Objective: To investigate the effect of asiaticoside on blood pressure and relaxation of thoracic aorta in rats and explore the underlying mechanism.
Methods: SD rats treated with 50 and 100 mg/kg asiaticoside by daily gavage for 2 weeks were monitored for systolic blood pressure changes, and histological changes of the thoracic aorta were evaluated using HE staining. In isolated rat endothelium-intact and endothelium-denuded thoracic aorta rings, the effects of asiaticoside on relaxation of the aortic rings were tested at baseline and following norepinephrine (NE)- and KCl-induced constriction. The vascular relaxation effect of asiaticoside was further observed in NE-stimulated endothelium-intact rat aortic rings pretreated with L-nitroarginine methyl ester, indomethacin, zinc protoporphyrin Ⅸ, tetraethyl ammonium chloride, glibenclamide, barium chloride, Iberiotoxin, 4-aminopyridine, or TASK-1-IN-1. The aortic rings were treated with KCl and NE followed by increasing concentrations of CaCl2 to investigate the effect of asiaticoside on vasoconstriction induced by external calcium influx and internal calcium release.
Results: Asiaticoside at 50 and 100 mg/kg significantly lowered systolic blood pressure in rats without affecting the thoracic aorta histomorphology. While not obviously affecting resting aortic rings with intact endothelium, asiaticoside at 100 mg/kg induced significant relaxation of the rings constricted by KCl and NE, but its effects differed between endothelium-intact and endothelium-denuded rings. In endothelium-intact aortic rings pretreated with indomethacin, ZnPP Ⅸ, barium chloride, glyburide, TASK-1-IN-1 and 4-aminopyridine, asiaticoside did not produce significant effect on NE-induced vasoconstriction, and tetraethylammonium, Iberiotoxin and L-nitroarginine methyl ester all inhibited the relaxation effect of asiaticoside. In KCland NE-treated rings, asiaticoside obviously inhibited CaCl2-induced vascular contraction.
Conclusion: Asiaticoside induces thoracic aorta relaxation by mediating high-conductance calcium-activated potassium channel opening, promoting nitric oxide release from endothelial cells and regulating Ca2+ influx and outflow, thereby reducing systolic blood pressure in rats.
目的: 研究积雪草苷降血压和对大鼠胸主动脉的舒张作用及机制。
方法: 将SD大鼠分为正常对照组、积雪草苷低剂量组(50 mg/kg)和积雪草苷高剂量组(100 mg/kg)，6只/组，治疗组每日予以积雪草苷对应剂量灌胃处理，分别在给药前1 d、给药第8天和给药第15天测大鼠尾动脉收缩压，HE染色评估大鼠胸主动脉血管组织形态变化。取大鼠胸主动脉血管环，以舒张血管百分比为指标，考察不同浓度积雪草苷对基础状态血管环、去甲肾上腺素(NE，1×10-6 mol/L)及氯化钾(KCl，60 mmol/L)收缩的内皮保留或去内皮胸主动脉血管环的舒张作用；对内皮保留的血管环，分别以左旋硝基精氨酸甲酯(0.1 mmol/L)、吲哚美辛(1×10-5 mol/L)、锌原卟啉Ⅸ(10 μmol/L)和6种钾离子通道阻滞剂：四乙基氯化铵(5 mmol/L)、格列苯脲(1×10-5 mol/L)、氯化钡(0.1 mmol/L)、Iberiotoxin(0.1 μmol/L)、4-氨基吡啶(0.1 mmol/L)、TASK-1-IN-1(1×10-5 mol/L)预孵育血管环，加NE(1×10-6 mol/L)预收缩，考察不同浓度积雪草苷对血管环的舒张作用；以血管收缩百分率为指标，在无钙条件下，分别以KCl (60 mmol/L)、NE(1×10-6 mol/L)刺激血管，再分别累积加入CaCl2(0.1、0.3、1、3、10 mmol/L)，考察积雪草苷对CaCl2导致外钙内流及内钙释放引起的血管收缩的影响。
结果: 与正常对照组相比，积雪草苷50和100 mg/kg组大鼠收缩压降低(P < 0.05)，胸主动脉组织形态未见明显改变。累积浓度积雪草苷对静息状态下的胸主动脉内皮保留的血管环无明显收缩和舒张作用。积雪草苷(30、50、100 μmol/L)对KCl和NE提前收缩的血管环具有舒张作用(P < 0.01)，积雪草苷100 mg/kg浓度组对去内皮和内皮保留的NE预收缩的血管舒张有差异(P < 0.05)。经吲哚美辛、ZnPP Ⅸ、氯化钡、格列本脲、TASK-1-IN-1和4-氨基吡啶预孵育后，不同浓度的积雪草苷对经NE预收缩的血管环无显著影响(P>0.05)，四乙基铵、Iberiotoxin和左旋硝基精氨酸甲酯均可抑制积雪草苷对NE预收缩血管环的舒张作用(P < 0.05)。在无钙条件下，血管环经KCl、NE作用，积雪草苷能抑制CaCl2导致外钙内流、内钙释放引起的收缩(P < 0.01)。
结论: 积雪草苷通过介导高电导钙激活性钾离子通道开放、促进内皮细胞一氧化氮释放并调节钙离子内外流诱导大鼠胸主动脉舒张，从而降低大鼠收缩压。
Keywords: asiaticoside; calcium channel; lowering blood pressure; potassium channel; vasodilation of blood vessels.