Abstract EN:

The non-competitive anti-estrogenic effects of RU 486 were examined using estradiol (E2)-treated ovariectomized monkeys given RU 486, progesterone (P4), or both. The E2 -induced LH surge of control animals was abrogated by P4 and/or RU 486. Secretory transformation by P4 was inhibited by RU 486 co-administration. RU 486 alone (1 mg/kg) induced endometrial secretory transformation, but higher doses (5 mg/kg) inhibited proliferation and secretory activity. Thus, in the presence of P4, RU 486 is antagonistic but, in absence of P4, exhibits endometrial progestational effects at low doses and an antiproliferative (anti-estrogenic) effect at higher doses. These data encourage continued evaluation of RU 486 as a potential contraceptive agent acting at the pituitary and/or endometrial level