OXYGEN-CONSUMPTION BY DAY-7 BOVINE BLASTOCYSTS - DETERMINATION OF ATPPRODUCTION

Using a fluorescence technique which measures changes in oxygen concen tration in embryo incubation medium, we have measured the uptake of ox ygen by small groups of Day 7 bovine embryos recovered from superovula ted and inseminated heifers (n = 8). The amount of glucose consumed by the embryos was also determined by analysing the spent medium followi ng 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 b etween blastocyst stage (0.84 +/- 0.09) and expanded blastocyst stage (0.51 +/- 0.09) embryos (P < 0.05). Mean +/-(SEM) glucose uptake was 1 4.7 +/- 1.9 pmol e(-1) h(-1) for all blastocysts; there was no signifi cant difference in glucose consumption between blastocyst and expanded blastocyst stage embryos. From these values and assuming virtually al l the glucose is metabolised via the Embden-Meyerhoff pathway, the rat e 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 com parable to that of the more active tissues of the body.