Age-related changes in rates of protein synthesis and degradation in rat tissues

It has been hypothesised that a diminished capacity for protein synthesis and degradation underlies a decreased adaptability to environmental stimuli seen during ageing. In this study rates of total protein synthesis and degradation were examined in rats between 1 and 24 months of age. Synthesis rates in heart, lung, skeletal muscle and skin were based on the uptake of [14C]proline into protein when administered with a flooding dose of unlabelled proline. Degradation rates were derived from the difference between protein deposition and synthesis rates. Total protein synthesis rates in 1-month-old animals ranged from 20.4 +/- 1.3% per day (S.E.M.) in skeletal muscle to 39.6 +/- 1.3% per day in lung. In heart, lung and skeletal muscle, synthesis rates decreased 2-fold during the first 6 months of life, while over the same period in skin they decreased 6-fold. Degradation accounted for the bulk of protein synthesised at all ages, and the age-related changes for rates for breakdown closely mirrored those for synthesis. These results, do not support the hypothesis that a general decrease in protein turnover underlies a diminished adaptability in older animals.