SEX-DIFFERENCES IN THE CARDIOVASCULAR AND RENAL ACTIONS OF VASOPRESSIN IN CONSCIOUS RATS

The present study was carried out to investigate whether prostaglandin s (PCT) are involved in the mechanism that contributes to the sex diff erence in the antidiuretic and presser actions of vasopressin. The exp eriments were performed in conscious male and nonestrous female rats. In hydrated rats, the graded infusion of vasopressin (10-1,000 pg . mi n(-1) kg body wt(-1)) resulted in a dose-dependent antidiuresis: decre ases in urine flow and free water clearance and an increase in urine o smolality. These responses were significantly greater in male than in nonestrous female rats. Pretreatment with a cyclooxygenase inhibitor, indomethacin (10 mg/kg body wt iv), significantly enhanced the antidiu retic response to vasopressin in both sexes. However, the magnitude of this enhancement was greater in female than in male rats. Thus indome thacin abolished the sex difference in the antidiuretic response to va sopressin. In a separate experiment in rats without water hydration an d urine collection, infusion of presser doses of vasopressin (1,000-6, 000 pg . min(-1). kg body wt(-1)) resulted in a greater increase in bl ood pressure in male than in nonestrous female rats. Treatment with in domethacin enhanced this response equivalently in both sexes and thus did not affect the sex difference in the presser action of vasopressin . These data indicate that renal PG may mediate, at least in part, the sex difference in the antidiuretic action of vasopressin, whereas vas cular PG seem not to play an important role in the sex difference in t he presser action of vasopressin.