Splanchnic and whole-body leucine kinetics in young and elderly men.
Whole-body and splanchnic protein metabolism were determined in six young (mean age: 22.7 y) and six old (68.2 y) men before and during a standardized meal (41.8 kJ/kg) containing 15.6% protein, by using a combination of intravenous ([13C]leucine) and oral ([2H3]leucine) tracers. In the postabsorptive state, leucine flux and oxidation were similar in both groups when corrected for lean body mass (mean +/- SEM: 1.80 +/- 0.09 compared with 1.79 +/- 0.07 mumol.kg-1.min-1 and 0.55 +/- 0.02 compared with 0.49 +/- 0.04 mumol.kg-1.min-1 for young and old men, respectively, NS). The pattern of response to the meal was also similar in young and old men: increased flux and oxidation, decreased protein breakdown, and unchanged protein synthesis. Splanchnic extraction of dietary leucine was twice as high in elderly men (50 +/- 11% compared with 23 +/- 2%, P < 0.05), was inversely related to plasma leucine concentration (r = -0.771, P < 0.01), and was positively related to body mass index (r = 0.861, P < 0.001). In conclusion, in elderly men there is higher leucine extraction by the gut, liver, or both during feeding, which could lead to a lower peripheral availability of dietary leucine.
Boirie
Y
Y
Laboratoire de Nutrition Humaine, Université Clermont Auvergne, Clermont-Ferrand, France.
Gachon
P
P
Beaufrère
B
B
D000328:Adult; D000368:Aged; D000375:Aging / Q000378:metabolism*; D001823:Body Composition; D004032:Diet; D006801:Humans; D007408:Intestinal Absorption; D007930:Leucine / Q000008:administration & dosage / Q000378:metabolism* / Q000493:pharmacokinetics; D008297:Male; D008643:Mesentery / Q000378:metabolism*; D019518:Postprandial Period; D011506:Proteins / Q000378:metabolism*
D011506:Proteins; D007930:Leucine