THE EFFECTS OF EPIDERMAL GROWTH-FACTOR AND INSULIN-LIKE-GROWTH-FACTOR-I ON THE METABOLIC-ACTIVITY, NUCLEAR MATURATION AND SUBSEQUENT DEVELOPMENT OF CATTLE OOCYTES IN-VITRO

The effects of epidermal growth factor (EGF) and insulin-like growth f actor I (IGF-I) on the maturation and subsequent development of cattle oocytes in vitro were evaluated in three experiments. Cumulus-oocyte complexes (COC) were collected from cattle ovaries and matured for 20- 24 h in control medium or in medium containing 50 ng EGF m(- 1), 100 n g IGF-I ml(- 1), EGF + IGF-I, or 10% (v/v) fetal calf serum plus 0.1 i .u. human menopausal gonadotrophin ml(- 1) (hMG). In Expt 1, treatment with EGF + IGF-I stimulated cumulus expansion, the metabolism of pyru vate and glutamine, and nuclear maturation. In Expt 2, only the metabo lic measurements from oocytes that reached metaphase II were considere d, and EGF + IGF-I stimulated pyruvate metabolism to the same extent a s serum + hMG. In Expt 3, the oocytes were fertilized after maturation culture, and the resultant embryos cultured for up to 8 days. The cle avage was greater in the EGF and EGF + IGF-I groups than in the contro ls but less than in the serum + hMG group. Moreover, the number of bla stocyst cells at 7 days after insemination and the proportion of cleav ed embryos that developed to the blastocyst stage by day 8 was greater in the serum + hMG group than in the control group indicating that ma turation treatment can affect early embryonic development. In conclusi on, EGF + IGF-I can stimulate cumulus expansion, oxidative metabolism, nuclear maturation and cleavage after fertilization of bovine oocytes in vitro. The relative effects of the treatments on oocyte pyruvate m etabolism in Expts 1 and 2 generally paralleled their effects on cleav age and subsequent development in Expt 3, suggesting that mitochondria l function is related to developmental potential. Further investigatio n is required to determine which component(s) of serum or gonadotrophi n treatment is responsible for the effects on subsequent embryonic dev elopment.