Oxygen consumption by Day 7 bovine blastocysts: determination of ATP production

Using a fluorescence technique which measures changes in oxygen concentration in embryo incubation medium, we have measured the uptake of oxygen by small groups of Day 7 bovine embryos recovered from superovulated and inseminated heifers (n = 8). The amount of glucose consumed by the embryos was also determined by analysing the spent medium following the oxygen assay. Oxygen consumption was successfully recorded from 17 out of 22 attempted assays and measured at 0.66 ± 0.08 nl embryo−1 h−1. There was a significant difference in oxygen consumption between blastocyst stage (0.84 ± 0.09) and expanded blastocyst stage (0.51 ± 0.09) embryos (P < 0.05). Mean ±(SEM) glucose uptake was 14.7 ± 1.9 pmol e−1 h−1 for all blastocysts; there was no significant difference in glucose consumption between blastocyst and expanded blastocyst stage embryos. From these values and assuming virtually all the glucose is metabolised via the Embden-Meyerhoff pathway, the rate of ATP production can be calculated at 205 ± 23 pmol e−1 h−1 (range 45–390 pmol e−1 h−1), of which approximately 85% is derived from oxidative phosphorylation. This rate represents a rapid turnover of ATP and demonstrates that metabolism in Day 7 bovine embryos is comparable to that of the more active tissues of the body.