Antiarrhythmic effect of magnolol and honokiol during acute phase of coronary occlusion in anesthetized rats: influence of L-NAME and aspirin.

This study was designed to evaluate the in vivo effect of magnolol and honokiol on the acute phase of coronary ligation in the presence of nitric oxide inhibitor (L-NAME) or cyclooxygenase inhibitor (aspirin). After Sprague-Dawley rats were anesthetized with urethane, the changes of ventricular arrhythmia induced by coronary ligation for 30 min were determined with or without pretreatment with study medications. The incidence and duration of ventricular arrhythmia were significantly reduced after intravenous pretreatment (15 min before coronary ligation) with 10(-7) g/kg magnolol or 10(-7) g/kg honokiol. However, the antiarrhythmic effect of magnolol or honokiol could be abolished with the pretreatment of 1 mg/kg L-NAME, but not with pretreatment of 100 mg/kg aspirin. The abolishment of the myocardial beneficial effect of magnolol and honokiol by L-NAME, instead of aspirin, suggests an involvement of an increased nitric oxide synthesis in the protection offered by magnolol and honokiol against arrhythmia during myocardial ischemia.     

Magnolol reduces myocardial ischemia/reperfusion injury via neutrophil inhibition in rats.

The accumulation of oxygen-free radicals and activation of neutrophils are strongly implicated as important pathophysiological mechanisms mediating myocardial ischemia/reperfusion injury. It has been proven that various antioxidants have cardioprotective effects. Magnolol, an active component extracted from the Chinese medicinal herb Magnolia officinalis, possesses potent antioxidant and free radical scavenging activities. In this study, the cardioprotective activity of magnolol was evaluated in an open-chest anesthetized rat model of myocardial ischemia/reperfusion injury. The results demonstrated that pretreatment with magnolol (0.2 and 0.5 microg/kg, i.v. bolus) at 10 min before 45 min of left coronary artery occlusion, significantly suppressed the incidence of ventricular fibrillation and mortality when compared with the control group. Magnolol (0.2 and 0.5 microg/kg) also significantly reduced the total duration of ventricular tachycardia and ventricular fibrillation. After 1 h of reperfusion, pretreatment with magnolol (0.2 and 0.5 microg/kg) caused a significant reduction in infarct size. In addition, magnolol (0.2 microg/kg) significantly reduced superoxide anion production and myeloperoxidase activity, an index of neutrophil infiltration in the ischemic myocardium. In addition, pretreatment with magnolol (0.2 and 0.5 microg/kg) suppressed ventricular arrhythmias elicited by reperfusion following 5 min of ischemia. In vitro studies of magnolol (5, 20 and 50 microM) significantly suppressed N-formylmethionyl-leucyl-phenylalanine (fMLP; 25 nM)-activated human neutrophil migration in a concentration-dependent manner. It is concluded that magnolol suppresses ischemia- and reperfusion-induced ventricular arrhythmias and reduces the size of the infarct resulting from ischemia/reperfusion injury. This pronounced cardioprotective activity of magnolol may be mediated by its antioxidant activity and by its capacity for neutrophil inhibition in myocardial ischemia/reperfusion.     

Antiarrhythmic effects of a benzothiazine derivative (SD-3211) and its stereoisomer (SA3212) in anaesthetized rats and isolated perfused rat hearts compared with bepridil

Summary The antiarrhythmic effects of a new calcium channel blocking agent (SD-3211) and its stereoisomer with additional sodium channel blocking activity (SA3212), were compared with those of a known antiarrhythmic drug (bepridil), using the left coronary artery ligation- and reperfusion-associated arrhythmia models both in isolated rat hearts and in anaesthetized rats.Isolated and perfused rat hearts were subjected to regional ischaemia for 15 min and subsequent reperfusion for 5 min. SD-3211 and SA3212 showed dose-dependently prolongations of the time interval between coronary ligation and first appearance of ventricular premature beats, reductions in the number of total ventricular premature beats during the ligation period and reductions in the incidence of reperfusion-induced ventricular fibrillation. The values of the negative logarithm of IC₅₀ (mol/l) of SD-3211, SA3212 and bepridil were 7.97, 7.41 and 6.64 for the reduction of ventricular premature beats during ligation and 6.43, 7.49 and 6.17 for the reduction of ventricular fibrillation during reperfusion, respectively. In a separate study on force of concentration and coronary flow in perfused heart paced at 340–360 beats/min SD-3211 caused a significant negative inotropic effect between 10^–7 and 10^–6 mol/l. SA3212 at the concentration of < 10^–6 mol/l did not result in any significant change in force of contraction. The coronary flow was increased dose-dependently by SA3212, while it was first increased and then reduced in the presence of higher concentration of SD-3211 (> 10^–7 mol/l). Hearts of aneasthetized rats were also subjected to regional ischaemia for 7 min and subsequent reperfusion. SD-3211, even at the lowest dose tested (25 mg/kg), had a marked protective effect against the ligation-associated arrhythmias. The highest dosage of SA3212 tested (100 mg/kg) also reduced them. SA3212, even at the lowest dosage (25 mg/kg), resulted in a significant reduction of the incidence of reperfusion-induced ventricular fibrillation, while only the highest dosage of SD-3211 (100 mg/kg) reduced it. As for the protective effect against ligation-associated ventricular premature beats SD-3211 is about seven times as potent as bepridil, and for the reduction in the incidence of reperfusion-induced ventricular fibrillation SA3212 is about fourteen times as potent as bepridil. Significant falls in systolic blood pressure and heart rate were observed at the higher doses of SD-3211 (50 and 100 mg/kg).Thus, SD-3211 affords substantial protection against ischaemia-induced ventricular antiarrhythmias partly through the negative inotropic and chronotropic effects, and reduction of afterload. The antiarrhythmic action of SA3212 against reperfusion-induced ventricular fibrillation may be partly explained by depression of automaticity together with a reduction of the inward sodium current.Send offprint requests to M. Fukuchi at the above address     

Beneficial effects of magnolol in a rodent model of endotoxin shock

Magnolol is a compound extracted from the Chinese medicinal herb Magnolia officinalis. It has multiple pharmacological effects, notably as an anti-oxidant. The aim of this study was to evaluate the effects of magnolol on sepsis induced by intravenous (i.v.) administration of lipopolysaccharide (LPS; 10 mg/kg) in anaesthetized Wistar rats. Magnolol (4 μg/kg, i.v.) was administered at 30 min after LPS injection. Post-treatment with magnolol significantly attenuated the deleterious haemodynamic changes (e.g., hypotension and bradycardia) caused by LPS. Meanwhile, magnolol significantly inhibited the elevation of plasma levels of tumor necrosis factor alpha, glutamate-oxaloacetate transaminase, glutamate-pyruvate transaminase and blood urine nitrogen caused by LPS. The induction of inducible nitrous oxide (NO) synthase and the overproduction of NO and superoxide anions by LPS were also significantly reduced by post-treatment with magnolol. Moreover, the plasma level of the thrombin-antithrombin complex following administration of LPS was also reduced by post-treatment with magnolol. Thus, the beneficial effects of magnolol on LPS-induced sepsis result from its anti-inflammatory, anti-coagulatory, and anti-oxidant effects.     

丹参饮对冠脉结扎大鼠心肌缺血的保护研究

目的评价丹参饮对冠脉结扎大鼠心肌缺血的保护作用,并探讨其作用机制。方法雄性Wistar大鼠按体质量随机分为对照组、模型组、硝苯地平组、复方丹参片组和丹参饮低、中、高剂量组,每组各10只。硝苯地平剂量为0.167 mg/kg、复方丹参片剂量为10 g/kg,按10 m L/kg ig给药;丹参饮按0.5、1.0、2.0 m L/kg(相当于原药材0.27、0.54、1.08 g/kg)ig给药。各组动物均连续给药7 d。于第7天给药30 min后通过结扎冠脉建立大鼠心肌缺血模型。分别记录正常和结扎后心电图S-T段变化,测定血清乳酸脱氢酶(LDH)、肌酸激酶(CK)活性,计算心脏指数、左心室指数、左心室/心脏质量比和心肌梗死率。结果与模型组各时间点比较,丹参饮组在结扎后15~180 min心电图S-T段均明显降低,差异具有统计学意义(P0.05)。与模型组比较,各组LDH、CK活性均明显降低,差异具有统计学意义(P0.05);各组大鼠心脏指数、左心室指数、左心室/心脏质量比均明显降低,差异具有统计学意义(P0.05);各组心肌梗死质量和梗死率均明显降低,差异具有统计学意义(P0.05)。结论丹参饮对冠脉结扎大鼠心肌缺血具有保护作用,可能是增强冠脉供血和心肌代谢,改善心功能,有效抑制大鼠心肌缺血梗死。     

Antagonizing bradykinin (BK) obliterates the cardioprotective effects of bradykinin and angiotensin-converting enzyme (ACE) Inhibitors in ischemic hearts

Bradykinin (BK) (1 × 10 ^?12?1 × 10^?8 mol/l) and the ACE inhibitor ramiprilat (2.58 × 10 ^?9?2.58 × 10^?5 mol/l) markedly reduced the incidence and duration of reperfusion arrhythmias in the isolated ischemic rat heart. Pretreatment with ramipril (1 mg/kg p.o.), enalapril (10 mg/kg p.o.), but not captopril (50 mg/kg p.o.) had similar effects. Active compounds also improved cardiodynamics and reduced lactate dehydrogenase (LDH) and creatine kinase (CK) activities, as lactate formation in coronary venous effluent. Cardiac tissue levels of glycogen, adenosine triphosphate (ATP), and creatine phosphate (CP) were preserved. The BK antagonist D-Arg-[Hyp², Thi^5,8, D-Phe⁷]BK abolished the beneficial effects of BK, ramipril, and ramiprilat in a competitive way. Increased concentrations of BK or ramiprilat were able to reverse the antagonism. In anesthetized dogs an infusion of BK, at the dose of 1 ng/kg/min during coronary occlusion and reperfusion was devoid of cardiovascular effects but reduced mortality and the decrease of LDH activity and lactate concentration in coronary sinus blood and preserved tissue levels of glycogen and energy-rich phosphates in the ischemic myocardium.     

Thaliporphine protects ischemic and ischemic‐reperfused rat hearts via an NO‐dependent mechanism

In ischemia or ischemia‐reperfusion (I/R), nitric oxide (NO) can potentially exert several beneficial effects. Thaliporphine, a natural alkaloid with Ca²⁺ channel‐activating and Na⁺/K⁺ channel‐blocking activities, increased NO levels and exerted cardioprotective action in ischemic or I/R rats. The role of NO in the cardioprotective actions of thaliporphine was assessed. The severity of rhythm disturbances and mortality in anesthetized rats with either coronary artery occlusion for 30 min, or 5 min followed by 30‐min reperfusion, were monitored and compared in thaliporphine‐ vs. placebo‐treated groups. Thaliporphine treatment significantly increased NO and decreased lactate dehydrogenase (LDH) levels in the blood during the end period of ischemia or I/R. These changes in NO and LDH levels by thaliporphine were associated with a reduction in the incidence and duration of ventricular tachycardia (VT) and ventricular fibrillation (VF) during ischemic or I/R period. The mortality of animals was also completely prevented by 1 × 10^–8 moles/kg of thaliporphine. In animals subjected to 4 h of left coronary artery occlusion, 1 × 10^–7 moles/kg of thaliporphine dramatic reduced cardiac infarct zone from 46 ± 6% to 7.1 ± 1.9%. Inhibition of NO synthesis with 3.7 × 10^–6 moles/kg of N^ω ‐nitro‐L‐arginine methyl ester (L‐NAME) abolished the beneficial effects of thaliporphine during 30 min or 4 h myocardial ischemia. However, the antiarrhythmic activity and mortality reduction efficacy of thaliporphine during reperfusion after 5 min of ischemia was only partially antagonized by L‐NAME. These results showed that thaliporphine efficiently exerted the cardioprotections either in acute or prolonged coronary artery occlusion or occlusion‐reperfusion situations. The fact that thaliporphine induced cardioprotective effects were abrogated by L‐NAME indicates that NO is an important mediator for the cardioprotective effects of thaliporphine in acute or prolonged ischemia, whereas antioxidant activities may contribute to the protection of I/R injury. Drug Dev. Res. 52:446–453, 2001. © 2001 Wiley‐Liss, Inc.     

Intravenous pretreatment with magnolol protects myocardium against stunning

Magnolol, an antioxidant, has been reported to possess various protective effects on the cardiovascular system. However, its effect on myocardial stunning has not been elucidated. The purpose of this study was to investigate the antistunning effect of magnolol by evaluating the recovery of regional myocardial function after 10-minute coronary artery occlusion in anesthetized, open-chest rabbits. There was no significant hemodynamic change after intravenous infusion of magnolol. Systolic wall thickening fraction (WThF) measured with an epicardial Doppler sensor in animals pretreated with normal saline and vehicle solution remained significantly depressed (60 +/- 7% and 77 +/- 4% of baseline WThF, respectively) 3 hours after coronary artery reperfusion (CAR). Pretreatment with magnolol (10(-7) and 10(-6) g/kg, intravenous infusion) significantly enhanced the recovery of systolic wall thickening fraction (98 +/- 1 and 99 +/- 1% of baseline WThF, respectively) 60 minutes after CAR. This study demonstrated that intravenous pretreatment with magnolol protected myocardium against stunning.     

Magnolol Attenuates Concanavalin A‐induced Hepatic Fibrosis,Inhibits CD4+ T Helper 17 (Th17) Cell Differentiation and Suppresses Hepatic Stellate Cell Activation: Blockade of Smad3/Smad4 Signalling

Magnolol is a pharmacological biphenolic compound extracted from Chinese herb Magnolia officinalis, which displays anti‐inflammatory and antioxidant effects. This study was aimed at exploring the potential effect of magnolol on immune‐related liver fibrosis. Herein, BALB/c mice were injected with concanavalin A (ConA, 8 mg/kg/week) up to 6 weeks to establish hepatic fibrosis, and magnolol (10, 20, 30 mg/kg/day) was given to these mice orally throughout the whole experiment. We found that magnolol preserved liver function and attenuated liver fibrotic injury in vivo. In response to ConA stimulation, the CD4⁺ T cells preferred to polarizing towards CD4⁺ T helper 17 (Th17) cells in liver. Magnolol was observed to inhibit Th17 cell differentiation in ConA‐treated liver in addition to suppressing interleukin (IL)‐17A generation. Hepatic stellate cells were activated in fibrotic liver as demonstrated by increased alpha smooth muscle actin (α‐SMA) and desmin. More transforming growth factor (TGF)‐β1 and activin A were secreted into the serum. Magnolol suppressed this abnormal HSC activation. Furthermore, the phosphorylation of Smad3 in its linker area (Thr179, Ser 204/208/213) was inhibited by magnolol. In vitro, the recombinant IL‐17A plus TGF‐β1 or activin A induced activation of human LX2 HSCs and promoted their collagen production. Smad3/Smad4 signalling pathway was activated in LX2 cells exposed to the fibrotic stimuli, as illustrated by the up‐regulated phospho‐Smad3 and the enhanced interaction between Smad3 and Smad4. These alterations were suppressed by magnolol. Collectively, our study reveals a novel antifibrotic effect of magnolol on Th17 cell‐mediated fibrosis.     

Catalpol decreases peroxynitrite formation and consequently exerts cardioprotective effects against ischemia/reperfusion insult

Context: Peroxynitrite (ONOO^?) formation triggers oxidative/nitrative stress and contributes to exacerbated myocardial ischemia/reperfusion (MI/R) injury. Catalpol, an iridoid glycoside, abundantly found in the roots of Rehmannia glutinosa L. that is included in the family Phrymaceae in the order Lamiales, endemic to China, was found to have neuroprotective effects. However, the effect of catalpol on MI/R injury has not been identified.

Objective: This study investigated whether catalpol attenuates oxidative/nitrative stress in acute MI/R.

Materials and methods: Adult male rats were subjected to 30?min of myocardial ischemia and 3?h of reperfusion and were treated with saline, catalpol (5?mg/kg, i.p., 5?min before reperfusion) or catalpol plus wortmannin (15 µg/kg intraperitoneally injected 15?min before reperfusion).

Results: Pretreatment with catalpol significantly improved cardiac functions, reduced myocardial infarction, apoptosis and necrosis of cardiomyocytes after MI/R (all p < 0.05). Meanwhile, ONOO^? formation was markedly reduced after catalpol treatment (3.01?±?0.22 vs. 4.66?±?0.53 pmol/mg protein in vehicle, p < 0.05). In addition, catalpol increased Akt and endothelial nitric oxide synthase phosphorylation, nitric oxide (NO) production, anti-oxidant capacity and reduced MI/R-induced inducible nitric oxide synthase expression and superoxide anion (·O₂^?) production in I/R hearts. PI3K inhibitor wortmannin not only blocked catalpol-induced Akt activation, but also attenuated all the beneficial effects of catalpol. Suppression of ONOO^? formation by either catalpol or an ONOO^? scavenger uric acid (5?mg/kg) reduced myocardial infarct size in MI/R rats.

Discussion and conclusion: In conclusion, catalpol affords cardioprotection against MI/R insult by attenuating ONOO^? formation, which is attributable to increased physiological NO and decreased ·O₂^? production.     

丹酚酸B预处理对心肌缺血/再灌注损伤能量代谢的影响

目的 观察丹酚酸B预处理对大鼠心肌缺血/再灌注损伤（MI/RI）能量代谢的作用。方法 通过结扎冠状动脉30min再灌注2 h建立大鼠MI/RI模型,随机分为4组：假手术组、模型组及丹酚酸B高、低（20、10 mg/kg）组,于建立模型前7 d开始ip给药,每天1次;再灌注结束后,采用比色法测定血清乳酸脱氢酶（LDH）、肌酸激酶（CK）活力,染色法测定心肌梗死面积（MIA）,定磷法测定心肌组织Na⁺-K⁺-ATP酶、Ca²⁺-Mg²⁺-ATP酶活性。结果 与模型组（42.60%）比较,丹酚酸B高、低剂量组的MIA分别缩小至35.93%和37.21%,差异显著（P<0.05）;与模型组比较,丹酚酸B高、低剂量组血清CK、LDH活力均显著降低（P<0.05、0.01）;与模型组比较,丹酚酸B高、低剂量组心肌组织Na⁺-K⁺-ATP酶、Ca²⁺-Mg²⁺-ATP酶活性均显著升高（P<0.05、0.01）。结论 丹酚酸B预处理可保护MI/RI所致心肌损伤,作用途径可能与改善心肌组织的能量代谢相关。     

Cardioprotective effects of hexasulfobutylated C60 (FC4S) in anesthetized rats during coronary occlusion/reperfusion injury

The effects of hexasulfobutylated C₆₀ (FC₄S) on (1) coronary occlusion/reperfusion and (2) isolated aortic ring preparation of rats were studied in vivo and in vitro. In the in vivo studies, FC₄S (1–10 μg/kg, iv) reduced the incidence and duration of ventricular tachycardia and ventricular fibrillation during the coronary artery occlusion phase and the reperfusion phase. FC₄S increased nitric oxide (NO) and decreased lactate dehydrogenase in plasma during the period of cardiac ischemia and reperfusion. In animals subjected to 4 h of coronary occlusion, pretreatment with FC₄S (10 μg/kg, iv) reduced the cardiac infarct zone (expressed as percent of area at risk) from 39.7 ± 4.8% to 11.3 ± 4.1 %. Mortality during cardiac ischemia and reperfusion was completely prevented after injection of FC₄S (10 μg/Kg iv). In the isolated endothelium‐containing aortic ring preparation, phenylephrine (PE) elicited contractions and FC₄S elicited a significant relaxing effect on PE‐precontracted aortic rings. This relaxing effect of FC₄S was reduced by pretreatment with N(G)‐nitro‐L ‐arginine methyl ester (1 mM), a blocker of NO synthase. It is concluded that FC₄S may be useful as a potential cardioprotective agent for cardiac ischemia and reperfusion. The beneficial effect of FC₄S may be partly correlated with its antioxidant property and also by the upregulation of NO production and vasodilation effects. Drug Dev. Res. 53:244–253, 2001. © 2001 Wiley‐Liss, Inc.     

Cardiovascular effects of acebutolol following coronary artery occlusion and reperfusion in anaesthetized dog.

1 The effects of 5 mg/kg acebutolol given intravenously were investigated in anaesthetized dogs after (a) ligation of the left anterior descending coronary artery and (b) coronary reperfusion following 60 min of ligation of the anterior descending coronary artery. 2 Coronary artery ligation produced, after 4 to 6 h, persistent multiple ventricular ectopic beats and abnormalities of R and T waves and of the S-T segment. Administration of acebutolol, after the development of persistent ventricular arrhythmias, restored normal sinus rhythm within 5 min of injection. Electrocardiographic abnormalities were also reduced. 3 Coronary artery reperfusion (following 60 min of ligation) resulted in multiple ventricular ectopic beats, ventricular tachycardia and/or ventricular fibrillation. Pretreatment with acebutolol, 15 min before starting reperfusion, markedly reduced the arrhythmias. 4 Acebutolol did not affect peak inspiratory airway pressure. 5 Acebutolol produced significant bradycardia and slight, transient, hypotension. It was without effect on left ventricular systolic pressure, left ventricular end-diastolic pressure, cardiac output or pulmonary arterial pressure. 6 These results suggest beneficial effects of acebutolol in myocardial ischaemia and coronary reperfusion, without any significant risk of cardiodepression or bronchospasm.     

Pharmacokinetics and Brain Distribution of Magnolol in the Rat after Intravenous Bolus Injection

The pharmacokinetics of magnolol in rats was studied after 2, 5, or 10 mg kg^?1 intravenous bolus injection. Plasma concentration-time profiles of magnolol were fitted by a two-compartment open model. There were no significant differences in the elimination half-life, the total body clearance, steady-state volume of distribution, or mean residence time. The area under the plasma-time curve and area under the moment-time curve of magnolol appears to increase proportionally from a dose of 2 to 10 mg kg^?1. These results suggest that magnolol possesses linear pharmacokinetics. Notwithstanding, brain concentration of magnolol showed no significant difference among various regions (cerebral cortex, olfactory bulb, hippocampus, striatum, cerebellum, brain stem and rest of brain) after 10 min of magnolol (5 mg kg^?1 i.v.) administration, the mean brain drug concentration was approximately fourfold that of magnolol in plasma.     

Effects of azimilide, a KV(r) and KV(s) blocker, on canine ventricular arrhythmia models.

Using canine coronary artery ligation/reperfusion and adrenaline arrhythmia models, we determined the effects of azimilide, a class III antiarrhythmic agent, E-1-[[(5-(4-chlorophenyl)-2-furanyl) methylene]-amino]-3-[4-(4-methyl-1-piperazinyl)butyl]-2,4-imidazolidi nedione dihydrochloride. The coronary ligation/reperfusion arrhythmia experiments were divided into two groups, one using low heart rate halothane-anesthetized and the other using high heart rate pentobarbital-anesthetized dogs. Azimilide (6 mg kg(-1) + 0.1 mg kg(-1) min(-1) i.v.) prolonged the corrected QT interval (QTc), decreased the heart rate and suppressed the premature ventricular complexes during ligation (35 +/- 17 beats/30 min as compared with 909 +/- 246 in the control group), and also suppressed ventricular fibrillation induced by coronary ligation/reperfusion in the two groups (1/8 halothane-anesthetized dogs as compared with 7/8 dogs in the control group and 2/8 pentobarbital-anesthetized dogs as compared with 8/8 dogs in the control group). In adrenaline arrhythmia, azimilide hastened the onset of adrenaline arrhythmias and also aggravated the arrhythmias, showing proarrhythmic effects.     

R56865, a potent new antiarrhythmic agent, effective during ischemia and reperfusion in the rat heart.

The antiarrhythmic effects of R56865 were characterized both in vivo and in vitro. Four groups (n = 12 per group) of anesthetized rats, subjected to 5- or 30-min coronary artery ligation and reperfusion, were studied: saline, dimethyl sulfoxide (DMSO) carrier, and R56865 (0.5 or 2 mg/kg) were administered as an intravenous (i.v.) bolus before ligation. After 5 min of ischemia, the incidences of reperfusion-induced ventricular tachycardia (VT) and fibrillation (VF), which were high in the saline (100 and 75%, respectively) and DMSO (100 and 82%, respectively) control groups, were abolished with both doses of R56865. With 30 min of ischemia, R56865 (2 mg/kg) significantly reduced the incidences of ischemia-induced VT and VF (from 100 and greater than 50% to 25 and 8%, respectively). For in vitro studies, five groups (n = 12 per group) of isolated rat hearts subjected to 10- or 30-min coronary ligation and reperfusion were studied: unmodified buffer and buffer containing DMSO or R56865 (10(-7), 10(-8), 10(-9) M). After 10 min of ischemia, R56865 (10(-7) M) decreased reperfusion-induced VT and VF (from 100 and 75% in buffer controls to 42 and 8%, respectively) when administered throughout the experiment. With 30 min of ischemia, R5685 (10(-7) M) reduced the incidences of ischemia-induced VT and VF (from 75 and 67% in the buffer controls to 25 and 25%, respectively). Although reperfusion after 30 min of ischemia did not induce VF in any of the groups studied, VT and other arrhythmias did occur and their incidences were reduced significantly by R56865. To investigate whether calcium overload might mediate the effects of R56865, hearts were perfused aerobically with a high-calcium/low-sodium medium. VT and VF occurred in 80% of control hearts; R56865 (10(-7) M) did not prevent these arrhythmias. In conclusion, R56865 exerts a potent effect against ischemia- and reperfusion-induced arrhythmias through a mechanism which appears to operate during ischemia.     

Effects of magnolol on vascular contraction in rat aortic rings

1. Magnolol (5,5′‐diallyl‐2,2′‐dihydroxybiphenyl) is a major phenolic compound purified from Magnolia officinalis. The aim of the present study was to elucidate the effects of magnolol on vascular contractions. 2. Rat aortic rings were mounted in organ baths. Magnolol was added cumulatively (0.3–30 μmol/L) to elicit relaxation in endothelium‐intact and ‐denuded rat aortic rings precontracted with U46619 (30 nmol/L, 20 min), NaF (8.0 mmol/L, 40 min), phenylephrine (1.0 or 0.1 μmol/L, 15 min) or phorbol‐12,13‐dibutyrate (PDBu, 0.3 or 0.1 μmol/L, 40 min). In separate experiments, cumulative concentration?response curves were obtained for NaF (2.0–12 mmol/L), U46619 (1.0 nmol/L?1.0 μmol/L) or PDBu (1.0 nmol/L?1.0 μmol/L) after pretreatment with either magnolol or vehicle for 30 min in endothelium‐denuded aortic rings. After completion of the functional study, we measured the amount of guanosine triphosphate (GTP) RhoA by using a G‐LISA RhoA Activation Assay, as well as the phosphorylation of 20 kDa myosin light chain (MLC₂₀), myosin phosphatase‐targeting subunit 1 (MYPT1) and protein kinase C‐potentiated inhibitory protein for heterotrimeric myosin light‐chain phosphatase of 17 kDa (CPI‐17) by immunobloting. 3. Magnolol (0.3–30 μmol/L) reduced vascular tension induced by the thromboxane A₂ agonist U46619 (30 nmol/L), sodium fluoride (NaF) (8.0 mmol/L) and the α₁‐adrenoceptor agonist phenylephrine (1.0 or 0.1 μmol/L) in both endothelium‐intact and ‐denuded rings. The magnitude of the relaxation effects of magnolol on the contraction induced by each of the drugs were similar. The magnitude of the effect of magnolol in endothelium‐intact and ‐denuded rings were similar. 4. Pretreatment of rat aortic rings with 1.0, 3.0 or 10 μmol/L magnolol for 30 min dose‐dependently inhibited the maximum response on the concentration–response curves to NaF and U46619, but not to phorbol‐12,13‐dibutyrate (PDBu). 5. Magnolol (3.0 or 10 μmol/L) decreased RhoA activation, as well as the phosphorylation of MLC₂₀, MYPT1_Thr855 and CPI‐17_Thr38 induced by either 8.0 mmol/L NaF or 30 nmol/L U46619. In contrast, magnolol did not affect PDBu (0.1 μmol/L)‐induced phosphorylation of CPI‐17_Thr38. 6. In conclusion, magnolol reduces vascular contraction by inhibiting the RhoA/Rho kinase pathway in endothelium‐denuded rat aorta.     

Ischemia- and reperfusion-induced arrhythmias: beneficial actions of nifedipine

The effects of nifedipine against ischemia- and reperfusion-induced arrhythmias were investigated using anesthetized rats with transient coronary artery occlusion. Nifedipine (5 micrograms/kg i.v.) administered 10 min prior to occlusion significantly decreased the incidence of arrhythmias occurring during 20-min coronary occlusion. The incidence and duration of reperfusion-induced ventricular fibrillation and subsequent mortality following 5-min coronary occlusion were also significantly reduced by this intervention. However, administration of nifedipine 1 min prior to reperfusion afforded no protection against reperfusion arrhythmias. To investigate whether nifedipine possesses a true antiarrhythmic action or merely extends the ischemic duration prior to reperfusion resulting in maximal rhythm disturbances, reperfusion was initiated after 3, 5, 7, 10, 20, and 30 min of ischemia. Nifedipine reduced the incidence of reperfusion-induced ventricular fibrillation after all ischemic intervals, with no change in the time of peak vulnerability to reperfusion arrhythmias. Measurements of coronary flow with 153Gadolinium microspheres indicated that flow within ischemic tissue relative to that in normal tissue was significantly increased by nifedipine. Thus, administration of nifedipine prior to occlusion affords a protective effect against ischemia- and reperfusion-induced arrhythmias, and this action is not due to extension of the ischemic duration prior to reperfusion resulting in maximal rhythm disturbances.     

Prophylactic effects of m-nisoldipine and nisoldipine on reperfusion arrhythmias exacerbated by free radical generating system in Langendorff heart of rat

Xanthine-xanthine oxidase (X-XOD, 500 mumol/L + 100 nmol/L) free radical generating system was perfused 10 min prior to coronary artery ligation until the end of the experiment. It exacerbated the reperfusion ventricular fibrillation, reduced the activities of superoxide dismutase and catalase and increased the contents of malondialdehyde in Langendorff heart of rats. m-Nisoldipine or nisoldipine (0.05 mumol/L) was perfused 10 min prior to coronary artery ligation until the end of the experiment. They prevented reperfusion arrhythmias exacerbated by X-XOD and decreased the free radicals generated by X-XOD.