Uptake of a mixture of amino acids by mouse blastocysts

Preimplantation mouse embryos exhibit growth at the blastocyst stage when there is a dramatic increase in protein content between days 4 and 5 after hCG treatment. This increse in protein synthesis requires the uptake of amino acids from the surrounding medium, but the consumption of individual amino acids present as a mixture has not been examined. We therefore measured the simultaneous depletion of 18 amino acids by mouse blastocysts in culture on days 4 and 5 after hCG treatment. Two culture media were used: one with amino acids present at concentrations largely based on those reported to give optimal rates of embryo development (M16/mix AA), and a second with the amino acids each at 0.1 mmol l-1 (M16/0.1 AA). After derivatization with o-phthaldialdehyde to yield highly fluorescent products, amino acid concentrations in the media were measured by HPLC. On day 4, seven amino acids were depleted from M16/mix AA at rates significantly greater than zero: aspartate, arginine, glycine, alanine, isoleucine, leucine and lysine; on day 5, nine amino acids were depleted at significant rates: aspartate, glutamate, asparagine, tyrosine, methionine, valine, phenylalanine, isoleucine and leucine. Average amino acid depletion from M16/mix AA was 32% greater on day 5 than on day 4. Aspartate, glutamate, arginine, isoleucine and leucine appeared to be the key amino acids sought by embryos on both days tested. Embryos grown in amino-acid-containing media appeared morphologically normal and their volume increased compared with embryos cultured in the absence of amino acids.