1. We have investigated the interaction between the recently discovered natriuretic factor alpha human atrial natriuretic peptide (alpha h-ANP) and the renin-angiotensin-aldosterone system in man.
2. Angiotensin II infused with placebo produced a significant rise of plasma aldosterone concentration (mean ± sem increment 352 ± 23 pmol/l, n = 7, P < 0.001). The infusion of alpha h-ANP together with angiotensin II largely abolished the aldosterone response (P < 0.001).
3. Diastolic blood pressure rose in response to the infusion of angiotensin II with placebo (mean increment 21.0 ± 0.9 mmHg, P < 0.001). Systolic blood pressure increased to a lesser degree (mean increment 12.5 ± 0.7 mmHg, P < 0.001).
4. The infusion of alpha h-ANP together with angiotensin II significantly blunted the diastolic pressor response (P < 0.01). This ability of alpha h-ANP to blunt the pressor effect of angiotensin II may be important in the control of systemic blood pressure.
5. The inhibition of angiotensin II-stimulated aldosterone release demonstrates that alpha h-ANP may not only be a circulating natriuretic factor in its own right but that it may also act as a modulator of a related endocrine system.