Background: Aging, obesity, and diabetes favor vascular dysfunction. Endothelial activation of adenosine monophosphate-activated protein kinase (AMPK) has protective effects in diabetes. Methods: Mice with constitutive endothelial activation of AMPK (CA-AMPK) were given a high fat diet to induce obesity or kept on standard chow as lean controls for up to 2 years. A subset of obese animals was changed to standard chow after 30 weeks of high fat feeding. En-dothelium-dependent and endothelium-independent responses were examined by isometric tension recording. Results and Conclusion: Endothelium-dependent nitric oxide (NO)- and apamin plus charybdotoxin-sensitive relaxations were preserved and similar between aortic or renal arterial preparations of lean and obese CA-AMPK mice and their wild-type littermates. Despite comparable release of vasoconstrictor prostanoids, cyclooxygenase-dependent contractions were enhanced during NO synthase inhibition in carotid arterial rings of obese CA-AMPK mice. Contractions to the α1-adrenoceptor agonist phenylephrine were augmented in renal arteries of obese animals, a genotype-independent phenomenon reversible by weight loss. These data indicate a higher α1-adrenergic reactivity in renal arteries of aged mice with obesity. The current results highlight the potential of weight loss to alleviate vascular dysfunction. However, endothelial activation of the AMPK pathway in obesity may not be sufficient to prevent vascular dysfunction without lifestyle changes.