OBJECTIVE The extracts of the Apocynum venetumleaves(AVLE),also known as Luobuma,is an antihypertensive medicinal herb used widely in TCM.AVLE has been reported to exert antihypertensive action by dilating the blood v...OBJECTIVE The extracts of the Apocynum venetumleaves(AVLE),also known as Luobuma,is an antihypertensive medicinal herb used widely in TCM.AVLE has been reported to exert antihypertensive action by dilating the blood vessels in an endothelium-dependent and concentration-dependent manner with optimal effect seen at as low as 10μg·mL.The present study seeks to further evaluate the free radical scavenging actions and cellular mechanism underlying the nitric oxide(NO)-releasing property of AVLE in rat aorta and human umbilical vein endothelial cells(HUVECs).METHODS Endothelium-dependent relaxation induced by AVLE was assessed in organ chambers in the presence or absence of NG-nitro-L-arginine(LNAME,100μmol·L-1),endothelial NO synthase inhibitor(eNOS),ODQ(1μmol·L-1),soluble guanylyl cyclase inhibitor,polyethyleneglycol catalase(PP2,20μmol·L-1),inhibitor of Src kinase and wortmannin(30nmol·L-1),and LY294002(20μmol·L-1),PI3-Kinase inhibitor.Total nitrite and nitrate(NOx)level were measured by Greiss reagent.The cellular effects of AVLE was tested in HUVECs at different concentration with or without inhibitors.The phosphorylation level of Akt and eNOS were assessed by Western blotting.RESULTS In the rat aorta,AVLE(0.3-10μg·mL-1)dose-dependently inhibited the contraction to phenylephrine(1μmol·L-1)and significantly suppressed theβ-NADPH-induced generation of superoxide anion(SOA).Removal of endothelium,treatment with L-NAME or ODQ prevented the vasorelaxant effects of AVLE.Similarly,pre-treatment with PP2,wortmannin and LY294002 reduced the vasorelaxant effects of AVLE.AVLE significantly increased of total NOx level in rat aorta compared to control.It also caused phosphorylation of AKT and eNOS in cultured HUVECs in a dose-dependent manner and which were markedly suppressed by PP2,wortmannin and LY294002.CONCLUSION The present results suggest that the vasorelaxant effect of AVLE is due to its dual ability of releasing NO and protecting it from the scavenging actions of the SOA.Furthermore,AVLE causes endothelium-dependent NO mediated relaxations of rat aortas through Src/PI3K/Akt dependent NO signalling pathway.展开更多
文摘OBJECTIVE The extracts of the Apocynum venetumleaves(AVLE),also known as Luobuma,is an antihypertensive medicinal herb used widely in TCM.AVLE has been reported to exert antihypertensive action by dilating the blood vessels in an endothelium-dependent and concentration-dependent manner with optimal effect seen at as low as 10μg·mL.The present study seeks to further evaluate the free radical scavenging actions and cellular mechanism underlying the nitric oxide(NO)-releasing property of AVLE in rat aorta and human umbilical vein endothelial cells(HUVECs).METHODS Endothelium-dependent relaxation induced by AVLE was assessed in organ chambers in the presence or absence of NG-nitro-L-arginine(LNAME,100μmol·L-1),endothelial NO synthase inhibitor(eNOS),ODQ(1μmol·L-1),soluble guanylyl cyclase inhibitor,polyethyleneglycol catalase(PP2,20μmol·L-1),inhibitor of Src kinase and wortmannin(30nmol·L-1),and LY294002(20μmol·L-1),PI3-Kinase inhibitor.Total nitrite and nitrate(NOx)level were measured by Greiss reagent.The cellular effects of AVLE was tested in HUVECs at different concentration with or without inhibitors.The phosphorylation level of Akt and eNOS were assessed by Western blotting.RESULTS In the rat aorta,AVLE(0.3-10μg·mL-1)dose-dependently inhibited the contraction to phenylephrine(1μmol·L-1)and significantly suppressed theβ-NADPH-induced generation of superoxide anion(SOA).Removal of endothelium,treatment with L-NAME or ODQ prevented the vasorelaxant effects of AVLE.Similarly,pre-treatment with PP2,wortmannin and LY294002 reduced the vasorelaxant effects of AVLE.AVLE significantly increased of total NOx level in rat aorta compared to control.It also caused phosphorylation of AKT and eNOS in cultured HUVECs in a dose-dependent manner and which were markedly suppressed by PP2,wortmannin and LY294002.CONCLUSION The present results suggest that the vasorelaxant effect of AVLE is due to its dual ability of releasing NO and protecting it from the scavenging actions of the SOA.Furthermore,AVLE causes endothelium-dependent NO mediated relaxations of rat aortas through Src/PI3K/Akt dependent NO signalling pathway.
