The toxic effect of short exposures to the atmospheric oxygen concentration on early mouse embryonic development.

When culture conditions of mouse preembryos include an O2 concentration of 20%, preembryos that initiate in vitro culture at the 1-cell stage have a lower survival rate than preembryos that are harvested for culture at the 2-cell stage. This "toxic" effect of O2 is not seen at 5% O2 concentrations, suggesting that atmospheric O2 concentrations are toxic to preembryos. The present study examined the effect of short-term exposures to 20% O2, as may occur during in vitro fertilization procedures. The results demonstrated that when 1-cell preembryos were exposed to the atmospheric oxygen concentration for as little as 1 hour, their development was inhibited. Furthermore, such toxic effects did not become apparent until after four to five divisions. The authors conclude that it is critical to minimize exposure of zygotes to the atmospheric O2 concentration for optimal development to continue past the 8- to 16-cell stage, at least in the mouse.