In vitro vasorelaxation mechanisms of Isoapiole extracted from Lemonfragrant Angelica Root on rat thoracic aorta

Ethnopharmcological relevanceLemonfragrant Angelica (Ostericum citriodorum (Hance) C. Q. Yuan & Shan) is a traditional Chinese herb for treatment of angina pectoris, stomach pain and abdominal pain. However, its active components and mechanisms of action were not well understood.Aims of the studyIn this study, we investigated whether the isoapiole extracted from Lemonfragrant Angelica Root (LAR) could directly stimulate the production of nitric oxide (NO) in vascular endothelial cells (VECs) and lead to the vascular relaxationMaterials and methodsVascular activity experiments were performed in aortic rings isolated from Wistar rats using standard muscle bath procedures. Isoapiole was added with different concentrations (0.75, 2.5, 5 μg/mL), and vessel relaxation of rat aortic rings pre-contracted with norepinephrine (NE) or potassium chloride was recorded. NO release from aortic rings exposed to isoapiole (5 μg/mL) was measured by Griess method. The endothelial nitric oxide synthase (eNOS) expression in primary human umbilical vein endothelial cells (HUVECs) incubated with isoapiole was determined using Western blot and microplate reader assay. Classical receptor antagonists, channel and enzymatic inhibitors were used to check the mechanisms involved.ResultsIsoapiole (0.75, 2.5, 5 μg/mL) inhibited norepinephrine-induced contraction in endothelium-intact rat aortic rings. However, a very weak relaxation of aortic rings was obtained in endothelium-denuded preparations. Isoapiole (0.75, 2.5, 5 μg/mL) did not have vascular relaxative effect on neither endothelium-intact nor endothelium-denuded aortas pre-contracted with KCl (60 mmol/L). The vasorelaxation effect of isoapiole on rat aortic rings was attenuated by the eNOS inhibitor, NG-nitro-L-arginine methyl ester (L-NAME). This result suggested that suggested that the isoapiole action was at least partially mediated by promoting eNOS expression. It was further found that isoapiole (5 μg/mL) increased NO production in isolated rat thoracic aorta rings. Isoapiole increased eNOS expression leading to NO production in HUVECs.ConclusionIsoapiole stimulates NO production in the endothelium, leading to vascular dilatation.

Original picture from: http://home.sysu.edu.cn/wjf/5/course/c541.htm Endothelial cells (ECs) synthesize NO by the action of eNOS. NO diffuses into the vascular smooth muscle cells (VSMCs) and activates the soluble guanylate cyclase enzyme, and this leads to the generation of cGMP, and leads to the relaxation of blood vessel. Isoapiole induced the rapid activation of NOS (eNOS in paper) expression, leading to blood vessel relaxation therewith NO production increasing.Figure optionsDownload high-quality image (263 K)Download as PowerPoint slide