[Betulinic acid ameliorates impairment of endothelium-dependent relaxation induced by oxidative stress in rat aorta].

Objective: To investigate the effect of betulinic acid(BA) on relaxation in isolated rat aortic rings and its antioxidant property on oxidative stress of blood vessels.Methods: Aortic rings were isolated and BA was cumulatively added into organ bath.Isometric tension of endothelium intact or endothelium denuded thoracic aortic rings previously contracted by phenylephrine(PE) was recorded.Then aortic rings were randomly divided into normal control group,BA control group,H2O2 group and BA+ H2O2 group,after being previously contracted by PE,isometric tension of endothelium-dependent relaxation induced by Ach was recorded.Results: Exposure of intact endothelium rings previously contracted by PE to BA at the concentrations of 10-7 mol/L-10-4 mol/L evoked a significant concentration dependent relaxation,which was inhibited by pretreatment with Nω-nitro-L-arginine methyl ester(L-NAME,10-4mol/L),but not by indometacin(10-5mol/L).The pD2 value of BA was 5.24±0.04,and the EC50 value was 2.45×10-6 mol/L.Exposure of endothelium denuded rings previously contracted by PE to BA did not affect the relaxation in isolated aortic rings.ACh induced a dose-dependent relaxation that was weakened by pretreatment with H2O2(5 10-4 mol/L) for 15 min.The EC50 of BA markedly attenuated the inhibition of relaxation induced by H2O2.Conclusions: BA can evoke a concentration-dependent relaxation in aortic rings previously contracted by PE,which may be mediated by NO.And the decrease of endothelium-dependent relaxation in rat aortic rings exposed to H2O2 can be markedly attenuated by BA,which may be mediated by reducing oxidative stress and maintaining the activity of NO in aortic rings.