Coronary Hemodynamics in Diabetic Spontaneously Hypertensive Rats

We investigated the coronary hemodynamics in conscious spontaneously hypertensive (SHR) and Wistar-Kyoto (WKY) rats 4 and 20 weeks after streptozotocin or vehicle injection. The hemodynamic parameters were measured at rest and during maximal coronary vasodilation with dipyridamole. Streptozotocin, 40 or 60 mg/kg, produced moderate or severe diabetes in both strains, but resulted in a mortality of 11.3 or 40.8% in SHR alone. The left and right ventricular weights were decreased with no change in their ratios to body weight in both strains. Severely diabetic SHR and WKY revealed hypotension, bradycardia, an increased cardiac index and decreased total peripheral resistance index at both weeks. Moderately diabetic SHR revealed similar changes except for an unaltered cardiac index. Short-term severely diabetic SHR alone displayed an increased basal bi-ventricular coronary flow (per unit mass). The maximal coronary flow was unaltered in any group by diabetes. The left ventricular transmural flow distribution was also unaltered in any group. However, severe diabetes in SHR diminished a coronary flow reserve (maximal minus basal flow) of the left ventricle at 4 weeks, and that of both ventricles at 20 weeks. Thus, the severity and duration of diabetes had a strain-related influence on the systemic and coronary hemodynamics, with deaths and a reduced coronary flow reserve in SHR alone. The minimal coronary vascular resistance in both ventricles (per unit mass) showed no increase in each group by diabetes, suggesting no overall decrease in functional cross-sectional area of the coronary vasculature.