Effect of dietary sodium intake on the intrarenal distribution of nephron glomerular filtration rates in the rat.

Abstract

Redistribution of single nephron glomerular filtration rate (SNGFR) between superficial (S) and juxtamedullary (JM) nephrons is thought to participate in the renal adaptation to different levels of dietary sodium intake. This possibility was examined using the Hanssen technique which measures SNGFR as the 14 C-ferrocyanide content of microdissected nephrons factored by the mean plasma concentration following a 12-second infusion. Rats from the same litter were placed on a low-sodium (0.8 mEq/day) or a high-sodium (9 mEq/day) diet. The distribution of SNGFR was measured as the S/JM (mean of S nephrons/mean of JM nephrons) SNGFR ratio. In spite of an eightfold change in sodium excretion, there was no significant change in the S/JM SNGFR ratio (low sodium - high sodium: -0.0033 ± 0.048 [ SE ], P > 0.9). Seven rats that were not littermates were maintained on a standard diet but drank saline (13 mEq sodium/day); carotid and ureteral catheterization and the duration of the diet (3-14 weeks) had no effect on the S/JM SNGFR ratio ( P > 0.1), which was similar to that of nine rats maintained on a standard diet with water for drinking (3 mEq sodium/day). The value of the S/JM SNGFR ratios were 0.77 and 0.83, respectively. These variations in dietary sodium intake appeared to have no detectable effect on the intrarenal SNGFR distribution.