Modulation of vascular tonus by the endothelium in experimental diabetes.

The role of the vascular endothelium in the contractile response of aortas from streptozotocin-induced diabetic rats was investigated using selected agents. Contractile response to KCl was not affected by removal of the endothelium in both diabetic and control groups, but was diminished in the diabetic rats compared to the control rats. Contractile response to clonidine markedly increased after removal of the endothelium in the control group, with the increment being less in the diabetic group. After removal of the endothelium, contractile response to clonidine was poorer in the diabetic group than the control group. Vascular relaxation induced by acetylcholine disappeared when the endothelium was removed in both diabetic and control groups. The degree of reaction to acetylcholine did not significantly differ between the two groups. These results suggest that in diabetic rats, abnormality of the endothelium-dependent vascular relaxation is specific for alpha 2 receptor while that of the vascular smooth muscle reactivity is not receptor-specific.