Age-related changes in the proportion of types I and III collagen.

Previous studies of the age-related changes in interstitial collagens, have suggested that the proportion of type III collagen compared with type I decreases with age. In this study collagen concentration and the proportion of types were measured in heart, lung and skin of male Lewis rats aged between 1 day and 2 years. Collagen concentration, based on hydroxyproline levels, increased in all tissues up until 6 months of age, thereafter it increased in heart and lung, yet decreased in skin. The relative proportions of types I and III collagen were assessed after cyanogen bromide digestion of the tissue and separation of the resultant peptides by sodium dodecyl sulphate polyacrylamide gel electrophoresis. At 2 weeks of age collagen type III represented about one-third of types I and III in all tissues. After this age the proportion of type III increased up to 1 year in both heart (53.9 +/- 1.8%) and lung (47.7 +/- 2.8%), whereas it decreased in skin (18.6 +/- 1.5%). These data show that there are age-related changes in both collagen concentration and the relative proportions of types I and III collagen, but that the direction of these changes differs between tissues.