Energy substrates, mitochondrial membrane potential and human preimplantation embryo division

Carbohydrate additives to modern embryo culture media are based on three basic energy sources, glucose, pyruvate and lactate. Although the use of these substrates is almost universal, debate continues as to the roles of the individual components in the human. This is mainly due to the lack of human embryos for research and the reliance on animal model systems. In the present work, the human embryo was used to study the role of the above simple substrates in the maintenance of the mitochondrial membrane potential and cell division. The mitochondrial membrane potential was measured with fluorescence techniques. Cell division was scored as the number of blastomeres on day 3. Both the mitochondrial membrane potential and cell division were dramatically lost in the absence of energy sources. The mitochondrial membrane potential and cell division were normal in media containing all three energy sources, or in pyruvate-containing media. Both glucose and lactate individually proved poor energy sources for the maintenance of the mitochondrial membrane potential. However, cell division continued in the presence of glucose, suggesting that some energy production can continue. These data suggest that pyruvate is an absolute requirement for mitochondrial respiration and cell cleavage during human preimplantation development. The role of lactate is as yet unclear.