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 durin g peri-compaction of in vitro produced bovine embryos was investigated. Thi s 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 oxida tive phosphorylation from electron transport. The development of embryos un der various O-2 concentrations from day 5 to day 7 of development indicated that an optimal concentration occurred at about 2%. Addition of NaN3 revea led 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 co ncentrations of NaN3 or 2,4-dinitrophenol that stimulated embryo developmen t, 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 uptak e was significantly lower at inhibitory doses (100 mu mol l(-1)). A signifi cant (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 result s demonstrate that ATP production via oxidative phosphorylation is essentia l for bovine embryo development in vitro. However, transient (subacute) inh ibition appears to be beneficial to embryo development and the number of ce lls, perhaps by creating a more favourable intracellular environment.