Induction of menstruation by an antiprogesterone steroid (RU 486) in primates: site of action, dose-response relationships, and hormonal effects.

The antiprogesterone compound RU 486 (17 beta-hydroxy-11 beta-[4-dimethylaminophenyl]-17 alpha-[ 1-propynyl]estra-4,9-dien-3-one; Roussel-Uclaf, Paris, France) was used to induce menstruation in a randomized controlled trial. Castrated adult female cynomolgus monkeys (n = 17) received sequential subcutaneous Silastic capsules of estradiol or progesterone over a 49-day regimen which stimulated the steroidal milieu of the fertile ovarian/menstrual cycle. RU 486 was injected at 10.0, 1.0 to 3.0, or 0.1 mg/kg from days 31 to 34 of this protocol. At all concentrations tested, menstruation followed RU 486 injection within 48 hours and persisted through 72 hours. No bleeding followed placebo injections. All monkeys that menstruated after RU 486 administration also manifested vaginal bleeding after removal of exogenous steroid treatments. No changes in daily serum follicle-stimulating hormone, luteinizing hormone, prolactin, or serum and urinary free cortisol accompanied RU 486 treatment. We conclude that (1) RU 486 promptly induces menstruation by a local action upon the endometrium; (2) familiar endometrial proliferation and withdrawal bleeding can redevelop after exposure to this compound; (3) no effects of RU 486 on serum cortisol or pituitary gonadotropins were noted; and (4) extensive combination therapy with estrogen and progesterone causes mild hyperprolactinemia.