Ovarian Follicular Development during the Rat Estrous Cycle: Gonadotropin Receptors and Follicular Responsiveness1

Abstract

The LH and FSH receptor content in thecal and granulosa cells of large antral follicles was measured by in vitro binding assays and in vivo autoradiography during the rat estrous cycle. Specific binding of l’25I]-hCG to granulosa cells increased from <1000 cpm/llg DNA on estrus, metestrus and diestrus to 6000 CPM/Mg DNA on proestrus. Specific binding of l’2511-hFSH to granulosa cells was consistently between 2000 and 3000 cpm/ g DNA throughout the cycle. Specific hCG binding to thecal cells also increased between diestrus and proestrus, while specific hFSH binding to thecal cells was essentially nondetectable. The increase in LH receptors in large antral follicles from diestrus to proestrus could be correlated with an increased ability of these follicles to produce cyclic AMP and estradiol during in vitro incubations with increasing concentrations (0.06-60 pg/mI) of 0LH. Incubation of antral follicles collected on metestrus, diestrus and proestrus with and without testosterone revealed a progressive increase in both follicular aromatase activity and endogenous androgen production. It is concluded that in the presence of low and unchanging LH and FSH concentrations from metestrus to proestrus large antral follicles become more responsive to LH. This responsiveness is associated with an increase in LH receptors both in thecal and granulosa cells and increased production of estradiol. Although the hormonal stimulus for the increase in granulosa cell LH receptor on proestrus is not known, it is suggested that increased follicular estradiol might play a pivotal role.