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In order to determine why granulosa cells obtained from large preovulatory porcine follicles luteinize spontaneously in culture, whereas cells obtained from adjacent less mature small follicles fail to luteinize spontaneously, or in the presence of exogenous gonadotropin, gonadotropin receptors in granulosa cells obtained from increasingly mature small, medium and large porcine follicles have been studied. Granulosa cells obtained from small, medium and large follicles did not differ significantly in size. Granulosa cells obtained from small (1–2 mm), medium (3– 5 mm) and large porcine follicles were incubated with 125I—hCG. Granulosa cells obtained from large follicles bound 10–lOOO–fold more 125I—hCG (623,300 ± 44,890 cpm/5 X 106 cells; n = 12) compared to small follicles of the same ovary or from other ovaries (7,554 ± 1,983 cpm/5 X 106 cells; n = 16). Medium follicle cells bound only a slightly greater amount of hCG than small follicle cells. Qualitatively the binding of small, medium and large follicle granulosa cells to 125I—hCG was roughly similar. Binding reached a plateau between 30 and 90 minutes. Furthermore, if the concentration of 125I—hCG was raised (from 0.01 to 0.5 μg/ml) there was exhibition of saturation. When unlabeled hCG or LH was added to cells from any follicle size immediately prior to addition of 125I—hCG it could inhibit the binding 90–95%, demonstrating similarity of LH and hCG receptors. Evidence that the binding was strong and that there was slow turnover of hCG at its receptor site has been found. (Endocrinology92: 531, 1973)
Channing et al. (Thu,) studied this question.