Correlation between histopathological changes and mechanical dysfunction in diabetic rat hearts

Recent clinical and experimental studies have suggested that diabetic patients may develop myocardial dysfunction in the absence of coronary heart disease and hypertension. In this study, the correlation between histopathological changes and myocardial dysfunction was studied in experimental diabetic rat hearts. Male Wistar rats were made diabetic at 9 weeks of age with a single intravenous injection of streptozotocin 50 mg/kg. The diabetic rats were studied along with age-matched control and insulin-treated rats at 4, 8, 12 and 24 weeks after the induction of diabetes to investigate isolated papillary muscle contraction and the histopathological picture simultaneously. In the isometric contractions, resting and developed tensions were similar. Time to peak tension and time to 1/2 relaxation were prolonged and the peak rate of tension rise and tension fall was depressed. On histological examination of left ventricular walls, diameters of myocytes were similar at all disease durations. Interstitial fibrosis and disarrangement of myocytes after 12 weeks were slightly increased in the diabetic hearts. Mechanical parameters did not worsen in parallel with the duration of diabetes and histological changes, but correlated with the blood glucose level. These data suggest that short-term mechanical defects in the experimental diabetic rat heart result from the metabolic disorder itself, with histopathological changes occurring later.