PARENT SESSION
Follicular Development

EFFECTS OF INSULIN, IGF-I AND FSH ON THE GROWTH AND DEVELOPMENT OF BOVINE LATE PREANTRAL/ EARLY ANTRAL FOLLICLES AND OOCYTES IN VITRO.

Itoh, Takehiro¹, Kacchi, Masayuki¹, Abe, Hiroyuki¹, Hoshi, Hiroyoshi¹, ¹

ABSTRACT- To elucidate the mechanism of early stage of follicle/oocyte growth and development, the effects of insulin, IGF-I and FSH on the growth and development on late preantral/ early antral stage follicles were determined under serum- free culture conditions. These follicles (mean diameter 218.0±12.4 m) were microsurgically dissected from bovine ovaries. Follicles were embedded in 0.15% type I collagen gels and cultured in the serum- free medium (HP-M199+ 10 mg/ml BSA+ 2 mM hypoxanthine+ 50 U/ml aprotinin) for 9 days at 38.5°C in 5% CO₂/ air. Insulin (20 ng/ml), IGF-I (20 ng/ml) and FSH (100 ng/ml) were individually or simultaneously added to the basal culture medium. Diameter of follicles, antrum formation and estradiol (E₂) production were determined through the culture period. When the follicles were cultured in the basal medium, follicle diameters were gradually decreased with no antrum formation and oocyte diameters were unaltered after 9 days of culture. Insulin, IGF-I or FSH individually increased the follicle and oocyte growth, and antrum formation. Additive effect was observed when insulin and FSH were simultaneously present. Insulin by itself stimulated E₂ production and no promoting effect was found in the presence of FSH. However, E₂ production by insulin was further enhanced in the addition of FSH. Gene expressions of insulin and IGF-I receptors were dominant in both isolated and cultured follicles than IGF-II receptor. In conclusion, Insulin signaling pathway is essential for growth and development in bovine late preantral/ early antral follicles in vitro. (Supported by PRO-BRAIN)

KEY WORDS: Follicle growth, Bovine, In vitro culture, Insulin