Experimental diabetes and the lung. II. In vivo connective tissue metabolism

In vivo lung connective tissue and DNA synthesis, following intraperitoneal injection of [14C]proline and [3H]thymidine, were studied in streptozotocin-induced diabetic rats fed ad libitum. Insulin-treated diabetic and normal rats similarly fed, and undernourished rats weight-matched to the untreated diabetics, served as comparison groups. The ratio of unbound [14C]hydroxyproline to total [14C]hydroxyproline in the lung was used to assess connective tissue degradation. Compared to the normal group, the untreated diabetic animals showed similar synthesis of collagen and elastin, reduced synthesis of total protein and DNA, and decreased degradation of connective tissue. When compared with the normal group, the undernourished animals showed diminished synthesis of total protein, collagen, elastin, and DNA, and increased degradation of connective tissue. In comparison to the undernourished group, the untreated diabetic animals indicated increased synthesis of collagen and elastin, and diminished degradation of connective tissue; total protein and DNA syntheses were similar. The insulin-treated diabetic animals showed increased collagen and DNA synthesis. We conclude that experimental diabetes has a profound effect on lung connective tissue metabolism, supporting previous observations of connective tissue abnormalities and morphometric changes. The increase in lung collagen and elastin in diabetes is in part due to reduced breakdown of the connective tissue proteins.