Previous studies reported the ability of raloxifene to acutely relax arterial and venous vessels, but the underlying mechanisms are controversial. Anti-inflammatory effects of the drug have been reported in nonvascular tissues. Therefore, the aim of this study was to investigate the nature of short-and longterm effects of raloxifene on selected aspects of vascular function in rat aorta. Isometric tension changes in response to raloxifene were recorded in aortic rings from ovariectomized female rats that underwent estrogen replacement, whereas long-term experiments were performed in isolated aortic smooth muscle cells (SMCs). Raloxifene (0.1 pM-0.1 M) induced acute vasorelaxation through endothelium-and nitric oxide (NO)-dependent, prostanoid-independent mechanisms. The relaxant response to raloxifene was significantly weaker than that to 17-estradiol and was sensitive to neither the nonselective estrogen receptor antagonist ICI 182,780 [7,4,5,5,sulfinyl]nonyl]estra-1,3,5(10)-triene-3,17-diol] nor a selective estrogen receptor (ER) ␣ antagonist. This rapid vasorelaxant effect was retained in aortic rings from rats treated with 0.1 mg/kg, but not 1 mg/kg, lipopolysaccharide, 4 h before sacrifice. In cultured aortic SMCs, raloxifene treatment (1 nM-1 M) for 24 h reduced inducible NO synthase activation in response to cytokines. This effect was prevented by the selective ER␣ antagonist and was associated with upregulation of ER␣ protein levels, which dropped markedly upon cytokine stimulation. These findings illustrate the relevance of classic ER-dependent pathways to the vascular anti-inflammatory effects rather than to the nongenomic vasorelaxation induced by raloxifene and may assist in the design of novel ER isoform-selective estrogen-receptor modulators targeted to the vascular system.Raloxifene is a selective estrogen-receptor modulator (SERM) approved for use in osteoporosis and has been suggested to be cardioprotective in women at high risk for coronary heart disease (Barrett-Connor et al., 2002), although these results were from post hoc analyses. In fact, the results of the recently completed RUTH (Raloxifene Use for The Heart) study indicate that treatment with raloxifene does not significantly affect the risk of coronary events in postmenopausal women at risk for coronary disease (Barrett-Connor et al., 2006). Thus, a more detailed understanding of raloxifene pharmacological action in vascular tissues is required to better define and unravel potential benefits of treatment with raloxifene and other SERMs.A certain number of studies have examined the direct effects of raloxifene on the vessel wall. It has been consistently shown that the drug acutely relaxes different arterial (Figtree et al., 1999;Tsang et al., 2004;Chan et al., 2005;Leung et al., 2005) and venous (Bracamonte et al., 2002;Chan et al., 2005) vessels from different animal species. A variety of underlying mechanisms, however, can be involved, including enhanced endothelial NO production (Figtree et al., 1999;Bracamonte et al., 200...