Dietary sodium intake increases vasopressin secretion in man

Plasma vasopressin concentration and urinary vasopressin excretion were measured in a control situation, during sodium depletion and on days 1, 2, and 7 during high sodium intake in twelve 23-26-year-old men on a free-water intake. Urinary vasopressin excretion decreased from 6.7 +/- 1.0 ng/hr (control) to 3.9 +/- 0.3 ng/hr (p less than 0.01) when sodium excretion decreased from 188 +/ 18 to 16 +/- 2 mmol/24 hr. During the first day of high sodium intake, the urinary vasopressin excretion increased to 10.0 +/- 1.2 ng/hr (p less than 0.01) compared with control and remained high throughout the sodium repletion. Through all collection periods at low, normal, and high sodium intake, vasopressin excretion increased concomitantly with serum sodium concentration and osmolality. After low sodium intake for 7 days, the serum vasopressin concentration averaged 2.7 +/- 0.6 ng/l, and this level was maintained throughout the sodium repletion period. These results are compatible with a stimulatory effect of dietary sodium intake on pituitary vasopressin secretion in man. Dietary sodium may stimulate vasopressin secretion through extracellular osmolality or even by a direct effect of extracellular sodium on periventricular receptors. Plasma renin concentrations or sympathetic nervous activity offered no further explanations. Urinary vasopressin excretion provides more useful information than do plasma concentrations, as the latter can fluctuate rapidly.