1. In order to examine the relationship between the renin–aldosterone system and atrial natriuretic polypeptide (ANP), we investigated the effects of α-human atrial natriuretic polypeptide (α-hANP) on the plasma concentrations of renin (PRC) and aldosterone (PAC), as well as the effects of captopril pretreatment on the natriuresis and blood pressure reduction induced by α-hANP in rats.

2. Although α-hANP infused into conscious rats at 0.67 μg min−1 kg−1 markedly increased the urinary excretion of sodium and decreased mean arterial pressure, its infusion did not change PRC; however, it significantly lowered PAC. Frusemide infusion at 20.8 μg min−1 kg−1 induced natriuresis comparable with that of α-hANP and it elevated both PRC and PAC, but mean arterial pressure was not altered.

3. Pretreatment of rats with captopril did not have any significant influence on the acute natriuretic and hypotensive effects of α-hANP.

4. Although the inhibitory effect of ANP on the renin-aldosterone system may be involved in the chronic modulation of body fluid volume and blood pressure, this effect does not seem to be directly involved in the acute natriuretic and hypotensive effects of the peptide.

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