Nephron functional heterogeneity in the postobstructive kidney

Abstract

The purpose of this study was to determine the distribution of nephron filtration rates between superficial and juxtamedullary nephrons (S/J ratio) in kidneys studied immediately after relief of 24 hr total obstruction (acute) and after relief of prolonged partial obstruction (chronic). Injection of 14C-ferrocyanide and microdissection (modified Hanssen's technique) was used to provide an index of superficial and deep nephron glomerular filtration rate (GFR), and standard clearance determinations were done. In normal kidneys S/J ratio of 14C content (nephron GFR) was 0.73 plus or minus 0.03, a value similar to those obtained by other workers. After relief of acute obstruction, nephron GFR was too low for accurate measurement in 22% of superficial and 13% of deep nephrons. The mean S/J ratio of 14C content was similar to control, being 0.67 plus or minus 0.07, with only three of seven kidney showing loss of the normal S/J ratio. Since redistribution of nephron GFR was an inconsistent finding, while marked diuresis and natriuresis occurred in all rats, it appears that redistribution of nephron GFR is not an important factor in the phenomenon of postobstructive diuresis. After relief of chronic obstruction, diuresis and natriuresis were less marked but the mean S/J ratio of 14C content was 0.95 plus or minus 0.11, and in the majority of kidneys (six of eight), there was loss of distinction between superficial and deep nephron GFR. This redistribution of nephron function after relief of chronic, rather than acute, obstruction may be due to the more severe structural damage to the renal medulla of such kidneys and, although not responsible for postobstructive diuresis, it may be important in the diminished capacity of the chronically hydronephrotic kidney to conserve salt and water.