Insulin and insulin-like growth factor-1 promote rabbit blastocyst development and prevent apoptosis

Insulin as well as insulin-like growth factor-I (ICF-I) promote early embryo development, and ICF-I binds to the coats of preimplantation rabbit embryos, As the IGF-I receptor is expressed from the morula stage onwards, the embryos are capable of responding to insulin and ICF-I, which is present in the oviductal and uterine secretions that surround them. The embryonic coats were removed to exclude any influence by ICF-I bound to the coats, The in vitro development of such embryos under classical conditions appears to be retarded. Addition of IGF-I (68 pM-6.8 nM) or insulin (68 nM-6.8 mu M), however, promotes blastocyst formation. Embryo development under such conditions is not significantly different from that of embryos cultured with intact coats. In contrast, coat-free embryos cultured without ICF-I or insulin supplementation show apoptosis, Because IGF-I stimulates cell proliferation and prevents apoptosis, we investigated whether insulin or IGF-I may act as "survival factors" in preimplantation development, Therefore, apoptosis was induced by slight UV irradiation (254 nm wave length; 11.8 W/m(2)). Compared to the untreated controls, embryos displaying retarded development or degeneration were increased by 22% and 14%, respectively. Addition of ICF-I or insulin to the culture medium of UV-irradiated embryos improved [H-3]thymidine incorporation and blastocyst formation significantly. By immunohistochemistry we could show that addition of insulin (0.68-68 nM) decreased apoptosis and increased cell proliferation in a dose-dependent manner, supporting blastocyst. development significantly.