Analysis of the Role of Nitric Oxide in the Relaxant Effect of the Crude Extract and Fractions from Eugenia uniflora in the Rat Thoracic Aorta

This study has evaluated the possible role played by the l-arginine-nitric oxide pathway in the vasorelaxant action of the hydroalcoholic extract from Eugenia uniflora, and fractions from the extract, in rings of rat thoracic aorta. The addition of an increasing cumulative concentration of hydroalcoholic extract from E. uniflora (1–300 μg mL^?1) caused a concentration-dependent relaxation response in intact endothelium-thoracic aorta rings pre-contracted with noradrenaline (30–100 nm). The IC50 value, with its respective confidence limit, and the maximum relaxation (R_max) were 7.02 (4.77–10.00) μg mL^?1 and 83.94 ± 3.04%, respectively. The removal of the endothelium completely abolished these responses. The nitric oxide synthase inhibitors N^ω-nitro-l-arginine (l-NOARG, 30 μm) and N^ω-nitro-l-arginine methyl ester (l-NAME, 30 μm), inhibited the relaxation (R_max) to ?10.43 ± 7.81% and ?3.69 ± 2.62%, respectively. In addition, l-arginine (1 mm), but not d-arginine (1 mm), completely reversed inhibition by l-NOARG. Methylene blue (30 μm), a soluble guanylate cyclase inhibitor, reduced the relaxation induced by the extract to 14.60 ± 7.40%. These data indicate that in the rat thoracic aorta the hydroalcoholic extract, and its fractions, from the leaves of E. uniflora have graded and endothelium-dependent vasorelaxant effects.     

Cardiovascular effects induced by N-(4'-dihydro)-piperoylthiomorpholine in normotensive rats

Objectives We have tested the cardiovascular effects of N‐(4′‐dihydro)‐piperoylthiomorpholine (LASSBio 365) on rats using an in‐vivo and in‐vitro approach. Methods LASSBio 365 (0.025, 0.05, 0.1, 0.25, 0.5 or 1 mg/kg, randomly injected) was administered to conscious unrestrained rats and the mean arterial pressure and heart rate were measured. The effects of LASSBio 365 (3 × 10^?6–3 × 10^?4m ) on rat isolated aortic rings with and without endothelium were investigated. Key findings LASSBio 365 induced a dose‐dependent decrease in mean arterial pressure and heart rate (ED50 = 158 ± 53 µg/kg). The effects evoked by LASSBio 365 (0.5 mg/kg) were inhibited by pretreatment with atropine. In anaesthetized rats, electrocardiogram recordings revealed second/third degree sinoatrial and atrioventricular blockade induced by the compound, which were completely inhibited after cardiac muscarinic blockade or cervical bilateral vagotomy. In rat isolated aortic rings, LASSBio 365 (3 × 10^?6–3 × 10^?4m ) was capable of antagonizing the contractile effects induced by phenylephrine (1 µm ) or KCl (80 mm ) (IC50 = 107 ± 6; 92 ± 6 µm , respectively). This effect was not inhibited after removal of the vascular endothelium (IC50 = 84 ± 4; 92 ± 10 µm , respectively). LASSBio 365 (10^?6–10^?4m ) antagonized CaCl₂‐induced contractions in a concentration‐dependent manner. Furthermore, LASSBio 365 (98 µm ) inhibited contractions produced by noradrenaline (1 µm ), but not those induced by caffeine (20 mm ). Conclusions These results suggested that LASSBio 365 produced negative chronotropism and reduced peripheral resistance that were probably due to the stimulation of cardiac muscarinic pathways. Peripheral vasodilation was probably linked to voltage‐dependent Ca²⁺‐channel blockade and/or specific inhibition of Ca²⁺ release from noradrenaline‐sensitive intracellular stores.     

Warifteine,a bisbenzylisoquinoline alkaloid,induces relaxation by activating potassium channels in vascular myocytes

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1,8‐Cineole induces relaxation in rat and guinea‐pig airway smooth muscle

Objectives 1,8‐Cineole is a monoterpene with anti‐inflammatory, vascular and intestinal smooth muscle relaxant activity. We have evaluated the potential bronchodilatatory activity of this compound. Methods 1,8‐Cineole was tested against carbachol, histamine, K⁺ 80 mM and ovalbumin‐induced bronchial contractions in Wistar rat or guinea‐pig tissues. Some of the guinea‐pigs had been previously sensitized with an intramuscular injection of 5% (w/v) ovalbumin/saline solution. Control animals received 0.3 ml saline. In separate experimental groups the response to 1,8‐cineole (1–30 mg/kg), phenoterol (0.05–5 mg/kg) or vehicle (0.3% Tween in saline) was studied. Key findings 1,8‐Cineole decreased, in vivo, rat bronchial resistance with similar efficacy as phenoterol (66.7 ± 3.2% vs 72.1 ± 5.3%). On the other hand, the maximal relaxant response to 1,8‐cineole in carbachol‐precontracted rat tracheas was 85.5 ± 5.7% (IC50 = 408.9 (328–5196) μg/ml) compared with 80.2 ± 4.8% (IC50 = 5.1 (4.3–6.1) μg/ml) with phenoterol. The addition of 1,8‐cineole to guinea‐pig tracheal rings tonically contracted with K⁺ 80 mM induced a concentration‐related relaxation. The maximal relaxation elicited by 1,8‐cineole was 113.6 ± 11.7% (IC50 127.0 (115.9–139.2) μg/ml) compared with 129.7 ± 14.6% (IC50 0.13 (0.12–0.14) μg/ml) achieved after phenoterol administration. In addition, the incubation of tracheal rings with 1,8‐cineole (100, 300 or 1000 μg/ml), 15 min before inducing phasic contractions with K⁺ 80 mM, decreased the maximal amplitude of the contraction by 31.6 ± 4.6, 75.7 ± 2.7 and 92.2 ± 1.5%, respectively. In another set of experiments, neither the maximal response nor the IC50 for the 1,8‐cineole‐induced relaxation were different between normal and ovalbumin‐sensitized tissues. Moreover, the relaxation of bronchial rings contracted after exposure to 1 μg/ml ovalbumin occurred at a faster rate in rings pre‐incubated with 1,8‐cineole when compared with rings pre‐incubated with vehicle only (Tween 0.3%). Therefore, in the first minute after the antigen challenge, the tracheal tissue relaxed after the peak contraction by 6.5, 21.4 (P < 0.05 vs control) and 66.9% (P < 0.05 vs control) in the presence of 100, 300 or 1000 μg/ml 1,8‐cineole, respectively. Conclusions 1,8‐Cineole relaxed rat and guinea‐pig (nonsensitized and ovalbumin‐sensitized) airway smooth muscle by a nonspecific mechanism.     

Analysis of Adenosine Vascular Effect in Isolated Rat Aorta: Possible Role of Na+/K+‐ATPase

Abstract: The present experiments were undertaken in order to examine the effect of adenosine in isolated rat aorta, to investigate the possible role of intact endothelium and endothelial relaxing factors in this action and to determine which population of adenosine receptors is involved in rat aorta response to adenosine. Adenosine (0.1–300 μM) produced concentration‐dependent (intact rings: pD₂=4.39±0.09) and endothelium‐independent (denuded rings: pD₂=4.52±0.12) relaxation of isolated rat aorta. In the presence of high concentration of K⁺ (100 mM) adenosine‐evoked relaxation was significantly reduced (maximal relaxation in denuded rings: control – 92.1±9.8 versus K⁺– 54.4±5.0). Similar results were obtained after incubation of ouabain (100 μM) or glibenclamide (1 μM). In K⁺‐free solution, K⁺ (1–10 mM)‐induced rat aorta relaxant response was significantly inhibited by ouabain (100 μM). Application of indomethacin (10 μM), N^G‐nitro‐L‐arginine (10 μM) or tetraethylammonium (500 μM) did not alter the adenosine‐elicited effect in rat aorta. 8‐(3‐Chlorostyril)‐caffeine (0.3–3 μM), a selective A_2A‐receptor antagonist, significantly reduced adenosine‐induced relaxation of rat aorta in a concentration‐dependent manner (pK_B=6.57). Conversely, 1,3‐dipropyl‐8‐cyclopentylxanthine (10 nM), an A₁‐receptor antagonist, did not affect adenosine‐evoked dilatation. These results indicate that in isolated rat aorta, adenosine produces endothelium‐independent relaxation, which is most probably dependent upon activation of smooth muscle Na⁺/K⁺‐ATPase, and opening of ATP‐sensitive K⁺ channels, to a smaller extent. According to receptor analysis, vasorelaxant action of adenosine in rat aorta is partly induced by activation of smooth muscle adenosine A_2A receptors.     

Trimebutine maleate relaxes the isolated rat thoracic aorta: The role of nitric oxide and L‐type calcium channels

Trimebutine maleate (TMB), a widely prescribed drug for functional gastrointestinal disorders, has been reported to regulate smooth muscle contractility by modulating multiple ion channel activities in the gastrointestinal tract. However, its action on isolated aorta has not yet been reported. The aim of the present study was to evaluate in vitro vasorelaxant properties and the underlying pharmacological mechanisms of TMB in isolated rat thoracic aortic rings. Vascular activity experiments were performed on thoracic aorta isolated from Sprague‐Dawley rats in vitro, including endothelium‐intact and endothelium‐denuded aortic rings. TMB (10^?10‐10^?5 mol/L) induced relaxation in endothelium‐intact aortic rings precontracted by phenylephrine with a potency similar to that of carbachol. TMB‐induced relaxation was not altered by glibenclamide and atropine in endothelium‐intact aortic rings. However, L‐NAME and endothelium denudation significantly reduced but not completely reversed the vasorelaxant effect of TMB. Also, TMB‐induced relaxation wasn't affected by diclofenac in endothelium‐intact aortic rings. TMB at 10^?5 mol/L significantly reduced the CaCl₂‐induced contractions in endothelium‐intact aortic rings stimulated with KCl, but not stimulated with phenylephrine under Ca²⁺free conditions. Moreover, TMB at 10^?5 mol/L effectively attenuated Bay‐K8644‐induced contractions in aortic rings. These results suggest that TMB‐induced relaxation was mediated by both endothelium‐dependent and endothelium‐independent manner in isolated rat thoracic aorta. The mechanism of TMB‐induced relaxation at low concentrations is partially related to NO‐ and endothelium‐dependent but unrelated to prostanoids formation. However, inhibition of Ca²⁺ influx through voltage‐operated calcium channels and L‐type Ca²⁺channel blocking effect appears to be involved in the mechanism of vasorelaxant effect of TMB at high concentrations.     

Vasorelaxant effect of quercetin on cerebral basilar artery in vitro and the underlying mechanisms study

The aim of this study is to investigate the vasorelaxant effect of quercetin on cerebral basilar artery in vitro and provide a preliminary discussion concerning the underlying mechanisms. Using a DMT-isolated micro vessel system, quercetin was found to exhibit a vasodilatory effect on basilar arteries contracted by potassium chloride (KCl), endothelin-1 (ET-1), and 5-hydroxytryptamine (5-HT). The vasorelaxant effect of quercetin was partially attenuated when endothelium cells were removed. L-NAME, indomethacin, and ODQ treatment also decreased the potency of quercetin. In endothelium-denuded rings, the vasorelaxant effect of quercetin was not influenced by K⁺ channel inhibitors. However, quercetin inhibited KCl induced extracellular calcium influx and ET-1 induced transient intracellular calcium release in a Ca²⁺-free solution. In conclusion, quercetin induced relaxation of the basilar artery in vitro is partially dependent on endothelium, which is mainly related to NO and COX pathways. It also induces relaxation through blockage of calcium channels.     

Relaxant effects of the essential oil of Mentha pulegium L. in rat isolated trachea and urinary bladder

Objectives We evaluated the relaxant activity of the essential oil of Mentha pulegium L. (EOMP) and pulegone in rat isolated tracheal and bladder smooth muscles. Methods Isometric contractions of isolated tracheal and bladder strips from male Wistar rats were induced by KCl (K60; 60 mm ) or acetylcholine (ACh; 10 µm ). EOMP and its majory compound pulegone were incubated, after contracting agent, with the tissues in cumulating concentrations. Key findings EOMP (3–300 µg/ml) inhibited the contractions induced by ACh and K60 in both tissues, but was more effective against the contractions induced by K60 in trachea (IC50 = 40.47 ± 3.27 µg/ml) compared with ACh. Its relaxant action rules out ganglia and NO participation. Pulegone (10^?7 to 10^?3 m ) inhibited the contractions induced by ACh and K60 in both tissues. EOMP concentration‐dependently inhibited the contractions evoked by addition of CaCl₂ in depolarised trachea, suggesting inhibition of extracellular calcium entry. Conclusions These findings suggests that EOMP induced relaxant responses in pre‐contracted smooth muscles of rat trachea and bladder, which are likely to be mediated via inhibition of calcium entry, mainly by its major compound, pulegone. These effects are coherent with the popular use of EOMP as an antispasmodic agent.     

Hypotensive and Vasorelaxant Effects of Citronellol,a Monoterpene Alcohol,in Rats

Abstract: Citronellol is an essential oil constituent from the medicinal plants Cymbopogon citratus, Cymbopogon winterianus and Lippia alba which are thought to possess antihypertensive properties. Citronellol‐induced cardiovascular effects were evaluated in this study. In rats, citronellol (1–20 mg/kg, i.v.) induced hypotension, which was not affected by pre‐treatment with atropine, hexamethonium, N^ω‐nitro‐l ‐arginine methyl ester hydrochloride or indomethacin, and tachycardia, which was only attenuated by pre‐treatment with atropine and hexamethonium. These responses were less than those obtained for nifedipine, a reference drug. In intact rings of rat mesenteric artery pre‐contracted with 10 μM phenylephrine, citronellol induced relaxations (pD₂ = 0.71 ± 0.11; E_max = 102 ± 5%; n = 6) that were not affected by endothelium removal, after tetraethylamonium in rings without endothelium pre‐contracted with KCl 80 mM. Citronellol strongly antagonized (maximal inhibition = 97 ± 4%; n = 6) the contractions induced by CaCl₂ (10^?6 to 3 × 10^?3 M) and did not induce additional effects on the maximal response of nifedipine (10 μM). Finally, citronellol inhibited the contractions induced by 10 μM phenylephrine or 20 mM caffeine. The present results suggest that citronellol lowers blood pressure by a direct effect on the vascular smooth muscle leading to vasodilation.     

Vasorelaxant Effect of Mexican Medicinal Plants on Isolated Rat Aorta

Abstract

The vasorelaxant effect of methanol extracts (0.86–50 µg/ml) of Iresine calea, Psyttacanthus calyculathus. (DC.) G. Don, Laelia autumnalis. (Lex.) Lindley, Brickellia cavanillesii. (Cass.) Gray, and Lepechinia caulescens. (Ortega) Epling, plant species used in Mexican folk medicine for the treatment of hypertension and related diseases, were evaluated in isolated rat aortic rings. The extracts of I. calea. and P. calyculathus. did not show a vasorelaxant activity on norepinephrine-evoked contraction (NE, 1 × 10^?7.5 M) in endothelium-intact (+ E) and endothelium-denuded (? E) rat aorta rings. On the other hand, L. autumnalis. and B. cavanillesii. induced a concentration-dependent and endothelium-independent relaxation on rat aorta. However, the methanol extract of L. caulescens. produced a significant vasodilator effect in a concentration-dependent and endothelium-dependent manner. In order to determine the mode of the vasorelaxant action evoked by L. caulescens., the extract was evaluated in the presence of L-NAME (inhibitor of nitric oxide synthase at 1 × 10^?4 M) and indomethacin (inhibitor of cyclooxygenases at 1 × 10^?5 M). Relaxation was blocked by L-NAME, indicating the extract vasodilating properties are endothelium mediated due to liberation of nitric oxide.     

Cardiovascular effects induced by Cymbopogon winterianus essential oil in rats: involvement of calcium channels and vagal pathway

Objectives This study has investigated the cardiovascular effects of the Cymbopogon winterianus essential oil (EOCW) in rats. C. winterianus is a plant used in folk medicine for the treatment of hypertension. Methods For the measurement of haemodynamic and ECG parameters, male Wistar rats under anaesthesia were cannulated in the abdominal aorta and lower vena cava and electrodes were subcutaneously implanted in their paws. For an in‐vitro approach, the rats were killed and the superior mesenteric artery was removed and cut into rings (1–2 mm). These rings were then mounted in organ baths containing Tyrode's solution at 37 °C and gassed with carbogen. Key findings In rats, EOCW (1–20 mg/kg, i.v.) induced dose‐dependent hypotension and tachycardia. These effects were not affected by L‐NAME or indometacin, but were partially reduced after atropine administration. EOCW (20 mg/kg only) also induced bradycardia‐associated sinoatrial blockade, junctional rhythm, and first‐degree atrioventricular block, which was abolished after atropine administration or vagotomy. In arterial rings, EOCW (0.1–3000 μg/ml) induced relaxation of phenylephrine tonus that was not affected by removal of the endothelium. These relaxations were similar to those observed in rings without endothelium precontracted with KCl 80 mm . EOCW was able to antagonize the CaCl₂ (30–300 μm ) induced contractions in depolarizing solution (KCl 60 mm ). Conclusions These results demonstrated that EOCW induced hypotension and vasorelaxation. These effects appeared to be mainly mediated by Ca⁺²‐channel blocking. Furthermore, the higher dose of EOCW induced transient bradycardia and arrhythmias due to a cardiac muscarinic activation secondary to a vagal discharge.     

Vasorelaxant effects of the extracts and some flavonoids from the buds of Coreopsis tinctoria

Abstract

Context: The buds of Coreopsis tinctoria Nutt (Compositae) are used in the treatment of hypertension in the Uyghur folk medicine in China.

Objective: To investigate vasorelaxant properties of extracts and some flavonoids from C. tinctoria (CT) and their underlying mechanisms in isolated rat thoracic aortic rings.

Materials and methods: Vasorelaxant effects of ethanol extracts of CT (CTA) and its flavonoids as well as water–ethanol eluates from CTA by AB-8 resins (CTAA～CTAF) were evaluated on rat aortic rings pre-contracted with phenylephrine (PE, 1?µM) or high KCl (60?µM). We evaluated the effect of CTA, CTAD and CTAE on PE-induced contraction in a Ca²⁺-free medium and a dose–effect curve of Ca²⁺ in pre-contracted ring with high KCl.

Results: Endothelial removal did not modify the effect of CTAD and CTAE (3.00?g/L) neither on PE-pre-contracted rings (164.78?±?21.44 and 191.47?±?16.75%) nor on KCl-pre-contracted rings (75.68?±?10.76 and 125.14?±?17.41%) compared with intact-endothelium rings pre-contracted with high KCl (100.49?±?17.30 and 110.81?±?16.33%). CTAD and CTAE (3.00?g/L) down-regulated the dose–effect curve of Ca²⁺ in pre-contraction with high KCl, and inhibited the pre-contraction with PE in a Ca²⁺-free medium (p?<?0.05). Seven flavonoids were obtained from CTAD, of which luteolin (5) and quercetin (6) were found to be the most effective relaxation in rings precontracted with PE (EC₅₀: 0.006 and 0.039?g/L, p?<?0.05) or high KCl (EC₅₀: 0.023 and 0.045?g/L, p?<?0.05).

Discussion and conclusion: These data demonstrated the vasorelaxant effect of CT, and its mechanism is likely due to an inhibitory effect on calcium movements through cell membranes.     

Biphasic responses of equine colonic vessel rings to vasoactive inflammatory mediators

1 The role of endothelium in modulating equine colonic vessel responses to histamine (HST), 5-hydroxytryptamine (5-HT), bradykinin (BK) and acetylcholine (ACh) was evaluated in vitro. 2 Segments of mesenteric arteries and veins were collected from the left ventral colon of six adult horses destined for euthanasia for reasons unrelated to cardiovascular or gastrointestinal systems. Vessels were gently cleansed and cut into 4 mm wide rings. 3 Three vessel conditions namely endothelium intact, endothelium removed and N^ω-nitro-L-arginine methyl ester (L-NAME)-treated were used for both arterial and venous rings. Each ring was placed in an organ bath with oxygenated Tyrode’s solution. One side of the ring was fixed to the floor of the bath and the other side to a force-displacement transducer interfaced with a polygraph. 4 An initial tension of 2 g was applied to rings which were allowed to equilibrate for 45 min. The bath solution was gently replaced every 15 min and tension was readjusted to 2 g each time except following the last wash. 5 Rings were precontracted with a single EC₂₅ dose of noradrenaline and after the response plateaued, cumulative concentration (10^??12–10^??4 m ) response curves were determined for each agent on separate rings. The relaxation from the precontracted level to the baseline was considered as 100% relaxation. Maximal relaxation and maximal contractions were statistically analyzed. 6 All agents induced a relaxation response initially, followed by a contractile phase as the concentrations increased in both arteries and veins, thus, making a biphasic concentration–response curve. In arteries, relaxation produced by ACh was significantly greater than 5-HT. Endothelium removal and L-NAME treatment significantly reduced relaxation in arteries. Only endothelium removal produced a significant reduction of relaxation in veins. 7 In both arteries and veins, HST and 5-HT produced significantly greater contraction than ACh or BK. No significant change in contraction was observed in arteries either by endothelium removal or L-NAME treatment, however, contraction was significantly reduced in veins by endothelium removal. 8 These findings suggest that the endothelium plays a major role in modulating equine colonic arterial relaxation via nitric oxide and venous contraction via endothelium-derived contractile mediators, probably endothelin and/or arachidonates.     

Isoliquiritigenin‐induced vasodilation by activating large‐conductance Ca2+‐activated K+ channels in mouse mesenteric arteries

Isoliquiritigenin (ISL) is a flavonoid substance with a chalcone structure, which exerts anti‐tumour, anti‐oxidation and anti‐inflammatory activity. The large‐conductance calcium‐activated potassium channel (BK_Ca) is an important potassium channel with negative feedback regulation on the vascular smooth muscle cells (VSMCs) membrane. The activation of BK_Ca channel causes the hyperpolarization of VSMCs. It plays an important role in relaxation of blood vessels. Previous studies have shown that ISL causes the relaxation of the aorta and the basilar artery of the rat. However, there have not been studies on regulation of ISL in mesenteric arteries. To examine whether ISL causes the relaxation of the mesenteric artery of mice, we recorded vasodilation of mouse mesenteric arterial rings with a myograph. After contraction of arterial rings with phenylephrine, we added ISL to the arterial rings and measured its relaxation effect. To further examine which channel was involved in this relaxation effect, we tested the effects of ISL on endothelium‐dependent and endothelium‐independent vasodilation. Then we used BK_Ca channel blockers tetraethylammonium and iberiotoxin, to detect whether the BK_Ca channel is involved in ISL‐induced vasodilation. Mesenteric arterial smooth muscle cells were isolated by enzyme digestion. Bis‐(1, 3‐dibutylbarbituric acid) trimethine oxonol staining was used to measure membrane potential of mesenteric arterial smooth muscle cells. We identified a vasodilation effect caused by ISL on mouse mesenteric arterial rings pre‐contracted by phenylephrine in a concentration‐dependent manner, with an EC₅₀ of 13.71 ± 1.1 μmol/L. The vasodilation effect of ISL is endothelium‐independent. K⁺ channel inhibitors tetraethylammonium and iberiotoxin reduced the vasodilation induced by ISL which suggested the involvement of BK_Ca channel.     

KMUP 880708: A vanyllilamide‐based β1‐adrenoceptor antagonist with α‐adrenoceptor blocking and potassium channel opening activities

A vanillylamide‐based propanolamine derivative, KMUP 880708, was first investigated both in vivo and in vitro. KMUP 880708 (0.1, 0.5, 1.0, and 2.0 mg kg^–1, iv) produced dose‐dependent hypotensive and bradycardia responses in pentobarbital‐anesthetized Wistar rats. KMUP 880708 (0.1, 0.5, and 1.0 mg kg^–1, iv) also markedly inhibited both the tachycardia effects induced by (–)isoproterenol and arterial pressor responses induced by phenylephrine. KMUP 880708 competitively antagonized (–)isoproterenol‐induced positive inotropic and chronotropic effects of the atria and tracheal relaxation responses on isolated guinea pig tissues. The apparent pA₂ values for KMUP 880708 was 7.82 ± 0.06 in the right atria, 7.51 ± 0.13 in the left atria, and 6.31 ± 0.07 in the trachea, respectively, indicating that KMUP 880708 was selective β₁‐adrenoceptor blocker. In thoracic aorta experiments, KMUP 880708 also produced a competitive antagonism of norepinephrine‐induced contraction with pA₂ value of 7.92 ± 0.52, indicating that KMUP 880708 was α‐adrenoceptor antagonist. In isolated rat thoracic aorta, KMUP 880708 more potently relaxed the contractions induced by phenylephrine (10^–5 M) than those by high K⁺ (75 mM). KMUP 880708‐induced relaxation was significantly reduced by endothelium removal and by exposure to L‐N^G‐nitro arginine methyl ester (L‐NAME, 1 and 3 × 10^–4 M), indomethacin (3 × 10^–5 M), methylene blue (10^–5 M) and 1H‐[1,2,4]oxadiazolol[4,3,‐a]quinoxalin‐1‐one (ODQ, 10^–6 M). The vasorelaxant effect of KMUP 880708 on phenylephrine‐induced contraction was attenuated by the pretreatment with tetraethylammonium (TEA), glibenclamide, charybdotoxin, and apamin, but not by 4‐aminopyridine (4‐AP). In addition, KMUP 880708 inhibited phenylephrine‐induced biphasic contraction and affected the fast‐twitch phase more significantly than the slow tonic phase. In the radioligand‐binding assay, the K_i values of [³H]CGP‐12177 binding to rat ventricle and lung membranes were 15.14 and 524.81 nM, respectively, and the value of [³H]prazosin binding to rat brain membrane was 3.89 nM. The ranking order of inhibition for [³H]CGP‐12177 binding on β‐adrenoceptor was propranolol > labetalol > KMUP 880708 > atenolol, and that for [³H]prazosin binding to α‐adrenoceptor was KMUP 880708 > labetalol. In conclusion, KMUP 880708 was found to be a new generation α/β‐adrenoceptor blocker with selective β₁‐adrenoceptor blocking and vascular smooth muscle relaxation activities. Furthermore, the vasodilator effect of KMUP 880708 is attributed to the release of NO or NO‐related substance from vascular endothelium. While the endothelium‐independent mechanism involved in the relaxation of KMUP 880708 is probably linked to K⁺ channel activation in these vessels. Drug Dev. Res. 55:104–117, 2002. © 2002 Wiley‐Liss, Inc.     

Vasorelaxant effects on rat aortic artery by two types of indole alkaloids, naucline and cadamine

Two indole alkaloids, naucline from Nauclea officinalis and cadamine from Ochreinauclea maingayii, were individually evaluated for vasorelaxant effects on phenylephrine-precontracted aortic rings. Naucline induced concentration-dependent relaxation in aortic rings. Respective EC₅₀ values of naucline on aorta rings with/without endothelium did not show a significant difference, indicating that naucline-induced relaxation was independent of the endothelium. In further experiments with various inhibitors, naucline was found to possess inhibitory effects on both voltage-dependent Ca²⁺ channel (VDC)- and receptor-operated Ca²⁺ channel (ROC)-dependent Ca²⁺ influx in smooth muscle. Cadamine showed concentration-dependent relaxation in endothelium-intact aortic rings, which was inhibited by addition of l-NMMA, NOS inhibitor. These results suggested that the vasorelaxant effect of cadamine is partly mediated through the increased release of NO from endothelial cells. In addition to NO involvement, vasorelaxation induced by cadamine was also attributed to inhibition of both VDC- and ROC-dependent Ca²⁺ influx.     

Cardiovascular effects elicited by milonine, a new 8,14-dihydromorphinandienone alkaloid

Abstract: The mechanisms underlying the cardiovascular responses evoked by milonine (i.v.), an alkaloid, were investigated in rats. In normotensive rats, milonine injections produced hypotension and tachycardia, which were attenuated after N^w‐nitro‐l ‐arginine methyl esther (l ‐NAME; 20 mg/kg, i.v.). In phenylephrine (10 μM), pre‐contracted mesenteric artery rings, milonine (10^?10 M to 3 × 10^?4 M) caused a concentration‐dependent relaxation (EC₅₀ = 1.1 × 10^?6 M, E_max = 100 ± 0.0%) and this effect was rightward shifted after either removal of the vascular endothelium (EC₅₀ = 1.6 × 10^?5, p < 0.001), or after l ‐NAME 100 μM (EC₅₀ = 6.2 × 10^?5, p < 0.001), hydroxocobalamin 30 μM (EC₅₀ = 1.1 × 10^?4, p < 0.001) or ODQ 10 μM (EC₅₀ = 1.9 × 10^?4p < 0.001). In addition, in rabbit aortic endothelial cells, milonine increased NO₃^? levels. The relaxant effect induced by milonine was attenuated in the presence of KCl (20 mM), a modulator efflux K⁺ (EC₅₀ = 1.2 × 10^?5, p < 0.001), or different potassium channel blockers such as glibenclamide (10 μM) (EC₅₀ = 6.3 × 10^?5, p < 0.001), TEA (1 mM) (EC₅₀ = 2.3 × 10^?5 M, n = 6) or Charybdotoxin (0.2 μM) plus apamin (0.2 μM) (EC₅₀ = 3.9 × 10^?4 M, n = 7). In addition, pre‐contraction with high extracellular potassium concentration prevented milonine‐induced vasorelaxation (EC₅₀ = 1.0 × 10^?4, p < 0.001). Milonine also reduced CaCl₂‐induced contraction in Ca²⁺‐free solution containing KCl (60 mM). In conclusion, using combined functional and biochemical approaches, we demonstrated that the hypotensive and vasorelaxant effects produced by milonine are, at least in part, mediated by the endothelium, likely via nitric oxide release, activation of nitric oxide‐cGMP pathway and opening of K⁺ channels.     

Acute Treatment with Lauric Acid Reduces Blood Pressure and Oxidative Stress in Spontaneously Hypertensive Rats

The effects of acute administration of lauric acid (LA), the most abundant medium‐chain fatty acid of coconut oil, on blood pressure, heart rate and oxidative stress were investigated in spontaneously hypertensive rats (SHR). Intravenous doses of LA reduced blood pressure in a dose‐dependent fashion (1, 3, 4, 8 and 10 mg/kg) in both SHR and Wistar Kyoto rats. LA (10^?8 to 3 × 10^?3 M) induced vasorelaxation in isolated superior mesenteric artery rings of SHR in the presence (n = 7) or absence (n = 8) of functional endothelium [maximum effect (ME) = 104 ± 3 versus 103 ± 4%]. After exposure to KCl (60 mM), LA also induced concentration‐dependent vasorelaxation (n = 7) compared to that under Phe‐induced contraction (ME = 113.5 + 5.1 versus 104.5 + 4.0%). Furthermore, LA‐induced vasorelaxation in vessels contracted with S(?)‐BayK8644 (200 nM), a L‐type Ca²⁺ channel agonist (ME = 91.4 + 4.3 versus 104.5 + 4.0%, n = 7). Lastly, LA (10^?3 M) reduced NADPH‐dependent superoxide accumulation in the heart (18 ± 1 versus 25 ± 1 MLU/min/μg protein, n = 4, p < 0.05) and kidney (82 ± 3 versus 99 ± 4 MLU/min/μg protein, n = 4, p < 0.05). Our data show that LA reduces blood pressure in normotensive and hypertensive rats. In SHR, this effect might involve Ca⁺² channels in the resistance vessels and by its capability of reducing oxidative stress in heart and kidneys.     

Antioxidant and vasorelaxant activities of the Turraeanthus africanus methanol extract

The present studies evaluate the antioxidant and vasorelaxant activities of the methanol stem bark extract of Turraeanthus africanus (Welw.) Pellegr. (Meliaceae). The antioxidant property investigated through the DPPH scavenging activity showed that the methanol extract from the stem bark of T. africanus was active with an inhibition rate of 72.47% at 500 μg/mL and IC₅₀ of 29.2 μg/mL. This extract (0.1–700 μg/mL) induced a concentration-dependent relaxation of guinea-pig aortic rings precontracted with noradrenaline or KCl, with a maximum relaxation reaching 87.55 and 97.42%, respectively, at a concentration of 700 μg/mL. The extract showed no significant effect on the electrically induced contraction of the guinea-pig papillary muscle. The results of this study indicate that the extract from the stem bark has interesting antioxidant and vasorelaxant properties and represents a potential source of medicine for the treatment of cardiovascular diseases.     

VASOCONSTRICTOR RESPONSES TO POLYMORPHONUCLEAR LEUCOCYTES FROM ATHEROSCLEROTIC RABBITS

1. The vascular contractile effects of polymorphonuclear leucocytes (PMN) isolated from control rabbits and from rabbits made atherosclerotic by 1% cholesterol feeding for 8 weeks were examined. 2. Rings of control rabbit thoracic aorta with or without endothelium were mounted at 2g tension in 10 mL organ baths and were submaximally contracted by phenylephrine (0.1 μmol/L). After 30 min incubation at 37° C, the supernatant of PMN (5X10⁷/mL, in Tyrode solution containing 0.25% bovine serum albumin) was obtained by centrifugation for addition to the vascular preparation. 3. Control PMN supernatant (443 μL) caused contraction (0.58±0.15g, n= 11) of phenylephrine-contracted aortic rings, which was prevented by removal of the endothelium (0.11 ± 0.07g, n= 5, P<0.05). However, the control PMN supernatant had no contractile effect on aortic rings at resting tension (0.00 ± 0.00g, n= 8). 4. By comparison, atherosclerotic PMN supernatant (443 μL) caused a significantly greater contraction of the aortic rings (1.41± 0.13g, n= 9, P<0.05 vs control PMN supernatant) that was only partly inhibited by removal of the endothelium (0.45 ± 0.20g, n= 9, P<0.05). Moreover, PMN supernatants from four of seven atherosclerotic rabbits contracted aortic rings at resting tension (3.5 ±1.4g, n= 7). 5. These results suggest that the release of a stable vasoconstrictor substance(s) by PMN is enhanced under conditions of atherosclerosis. The constrictor action of this substance(s) appears to be greater in the presence of a functional endothelium, and part of its action may involve inactivation of endothelium-derived nitric oxide.