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Hexokinase activity in mouse embryos developed in vivo and in vitro.

Micro-determination methods were used for quantitative examination of possible differences in energy metabolism in mouse embryos arising after spontaneous ovulation or after gonadotrophin stimulation. Comparisons of embryonic development in vivo and in vitro were also made. The relevance of the results to human development and their clinical significance are discussed. The enzymatic activity of hexokinase, phosphofructokinase, glucose 6-phosphate dehydrogenase, malate dehydrogenase and lactate dehydrogenase in individual mouse embryos throughout preimplantation development was evaluated. Hexokinase activity in 1-cell embryos was the lowest by far of the five enzymes measured, and the 0.035 +/- 0.010 pmol of nicotinamide adenine dinucleotide phosphate hydrogenase formed/embryo/min was also lower than in any of the somatic organs examined. Hexokinase activity, unlike the other enzymes, progressively increased in the morulae and blastocyst stages in embryos obtained either by spontaneous ovulation or via gonadotrophin stimulation. Although there is a significant delay, this increase was also observed when 2-cell embryos developed in vitro. Increases in hexokinase activity were observed 68-75 h after human chorionic gonadotrophin administration in vivo, but after 80-86 h in vitro. These increases in vitro were inhibited by the administration of actinomycin D added to the medium. The results suggest that hexokinase may be a key enzyme synthesized as the zygotic genome is expressed in preimplantation embryos, and its measurement may help to assess the quality of embryos developed in vitro.