FSH AND LH UP-REGULATE EPIDERMAL GROWTH-FACTOR RECEPTORS IN RAT GRANULOSA-CELLS

Epidermal growth factor (EGF) modulates ovarian folliculogenesis and steroidogenesis and its binding sites have been demonstrated in the ovary. We investigated the localization of EGF-binding sites in the rat ovary, and the effects of FSH and LH on EGF binding to cultured granulosa cells. Autoradiographic localization of I-125-labelled mouse EGF-binding sites was demonstrated in the granulosa and luteal cells. Displacement study and Scatchard analysis showed that a single class of specific binding sites for I-125-labelled mouse EGF was present in the granulosa cells, obtained from the ovaries of immature rats treated with diethylstilboesterol. The number of binding sites and the apparent dissociation constant were 4336 binding sites/cell and 3.42 pmol/l respectively. The granulosa cells were cultured for 48 h at 37-degrees-C in medium alone or with increasing amounts of ovine FSH (oFSH; 1-1000 mug/l). FSH treatment increased I-125-labelled mouse EGF binding to the granulosa cells in a dose-dependent manner. After culture with oFSH (100 mug/l) for 48 h, the cells were cultured in medium alone or with increasing amounts of ovine LH (oLH; 1-1000 mug/l) for an additional 48 h. LH treatment also increased I-125-labelled mouse EGF binding in a dose-dependent manner, compared with the control. However, neither FSH nor LH altered receptor-binding affinity. Furthermore, after culture with oFSH (FSH-primed) or oFSH followed by oLH (LH-primed), tissue plasminogen activator (tPA) activities in the conditioned media were examined by fibrin autography. FSH-primed or LH-primed granulosa cells were more responsive to EGF action to induce an increase in tPA activity. In conclusion, it is suggested that functional receptors for EGF in rat granulosa cells are up-regulated by FSH and LH.