Radioreceptor and autoradiographic analysis of FSH, hCG and prolactin binding sites in primary to antral hamster follicles during the periovulatory period

As measured by radioreceptor assays, binding sites for FSH and prolactin were present at 09:00 h on the day of pro-oestrus in Stage 1-10 follicles (primary to antral) with prolactin receptors 3-6 times higher than FSH sites in Stages 1-3 (3 layers of granulosa cells). Specific binding sites for hCG were present in Stage 1 and 2 follicles (2 layers of granulosa cells) but thereafter their distribution was erratic and they were not consistently detectable until Stage 5, when thecal cells first appeared. Using topical autoradiography, specific binding for FSH was evident in Stage 1-4 follicles (4 layers granulosa cells) whereas specific hCG-binding was not. After the preovulatory gonadotrophin surges, by 21:00 h on pro-oestrus, FSH receptors declined in Stages 5-10, prolactin receptors fell in Stages 8 and 10 (small and large antral follicles) and hCG receptors were reduced in Stages 7 (start of antral cavity) to 10. On the morning of oestrus, for follicles from Stage 4 onwards, receptor numbers usually returned to levels found at 09:00 h on pro-oestrus. At oestrus, the few remaining Stage 10 follicles were all atretic and contained significantly reduced FSH and prolactin receptors but numbers of hCG binding sites comparable to those at 09:00 h of pro-oestrus. These results provide evidence of gonadotrophin receptors in small primary and secondary follicles which is consistent with increased DNA synthesis in small hamster follicles on the afternoon of pro-oestrus and on the morning and afternoon of oestrus. Periovulatory changes in gonadotrophin concentrations may therefore affect early stages of folliculogenesis.