Effects of the superoxide dismutase mimetic tempol on impaired endothelium-dependent and endothelium-independent relaxations in type II diabetic rats

Endothelium-derived hyperpolarizing factor (EDHF)-mediated hyperpolarization and relaxation, and endothelium-independent relaxations to the nitric oxide donor sodium nitroprusside and the adenosine 5′-triphosphate (ATP)-sensitive K⁺-channel opener levcromakalim were both impaired in mesenteric arteries of type II diabetic Goto-Kakizaki rats. The treatment with the superoxide dismutase mimetic tempol or its combination with the angiotensin II type 1 receptor blocker candesartan failed to improve EDHF-mediated responses, although both treatments partially improved endothelium-independent relaxations. These findings suggest that increased oxidative stress may in part account for the impaired endothelium-independent relaxations in diabetes, while it does not play a major role in the impaired EDHF-mediated responses.