Unilateral ovariectomy, flutamide treatment and HCG reverse the anovulatory action of antiprogesterone RU486 in rat.

Administration of antiprogesterone RU486 (4 mg/day) from estrus through proestrus to cyclic rats blocked ovulation. Moreover, RU486 increased basal serum concentrations of LH, PRL, testosterone and estradiol, while it decreased basal serum concentration of FSH. Both unilateral ovariectomy and antiandrogen flutamide treatment, as well as an ovulatory injection of HCG in the proestrus afternoon partially reversed, the ovulatory blockade of RU486. These results indicate that both the decreased FSH concentration and the increased testosterone concentration, as well as the reduced ovulatory LH release are responsible for the anovulatory effects of RU486.