Interaction between thiol-modifying agents and P1075, a KATP channel opener, in rat isolated aorta

In vascular smooth muscle, openers of ATP-dependent potassium channels (K _ATP channels), such as P1075 (N-cyano-N’-(1,1-dimethylpropyl)-N’’-3-pyridylguanidine), produce relaxation. In this study we have investigated the effects of thiol-modifying agents on the binding of P1075 and on the ⁸⁶Rb⁺ efflux stimulating and vasorelaxant effects of the opener in rat aortic rings. The increase in ⁸⁶Rb⁺ efflux induced by P1075 was taken as a qualitative measure of K⁺ channel opening. The hydrophilic SH-group-oxidizing substance, thimerosal (1 to 100μM), abolished specific binding of [³H]-P1075 with an IC₅₀ value of 7.6±1.2μM; at 30μM, the half time for inhibition was 38min. Two other thiol-oxidizing agents, PMB (4-hydroxy-mercuribenzoic acid) and DTBNP (2,2’-dithio-bis(5-nitropyridine)), inhibited binding up to 86% and 44%, respectively. The disulphide bond reducing substance, DTT (1,4-dithiothreitol, 0.1 to 1mM), reduced [³H]-P1075 binding by up to 20% and partially reversed the inhibitory effect of thimerosal. In ⁸⁶Rb⁺ efflux experiments, thimerosal (3 to 100μM) concentration-dependently increased basal efflux but inhibited P1075-stimulated tracer efflux with an IC₅₀ value of 7±1μM. The inhibitory effect occurred with a half-time of approximately 8min and was essentially reversed by DTT. In rings precontracted with noradrenaline, thimerosal inhibited the vasorelaxant effect in a noncompetitive manner, shifting the concentration-relaxation curves to the right and reducing maximum relaxation.The data show that oxidation of thiol groups interferes with the binding of the K _ATP channel opener, P1075; concomitantly, the ⁸⁶Rb⁺ efflux stimulating and the vasorelaxant effects are inhibited. Reduction of disulphide bonds by DTT has only minor effects on the action of P1075. Collectively, the results suggest that intact thiol groups are essential for the functioning of the K_ATP channel in rat aorta. The different kinetics governing the inhibition of opener binding and of opener-stimulated ⁸⁶Rb⁺ efflux suggest that the SH-groups involved in the two processes differ in their accessibility to thimerosal and/or in their reactivity. Received: 7 April / Accepted: 9 July 1997     

Ba2+ differentially inhibits the Rb+ efflux promoting and the vasorelaxant effects of levcromakalim and minoxidil sulfate in rat isolated aorta

The K⁺ channel openers activate ATP-sensitive K⁺ channels (K_ATP) in vascular smooth muscle and induce relaxation. In this study, the relationship between these two effects was examined in rings of rat aorta using levcromakalim and minoxidil sulfate as the openers and Ba²⁺ as the K⁺ channel blocker; K⁺ channel opening was assessed by determining the rate constant of ⁸⁶Rb⁺ efflux from the preparation.Ba²⁺ inhibited the ⁸⁶Rb⁺ efflux stimulated by levcromakalim in a noncompetitive manner with an IC₅₀ value of 29 M and a Hill-coefficient of 1.2. At concentrations > 300 M, Ba²⁺ increased the tension of rat aortic rings concentration-dependently. Levcromakalim relaxed contractions to Ba²⁺ (0.5 and 1 mM) with potencies similar to those determined against KCl (25 mM) or noradrenaline as spasmogens (EC₅₀ values 15–40 nM). The vasorelaxant effect against Ba²⁺ was inhibited by the K_ATP channel blockers, glibenclamide and tedisamil, and abolished in depolarizing medium (55 mM KCl). At 3 mM Ba²⁺, levcromakalim was still able to transiently induce complete relaxation; however, within 1 h oscillations in tension developed, leading to a stable level of only 15% relaxation. A similar level of relaxation was achieved against 10 mM Ba²⁺ whereas the combination of 0.5 mM Ba²⁺ and 3 M tedisamil blocked the relaxant effect of levcromakalim completely. With minoxidil sulfate as the K_ATP channel opener the results of the ⁸⁶Rb⁺ efflux and tension experiments were similar to those obtained with levcromakalim.It is concluded that Ba²⁺ is more potent in inhibiting the K⁺ channel opening than the vasorelaxant effects of the openers. On the basis of the ⁸⁶Rb⁺ efflux experiments it is estimated that at least 97% of the channels opened by the activators can be blocked without major effects on vasorelaxation suggesting a dissociation between the two effects. However, if the block is pushed to extremes ( 99.95%) the vasorelaxant effect of the openers is also abolished suggesting a link between both effects. This paradoxon remains to be solved.     

Korean Red Ginseng Water Extract Restores Impaired Endothelial Function by Inhibiting Arginase Activity in Aged Mice

Cardiovascular disease is the prime cause of morbidity and mortality and the population ages that may contribute to increase in the occurrence of cardiovascular disease. Arginase upregulation is associated with impaired endothelial function in aged vascular system and thus may contribute to cardiovascular disease. According to recent research, Korean Red Ginseng water extract (KRGE) may reduce cardiovascular disease risk by improving vascular system health. The purpose of this study was to examine mechanisms contributing to age-related vascular endothelial dysfunction and to determine whether KRGE improves these functions in aged mice. Young (10±3 weeks) and aged (55±5 weeks) male mice (C57BL/6J) were orally administered 0, 10, or 20 mg/mouse/day of KRGE for 4 weeks. Animals were sacrificed and the aortas were removed. Endothelial arginase activity, nitric oxide (NO) generation and reactive oxygen species (ROS) production, endothelial nitric oxide synthase (eNOS) coupling, vascular tension, and plasma peroxynitrite production were measured. KRGE attenuated arginase activity, restored nitric oxide (NO) generation, reduced ROS production, and enhanced eNOS coupling in aged mice. KRGE also improved vascular tension in aged vessels, as indicated by increased acetylcholine-induced vasorelaxation and improved phenylephrine-stimulated vasoconstriction. Furthermore, KRGE prevented plasma peroxynitrite formation in aged mice, indicating reduced lipid peroxidation. These results suggest KRGE exerts vasoprotective effects by inhibiting arginase activity and augmenting NO signaling and may be a useful treatment for age-dependent vascular diseases.     

Mechanisms of endothelium-dependent vasorelaxation induced by procyanidin B2 in venous bypass graft

Cardioprotective abilities of procyanidins, might, at least in part, attribute to their vasodilator properties. The present study was undertaken to assess the vasorelaxant effect of procyanidin B2 on isolated human saphenous vein (HSV) and its underlying mechanisms. Procyanidin B2 relaxed phenylephrine-induced contraction of HSV rings in concentration-dependent manner. The relaxation was dependent on the presence of endothelium and was strongly affected by l-NAME, hydroxocobalamin or ODQ, the inhibitors of NO/cGMP pathway. Indomethacin significantly affected only the relaxation produced by the highest concentrations of procyanidin B2. Apamin and TRAM-34 combination, in the presence of l-NAME and indomethacin, did not additionally decreased procyanidin B2-induced relaxation. In the presence of K⁺ channel blockers, relaxation induced by procyanidin B2 was partially attenuated by 4-aminopyridine, significantly inhibited by glibenclamide and almost abolished by iberiotoxin. Procyanidin B2 also relaxed the contractions induced by phenylephrine or caffeine in Ca²⁺-free solution. Finally, nifedipine slightly, while thapsigargin strongly antagonized HSV relaxation. Our results indicate that procyanidin B2 induces endothelium-dependent relaxation of HSV, which results primarily from stimulation of NO production, as well K⁺ channels opening, especially BK_Ca, and partially K_ATP and K_V. Regulation of the intracellular Ca²⁺ release and inhibition of Ca²⁺ influx probably contribute to procyanidin B2-induced relaxation.     

Cryptostrobin and catechin isolated from Eugenia mattosii D. Legrand leaves induce endothelium-dependent and independent relaxation in spontaneously hypertensive rat aorta

BackgroundConsidering the therapeutic potential of phenolic compounds, the purpose of the present study was to investigate the mechanisms involved in the relaxation induced by cryptostrobin and catechin, isolated from Eugenia mattosii D. Legrand leaves, in the aorta of spontaneously hypertensive rats (SHR).MethodsThe thoracic aorta was isolated from SHR and kept in the organ bath system by recording contractile or relaxant responses.ResultsThe addition of cumulative concentrations of cryptostrobin and catechin induced endothelium-dependent and-independent relaxation in aorta rings from SHR, as well as both compounds were effective in reducing phenylephrine-induced contraction. Pretreatment of aortic rings with N_ω-nitro-l-arginine methylester (L-NAME, an inhibitor of nitric oxide synthase) or 1H-[1,2,4] oxadiazolo[4,3-a]quinoxalin-1-one (ODQ, an inhibitor of soluble guanylate cyclase), resulted in a significant change of relaxant effect induced by catechin, and a slight influence on cryptostrobin-induced relaxation. Muscarinic receptor and potassium channels are involved in catechin-induced relaxation as assessed using atropine (a muscarinic receptor antagonist), tetraethylammonium (a non-selective K⁺ channel blocker) and glibenclamide (an ATP-sensitive K⁺ channel blocker). Conversely, cryptostrobin, but not catechin, blunted the contraction induced by the addition of phenylephrine in a calcium-free solution. Besides that, cryptostrobin attenuated the contraction of rat aorta rings induced by internal Ca²⁺ release and external Ca²⁺ influx.ConclusionsThese findings indicated that cryptostrobin and catechin alter vascular smooth muscle reactivity, and this effect may be involved, at least in part, by enhancing the endothelium NO/cGMP pathway and potassium channels activation. In addition, cryptostrobin reduced the phenylephrine, KCl and CaCl₂-induced contractions in a calcium-free solution.     

胰岛素抵抗高血压大鼠血管舒张功能异常的机制

目的探讨胰岛素抵抗高血压（ＩＲＨ）大鼠血管舒张功能的改变及其可能机制。方法采用离体血管功能实验方法,观察大鼠主动脉的舒张功能及其平滑肌钙代谢功能;应用逆转录多聚酶链反应技术检测主动脉平滑肌Ｃａ２＋－ＡＴＰ酶ｍＲＮＡ的表达水平。结果（１）ＩＲＨ大鼠主动脉舒张速度减慢;（２）用无钙ｋｒｅｂｓ液灌流后苯肾上腺素引起的收缩反应显著低于对照大鼠;（３）ＩＲＨ大鼠主动脉平滑肌Ｃａ２＋－ＡＴＰ酶ｍＲＮＡ表达水平显著低于对照大鼠。结论ＩＲＨ大鼠主动脉舒张功能下降与Ｃａ２＋－ＡＴＰ基因酶ｍＲＮＡ水平表达下降引起的平滑肌Ｃａ２＋代谢功能障碍有关。     

Vasorelaxation and hyperpolarisation of rat small mesenteric artery by the quaternary anion tetraphenylboron

This study characterises the vasorelaxation and hyperpolarisation effects of the negatively charged quaternary compound tetraphenylboron (TPB) in the rat small mesenteric artery. Segments of rat small mesenteric artery were mounted in a myograph and vessel tone and membrane potential were measured simultaneously. In vessels pre-contracted with vasopressin (0.3–0.6 nM), U46619 (30–90 nM) or methoxamine (0.3–3 M), TPB (0.1–100 M) produced a marked endothelium-independent relaxation. However, vasorelaxation responses to TPB were abolished in tissues pre-contracted with K⁺ (50 mM), and significantly inhibited by glibenclamide (glib, 10 M).In the absence of tone, TPB (1–30 M) caused a concentration-dependent membrane hyperpolarisation of rat mesenteric artery smooth muscle cells, which was not dependent on the endothelium, but sensitive to glibenclamide (10 M). In methoxamine (0.3–3 M) pre-contracted vessels, the relaxation response was associated with a marked hyperpolarisation, which was also sensitive to glibenclamide (10 M), further inhibited by a combination of K⁺ channel blockers (glib [10 M], charybdotoxin [100 nM], apamin [100 nM], 4-aminopyridine [1 mM] and Ba²⁺ [30 M]) and abolished by 50 mM K⁺.The results of this study show that TPB causes a vasorelaxation and hyperpolarisation response in the rat small mesenteric artery through a direct action on the vascular smooth muscle. TPB exerts its effects partially via the activation of K_ATP channels, but also by another mechanism involving K⁺-dependent hyperpolarisation.Abbreviations 4-AP 4-Aminopyridine - ACh Acetylcholine - ChTX Charybdotoxin - Glib Glibenclamide - ODQ 1H-[1,2,4]Oxadiazolo[4,3-a]quinoxalin-1-one - TPB Tetraphenylboron - TPP Tetraphenylphosphonium - U46619 9,11-Dideoxy-9,11-epoxymethanoprostaglandinF₂     

内源性大麻素系统心血管作用的研究进展

内源性大麻素系统在心血管系统中的作用涉及到血压、心率、心肌收缩力的调节等许多方面,在生理条件下主要通过刺激大麻素1受体(CB1受体)发挥降低血压和心脏抑制效果;在多种病理条件中也起了重要作用,包括通过CB1受体活化参与出血、内毒素和心源性休克、肝硬化伴随的低血压,降低高血压大鼠的血压;通过大麻素2受体(CB2受体)活化防止动脉粥样硬化进展,还能对缺血再灌注后的心肌起保护作用,但CB1受体和CB2受体谁在其中起主要作用尚不明确。对其机制的深入研究对研制新的药物,治疗心血管疾病有着深远意义。     

绿茶多酚减轻环孢素A致血管收缩和肾毒性的实验研究

目的探讨绿茶多酚（GTP）对环孢素A（CsA）大鼠胸主动脉环血管舒张功能和肾毒性的作用机制。方法将30只SD大鼠随机平均分为3组：CsA组、对照组和CsA＋GTP组。建立CsA动物模型5周后,检测血尿素氮（BUN）、肌酐（Cr）;取胸主动脉环,观察乙酰胆碱（Ach）诱发的血管舒张反应、L—NAME和吲哚美辛预处理对舒张功能的影响,检测血管组织一氧化氦（NO）水平;并观察各组肾脏组织病理学变化。结果5周后,CsA组大鼠BUN、Cr水平高于对照组和CsA＋GTP组,差异有统计学意义（P〈0．05）。CsA组大鼠Ach引起的胸主动脉环的最大舒张度为（42.5±4．3）％,低于对照组的（81．2±76）％和CsA＋GTP组的（70．1±6．5）％,差异均有统计学意义（P〈0.05）。经L—NAME预处理后,CsA组和CsA＋GTP组动脉环的舒张反应低于对照组;经吲哚美辛预处理后对照组和CsA＋GTP组的舒张反应高于CsA组（均P〈0．05）。CsA组大鼠血管组织中NO含量显著低于对照组和CsA＋GTP组（P〈0．05）。肾脏组织病理学检测：CsA组肾小管、间质损伤评分显著高于对照组,而GTP＋CsA组则显著低于CsA组（均P〈0.05）。结论CsA可对肾脏的结构和功能产生损害,并引起NO介导的内皮依赖性血管舒张功能异常。绿茶多酚能保护肾脏的结构和功能,改善内皮细胞依赖性的血管舒张功能。     

Vasorelaxing Activity of Ulmus davidiana Ethanol Extracts in Rats: Activation of Endothelial Nitric Oxide Synthase

Ulmus davidiana var. japonica Rehder (Urticales: Ulmaceae) (UD) is a tree widespread in northeast Asia. It is traditionally used for anticancer and anti-inflammatory therapy. The present study investigated the effect of an ethanol extract of UD on vascular tension and its underlying mechanism in rats. The dried root bark of UD was ground and extracted with 80% ethanol. The prepared UD extract was used in further analysis. The effect of UD on the cell viability, vasoreactivity and hemodynamics were investigated using propidium iodide staining in cultured cells, isometric tension recording and blood pressure analysis, respectively. Low dose of UD (10~100μg/ml) did not affect endothelial cell viability, but high dose of UD reduced cell viability. UD induced vasorelaxation in the range of 0.1~10μg/ml with an ED(50) value of 2μg/ml. UD-induced vasorelaxation was completely abolished by removal of the endothelium or by pre-treatment with L-NAME, an inhibitor of nitric oxide synthase. UD inhibited calcium influx induced by phenylephrine and high K(+) and also completely abolished the effect of L-NAME. Intravenous injection of UD extracts (10~100 mg/kg) decreased arterial and ventricular pressure in a dose-dependent manner. Moreover, UD extracts reduced the ventricular contractility (+dP/dt) in anesthetized rats. However, UD-induced hypotensive actions were minimized in L-NAME-treated rats. Taken together, out results showed that UD induced vasorelaxation and has antihypertensive properties, which may be due the activation of nitric oxide synthase in endothelium.