Whole Body Branched-Chain L-Amino Acid Oxidation in Overnight Fasted Human Subjects

Abstract

Catabolism of the natural branched-chain L-amino acids in overnight fasted healthy volunteers was comparatively studied by performing oral loading tests with 1-¹³C-labelled L-leucine, L-valine, and L-isoleucine (38 μmol x kg (body weight)^?1), respectively. On the basis of the ¹³CO₂ exhalation and the ¹³C-isotope enrichment in the plasma branched-chain compounds, whole body branched-chain L-amino acid oxidation rates were estimated applying a seven compartment model and non-linear regression analysis. Mean computed in vivo oxidation rates were in the order L-leucine ? L-valine > L-isoleucine and amounted to 0.32 ± 0.06, 0.22 ± 0.04, and 0.17 ± 0.05 μmol x (kg body wt.)^?1 x min^?1 (n = 5), respectively. The data are discussed with respect to current estimates of human branched-chain L-amino acid requirements.