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

Biology of Reproduction v.65, i.3 Sep01

^a Department of Population Health & Reproduction, School of Veterinary Medicine, University of California, Davis, California 95616
^b Animal Physiology Department, Veterinary School, Universidad Complutense de Madrid, 28040 Madrid, Spain
^c Department of Animal Reproduction, Faculdade de Veterinaria, Universidade Federal de Pelotas, RS 96010-900, Brazil
^d Animal Reproduction Laboratory, Temperate Climate Research Corporation, EMBRAPA, BR 392 Km 78 Cx. P. 403 Pelotas, RS 96001-970, Brazil
^e Department of Animal Science, University of California, Davis, California 95616

ABSTRACT
The effects of insulin-like growth factor-I (IGF-I) and its interaction with gonadotropins, estradiol, and fetal calf serum (FCS) on in vitro maturation (IVM) of equine oocytes were investigated in this study. We also examined the role of IGF-I in the presence or absence of gonadotropins, estradiol, and FCS in parthenogenic cleavage after oocyte activation with calcium ionophore 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 experiment 1, oocytes were cultured in TCM-199 supplemented with BSA, antibiotics, and IGF-I at 0 (control), 50, 100, 200 ng/ml, at 39°C 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 promoted the highest nuclear maturation rate in experiment 1. In experiment 3, oocytes from the three experimental groups (IGF-I; hormones; and IGF-I + hormones) were chemically activated by exposure to calcium ionophore followed by culture in 6-DMAP. In experiment 1, IGF-I stimulated equine oocyte maturation 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 maturation was observed in experiment 2. In experiment 3, a significant difference in cleavage rate was observed between the hormone + IGF-I group (15 of 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 nuclear maturation, but resulted in a positive effect on cytoplasmic maturation of equine oocytes measured by parthenogenic cleavage.

FOOTNOTES
First decision: 7 February 2001.

¹ This project was supported in part by Club Hipico La Silla, Monterey, Mexico, and by Center for Equine Health with funds provided by the Oak Tree Racing Association, the State of California parimutuel fund, and contributions by private donors. G.C. is a research fellow recipient of CAPES/MEC, Brazil. Part of this work was presented as a poster at the International Embryo Transfer Society Meeting (IETS), Omaha, NE, 13–16 January 2001.

² Correspondence: Irwin K.M. Liu and Gustavo F. Carneiro, Department of Population Health and Reproduction, School of Veterinary Medicine, 1114 Tupper Hall, University of California, Davis, CA 95616. FAX: 530 752 4278; ikliu@ucdavis.edu and gfcarneiro@ucdavis.edu