Skin collagen metabolism in the streptozotocin-induced diabetic rat. Enhanced catabolism of collagen formed both before and during the diabetic state.

Collagen catabolism has been measured in skins of streptozotocin-induced diabetic rats. For measuring catabolism of collagen synthesized de novo during the diabetic state, we measured the amounts of [3H]hydroxyproline-containing degradation products in skins of diabetic rats, killed 4 h after [3H]proline injection (protocol 1); degradation products were isolated in TCA-soluble fractions of skin homogenates. For measuring catabolism of collagen preexisting before the induction of the diabetic state, we measured the 21-day loss of [3H]hydroxyproline (and hydroxyproline) in entire skins of rats that were streptozotocin-treated after [3H]proline injection (protocol 2). A 2.5-fold increase in the relative amounts of [3H]hydroxyproline-containing degradation products was measured in the TCA-soluble fractions of skins from diabetic rats (protocol 1). These degradation products had a low molecular weight (as evident from their diffusibility), and they were derived from recently synthesized collagen, possibly procollagen (as evident from their high [3H]hydroxyproline specific activity). Furthermore, they were not derived from the degradation of [3H]hydroxyproline-labeled collagen present before induction of the diabetic state (protocol 2). Evidence for this conclusion is as follows: the amounts of [3H]hydroxyproline-containing degradation products in skins of diabetic rats were not greater than that in skins of control rats, despite a 50% resorption of collagen in skins of diabetic rats. Overall, the catabolism of collagen formed de novo during the diabetic state was distinguished from the catabolism of collagen formed before, and both catabolic processes were enhanced in rat skins of streptozotocin-induced diabetic rats.