AJP - Endocrinology and Metabolism, Vol 267, Issue 6 E907-E914, Copyright © 1994 by American Physiological Society
Leucine kinetics are different during feeding with whole protein or oligopeptides
C. Collin-Vidal, M. Cayol, C. Obled, F. Ziegler, G. Bommelaer and B. Beaufrere
Centre de Recherche en Nutrition Humaine d'Auvergne, Universite Clermont Auvergne, Clermont-Ferrand, France.
To determine if the molecular form of nitrogen intake affects protein
metabolism during feeding, 12 normal volunteers received, by continuous
nasogastric infusion, a protein or a peptide-based diet. Leucine kinetics
(oral [13C]leucine and intravenous [2H3]leucine) were measured during the
following three consecutive periods: first carbohydrates and lipids alone,
then with either whole casein or oligopeptides in a randomized crossover
design, with these two latter periods being isonitrogenous, isocaloric, and
of identical amino acid compositions. Leucine concentration, turnover,
oxidation, and nonoxidative disposal increased during nitrogen
administration (all P < 0.01) and were higher with oligopeptides than
with casein (242 +/- 44 vs. 188 +/- 31 mumol/l; 2.75 +/- 0.45 vs. 2.23 +/-
0.31; 1.14 +/- 0.19 vs. 0.82 +/- 0.22 mumol.kg-1.min-1, all P < 0.001;
1.64 +/- 0.32 vs. 1.44 +/- 0.33 mumol.kg-1.min-1, P < 0.05,
respectively). Endogenous leucine production was less inhibited by
oligopeptides than by casein (0.82 +/- 0.41 vs. 0.38 +/- 0.31
mumol.kg-1.min-1, P < 0.001), whereas splanchnic extractions were
similar. Finally, leucine balance was more positive with casein than with
oligopeptides (P < 0.001). In conclusion, the response of leucine
kinetics to feeding is modified by the molecular form of nitrogen intake,
with the oligopeptides inducing a higher oxidation and protein synthesis
and a lesser inhibition of protein breakdown.
