| Background: Ixeris sonchifolia (Bge.) Hance (I. sonchifolia Hance) are recorded in The Traditional Chinese Medicine of Mongolia. According to ethnobotancical data collected in China, I. sonchifolia (Bge.) Hance's nature and flavour is bitter and cold. I. sonchifolia (Bge.) Hance has the characteristics of clearing heat and removing toxicity and discharging pus,cooling blood,promoting blood circulation,and it can be treat appendicitis,enteritis,dysentery,furuncle,carbuncle,hematemesis and bleeding from five aperture or subcutaneous tissue . Recently, it has received more attention that the fact that I. sonchifolia (Bge.) Hance possessed to inhibit oxy radical,treat injure of ischemia/reperfusion injury,relax blood vessel,increase blood flow,improve microcirculation,remain calm,relieve pain and relieve spasm of smooth muscle. A great deal of studies demonstrated that I. sonchifolia (Bge.) Hance was beneficial on the process of pectoris angina,celebral infarction, et al.However,the mechanism(s) of action has not been fully elucidated.Aims:The objective of the present study were to examine the effect of I. sonchifolia (Bge.) Hance on relaxation or contraction of isolated rat aortic rings and to elucidate the underlying mechanism(s).Methods: Preparation of thoracic aortic rings from Sprague-Dawley rats, rats were euthanized by decapitation using small animal guillotine. The thoracic aorta was immediately isolated and immersed in oxygenated K-H solution 4 ℃ .Then the adherent connective tissue was cleaned and blood vessel was cut into 3-4 mm rings, with the special care of avoiding damage of endothelium. In some preparations, endothelium was mechanically removed by gently rubbing the lumen. The rings were mounted horizontally between two stirrups in organ bath filled with 5mL K-H solution at 37 ℃, ventilated continuously with 95% O2 and 5% CO2. The isometric tension was recorded with a force transducer and Medlab v 5.0 recording system. Rings were equilibrated for 60 min at 2.0 g resting tension, and then challenged with potassium chloride (KCl) (6.0 × 10-2M) at least 3 times until a reproducible maximal contractile response was obtained. After a further equilibration period of 30 min, the integrity of the endothelium was assessed in all preparations by determining the ability of Acetylcholine (ACh) (1.0×10-5 M) to induce more than 80% relaxation of rings pre-contracted with phenylephrine(PE) (1.0 × 10-6 M). The endothelium was considered to be removed when there was less than 10% relaxation response to ACh. I. sonchifolia (Bge.) Hance 0.01～300g ? L-1 was cumulatively added into organ bath. Isometric tension of endothelium-intact or endothelium-denuded thoracic aortic rings in basal tension ,preconstricted by PE or KCl,respectively,was recorded,and calculated as the percentage of the maximal tention induced by PE or KCl. All results are expressed as means ± SD.Statistical analysis was performed with t test or AVOVA followed by Newman-Keuls test .Differences were accepted as statistically significantat P values < 0.05.Results: Cumulative administration of I. sonchifolia (Bge.) Hance 0.01～300 g ? L-1 did not affect the vasomotion of aortic rings with endothelium or without endothelium in basal tension. Exposure of intact endothelium rings preconstricted by PE to I. sonchifolia (Bge.) Hance at low concentration (0.03～10 g ? L-1) induced a significant concentration-dependent relaxation,which was inhibited by preincubation with Nω-nitro-L-arginine methyl ester or methylene blue or indomethacin. Exposure of intact endothelium rings preconstricted by KCl to I. sonchifolia (Bge.) Hance at low concentration (0.01 ～10 g ? L-1) did not affect the vasomotion. Exposure of intact endothelium rings preconstricted by PE or KCl to I. sonchifolia (Bge.) Hance at high concentration (20～160 g ? L-1) induced a significant constriction , which was inhibited by preincubation with captopril, but which was not inhibited by phosphoramidon or indomethacin. Exposure of endothelium-denuded rings preconstricted by PE or KCl did not effect the vasomotor .Conclution: I. sonchifolia (Bge.) Hance has endothelium-dependent diphasic effects of relaxation and contraction on aortic rings.The effect of relaxation may be mediated by the NO-guanylyl cyclase pathway and cyclooxygenase pathway at low concentration,while the effect of contraction may be enhance angiotensin converting enzyme activity and promote endothelium to synthesize angiotensin II at high concentration. It has no relationship to endothelin or thromboxane A2.
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