FETO‐MATERNAL AMINO ACID METABOLISM

Concentrations of amino acids and related compounds in 111 samples of amniotic fluid obtained by transabdominal amniocentesis, and 89 corresponding maternal plasmas were measured using a Beckman 121 Automatic amino acid analyzer. Thirty‐six amino acids and related compounds were identified in amniotic fluid and/or maternal plasma samples. The concentration of eight amino acids (Phe, Tyr, Val, Leu, He, Lys, Ala and His) decreased towards the end of pregnancy in amniotic fluid but the Phe/Tyr ratio remained constant. Thirteen amino acids (Gly, Ser, Thr, Asp, Asn, Glu, Arg, Met, Pro, Orn, Ans, Tau, Cit) showed no significant change from the 10th to the 40th week of gestation, while ten were present in trace amounts during the same period (lMeh, 3Meh, PSer, PEam, Asp, αAAD, αABA, 1/2CyS, Cyth, Hyp). Our results show that the great variation in lysine concentration between the 10th to the 20th week does not permit fetal age correlation studies. We found that alanine was measurable both in early and late pregnancy with a mean of 0.4 mM. at 10 weeks and 0.1 mM. at 40 weeks. The mean serine, glycine and arginine concentrations showed no statistically significant variation from the 10th to the 40th week of pregnancy. Hydroxyproline was found at a concentration of less than 0.01 mM. in amniotic fluid from the 22nd to the 37th week of pregnancy in our study, but homocarnosine was too low for accurate measurement. Ethanolamine was present at levels of less than 0. 03 mM. in 27 amniotic fluid and 8 maternal plasma samples throughout gestation. There was a marked elevation of amino acid concentrations in amniotic fluid obtained from sacs containing two fetuses. The glycine concentration in one amniotic fluid sample obtained around the 45th day of gestation was 6.1 mM.