Increased rat myocardial type VI collagen in diabetes mellitus and hypertension

Diabetic cardiomyopathy, a condition characterized by the accumulation of carbohydrate-containing material surrounding the myocardial small blood vessels, has been studied in alloxan-diabetic normotensive and hypertensive rats. Immunochemical techniques were used to monitor several extracellular matrix constituents present in extracts of cardiac tissue, namely types I, IV and VI collagen, laminin and fibronectin, as well as myosin. These studies have indicated that after induction of diabetes, type VI collagen but none of the other matrix components studied, was significantly increased (from 2.29 +/- 0.04 mg/g in normal to 2.85 +/- 0.18 mg/g in diabetic ventricles, p < 0.01). Hypertension, whether induced by the clipping of one renal artery or genetically determined (spontaneously hypertensive rats), resulted in a similar elevation in type VI collagen (2.71 +/- 0.12 mg/g, p < 0.005 compared to normal rats). In the presence of diabetes plus hypertension the effect was not additive, the type VI collagen level being 2.93 +/- 0.15 (p < 0.001 compared to normal rats). Basement membrane collagen (type IV) in the myocardium appeared to be unaffected by diabetes or hypertension and the myosin contents of the hearts of the four experimental groups were similar. Quantitative determinations indicate that compared to type IV collagen, laminin or fibronectin, type VI collagen represents the major periodic acid-Schiff-reactive extracellular constituent of the rat ventricle. Its preferential increase in the heart in diabetes may provide insight into the molecular mechanisms of the diabetic microvascular disease.