Trimebutine maleate (TMB), a widely prescribed drug for functional gastrointestinal disorders, has been reported to regulate smooth muscle contractility by modulating multiple ion channel activities in the gastrointestinal tract. However, its action on isolated aorta has not yet been reported. The aim of the present study was to evaluate in vitro vasorelaxant properties and the underlying pharmacological mechanisms of TMB in isolated rat thoracic aortic rings. Vascular activity experiments were performed on thoracic aorta isolated from Sprague-Dawley rats in vitro, including endothelium-intact and endothelium-denuded aortic rings. TMB (10(-10)-10(-5) mol/L) induced relaxation in endothelium-intact aortic rings precontracted by phenylephrine with a potency similar to that of carbachol. TMB-induced relaxation was not altered by glibenclamide and atropine in endothelium-intact aortic rings. However, L-NAME and endothelium denudation significantly reduced but not completely reversed the vasorelaxant effect of TMB. Also, TMB-induced relaxation wasn't affected by diclofenac in endothelium-intact aortic rings. TMB at 10(-5) mol/L significantly reduced the CaCl2-induced contractions in endothelium-intact aortic rings stimulated with KCl, but not stimulated with phenylephrine under Ca(2+)free conditions. Moreover, TMB at 10(-5) mol/L effectively attenuated Bay-K8644-induced contractions in aortic rings. These results suggest that TMB-induced relaxation was mediated by both endothelium-dependent and endothelium-independent manner in isolated rat thoracic aorta. The mechanism of TMB-induced relaxation at low concentrations is partially related to NO- and endothelium-dependent but unrelated to prostanoids formation. However, inhibition of Ca2+ influx through voltage-operated calcium channels and L-type Ca(2+)channel blocking effect appears to be involved in the mechanism of vasorelaxant effect of TMB at high concentrations.