AJP - Endocrinology and Metabolism, Vol 270, Issue 6 E980-E987, Copyright © 1996 by American Physiological Society
Precursor pool for hepatic protein synthesis in humans: effects of tracer route infusion and dietary proteins
M. Cayol, Y. Boirie, J. Prugnaud, P. Gachon, B. Beaufrere and C. Obled
Centre de Recherche de Nutrition Humaine d'Auvergne, Laboratoire d'Etude du Metabolisme Azote, Saint-Genes-Champanelle, France.
The estimation of the hepatic protein synthesis precursor pool was
investigated through the measurement of very low-density lipoprotein (VLDL)
apolipoprotein (apo)B100 labeling in healthy volunteers. L-[1-13C]leucine
and L-[5,5,5-2H3]leucine were administered intravenously and
intragastrically, respectively. Subjects were continuously fed with
isoenergetic meals providing either 16% protein or no protein. The labeling
of leucine incorporated into VLDL apoB100 (leucine-apoB) was lower than
plasma leucine or alpha-ketoisocaproate (KIC) enrichments with the
intravenous tracer. By contrast, with the oral tracer, leucine-apoB
enrichment was higher than either plasma free leucine or KIC labeling. The
KIC and leucine-apoB enrichments relative to plasma leucine enrichment were
not affected by protein intake. Albumin or fibrinogen synthesis rates were
similar whatever the administration route of the tracer when leucine-apoB
was used to indicate the precursor, which was not the case for plasma
leucine or KIC. The present data suggest that leucine-apoB enrichment
represents a reliable indicator of the hepatic precursor pool for protein
synthesis. The effect of dietary protein on the calculated rates of albumin
and fibrinogen synthesis is also reported in relation to the choice of the
precursor.
