Epidermal growth factor binding sites in porcine granulosa cells and their regulation by follicle-stimulating hormone.

Epidermal growth factor (EGF) modulates ovarian function, including folliculogenesis and steroidogenesis. We investigated the localization of EGF binding sites in the porcine ovary, and the effect of FSH on EGF binding to cultured granulosa cells. Autoradiographic study demonstrated that the binding sites for 125I-labeled mouse EGF in the porcine ovary were present in the granulosa and luteal cells, but not in the thecal cells. Porcine granulosa cells were collected by the needle aspiration method from small (1-2 mm) and medium-sized (3-5 mm) follicles. Scatchard analysis showed that a single class of the specific binding sites for EGF was present in the granulosa cells. The number of binding sites and the apparent dissociation constant were 5,540 binding sites/cell and 0.23 nM (medium-sized follicle), respectively. No significant difference was observed between small and medium-sized follicles. Granulosa cells were cultured for 48 h at 37 degrees C in medium alone or with increasing doses of ovine FSH (1-100 ng/ml). FSH treatment significantly increased EGF binding in a dose-dependent manner. In conclusion, it is suggested that the specific high affinity, low capacity binding sites for EGF are present in porcine granulosa cells, and that they are up-regulated by FSH.