FACTORS INFLUENCING RESUMPTION OF MEIOTIC MATURATION AND CUMULUS EXPANSION OF PORCINE OOCYTE-CUMULUS CELL COMPLEXES IN-VITRO

The present study was undertaken to examine effects of various combinations of epidermal growth factor (EGF), transforming growth factor-beta1 (TGF-beta1), follicle-stimulating hormone (FSH), luteinizing hormone (LH), androstenedione (A4), and estradiol-17beta (E2) on meiotic maturation and cumulus expansion in the pig using an in vitro model system. Oocyte-cumulus cell complexes (OCC) were cultured in the media containing the above-mentioned agents for 24 hr and were observed for germinal vesicle breakdown (GVBD), indicative of initiation of meiotic maturation, and for expansion of their cumulus cells. Treatment with EGF significantly increased (P < 0.05) incidence of GVBD, with maximal stimulation occurring at 1 ng/ml (55% vs. 12% in the control). Concentrations of EGF as low as 100 pg/ml significantly stimulated GVBD over control (37% vs. 12%). Addition of EGF (1 ng/ml) and FSH (1.5 mug/ml) together and LH (2 mug/ml) and FSH (1.5 mug/ml) together resulted in significantly higher (P < 0.01) GVBD levels than were observed in response to EGF, FSH, or LH alone. Addition of E2 (1 mug/ml) had no effect by itself but significantly decreased the incidence of GVBD in the presence of FSH and of LH + FSH. Addition of A4 (1 mug/ml) significantly reduced the percentage of oocytes undergoing GVBD when added alone or with FSH. Although both EGF and LH stimulated cumulus expansion, FSH was more effective in stimulating cumulus expansion than EGF or LH. TGF-beta1 had no effect on GVBD or cumulus expansion. These studies indicate that these hormones may have differing roles in oocyte maturation and that their interactions may be part of an intricate system regulating the maturation of oocytes during follicular development in vivo. (C) 1993 Wiley-Liss, Inc.