title: Distribution of protein turnover changes with age in humans as assessed by whole-body magnetic resonance image analysis to quantify tissue volumes.
abstract: We tested the hypothesis that nonmuscle lean tissue mass and its rate of protein catabolism remain constant with aging despite changes in the proportional contribution of these tissues to whole-body protein metabolism. Whole-body protein kinetics, using the 60-h oral [(15) N]glycine method, and muscle and nonmuscle protein catabolism, based on protein kinetic data, urinary N(tau)-methylhistine excretion and lean tissue volumes defined by whole-body magnetic resonance imaging, from eight healthy elderly subjects (5 females and 3 males, mean age 71.5 y) were compared with those of seven young persons (3 females and 4 males, mean age 28 y). There were no significant age or gender effects on rates of protein kinetics per L total lean tissue. There was a lower (P < 0.004) rate of muscle protein catabolism in the elderly (1.8 +/- 0.2 vs. 2.6 +/- 0.1 g. L(-1). d(-1)) and a trend (P = 0.08) for lower muscle volume (19.7 +/- 1.5 vs. 25.0 +/- 2.4 L). This contrasted with intraabdominal lean tissue, where the rate of protein catabolism (13. 8 +/- 0.6 vs. 13.2 +/- 0.9 g. L(-1 ). d(-1)) and volume (7.5 +/- 0.3 vs 8.0 +/- 0.5 L) did not differ between age groups. Thus, the decrease in the contribution by muscle to whole-body protein metabolism with age is associated with an increase from 62 to 74% (P < 0.001) in the contribution by nonmuscle lean tissues. These findings have potential implications for the nutrition of both normal and sick elderly persons.
authors.affiliation: McGill Nutrition and Food Science Centre and. Division of Geriatric Medicine, Royal Victoria Hospital, Montreal, Canada.
authors.forename: J A
authors.initials: JA
authors.lastname: Morais
authors.forename: R
authors.initials: R
authors.lastname: Ross
authors.forename: R
authors.initials: R
authors.lastname: Gougeon
authors.forename: P B
authors.initials: PB
authors.lastname: Pencharz
authors.forename: P J
authors.initials: PJ
authors.lastname: Jones
authors.forename: E B
authors.initials: EB
authors.lastname: Marliss
mesh_terms: D000368:Aged; D000375:Aging / Q000378:metabolism*; D002149:Energy Intake; D004734:Energy Metabolism; D005260:Female; D006728:Hormones / Q000097:blood; D006801:Humans; D007700:Kinetics; D008279:Magnetic Resonance Imaging; D008297:Male; D008762:Methylhistidines / Q000652:urine; D009124:Muscle Proteins / Q000378:metabolism; D011506:Proteins / Q000378:metabolism*; D014018:Tissue Distribution; D014781:Viscera / Q000378:metabolism
chemical_list: D006728:Hormones; D008762:Methylhistidines; D009124:Muscle Proteins; D011506:Proteins; C028118:3-methylhistidine