Houghton, Franchesca D.
Preimplantation embryo metabolism
Biology of Reproduction, (Supplement), .
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Preimplantation embryos are remarkably adaptable, being able to develop in a variety of culture media containing different energy sources. Routinely, embryos are cultured in a simple balanced salt solution supplemented with pyruvate, glucose, lactate, amino acids and a protein source; any of which may be metabolised as a potential energy source for the embryo. Energy metabolism results in the generation of ATP and is integral for successful embryo development. The best global indication of the ability of an embryo to produce energy is oxygen consumption, which together with the amount of lactate produced can be used to calculate ATP production. Prior to the blastocyst stage ATP formation remains low but cavitation is associated with a large increase in ATP production. Using immunosurgery to isolate inner cell mass (ICM) cells, it can be calculated that the trophectoderm produces approximately 80% of the ATP generated at the blastocyst stage with the ICM contributing 20%. It is likely that the majority of this energy is used to fuel Na+ pumping via the Na+, K+, ATPase. Energy metabolism is intrinsic to embryo health and may be used to predict developmental capacity. In vitro fertilisation has permitted many thousands of couples to conceive but is limited by a low pregnancy rate and high multiple birth rate due to the transfer of more than one embryo. At present, embryos are selected for transfer based on their morphology, but this is subjective and a poor predictor of viability. Amino acid profiling offers the potential to predict non-invasively the developmental capacity of single human embryos as early as day 2 post-insemination, obviating the need for prolonged culture to the blastocyst stage.
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