Effect of Physical Activity on the Metabolism of Collagen in Aged Mice

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Abstract
Male mice, 12–14 months old, were exercised on a treadmill daily for an average of 4 weeks. Another group of mice were kept in small cages, in which their motility was considerably limited. A third group served as controls under normal laboratory conditions. Tritiated proline was injected intraperitoneally into the mice at the end of the experimental period, where upon die turnover of collagen and other proteins was measured and the contents of hexosamine, hydroxyproline, nitrogen, calcium, potassium and sodium were determined in various tissues. Metabolism of collagen was increased by exercise and decreased by physical inactivity especially in Achilles tendons and long bones. The ratio of hydroxyproline to nitrogen was highest in the Achilles tendons of the exercised mice. The content of hexosamine was increased by exercise in the skin and decreased by physical inactivity in long bones. No significant differences in the concentrations of calcium, potassium and sodium ions in long bones and in the heart and skeletal muscles were observed. The results show that the metabolism of connective tissues is influenced by degree of physical activity even in relatively old animals.