Endothelium‐Independent Vasorelaxation Effects of Sigesbeckia glabrescens (Makino) Makino on Isolated Rat Thoracic Aorta

The present study aimed to investigate the vasorelaxant effect of the methanol extract of Sigesbeckia glabrescens (Makino) Makino (MESG) on rat aortic rings and mechanism of action. MESG inhibited both noradrenaline bitartrate (NA)‐ and potassium chloride (KCl)‐induced contraction of endothelium‐intact aortic rings in a concentration‐dependent manner. Removal of the endothelium did not influence the effect of MESG on NA‐precontracted aortic rings. Pretreatment with MESG (250 µg/mL) inhibited calcium chloride‐induced vasocontraction of NA‐ or KCl‐precontracted endothelium‐denuded aortic rings. It also relaxed phorbol‐12‐myristate‐13‐acetate‐induced contraction of aortic rings in a concentration‐dependent manner. In addition, Bay K8644 (an L ‐type calcium channel opener) vasocontracted in MESG pretreated aortic rings. On the other hand, the inositol 1,4,5‐triphosphate receptor, the ryanodine receptor, the Rho‐kinase inhibitor (Y‐27632), a soluble guanylyl cyclase blocker (1‐H‐[1,2,4]‐oxadiazolo‐[4,3a]‐quinoxalin‐1‐one), and K⁺ channel blockers (glybenclamide, tetraethylammonium, and 4‐aminopyridine) did not affect the effect of MESG. These results suggested that the mechanism underlying the vasorelaxant effect of MESG is mediated by endothelium‐independent pathways. This specifically refers to blockade of the influx of extracellular Ca²⁺ via receptor‐operative Ca²⁺ channels and voltage‐dependent Ca²⁺ channels and inhibition of a protein kinase C‐mediated cellular pathway. 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。     

(−)‐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.     

天钩降压胶囊对家兔主动脉血管条收缩反应的影响

目的:观察天钩降压胶囊对家兔主动脉条收缩反应的影响,探讨其降压作用机制.方法:将家兔离体主动脉条置于灌流肌槽中,记录天钩降压胶囊提取物对去甲肾上腺素(NE)、氯化钾(KCl)、氯化钙(CaCl2)诱导的主动脉条收缩作用的影响,以及对NE诱导的主动脉条细胞内钙及细胞外钙依赖性收缩反应的影响.结果:天钩降压胶囊1,3,5g·L-1剂量组均能使NE,CaCl2引起的主动脉条最大收缩反应降低(P＜0.01);对NE诱发主动脉条细胞内钙及细胞外钙依赖性收缩均有明显抑制(P＜0.01),对细胞外钙依赖性收缩的抑制作用更显著;对KCl引起的动脉条收缩反应无明显影响.结论:天钩降压胶囊可通过影响细胞内钙离子浓度促进血管平滑肌舒张从而发挥降压作用.其机制可能主要通过影响受体操纵的Ca2+通道(ROC),对电压依赖性Ca2+通道(PDC)作用不显著.对NE诱发主动脉条细胞外钙依赖性收缩的抑制作用优于对细胞内钙依赖性收缩的作用.     

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.     

隔山香正丁醇部位对大鼠胸主动脉的舒张作用及机制的影响

目的:研究隔山香(Lemonfragrant Angelica Root,LAR)正丁醇部位对大鼠胸主动脉环的舒张作用,并探讨其可能的作用机制。方法:采用离体大鼠胸主动脉血管环灌流方法,考察0.34,0.65,1.22 g·L-1隔山香正丁醇部位对氯化钾(KCl)和去甲肾上腺素(norepinephrine,NE)预收缩的血管环张力的影响。在无Ca2+Kreb’s液中,考察0.34,0.65,1.22 g·L-1隔山香正丁醇部位对氯化钙(Ca Cl2)量效曲线的影响和NE预收缩的血管环张力的影响。激光共聚焦扫描显微镜检测平滑肌细胞内[Ca2+]i的变化。结果:隔山香正丁醇部位对KCl和NE预收缩的内皮完整和去除内皮血管环均具有浓度依赖性的舒张作用(P0.01),并且去除内皮后的舒张作用未受影响;无Ca2+条件下,隔山香正丁醇部位能使Ca Cl2,NE预收缩强度显著性降低(P0.01)。激光共聚焦扫描显微镜下,隔山香正丁醇部位(1.22 g·L-1)能抑制KCl,NE和毒胡萝卜素(thapsigargin,TG)引起的平滑肌细胞内[Ca2+]i升高。结论:隔山香正丁醇部位对大鼠胸主动脉血管有一定的舒张作用,可能通过抑制外钙内流和内钙释放发挥作用。本实验为隔山香水蒸气蒸馏后煎煮入药的成药制备工艺和水溶性药效指标成分的分离提供了依据。     

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.     

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 and mechanisms of action of Heracleum sphondylium L. (Apiaceae) in rat thoracic aorta

Ethnopharmacological relevance

Aerial parts of Heracleum sphondylium L. (HS) are used in traditional medicine to treat hypertension. To provide pharmacological basis for this use, we investigated the vasorelaxant effects of a dichloromethane extract of HS (HSDE) and the mechanisms involved.

Materials and methods

Activity of HSDE was evaluated on rat isolated thoracic aortic rings.

Results

HSDE induced vasorelaxation in phenylephrine (PE, 10⁻⁶ mol/L) and high KCl—(6×10⁻² mol/L) pre-contracted aortic rings that was independent on the presence of endothelium. HSDE markedly decreased extracellular Ca²⁺-induced contraction in high-KCl and PE pre-challenged rings. It also inhibited the intracellular Ca²⁺ release sensitive to PE (10⁻⁶ M). The relaxant effect of HSDE were blunted by 4-amino-pyridine (4-AP, 10⁻³ mol/L), an inhibitor of voltage-dependent K⁺ channels.

Conclusion

Our results provide the first evidence that a dichloromethane extract of Heracleum sphondylium L. exhibits vasorelaxant properties through endothelium-independent mechanisms involving the inhibition of Ca²⁺ mobilization and changes in Kv channel conductances. These data argue for its use as antihypertensive therapy in traditional medicine.     

莲心碱对家兔主动脉条收缩性能的影响

 目的　观察莲心碱 (liensinine,Lien)对氯化钾(KCl),去甲肾上腺素(NE)和组织胺(Hist)所致家兔主动脉条收缩的作用。并研究其对血管条依内钙性收缩和依外钙性收缩的影响。方法　离体平滑肌实验方法。结果　不同剂量Lien及维拉帕米(Ver)对KCl,NE,Hist诱导的主动脉条均呈抑制作用,并可非竞争性拮抗组胺的量效曲线,PD₂′值分别为4.31,6.89。Lien和Ver均能抑制组胺诱导的依内钙收缩,而对依外钙收缩作用较弱。结论　Lien可舒张兔主动脉条,该作用与钙离子拮抗有关,且对主动脉依内钙性收缩的敏感性大于依外钙性收缩。     

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.     

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.     

黄芩素对大鼠离体胸主动脉的舒张作用及其机制

目的:研究黄芩素(BAI)对去甲肾上腺素(NE,1×10-6mol· L-1)和氯化钾(KCl,6×10-2 mol·L-1)预收缩健康成年雄性大鼠胸主动脉环的舒张作用,并探讨其作用机制.方法:应用离体血管环技术观察BAI对大鼠胸主动脉环张力的作用,记录NE预收缩的离体大鼠胸主动脉环张力变化.采用一氧化氮合酶(eNOS)抑制剂L-硝基精氨酸甲酯(L-NAME,1×10-4mol·L-1)、环氧合酶抑制剂吲哚美辛(INDO,1×10-5mol· L-1)和鸟苷酸环化酶抑制剂亚甲蓝(MB,1×10-5mol· L-1)和不同的钾通道阻滞剂预孵后观察BAI对血管环张力改变的影响,并观察对NE诱发的内钙释放和CaCl2引起的外钙内流的影响.结果:BAI对NE或KCl预收缩的内皮完整和去内皮大鼠离体胸主动脉环均产生明显的舒张作用,与溶剂组相比差异有统计学意义.预先用L-NAME,MB,KV通道阻断剂四氨基吡啶(4-AP,1×10-4mol· L-1),KC.通道阻断剂四乙胺(TEA,1×10-3mol· L-1),Kir通道阻断剂氯化钡(BaCl2,1×10-4mol·L-1)孵育后,BAI对预收缩的血管张力的改变与无阻断药时比较,差异均无统计学意义;预先用KATP通道阻断剂格列苯脲(Gli,1×10-5mol·L-1)和INDO孵育后,BAI的舒张血管作用减弱,与无阻断药比较差异有统计学意义(P＜0.05);且BAI对NE外钙内流引起的收缩有明显的抑制作用.结论:黄芩素可明显降低由NE诱发的血管环张力的升高,且其作用具有浓度依赖性,此作用有内皮依赖性和非内皮依赖性的特点.内皮依赖性收缩可能与前列环素(PGI2)途径有关,非内皮依赖机制与KATP通道和钙离子通道有关.     

Vasodilatory effects of ethanol extract of Radix Paeoniae Rubra and its mechanism of action in the rat aorta

Ethnopharmacological relevance

Radix Paeoniae Rubra (RPR) is an important traditional Chinese medicine (TCM) commonly used in clinic for a long history in China. RPR is the radix of either Paeonia lactiflora Pall. or Paeonia veitchii Lynch. RPR has a wide variety of pharmacological actions such as anti-thrombus, anti-coagulation, and anti-atherosclerotic properties, protecting heart and liver. However, the mechanisms involved are to be defined.

Aim of the study

The aim of the present study was to define the effect of Paeonia lactiflora Pall. extracts on vascular tension and responsible mechanisms in rat thoracic aortic rings.

Materials and methods

Ethanol extract of Paeonia lactiflora Pall. (EPL) was examined for their vascular relaxant effects in isolated phenylephrine-precontracted rat thoracic aorta.

Results

EPL induced relaxation of the phenylephrine-precontracted aortic rings in a concentration-dependent manner. Vascular relaxation induced by EPL was significantly inhibited by removal of the endothelium or pretreatment of the rings with N^G-nitro-l-arginine methylester (l-NAME) or 1H-[1,2,4]-oxadiazolo-[4,3-α]-quinoxalin-1-one (ODQ). Extracellular Ca²⁺ depletion or diltiazem significantly attenuated EPL-induced vasorelaxation. Modulators of the store-operated Ca²⁺ entry (SOCE), thapsigargin, 2-aminoethyl diphenylborinate and Gd³⁺, and an inhibitor of Akt, wortmannin, markedly attenuated the EPL-induced vasorelaxation. Further, the EPL-induced vasorelaxation was significantly attenuated by pretreatment with tetraethylammonium, a non-selective K_Ca channels blocker, or glibenclamide, an ATP-sensitive K⁺ channels inhibitor, respectively. Inhibition of cyclooxygenases with indomethacin, and adrenergic and muscarinic receptors blockade had no effects on the EPL-induced vasorelaxation.

Conclusions

The present study suggests that EPL relaxes vascular smooth muscle via endothelium-dependent and Akt- and SOCE-eNOS-cGMP-mediated pathways through activation of both K_Ca and K_ATP channels and inhibition of L-type Ca²⁺ channels.     

Mechanisms underlying the vascular relaxation activities of Zingiber officinale var. rubrum in thoracic aorta of spontaneously hypertensive rats

ObjectiveTo evaluate vasorelaxant and vasoconstriction effects of Zingiber officinale var. rubrum (ZOVR) on live rats and isolated aortic rings of spontaneously hypertensive rats (SHRs).MethodsExtracts of ZOVR were subjected to in-vivo antihypertensive screening using noninvasive blood pressures in SHRs. The most potent extract, ZOVR petroleum ether extract (ZOP) was then fractionated using n-hexane, chloroform and water. Isolated thoracic aortic rings were harvested and subjected to vascular relaxation studies of n-hexane fraction of ZOP (HFZOP) with incubation of different antagonists such as N^ω-nitro-l-arginine methyl ester (L-NAME, 10 µmol/L), indomethacin (10 µmol/L), methylene blue (10 µmol/L), atropine (1 µmol/L), glibenclamide (10 µmol/L), prazosin (0.01 µmol/L), and propranolol (1 µmol/L).ResultsDuring the screening of various ZOVR extracts, ZOP produced the most reduction in blood pressures of SHRs and so did HFZOP. HFZOP significantly decreased phenylephrine-induced contraction and enhanced acetylcholine-induced relaxation. L-NAME, indomethacin, methylene blue, atropine, and glibenclamide significantly potentiated the vasorelaxant effects of HFZOP. Propranolol and prazosin did not alter the vasorelaxant effects of HFZOP. HFZOP significantly suppressed the Ca²⁺-dependent contraction and influenced the ratio of the responses to phenylephrine in Ca²⁺-free medium.ConclusionThis study demonstrates that ZOP may exert an antihypertensive effect in the SHR model. Its possible vascular relaxation mechanisms involve nitric oxide and prostacyclin release, activation of cGMP-K_ATP channels, stimulation of muscarinic receptors, and transmembrane calcium channel or Ca²⁺ release from intracellular stores. Possible active compounds that contribute to the vasorelaxant effects are 6-gingerol, 8-gingerol and 6-shogaol.     

Water extract of Zanthoxylum piperitum induces vascular relaxation via endothelium-dependent NO-cGMP signaling

Aim of the study

The aim of the present study was to define the effects of extracts of leaves of Zanthoxylum piperitum (ZP) on the vascular tension and its mechanisms responsible in rat thoracic aortic rings.

Materials and methods

Methanol extract of ZP and aqueous fraction of the methanol extract (AZP) were examined for their vascular relaxant effects in isolated phenylephrine-precontracted aortic rings.

Results

Methanol extract of ZP and aqueous fraction of the methanol extract (AZP) induced relaxation of the phenylephrine-precontracted aortic rings in a concentration-dependent manner. Endothelium-denudation abolished the AZP-induced vasorelaxation. Pretreatment of the endothelium-intact aortic rings with N^G-nitro-l-arginine methylester (L-NAME) and 1H-[1,2,4]-oxadiazolo-[4,3-α]-quinoxalin-1-one (ODQ) inhibited the AZP-induced vasorelaxation. Inhibition of Ca²⁺ entry via L-type Ca²⁺ channels failed to block the AZP-induced vasorelaxation. Extracellular Ca²⁺ depletion slightly but significantly attenuated the AZP-induced vasorelaxation. Thapsigargin significantly attenuated the AZP-induced vasorelaxation. Further, Gd³⁺ and 2-aminoethyl diphenylborinate (2-APB), inhibitors of store-operated Ca²⁺ entry (SOCE), markedly attenuated the AZP-induced vasorelaxation. Also, wortmannin, an inhibitor of Akt, an upstream signaling molecule of eNOS, attenuated the AZP-induced vasorelaxation. AZP increased cGMP levels of the aortic rings in a concentration-dependent manner and the effect was blocked by L-NAME, ODQ, thapsigargin, Gd³⁺, 2-APB, and wortmannin. K⁺ channel inhibition with glibenclamide and tetraethylammonium, cyclooxygenase inhibition with indomethacin, and adrenergic and muscarinic receptors blockade had no effects on the AZP-induced vasorelaxation.

Conclusion

Taken together, the present study suggests that AZP relaxes vascular smooth muscle via endothelium-dependent activation of NO-cGMP signaling through the Akt- and SOCE-eNOS pathways.     

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.     

Vascular relaxation by ethanol extract of Xanthoceras sorbifolia via Akt- and SOCE-eNOS-cGMP pathways

Aim of the study

The aim of the present study was to define the effect of Xanthoceras sorbifolia extracts (XS) on vascular tension and responsible mechanisms in rat thoracic aortic rings.

Materials and methods

Ethanol extract of the leaves of XS (EXS) was examined for their vascular relaxant effects in isolated phenylephrine-precontracted rat thoracic aorta.

Results

EXS (0.1-100 μg/ml) induced relaxation of the phenylephrine-precontracted aortic rings in a concentration-dependent manner. Endothelium-denudation abolished EXS-induced vasorelaxation. Pretreatment of the endothelium-intact aortic rings with N^G-nitro-l-arginine methylester (l-NAME) and 1H-[1,2,4]-oxadiazolo-[4,3-α]-quinoxalin-1-one (ODQ) inhibited EXS-induced vasorelaxation. Inhibition of Ca²⁺ entry via l-type Ca²⁺ channels failed to block the EXS-induced vasorelaxation. Extracellular Ca²⁺ depletion significantly attenuated EXS-induced vasorelaxation. Modulators of the store-operated Ca²⁺ entry (SOCE), thapsigargin, 2-aminoethyl diphenylborinate (2-APB) and Gd³⁺, and an inhibitor of Akt, wortmannin, markedly attenuated the EXS-induced vasorelaxation. EXS increased cGMP levels of the aortic rings in a concentration-dependent manner and the effect was blocked by l-NAME, ODQ, thapsigargin, Gd³⁺, 2-APB, and wortmannin. Further, EXS-induced vasorelaxation was significantly attenuated by tetraethylammonium, a non-selective K_ca channels blocker, but not by glibenclamide, an ATP-sensitive K⁺ channels inhibitor. Inhibition of cyclooxygenase with indomethacin, and adrenergic and muscarinic receptors blockade had no effects on EXS-induced vasorelaxation.

Conclusions

The present study suggests that EXS relaxes vascular smooth muscle via endothelium-dependent NO-cGMP signaling through activation of the Akt- and SOCE-eNOS-sGC pathways, which may, at least in part, be related to the function of K⁺ channels.     

木犀草素对大鼠主动脉的舒张作用及相关机制研究

 目的观察木犀草素的舒血管作用并探讨其作用机制。方法大鼠胸主动脉环张力测定法。结果在内皮完整及去内皮血管上,木犀草素均浓度(4.5～36 μmol·L^-1)依赖性地降低苯肾上腺素(PE)预收缩血管的张力,拮抗高钾引起的血管收缩;木犀草素使PE收缩曲线非平行右移,且使最大张力减小;L-NAME,propranolol对木犀草素的舒血管作用无显著影响;钾通道阻断剂TEA,4-AP,BaCl₂,5-HD均能显著减弱木犀草素的血管舒张作用;木犀草素可以显著地对抗无钙、无钾、无钙环境下渐复钙后由PE引起的血管收缩。结论木犀草素对血管的舒张作用表现为非内皮依赖性,其舒张作用与其直接抑制电压依从性钙通道、受体操纵性钙通道、细胞内钙释放,以及激活钾通道有关,而与α,β受体无关。     

Mechanisms of the dilator action of the Erigerontis Herba on rat aorta

Ethnopharmacological relevance

Erigerontis Herba is widely used as a traditional Chinese medicine and is commonly used for neuroprotection and vascular protection.

Aim of study

In this study, the vasodilator effects of Erigerontis Herba (DZXX) were investigated using rat isolated aorta rings.

Material and method

The involvement of endothelium in the vasorelaxation was studied by comparing response of endothelium-intact and endothelium-denuded aorta rings which precontracted with U46619. The involvement of K⁺ channels was studied by pretreatment of the aorta rings with various K⁺ channel inhibitors. The involvement of Ca²⁺ channel was studied by incubating aorta rings with Ca²⁺-free solution, primed with U46619 prior to elicit contraction by addition of Ca²⁺ solution.

Results

DZXX (0.2–2 mg/ml) induced a concentration-dependent relaxation on U44619-precontracted aorta rings with EC₅₀ of 0.354±0.036 mg/ml. Removal of endothelium or pretreatment with a BK_Ca inhibitor iberiotoxin, K_IR inhibitor barium chloride or K_v inhibitor 4-aminopyridine produced no effect on the DZXX-induced vasorelaxation. However, pretreatment with a K_ATP inhibitor glibenclamide or a non-selective K⁺ channel inhibitor tetraethylammonium produced significant inhibition on the DZXX-induced vasorelaxation by 29.9% and 21.3%, respectively. Pretreatment with DZXX (0.4, 1.2 and 2 mg/ml) produced a concentration-dependent inhibition on Ca²⁺-induced vasoconstriction.

Conclusions

These results suggest that the vasodilator effect of DZXX was endothelium-independent, mediated by decreasing the influx of Ca²⁺ by calcium channel inhibition and increasing the influx of K⁺ by opening of a K_ATP channel.