Further investigation of the antifertility effects in the rat of the antiprogestational steroid, RMI 12,936, and related compounds.

The antifertility activities of RMI 12,936 and 7alpha-methyltestosterone may be reversed by progesterone implants in ovariectomized, but not in intact, rats on Day 8 of pregnancy. The presence of the ovary for 48 h after administration of RMI 12,936 is necessary for irreversible antifertility activity to be developed, and it is concluded that this activity is due to a metabolite other than 7alpha-methyltestosterone. 7alpha-Methylandrostenedione was significantly less potent than RMI 12,936 in antifertility tests, while the uterotrophic activity of RMI 12,936 was not inhibited by aromatization inhibitors, suggesting that the active metabolite is not produced by dehydrogenation or aromatization of 7alpha-methyltestosterone.