Transient receptor potential vanilliod 1 (TRPV1) channels have recently been postulated to play a role in the vascular complications/consequences associated with diabetes despite the fact that the mechanisms through which TRPV1 regulates vascular function are not fully known. Accordingly, our goal was to define the mechanisms by which TRPV1 channels modulate vascular function and contribute to vascular dysfunction in diabetes. We subjected mice lacking TRPV1 [TRPV1 (Ϫ/ Ϫ)], db/db, and control C57BLKS/J mice to in vivo infusion of the TRPV1 agonist capsaicin or the ␣-adrenergic agonist phenylephrine (PE) to examine the integrated circulatory actions of TRPV1. Capsaicin (1, 10, 20, and 100 g/kg) dose dependently increased MAP in control mice (5.7 Ϯ 1.6, 11.7 Ϯ 2.1, 25.4 Ϯ 3.4, and 51.6 Ϯ 3.9%), which was attenuated in db/db mice (3.4 Ϯ 2.1, 3.9 Ϯ 2.1, 7.0 Ϯ 3.3, and 17.9 Ϯ 6.2%). TRPV1(Ϫ/Ϫ) mice exhibited no changes in MAP in response to capsaicin, suggesting the actions of this agonist are specific to TRPV1 activation. Immunoblot analysis revealed decreased aortic TRPV1 protein expression in db/db compared with control mice. Capsaicin-induced responses were recorded following inhibition of endothelin A and B receptors (ET A /ETB). Inhibition of ET A receptors abolished the capsaicin-mediated increases in MAP. Combined antagonism of ET A and ETB receptors did not further inhibit the capsaicin response. Cultured endothelial cell exposure to capsaicin increased endothelin production as shown by an endothelin ELISA assay, which was attenuated by inhibition of TRPV1 or endothelin-converting enzyme. TRPV1 channels contribute to the regulation of vascular reactivity and MAP via production of endothelin and subsequent activation of vascular ET A receptors. Impairment of TRPV1 channel function may contribute to vascular dysfunction in diabetes.transient receptor potential vanilloid 1 channel; capsaicin THE TRANSIENT RECEPTOR POTENTIAL VANILLOID (TRPV) channels represent one of the known TRP subfamilies and are characteristically gated by chemical and physical stimuli including acid, heat, ethanol, and vanilloid compounds, such as capsaicin, the active component from chili peppers (5). The TRPV1 channel, a ligand-gated nonselective cation channel, regulates intracellular Ca 2ϩ -homeostasis. TRPV1 channels, primarily expressed in sensory nerves innervating the heart and blood vessels, are known to function as molecular integrators of multiple stimuli, including protons, noxious heat, endovanilloids, as well as numerous endogenous inflammatory mediators (5). Previous studies (1,4,6,8,23,27,46,49,50) from our laboratory and others have revealed the presence of TRP channel expression in vascular smooth muscle cells and endothelial cells, suggesting that these channels may regulate and/or modulate vascular functions. Consistent with these observations, in previous studies from our laboratory (4), we found that TRPV1 channels are involved in the regulation of coronary tone, largely through Ca 2ϩ entry via endothelial TRPV1 chann...