Elevated plasma levels of the vasoconstrictor peptide endothelin-1 (ET-1) are associated with cardiovascular risk factors such as obesity, diabetes and hypertension, in which endothelium-dependent contractions are prominent. Exogenous ET-1 promotes the release of endothelium-derived contracting factors (EDCF), but the role of endogenously produced ET-1 in these processes is unknown. Therefore, mice with tie-1 promoter driven endothelium-restricted heterozygous overexpression of ppET-1 (TET+/-) and WT littermates were kept on standard chow as lean controls or administered a high fat diet for 30 weeks to induce obesity. At sacrifice, fasting glucose levels were significantly elevated in obese animals (8.3±0.3 vs. 5.3±0.2 mmol/l in lean controls, n=6, P<0.001). Isometric tension was measured in aortic and carotid arterial rings in wire myographs. In phenylephrine-contracted aortic rings, endothelium-dependent and −independent relaxations to acetylcholine and sodium nitroprusside, respectively, were unaltered between groups. In carotid arteries, the potency of phenylephrine to evoke contractions was greater in preparations from obese TET+/- mice (pD2 6.71±0.07 vs. lean TET+/- 6.34±0.13, n=5-6, P<0.05), whereas there was no change in the contractile response to the α1-adrenergic agonist by diet-induced obesity in WT littermates. The augmented EDCF responses to acetylcholine of quiescent carotid arterial rings of obese animals were further potentiated by TET+/- (Emax 51.3±1.1% vs. 40.6±1.3% KCl in WT obese, n=6, P<0.001). The production of 6-keto PGF1α − the stable metabolite of prostacyclin − was increased significantly in preparations from obese TET+/- mice (238.4±30.0 vs. 127.0±12.7 pg/mL in obese WT littermates, n=4-6, P<0.05). In the presence of L-NAME, TP receptor activation by U46619 was more effective in obese TET+/- (Emax 151.8±5.4% vs. 126.1±4.7% KCl in WT obese, n=4-6, P<0.05). Overall, TET+/- had no effect on relaxations in obese animals, but contractile responses − EDCF-mediated ones in particular − were facilitated. The present results suggest that this is due to an increased production of vasoconstrictor prostanoids possibly combined with an augmented responsiveness of the underlying vascular smooth muscle.