Effects of oral salt load on arginine-vasopressin secretion in normal subjects

Arginine-vasopressin (AVP) plays an important role in regulating water balance in humans. Its secretion is under control of several mechanisms, some of which are not completely understood. The purpose of the present study was to evaluate the effects of an acute oral salt load on AVP secretion in normal subjects. Six normal volunteers received 350 mEq of NaCl per os. Pulmonary capillary wedge pressure and right atrial pressure, plasma AVP, plasma sodium and potassium concentration, plasma osmolality, hematocrit, urinary sodium and potassium excretion, and urinary flow were measured at baseline and every 30 minutes for two hours after the salt load. Hemodynamics as well as urinary sodium and potassium excretion did not change over the study. Ninety minutes after the salt load, plasma AVP increased from the basal value of 6.0 +/- 0.9 pg per ml to 10.1 +/- 1.2 pg per ml (mean +/- SE, p less than 0.005) and a significant reduction in diuresis of about 50% was observed. However, plasma osmolality and plasma sodium concentration increased significantly only 120 min after the salt load, from the initial value of 277.7 +/- 2.2 mOsm per kg and 145.3 +/- 1.4 mEq per 1 (mean +/- SE) to 284.8 +/- 2.5 mOsm per kg and 148.7 +/- 1.5 mEq per 1, respectively (p less than 0.01). Ninety minutes after the salt load, no correlation was found between plasma osmolality and plasma AVP concentration, indicating that AVP secretion was independent of changes in systemic blood osmolality.(ABSTRACT TRUNCATED AT 250 WORDS)