ROLE OF VASOPRESSIN IN SALT-INDUCED HYPERTENSION IN BARORECEPTOR-DENERVATED UNINEPHRECTOMIZED RABBITS

To elucidate the contributions of renal, humoral, and arterial baroreceptor reflex components to salt-induced hypertension, we administered 10% NaCl intravenously for 10 days to sinoaortic-denervated rabbits with unilateral nephrectomy (n = 7), sinoaortic-denervated rabbits with intact kidneys (n = 7), and sham-operated sinoaortic-denervated rabbits with unilateral nephrectomy (n = 7). Serial changes in mean arterial pressure (MAP), heart rate, and blood pressure variability were recorded. In sinoaortic-denervated rabbits with unilateral nephrectomy, MAP increased significantly from 109 +/- 2 to 124 +/- 3 mm Hg (day 4) and remained elevated for the rest of the experiment. This elevation of MAP was accompanied by a reduction in the standard deviation of MAP, with significant elevations in plasma vasopressin, norepinephrine, and atrial natriuretic peptide concentrations and in sodium retention. In the other groups, there were no significant changes in these vasoactive hormones. In the sham-operated sinoaortic-denervated rabbits with unilateral nephrectomy, sodium retention was similar to that of sinoaortic-denervated rabbits with unilateral nephrectomy. Continuous infusion (1-mu-g/kg/hr) of a V1 antagonist prevented the elevation of blood pressure and plasma norepinephrine, the accumulation of sodium, and the reduction of blood pressure lability, whereas a bolus injection (10-mu-g/kg) on day 4 reduced blood pressure from 128 +/- 3 to 115 +/- 2 mm Hg (p < 0.005). These results imply that vasopressin plays a crucial role in the expression of salt-induced hypertension in rabbits with compromised baroreceptor and renal function.