Effects of gonadectomy on sexually dimorphic antidiuretic action of vasopressin in conscious rats

Abstract

The present study examined whether the antidiuretic response to vasopressin is affected by the estrous cycle and by gonadectomy in conscious, chronically instrumented hydrated rats. Infusion of vasopressin (10-100 pg.min-1.kg body wt-1) resulted in a dose-dependent antidiuresis. Urine volume and free water clearance decreased and urinary osmolality increased with no significant changes in mean arterial blood pressure, heart rate, osmolar clearance, and urinary sodium and potassium excretion. The antidiuretic response to vasopressin was significantly greater in intact male and estrous female rats than in intact female rats in the other phases of the estrous cycle. Thus the calculated doses of vasopressin to reduce urine flow and free water clearance, as well as to increase urinary osmolality 50% from their control values, were significantly higher in nonestrous females than in males and estrous females. Gonadectomy was without effect on the antidiuretic potency of vasopressin in males, but in gonadectomized females the antidiuretic response to vasopressin was enhanced to a level similar to that observed in intact males. These data indicate that the antidiuretic activity of vasopressin is affected not only by gender but also by phase of the estrous cycle and that the ovarian hormone(s) may modulate the antidiuretic action of vasopressin.