Preimplantation mouse embryos were cultured for varying times in the presence of different energy substrates. The levels of ATP were then measured and compared to those of freshly collected embryos.
There were no differences in the levels of ATP between embryos cultured from the two- or eight-cell stage to the morula stage and freshly collected embryos at similar stages of development, while embryos which were cultured to the blastocyst stage had more ATP than freshly collected blastocysts. Both eight-cell embryos and morulae which were cultured for 24 to 48 hr in medium containing pyruvate plus lactate had greater amounts of ATP than embryos cultured in either energy substrate-free medium or medium containing glucose.
At the one- and two-cell stage, a combination of pyruvate and lactate was more effective than either energy substrate alone in maintaining the levels of ATP during a 6-hr culture period. As development progressed, the higher levels of ATP in embryos cultured in medium containing glucose as compared to the levels in embryos cultured in energy substrate-free medium indicated that glycolysis played an increasingly important rôle in maintaining the levels of ATP.
The level of ATP in embryos cultured for up to 48 hr beyond the morula stage increased to values equivalent to those at the one- and two-cell stage. However, the ratio of ATP to ADP in morulae and blastocysts was considerably lower than this ratio at the one- and two-cell stage. It is suggested that this high ATP to ADP ratio in one- and two-cell embryos may limit the rate of glycolysis during early development.
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