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Division of Perinatal Medicine, Departments of Physiology, Obstetrics-Gynecology and Pediatrics, University of Colorado School of Medicine, Denver, Colorado 80262
Uterine and umbilical
uptakes of plasma amino acids were measured simultaneously in eighteen
singleton pregnant ewes at 130 ± 1 days gestation for the purpose
of establishing which amino acids are produced or used by the
uteroplacenta under normal physiological conditions and at what rates.
The branched-chain amino acids (BCAA) had uterine uptakes significantly
greater than umbilical uptakes. Net uteroplacental BCAA utilization was
8.0 ± 2.5 µmol · kg
fetus
1 · min1
(P < 0.005) and represented 42% of the total
BCAA utilization by fetus plus uteroplacenta. There was placental
uptake of fetal glutamate (4.2 ± 0.3 µmol · kg
fetus1 · min1,
P < 0.001) and no uterine uptake of
maternal glutamate. Umbilical uptake of glutamine was ~61%
greater than uterine uptake, thus demonstrating net uteroplacental
glutamine production of 2.2 ± 0.9 µmol · kg
fetus1 · min1
(P < 0.021). In conjunction with
other evidence, these data indicate rapid placental metabolism of
glutamate, which is in part supplied by the fetus 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 of maternal serine and
umbilical uptake of glycine produced by the placenta. Maternal serine
utilization and glycine umbilical uptake were virtually equal (3.14 ± 0.50 vs. 3.10 ± 0.46 µmol · kg
fetus1 · min1).
This evidence supports the conclusion that the ovine placenta converts
large quantities of maternal serine into fetal glycine.
fetus; uptakes; placental metabolism; branched-chain amino acids; serine; glycine; glutamate; glutamine
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