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 125I-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 125I-labelled mouse EGF was present in the granulosa cells, obtained from the ovaries of immature rats treated with diethylstilbestrol. 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 micrograms/l). FSH treatment increased 125I-labelled mouse EGF binding to the granulosa cells in a dose-dependent manner. After culture with oFSH (100 micrograms/l) for 48 h, the cells were cultured in medium alone or with increasing amounts of ovine LH (oLH; 1-1000 micrograms/l) for an additional 48 h. LH treatment also increased 125I-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.(ABSTRACT TRUNCATED AT 250 WORDS)