Aldosterone and renin inhibition by physiological levels of atrial natriuretic factor

This study was designed to examine, in the rat, the inhibition of renin release and aldosterone secretion by physiological plasma levels of atrial natriuretic factor (ANF). Intravascular volume expansion over 30 min with donor blood equal to 3% body weight increased plasma ANF concentration from a base line of 216 ± 28 to 1,590 ± 240 pg/ml (P < 0.001) in sodium-replete rats. Basal plasma ANF levels were decreased to 125 ± 9 pg/ml in animals fed a low-sodium diet, and the infusion of synthetic ANF into separate groups of these rats at doses of 15 or 45 ng·kg^-1·min^-1 elevated plasma ANF to 346 ± 38 and 720 ± 96 pg/ml, respectively (P < 0.001 for both values). Infusion of ANF at 15 ng·kg^-1·min^-1 resulted in a significantly lower plasma renin activity [30 ± 3 vs. 69 ± 5 ng angiotensin I (ANG I)·ml^-1·h^-1, P < 0.05], but there was no difference in aldosterone secretion between control and infused groups (7.00 ± 0.49 vs. 7.29 ± 0.95 ng/min, P > 0.05). However, the higher ANF dose of 45 ng·kg^-1·min^-1 did reduce aldosterone secretion ~ 40% to 4.18 ± 0.36 ng/min (P < 0.001) with no further suppression in plasma renin activity. In sodium-replete rats, infusion of ANF at 45 ng·kg^-1·min^-1 resulted in lower plasma renin activity compared with the control noninfused group (14 ± 4 vs. 22 ± 2 ng ANG I·ml^-1·h^-1, P < 0.05), but aldosterone secretion was not different (P > 0.05) between the two groups. These results demonstrate that ANF inhibits both renin and aldosterone secretion at physiologically relevant plasma concentrations and suggest a difference in the threshold of the renin and aldosterone secretory responses to ANF in the sodium-deplete rat.