Increased leucine turnover in women during the third trimester of uncomplicated pregnancy.

Abstract Plasma amino acid concentrations decrease in pregnancy despite increased requirements for both maternal and fetal protein accretion. There are few published data on changes in amino acid turnover in pregnancy. The aim of this study is to test the hypotheses that (1) whole body nonoxidative leucine disposal (NOLD) is higher and (2) whole body oxidative leucine disposal (OLD) is lower in the third trimester of pregnancy than in the nonpregnant state. After an overnight fast 8 pregnant women between 33 and 35 weeks gestation had a primed infusion of labeled [1- 13 C] leucine and a prime dose of NaH 13 CO 3 . Carbon dioxide production was measured using indirect calorimetry. Gas chromatography-mass spectrometry was used to determine 13 CO 2 enrichment of expired air and oxidative and nonoxidative leucine turnover by measuring 13 C keto-isocaproate plasma enrichment, which reflects intracellular leucine enrichment. Women acted as their own controls after the puerperium. Whole body leucine turnover expressed per unit body weight was increased in pregnancy (median [interquartile range or IQR]: pregnant = 103.1 [14.9] v nonpregnant = 90.1 [10.9] μmol/kg/h). The mean (±SD) of the differences was 11.4 ± 5.6 μmol/kg/h, P = .0006. NOLD was increased in pregnancy (pregnant = 86.8 [10.1] v nonpregnant = 73.3 [9.5] μmol/kg/h). The mean (±SD) of the differences was 10.6 ± 5.4 μmol/kg/h, P = .0008. OLD was not significantly altered in pregnancy (pregnant = 17.3 [4.5] v nonpregnant = 15.91 [2.4] μmol/kg/h). The mean (±SD) of the differences was 0.84 ± 1.94 μmol/kg/h, P = .26. In conclusion, women have significantly higher NOLD in the third trimester of pregnancy than when not pregnant but there are no significant changes in OLD.