EFFECT OF INSULIN-LIKE-GROWTH-FACTOR-I AND ITS INTERACTION WITH GONADOTROPINS ON IN-VITRO MATURATION AND EMBRYONIC-DEVELOPMENT, CELL-PROLIFERATION, AND BIOSYNTHETIC ACTIVITY OF CUMULUS-OOCYTE COMPLEXES AND GRANULOSA-CELLS IN BUFFALO

In this study we have examined the effect of insulin like growth facto r I (IGF-I) and its interaction with gonadotropins in the presence or absence of granulosa cell coculture on in vitro oocyte maturation (IVM ) and their subsequent embryonic development in buffalo. We also have examined the role of IGF-I alone or in combination with gonadotropins on DNA synthesis, steroidogenesis, and protein synthesis of cumulus-oo cytes complexes (COCs) and granulosa cells. Results showed that IGF-I stimulates oocytes maturation in a dose-dependent manner, with maximal effect at a dose of 100 ng/ml (P < 0.05). IGF-I showed positive inter action with follicle-stimulating hormone (FSH) in the presence or abse nce of granulosa cells on meiotic maturation and synergistically enhan ced DNA synthesis, protein synthesis, and steroidogenesis in the prese nce of granulosa cells. This synergistic effect Is mainly caused by th e increase of IGF-I receptors in granulosa cells by FSH, as evident by [I-125]IGF-I binding study. Luteinizing hormone (LH), however, was fo und to suppress IGF-I and IGF-I + FSH stimulated oocyte maturation. Ad dition of LH to cultures containing IGF-I + FSH, on the contrary, caus ed a significant increase in oocyte maturation when cocultured with gr anulosa cells. Addition of IGF-I during IVM significantly improve clea vage and blastocyst development rate over the control group. However, there was no cumulative effect when IGF-I and gonadotropins were prese nt together. Addition of granulosa cells during IVM, however, enhanced blastocyst development in the IGF-I + FSH and IGF-I + FSH + LH groups . Our results demonstrated that IGF-I is a major follicular factor res ponsible for stimulating oocyte maturation in the buffalo. Interaction between IGF-I and FSH suggests that they seem to act synergistically as an autocrine and paracrine regulator of granulosa cells and therefo re together promote mitosis, steroidogenesis, and protein synthesis. ( C) 1998 Wiley Liss, Inc.