Mechanisms of Vasorelaxation Induced by Hexahydrocurcuminin Isolated Rat Thoracic Aorta

This study was designed to examine the vasorelaxant effects of hexahydrocurcumin (HHC), one of the major natural metabolites of curcumin from Curcuma longa, on rat isolated aortic rings, and the underlying mechanisms. Isometric tension of the aortic rings was recorded using organ bath system. HHC (1 nM to 1 mM) relaxed the endothelium‐intact aortic rings pre‐contracted with PE and KCl in a concentration‐dependent manner. Removal of the endothelium did not alter the effect of HHC‐induced relaxation. In Ca²⁺‐free Krebs solution, HHC significantly inhibited the CaCl₂‐induced contraction in high K⁺ depolarized rings and suppressed the transient contraction induced by PE and caffeine in a concentration‐dependent manner. HHC was also observed to relax phobal‐12‐myristate‐13‐acetate (PMA), an activator of protein kinase C (PKC), precontracted aortic rings in a concentration‐dependent manner with EC₅₀ values equivalent to 93.36 ± 1.03 μM. In addition, pre‐incubation with propranolol (a β‐adrenergic receptor blocker) significantly attenuated the HHC‐induced vasorelaxation. These results suggest that the vasorelaxant effect of HHC is mediated by the endothelium‐independent pathway, probably because of the inhibition of extracellular Ca²⁺ influx through voltage‐operated Ca²⁺ channels and receptor‐operated Ca²⁺ channels, the inhibition of Ca²⁺mobilization from intracellular stores, as well as inhibition of PKC‐mediated Ca²⁺‐independent contraction. Moreover, HHC produces vasorelaxant effects probably by stimulating the β‐adrenergic receptor. Copyright © 2015 John Wiley & Sons, Ltd.     

Vasodilatory Effects of Cinnamic Acid via the Nitric Oxide–cGMP–PKG Pathway in Rat Thoracic Aorta

Cinnamic acid (CA) and its derivatives have a broad therapeutic spectrum that includes antimicrobial, antifungal, and antitumoral activities. However, the vasodilative effect of CA has not been demonstrated. The present study characterizes the vasodilative activity and the mechanism of CA in rat thoracic aorta. The vasomotion of aortic strips following CA treatment was measured in an organ bath system. In addition, vascular strips and human umbilical vein endothelial cells (HUVECs) were used in organ bath, Western blot, nitrite, and cyclic guanosine monophosphate (cGMP) measurements. CA relaxed phenylephrine‐precontracted aortic strips in an endothelium‐dependent manner. Pretreatment of the endothelium‐intact aortic strips with N^G‐nitro‐l ‐arginine methyl ester (10^?4 M), 1 H‐[1,2,4]‐oxadiazolole‐[4,3‐a] quinoxalin‐10‐one, (10^?6 M) and methylene blue (10^?5 M) inhibited CA‐induced vasorelaxation. CA also increased the phosphorylation of endothelial nitric oxide synthase and nitric oxide generation in a concentration‐dependent manner in HUVECs. In addition, cGMP generation and cGMP‐dependent protein kinase G (PKG) expression in aortic strips were increased by CA treatment. Furthermore, CA‐induced vasorelaxation was inhibited by the PKG inhibitor KT5823 (0.3 μM) and the Ca²⁺‐activated K⁺ channel inhibitor tetraethylammonium (10^?3 M). These findings suggest that CA exerts an endothelium‐dependent vasodilation effect via the nitric oxide–cGMP–PKG‐mediated pathway in rat thoracic aorta. Copyright © 2012 John Wiley & Sons, Ltd.     

白藜芦醇对大鼠离体胸主动脉环的舒张作用

目的:观察白藜芦醇(resveratrol,RVL)对大鼠离体胸主动脉血管的舒张作用并探讨其机制。方法:采用离体血管环灌流方法,观察RVL在含Ca²⁺或无Ca²⁺ Krebs液孵育条件下对去甲肾上腺素(NA)引起的血管平滑肌收缩的影响;同法观察RVL对30,80mmol·L^-1的KCl引起的血管平滑肌收缩的影响;RVL对NA引起的依赖于细胞内钙和细胞外钙收缩反应的影响,以及加入N-G-硝基-L-精氨酸(L-NNA)和优降糖后RVL舒张大鼠离体主动脉环效应的变化。结果:RVL呈浓度依赖性舒张NA引起的血管收缩;无Ca²⁺ 组RVL抑制NA所致血管平滑肌收缩效应大于含Ca²⁺ 组;RVL能够拮抗NA诱发的依内钙的收缩反应,而对外钙收缩无抑制。RVL对80,30mmol·L^-1 的KCl引起的血管平滑肌收缩均有抑制作用,且前者量效曲线明显上移。L-NNA使RVL舒血管效应降低(26.0±4.6)%;优降糖组的血管舒张受抑程度与对照组无显著差别(P>0.05)。结论:RVL可呈内皮依赖性舒张血管平滑肌,其作用机制可能与该药促进NO合成释放,开放钙激活的钾通道以及抑制血管平滑肌细胞外钙内流和内钙释放有关。     

Cardiovascular pharmacology of 3-n -butylphthalide in spontaneously hypertensive rats

The hypotensive and vasorelaxant effects of 3-n -butylphthalide (BuPh) and its possible mechanisms of action were investigated in spontaneously hypertensive rats (SHR) for the first time. A 13-day intraperitoneal infusion of BuPh at doses of 2.0 and 4.0 mg/day produced a transient hypotensive effect while a dose of 0.5 mg/day showed a significant hypotensive effect only on day 12. BuPh at 0.5 mg/day had no effect on the plasma and tissue angiotensin converting enzyme (ACE) activities, or on the tissue lipid peroxidation index. BuPh relaxed endothelium-intact and denuded aortic rings precontracted with phenylephrine and KCl. N^G-nitro-L -arginine methyl ester, an inhibitor of nitric oxide synthase, did not attenuate the vasorelaxant activity of BuPh. The cumulative concentration response curves of phenylephrine and Ca²⁺ (in CaCl₂-free, high KCl medium) were non-competitively inhibited by BuPh. However, BuPh did not interfere with the caffeine-induced release of intracellular Ca²⁺. It appears that the vasorelaxant effect of BuPh could be attributed to the blockade of Ca²⁺ entry, possibly through voltage- and receptor-operated Ca²⁺ channels, thereby lowering the systolic blood pressure of SHR. © 1997 John Wiley & Sons, Ltd.     

茉莉花水提物对大鼠胸主动脉的舒张作用及机制

 目的 观察中药茉莉花水提物（AEJ）的血管舒张效应并探讨其机制。方法 采用大鼠胸主动脉环灌流,记录张力的变化;激光扫描共聚焦显微镜技术检测血管平滑肌细胞内 Ca2+浓度。结果 AEJ（0.375～6 g·L-1）能够浓度依赖性降低苯肾上腺素（PE,10 μmol·L-1)及 KCl (60 mmol·L-1)引起的主动脉环张力。在无钙环境下,AEJ 能抑制高浓度氯化钾 (KCl 60 mmol·L-1)环境下累计加入 CaCl₂(0.5～8 mmol·L-1)引起的收缩,抑制 PE (10 μmol·L-1) 引起的去内皮主动脉环的短暂收缩 (P<0.01)。钾通道阻断剂 4-氨基吡啶(5 mmol·L-1)可显著抑制 AEJ 的舒血管作用。激光扫描共聚焦检测细胞内 Ca2+的结果表明,AEJ 浓度依赖性（6,12 g·L-1）降低了 KCl 除极诱导的滑肌细胞胞浆内 Ca2+的升高幅度（P<0.05）。结论 AEJ 能够浓度依赖性舒张大鼠胸主动脉,其作用机制可能是减少 Ca2+经电压依赖性钙通道和受体操纵性钙通道流入血管平滑肌细胞及抑制内质网内 Ca2+释放有关;电压敏感型 K+通道（K_V）的激活部分参与了 AEJ 舒血管作用。     

New Findings on the Effects of Tannic Acid: Inhibition of L‐Type Calcium Channels,Calcium Transient and Contractility in Rat Ventricular Myocytes

Tannic acid (TA) is a group of water‐soluble polyphenolic compounds that occur mainly in plant‐derived feeds, food grains and fruits. Many studies have explored its biomedical properties, such as anticancer, antibacterial, antimutagenic, antioxidant, antidiabetic, antiinflammatory and antihypertensive activities. However, the effects of TA on the L‐type Ca²⁺ current (I_Ca‐L) of cardiomyocytes remain undefined. The present study examined the effects of TA on I_Ca‐L using the whole‐cell patch‐clamp technique and on intracellular Ca²⁺ handling and cell contractility in rat ventricular myocytes with the aid of a video‐based edge detection system. Exposure to TA resulted in a concentration‐ and voltage‐dependent blockade of I_Ca‐L, with the half maximal inhibitory concentration of 1.69 μM and the maximal inhibitory effect of 46.15%. Moreover, TA significantly inhibited the amplitude of myocyte shortening and peak value of Ca²⁺ transient and increased the time to 10% of the peak. These findings provide new experimental evidence for the cellular mechanism of action of TA and may help to expand clinical treatments for cardiovascular disease. Copyright © 2016 John Wiley & Sons, Ltd.     

The source of ca2+ for the spasmolytic actions of longicaudatine,a bisindole alkaloid isolated from Strychnos trinervis (Vell.) Mart. (Loganiaceae)

Longicaudatine, a tertiary bisindole alkaloid isolated from the root bark of Strychnos trinervis (Vell.) Mart. (Loganiaceae), antagonized in a noncompetitive manner, carbachol and histamine induced contractions of the guinea-pig ileum and bradykinin responses in the rat uterus. The respective pD₂' values (mean ± SE) were 4.61 ± 0.21, 4.98 ± 0.04 and 4.49 ± 0.01. Longicaudatine, unlike verapamil, had no effect on voltage dependent Ca²⁺ channels, as it failed to inhibit KCI or CaCl₂ induced contractions of guinea-pig ileum and depolarized rat uterus respectively. When compared with sodium nitroprusside, an antagonist of receptor operated Ca²⁺ channels, longicaudatine produced a slower and weaker inhibition of noradrenaline induced sustained contractions of rabbit aortic strips. However, in the aorta, the alkaloid antagonized the intracellular calcium dependent transient contractions of noradrenaline and longicaudatine (IC₅₀, 5.01 × 10^?7 M) was approximately 133 times more potent that procaine (IC₅₀, 6.68 × 10^?5 M), a known inhibitor of the release of Ca²⁺ from intracellular stores. Longicaudatine may exert nonspecific spasmolytic effects by acting on intracellular Ca²⁺ stores, rather than on depolarization dependent or receptor operated Ca²⁺ channels.     

天麻素对离体大鼠胸主动脉环的舒张作用及其机制

目的:研究天麻素对离体大鼠胸主动脉环的舒张作用并探讨其可能的机制。方法:记录去甲肾上腺素(NE)和KCl预收缩的离体大鼠主动脉环张力变化,观察天麻素的舒血管作用及不同工具药对其作用的影响。结果:天麻素对去甲肾上腺素(NE,1×10-6mol.L-1)和KCl(6×10-2mol.L-1)引起的去内皮和内皮完整胸主动脉环的收缩均有舒张作用,二者没有显著差别;L-硝基精氨酸甲酯(L-NAME,1×10-4mol.L-1)、亚甲蓝(MB,1×10-5mol.L-1)、吲哚美辛(INDO,1×10-5mol.L-1)并不能抑制天麻素对胸主动脉环的舒张作用;钾离子通道阻断剂4-氨基吡啶(4-AP,1×10-4mol.L-1)、四乙基胺(TEA,1×10-3 mol.L-1)、格列苯脲(glibenclamide,1×10-5mol.L-1)、BaCl2(1×10-4mol.L-1)均能抑制天麻素对血管环的舒张作用;在无钙环境下,预孵育天麻素对去甲肾上腺素收缩有明显抑制作用。结论:天麻素有浓度依赖性的血管舒张作用,此作用不依赖血管内皮,与钾离子通道及抑制血管平滑肌细胞内质网储存钙的释放和外钙内流有关系。     

Analysis of the mechanisms underlying the vasorelaxant action of coptisine in rat aortic rings

The aim of the present study was to evaluate the vasorelaxant effects of coptisine and its possible mechanisms in isolated rat aortic rings. Coptisine was evaluated on isolated rat aortic rings precontracted with norepinephrine (NE) and KCl. The mechanisms were evaluated in the presence or absence of specific pharmacological inhibitors. Coptisine (1 ~ 200 μM) relaxed NE (1 μM) or KCl (60 mM) induced sustained contraction with pEC(50) values of 4.49 ± 0.48 and 4.85 ± 0.57 in a concentration dependent manner. Pretreatment with coptisine (10, 50 or 100 μM) also inhibited concentration-response curves to NE and KCl. The vasorelaxant effect of coptisine was attenuated significantly by endothelium removal, and incubation with Nω-nitro-L-arginine methyl ester (L-NAME, 100 μM), methylene blue (10 μM) and indomethacin (5 μM) partially reduced the vasorelaxant effect of coptisine. In endothelium-denuded rings, the vasorelaxant effect of coptisine was reduced significantly by 4-aminopyridine (4-AP, 100 μM), but not glibenclamide (10 μM) ortetraethylammonium (TEA, 5 mM). Coptisine also reduced NE-induced transient contraction in Ca(2+)-free solution, and inhibited contraction induced by increasing external calcium in Ca(2+)-free medium plus 60 mM KCl. It was concluded that coptisine induced both endothelium-dependent and -independent relaxation in rat aortic rings. The NO-cGMP mediated pathway may be involved in the endothelium-dependent relaxation and in the activation of voltage-dependent K(+) channels, contributing in part to the endothelium-independent relaxation bycoptisine. Coptisine also blocks extracellular Ca(2+) influx by interacting with both voltage- and receptor-operated Ca(2+) channels.     

参麦注射液对猪冠状动脉环的舒张作用及机制研究

目的:观察参麦注射液对猪离体冠状动脉环的舒张作用,并探讨其作用机制.方法:采用离体血管张力的实验方法,观察0.1,0.5,1,5,10,50 mL·L-1的参麦注射液对KCl(30 mmol·L 1)诱发的猪离体冠脉环收缩的影响.观察内皮、Na+/Ca2+交换体阻断剂KB-R7943(1×10-6mol·L-1)、KV通道阻断剂四胺基吡啶(4-AP,1×10-3 mol·L 1)、KATP通道阻断剂格列苯脲( Gli,1×10-5mol·L-1)、KCa通道阻断剂四乙胺(TEA,1×10-2 mol·L-1)、KiR通道阻断剂氯化钡(BaC12,1×10-3mol·L-1)对参麦注射液作用的影响.结果:参麦注射液对KCI(30 mmol·L-1)预收缩的猪离体冠脉环产生浓度依赖性的舒张作用,去内皮,KB-R7943,BaC12及Gli预处理的血管环对参麦注射液的舒张反应与未经处理时比较无显著性差异.4-AP及TEA可显著减弱参麦注射液对血管环的舒张作用(P＜0.05).结论:参麦注射液对KC1预收缩的猪离体冠脉环具有浓度依赖性的舒张作用,其舒张反应无内皮依赖性,与Na+/Ca2交换体无关,可能与KCa通道及KV通道有关.     

The Lignan (‐)‐Cubebin Inhibits Vascular Contraction and Induces Relaxation Via Nitric Oxide Activation in Isolated Rat Aorta

Cubebin, the most abundant lignan in Piper cubeba, has been described as having several effects as trypanocidal, antimycobacterial, antispasmodic, antimicrobial, anti‐inflammatory, and analgesic. This study investigated the vasorelaxant effect produced by (‐)‐cubebin in isolated rat aortic rings pre‐contracted with phenylephrine (Phe), and the possible mechanism involved in this event was evaluated. Endothelium‐dependent relaxation was evoked by acetylcholine and (‐)‐cubebin in intact aortic rings, while endothelium‐independent vasorelaxation was elicited by sodium nitroprusside and (‐)‐cubebin in denuded rings. Cumulative concentration–response curves for Phe (10^?10–10^?5 M) were determined for endothelium‐intact and endothelium‐denuded aortic rings in either the presence or absence of (‐)‐cubebin. Dose–response curves were also constructed for pre‐incubation of vascular rings with Nω‐nitro‐L‐arginine methyl ester (L‐NAME) (a non‐specific nitric oxide synthase inhibitor), indomethacin (an unspecific cyclooxygenase inhibitor), and 1H‐[1,2,4] oxadiazolo [4,3‐a]quinoxalin‐1‐one (ODQ) (a guanylyl cyclase inhibitor). (‐)‐Cubebin was found to exert a vasorelaxant effect irrespective of the presence of endothelium, which was abolished by pretreatment with L‐NAME and ODQ, but not with indomethacin. In addition, (‐)‐cubebin was able to reduce Phe contraction in the case of intact rings. These results suggest that (‐)‐cubebin promotes vasorelaxation via NO/cGMP pathway in rat aorta, without prostacyclin involvement. Copyright © 2013 John Wiley & Sons, Ltd.     

Vasorelaxant effects of extracts of the stem bark of Terminalia superba Engler & Diels (Combretaceae)

Aim of the study

The stem bark of Terminalia superba (Combretaceae) (TS) is used in traditional Cameroonian medicine as antihypertensive remedy. In the present study, we investigated the vasorelaxant properties of different extracts of TS and their underlying mechanisms.

Materials and methods

Activities of aqueous (AQU), methanolic (MET), methylene chloride (MC), and methylene chloride–methanol (MCM) extracts of TS were evaluated on isolated rat aortic rings precontracted with phenylephrine (PE) or high KCl.

Results

All extracts induced a vasodilating effect both on KCl- and PE-induced contractions. The effects of MC and MCM extracts were greater than those of AQU or MET extracts (P < 0.05). MC had an endothelium-independent effect and reduced Ca⁺⁺-induced contraction following PE or KCl challenge (P < 0.05). After incubation with verapamil, MC induced a relaxation in rings precontracted by PE (P < 0.001). By contrast, the effect of MCM was endothelium-dependent and decreased by the nitric oxide synthase inhibitor N_W-nitro-l-arginine methyl ester (P < 0.05).

Conclusions

These data demonstrate that the MC extract exhibits vasorelaxant effects that are partly due to inhibition of extracellular Ca⁺⁺ influx and/or inhibition of intracellular Ca⁺⁺ release in vascular smooth muscle cells. By contrast, the effect of the MCM extract was found to be endothelium- and nitric oxide dependent.     

Ellagic Acid‐Induced Endothelium‐Dependent and Endothelium‐Independent Vasorelaxation in Rat Thoracic Aortic Rings and the Underlying Mechanism

The present study first investigated the mechanisms of vasorelaxation induced by ellagic acid (EA), which is one of the major compounds extracted from the pomegranate in the rat thoracic aorta. Male Wistar rats aged 10 to12 weeks weighing 250–350 g were used for the present study. The animals were killed by decapitation, and thoracic aortas were immediately excised and placed in Krebs solutions, cleaned, and freed from surrounding connective tissue. The isolated arteries were cut into rings (4‐ to 5‐mm long) and placed in 20‐mL tissue chambers filled with Krebs solution. Initially, the aortic rings were equilibrated for 60 min until a resting tension of 1.0 gr. After the equilibration period, aortic rings were firstly contracted with phenylephrine to increase tone. Once a stable contraction was achieved, EA (10^?8 to 10^?4 M) was added cumulatively on aortic rings with or without endothelium into organ bath. To characterize the mechanisms involved in EA‐induced vasorelaxant effect, the aortic rings were incubated with each inhibitor added to the bath for 30 min before phenylephrine was added to increase tone. The results of the present study have demonstrated in the rat thoracic aorta that EA causes vasorelaxations, which are partly modulated via endothelium‐dependent mechanisms and through inhibition of calcium influx. Copyright © 2012 John Wiley & Sons, Ltd.     

Vasorelaxant effects of Cerebralcare Granule are mediated by NO/cGMP pathway,potassium channel opening and calcium channel blockade in isolated rat thoracic aorta

Ethnopharmacological relevance

Cerebralcare Granule (CG), one of the famous classical recipes in traditional Chinese medicine, is developed from the “Decoction of Four Drugs”. It has been used for treatment of cerebrovascular related diseases, such as hypertension. It is well known that vasodilatation plays a very important role in hypertensive. Despite the popular medicinal use of CG, little data was available to its activity and mechanism involved in vasodilatation. Therefore, we aimed to investigate the vasorelaxant effects of CG on isolated rat thoracic aorta so as to assess some of the possible mechanisms. The present study was performed to examine the vasodilative activity of CG and its mechanisms in isolated rat thoracic aorta.

Materials and methods

CG was studied on isolated rat thoracic aorta in vitro, including endothelium-intact and endothelium-denuded aortic rings. In present study, specific inhibitors including NO synthase inhibitor N^G-nitro-l-arginine methyl ester (l-NAME), cyclooxygenase (COX) inhibitor indomethacin (INDO), non-selective K⁺ channel inhibitor tetraethylammonium chloride (TEA), K_ir channel inhibitor BaCl₂, K_ATP channel inhibitor Glibenclamide (Gli) and cholinergic receptor antagonist atropine were used, they were added 20 min before NE contraction and then added CG-induced vasodilation.

Results

Removal of endothelium or pretreatment of aortic rings (intact endothelium) with l-NAME (0.1 mM) or INDO (0.01 mM) significantly blocked the CG induced relaxation. Pretreatment with the non-selective K⁺ channel inhibitor TEA (1 mM), or the K_ir channel inhibitor BaCl₂ (0.1 mM), neither of them had no influence on the CG-induced response (p>0.05). However, pretreatment with the K_ATP channel inhibitor Gli (0.01 mM) produced significant inhibition on the CG-induced response (p<0.01). Besides, CG also inhibited the contraction triggered by NE in endothelium-denuded rings in Ca²⁺-free medium. CG (0.4, 0.8 and 3.2 mg/mL) produced rightward parallel displacement of CaCl₂ curves and reduced the maximum contraction induced by 30 mM CaCl₂ to 31.1±9.3%, 18.8±6.9% and 9.4±4.5%, respectively. The relaxation, induced by CG on endothelium-intact rat aortic rings pre-contracted with NE, was significantly attenuated in the presence of atropine (EC₅₀=3.7 mg/mL, p<0.01).

Conclusions

Our results suggest that CG induces relaxation in rat aortic rings through an endothelium-dependent pathway mediated by NO/cGMP pathway and an endothelium-independent pathway involving blockade of Ca²⁺ channels, inhibition of Ca²⁺ mobilization from intracellular stores, opening of K_ATP channel. In addition, the muscarinic receptor stimulation is also one of the vasorelaxant mechanisms.     

Bisnordihydrotoxiferine and vellosimine from Strychnos divaricans root: Spasmolytic properties of bisnordihydrotoxiferine

Bisnordihydrotoxiferine and vellosimine, two tertiary indole alkaloids have been isolated from the root of Strychnos divaricans. Bisnordihydrotoxiferine antagonized in a nonspecific manner, oxytocin and acetylcholine induced contractions in the rat uterus and acetylcholine and histamine responses in the guinea-pig ileum. Bisnordihydrotoxiferine, like verapamil, produced effects on voltage dependent Ca²⁺ channels. For example in guinea-pig ileum, bisnordihydrotoxiferine (pD'₂ 3.92±0.09) and verapamil (pD'₂ 6.00±0.11) inhibited KCl induced contractions. Furthermore, bisnordihydrotoxiferine (pD'₂ 4.37±0.02) and verapamil (pD'₂ 6.83±0.10) also antagonized CaCl₂ induced contractions of K⁺-depolarized rat uterus. When compared with sodium nitroprusside, an antagonist of receptor operated Ca²⁺ channels, bisnordihydrotoxiferine had no effect. However, in the aorta, the alkaloid (IC₅₀, 6.10 × 10^?6M) antagonized the intracellular calcium dependent transient contractions of noradrenaline and it was about four times more potent than procaine (IC₅₀, 2.30 × 10^?5M), a known inhibitor of the release of Ca²⁺ from intracellular stores. Bisnordihydrotoxiferine may produce nonspecific spasmolytic actions mainly by inhibiting intracellular calcium mobilization and to a lesser extent by inhibiting voltage dependent calcium channels in smooth muscles.     

(−)‐Epicatechin‐induced relaxation of isolated human saphenous vein: Roles of K+ and Ca2+ channels

In this study, we aimed to investigate relaxant effect of flavanol (?)‐epicatechin on the isolated human saphenous vein (HSV), as a part of its cardioprotective action, and to define the mechanisms underlying this vasorelaxation. (?)‐Epicatechin induced a concentration‐dependent relaxation of HSV pre‐contracted by phenylephrine. Among K⁺ channel blockers, 4‐aminopyridine, margatoxin, and iberiotoxin significantly inhibited relaxation of HSV, while glibenclamide considerably reduced effects of the high concentrations of (?)‐epicatechin. Additionally, (?)‐epicatechin relaxed contraction induced by 80 mM K⁺, whereas in the presence of nifedipine produced partial relaxation of HSV rings pre‐contracted by phenylephrine. In Ca²⁺‐free solution, (?)‐epicatechin relaxed contraction induced by phenylephrine, but had no effect on contraction induced by caffeine. A sarcoplasmic reticulum Ca²⁺‐ATPase inhibitor, thapsigargin, significantly reduced relaxation of HSV produced by (?)‐epicatechin. These results demonstrate that (?)‐epicatechin produces endothelium‐independent relaxation of isolated HSV rings. Vasorelaxation to (?)‐epicatechin probably involves activation of 4‐aminopyridine‐ and margatoxin‐sensitive K_V channels, BK_Ca channels, and at least partly, K_ATP channels. In addition, not only the inhibition of extracellular Ca²⁺ influx, but regulation of the intracellular Ca²⁺ release, via inositol‐trisphosphate receptors and reuptake into sarcoplasmic reticulum, via stimulation of Ca²⁺‐ATPase, as well, most likely participate in (?)‐epicatechin‐induced relaxation of HSV.     

Effects of Total Alkaloids in Buxus microphylla Leaves on Aorta Smooth Muscle of Rats and Their Mechanisms

Objective To investigate the effects of total alkaloids in Buxus microphylla leaves(ABML)on isolated rats thoracic aorta rings,and then to explore the possible mechanisms underlying the effects.Methods Thoracic aortas of Wistar rats were isolated,removed,and mounted onto an organ bath.The effects of ABML at different concentration on the contraction of isolated thoracic aorta rings(with and without endothelium)precontracted with KCl or PE were observed with organ bath technique.Dose-effect curves of CaCl2 were recorded by organ bath technique.The concentration of intracellular Ca 2+ ([Ca 2+ ]i)increased by PE,KCI,and caffeine in the presence of ABML was determined using Ca 2+ sensitive fluorescence indicator Fura-2/AM loaded thoracic aorta vascular smooth muscle (VSM)cells of rats.Results In aorta rings precontracted with PE and KCl,ABML produced concentration- dependent relaxation in both intact and denuded endothelium ring groups.There was no difference in the inhibition of contraction between the intact and denuded endothelium ring groups at the same concentration.Exposure of isolated thoracic aorta rings to ABML led to a significant reduction in the contracting response induced by CaCl2,and shifted the cumulative concentration-response curves to right.ABML could significantly inhibit the extracellular Ca 2+ influx induced by PE and KCl under[Ca 2+ ]0 of 1.5 mmol/L,with inhibitory ratios of 40.2%and 49.9%,respectively.In the case of Ca 2+ -free,ABML could significantly inhibit the intracellular Ca 2+ release induced by PE,with inhibitory ratio of 72.4%.Conclusion ABML relaxes thoracic aorta VSM cells by suppressing influx of extracellular Ca 2+ via voltage-dependent Ca 2+ channel and receptor-operated Ca 2+ channel.     

Bronchodilator Activity of Aerial Parts of Polygonatum verticillatum Augmented by Anti‐inflammatory Activity: Attenuation of Ca2+ Channels and Lipoxygenase

Polygonatum verticillatum is commonly used for the treatment of asthma and inflammation. The current study was aimed to scrutinize the pharmacological profile of methanolic extract of the aerial parts (PA). Isolated tracheal preparations were used for the evaluation of bronchodilatory activity, whilst the in vivo carrageenan‐induced paw oedema test and an in vitro lipoxygenase (LOX) inhibitory assay were used for the assessment of the anti‐inflammatory profile of PA. When tested against carbachol and K⁺ (80 mM)‐induced contractions, PA caused complete inhibition of isolated rabbit tracheal preparations in a dose‐dependent mode, similar to verapamil. While elucidating possible mechanism, PA shifted the Ca²⁺ concentration–response curves to the right, analogous to that produced by verapamil, confirming a Ca²⁺ channel blocker‐like activity. PA provoked profound reduction in paw oedema with a maximum protection of 60.87% at 200 mg/kg i.p. in a dose‐dependent manner which was augmented by its prominent LOX inhibitory activity (IC₅₀: 125 µg/mL). These findings authenticated its therapeutic potential in the treatment of asthmatic and inflammatory conditions. Copyright © 2012 John Wiley & Sons, Ltd.     

大黄素对大鼠主动脉非内皮依赖性的舒张作用及其机制研究

 目的观察大黄素的舒血管作用并探讨其舒张作用机制。方法采用大鼠胸主动脉环张力测定法。结果大黄素对苯肾上腺素(PE,10^-6mol·L^-1)预收缩的内皮完整或去内皮血管环均产生浓度依赖性的舒张作用;对高钾预收缩血管环也产生浓度依赖性的舒张作用。普奈洛尔(propranolol,1.0×10^-6 mol·L^-1)对大黄素的舒血管作用无显著影响;非特异性钾通道抑制剂CsCl和Ca²⁺激活钾通道抑制剂四乙胺(TEA,5.0×10^-3 mol·L^-1)预处理能显著减弱大黄素的舒血管作用;大黄素可以显著地对抗无钙环境下由咖啡因或无钾环境下由PE引起的血管收缩。结论大黄素非内皮依赖性血管舒张作用与其直接抑制细胞外钙内流、肌浆网内钙离子的释放,以及激活Ca²⁺激活钾通道(Kca)有关,而与β-受体无关。     

Possible mechanisms of vasorelaxation for 5,7-dimethoxyflavone from Kaempferia parviflora in the rat aorta

The present study investigated the vascular effects of 5,7-dimethoxyflavone (DMF), isolated from the rhizomes of Kaempferia parviflora (KP), on rat isolated aortic rings and its possible mechanisms. DMF (1-100 μM) caused concentration-dependent relaxations in aortic rings precontracted with methoxamine. This effect was significantly reduced by removal of the endothelium, and after pretreatment with N(G)-nitro-L-arginine methyl ester (L-NAME, 300 μM), indomethacin (10 μM) and 1H-[1,2,4]oxadiazolo-[4,3-a]quinoxalin-1-one (ODQ, 10 μM), but not 9-(tetrahydro-2-furanyl)-9H-purine-6-amine (SQ22536, 100 μM). Relaxant responses to DMF were significantly inhibited by high KCl (60 mM) in both endothelium-intact and -denuded rings. In addition, the relaxations to DMF were significantly reduced by pretreatment with tetraethylammonium (TEA, 5 mM), glibenclamide (10 μM), 4-aminopyridine (1 mM) or barium chloride (10 μM). Preincubation with DMF (10 and 100 μM) for 30 min significantly inhibited the contractile responses to CaCl(2) in a Ca(2+)-free, high K(+) buffer. The present study demonstrated that DMF causes endothelium-dependent relaxation that is partly mediated by NO-cGMP and cyclooxygenase pathways. Interestingly, DMF-induced responses are mainly due to increasing K(+) efflux, and inhibition of Ca(2+) influx from the extracellular space. The vasodilator effects of DMF provide experimental support for the potential use of KP as a medical plant in the treatment of cardiovascular diseases.