ESTRADIOL ATTENUATES THE ANTIDIURETIC ACTION OF VASOPRESSIN IN OVARIECTOMIZED RATS

To determine which ovarian hormone is involved in the sexually dimorph ic antidiuretic action of vasopressin, the antidiuretic response to va sopressin was examined in sham-operated nonestrous female rats chronic ally treated with vehicle and in ovariectomized rats treated with vehi cle, progesterone, estradiol, or the combination of estradiol and prog esterone, respectively. Three-week-old female rats were sham operated or ovariectomized, and a slow-release hormone pellet was implanted at the 6th wk. The experiment was performed at the 10th to 12th wk in con scious, chronically instrumented rats hydrated with tap water (2% body wt). Infusion of vasopressin at rates of 10-1,000 pg . min(-1) . kg b ody wt(-1) resulted in a dose-dependent antidiuretic response that was significantly enhanced in ovariectomized rats compared with the intac t nonestrous females. Progesterone had no effect, whereas estradiol at tenuated and restored the antidiuretic response to vasopressin to a le vel similar to that in intact nonestrous female rats. These results su ggest that it is estrogen, but not progesterone, that reduces the anti diuretic response to vasopressin in the female rat.