PARENT SESSION
Oocyte Development
91
DETRIMENTAL EFFECTS OF DIABETES ON hCG-INDUCED OOCYTE MATURATION, OVULATION AND PREIMPLANTATION DEVELOPMENT.
Colton, Shannondoah1, Downs, Stephen1, 1
ABSTRACT- Previous work in our laboratory has shown that the diabetic condition suppresses meiotic induction in cumulus cell-enclosed oocytes in vitro. It was therefore important to assess how oocyte maturation in vivo was affected. Immature mice were rendered diabetic with streptozotocin (STZ) and three days later were primed with equine chorionic gonadotropin (eCG). Two days after priming, mice received 5 IU human CG (hCG), the ovaries were removed at 1.5, 2, 2.5, 3, 5 and 10 h post-hCG, and oocytes from antral follicles were assessed for germinal vesicle breakdown (GVB). Up to 5 h post-hCG, maturation was suppressed in oocytes from diabetic mice compared to controls. At 2.5 h, 83% of control oocytes had undergone maturation while only 45% of oocytes from diabetic mice had matured. By 10 h post-hCG, however, meiotic resumption had recovered in diabetic mice (67.3% GVB compared to 78.9% in controls). When diabetic mice received insulin, suppression of meiotic induction was eliminated, indicating that the STZ effect is due to the diabetic condition. To assess how diabetes affects ovulation, eCG-primed control and diabetic mice received hCG, and ovulated ova were counted 12 and 14 h post-hCG. The ova were fixed and stained with Hoechst dye to observe meiotic status. At both time points, the number of ovulated ova was significantly lower in diabetic mice (17 and 29 ova at 12 and 14 h in diabetic mice versus 40 and 48 ova, respectively, in control mice). In addition, fewer ova from diabetic mice had reached metaphase II compared to controls (48.8% versus 75.8%, respectively, at 12 h), and this effect was eliminated by insulin treatment. To determine how the diabetic state affects embryo development, control and diabetic mice were superovulated with eCG/hCG and mated. Pronuclear-stage embryos were collected 24 h later and cultured for 5 d in KSOM containing 0.18, 5.5 or 22 mM glucose. Fewer embryos from diabetic mice developed to the blastocyst stage compared to control embryos. Higher glucose concentrations decreased development to blastocyst in both groups, but this effect was more pronounced in embryos from diabetic mice. These data indicate that diabetes suppresses hCG-induced meiotic resumption and ovulation. These detrimental effects during the preovulatory period may contribute to compromised embryo productivity.
KEY WORDS: diabetes, oocyte maturation, ovulation, embryo development