Calcium dependence of norepinephrine-induced vascular contraction in experimental diabetes.

The purpose of the study was to examine changes in the contractile responses to norepinephrine of aortas obtained from streptozotocin-induced diabetic rats and to determine the effects of changes in extracellular calcium (Ca++) concentrations on those contractile responses. Aortic rings from rats diabetic 14 to 20 days were supersensitive to norepinephrine in 0.20, 0.40 and 0.80 mM Ca++, but not in 2.50 mM Ca++. Aortas from rats diabetic 28 to 35 days showed a marked increase in contractile force to norepinephrine in 0.20, 0.40, 0.80 and 2.50 mM Ca++. The contractile force was significantly greater in the 28 to 35 day diabetic group as compared to the 14 to 20 day diabetic group. When the Ca++ concentration was changed from 2.50 mM to 0.20 and 0.40 mM, the aortas from the 28 to 35 days diabetic rats showed a significant decrease in developed tension. These data indicate that vascular reactivity is altered in experimental diabetes, and this alteration is related to the duration of the diabetic state and to the extracellular Ca++ concentration.