THE RENAL CIRCULATION 



1471 



Gewebsflussigk. 

 800 - 



fig. 16. Urea distribution in the dog kidney during hy- 

 dropenia {upper curves) and diuresis (lower curves). [After Ullrich 

 & Jarausch (312).] 



vasculature for a total of 13.0 per 100 g of kidney. 

 The interstitial fluid volume also averaged 13.0 ml 

 per 100 g tissue (303). Hematocrit of kidney fluid 

 drained from vein and artery was 27.0 per cent com- 

 pared to the systemic hematocrit of ca. 43 per cent; 

 this probably represented a combination of blood and 

 "diluting" fluid (interstitial fluid). On the other hand, 

 Morgan (219) placed a dog kidney, continuously- 

 pressured with blood from a carotid artery in a cham- 

 ber filled with saline solution and intermittently 

 stopped flow and expressed blood from the vessels 

 (largely from the vein) by increasing the fluid pres- 

 sure within the chamber. These samples showed hem- 

 atocrit values only slightly lower than arterial blood. 

 The expressed volume represented an average of 11.3 

 per cent of the kidney weight. Using Weaver's data 

 for proportions, venous blood volume would be 54 



per cent of the total. As to whether or not Morgan's 

 samples contained more than venous blood would 

 depend upon the figure accepted for renal blood 

 volume. All injection methods yield values of 20 ml 

 or more of blood per 100 g of kidney. 



Computation of blood volume from the product of 

 mean transit time and minute flow yields values of 

 20 to 24 ml per 100 g of kidney (66, 183, 185, 188) 

 with a kidney hematocrit/large vessel hematocrit ratio 

 of ca. 0.90. Transit time for red cells (t,.) through the 

 kidney is slightly faster than plasma (t p ), e.g., t c = 

 6.4 and t p = 7.6 sec (t c /t P = 0.83 ± 5) (183). The 

 question as to whether this small difference in transit 

 time supports the idea of red-cell shunting is de- 

 batable. However, Morgan (219) has advanced a 

 cogent mathematical argument to show that a 

 kidney/systemic hematocrit ratio as high as 0.83 

 could be enough to account for passage of significant 

 amounts of cell-rich blood through shunting channels. 

 Hemorrhage with lowered blood pressure did not 

 influence the renal hematocrit (188) nor did KCN 

 toxicity, which eliminates autoregulation of the flow 

 (234). Hence the intrarenal hematocrit is not related 

 to this phenomenon, a fact which argues against the 

 cell-separation hypothesis of Pappenheimer & Kinter 

 (240). 



The third method tends to yield the largest volumes, 

 averaging 27 ml per 100 g of kidney (84, 99, 182, 186, 

 240). The hematocrit ratio averages 20 per cent, 

 slightly less than half of the systemic hematocrit ratio. 

 It appears reasonable to assume that this method 

 measures extravascular volume to a certain degree, 

 accounting in the main for the difference from other 

 methods. During the editing of this chapter a pre- 

 liminary note has come to the author" s attention 

 (249a) in which it is claimed that washing out the 

 renal vasculature yields a renal hematocrit part way 

 between those given by the homogenate method and 

 the mean transit time method. 



The distribution of cells and plasma in various 

 zones of the kidney appears in table 2 (186). 



The findings of Emery et al. (84) are in essential 

 agreement with the above with one exception: the 

 papillary hematocrit is 47 per cent of the large vessel 

 hematocrit; but this value is extremely variable in 

 both groups of data, and may reflect the fact that 

 this critical anatomical zone is supplied from two 

 sources, the vasa recta and the spiral arteries. 



Lilienfield et al. (184) point out that no significant 

 difference in hematocrit exists between outer and 

 inner cortex. This is interpreted as evidence against 

 the cell-separation hypothesis for autoregulation of 



