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

We tested the hypothesis that decreased fetal amino acid (AA) supply, produced by maternal hypoaminoacidemia (low AA) during hyperglycemia (HG), is reversible with maternal AA infusion and regulates fetal insulin concentration (I]). We measured net uterine and umbilical AA uptakes during maternal HG/low AA concentration (AA]) and after maternal intravenous infusion of a mixed AA solution. After 5 days HG, all maternal AA] except glycine were decreased >50%, particularly essential AA] (P < 0.00005). Most fetal AA] also were decreased, especially branched-chain AA (P < 0.001). Maternal AA infusion increased net uterine uptakes of Val, Leu, Ile, Met, and Ser and net umbilical uptakes of Val, Leu, Ile, Met, Phe, and Arg but did not change net uteroplacental uptake of any AA. Fetal I] increased 55 +/- 14%, P < 0.001, with correction of fetal AA], despite the lack of change in fetal glucose concentration. Thus generalized maternal hypoaminoacidemia decreases uterine and umbilical uptakes of primarily the essential AA and decreases fetal branched-chain AA]. These changes are reversed with correction of maternal AA], which also increases fetal I].