In Vitro Steroidogenesis by Primary to Antral Follicles in the Hamster During the Periovulatory Period: Effects of Follicle-Stimulating Hormone, Luteinizing Hormone, and Prolactin1

Hamster ovarian follicles at Stages 1 to 10 (Stages 1–4: follicles with 1–4 layers of granulosa cells (GC); Stages 5–7: 5–10 layers GC plus theca; Stages 8–10: antral follicles) were isolated on the morning of proestrus or estrus and incubated for 2 h in the absence or presence of follicle-stimulating hormone (FSH), luteinizing hormone (LH), prolactin (Prl), progesterone (P4), 17α-hydroxyprogesterone (17OHP), or androstenedione (A). Steroid accumulations in the media were measured by radioimmunoassay (RIA). On proestrus, without any hormonal stimulus, consistent accumulation of P4 through estradiol-17β (E2) occurred in low amounts only from Stage 6 and on; both FSH (5–25 ng) and LH (1–25 ng) significantly stimulated steroidogenesis by Stage 6–10 follicles, and the effects of FSH, except for Stage 10, were largely attributable to LH contamination. However, 25 ng FSH significantly stimulated A production by Stages 1–4, whereas 1–25 ng LH was ineffective. On estrus, follicles at all stages, especially 1–6, showed significant and dose-dependent increases in P4 production in response to FSH; both FSH and LH significantly stimulated P4 and 17OHP accumulation from Stage 5 onwards; however, there was no increase in A and E2 compared to controls. Even the smallest estrous follicles showed a shift to predominance of P4 accumulation. On proestrus, Prl had a negative influence on LH-induced accumulation of P4 and 17OHP by Stages 7–9 and 6–8, respectively, without affecting A or E2. In the presence of 10 ng P4, 17OHP or A, proestrous follicles accumulated increased amounts of 17OHP from Stages 5–8; increased A production for Stages 1–8 and 10, and E2 for Stages 4–10. On estrus, conversion of P4 to 17OHP and A occurred only in Stages 6–8 and to E2 in Stages 7–8. Only A induced E2 production by stages 3–5. These results show that the smallest follicles in the hamster ovary respond to gonadotropins by producing steroids in vitro, and that small follicles without thecal cells produce A; however, E2 cannot be detected in these follicles unless exogenous substrate is provided.