THE RENAL CIRCULATION 



'499 



table 1 1 . Effect of Albumin Infusion on Renal Function in Man 

 \-75 S dlb. (300 ml) infused in 10-24 m '"l 



Total RPF (total renal plasma flow) = (Cpah/Epab)' 100. 

 Cpah- [After Cargill (48).] 



Med. RPF (medullary renal plasma flow) = Total RPF — 



glomerular closure during epinephrine and arterenol 

 infusion. Epinephrine and histamine caused a de- 

 crease in ispAH of only 1 1 .4 per cent at the maximum 

 in the human (254). Tilting, with resultant increased 

 sympathetic activity as evidenced by reduction in 

 RPF (C PAH £pah)j induced no change in £ PAH (39)- 

 An interesting exception, and at present the only 

 type of positive evidence of increased flow through 

 the medullary circuit, is supplied by Cargill (48) on 

 the effects of iv administration of serum albumin on 

 renal function of human subjects in water diuresis. 

 The results are summarized in table 1 1 . Note that 

 ■Epah decreased and the calculated medullary plasma 

 flow increased from no to 298 ml per min. Michie 

 et al. (204) have supplied excellent confirmation of 

 these results. In their studies, the constancy of Tm G 

 and Tmp A H suggested that no nephrons were shut 

 off as RPF increased up to 200 per cent. They sug- 

 gested that this was due to opening of intrarenal 

 shunts without diversion of cortical blood. Barker et 

 al. (11) concur with the observations of Michie et al. 

 They found also that A-V oxygen decreased by 30 to 

 40 per cent as the total renal blood flow increased, a 

 fact consonant with the above interpretation. 



Role of the Medullary Circulation 

 in Diuresis and Antidiuresis 



The Oxford workers originally suggested juxta- 

 medullary diversion of blood, with diminished filtra- 

 tion and greater reabsorption of water in the thin 

 segment, as a mechanism explaining the antidiuretic 

 action of Pitressin, spontaneous changes in urine flow 

 in the erect and supine position, during emotional 



excitation, and in other circumstances involving 

 endogenous ADH secretion. The medullary diversion 

 of blood was first proposed as an explanation of anti- 

 diuresis by Frey (96) in 1934. 



From this it has been assumed by Maxwell et al. 

 (198) that changes in E PAH should accompany diure- 

 sis. This was not the case in a series of human sub- 

 jects presented by them with a range of urine flow 

 from 0.68 to 19.7 ml per min. £ ]>AH remained within 

 a normal range of 0.88 to 0.96. However, their ob- 

 servations of entire diuretic cycles were few. Further- 

 more, inhibition of water diuresis with doses of 

 Pitressin as high as 2000 to 5000 milliunits per hour 

 caused no significant alteration in E PAH , Ei n , and 

 A-V oxygen difference. 



The application of the intrarenal photoelectric 

 technique for measuring regional dye transit time 

 (T-1824) has disclosed interesting new facts about 

 this mechanism. The technique as applied by Kramer 

 et al. (166, 309) is shown in figure 32. Normally, 

 mean transit time averages 27.7 sec for the medulla, 

 and 2.5 sec for the cortex of the canine kidney. When 

 the perfusion pressure was elevated (carotid sinus de- 

 nervation and vagal block by narcosis, or by pump), 

 medullary transit time was markedly reduced, while 

 cortical transit time and total renal blood flow (ro- 

 tameter) remained constant. With this, urine volume 

 increased noticeably. Two representative experiments 

 appear in table 12 (308). From such evidence, they 

 conclude that the juxtamedullary glomeruli and the 

 vasa recta system do not demonstrate autoregulation 

 of flow. (It is possible that enhanced perfusion of the 

 medulla at higher pressure via shunts of other types, 

 e.g., the spiral arteries, arteriolae rectae verae, or 



