn carrier amplifiers while the output of the weight transducer was amplified by a Brush Universal.Strain Analyzer. In order to regulate arterial pressure at the kidney, the dog was placed on a platform of readily adjustable height. By varying the height of the animal with respect to the kidney, a hydrostatic pressure was developed which modified the arterial pressure at the kidney. After perfusing ten to fifteen minutes in the warm, humid chamber, the arterial cannula was clamped and the organ was allowed to drain as completely as possible while the venous pressure was set at zero. This was taken to be the drained weight of the kidney and distention was defined as the increase in weight above this drained value. The arterial pressure was then adjusted to a low level @N'35 mm Hg) and flow re-established with the venous pressure set at some point between zero and 6 mm Hg. When distention was thus equilibrated, blood flow was measured. Arterial pressure was then raised in approximately 10 mm Hg increments, with arterial pressure, distention, and flow measured at each step until the arterial pressure was in the range of 200 mm Hg. The arterial pressure was next dropped by similar increments until it was again at low levels with measurements of flow and distention taken at each increment. The renal arterial cannula was now clamped and the organ .13.. _.\hw\ , \NKKV D .14- allowed to drain with venous pressure at zero mm Hg as before. Venous pressure was then raised in increments of 5 mm.Hg and time was allowed for distention equilibration at each pressure. After a venous pressure of 60 mm.Hg was reached the organ was drained in a similar manner. This procedure was used to de- termine the relationship of peritubular capillary pressure to distention. In several of the kidneys studied arterial pressure was held constant and venous pressure was raised in small increments starting at zero mm Hg and ending at 50 mm.Hg while flow was maintained instead of maintaining a constant venous pressure and varying the arterial pressure. -15e RESUITS Employing the procedure previously described in the discussion of methods, data were obtained on renal blood flow, renal weight, arterial and venous pressures. From these the resistance values were calculated. Pressures: A description of the symbols used in this study follows. arterial pressure, in mm Hg, at the kidney. venous pressure in mm Hg taken at the kidney. mean peritubular capillary pressure in mm.Eg. the pressure drop between the arterial and the venous pressure measuring points, in mm Hg. the pressure dr0p between the point of mean peri- tubular capillary pressure and the point of measurement of venous pressure, in mm Hg. Resistances: BK: RT: RP: Others: Q: total renal resistance, in peripheral resistance units, to blood flow. ’ resistance in peripheral resistance units from the site of mean peritubular capillary pressure to the site of venous pressure measurement. resistance, in peripheral resistance units, between the point of mean peritubular capillary pressure and the point of arterial pressure measurement.. flow of blood through the kidney in ml/min. -169 The first group of figures (1-6) illustrates the relation- ship of the renal blood pressure drop (PA — Pv) to blood flow. The renal venous pressure was maintained at a constant value throughout each of the trials. The original experimental values accompany each plot, except the values for resistance which were calculated. All original data are in Appendix 4 . 117.. Figure 1 12-18e59 120‘ 1 (DC) CD ‘ O EEK oo- pru C) (3 fi so 100 Q cc/min PRK 40 56 66 81 94 94 Q 40 52 6o ' 69 72 75 Figure 2 12-17-59 120 - C) C) J (D C) P RX 60- O pru -.J 50 100 Q cc/min PER 85 88 113 118 66 Q 57 63 72 80 4o “.18.. 1 m16=6OA Figure 3 120 - O 0 PER 60. O O pru O 160 200 Q cc/min PRK 42 52 61 81 97' Q 54 80 106 120 128 1416—603 Figure 4 1201 _ O 0 PM 60 ' O pru O O 100 200 Q cc/min PRK 36 48 59 78 93 q 1.0 52 '70 88 100 1.19.... 12-1 6-59 Figure 5 120 1 Fax 60-1 (j;) PHI 0 1 100 200 Q cc/min PRK 62 78 84 39 57 Q 106 120 120 70 100 Figure 6 1.2360 120 1 O O O O '1 OO Phx. ‘60' (§D pru 100 200 Q cc/min Fax 66 67 82 86 99 108 112 118 Q 104 108 128 136 150 168 180 200 120, Figures 7—11 depict the relationship between mean peritubular capillary pressure and post-peritubular capillary resistance. In this group venous pressure was maintained at a constant value and changes in peritubular capillary pressure were achieved by elevating the arterial pressure. Figure 11 is a composite of the data obtained in four separate series of arterial pressure elevations in the same kidney at the same venous pressure. ~21 .. 12—18-59 Fi re '7 0550 l gu B. O O .275 j pru m 0 0 PD mm Hg. PD 8 16 18 21.5 29 31 RT .100 .230 ‘ .233 .253 .346 ..360 Figure 8 .550« 1-16.60 C) RT .275 ' O pru C) O O 25 ’ 50 Pp mm Hg. a, 10 14 23.5 43.5 49 RT .054 .062 .136 .287. .313 .22- 11125259 Figure9 .‘350‘1 0 RT .2784 (D pru ,C> ‘ 2% 5b PD mm Ego P, 2 2.3 3.2 3.8 4.0 12 25.5 37 RT 0 .004 .016 .024 0028 .085 .287 .530 1-23.60 °55°‘1 Figure 10 ET 0275 '4’ pru I C) C) o o 09 O C) 2;? . 50 RD mm 3E0 Pb 8 13 16 19.2 22 25.5 43 50 RT .058 .108 ..108 .117 .126 .128 .223 .235 .23, Figure 11 12-16-59 .550- A Hr A .275" pru Q! Jag (ID (3 37.5 ' 75 Pp mm Hg. 1st filling (O) . PD 15 21 .5 29 RT .113, .155 .216 2nd filling (A) 30 29 33.5 47 RT .192 .182 .245 3rd filling (()) Pb 6.5 8.5 17 32 33.5 RT .057 .057 .112 .195 .200 4th filling (A) ED 47 59 71.5 Rm .260 .317 .320 _24_ Figures 12115 also illustrate a relationship of the mean peritubular capillary pressure to the posteperitubular capillary resistance. However, in these cases, elevations of peritubular~ capillary pressure were obtained by elevating the venous pressure while the arterial pressure remained constant. In the previous group of plots the arterial pressure was varied. Figures 12 and 14 are composites of all data obtained on one dog at arterial pressures of 60-68 and 81-87 mm Hg respectively. At no other arterial pressure was there a sufficient grouping of data from this animal to justify another figure. Figure 15 is derived from data obtained similarly from another animal. Data plotted in figure 13 were obtained at a fairly steady arterial pressure (56-72) and during a single filling of the kidney. -25- Figure 12 12-16-59 .6- 1 Br 03" Prn (:> o O Q63 0 Pa» 60 to 68 40 80 Pb mmHg Pb 8.5 15 17 29 33.5 47 ET .057 .113 .112 .192 .182 .260 Figure 1.3 11-25-59 .61' O B. .3_ o pru O . - Lill> . .Pa“/561t° 72 40 80 .Po m "E Pb 3.8 4 12 25.5 37 R? .024 .028 .083 .287 . .530 .126... Figure 14 12-16-59 .6‘ RT 03" 0 PW O C) (3 Pa 82 to 88 40 80 PD mmH‘g. PD 21.5 33.5 47 71.5 RI: .155 .200.245 .302 Figure 15 12-18-59 .61 o (D (3 Br 1 O o .3 Pru l O 1 l 1 20 80 PD mm Ego p, 21.5 21.5 31 34 34 41 .362 .253 .510 .410 .340 .577 A? .27.. If the renal resistance is separated into two components, the pre- and post-peritubular capillary resistances, as described in Theoretical Principles, it should be possible to show the relative contribution of each to the total resistance under varying flow conditions. 'The following 6 figures (16-21) show these relationships. -28- 12-16-59 Figure 16 1.01 8 R A AA ,.5 O 00 Q pru o o O Q 0 100 200 Q cc/min Q 106 120 120 70 100 me) .113 .155 .216 .057 .057 Rpm) .517 .495 .484 .503 .533 Figure 17 1-23-60 1.0 A g A A AA A R , .5. ‘ 00 O o pru O O 0 0 o 00 O O 1 O A 7 100 ' 200 Q cc/min Q 104 108 128 136 150 168 180 200 (o) .058 .108 .108 .119 .126 .128 .223 .235 RP( O) ‘ e574 0514 0532 .551 e526 0512 0399 0355 RK(43) .632 .622 .640 .670 .652 .640 .622 .590 .29.. Figure 18 12-18-59 1.35 A A A A A H ' , 62‘ pru 9° 0 Q) 9 40 g 80 Q cc/min Q. 52 6o 69 72 75 Me) .230 .233 .253 .346 .360 RP(()) .850 .867 .917 .974 .890 EK(A) 1.08 1.10 1.17 1.32 1.25 Figure 19 1.35 7 11-25—59 R .621 6 .06 pru ‘ 9‘ $2“ 40 ‘ 80 Q cc/min Q 5 70 74 74 76 72 1113(8) .000 .004 .016 .024 .028 RP( ) e655 e701 e849 0856 .972 Rch.) .655 .705 .865 .880 1.00 -30- Figure 20 1=-16=—60A 1.0 A A A 4‘ R A .5. O 0 7C 140 54 80 106 120 128 111(0) .350 .300 .300 .435 .455 115(0) .425 .350 .275 .245 .300 R KA() .775 .650 .575 .680 .755 Figure 21 1-16-6OB 1.0 4: ‘3 4; ‘3 R .5‘ pru C) (3 ‘3 <3 o . 7B ‘ 140 Q cc/min 4O 52 70 88 100 11.,(0) .058 .127 .128 .175 .175 R P(Q) .842 .793 .712 .710 .755 R:(A) .900 .920 .840 .885 .930 -31.. DISCUSSION Autoregulation was present in some degree in most kidneys studies. However, Figure 6 shows no tendency toward an increase in resistance to blood flow at high flow rates, and consequently no autoregulation. The presence of auto- regulation in Figure 4 is questionable. Note that Figure 4 is from.data obtained on a second perfusion of the kidney of dog 1—16-60. In an earlier perfusion, this organ showed a marked ability to autoregulate (Figure 3). Previous studies on isolated perfused dog kidneys have revealed that autoregu- lation varied in intensity and in some cases it was absent altogether (Haddy gt gl., 1958). Weiss gt 91. (1959) reported that prolonged perfusion of isolated dog kidneys resulted in the loss of autoregulation. The absence of this phenomenon was explained by Buddy gt gl.(1958) as death of the organ. This hypothesis is reinforced by studies showing the abolition of autoregulation by treatment of the organ with cyanide. In this study however, no perfusions were carried out in which there was not a noticeable color difference between arterial and venous blood. This observation does not rule out the possibility of the structures responsible for autoregulation being dead, but it does indicate that there was oxygen uptake in some portion of the organ. Figures 7 through 15 illustrate the relationship between -32- mean peritubular capillary pressure and post-peritubular capillary resistance. There are several possible explanations of this phenomenon. The rise in postaperitubular capillary resistance could be brought about by a reflexly induced vasoconstriction. The pressure sensi- tive receptors would then be located in the peritubular capillary bed. Such a reflex was proposed by Lochner and Ochwadt (1954) although he did not locate the receptors. Further studies will be necessary before this theory can be adequately evaluated. The observation that peritubular capillary pressure is essentially identical with interstitial pressure (Gottschalk, 1956) allows explanation of the data from figures 7-15 on the basis of partial collapse of the intrarenal veins by the interstitial pressure. The degree of collapse is dependent upon the interstitial pressure and the resultant reduction in vessel lumina are responsible for the increase in resistance (Replogle, 1960). Hinshaw’gtlgl. (1959) has recently reported a close relationship between interstitial pressures as measured by renal puncture and total renal resis- tance. Figures 16-21 are presented to demonstrate the relative contributions of the pre- and post-peritubular capillary resis- tance to the total renal resistance. In every case in which autoregulation is seen, the rise in total resistance 03K) is derived from increases in.post~perituhular capillary resistance (RT) (Figures 16, 18, 20). The pre-peritubular capillary re- A335. sistance (RP) tended to remain constant, or to decrease with increased blood flow. Theories explaining autoregulation as renal arteriolar constriction (Forster and Maes, 1947, Shipley and Study, 1951, Thompson gt g;., 1957, Haddy gt g;., 1958) would place the resistance increases of autoregulation proximal to the peritubular capillary bed. Such theories are incompatible with the findings presented in figures 16221. Pappenheimergs plasma skimming theory (Pappenheimer and Kinter, 1956) would place the resistance rise in shunts parallel to the peritubular capillaries. At high flows the blood presented to the veins draining the peritubular capillaries would be relatively cell poor and thus less viscous. This should result in a lower apparent resistance in the postwperitubular capillary vessels. The data presented in figures 16~21 appear to be in sharp disagreement with this theory. The resistance in question appears to be elevated, if anything. Lochner's theory that autoregulation was due to an intra- renal reflex did not specify the location of the pressure sensitive structures nor the site of the reflex vasoconstriction. In order for this theory to fit the findings of this study, the location of the vasoconstriction must be somewhere in the vascular system beyond the peritubular capillary bed, and the pressure sensitive structures located in the peritubular capillaries. The sparcity of muscle in the vein walls would cast doubt on theories crediting autoregulation to generalized renal vein constriction and no well differentiated renal vein sphincters have been described. Histological evidence of peritubular capillary pressure receptors is also lacking. Replogle's theory of partial collapse of the intrarenal veins by interstitial pressure is in agreement with these findings, however, a precise explanation of the physical principles involved has not yet been accomplished. The venous sinusoidal cushions (Koester gt gl., 1955), by virtue of their location and structure, should also be considered as a possible source of this changing resistance. If these struc— tures were to become engourged, and distend into the vascular lumina as the interstitial pressure was increased, the resultant reduction in venous lumina could account for the resistance rise. None of these theories offer a ready explanation of the effect of cyanide on the kidney. It is known that cyanide abolishes autoregulation (lochner and Ochwadt, 1954) but little is known of the mechanism by which this is accomplished. The two cases of lack of autoregulation (Figures 17, 21) appear to have little in common. In Figure 17 there is a rise in the post-peritubular capillary resistance as the blood flow in- creases, but this is offset by a similar drop in pre-peritubular capillary resistance. Figure 21, however, shows very little change in pre- or post-peritubular capillary resistances at flows above 50 cc/min. No explanation is offered for the lack of post-peritu- bular capillary resistance response to peritubular capillary pressure increases in this perfusion. SUMMARY AND CONCLUSIONS (1) Isolated dog kidneys were perfused with the dogs' own blood at varying arterial and venous pressures. Direct measurement of arterial and venous pressure, and blood flow, and ailindirect measurement of the mean peritubular capillary pressure allowed calculation of the total renal resistance to blood flow and the resistances imposed by its prew and post- peritubular capillary segments. These resistances were calculated at a var— iety of blood flow rates. (2) Autoregulation as manifest by rise in resistance at high flow rates, was present in the majority of the kidneys perfused. (3) The data indicate a linear relationship between the mean peritubular capillary pressure and the post—peritubular capillary resistance. (4) Simultaneous determinations of pre- and post- peritubular capillary resistances at varying flow rates supplied evidence that post—peritubular capillary resistance changes are the cause of renal autoregulation. This mechanism furnishes a new explanation for the autoregulation phenomenon. -36.. APPENDIX 1 237a PERFUSION CHAMBER The perfusing chamber was designated to bathe the kidney in an atmosphere of 100% relative humidity at 38°C. The air was continuously recirculated through a blower powered duct system. Steam was introduced into the duct to saturate the air at that point. A wet burlap screen separated the chamber into two compart- ments. All circulating air was forced through this screen and evaporation from it contributed to atmospheric saturation with water vapor. Temperature control was accomplished by use of an elec- tric heater placed on the side of the screen opposite the kidney. The heater was controlled by a thermostat placed in the roof of the chamber above the kidney. The weight transducer was mounted in the roof of the chamber with the kidney in a wire basket suspended from it. The pressure transducers were mounted on the exterior of the perfusing chamber and connected to the cannulae by polyethylene T tubes. Polyethylene extentions of the femoral cannula and ‘venous draining apparatus were rigidly attached to the wall of the chamber at the height of the kidney and pro- vided points for attachment of the renal vascular cannulae. 1381 APPENDIX 2 440.. VENODS BUBBIE TRAP“ The overflow drain from the venous pressure apparatus to the Sigma Motor Pump was open to the atmosphere and conse; quently air was mixed with the blood being pumped back to the animal. This mixture was pumped into atreservoir which drained into the donor dog's femoral veins. The bottom of the reservoir narrowed to a 1 cm inside diameter polyethylene tube that was placed vertically so that its lower most portion was at the level of the animal's spine. From here cannulae ran upward to the femoral veins. Under static conditions the level of blood in this vertical tube was determined by the animal's venous pres- sure. The animal would have to develop a strong negative venous pressure in order to lower the blood level in the reservoir sufficiently for entry of air into the vascular system. APPENDIX 3 AN APPARATUS FOR THE REGULATIGI OF VENOUS PRESSURE Venous pressure was maintained by the level of a column of blood with relation to the kidney. The tubing used was of sufficient diameter that its resistance to blood flow was negligible. The pressure was maintained at a constant value by delivering the blood to a point beneath the surface of a reservoir which was open to the atmosphere. This fluid level was governed by an overflow tube. By adjusting the height of the overflow reservoir venous pressure could be altered. APPENDIX 4 40/30 50/40 57/50 80/70 95/85 45/37 55/50 70/60 87/80 100/95 85/60 87/60 96/80 108/90 115/95 121/108 125/110 132/115 45/40 50/45 55/52 68/61 71 /65 77/69 75/70 70/65 65/52 I : 044- Table 1 o PRESSURE, FLOW, WEIGHT MEASUREMENTS 14 PD* ng. . D%*’ Qcc/min. RT“ Dog 1-16-695 Kidney Weight 73.41g2 10 9.9 13.5 54 .351 14 12.6 17.1 80 .300 23.5 17.9 24.4 106 .300 43.5 27.3 37.2 120 .435 49 29.9 40.7 128 .458 Dog 1-16-6OB Kidngy Weight 73.4 gm 4 6.3 5.9 8.05 40 .058 4 10.6 9.9 13.5 52 .127 4 13 11.3 15.4 70 .128 4 19.4 15.3 20.8 88 .175 4 21.5 16.6 22.6 100 .175 Dog 1-23-60 Kidnez'Weight 80 gt 2 8 24 30 104 .058 2 13 28 35 108 .108 3 16 30 37.4 128 .108 3 19.2 32 40 136 .119 3 22 34 42.5 150 .126 4 25.5 36 45 168 .128 3 43 40 50 180 .223 3 50 42 52.5 200 .235 222 11-25-594gidney'Weight 59 gt 2 2 3.75 6.6 56 .00 2 2 3.5 6.2 70 .00 2 2.3 4.5 7.9 74 .004 2 3.2 5.5 9.7 74 .016 2 3.8 6.5 11.5 76 .024 2 4 7 2 72 .028 6.5 12 9 16 66 .083 25.5 12.0 21 40 .287 37 14.5 25.5 32 .530 20 calculated values 75 /60 92/75 100/80 50/37 75/55 80/60 90/70 95/77 70/55 75/65 92/77 72/60 80/65 97/83 48/42 65/58 75/68 90/82 105/95 1 05/95 70/62 72/62 95/85 88/77 90/80 90/82 90/80 ~45; PV PD* ng. D% Qcc/min RT* 22g,12-16-59 gidney'Weight 85 $9 3 15 16 19 106 .113 3 21.5 18 21 120 .155 3 29 20 23.5 120 .216 2.3 6.5 11 13 70 .057 2.8 8.5 14 16.5 100 .057 9 17 16.5 19.5 78 .112 9 32 21 24.5 118 .195 9.5 33.5 21.5 25 120 .200 9.2 29 20 23.5 104 .192 19 33.5 21.5 25 80 .182 20 47 24 28 110 .245 20 47 24 28 104 .260 33.5 59 26 30.5 80 .317 34 71.5 28 33 124 .302 QQgA12~18-59 Kidney'Weight 58_gg 4 8 11 19 40.5 .100 4 16 14 24 52 .230 4 18 14.5 25 60 .233 4 21.5 16 27.5 69 .253 4 29 17 29.5 72 .346 4 31 17.5 30 75 .360 11 31 17.5 30 72 .277 28 41 19 33 60 .216 0 21.5 16 24.5 58 .362 4.5 31 17.4 30 52 .520 11 34 18 31 56 .420 16 34 18 31 50 .360 20 41 19 33 .577 .630 .650 .700 .560 .590 .840 .420 .690 .580 .850 .745 0615 .875 .720 1.00 1.08 1.10 1.17 1.32 1.25 .905 0940 0660 .650 .675 .585 .532 STATIC WEIGHT AND DISTENDING PRESSURE MEASUREMENTS PD 1 1 Egg 12-16g59 Kidnexlwt 8 e o OOOOOOOOOU‘O \Jth moowo O 0 ° mummng—t bNxOb O 0 Egg 1—23-60 gggney'wt 80 gg mowmxnoow 0 00000000 \J‘\J'II.\\».)I\)--*--s * ng = the increase in weight due to the distending pressure. = per cent increase in weight “713% ng.* 2.0 7.0 13.0 16.0 18.7 21.0 23.0 25.0 26.0 28.0 29.0 2.0 9.0 15.0 19.5 21.0 23.0 24.0 27.0 13%“! Dog 11-25-59 Kidney wt 5782 o o e o OOWU‘OOOOWNW wwwNNNNA-J t~\n<3\o~qxn70\o\ncnzo 0 2.5 11.2 18.7 24.5 26.3 28.7 30.0 33.8 5 0 5 0 0 .5 5_EE 6.0 10.0 14.0 18.0 24.0 28.0 34.0 40.0 47.5 54.0 61.0 109 9.8 12.6 14.0 18.5 20.0 21.0 25.0 28.5 32.5 35.4 PD ng05 D%** Dog 12-1 8-59 Kidney wt 58g]! 8.0 11.0 19.0 22.0 16.0 28.0 30.0 17.0 29.5 38.0 18.2 31.5 46.0 19.5 34.0 72 o 0 22 o 5 39 0 o Qgg_1-16-60 Kidney wt 73.4gm 2.6 13.5 17.2 19.0 25.3 27.2 28.9 34.5 39.0 44.5 48.1 G: if. Om $57.9 «47 ., CU.¢.-«. 1 Q6. 47‘ +8 9.0. ON... 8 ‘ REFERENCES Burton, A. C. (1951) 'On Physical Equilibrium of Small Blood Vessels." Amer. J. Physiol., 164, 319-329. Collings, W. D. and Swann, H. G. (1958) "Blood and Intersti- tial Spaces of the Functional Kidney." Fed. Proc., 17, 28. Corcoran, A. C. and Page, I. H. (1941) 'Renal Blood Flow in Experimental Hypertension Due to Constriction of the Renal Artery.‘t Amer. J. Physiol., 133, 249-250. Corcoran, A. G. and Page, I. H. 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