Modulation of redox state by hydrogen peroxide in the stage of oocyte maturation: Effect on embryonic development in cattle

Oxidative stress is defined as an imbalance between the production of oxidants and antioxidants. The induction of stress tolerance in oocytes leads to a better embryonic development. In cattle incubating mature oocytes with different stressors (thermal, high hydrostatic pressure, oxidative) increase the generation rate of blastocysts. The purpose of this study was to evaluate the effect of modulating the redox state increasing the oxidative stress through H2O2 in mature oocyte under in vitro culture conditions and its effect on the potential of embryonic development. To do this, oocytes from slaughterhouse ovaries were matured in TCM-199 medium supplemented for 22-23 h at 38.5 degrees C, 5 % CO2 and humidified atmosphere. At the end of 22-23 h, the treatments with 0, 50, 100 and 200 mu M H2O2 were applied for 1 h. IVF was performed co-incubating the eggs for 18 h with a final concentration of 1x10(6) sperm/mL. The presumptive zygotes were denuded and cultured in medium KSOM-0.4 % BSA to 38.5 degrees C in an atmosphere of low concentration of O-2 (5 % O-2, 5 % CO2 and 90 % N-2) and humidified atmosphere. The results show that the induction of oxidative stress by H2O2 produces a similar effect using a concentration of 50 and 100 mM in the cleavage rate of embryos compared to control (88.7 %, 83.2 % and 86,4 % respectively, p>0.05) and decreasing significantly by using a concentration of 200 mM (58.8 %, p<0.05). Also, H2O2 caused a similar effect on the rate of blastocysts with 50 mu M (20.4 % vs. 25.8 control, p>0.05) but decreased significantly with 100 and 200 mu M (10.7 % and 3.3 % respectively, p<0.05). It is possible that these embryos resistant to oxidative stress may have a higher survival in the cryopreservation processes that generating high levels of reactive oxygen species.