Effect of Na and Cl infusion on loop function and plasma renin activity in rats.

Inhibition of plasma renin activity (PRA) by saline has been shown to be related to a specific effect of chloride. The purpose of this study was to test the hypothesis that inhibition of renin release by selective chloride infusion in the rat is related to increased chloride transport in the thick ascending limb of the loop of Henle (TALH). Measurements of loop of Henle function were obtained by micropuncture before and after a 5% body wt infusion of solutions containing either 0.15 mol/l NaCl, 0.15 mol/l lysine monohydrochloride (LysCl), or 0.15 mol/l Na-assorted anions (NaAA). Both NaCl and LysCl infusion lowered PRA (60.8 +/- 11.9 to 22.6 +/- 3.7 ng angiotensin I (ANG I).ml-1.h-1 and 53.3 +/- 6.8 to 34.5 +/- 4.6 ng ANG I.ml-1.h-1; P less than 0.05), whereas NaAA infusion had no effect on PRA (66.7 +/- 15.1 to 59.1 +/- 12.4 ng ANG I.ml-1.h-1). Analysis of late proximal and early distal fluid showed that chloride transport in the TALH was significantly elevated by infusion in all three groups, and there were no differences among the groups after infusion. Distal chloride concentration increased in the NaCl and LysCl groups (26 +/- 2 to 37 +/- 1 meq/l and 26 +/- 2 to 36 +/- 2 meq/l; P less than 0.05), but distal chloride concentration decreased in the NaAA group (28 +/- 2 to 22 +/- 1 meq/l; P less than 0.05). There was no correlation between PRA and fluid flow rate or chloride delivery to the distal tubule.(ABSTRACT TRUNCATED AT 250 WORDS)