Functional heterogeneity of nephrons

Summary

Intraluminal flow velocities and tubular dimensions were estimated for superficial and deep proximal tubules of non-diuretic kidneys with a technique developed byHanssen. Kidneys of anesthetized rats were frozen in vivo 4–20 sec after an i.v. injection of 0.05 ml 10–20% Na ferrocyanide. Ferrocyanide was located as prussian blue in microdissected tubules after freeze-substitution and maceration of the kidneys. Its position was used to indicate the movement of glomerular filtrate along the tubule. Ferrocyanide clearance was slightly less than that of inulin at low plasma ferrocyanide levels. They were equal at higher plasma levels. The two clearances were sufficiently alike, however, to justify using ferrocyanide as an indicator of glomerular filtrate in these experiments. Transient small decreases in systemic blood pressure and increases in renal blood flow followed i.v. injections of 0.05 ml ferrocyanide and 0.05 ml 5% lissamine green. There was no evidence of continuing intraluminal flow when the kidney was rendered ischemic by ligating the renal pedicle. The mean distance between glomerulus and prussian blue front in kidneys frozen at different intervals after a ferrocyanide injection increased curvilinearly with time in a manner compatible with its indicating mean flow velocity. The distance between glomerulus and dye front in tubules from any one kidney was proportional to tubular length. Flow velocities were similar when measured with lissamine green in vivo or with ferrocyanide in microdissected tubules. Velocities decreased whenC inulin was reduced by partial compression of the renal artery. The reduction was greater in superficial than in deep tubules suggesting that flow velocities vary non-uniformly as gfr changes. Luminal diameters measured in microdissected tubules were similar to other estimates of in vivo tubular dimensions. There was no apparent difference between the length or luminal diameter of proximal tubules from the surface and deeper portions of the cortex in these rats.