Follicle-Stimulating Hormone-Mediated Induction of Functional Luteinizing Hormone/Human Chorionic Gonadotropin Receptors during Monolayer Culture of Porcine Granulosa Cells*

Abstract

The LH/hCG receptor content of porcine ovarian granulosa cells from 1- to 3-mm follicles can be increased to 4–5 times the preculture level during monolayer culture in serumcontaining media supplemented with insulin and FSH. The binding of [¹²⁵I]iodo-hCG declines during the first 2 days of culture, but then uniformly increases through 6 days, achieving a 14- to 15-fold increase relative to the 2-day level under optimal conditions. Analysis of receptor binding by autoradiography indicates that after 2 days, the number of cells specificallybinding [¹²⁵I]iodo-hCG increases significantly during culture, as does the intensity of binding on receptor-bearing cells. Granulosa cells in monolayer culture exhibit heterogeneous receptor induction, indicating that normalized [¹²⁵I]iodo-hCG binding data cannot be used to estimate receptor concentration per cell. Receptor affinities in the initial and induced populations are identical. LH/hCG receptors induced in granulosa cells during culture are functional, as demonstrated by specific hCG-stimulated progesterone secretion. 17β-Estradiol produces a differential effect in vitro, generally increasing [¹²⁵I]iodo-hCG binding with respect to FSH-induced levels but consistently depressing the subsequent hCG-stimulated steroidogenic response of cells bearing the induced receptor. The porcine granulosa cell monolayer system thus appears to be a useful model with which to study, in vitro, mechanisms of steroid and gonadotropin regulation of granulosa cell differentiation and overall follicular development.