['High-angiotensin-converting enzyme (ACE)-levels are associated with cardiovascular disease, but little is known about the regulation of its expression.', 'To assess the molecular mechanisms regulating endothelial ACE expression focusing on the role of the AMP-activated protein kinase (AMPK) and miR-143/145.', 'Shear stress decreased ACE expression in cultured endothelial cells, an effect prevented by downregulating AMPKα2 but not AMPKα1. AMPKα2(-/-) mice expressed higher ACE levels than wild-type littermates resulting in impaired hindlimb vasodilatation to the ACE substrate, bradykinin. The latter response was also evident in animals lacking the AMPKα2 subunit only in endothelial cells. In cultured endothelial cells, miR-143/145 levels were increased by shear stress in an AMPKα2-dependent manner, and miR-143/145 overexpression decreased ACE expression. The effect of shear stress was unrelated to an increase in miR-143/145 promoter activity and transcription but could be attributed to post-transcriptional regulation of precursor-miR-143/145 by AMPKα2. The AMPK substrate, p53, can enhance the post-transcriptional processing of several microRNAs, including miR-143/145. We found that shear stress elicited the AMPKα2-dependent phosphorylation of p53 (on Ser15), and that p53 downregulation prevented the shear stress-induced decrease in ACE expression. Streptozotocin-induced diabetes mellitus in mice was studied as a pathophysiological model of altered AMPK activity. Diabetes mellitus increased tissue phosphorylation of the AMPK substrates, p53 and acetyl-coenzyme A carboxylase, changes that correlated with increased miR-143/145 levels and decreased ACE expression.'] Does aMP-activated protein kinase regulate endothelial cell angiotensin-converting enzyme expression via p53 and the post-transcriptional regulation of microRNA-143/145?