Although the deterimental effects of diabetes mellitus on the kidney and eye have long been recognized, it has only recently become clear that this disease causes functional changes in the heart which are distinct from coronary atherosclerosis. This condition, termed diabetic cardiomyopathy, is characterized by the accumulation of periodic acid-Schiff reactive material around muscle fibers and small blood vessels; the nature and source of the carbohydrate-rich interstitial deposits are not yet known although it has been observed in experimentally induced diabetes that hypertension accelerates their formation. To obtain information about this condition an investigation of the effect of diabetes on the constituents of the myocardial cell membranes and extracellular materix has been initiated during the past grant period and the model used has been the alloxan-diabetic rat with or without hypertension. Radiolabeling experiments and polyacrylamide gel electrophoresis have permitted identification of several matrix glycoproteins (Mr = 200K, 150K, 100K and 70K) of which the major PAS-reactive component is the 150K component (HMGP). Antibodies produced in rabbits against HMGP react with the 150K band but more effectively with the 200K component. Upon treatment of heart sections from diabetic-hypertensive rats with the anti-HMGP antiserum, followed by FITC-labeled anti rabbit IgG, fluorescent areas are seen adjacent to small blood vessels; these correspond to PAS- reactive deposits in the blood vessel walls which we find to be increased in the heart from the diabetic-hypertensive rat. Evaluation of the levels of a number of matrix components in normal and diabetic hearts by immunoblotting using antisera againts the 150K and 200K components as well as Types I and IV collagen indicated that only the 200K molecule was increased in diabetes (P less than 0.05). Both the 200K and 150K molecules are being purified to permit a determination of the nature of their saccharide units and core proteins and to see if they bear any relationship to known collagen types. Using the antiserum prepared against HMGP, studies in culture of separated myocardial cell types will be carried out to determine which cells synthesize these PAS-reactive molecules and what stimuli in the diabetic milieu may be responsible for inducing the increased formation of the 200K component. Studies will also be continued on the major myocardial proteoglycan (Mr = 85,000) to determine its structure and metabolism in the diabetic heart and its relevance to the extracellular matrix changes of diabetes.
