EFFECTS OF ANTIPROGESTERONE COMPOUND RU486 ON OVULATION IN IMMATURE MICE TREATED WITH PMSG HCG/

The effects of RU486, a competitive antagonist of progesterone, on ovu lation were studied in PMSG/hCG-treated immature mice. PMSG/hCG was ad ministered to 3-week-old female mice to induce ovulation. A dose of 0. 5 mg of RU486 was administered 3 h before hCG injection, simultaneousl y with hCG injection, or 3, 4.5, 6, 7.5 or 9 h after hCG administratio n. The lowest number of ovulated eggs was observed in the group given RU486 6 h after hCG injection. Although the mean number-of ovulated eg gs was only 4.4 in this group, it was increased to 25.7 by supplementa ry administration of 2.0 mg of progesterone. It was demonstrated that RU486 had inhibitory effects on ovulation, and the inhibition could be prevented by supplementary administration of progesterone.