THE EFFECT OF HYPOTHALAMIC STIMULATION AND PROGESTERONE ON OVULATION IN FEMALE RATS TREATED WITH THE OESTROGEN ANTAGONIST ICI 46,474

Abstract

ABSTRACT A single dose (0.2 mg) of the antioestrogen ICI 46,474 at 15:00 h on the second day of dioestrus inhibited ovulation in the female rat. This inhibition could not be overcome by electrochemical stimulation of the basal hypothalamus on the afternoon of pro-oestrus. In contrast, progesterone (1.0 mg) treatment at 10:30 h on pro-oestrus induced ovulation at the expected time. The facilitatory effect of progesterone was prevented by administration of Nembutal (35 mg/kg) at 11:00 h on pro-oestrus. Progesterone did not induce ovulation in rats treated with ICI 46,474 on both dioestrus day 1 and 2. Sexual receptivity in ovariectomized oestradiol-treated (2.0 μg/day) rats was significantly depressed by the antioestrogen (1.0 mg/day) whether it was given 1 h before, 1 h after, or at the same time as the oestradiol. The compound also prevented the uterine weight increase in response to oestradiol but exerted a significant effect on uterine weight itself when compared to oil treated controls.