Epidermal Growth Factor Induces Maturation of Rat Follicle-enclosed Oocytes

Gonadotropin-induced differentiation of ovarian granulosa cells in culture is inhibited by epidermal growth factor (EGF). The present study was undertaken to test a possible inhibitory effect of EGF on LH-induced maturation of rat follicle-enclosed oocytes. We have found that EGF not only failed to affect LH action but served by itself as an inducer of maturation of follicle-enclosed oocytes. EGF action on the oocytes was dose and time dependent and could be prevented by (Bu)2 cAMP. The response of the oocytes was specific to EGF and could not be elicited by other growth factors such as nerve growth factor and insulin. The response to EGF was not limited to the large antral follicles, as oocytes enclosed by small antral follicles (less than 0.4 mm) were induced to mature by EGF as well. In addition, we have demonstrated that oocytes, induced to mature by EGF, are concomitantly uncoupled from the follicular cells. Based on these results we suggest that EGF may terminate the transfer of a follicular inhibitor to the oocyte. It is also possible, however, that EGF induces oocyte maturation by a mechanism independent of its effect on communication between the cellular components of the follicle.