Effect on the Fetus of Infusing a Commercial Amino Acid Preparation into a Pregnant Sheep

Abstract

The common clinical practice of intravenous feeding of the pregnant woman poses the question of the effect on the fetus of such infusions. We have used the sheep as a model to study the change in fetal amino acid levels after a maternal infusion of Synthamin 13. The maternal plasma aminogram largely reflects the amino acid pattern in the infusate. However, in the fetal circulation only the branched chain amino acids (leucine, isoleucine and valine), phenylalanine and alanine rose significantly after infusion. Only leucine and isoleucine were observed to spill into the fetal urine. The results suggest that the ovine placenta selectively modifies the amino acid profile presented to the fetus when the maternal plasma aminogram is distorted. However, the fetus is not totally protected from changes in phenylalanine, which in high concentrations, is detrimental to normal development.

Regulation of uterine and umbilical amino acid uptakes by maternal amino acid concentrations

“…Little is know about how changes in the maternalfetal AA concentration gradient affect AA transfer to the fetus. Prior studies of maternal AA supplementation have significantly increased maternal but not fetal plasma AA concentrations (21,25). The present study clearly demonstrates that a decrease in maternal AA concentrations reduces the umbilical delivery of AAs to the fetus and decreases their fetal plasma concentration, particularly for the essential AAs.…”

“…There have been relatively few physiological studies examining the effect of maternal AA supplementation on fetal AA supply and concentrations. MacMahon et al (25) showed that a 1-h infusion of a commercial mixed AA solution into pregnant ewes increased the concentrations of most maternal AAs but only increased the fetal concentrations of phenylalanine and alanine. Jozwik et al (21) showed that a 12-h maternal AA infusion increased maternal concentrations of nearly all infused AAs, whereas fetal concentrations increased significantly only for phenylalanine and methionine, umbilical uptakes increased only for leucine and isoleucine, and net fetal nitrogen supply did not increase despite a significant increase in total nitrogen supply to the uterus.…”

Relationship of fetal alanine uptake and placental alanine metabolism to maternal plasma alanine concentration

“…Although this suggests alanine transport across the placenta, it is not known whether the alanine delivered to the fetus by the placenta is derived directly from the maternal circulation or represents a product of placental alanine turnover. Transport of maternal alanine to the fetus has been suggested by a study in which the intravenous infusion in pregnant sheep of a solution of several amino acids, including alanine, caused a significant increase in fetal plasma alanine concentration (9). However, the increase in fetal concentration was only 12% of the increase in maternal concentration, and there was no attempt to demonstrate that uterine and umbilical alanine uptakes had actually increased.…”