Uptake and Incorporation of Amino Acids By Cultured Mouse Embryos: Estrogen Stimulation1

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Abstract
The effect of estrogen on uptake and incorporation of amino acids was investigated in mouse embryos cultured in vitro from the 2-cell to hatched blastocyst stage. Embryos at various stages of preimplantation development were incubated with 14C-amino acids and different concentrations of 17β-estradiol, prepared for determination of amino acid uptake or incorporation into peptides and counted in a scintillation counter. Estradiol did not stimulate uptake or incorporation of 14C-valine into morulae. There was a slight but evident increase in both uptake and incorporation in early blastocysts. When expanded blastocysts were incubated with 14C-valine and 17β-estradiol, uptake and incorporation were significantly [p < 0.05] increased over control values at 10−10, 10−9, and 10−5M estradiol. At 10−8, 10−7, and 10−6M counts were equivalent to or lower than counts in embryos incubated in 14C-valine alone. The same pattern of estrogen stimulation was observed when these embryos were labeled with a mixture of 14C-valine, lysine, and aspartic acid. In hatched blastocysts, estradiol had no effect on valine incorporation but greatly stimulated its uptake. These results demonstrate that estrogen can stimulate uptake and incorporation of amino acids in preimplantation embryos by acting directly on the blastocyst, and they suggest that the mouse embryo may develop an estrogen-sensitive mechanism just prior to implantation.

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