High salt intake increases the vasorelaxant effect of ANF on the isolated perfused rat kidney.

1. The objective of the present study was to determine whether chronic salt load or depletion leads to adaptive changes in kinetics of atrial natriuretic factor (ANF) binding and/or responsiveness to ANF. We measured the equilibrium binding to and the steady-state dose-response effects of ANF1-28 on isolated kidneys from rats kept on a high (H) or low (L) salt diet for 15 days. 2. Twenty-four hour sodium excretion was 5.90 +/- 0.46 mEq for H vs 0.06 +/- 0.01 mEq for L (P less than 0.01). Plasma levels of immunoreactive ANF of H (42.2 +/- 3.9 pg/ml) were not significantly different from those for L (35.2 +/- 5.3 pg/ml). 3. There was no significant differences in distribution, apparent density or affinity of ANF specific binding sites determined in non-filtering isolated kidneys from rats kept on the H or L salt diet. 4. Dose-response curves for the hemodynamic and excretory effects of ANF1-28 in filtering isolated kidneys from rats kept on the H salt diet were not different from those of rats kept on the L salt diet. In contrast, the vasorelaxant response to ANF1-28 in isolated kidneys preconstricted by adding serum from 24-h nephrectomized rats to the perfusate (generation of angiotensin II) was significantly more pronounced in kidneys front rats chronically adapted to the high-salt diet. 5. This effect of ANF may contribute to the increased renal plasma flow and glomerular filtration rate occurring under conditions of chronic salt loading in intact animals.