Effect 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 pericompaction of in vitro produced bovine embryos was investigated. This was achieved by: (i) varying the atmospheric O2 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 O2 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 mumol l-1 were toxic to embryo development, but that concentrations of 5-10 mumol 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 mumol 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 O2 uptake was significantly lower at inhibitory doses (100 mumol 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 mumol 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.