Evidence against a pressor role for vasopressin in spontaneous hypertension.

The hypothesis that the vasoconstrictor action of vasopressin may contribute to the development of hypertension in spontaneously hypertensive rats (SHR) was tested by chronic infusion of a specific antagonist of the vascular effects of vasopressin. From 4 to 13 weeks of age, SHR and Wistar-Kyoto rats (WKY) received subcutaneously either isotonic saline or the vasopressin pressor antagonist, d(CH2)5Tyr(Me)arginine vasopressin by osmopump. Systolic blood pressure was measured by tail cuff from 5 to 11 weeks of age. In SHR, the vasopressin analogue did not alter the rate or magnitude of increase in systolic blood pressure. In WKY, systolic blood pressure in the vasopressin analogue group was slightly reduced compared with the saline infusion values until 10 weeks of age (F1, 10 = 10.18, p = 0.008). At 12 to 14 weeks of age, all animals were prepared with indwelling arterial and venous catheters. Resting mean arterial pressure was not altered significantly by the vasopressin analogue infusion in either strain, but the response to an acute vasopressin infusion of 5, 15, or 50 ng/kg body weight was markedly attenuated by the analogue treatment, indicating that plasma levels of the vasopressin analogue were sufficient to block pressor effects of endogenous vasopressin. A bolus injection of the angiotensin II converting enzyme inhibitor teprotide (SQ 20881) resulted in a decrease in mean arterial pressure (p less than 0.05) that was comparable in all groups, and serum renin concentration was not elevated in the vasopressin analogue-treated rat.(ABSTRACT TRUNCATED AT 250 WORDS)