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HANDBOOK OF PHYSIOLOGY 



CIRCULATION II 



zone, suggesting the diversion of blood accompanying 

 cortical ischemia. Tracheal occlusion in rabbits (92) 

 caused paling of the kidney and decrease in volume. 

 Sections of innervated kidneys removed at the height 

 of anoxia showed anemia of the cortical portions. In 

 the denervated, there was no such "diversion" of flow, 

 but it was possible to produce it in these by injections 

 of epinephrine. Arcadi & Farman (2) state that in 

 rabbits, blood was diverted almost exclusively to the 

 cortical circuit by pilocarpine and magnesium sulfate 

 injection and most prominently by water diuresis. 

 Dehydration, on the other hand, caused the accumula- 

 tion of ink in the medulla. The findings of Kuhlgatz 

 (168) in rats were very similar with respect to the 

 findings on diuresis and dehydration. Mover et al. 

 (222, 223) although finding uniform distribution of 

 India ink in dog and rabbit kidneys during sciatic 

 stimulation, nevertheless report cortical ischemia and 

 subcortical accumulation of ink after injection of 0.2 

 mg of epinephrine into the rabbit, but this finding does 

 not have to be interpreted as demonstrating the open- 

 ing of medullary shunts. 



Insull et al. ( 1 50) have pointed out that an adequate 

 filling pressure is needed for validity of the injection 

 methods. When Prussian blue was injected into fresh 

 rabbit kidneys at a pressure of 50 cm HoO, good 

 filling of the entire kidney, including cortex, was ob- 

 served; at 25 cm HoO, filling of the juxtamedullary 

 glomeruli and vasa recta only occurred. 



In some experiments involving sciatic stimulation, 

 stimulation of the perirenal plexus, or hemorrhage, 

 the juxtamedullary glomeruli were uniformly stained, 

 while the peripheral glomeruli were not. This oc- 

 curred only when renal blood flow was low. They in- 

 terpreted this as regional cortical ischemia but not as 

 increased flow through the medulla. 



The conclusions of Block et al. (24) and Kahn rt a/. 

 (156) are similar. Block et al. tried stimulation of renal 

 nerves in rabbits, clamping of the artery, injection of 

 constrictor agents, and sciatic nerve stimulations. 

 They concluded that a pale cortex and a medulla 

 filled with blood were not evidence that blood was 

 flowing largely through the medulla: the medulla 

 may be congested even though flow has stopped. Kahn 

 et al. found during sciatic stimulation in the rabbit a 

 normal distribution of ink in 8 of 1 1 animals. In 3, 

 however, the peripheral cortex had no ink, and the 

 juxtamedullary glomeruli and the medullary vessels 

 were well filled. 



In summary, the rabbit kidney during various types 

 of strong afferent stimulation or during epinephrine 

 action mav demonstrate a cortical ischemia, with 



maintained flow in the medulla. This cannot be 

 interpreted as diversion of flow to the medulla, and 

 particularly not as increased flow through this zone. 

 Nevertheless, the anatomical evidence of a dual circu- 

 lation is good, and there is some good functional 

 evidence of this. 



Daniel et al. (6g) have made excellent serial angio- 

 grams in cats and dogs which follow the progress of 

 Thorotrast through the kidney. The material passes 

 very rapidly through the cortex, but the diffuse 

 shadow of the medulla persists long after the veins 

 have emptied, demonstrating a much slower per- 

 fusion of the vasa recta system of the medulla. This 

 conforms with the studies of Kramer et al. (166) who 

 used a photoelectric technique. They bring evidence 

 that the role of the medullary vasa recta system may be 

 unique in connection with the role of the counter- 

 current system, and the dilution and concentration of 

 the urine. Other evidence is at hand in support of 

 this, and will be taken up in a later section. 



Functional Evidence; Interpretations 



Based on Clearance Data 



Scher (264) used a heated-thermocouple technique 

 in dogs, rabbits, and cats, one thermocouple being 

 placed in the cortex and the other in the medulla. 

 Although quantitative interpretations must be made 

 cautiously, focal flow paralleled total renal blood flow 

 during action of epinephrine and arterenol, acetyl- 

 choline, and stimulation of periarterial plexus. 



The clearance data are concerned mainly with 

 changes in A-V oxygen difference, and in £ PiH and 

 E ln . Mover et al. (223), during marked reduction in 

 flow (—46%) resulting from prolonged sciatic stimu- 

 lation in dogs, found the A-V oxygen difference in- 

 creased from 1.7 to 3.3 vol per cent; in rabbits, from 

 3.1 to 6.8 vol per cent in a group in which venous 

 flow was measured, and 3.5 to 9.2 vol per cent in a 

 venipuncture group. With epinephrine, resulting in 

 increased blood pressure and reduced flow (as much 

 as 70% reduction) in rabbits, A-V oxygen increased 

 as much as 313 per cent. Other investigtions de- 

 tected no significant alteration of oxygen extraction 

 in dogs or man during epinephrine injection ( 1 49, 224, 



254)- 



Epinephrine in dogs gave no evidence of a medul- 

 lary shunt, since £ PAH , E CT , extraction of oxygen and 

 Tm G did not significantly decrease in presence of 

 moderate to marked decrease in GFR, urine flow, 

 and RBF (149). Mover & Handley (224) observed no 

 reduction in E PXH in dogs, but Tm G decreased due to 



