The role for the uterine insulin-like growth factor I in early embryonic loss after superovulation in the rat *

Objectives To examine possible roles of the insulin-like growth factor (IGF) system in increased early embryonic loss after superovulation. Design Changes in the uterine IGF system were examined in superovulated rats. Insulin like growth factor I (IGF-I) was infused to the right uterine horns to mimic enhanced IGF-I actions after superovulation. Uterine luminal fluids were collected after IGF-I infusions and embryos were cultured with uterine luminal fluids. Main Outcome Measures Steroid hormones, IGF-I, IGF binding protein (IGFBP), and IGF-I receptor levels, developmental rate, and cell numbers of embryos. Results Elevated IGF-I levels and suppressed IGFBP levels were found from days 1 to 3 of pregnancy after superovulation. Uterine luminal fluids of the IGF-I infusion and superovulation groups impaired embryo development in vitro. Anti-IGF-I antibody infusions after superovulation reversed detrimental effects of superovulation. Dialysis of uterine luminal fluids of the IGF-I infusion and superovulation groups before culture improved embryo development. Conclusions Enhanced IGF-I actions in the uterus after superovulation may be responsible for the increase of early embryonic loss. The detrimental factor for embryo development seems a small molecule and is likely a local product of the uterus in which IGF-I actions are enhanced.