Disparity between surface and deep nephron function early after renal ischemia.

Experiments were performed using a variety of methods to assess the functional status of different nephron populations following 45 min of renal ischemia in the rat. Micropuncture techniques revealed that SNGFR and reabsorption in the surface nephrons are only modestly reduced after ischemia, whereas kidney GFR and reabsorption are more severely affected. Determinations of bolus velocity with the Hanssen technique or of glomerular blood flow with the microsphere method confirmed that both were highest in the surface nephrons, lower in the middle nephrons and lowest of all in the juxtamedullary nephrons after ischemia. It is concluded that surface nephron function is well-maintained following ischemia and that it is the functional deficiency of the deeper nephrons that is predominantly responsible for the impairment in whole kidney function. Although the pathogenic mechanism is not yet clear, neither tubular obstruction nor tubular leakage in the deeper nephrons seems to be involved. The present findings suggest that micropuncture of the surface nephrons is a technique of questionable validity for studying this type of acute renal failure, they explain the inability of the kidney to concentrate the final urine, and they predict a more pronounced deficiency in medullary than in outer cortical blood flow.