ROLE OF EGF, IGF-I, SERA AND CUMULUS CELLS ON MATURATION IN-VITRO OF BOVINE OOCYTES

We examined the effects of epidermal growth factor (EGF), insulin-like growth factor-I (IGF-I), the presence/absence of cumulus cells, and s era (fetal calf serum, FCS or estrous cow serum, ECS) on cumulus expan sion and meiotic maturation during in vitro bovine oocyte maturation. The oocytes obtained (n=4491) were divided into cumulus-oocyte complex es (COG) or denuded oocytes and were then cultured in 3 groups compris ing TCM-199 and sera: Group I(without serum), Group II (10% FCS), and Group III (10% ECS). Each group was subjected to 4 predefined treatmen ts with growth-factors: control (no growth factor), EGF, IGF-I, and EG F+IGF-I. At the end of the 24-h culture period, the oocytes were asses sed for degree of cumulus expansion and metaphase II stage. Treatments with EGF enhanced the incidence of full cumulus expansion in all 3 gr oups. Maximal stimulation for both cumulus expansion and nuclear matur ation occurred with EGF+IGF-I in all groups, mainly in the groups with serum. Regarding the denuded oocytes, no positive effects on nuclear maturation rates were observed for any treatment. These results sugges t that: 1) EGF, with or without IGF-I, stimulates cumulus expansion an d meiotic maturation significantly; and 2) the presence of FCS or ECS enhances the effect of these growth factors in bovine cumulus-oocyte c omplexes.