Importance of liver and kidney for the utilization of glutamine-containing dipeptides in man

The impact of hepatic and renal failure on the metabolism of L-alanyl-L-glutamine (Ala-Gln) and glycyl-L-glutamine (Gly-Gln) was investigated in 11 healthy volunteers, five patients with liver cirrhosis, and six patients with chronic renal failure. The clearance (mL.kg-1.min-1) of Ala-Gln was significantly higher than that of Gly-Gln in all three groups. Renal failure significantly reduced clearances of both Ala-Gln and Gly-Gln (13.27 +/- 0.71 and 3.06 +/- 0.28) when compared with control values (21.68 +/- 1.21 and 7.08 +/- 0.38). Liver failure had no significant influence on the clearances of Ala-Gln and Gly-Gln (22.62 +/- 2.89 and 6.20 +/- 0.88). Liver failure delayed and renal failure almost abolished the increases in plasma concentrations of free amino acid residues after peptide injection. It is concluded that other organs can substitute for the peptide-clearing function of the liver, but not of the kidney. Kidney is the most important organ for the clearance of dipeptides and the release of amino acid residues into circulation. Our data show that clearance rates of both Ala-Gln and Gly-Gln are sufficient to avoid accumulation of either peptide if infused in the presently recommended doses. Both Ala-Gln and Gly-Gln could therefore be used as sources for glutamine in parenteral nutrition even in patients with chronic renal failure.