Plasma amino acid pools in the umbilical cord artery show lower 15N natural isotope abundance relative to the maternal venous pools

N-15 natural isotope abundance (NIA) is systematically higher in infants' hair than in that of their mothers at birth. This study aimed to investigate this difference in plasma pools. We compared N-15 NIA values for plasma amino acid (AA) pools (free + protein-bound) in the umbilical cord artery (UCA) and vein (UCV) and in the maternal vein (MV) at birth. This preliminary study included 7 mother-infant dyads. Whole plasma was treated (HCl) to hydrolyze protein. Following derivatization, AAs were separated using gas chromatography and compound-specific(15)N NIA values were measured on-line using an isotope ratio monitoring mass spectrometer.N-15 NIA plasma AA pools in the UCA and UCV were highly correlated to the MV, r(2) > 0.89 and r(2) > 0.88 (bothP < 10(-4)) respectively. The full model found a significant effect of sampling compartment (P = 0.02) and AA type (P < 0.0001) on N-15 NIA plasma AA values.N-15 NIA plasma AA was 0.74 parts per thousand higher (P = 0.01) in the MV than in the UCA. This study indicates that a decrease in N-15 NIA for plasma AA pools occurs in the fetal-placental unit.

Automated summary

The study indicates a decrease in N-15 natural isotope abundance for plasma amino acid pools in the fetal-placental unit.