Gonadotropin Receptors of the Ovine Ovarian Follicle during Follicular Growth and Atresia1

Abstract

The binding of [125I]-labeled human follicle stimulating hormone ([125I]-FSH) and chorionic gonadotropin ([125I]-hCG) to intact ovine follicles was studied in vitro as a function of follicular diameter and stage of morphological atresia. Histological confirmation of the atretic classification was established and the incidence of atresia in those follicles studied was variable and directly related to follicular diameter (P<0.01). The binding of [125I]-hFSH and [125I]-hCG to theca was relatively constant when compared to the change in granulosa binding that was associated with increased follicular diameter or stage of atresia. When studied without regard to the stage of atresia, the binding of [125I]-hFSH to granulosa cells decreased and that of [125I]-hCG increased with increased follicular diameter. These changes were thought to reflect changes in the relative incidence of atresia within each size group rather than decreased binding per se. Subsequent analysis of [125I]-labeled gonadotropin binding to granuhosa cells as a function of both follicular diameter and stage of atresia simultaneously indicated that the extent of [125I]-hFSH binding was determined solely by stage of atresia rather than follicular diameter (P<0.05). Conversely, while [125I]-hCG binding was decreased by increased atresia, the overall extent of binding was determined by follicular diameter (P<0.01). It is concluded that macroscopic assessment of follicular atresia in ovarian follicular populations is directly related to follicular diameter. In addition, the ability of granulosa cells to bind [125I]-labeled gonadotropins in vitro varies as a function of follicular diameter and stage of atresia.