Extensive Degradation of Recently Synthesized Collagen in Gingiva of Normal and Streptozotocin-induced Diabetic Rats

The degradation of recently synthesized collagen (probably procollagen) in rat incisor gingiva was three times greater than that in skin. Concomitantly, the formation of undegraded (intact) collagen molecules in gingiva was slower than that in skin. This high basal rate of degradation in gingiva was just slightly increased in streptozotocin-induced diabetic rats, whereas the low basal rate in skin was dramatically increased by the diabetic state. The degradation of recently synthesized collagen was measured by the relative amounts(%) of [3H]hydroxyproline-containing material in the TCA-soluble fraction of a tissue, compared with the total amount (TCA-soluble + TCA-insoluble) of [3H]hydroxyproline-containing material. Separation of the TCA fractions allowed the formation of collagen degradation products (TCA-soluble) to be viewed separately from the formation of undegraded collagen molecules (TCA-insoluble). The [3H]hydroxyproline-containing material in the TCA-soluble fraction was greatest in amount and in specific activity, 30 min after [ 3H] proline injection, supporting the origin of this material as being procollagen. At this time period, the relative amounts of TCA-soluble [ 3H] hydroxyproline-containing material were 40.3% (gingiva) and 12.7% (skin). For diabetic rats, the values were 55% and 48.8%, respectively. For the [3H] hydroxyproline-containing material in the TCA-insoluble fraction, at 30 min, the specific activity of [3H] hydroxyproline was 4.3 for gingiva and 7.4 for skin. At all other time periods, the values were also greater for skin than for gingiva, making it unlikely that the formation of intact collagen molecules occurred faster in gingiva than in skin. Overall, the prevailing concept of rapid collagen turnover in oral tissues seems applicable to procollagen, but not to collagen of rat incisor gingiva.