3-hydroxy-3-methylglutaryl Coenzyme A (HMG-CoA) reductase inhibitors (statins) have several non-lipid-lowering actions; however, characteristics of their acute vasodilator effects remain to be elucidated. In this study, acute vasodilator effects of statins were examined in isolated rat blood vessels. After incubation with cerivastatin (1 microM) for 2 hours, acetylcholine-induced endothelium-dependent relaxations were enhanced in the rat aorta. This effect was abolished by a nitric oxide synthase (NOS) inhibitor, L-NNA, and by a PI3 kinase inhibitor, LY294002. Western blot analysis showed that the extent of phosphorylation of Akt, an active form of Akt, was increased by cerivastatin while it was reduced by LY294002, suggesting an involvement of PI3 kinase/Akt-dependent activation of endothelial NOS. At higher concentrations (1-300 microM), both cerivastatin and fluvastatin, but not pravastatin, directly relaxed the blood vessels, regardless of the presence or absence of the endothelium. These relaxations were abolished by KCl and were significantly inhibited by an inhibitor of Kv channel, 4-aminopyridine. These results indicate that multiple mechanisms are involved in the acute vasodilator effects of statins, including augmentation of nitric oxide-mediated endothelium-dependent relaxations through the PI3 kinase/Akt pathway and endothelium-independent relaxations via Kv channel-mediated smooth muscle hyperpolarizations. These acute vasodilator effects of statins may account, at least in part, for their beneficial effects on cardiovascular diseases associated with impaired organ blood flow.