Effects of RMI 12,936, a synthetic antiprogestational steroid, on the oestrous cycle and ovulation in the rat

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Abstract
RMI 12,936 [17.beta.-hydroxy-7.alpha.-methyl androst-5-en-3-one] inhibited the vaginal cycle and ovulation in the rat. This effect was not mimicked by estrogen and was partly reversed by progesterone. Ovulation was restoed by injection of hCG [human chorionic gonadotropin] and the inhibition was associated with reduced cyclic and tonic LH [luteinizing hormone] secretion while hypophysial LH levels were generally unaffected. Hypophysial sensitivity to LH-RH [LH releasing hormone] was reduced compared with that when ovulation was blocked with sodium pentobarbitone. Apparently RMI 12,936 blocks ovulation by causing a reduction in hypophysial sensitivity to LH-RH and this is probably an antiprogestational effect.