THE LIBERATION OF RENIN BY PERFUSION OF KIDNEYS FOLLOWING REDUCTION OF PULSE PRESSURE* BY K. O. KOHLSTAEDT, M.D.,,~m~ IRVINE H. PAGE, M.D.

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1 Published Online: 1 August, 1940 Supp Inf: Dwnladed frm jem.rupress.rg n September 11, 2018 THE LIBERATION OF RENIN BY PERFUSION OF KIDNEYS FOLLOWING REDUCTION OF PULSE PRESSURE* BY K. O. KOHLSTAEDT, M.D.,,~m~ IRVINE H. PAGE, M.D. (Frm the Lilly Labratry fr Clinical Research, Indianaplis City Hspital, Indianaplis) (Received fr publicatin, May 27, 1940) Despite the fact that much evidence indicates the participatin f renin in the genesis f experimental hypertensin it has nt been shwn t the satisfactin f mst investigatrs that renin is liberated frm the kidneys f hypertensive animals int the bld f the renal vein. The experiments which have been tried have either failed cmpletely t demnstrate any increased pressr actin f renal venus bld r the cnditins f the experiment were highly artificial and did nt allw f a single interpretatin. Even if it culd be shwn that renal venus bld exhibited greater pressr prperties than arterial bld, this wuld nt necessarily indicate that renin itself was being liberated. It was ur belief that t study this prblem the cnditins f the experiment shuld be made as simple and cntrllable as pssible. Islated kidneys perfused with bld were therefre emplyed allwing strict cntrl f extra-renal hemdynamic changes. Increase in the amunt f renin liberated was ascertained by additin f renin-activatr (Khlstaedt, Page, and Helmer, 1938, 1940) t samples f renal vein bld and perfusin f the mixture thrugh an islated rabbit's ear (Page, 1939, b). If renin is present it will react with the renin-activatr t prduce the pressr substance angitnin (Page and Helmer, 1939, 1940). Since renin itself is nt a pressr substance (Helmer and Page, 1939) it is understandable that attempts t shw increased pressr activity f renal vein bld except under artificial cnditins are fredmed t failure. In shrt, we believe that it is pssible t demnstrate increased liberatin f renin frm nrmal kidneys by altering the extra-renal hemdynamics and emplying what appears t be a specific activating system t demnstrate the increase. Methd A dg weighing 10 t 12 kg. was given 1/50 grain f atrpine sulfate subcutaneusly and anesthetized with ether. The lwer prtin f the abdminal arta and femral * A preliminary reprt f these experiments was made in Prc. Sc. Exp. Bil. and Med., 1940, 4~p

2 202 LIBERATION OF RENIN BY PERFUSION OF KIDNEYS vein were cannulated. Bld was cllected frm the arta and simultaneusly 200 cc. f Ringer-Lcke's slutin cntaining 30 gin. f acacia was infused int the femral vein. Artificial respiratin was begun as sn as spntaneus breathing ceased, t prevent develpment f pulmnary edema. The bld was defibrinated by stirring with a rubber brush and filtered thrugh washed cttn gauze. After n mre bld was btained frm the arta, 100 cc. f Ringer-Lcke's slutin cntaining 12 rag. f heparin was infused t prevent cltting in the lungs and kidneys. The right kidney was quickly remved tgether with several centimeters f its ureter and a part f the arta adjacent t the renal artery. The right kidney was used because in the perfusin apparatus the vein cmes t lie abve the artery. The renal artery was cannulated thrugh the attached prtin f the arta, s insuring perfusin f all its branches. A small glass cannula was inserted int the ureter. During preparatin f the kidney an assistant pened the thracic cavity. A glass cannula was inserted thrugh an incisin in the right ventricle int the pulmnary artery and tied in place by a ligature which extended arund the arch f the arta and the pulmnary artery near its junctin with the ventricle. Anther cannula was inserted int the left auricle by cutting ff the distal tip f the auricle and tying a ligature arund the auricle. The lungs, trachea, and heart were freed, remved frm the bdy, and suspended in a heated cntainer by attaching the tracheal cannula t a ring stand. Artificial respiratin with a mixture f 5 per cent CO2 and 95 per cent 02 was cntinued after the lungs were remved frm the bdy. The cannula in the pulmnary artery was cnnected with ne f the utflw tubes (E) f a duble Dale-Schuster (1928) perfusin pump,(fig. 1) fitted with Hemingway valve chambers, and the cannula in the left auricle was cnnected with the arterial reservir (D) f the ppsite pump by a glass tube (G), thus cmpleting a pulmnary circulatin. The cannula in the renal artery was cnnected t the utflw f the ther perfusin pump and the bld frm the renal vein was cllected in the venus reservir (V) which supplied bld t the pulmnary circulatin. The pumps were lcated at the bttm f a cpper tank (B) which was filled with water maintained at 38 C. by an electric heating unit. A Kelly flask lcated directly abve each pump made an excellent venus reservir because the utlet f the flask was at the bttm and therefre it culd be used with either large r small quantities f bld. As the bld left the chamber f the pump, it passed thrugh a heated glass cil (F) t insure the prper temperature. Beynd, n each utlet tube was a side arm which was cnnected t an adjustable flw resistance ((7). This mechanism was cnstructed by enclsing a sft rubber tube 4 cm. in length within a glass tube which was clsed tightly at bth ends arund the rubber tube. Cnstant pressure was maintained in the glass tube by cmpressing a rubber bulb (A) which was cnnected thrugh a small pening in the side f the glass tube. One end f the rubber tube was cnnected t the side arm f the utlet f the pump and the ther end f the rubber tube was cnnected t a glass tube which extended acrss the water tank t the reservir frm which the bld had been remved by the pump. Bld flwed thrugh the rubber tube nly when the pressure prduced by the pump exceeded the pressure in the glass tube which surrunded the rubber tubing. This device prtected the lungs and kidneys frm the increased pressure incident t vascnstrictin.

3 K. O. KOHLSTAEDT AND IRVINE H. PAGE 203 Bld pressure in the tube between the pump and kidney was recrded n the kymgraph by a mercury manmeter (S). 8 i ;Ge- Fx. 1. Apparatus fr perfusin f islated dg's kidney with bld. A, rubber bag fr maintaining peripheral resistance; B, cnstant temperature water bath; C, device fr prducing peripheral resistance; D, reservir fr arterial bld; E, utflw t pulmnary artery; F, warming cils; G, tube returned frm the lungs; H and I, valves in pumps; J, rubber diaphragms in pumps; K, screws fr altering strke f pumps; L, Brdie bellws; M, dg's kidney; N, glass cannula in renal artery; O, tube fr shunting bld arund kidney; P, renal vein; Q, ureteral catheter; R, balanced spn fr cllecting urine; S, mercury manmeter; T, Gaddum recrder; U, site f cnstrictin f renal artery; V, venus reservir. The cannula in the renal artery was cnstructed with a small side arm which was cnnected by a glass tube (0) t the pulmnary venus reservir. This arrangement enabled bld t be shunted arund the kidney and returned t the pulmnary circuit. It was used during the first part f the experiment, usually fr abut 30 minutes when the kidney vessels were cnstricted and bld flw was slw due, as Cushny shwed, t

4 204 LIBERATION OF RENIN BY PER.FUSION OF KIDNEYS a vascnstrictr substance present in defibrillated bld which can be remved by repeated circulatin thrugh the lungs. The kidney was placed in a small evaprating dish which was supprted by a glass funnel. Bld frm the renal vein filled the dish and ran ver int the funnel and was cllected in a Gaddum recrder (T). Frm the recrder the bld flwed int the reservir frm whence it was pumped int the pulmnary circulatin. Urine flw was measured by cllectin in a balanced spn (R) which recrded each spnful n the kymgraph. After the kidney and lungs had been cnnected t their respective peffusin pumps, perfusin was begun with a peripheral resistance f 160 mm. Hg n the,renal circuit and 80 mm. Hg n the pulmnary circuit. Pulse rate was 96 during the entire experiment. As sn as a steady level f urine and bld flw was reached, urea clearance was measured. Bld samples were taken fr plasma prtein determinatin and fr cmparative study f vascnstrictr prperties f the bld. When the urea clearance determinatin was cmpleted, a screw clamp was placed n the rubber tubing near the cannula in the renal artery and just prximal t the mercury manmeter (U, Fig. 1). The clamp was adjusted t reduce pulse pressure at least 50 per cent. The mean pressure was maintained as nearly cnstant as pssible by increasing the strke f the pump and raising peripheral resistance n the renal circuit. In mst experiments by careful adjustment f all three factrs, i.e., amunt f cnstrictin prduced by the clamp, increase in utput f the pump, and amunt f peripheral resistance added, it was pssible t reduce pulse pressure with minimal change in the mean pressure. In a grup f cntrl experiments the kidney was perfused fr an equal length f time with defibrinated bld but withut cnstricting the tube between pump and kidney r withut altering the utput f the pump. The hind leg f a dg was perfused with defibrinated bld in a similar manner. The cannula was placed in the femral artery and bld flwing frm the femral vein was cllected in a Gaddum recrder. The rubber tube cnnecting the femral artery and pump was cnstricted by a clamp and bld samples were taken befre and after its applicatin. The renal venus bld samples were studied fr vascnstrictr prperties by perfusin thrugh a rabbit's ear with pulsatile pressure. In ne grup f experiments the ear was perfused with Ringer-Lcke's slutin and mixtures f bld and renin-activatr r renin were injected. In a secnd grup the ear was perfused with the defibrinated bld which had been perfused thrugh the kidney and small amunts f renin r reninactivatr were injected thrugh a side arm f the perfusin apparatus int the artery f the rabbit's ear. RESULTS Perfusin f the Islated Kidney withut Cnstrictin f the Renal Artery Renal vascular relaxatin with increase in pulse pressure and renal bld flw ccurred as the cnstrictr substance nrmally present in bld directly after defibrinatin was remved by the lungs. When relaxatin appeared cmplete, the average pulse pressure was 49 mm. Hg, mean pressure 112

5 I K. G. KOHLSTAEDT AND IRVINE H. PAGE 205 mm. Hg, and bld flw 4.5 cc. per gm. f kidney per minute in 7 experiments (Table I). After 4 hurs f perfusin the average pulse pressure was 47 mm. Hg, mean pressure 114 ram. Hg, and bld flw 3.9 cc. Urine secretin which began as sn as an adequate renal bld flw was btained, cntinued thrughut the experiment. Urea clearance measured in 3 experiments (Ns. 2, 6, and 7) was fund t be 0.15 cc., 0.16 cc., and ; TABLE I Perfusin f the Islated Kidney withut Cnstrictin f the Renal Artery ~ ~ Bld ~ ~ ~ ~ pressure N ~, ~ ~ ~ g 9 ~ c9 Maximum bld flw End f experiment gnt. I rain. gnt'] 100 cc ram. ntnt. per per c.i per cc.i rant. Hg Hg Hg cent cent ntin. cent rain. 150/ / ~ Maximum bld flw End f experiment 240 Maximum bld flw 60 End f experiment / / blo 180 {J / / Maximum bld flw 44.2 End f experiment 240 Maximum bld flw End f experiment / / / / I Maximum bld flw 131 End f experiment I / / Maximum bld flw 32 End f experiment / / cc. per gm. f kidney per minute. These values were lwer than the urea clearance f 0.4 cc. per gm. f kidney per minute reprted fr intact dgs by Van Slyke, Rhads, Hiller, and Alving (1934). In the third experiment (N. 7) the urea clearance repeated after 4 hurs f perfusin was 0.18 cc. per gm. f kidney per minute. Tw hurs f perfusin in 2 experiments (Table III) caused the rate f xygen cnsumptin t vary insignificantly. Samples f renal venus bld cllected at the beginning and the end f

6 206 LIBERATION OF RENIN BY PERFUSION OF KIDNEYS TABLE II Perfusin f the Islated Kidney befre and after Cnstrictin f the Renal Artery e~ Cnditin at time f bservatin Befre clamping End f experiment Befre clamping End f experiment 10 Befre clamping End f experiment i Befre clamping End f experiment 12 Befre clamping End f experiment Befre clamping End f experiment Befre clamping End f experiment Befre clamping End f experiment Befre clamping End f experiment Befre clamping End f experiment Befre clamping End f experiment Befre clamping End f experiment

7 K. G. KOHLSTAEDT AND IRVINE H. PAGE Z Cnditin at time f bservatin TABLE II--Cncluded Befre clamping End f experiment Befre clamping End f experiment Befre clamping :End f experiment Befre clamping End f experiment Befre clamping End f experiment Befre clamping End f experiment each experiment shwed n difference in vascnstrictr prperties when tested with renin and renin-activatr n the islated rabbit's ear. Perfusin f the Islated Kidney befre and after Cnstrictin f the Renal Artery When maximum renal vascular relaxatin had ccurred, the average pulse pressure was 45 mm. Hg, mean pressure 114 mm. Hg, and bld flw 4.2 cc. per gm. f kidney per minute in 18 experiments befre the renal artery was cnstricted. Immediately after applying the clamp t the renal artery and increasing the utput f the perfusin pump, the average pulse pressure was 17 mm. Hg, mean pressure 109 mm. Hg, and bld flw 3.9 cc. (Table II). Changes in mean pressure which ccurred in sme experiments after cnstrictin f the renal artery, were nt accmpanied by similar variatins in renal bld flw. Fr example, renal bld flw decreased in 4 experiments (Ns. 9, 11, 13, and 18) immediately after clamping althugh mean pressure was higher and, cntrariwise, bld flw increased after applica-

8 208 LIBERATION OF 1LENIN BY PERFUSION OF KIDNEYS tin f the clamp in 2 experiments (Ns. 23 and 24) althugh the mean pressure was lwer. Renal functin as measured by the rate f urine secretin and urea clearance was impaired by cnstricting the renal artery. Urea clearance was reduced 41, 40, 20, and 70 per cent, 2 hurs after applicatin f a clamp in 4 experiments. The average rate f xygen cnsumptin befre clamping was cc. per gm. f kidney per minute and after cnstricting the renal artery cc. (4 experiments, Table III). These values were similar t the average f TABLE III Oxygen Cnsumptin f Islated Dg's Kidney during Perfusin with Defibrinated Bld Bld flw per ~f ney c../ m~n Bld sample cllected when maximum flw ccurred Urine flw cc./ mln Bld xygen cntent Vlumes per 100 cc. ArteriaI Venus 18.0& A-V differelite Vlumes per 100 ec Befre cnstrictin f renal artery Oxygen cnsumptin per gm. f kidney c.~rain O Time mln Sample cllected at end f experiment Bld flw per ~a f ney mln Urine flw CC./ Bld xygen cntent Vlumes per 100 c. Arte- I yerial aus After cnstrictin f renal artery t-v ffer- Oxygen ace cnsunlpr]- tin per nes gin. f ~cl.o0 kidney c.~rain ! cc. f xygen cnsumed per gm. f kidney per minute by intact dgs (Van Slyke, Rhads, Hiller, and Alving, 1934). Perfusin fr at least 80 minutes and at mst 240 minutes after cnstricting the renal artery resulted in a rise in mean renal arterial pressure distal t the cnstrictin (average befre clamping was 114 mm. Hg and at the terminatin f 18 experiments was 135 mm. Hg). Renal bld flw was reduced frm an average f 3.9 ce. t 2.9 cc. after cnstricting the renal artery. Pulse pressure was nt altered (average immediately after clamping was 17 mm. Hg and at end f experiment was 18 mm. Hg). Changes in renal bld flw and mean pressure did nt ccur until the renal artery had been cnstricted at least 40 minutes. Renal venus bld (0.2 cc.) cllected befre applicatin f a clamp t the

9 K. G. KOHLSTAEDT AND IRVINE H. PAGE 209 renal artery even after several hurs f perfusin caused n vascnstrictin when perfused with Ringer-Lcke's slutin thrugh an islated rabbit's ear. Additin f renin-activatr caused mdest cnstrictin but this was nt increased by prlnged perfusin (Experiments 6 and 7, Table IV). When the renal artery was cnstricted 100 minutes r mre (11 experiments) renal venus bld caused far greater vascnstrictin n additin f renin-activatr than bld remved befre clamping. Fr example in TABLE IV EA~ect f Injecti~ f a Mixture f 0.2 Cc. f Renin-Activatr and 02 Cc. f Defibrinated Bld int Ringer-Lcke's Slutin Perfusing a Rabbit Ear with Pulsatile Pressure Experiment N. Renal vein bld cllected as sn as maximum renal vascular relaxatin had ccurred Renal vein bld cllected at end f experiment Duratin f rcduc- Reductin f flw Duratin f reduc- Reductin f flw Length renal tin f flw tin f flw perfusin rain. per cent min. per c~ rain Renal vein bld cllected after renal artery cnstricted mre than 120 mln Experiment 9 (Table IV) injectin f renin-activatr plus renal venus bld cllected at the beginning f the perfusin f the kidney reduced the flw in the rabbit's ear 51 per cent fr 2 minutes, whereas bld cllected 100 minutes after applicatin f the clamp reduced the flw 81 per cent fr 8 minutes. The increase in vascnstricting pwer f mixtures f renal venus bld and renin-activatr did nt appear until 40 minutes after the renal artery was cnstricted. This change in vascnstrictr prperties was fllwed by a sharp reductin in renal bld flw and a rise in mean pressure in the kidney (Fig. 2). If, instead f perfusing the rabbit's ear with Ringer-Lcke's slutin,

10 210 LIBERATION OJP RENIN BY PERFUSION OP KIDNEYS bld frm the renal vein f a kidney perfused under nrmal pressure relatinships was substituted, additin f renin-activatr caused n vascnstrictin. Cntrariwise, additin f renin prduced cnstrictin. Altering the hemdynamics by reducing the pulse pressure caused a change t ccur in the renal vein bld such that the additin f renin-activatr prduced intense vascnstrictin, while renin itself caused nne (Table V). C.P R MIH.... t::1 I v.c.t. c.~*~.. U,. '4.6 c c.pe~ MI.. ~i xvg.~, c.~u~.'r,. ~.w i- f~el( (.ONSTR ICT 10~ OUeATIO~ ANO ; ~ ~ ~ ~ ~..... TIME MtHUTE5 FIG. 2. Experiment 21. Renal hemdynamics and changes in vascnstrictr prperties f renal venus bld befre and after reductin f pulse pressure. Kidney weight 26 gin. Vascnstrictin measured by injectin f plasma samples and renin-activatr int peffused rabbit's ear. Height f clumns represents per cent reductin f flw in the ear and width represents the duratin f reduced flw in minutes. Perfusin f the Hind Leg f a Dg befre and after Cnstrictin f the Femral Artery Perfusin f the hind leg f dgs under cnditins similar t that emplyed fr the kidneys furnished suitable cntrl experiments. Fr example, the bld pressure in the femral artery was 144/80 ram. Hg and bld flw 165 cc. per minute. The pulse pressure was reduced frm 65 t 22 ram. Hg and the mean pressure frm 112 t 99 mm. Hg with a bld flw f 136 cc. per minute. Despite this marked alteratin, perfusin fr 4 hurs caused n changes in bld pressure r bld flw. Nr did it alter the respnse f

11 K. G. KOHLSTAEDT AND IRVINE H. PAGE 211 the bld t renin and renin-activatr. Renin caused marked vascnstrictr prperties t manifest themselves bth befre and after reducing the pulse pressure but there was n appreciable difference even after 4 hurs f perfusin. TABLE Effect f Injectin f 1.0 Cc. f Renin and 1.0 C. f Renin-Activatr int Artery f Rabbit's Ear during Its Perfusin by Pulsatile Pressure with Oxygenated, Defibrinated Renal Vein Bld V Bld cllected when renal relaxatin maximal Bld sample cllected at end f experiments (renal artery nt cnstricted) Experiment N. 1.0 cc. renia injected Duratin f reductin rain. Reductin ~ flw p~ ce~ I cc. reninactivatr Reductin f flw Time perfuscd when sample cllected rain O O O 1.0 cc. renin injected Duratin f reductin mln Reductin f flw psr cent O cc. renin-activatr injected Duratin f reductin mln. Bld sample cllected after renal artery cnstricted by clamp Reductin f flw per ce~ DISCUSSION These experiments were designed t demnstrate the effect f altered hemdynamic states n the liberatin f renin frm islated kidneys. The kidneys were therefre perfused under cnditins which as nearly as pssible apprximated physilgical states. The average bld flw was maintained at levels cmparable t thse bserved by Van Slyke, Rhads, Hiller, and Alving (1934) and Creran and Page (1939), respectively 4.0 and 4.7 cc. per minute per gm. f kidney. Hwever, since their bservatins were made in uninephrectmized dgs whse remaining kidney had

12 212 LIBERATION OF RENIN BY PERFUSION OF KIDNEYS been explanted, this rate f flw is prbably higher than nrmal. The lw urea clearances and relatively high rates f renal bld flw suggest, as has been bserved by Shannn and Wintn (1940), that there is a lss f tne f glmerular afferent arteriles in the perfused kidney. Renal bld flw, urine flw, and urea clearance culd, in mst experiments, be maintained fr 4 r mre hurs. Frm measurements f the renal clearances f phenl red and inulin, Crcran and Page (1938) cncluded that hypertensin culd be btained in uninephrectmized dgs by cnstrictin f the renal artery with Gldblatt's clamp in the absence f renal ischemia. It was therefre decided t bserve the effect f cnstrictin n the liberatin f renin by the perfused kidney withut altering renal bld flw. Hence, when the renal artery was clamped, effrts were made t keep mean arterial pressure distal t the clamp apprximately the same as it had been befre clamping and thus t maintain renal bld flw near its frmer level. This was dne by increasing the strke f the perfusin pump and the peripheral resistance after applicatin f the clamp. Cnstrictin f the renal artery by the clamp reduced the pulse pressure in the renal artery by abut ne-half in 17 experiments. The mean pressure was nt easily readjusted t its initial level since bth pulse and mean pressures were raised by increasing the utput f the pump. Prbably as a result f lss f pulsatile pressure, bld flw was slightly reduced frm its cntrl level after restratin f mean pressure in mst experiments. The bld flw increased in 2 experiments after clamping and adjustment f mean pressure, presumably because the clamp had been applied befre maximum vasdilatin had ccurred. A critical pint was fund in each experiment beynd which tightening the clamp caused a precipitate decrease in mean pressure and bld flw. The stre f renin-activatr in bld is small and rapidly exhausted by the additin f renin (Page, 1939, b). Cnsequently, if renin were liberated by the islated kidney in mre than minute amunts, its presence culd nt be demnstrated until renin-activatr had been added t react with renin and liberate the vascnstrictr, angitnin (Page and Helmer, 1940). Renin-activatr was therefre added t renal venus plasma and, after 10 minutes incubatin, the renin cntent was assayed by perfusing the mixture thrugh the islated rabbit's ear perfused with Ringer-Lcke acacia slutin. The liberatin f renin culd alternatively be shwn in the rabbit ear system perfused with bld btained frm the renal vein. If sufficient renin had been liberated int the bld t saturate its stre f activatr,

13 K. G. KOHLSTAEDT AND IRVINE H. PAGE 213 additin f mre renin t the perfusin had n effect, while the additin f activatr caused vascnstrictin. Renin was present in n mre than minute amunts in bld samples frm the renal vein taken befre the clamp was applied r after several hurs f perfusin in cntrl experiments. The renin cntent f the venus plasma was regularly increased several fld after abut 90 minutes f perfusin at reduced pulse pressure, while bld flw and mean pressure were maintained at r near their frmer levels. This increased liberatin f renin was als demnstrated in the tw experiments in which renal bld flw increased after clamping. N liberatin f renin was bserved in a cntrl experiment in which the hind leg f a dg was perfused with bld at reduced pulse pressure. Renin is therefre liberated by the islated dg's kidney perfused at lwered pulse pressures. Cntinued perfusin at lw pulse pressures resulted in (a) gradual reductin f renal bld flw and (b) an increase in mean arterial pressure distal t the clamp, apparently the results f renal vascnstrictin. Similar cnstrictin did nt appear in 7 cntrl experiments in which the kidneys were perfused fr as lng a time, but in which the clamp was nt applied. Since, then, these changes are nt the artefacts f prlnged perfusin, they prbably result frm accumulatin f renin in the kidney. It is therefre nt unlikely that they are due t cnstrictin f glmerular efferent arteriles, caused by the liberatin f angitnin, which has been shwn t result frm infusin f renin r angitnin int nrmal dgs with explanted kidneys (Crcran and Page, 1940). If it be true that experimental renal hypertensin is caused by liberatin f renin frm the kidneys, it appears frm these experiments that adequate reductin f renal arterial pulse pressure is the necessary stimulus. Reductin f renal bld flw may fllw, either as a result f the peratin, r, gradually, as angitnin exerts its effect n the efferent arteriles. As has been the experience f mst investigatrs wh have used Gldblatt's (1934) methd f btaining renal hypertensin, best results are btained at a critical level f arterial cmpressin. If this level is nt reached, hypertensin is slight and transient, r des nt appear, while if it is exceeded, and a severe reductin f renal bld flw ccurs, in viv ischemic atrphy and uremia result. Within the parenchyma f the kidney, pulse pressure prbably falls rapidly as the bld passes frm small arteries t arteriles. Any additinal bstructin t the flw f bld, as, fr instance, pressure n the parenchyma, wuld greatly decrease pulse pressure thus supplying the stimulus

14 214 LIBERATION OF RENIN BY PER]~USION OF KIDNEYS t renin liberatin. This, we believe, ffers a reasnable explanatin fr the ease with which hypertensin is prduced by pressure n r cnstrictin f the renal parenchyma as in the cellphane methd fr prducing hypertensin (Page, 1939, a). The mechanism by which reductin f pulse pressure leads t the liberatin f renin frm the kidneys is a matter f cnjecture. Smthing f the pulse wave must ultimately lead t replacement f pulsatile by cntinuus flw. The effects f cntinuus flw f bld have nt been extensively studied in intact animals. Hwever, it iswell knwn that perfused rgans rapidly develp mrbid changes when cntinuus is substituted fr pulsatile pressure. McMaster and Parsns (1938) have shwn that edema ccurs rapidly in tissues thus perfused because pulsatile pressure is ne f the chief frces in draining lymph frm the intercellular spaces. A similar mechanism prbably btains in the perfused kidney. Evidence f renal anxia in hypertensin is cnflicting. The xygen cnsumptin f crtical tissue is believed t be reduced in experimental hypertensin (Gerbi, Rubenstein, and Gldblatt, 1940), althugh this view is cntradicted by Masn, Blalck, and Rbinsn (1940). Arterivenus xygen differences d nt differ significantly frm the nrmal in experimental hypertensin (Levy, Light, and Blalck, 1938). N unequivcal interpretatin f these bservatins can be made. Hwever, sme degree f ischemia f the renal tubular mass is regularly present in hypertensin in human beings (Smith, 1939). It is nt unlikely that the renal tubular tissue in experimental hypertensive animals is als anxic. Since renin is a prtein-like substance and f high mlecular weight, it wuld nt be anticipated that it wuld nrmally diffuse with facility thrugh the membranes f the cells f the tubules unless sme change ccurred which increased their permeability. Anxia is ne f the mst imprtant f such changes and may be a factr in the release f renin. T summarize these speculatins: reductin f pulse pressure leads t partial cnversin f pulsatile t cntinuus bld flw in the kidneys with edema and anxia f the cells f the tubules as the chief results. Increase in cellular membrane permeability fllws and allws the liberatin f the large renin mlecule. Renin reacts with renin-activatr t prduce angitnin which itself raises bld pressure and causes efferent glmerular arterilar cnstrictin and further tubular anxia. A vicius circle may be thus set up which results in sustained arterial hypertensin. Renal venus bld frm dgs made hypertensive either by silk perinephritis r clamping the renal artery als cntains greater than nrmal amunts f renin as demnstrated by additin f renin-activatr and per-

15 K. G. KOHLSTAEDT AND IRVINE H. PAGE 215 fusing the mixture thrugh an islated rabbit's ear (Page, 1940). The demnstratin f increased liberatin f renin frm perfused kidneys with reduced pulse pressure and frm kidneys f intact hypertensive animals adds weight t the belief that experimental hypertensin is due t the actin f renin. Stimulus t this prcess lies apparently in a reductin f pulse pressure within the kidney. SUMMARY 1. Islated dgs' kidneys have been perfused with defibrinated bld under hemdynamic cnditins similar t thse in the bdy. Under these circumstances bld flw, urine secretin, and xygen cnsumptin are well maintained, but urea clearance is lw. Renal venus bld cllected initially and at the end f 3 r mre hurs f perfusin exhibited n difference in vascnstrictin prperties when perfused alng with renin r renin-activatr thrugh an islated rabbit's ear. 2. Reductin f pulse pressure by cnstricting the renal artery may be perfrmed withut reducing mean pressure significantly. Impairment f urea clearance and rate f urine secretin fllw, and xygen cnsumptin is slightly reduced. 3. After an hur r mre f perfusin with reduced pulse pressure, gradual rise in mean renal arterial pressure distal t the clamp and reductin f bld flw ccur. 4. Renal venus bld cllected after abut ne hur f perfusin with reduced pulse pressure differs frm that cllected befre reductin f pulse pressure in that it causes intense vascnstrictin when perfused with renin-activatr thrugh an islated rabbit's ear. 5. Perfusin f a dg's hind leg under similar circumstances des nt cause this change in the venus bld t ccur. CONCLUSIONS It is pssible t demnstrate increased liberatin f renin frm the kidneys in the renal venus bld by additin f renin-activatr and perfusin f the mixture thrugh islated rgans. Kidneys perfused under what appear t be nrmal hemdynamic cnditins liberate little f it. Reductin f pulse pressure is the stimulus eliciting the utpuring f renin. Reductin f bld flw fllws but appears t be an effect rather than the cause f the increased liberatin f renin. BIBLIOGRAPHY Crcran, A. C., and Page, I. H., Am. J. Physil., 1938, 1~, 43. Crcran, A. C., and Page, I. H., Am. J. Physil., 1939, 126, 354.

16 216 LIBERATION OF RENIN BY PERFUSION OF KIDNEYS Crcran, A. C., and Page, I. H., Am. J. Physil., 1940, in press. Dale, H. H., and Schuster, E. H. ]., J. Physil., 1928, ~, 356. Gerbi, C., Rubenstein, B. B., and Gldblatt, H., J. Exp. Med., 1940, 71, 71. Gldblatt, H., Lynch, J. R., Hanzal, R. F., and Summerville, W. W., J. Exp. Meal., 1934, 59, 347. Helmer, O. M., and Page, I. H., J. Bil. Chem., 1939, 127, 757. Khlstaedt, K. G., Page, I. H., and Helmer, O. M., Prc. Sc. Exp. Bil. and Med., 1938, 39, 214. Khlstaedt, K. G., Page, I. H., and Helmer, O. M., Am. Heart J., 1940, 19, 92. Levy, S. E., Light, R. A., and Blalck, A., Am. J. Physil., 1938, 122, 38. Masn, M. F., Blalck, A., and Rbinsn, C. S., J. Bil. Chem., 1940, 133, p. lxiii. McMaster, P. D., and Parsns, R. J., J. Exp. Med., 1938, 68, 377. Page, I. H., J. Am. Med. Assn., 1939, a, 113, Page, I. H., J. Exp. Med., 1939, b, 70, 521. Page, I. H., Am. J. Physil., 1940, 130, 22. Page, I. H., and Helmer, O. M., Prc. Centr. Sc. Clin. Inv., 1939, 12, 17. Page, I. H., and Helmer, O. M., J. Exp. Med., 1940, 71, 29. Shannn, J. A., and Wintn, F. R., J. Physil., 1940, 98, 97. Smith, H. W., Prter Lectures, Studies in the physilgy f the kidney, Lawrence, University f Kansas, Van Slyke, D. D., Rhads, C. P., Hiller, A., and Alving, A. S., Am. J. Physil., 1934, 109, 336.