Recently, it has become evident that elevated levels of plasminogen activator inhibitor-1 (PAI-1) are associated with myocardial infarction and stroke, especially in patients with diabetes. The molecular mechanisms involved in hyperglycemia-induced PAI-1 expression in bovine aortic endothelial cells (BAEC) were investigated. PAI-1 expression in BAEC was significantly increased in accordance with the concentration of glucose in media from 5.7 mM to 23 mM. Stimulation with high glucose (23 mM) significantly increased small GTPase Rho A activation. Pretreatment with a Rho-kinase inhibitor, Y-27632 (1-10 microM), significantly blocked high glucose-induced PAI-1 expression. NF-kappaB activity determined using the luciferase reporter gene assay was significantly enhanced by high glucose, and pretreatment with Y-27632 inhibited high glucose-induced PAI-1 expression at the basal level. An inhibitor of NF-kappaB action, namely parthenolide (0.1 microM), BAY 11-7082 (5 microM) and SN50 (1 microM), significantly blocked high glucose-mediated PAI-1 expression to a level with low glucose (5.7 mM). These data suggested that high glucose-induced PAI-1 expression in endothelial cells is mediated by NF-kappaB activation through the Rho/Rho-kinase pathway. Inhibition of Rho/Rho-kinase signaling might be a novel target for diabetes and metabolic syndrome.