Increased sensitivity of the osmotic control of vasopressin in sheep with deoxycorticosterone acetate-induced hypertension.

The development of hypertension induced by deoxycorticosterone acetate (DOCA) in sheep was accompanied by increases in both the plasma concentration and the urinary excretion of vasopressin. The vasopressin response to an osmotic stimulus (i.v. infusion of 0.85 mol NaCl/l at 4 ml/min for 75 min) was studied before and after the development of hypertension induced by DOCA in six sheep. Before DOCA implantation, the osmotic stimulus resulted in an increase of plasma osmolality (POSM) from 290 +/- 1 to 303 +/- 1 (S.E.M.) mosmol/kg H2O and in plasma vasopressin concentration (PAVP) from 0.23 +/- 0.04 to 1.07 +/- 0.15 microunits/ml. At least 30 days after DOCA implantation when mean arterial blood pressure had risen from 81 +/- 3 to 117 +/- 5 mmHg, the same osmotic load caused an increase in POSM from 290 +/- 2 to 298 +/- 2 mosmol/kg H2O and PAVP from 0.45 +/- 0.05 to 2.02 +/- 0.27 microunits/ml. POSM and PAVP were significantly correlated in every experiment. However, the slope of the relationship increased significantly (P less than 0.01) after the animals had developed hypertension (0.185 +/- 0.026 vs 0.070 +/- 0.011 (microunits vasopressin/ml)/(mosmol/kg H2O]. The intercepts were similar. After the DOCA implant had been removed osmotic sensitivity returned to normal.