EPIDERMAL GROWTH-FACTOR RECEPTOR-BINDING AND BIOLOGICAL-ACTIVITY IN THE OVARY OF GOLDFISH, CARASSIUS-AURATUS

The receptor binding and biological activity of epidermal growth facto r-urogastrone (EGF) was characterized in the follicle-enclosed goldfis h oocyte. The binding of I-125-labeled mouse EGF (mEGF) to goldfish ov arian membrane preparation was peptide specific, saturable, reversible , and dependent on time and tissue concentration. Binding data analysi s indicated the presence of a single class of high-affinity binding si tes with an estimated equilibrium dissociation constant of 4.4 +/- 1.8 x 10(-10) M. The I-125-mEGF binding was displaced by unlabeled mEGF a nd by human recombinant transforming growth factor-alpha (hTGF-alpha). Both mEGF and hTGF-alpha were found to stimulate reinitiation of oocy te meiosis, as indicated by germinal vesicle breakdown (GVBD). Treatme nt with mEGF and hTGF-alpha stimulated GVBD from a basal level of 8.5 to similar to 30% with an estimated half-maximal effective dose for EG F of 5.80 +/- 0.82 x 10(-10) and for hTGF-alpha, 1.9 +/- 1.0 x 10(-10) M. Furthermore, treatment with mEGF marginally increased 17 alpha, 20 beta-dihydroxy-4-pregnen-3-one (DHP)-induced GVBD without significant ly influencing the gonaaotropin-induced response. Treatment with eithe r mEGF or hTGF-alpha significantly reduce-human chorionic gonadotropin -stimulated testosterone production in a concentration-related manner. These data suggest that members of the EGF family may play a role in the regulation of ovarian function in goldfish.