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 combina tions of epidermal growth factor (EGF), transforming growth factor-bet a1 (TGF-beta1), follicle-stimulating hormone (FSH), luteinizing hormon e (LH), androstenedione (A4), and estradiol-17beta (E2) on meiotic mat uration and cumulus expansion in the pig using an in vitro model syste m. Oocyte-cumulus cell complexes (OCC) were cultured in the media cont aining the above-mentioned agents for 24 hr and were observed for germ inal vesicle breakdown (GVBD), indicative of initiation of meiotic mat uration, and for expansion of their cumulus cells. Treatment with EGF significantly increased (P < 0.05) incidence of GVBD, with maximal sti mulation occurring at 1 ng/ml (55% vs. 12% in the control). Concentrat ions of EGF as low as 100 pg/ml significantly stimulated GVBD over con trol (37% vs. 12%). Addition of EGF (1 ng/ml) and FSH (1.5 mug/ml) tog ether and LH (2 mug/ml) and FSH (1.5 mug/ml) together resulted in sign ificantly 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 presen ce of FSH and of LH + FSH. Addition of A4 (1 mug/ml) significantly red uced the percentage of oocytes undergoing GVBD when added alone or wit h FSH. Although both EGF and LH stimulated cumulus expansion, FSH was more effective in stimulating cumulus expansion than EGF or LH. TGF-be ta1 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.