Studies on collagen metabolism in rats. I. Age-related changes in turnover and amino acid composition of the collagen of glomerular basement membrane and tail tendon.

To examine the effect of age on the collagen metabolism of glomerular basement membrane (GBM) and tail tendon, both structures were labeled in vivo by the injection of tracer amounts of radioactive proline. The analyses of the labeled proline and, especially, hydroxyproline revealed that synthesis and degradation are reduced in senescent rats. The calculated turnover rate for GBM-collagen is prolonged by about 40% with increased life span. The reduced catabolism is responsible for the age-related thickening of the GBM. In addition, compositional analyses of isolated GBM and tail tendon were performed. Substantial age changes were observed in the amino acid composition of both structures. The hydroxylated amino acids showed a progressive increase with age, while proline and lysine were found to decline.