[Tracer kinetics of amino acid]

In vivo turnover of an amino acid can be determined either by analysing the disappearance curve of a labeled amino acid after a single dose of labeled amino acid or by measuring the dilution of a continuously infused labeled amino acid at a steady state. From ethical concerns stable isotopically labeled amino acids, such as 13C-leucine and 15N-glycine have been routinely used to study amino acid kinetics with subsequent estimation of whole body protein turnover. Recently, instead of these 2 methods, pulse labeling by taking a single oral dose of labeled amino acid is more practical for the study of whole body protein turnover. We observed plasma 15N-glycine kinetics and urinary 15N excretion by a single oral dose of 15N-glycine simultaneously in healthy subjects and cirrhosis patients, and the results are discussed.