Plasma atrial natriuretic peptide: responses to modest and severe sodium restriction.

Plasma atrial natriuretic peptide (ANP), active renin and aldosterone concentrations were measured during modest and severe sodium restriction in 16 normal volunteers. Eight volunteers took, in two separate 4-day periods, diets containing 200 and 15 mmol sodium/day (plus frusemide, 40 mg, on day 1 of low sodium intake), in random order. With sodium restriction plasma ANP concentrations fell in parallel with cumulative sodium balance. Changes in plasma renin and aldosterone were reciprocal to those in plasma ANP. To assess the threshold and reproducibility of the effects of modest sodium restriction on plasma ANP concentrations, a further group of eight volunteers took identical constant sodium diets (80 mmol/day in two cases and 120 mmol/day in the remainder) for 4 days on two successive weeks. On both occasions similar individual and mean falls in plasma ANP values accompanied the small net sodium loss occurring on these regimes. Plasma active renin concentration rose significantly during both diet phases. These data suggest plasma ANP concentrations alter in response to minor changes in sodium status, and are consistent with a role for plasma ANP in physiological regulation of body fluid volumes.