Dissociation of Gonadotropin-Induced Ovulation and Steroidogenesis in Immature Rats1

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Abstract
To test the current hypothesis that gonadotropin—stimulated steroidogenesis is necessary for ovulation, we have examined rats treated with aminoglutethimide (AG) or cyanoketone (CK) for effects on ovulation and on plasma progesterone (P) as an index of steroid synthesis. Female Sprague—Dawley rats were injected with 12.5 IU of PMS on day 24 and on day 26 were given 30 IU of human chorionic gonadotropin (hCG). Either AG (5 mg/injection) or saline was administered at 0, 4 and 8 hr following hCG and in other experiments either CK (0.5, 1.0, 1.5 or 2.0 mg) in sesame oil or vehicle alone was given 1 hr before hCG. Blood was collected just before and 10 hr after injection of hCG. AG abolished the hCG—induced rise in plasma P, yet 11/18 rats ovulated compared to 19/20 controls (p < 0.01, X—square), with similar rates of ovulation. The rise in plasma P was not significantly different between control animals and those treated with up to 1.5 mg of CK, but at this dose level only 1 of 7 rats ovulated compared to 6 of 6 in the control group. Thus, ovulation can be induced by hCG when its effect on steroidogenesis is inhibited by AG, and CK can prevent ovulation when steroid synthesis is unaffected. The results indicate that the action of these inhibitors on ovulation is not mediated by their effect on steroid synthesis. (Endocrinology92: 1625, 1973)

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