1. Plasma levels of immunoreactive atrial natriuretic peptide (IrANP), plasma renin activity, aldosterone and vasopressin were measured in 11 normotensive subjects on a low (10 mmol/day), a normal (150 mmol/day) and a high (350 mmol/day) sodium intake.
2. Plasma levels of IrANP increased significantly with increasing dietary sodium intake with levels (means ± sd) of 3.9 ± 2.1 pg/ml on the fifth day of the low sodium diet, 6.1 ± 3.4 pg/ml on the fifth day of the normal sodium diet and 11.4 ± 4.6 pg/ml on the fifth day of the high sodium diet.
3. Plasma renin activity and aldosterone decreased significantly with increasing sodium intake whereas plasma vasopressin was highest on the high sodium intake.
4. These results suggest that the atrial peptides may be a new and important component in the overall control of sodium and water balance during increased sodium intake.