Dependent effect of drinking volume on vasopressin but not atrial peptide in humans

The act of drinking causes a fall in plasma arginine vasopressin (AVP) concentration that precedes changes in plasma osmolality. To investigate the specificity of this drinking stimulus on hormone secretion, six volunteers (5 male, 1 female, aged 22-39 yr) were water deprived for 36 h and then drank 15 ml/kg water at 10-12 degrees C using 15-20 swallowing actions/min over 3.5 +/- 0.5 min (mean +/- SE). This caused a fall in plasma AVP from 4.5 +/- 0.7 to 3.2 +/- 0.5 pmol/l (P less than 0.05) and in thirst (by 5.7 +/- 0.6 on a 10-cm linear analog scale) (P less than 0.05) 5 min after drinking. No significant changes occurred in mean arterial pressure, heart rate, or plasma atrial natriuretic peptide (ANP) concentration. A second study was undertaken to determine whether the reflex inhibition of AVP secretion is activated simply by the act of swallowing regardless of the volume of liquid consumed. The six volunteers were water deprived for 36 h and then sipped and swallowed 1 ml/kg water at 10-12 degrees C using 15-20 swallowing actions/min over 3.0 +/- 0.1 min. There was no change in plasma AVP concentration, although thirst was reduced by 2.3 +/- 0.6 (P less than 0.05) at 5 min. Plasma AVP 10 min after sipping and swallowing (4.2 +/- 0.8 pmol/l) was significantly greater than at 10 min after drinking 15 ml/kg (2.8 +/- 0.5 pmol/l) (P less than 0.05) despite the fact that plasma osmolality at this stage was similar in both studies. We conclude that the drinking-mediated reflex inhibition of AVP secretion in humans is dependent on swallowing an adequate volume and is not accompanied by changes in hemodynamics or in plasma ANP concentration.