Isotopic Studies on Collagen Degradation and the Urine Excretion of Hydroxyproline *

Abstract

Proline-C14 was injected into young rats, and the specific activity of the hydroxyproline-C14 excreted in urine was compared with the specific activity of hydroxyproline-C14 in soluble and insoluble collagen. After 15 hours, the specific activity of urine hydroxypro-line-C14 was comparable to specific activity of hydroxyproline-C14 in soluble collagen. After 4 weeks, the specific activity of urine hydroxy-proline was considerably greater than the specific activity of hydroxy-proline in soluble collagen but somewhat less than the specific activity of hydroxyproline in insoluble collagen. The results suggest that the endogenous hydroxyproline peptides excreted in urine originate from the degradation of both soluble and insoluble collagen. Also, they suggest that relatively large changes in the rate of collagen degradation are required to produce significant changes in urine hydroxyproline.