U-11634 effectively inhibits pregnancy in rats and mice following either parenteral or oral administration. A single dose administered to rats on Day 4 was as effective as treatment for the first 7 days of pregnancy; however, a single dose on other days of pregnancy was not effective. Pregnancy could not be inhibited in hamsters. At therapeutic doses this compound did not exhibit uterotrophic, anti-oestrogenic, androgenic, gonadotrophic-inhibiting, blastolytic or foetal toxicity activities.
Deciduomata formation in rats was inhibited by the compound. This effect was not reversed by progesterone or oestradiol administered simultaneously with U-11634 in ovariectomized, pseudopregnant rats with traumatized uterine horns. Inhibition of nidatory processes may be involved in the observed anti-fertility efficacy. The effects and the unique biological spectrum of this compound relative to other inhibitors of implantation are discussed.