Antifertility effects of RU-486 in combination with anordrin in rats

RU-486 and anordrin suspended or dissolved in tea seed oil, alone or in combination, were given orally to rats on d 6-8 or d 11-13 of pregnancy, respectively. Complete interruption of early pregnancy was obtained after RU-486 at 8 mg/kg alone or 2.5 mg/kg combined with anordrin 2 mg/kg when given on d 6-8 of pregnancy. A complete mid-trimester abortion was obtained after RU-486 10 mg/kg alone or 4 mg/kg combined with anordrin 3 mg/kg when given on d 11-13 of pregnancy. Results obtained from the endometrial transformation test, the uteri cytoplasmic progesterone receptor estimation in immature rabbits, the deciduoma-inhibited test in pseudopregnant rats and the serum progesterone level in pregnant rats showed that RU-486 in combination with anordrin did not possess progestational, but rather marked antiprogestational activities. Since anordrin is relatively easy to obtain in China, RU-486 combined with anordrin may be ready to be used clinically as an effective oral antifertility agent.