Increasing evidence suggests that aldosterone is implicated in the pathogenesis of cardiovascular diseases. We examined whether aldosterone contributes to the cyclic stretch (CS)-induced reactive oxygen species (ROS) generation in rat aortic smooth muscle cells (RASMCs). RASMCs were exposed to uniaxial CS and thereafter collected to evaluate the expressions of mRNA or protein relating aldosterone synthesis and the nicotinamide adenine dinucleotide phosphate (NADPH) oxidase activity. CS strength-dependently enhanced NADPH oxidase activity. CS induced cytochrome P450 aldosterone synthase (CYP11B2) and increased aldosterone synthesis but did not influence the levels of 11beta-hydroxysteroid dehydrogenase 2 and mineralocorticoid receptor (MR). This CYP11B2 induction was almost completely suppressed by treatment with an extracellular signal-regulated kinase (ERK) inhibitor, U0126, whereas olmesartan, an angiotensin II (Ang II) receptor blocker (ARB), only partially suppressed CS-induced CYP11B2 expression and ERK phosphorylation. A selective MR antagonist, eplerenone (10 micromol l(-1)), significantly attenuated the CS-induced NADPH oxidase activation even in the presence of ARBs. In conclusion, aldosterone synthesis, which is partially independent of Ang II, may have an important role in CS-stimulated ROS generation in cultured RASMCs. We also suggest the potential benefit of eplerenone in the treatment of cardiovascular diseases.