1. Atrial natriuretic peptide and brain natriuretic peptide have similar vasodilator and natriuretic properties, although little information is available regarding their relative effects as antagonists of the renin—angiotensin—aldosterone system. We have therefore compared how atrial natriuretic peptide and brain natriuretic peptide affect the systemic pressor and aldosterone responses to angiotensin II in eight male subjects.

2. Each subject was studied on three separate occasions, when they received a 60-min infusion of placebo, atrial natriuretic peptide (10 pmol min−1 kg−1) or brain natriuretic peptide (10 pmolmin−1 kg−1), with a concomitant infusion of angiotensin II (6 ng min−1 kg−1) given for the final 30 min of the infusion period. The change in haemodynamic parameters and plasma aldosterone induced by angiotensin II was measured. Plasma concentrations of atrial natriuretic peptide (182 ± 23 pmol/l) and brain natriuretic peptide (193 ± 25 pmol/l) achieved at steady-state during the infusion on each study day were not significantly different.

3. Increases in mean arterial pressure in response to angiotensin II were significantly lowered by concomitant infusion of atrial natriuretic peptide (21.0 ± 1.7 mmHg) and brain natriuretic peptide (20.1 ± 1.9 mmHg) compared with placebo (29.0 ± 4.1 mmHg). There were similar effects on systolic and diastolic blood pressure. Cardiac output was decreased on each study day to the same extent by angiotensin II infusion. Total systemic vascular resistance showed a non-significant trend towards an attenuated response to angiotensin II when atrial natriuretic peptide or brain natriuretic peptide was infused concomitantly in comparison with placebo.

4. Plasma aldosterone increased by 326 ± 49 pmol/l when angiotensin II was infused with placebo. Both atrial natriuretic peptide and brain natriuretic peptide significantly blunted this response, although the increase with atrial natriuretic peptide (19 ± 35 pmol/l) was significantly lower than the increase with brain natriuretic peptide (133 ± 19 pmol/l).

5. Atrial natriuretic peptide and brain natriuretic peptide were therefore equally effective in blunting the systemic pressor response to angiotensin II. It was apparent, however, in view of similar plasma concentrations at steady state, that on a molar basis atrial natriuretic peptide was a more potent inhibitor of angiotensin II-induced aldosterone secretion than brain natriuretic peptide. These results suggest a dissociation between the haemodynamic and hormonal effects of atrial natriuretic peptide and brain natriuretic peptide in terms of antagonism of the renin—angiotensin—aldosterone system.

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