DEVELOPMENTAL-CHANGES OF FREE AMINO-ACID-CONCENTRATIONS IN FETAL FLUIDS OF PIGS

Free amino acid concentrations were determined in amniotic and allanto ic fluids and in fetal and maternal uterine plasma of pigs during gest ation. Glycine and glutamine were the most abundant free amino acids i n maternal uterine arterial and fetal umbilical venous plasma, respect ively. Plasma fetal/maternal ratios were remarkably <1 for glycine, >2 for glutamine and =1 for total free alpha-amino acids. Glutamine was the most abundant free amino acid in amniotic fluid during the first 3 mo of gestation. The concentrations of most amniotic fluid amino acid s progressively decreased with increasing gestational age from 45 to 1 10 d. Glycine was the most predominant amino acid in allantoic fluid o n d 30 of gestation but decreased on d 45 and 60 of gestation. This de crease in allantoic fluid glycine coincided with a marked increase in concentrations of both ornithine and arginine, which accounted for 34- 36% of total free alpha-amino acids in allantoic fluid. Such an abunda nce of ornithine and arginine in allantoic fluid has not been reported for any other biological fluid. On d 90 and 110 of gestation, glycine again became the most abundant amino acid in allantoic fluid, or 47 a nd 29% of total free alpha-amino acids, respectively. Urea concentrati ons in amniotic and allantoic fluids progressively increased during th e second half of pregnancy, indicating enhanced fetal protein metaboli sm. Our results demonstrate the abundance of glutamine in fetal plasma , the unusual abundance of ornithine, arginine and glycine in allantoi c fluid and developmental changes in plasma fetal/maternal ratios of a mino acids. The predominance of these traditionally classified dispens able amino acids in fetal fluids raises important questions regarding their metabolism in placenta and their roles in fetal nutrition and me tabolism.