THE RENAL CIRCULATION 



1483 



minutes of renal ischemia in dogs resulted in a reduc- 

 tion in £p AH from 0.74 to 0.59 (269). Control flow 

 (Cpah) which gave 91 per cent of the simultaneous 

 direct blood flow measurement decreased to 30 

 per cent of the direct flow as a consequence of ische- 

 mia. Recovery occurred in 85 min. After 2 hours of 

 ischemia (246), £p A H (control, 0.90-0.94) was reduced 

 to 0.1 1 to 0.43. 



Phillips et al. (247) found adequate extraction of 

 PAH until renal plasma flow was reduced below 7 

 ml per min during hemorrhagic hypotension and 

 then clearances no longer reflected plasma flow 

 accurately. Corcoran & Page (62) stated that C D did 

 not have value as a measure of plasma flow during 

 severe, prolonged hypotension, nor immediately 

 after restoration of blood pressure by transfusion. 

 Diodrast clearance fell progressively on repeated 

 hemorrhage and transfusion, until in some instances 

 negative extraction values were obtained (as low as 



— 1 .59 compared to control of 0.757). C* n transfusion, 

 an "over-shooting" of clearances beyond the control 

 was observed during the early stages as a result ot 

 washing out of material accumulated in the interstitial 

 fluid and stagnant urine during hypotension. Selkurt 

 (270) compared C PAH with a direct blood flow method 

 in dogs during hemorrhagic hypotension and shock. 

 /;-Aminohippurate clearance virtually ceased during 

 hypotension (60-40 mm Hg) as direct flow fell to 1 1 

 per cent of control. On transfusion, although direct 

 flow was rapidly restored to near control, blood flow 

 calculated from C PAH averaged only 39 per cent of 

 direct flow, as the result of anoxic tubular impairment. 

 £ PAH during hypotension was low and variable with 

 numerous negative extraction values (range, —0.750 

 to 0.543 during a 90 min period at 60 mm Hg, and 



— 1.50-0.285 during 45 min at 40 mm Hg). After 

 transfusion, £V AH partially recovered, averaging 

 0.406 (0.03-0.69) compared to the control of 0.73. 

 Clearly the hypotensive anoxia had invalidated the 

 Cp A H clearance as a measure of plasma flow probably 

 because of consequent tubular damage. 



The negative extraction during hypotension has 

 been explained as the result either of back diffusion of 

 PAH from the lumina of damaged nephrons into 

 venous blood (270), or of absorption into the renal 

 venous blood of PAH accumulated during the period 

 of hypotension and impaired urinary excretion (62). 

 Again, this may be PAH concentrated in the vasa 

 recta and interstitial fluid in proximity (counter- 

 current mechanism), and will thus imply continued, 



table 6. Clearance Data in Mammals and 



Renal Blood Flow in Dog 



Per g K\V 

 ml min 



Ci„ 



CpAH 



Per kg Body Wt 

 ml, m in 



Cln Cpah 



Per i.7) m- 

 BSA ml min 



Cln CpAH 



A. Clearance Data in Mammals* 



K.W = kidney weight, BSA = body surface area. 

 * [From Smith (287).] f (From Handbook of Circulation, 



WADC Tech. Rpt. 59-593, '959) X 220 Observations; 

 direct venous outflow; urea, phenol red, and PAH extrac- 

 tion. §58 observations; (pentobarbital and chloralose) : 

 direct venous outflow, rotameter, and bubble flowmeter. 



but reduced, perfusion of the medullary zone, with 

 cortical ischemia. 



Renal Blood Flow Values 



Data have been culled from two important sources 

 in the summary presented in table 6. It will be noted 

 that the dog appears to have the lowest C PA h per 

 gram kidney weight. The rat's value for C PA h is least 

 per 1 .73 m- body surface area, increasing progressively 

 in the series to the value in man. The dog has the 

 highest filtration rate (C In ) relative to the effective 

 plasma flow (C'pah), giving a filtration fraction (FF) of 

 0.32. In man this is 0.20. 



In summary, as Smith has repreatedly stressed, the 

 clearance methods yield adequate information on 

 renal hemodynamics only under conditions of relative 

 stability of flow. They cannot accurately follow rapid 

 changes of blood flow, and changes in pathological 

 states (e.g., shock kidney) seriously handicap their 

 utility. 



EXTRINSIC REGULATION OF RENAL BLOOD FLOW 



A eurogenic Control 



The thoracolumbar sympathetic supply is a rich 

 source of vasoconstrictor fibers for the kidneys. The 



