Pyruvate prevents peroxide-induced injury of in vitro preimplantation bovine embryos

The impact of oxidative stress on the in vitro development of bovine embryo s in synthetic oviduct fluid medium (mSOF) was assessed by using H2O2 as a stress inducer. In a preliminary experiment, a chemiluminescent method was used to measure the antioxidative capacity of the mSOF culture medium. Pyru vate was the mSOF component displaying the highest H2O2 degrading ability. Essential and nonessential amino acids also significantly reduced the H2O2 concentration, whereas lactate and glutamine were ineffective. The effect o n further development of a short exposure of zygotes, 9-16-cell stage embry os and blastocysts to 0 M; 10(-7) M; 10(-6) M, and 10(-5) M H2O2 in pyruvat e-free mSOF was evaluated. Developmental rates of the H2O2-treated zygotes to the 5-8-cell or blastocyst stages and survival of H2O2-treated blastocys ts were reduced in a dose-dependent manner whereas the 9-16-cell embryos we re unaffected by those treatments. Blastocysts treated with H2O2 also tende d to have lower numbers of bisbenzimide-stained nuclei and showed increased nuclear fragmentation. Including pyruvate in the mSOF culture medium durin g a 10(-5) M H2O2 pulse highly reduced the H2O2 concentration as measured b y chemiluminescence and improved zygote and blastocyst development, but fai led to prevent blastocyst nuclei degradation. These experiments suggest tha t bovine embryos show developmental change in sensitivity to exogenous H2O2 , the 9-16-cell embryos being more resistant than zygotes and blastocysts a nd that H2O2 and its toxic effects can be attenuated by including pyruvate in the medium. Mol. Reprod. Dev. 52:149-157, 1999, (C) 1999 Witey-Liss, Inc .