Distribution of protein turnover changes with age in humans as assessed by whole-body magnetic resonance image analysis to quantify tissue volumes
2000
Morais, J.A. | Ross, R. | Gougeon, R. | Pencharz, P.B. | Jones, P.J.H. | Marliss, E.B.
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 [15N] 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 71.5y) were compared with those of seven young persons (3 females and 4 males, mean age 28y). 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.
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