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Maturation of bovine oocytes under low culture temperature decreased glutathione peroxidase activity of both oocytes and blastocysts.

It is known that the basic variable in the cellular environment is temperature and low temperature decreases cellular metabolism rate. Also, low cellular metabolic activity reduces oxidative stress, resulting in low ROS production. The aim of this study was therefore to investigate the effect of 36.5°C (low) and 38.5°C (conventional) incubation temperatures during IVM on glutathione peroxidase activity of oocytes and blastocysts following fertilization. Bovine oocytes were matured in medium-199 for 22 hours at either 36.5°C or 38.5°C and they were subjected to in vitro fertilization (IVF). Putative zygotes were then transferred randomly into SOFaa embryo culture media with or without antioxidant (a mixture of GSH and SOD) until development to the blastocyst stage. Glutathione peroxidase enzyme (GSH-Px) activity was lower (p⟨0.05) in oocytes matured at low temperature than those of conventional temperature. Similarly, GSH-Px activity was lower (p⟨0.05) in blastocysts, which were obtained from oocytes matured at low temperature and cultured in antioxidants-supplemented embryo media. The GSH-Px activity of blastocysts, obtained from oocytes matured in low temperature, cultured in antioxidants-free embryo media was similar to blastocysts obtained from oocytes matured in conventional temperature, cultured in antioxidants-supplemented embryo media. The results of the present study show that decreasing the in vitro maturation temperature decreases antioxidant enzyme activity in both oocyte and blastocyst. Additionally, maturation of bovine oocytes at 36.5°C incubation temperature may provide an optimal thermal condition for the enzymatic antioxidant system of both oocytes and blastocyst.