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Effects of FSH and LH on incorporation of [³H]thymidine into follicular DNA

Summary. To assess the roles of FSH and LH on follicular growth, after various experimental manipulations, hamster follicles were sorted into 10 stages and incubated for 4 h with [³H]thymidine. Stages 1–4 correspond to follicles with 1–4 layers of granulosa cells, respectively; Stage 5 = 5 or 6 layers of granulosa cells plus theca; Stage 6 = 7–8 layers of granulosa cells plus theca; Stage 7 = early formation of the antrum; Stages 8–10 = small, intermediate and large antral follicles, respectively.

Phenobarbitone sodium injected at 13:00 h on pro-oestrus blocked the normal rise of blood FSH and LH concentrations at 15:00 h and prevented the increase of [³H]thymidine incorporation into follicles of Stages 1–9. The optimal treatment to reverse the effects of phenobarbitone was 1 µg FSH and 2 pg LH injected i.p. at 13:00 h which restored DNA replication to follicles of Stages 2–10: FSH acted primarily on Stages 2–5 and LH on Stages 5–10. Injection of phenobarbitone at 13:00 h on prooestrus followed by 2·5 µg FSH at 22:00 h restored DNA synthesis by the next morning to follicles at Stages 1–8. In hamsters hypophysectomized at 09:00 h on the day of oestrus (Day 1), injection on Day 4 of 2·5 µg FSH restored DNA synthesis 6 h later to Stage 2–6 follicles. Unilateral ovariectomy on Day 3 resulted 6 h later in an acute rise in FSH and LH and change of follicles from Stage 4 to Stage 5 but, paradoxically, there was decreased synthesis of DNA in follicles of Stages 5–10. The incorporation of [³H]thymidine was at normal low levels for Stage 5–10 follicles by 24 h after unilateral ovariectomy with significant increases in follicles of Stages 1–4. We conclude that small preantral follicles are already dependent on FSH for DNA synthesis and LH action is manifested when the follicles acquire a theca (Stage 5 onwards) and when LH receptors appear in granulosa cells.

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