PRODUCTION AND UTILIZATION OF AMINO-ACIDS BY OVINE PLACENTA IN-VIVO

Uterine and umbilical uptakes of plasma amino acids were measured simu ltaneously in eighteen singleton pregnant ewes at 130 +/- 1 days gesta tion for the purpose of establishing which amino acids are produced or used by the uteroplacenta under normal physiological conditions and a t what rates. The branched-chain amino acids (BCAA) had uterine uptake s significantly greater than umbilical uptakes. Net uteroplacental BCA A utilization was 8.0 +/- 2.5 mu mol . kg fetus(-1) . min(-1) (P < 0.0 05) and represented 42% of the total BCAA utilization by fetus plus ut eroplacenta. There was placental uptake of fetal glutamate (4.2 +/- 0. 3 mu mol . kg fetus(-1) . min(-1), P < 0.001) and no uterine uptake of maternal glutamate. Umbilical uptake of glutamine was similar to 61% greater than uterine uptake, thus demonstrating net uteroplacental glu tamine production of 2.2 +/- 0.9 mu mol . kg fetus(-1) . min(-1) (P < 0.021). In conjunction with other evidence, these data indicate rapid placental metabolism of glutamate, which is in part supplied by the fe tus and in part produced locally via BCAA transamination. Most of the glutamate is oxidized, and some is used to synthesize glutamine, which is delivered to the fetus. There was net uteroplacental utilization o f maternal serine and umbilical uptake of glycine produced by the plac enta. Maternal serine utilization and glycine umbilical uptake were vi rtually equal (3.14 +/- 0.50 vs. 3.10 +/- 0.46 mu mol . kg fetus(-1) . min(-1)). This evidence supports the conclusion that the ovine placen ta converts large quantities of maternal serine into fetal glycine.