1. Previous studies have shown that atrial natriuretic peptide (ANP) inhibits the secretion of aldosterone by isolated adrenal glomerulosa cells stimulated by angiotensin II, adrenocorticotropic hormone and potassium in vitro. We have also demonstrated that this inhibitory effect of ANP on plasma aldosterone induced by angiotensin II and adrenocorticotropic hormone can be reproduced in vivo in conscious unrestrained rats. In this study, we have investigated the effect of an intravenous infusion of ANP on plasma aldosterone in conscious unrestrained sodium-depleted rats.

2. During sodium depletion, the rise in plasma renin activity which determines an increment in the circulating concentration of angiotensin II was accompanied by a rise in aldosterone secretion as expected. ANP infused intravenously at a dose which increased the plasma concentration of the peptide three- to five-fold, produced a significant decrement in the concentration of aldosterone in plasma after an infusion period of 120 min. There was no significant effect of ANP on plasma renin activity and plasma corticosterone concentration.

3. Since the increase in plasma aldosterone levels in sodium-depleted rats is mainly dependent on the activation of the renin–angiotensin system, we conclude that ANP may modulate the effect of endogenous as well as exogenous angiotensin II on plasma aldosterone secretion.

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