Age-related changes in rat muscle collagen.

Age-related studies of collagen in slow, fast and cardiac muscle of the rat indicate that different fractions of collagen as well as total collagen content vary with age and type of muscle. The total collagen level increases by 30% in slow, 40% in fast and 50% in cardiac muscle as age advances from 5 to 25 months. Collagen of the muscles of old animals is less susceptible to the collagen-degrading enzyme when compared to the young, and the activity of the enzyme decreases significantly with age. The decrease in (1) the solubility of collagen; (2) the amount of hydroxyproline released at 65 degrees C, and (3) the increase in the resistance of collagen to the degrading enzyme seen with aging, indicates that the stability of collagen increases in these muscles with aging.