Effects of progesterone or luteinizing hormone on folliculogenesis in intact or hypophysectomized immature hamsters

Since exogenous progesterone (P4) causes superovulation in hypophysectomized (hypoxed) cyclic hamsters treated with gonadotropins, the current study was performed to evaluate the roles of P4 and luteinizing hormone (LH) as a folliculotropic complex in the immature hamster. Intact or hypoxed immature hamsters were injected daily, beginning on Day 23, with 1 mg P4 and/or 20 micrograms LH for 4 days. Treatment with P4 alone or combined with LH in intact immature hamsters increased the number of antral follicles (6.7 and 4.3, respectively, vs. 1.5 per ovary in controls), but neither treatment maintained large follicles in hypoxed animals. In contrast, in hypoxed hamsters, the number of small preantral follicles was enhanced by P4 or LH (406 and 409, respectively, compared to 302 per ovary in untreated controls), but with no additive effects by combined treatment. The stimulatory effect of P4 in intact hamsters was unrelated to serum levels of follicle-stimulating hormone, estradiol, or LH. Moreover, in the hypoxed hamster, P4 or LH acts directly to increase the numbers of small preantral follicles with 2 to 5 layers of granulosa cells, whereas equally large doses of stilbestrol or estradiol cyclopentylpropionate are ineffective. In the hypoxed or intact hamster, the effects of P4 or LH may involve either recruitment of smaller follicles into larger stages or prevention of atresia. The present experimental design can not distinguish between these possibilities.