200 SYNCHRONIZATION OF OOCYTE MEIOTIC MATURATION IN SUPEROVULATED MICE IMPROVES IN VITRO FERTILIZATION RATE

In vitro synchronization of oocyte nuclear and cytoplasmic maturation has been found to improve the IVF rate of ovarian oocytes in several species, including humans, in comparison with nonsynchronized in vitro-matured oocytes. Here, we tested the hypothesis that synchronization of oocyte meiotic maturation by an in vivo system in superovulated mice would increase the oocyte fertilization rate when compared to that of conventional superovulated oocytes. Recently, we observed that cilostazol (CZL), a PDE3-I, was able to inhibit mouse oocyte meiotic maturation in both in vitro and in vivo systems. Administering CZL at 7.5 mg, 4 or 7 h pre-hCG allowed retrieval of ovulated oocytes of which >95% were at MI stage, scored by Nikon stereo microscope (SMZ 1500). A conventional superovulation program was adapted in all treated and their control groups, in which mice were injected with eCG and after 48 h with hCG (7.5 IU for each hormone). On the second morning, 13 to 14 h post-hCG, mice were killed and oocytes were collected from oviducts and in vitro fertilized (control). For the treated groups, CZL was administered in a single 7.5 mg oral dose (gavage) 4 or 7 h before the hCG injection. On the second morning, CZL-treated animals were killed at the same timing as control animals and oocytes were retrieved from the oviduct and in vitro matured for 6 h (for those gavaged with CZL, 4 h pre-hCG) or 3 h (for those gavaged with CZL, 7 h pre-hCG) to MII oocytes before IVF. These groups were designated as in vivo-in vitro synchronized/matured oocytes. In other groups treated with CZL, 4 or 7 h pre-hCG, the ovulated oocytes were allowed to mature in the oviduct (full in vivo synchronization and maturation) and oocytes were retrieved and fertilized with the same fertilization timings as the in vivo-in vitro synchronized/matured oocytes. Oocytes were cultured for 1 day after IVF and examined for cleavage. Statistical differences were analyzed by cross-tabulated chi-square test. The full in vivo synchronization and maturation (for both CZL dose timings of 4 and 7 h pre-hCG) gave significantly higher early embryonic development rates compared with those of the control [89% (n = 219) and 92.2% (n = 374) vs 81.8% (n = 198); P = 0.034 and P < 0.0001, respectively]. The in vivo-in vitro synchronized/matured oocytes (CZL dose timing at 7 h, but not 4 h pre-hCG) gave significantly higher early embryonic development rates compared with those of the control [88.5% (n = 339) vs 83.4% (n = 458), respectively; P = 0.043]. However, the increase of the IVF rate of the oocytes from mice treated with CZL, 4 h pre-hCG, in the in vivo-in vitro synchronized/matured group was not significantly different from the control group [88.5% (n = 399) vs 83.4% (n = 458), respectively; P = 0.43]. It is concluded from the present study that synchronization of oocyte meiotic maturation by the in vivo and in vivo-in-vitro protocols can increase the IVF rate of oocytes in superovulated mice.