Effects of 17β-hydroxy-7α-methylandrost-5-en-3-one on early pregnancy in the rat

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Abstract
A single s.c. injection of 1 mg 17.beta.-hydroxy-7.alpha.-methylandrost-5-en-3-one (RMI-12,936) given a few hours after mating interrupted pregnancy in all the treated rats. Circulating progesterone (.DELTA.4P) levels were higher in RMI-12,936 treated females than in controls on the corresponding days during the course of termination of pregnancy. Higher levels of .DELTA.4P were recorded on day 4 (P < 0.01) and day 6 (P < 0.05) of pregnancy. In addition to the changes in serum .DELTA.4P, an acceleration of egg transport was encountered. The eggs were prematurely expelled from the uterus within 48 h of the treatment. Although the estrous cycle of the RMI-12,936 treated females was disturbed, they were found sexually receptive. Successful matings resulting in normal gestation and morphologically normal fetuses were recorded 20-26 days after RMI-12,936 induced pregnancy termination. In addition to its mid-pregnancy terminating effect, RMI-12,936 is capable of interrupting early pregnancy when given soon after mating in the rat. The safety and efficacy of this compound as a post-coital contraceptive deserves further investigation.