Homologous Regulation of Hormone Receptors: Luteinizing Hormone Increases Its Own Receptors in Cultured Rat Granulosa Cells*

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Abstract
LH [luteinizing hormone] receptors in granulosa cells are essential for ovulation and luteinization of ovarian follicles. The possible role of LH to regulate its own receptors in vitro. Granulosa cells obtained from immature hypophysectomized estrogen-treated rats were primed with FSH for 2 days to induce LH receptors. The cells were then challenged with or without increasing doses of LH or hCG [human chorionic gonadotropin] for an additional 2 days, and the concentration of LH receptors was measured by [125I]iodo-hCG binding. FSH-induced LH receptors in granulosa cells decreased to negligible levels in cultures without gonadotropins, while LH receptor numbers were further increased by LH or hCG in a biphasic manner. Maximal stimulation of LH receptor content was obtained with gonadotropin doses of 6, 10 and 2.5 ng/ml for rat LH, ovine LH and hCG, respectively. In contrast, higher doses of the gonadotropins were less effective. LH stimulation of [125I]iodo-hCG-binding sites were associated with increases in the number of LH receptors, without changes in the Kd value (control, 1.22 .+-. 0.22 .times. 10-10 M; LH-treated, 2.55 .+-. 0.55 .times. 10-10 M). Also, the changes in LH receptor numbers were correlated with the responsiveness of granulosa cells to LH stimulation of cAMP production. LH and hCG did not affect overall granulosa cell protein content. Treatment with cycloheximide, a protein synthesis inhibitor, decreased LH-induced receptors by 46%, suggesting the involvement of new protein synthesis. These studies demonstrated that LH, like FSH, is capable of stimulating granulosa cell differentiation by inducing its own receptors. This serves as an interesting model for studies on the positive autoregulation of hormone receptors and explains the important role of LH during advanced stages of follicular maturation.