Free radical scavengers ameliorate the 2-cell block in mouse embryo culture

Mouse zygotes from a strain combination which fails to undergo cleavage in vitro (the 2-cell block) were cultured in a variety of media, using either low (5%) or normal (20%) oxygen tension in the gas phase. Development beyond the 4-cell stage was only achieved in medium containing serum and with normal oxygen tension. When serum-free medium was supplemented with free radical scavengers, reduced glutathione (1 mM), but not histidine, catalase or superoxide dismutase, development to the morula or blastocyst stage was promoted in 50% of zygotes cultured with normal oxygen tension. These data suggest that the 2-cell block is a consequence, at least in part, of free radical damage incurred by embryos during collection and culture, and that medium supplementation with the radical scavenger, reduced glutathione, can improve embryo development in vitro.