[Amino acid transfer at the fetal surface of the trophoblast and the characterization of its carrier in the rat placenta in vivo].

A new technique for injecting tracer into the rat fetus in utero, intraperitoneally, was employed to characterize the amino acid exchange at the fetal surface of the trophoblast and to study the transplacental amino acid transfer. Calculation of tissue fluid distribution via 3H-inulin space made it possible to estimate the placental intracellular amino acid concentration on the basis of the cord and maternal plasma concentration. The fetal plasma free amino acid was taken up at a considerable rate by the fetal surface of the placenta in umbilical circulation. The amino acid from fetal plasma was utilized for the protein synthesis and deamination in the placenta. It was speculated that the amino acid transfer at the fetal surface of the placenta was carrier-mediated facilitated diffusion, not simple diffusion, on the basis of the data showing the stereospecificity for the isomers. From these results it was considered that the fetal, not maternal, plasma free amino acid concentration greatly influenced the fetal amino acid net uptake.