FREE AMINO ACIDS IN HUMAN AMNIOTIC FLUID . A QUANTITATIVE STUDY BY ION-EXCHANGE CHROMATOGRAPHY

Extract:Amniotic fluid was collected at inductive amniotomy or just prior to delivery following full-term uncomplicated pregnancies. Table I lists the means, ranges, and standard deviations for the concentrations of amino acids obtained by ion-exchange chromatography of 16 specimens of amniotic fluid. Each specimen contained the following 22 amino acids: taurine, aspartic acid, threonine, serine, glutamine, proline, glutamic acid, citrulline, glycine, alanine, α-aminobutyric acid, valine, cystine, methionine, isoleucine, tyrosine, phenylalanine, ornithine, lysine, histidine, and arginine. In addition, tryptophan, which could not be detected by the ion-exchange chromatographic method employed, was found in each specimen by paper chromatography. The amino acids present in amniotic fluid were the same as those found in samples of maternal vein, umbilical artery, and umbilical vein serum (table II). Comparisons were made in the concentrations of several amino acids among amniotic fluid, maternal serum, umbilical artery and vein serum, and perinatal urine (table II). Taurine was present in considerably greater concentration in amniotic fluid than in maternal serum. This amino acid is also present in large quantities in umbilical artery and vein serum (table II) and is by far the greatest single contributor to the total free amino acid pool in perinatal urine [1]. In contrast, amino acids such as leucine, valine, and threonine, which are present in much smaller amounts in amniotic fluid than in either maternal or umbilical serum, are found in even lower concentrations in perinatal urine [1]. These comparisons suggest that amniotic fluid is derived from at least three sources, maternal blood, fetal blood, and fetal urine, a finding compatible with existing evidence [3, 24, 27, 30]. In order to detect metabolic disease at an early stage of pregnancy, it might be advantageous to obtain amniotic fluid early in pregnancy. Preliminary studies in this laboratory have revealed no significant differences in the concentration of free amino acid in amniotic fluid obtained between the sixth and ninth months of gestation. Speculation:The quantitative study of free amino acids in amniotic fluid could enable certain metabolic disorders or transport defects to be identified in utero, aid in the counseling of parents, and assist in establishing therapy prior to birth. © International Pediatrics Research Foundation, Inc. 1969. All Rights Reserved.