<p>Raloxifene is a selective estrogen receptor modulator; which plays beneficial roles in the treatment of cardiovascular diseases in women. However, its underlying mechanism remains unclear. In the present study, we investigated whether mitochondria-derived reactive oxygen species (ROS) are involved in raloxifene-induced vasodilation. Results showed that endothelium removal attenuated the vasodilatory effect of raloxifene in rat aortic rings, whereas treatment with the cyclooxygenase inhibitor indomethacin or the estrogen receptor antagonist ICI-182,780 had no significant effect, indicating that neither COX2 nor estrogen receptors are involved. The NADPH oxidase inhibitor apocynin also did not affect raloxifene-induced vasodilation. In contrast, the mitochondrial oxidase inhibitor rotenone and the mitochondrial antioxidant mito-tempo significantly attenuated raloxifene-induced vascular relaxation. In cultured vascular smooth muscle cells (VSMCs), phenylephrine (PE) markedly increased both total intracellular and mitochondrial ROS production, which was significantly inhibited by raloxifene. Accordingly, raloxifene effectively prevented the PE-induced increase in mitochondrial membrane potential, a key component of the mitochondrial electrochemical gradient. Finally, PE induced an acute decrease in uncoupling protein-2 (UCP2) expression, which was significantly prevented by raloxifene. In conclusion, this study demonstrates that raloxifene relaxes the rat aorta, at least in part, by inhibiting mitochondria-derived ROS.</p>