Effects of inhibitors and uncouplers of oxidative phosphorylation during compaction and blastulation of bovine embryos cultured in vitro

The effect of inhibiting ATP production via oxidative phosphorylation during peri-compaction of in vitro produced bovine embryos was investigated. This was achieved by: (i) varying the atmospheric O-2 concentration (0, 1, 2, 4 and 7%); (ii) addition of oxidative phosphorylation inhibitors, NaN3 and antimycin A; and (iii) addition of 2,4-dinitrophenol, an uncoupler of oxidative phosphorylation from electron transport. The development of embryos under various O-2 concentrations from day 5 to day 7 of development indicated that an optimal concentration occurred at about 2%. Addition of NaN3 revealed that doses above 100 mu mol l(-1) were toxic to embryo development, but that concentrations of 5-10 mu mol l(-1) stimulated embryo development by 10-25%. A similar result was observed after addition of 2,4-dinitrophenol, whereas antimycin A was inhibitory at doses as low as 1 mu mol l(-1). At concentrations of NaN3 or 2,4-dinitrophenol that stimulated embryo development, the number of cells of the resulting blastocysts was also significantly increased. Addition of NaN3 from day 1 of development inhibited subsequent development. Metabolic data of NaN3-treated embryos revealed that O-2 uptake was significantly lower at inhibitory doses (100 mu mol l(-1)). A significant (P < 0.05) log linear increase in glucose uptake was measured between the three concentrations of NaN3 (0, 10 and 100 mu mol l(-1)). These results demonstrate that ATP production via oxidative phosphorylation is essential for bovine embryo development in vitro. However, transient (subacute) inhibition appears to be beneficial to embryo development and the number of cells, perhaps by creating a more favourable intracellular environment.