Influence of insulin-like growth factor-I and its interaction with gonadotropins, estradiol, and fetal calf serum on in vitro maturation and parthenogenic development in equine oocytes

The effects of insulin-like growth factor-I (IGF-I) and its interaction wit h gonadotropins, estradiol, and fetal calf serum (FCS) on in vitro maturati on (IVM) of equine oocytes were investigated in this study. We also examine d the role of IGF-I in the presence or absence of gonadotropins, estradiol, and FCS in parthenogenic cleavage after oocyte activation with calcium ion ophore combined with 6-dimethylaminopurine (6-DMAP), using cleavage rate as a measure of cytoplasmic maturation. Only equine cumulus-oocyte complexes with compact cumulus and homogenous ooplasm (n = 817) were used. In experim ent 1, oocytes were cultured in TCM-199 supplemented with BSA, antibiotics, and IGF-I at 0 (control), 50, 100, 200 ng/ml, at 39 degreesC in air with 5 % CO2, 95% humidity for 36 or 48 h. In experiment 2, oocytes were cultured with FSH, LH, estradiol, and FCS with IGF-I at the concentration that promo ted the highest nuclear maturation rate in experiment 1. In experiment 3, o ocytes from the three experimental groups (IGF-I; hormones; and IGF-I + hor mones) were chemically activated by exposure to calcium ionophore followed by culture in 6-DMAP In experiment 1, IGF-I stimulated equine oocyte matura tion in a dose-dependent manner with the highest nuclear maturation rate at a concentration of 200 ng/ml. No significant effect of IGF-I on nuclear ma turation was observed in experiment 2. In experiment 3. a significant diffe rence in cleavage rate was observed between the hormone + IGF-I group (15 o f 33; 45.4%) compared with IGF-I (10 of 36; 27.8%) and hormone (4 of 31; 12 .9%) alone (P < 0.05). These results demonstrated that IGF-I has a positive effect on nuclear maturation rate of equine oocytes in vitro. The addition of IGF-I to an IVM medium containing hormones and FCS did not increase nuc lear maturation, but resulted in a positive effect on cytoplasmic maturatio n of equine oocytes measured by parthenogenic cleavage.