Osmoregulation of vasopressin during acute lowering of arterial pressure by clonidine in moderate hypertension

Hypertonic saline (100 mmol in 50 ml) was injected intravenously over 5 min in two groups of moderate essential hypertensive patients (group 1, n = 13; group 2, n = 6). In group 2, arterial pressure had been lowered by infusion of clonidine (0.3mg in 100ml saline), from 186 ±8/116 ±3 to 146 ± 9/98 ±5 mmHg (mean ± s.e.m.). The hypertonic stimulus increased the plasma osmolality of all subjects from 288 ± 1 to 296 ± 1 mosmol/kg (P <0.01). Plasma vasopressin increased from baseline values that were not significantly different (P