Renin secretion and distal tubule Na+ in rats

Abstract

The aim of these experiments was to examine the relationship between renin secretion rate (the product of renal plasma flow and renal venous minus arterial plasma renin) and distal tubule Na+ concentration and load (the product of tubular fluid Na+ concentration and flow rate). Conventional techniques were used to micropuncture the cortical distal tubules, as close as possible to the macula densa segment, of 3 groups of anesthetized rats: Na loaded, control and Na deprived. At 21% of total distal tubule length, Na+ concentrations were 82 .+-. 6 (n = 13), 62 .+-. 2 (n = 41) and 69 .+-. 6 (n = 15) meq/l (means .+-. SE), and Na+ loads were 629 .+-. 56, 466 .+-. 28 and 292 .+-. 26 peq/min in loaded, control and deprived rats, respectively. Arterial and renal venous blood was obtained from the same animals. Renal plasma flow (ml/min per kg body wt) was calculated according to the Fick principle, using inulin in arterial and renal venous plasma. Plasma samples were incubated with excess rat renin substrate, and radioimmunoassay was done to determine the rate of generation of angiotensin I (ng angiotensin I/ml plasma per h incubation). Renin secretion rates were 56 .+-. 14 (n = 6), 269 .+-. 48 (n = 22) and 2246 .+-. 415 (n = 7) ng angiotensin I/h incubation per min per kg body wt in loaded, control and deprived rats, respectively. Both tubular fluid Na+ and renin secretion were changed by dietary Na+ loading and restriction. The changes were not consistent with a relation between Na+ concentration and renin secretion, but were consistent with an inverse relation between Na+ load and renin secretion.