Abstract: AIM:To investigate the effects of pinocembrin on angiotensin II(Ang II)-induced vascular contraction,and to explore its molecular mechanism of actions.METHODS:The isometric vascular tone was measured in rat thoracic aortic rings with denuded endothelium.Phosphorylation level of myosin phosphatase target unit 1(MYPT1),and protein levels of Rho kinase 1(ROCK1,ROKβ or p160ROCK) and angiotensin II type-1 receptor(AT1R) were determined by Western blot analysis.RESULTS:Pinocembrin produced a relaxant effect on endothelium-denuded aortic rings contracted by Ang II(100 nmol·L-1) in a dose-dependent manner.In endothelium-denuded aortic rings stimulated by Ang II,pretreatment with pinocembrin(25 and 100 μmol·L-1) for 20 min significantly attenuated MYPT1 phosphorylation and ROCK1 protein levels.Meanwhile,the protein level of AT1R in response to Ang II was not affected by pinocembrin in rat aortic rings.CONCLUSION:These findings indicate that pinocembrin inhibits vasoconstriction induced by Ang II in rat endothelium-denuded aortic rings,and the mechanism at least in part,is due to the blockade of the RhoA/ROCK pathway.