Lactobacillus acidophilus versus placebo in the symptomatic treatment of irritable bowel syndrome: the LAPIBSS randomized trial.

Irritable bowel syndrome is a chronic functional gastrointestinal disorder characterized by abdominal pain/discomfort and altered bowel habits. The use of Lactobacilli as probiotics during irritable bowel syndrome is based on their interesting mechanisms of action and their excellent safety profile but little is known about their clinical efficacy due to the lack of adequately designed clinical trials. The current clinical trial protocol aims to determine the effects of a mixture of Lactobacillus acidophilus NCFM and LAFTI L10 as probiotics to improve irritable bowel syndrome symptoms (LAPIBSS). Eighty patients with a positive diagnosis of irritable bowel syndrome according to Rome III criteria were recruited to a multicentre, double-blinded, in parallel groups, placebo-controlled randomized trial. Patients were provided with a daily dose of two capsules with two strains of Lactobacilli (5x109cfu/capsule) or placebo for 8 weeks on a 1:1 ratio. The primary outcome is to obtain scores of abdominal pain/discomfort assessed with a 100-mm visual analogue scale. The secondary outcome is to obtain scores of bloating, flatus and rumbling tested with a 100-mm visual analogue scale, composite score, stool frequency and stool consistency/appearance assessed with the Bristol Stool Form scale. According to the hypothesis that abdominal pain is mainly the result of a visceral hypersensitivity, the current study protocol aims to provide high quality proof of concept data to elucidate the efficacy of a consumption of a mixture of Lactobacillus acidophilus probiotic strains after 8 weeks, for decreasing abdominal pain. Ethical approval was given by ethics committee French Consultative Committee for the Protection of Individuals in Biomedical Research of the South West (Number CPP08-014a) and ANSM (French National Agency for Medicines and Health Products Safety - Number B80623-40). The findings from LAPBISS will be disseminated through peer-reviewed publications and at scientific conferences. TRIAL REGISTRATION: EudraCT N°2008-A00844-51.

Anti-arrhythmic effects of I (Na), I (Kr), and combined I (Kr)-I (CaL) blockade in an experimental model of acute stretch-related atrial fibrillation.

INTRODUCTION: Atrial dilatation is commonly associated with atrial fibrillation (AF), but the electrophysiological mechanisms and the implications for anti-arrhythmic therapy are poorly understood. In a model of acute stretch-related AF in isolated rabbit hearts, we evaluated the electrophysiological effects of three different anti-arrhythmic drugs: dofetilide, flecainide and BRL-32872 (associating I (Kr) and I (CaL) blocking properties). METHODS: After 30 min of sustained stretch-related AF, we perfused BRL 10-7 M, BRL 3.10-7 M, BRL 10-6 M, flecainide 2.4 10-6 M and dofetilide 10-7 M and iteratively measured atrial effective refractory periods (ERPs), AF inducibility and AF cycle length (AFCL) 15, 30 and 60 min after drug perfusion, respectively. RESULTS: After a significant shortening of the ERPs by acute atrial stretch in the five groups individually (p < 0.001, stretch vs baseline for each group individually), drug perfusion led to a strong lengthening of AFCL, a very significant prolongation of ERPs (p < 0.001 vs stretch) and a reduction of AF inducibility (p < 0.01 vs control group) for each of the five experimental groups. The relative ERP increase was comparable in all groups, whereas a significantly lower AF inducibility was observed in the BRL 10-6 M group (p < 0.05 vs other BRL concentrations). CONCLUSION: In a model of acute stretch-related AF, dofetilide, flecainide and BRL-32872 terminated AF and prevented its immediate reinduction after having comparatively prolonged AFCL and ERPs. These comparative results suggest that those drugs are equally efficacious, albeit with different mechanisms, in the setting of acute atrial stretch.

Influence of atenolol on the kinetics of RT interval rate adaptation in conscious dogs.

The objective was to test an effect of atenolol independent of heart rate on electrocardiographic RT rate adaptation by investigating RT adaptation during spontaneous rate and after an abrupt change of atrial rate (study of RT delay). Digital electrocardiograms were recorded from eight conscious dogs. Analysis of RT interval (measured from QRS apex to end of T) was performed on a beat-to-beat basis. The protocol was repeated in the control state and after atenolol administration (2 mg/kg). Regarding spontaneous heart rate, an increased or decreased RR duration did not modify the beat-to-beat relative adaptation of RT to a change of RR (2.15 +/- 1% during control). Atenolol increased mean RR (p < 0.001) and decreased relative adaptation of RT (0.22 +/- 0.18%, p < 0.001). The inverse correlation between mean RR and the relative RT adaptation (r = -0.76, p < 0.05) disappeared after atenolol administration. Regarding RT delay, complete adaptation of RT required 3 min; 48 +/- 16% of this adaptation was observed after the first beat and 60 +/- 11% was observed after the 20th. Atenolol attenuated this adaptation during the first six beats following the abrupt cycle length change (p < 0.05). We concluded that the attenuation of RT rate adaptation after atenolol is related to heart rate modulation and to the time delay in RT rate adaptation.

Matrix metalloproteinase expression in cardiac myocytes following myocardial infarction in the rabbit.

Myocardial infarction (MI), leads to cardiac remodeling, thinning of the ventricle wall, ventricular dilation, and heart failure, and is a leading cause of death. Interactions between the contractile elements of the cardiac myocytes and the extracellular matrix (ECM) help maintain myocyte alignment required for the structural and functional integrity of the heart. Following MI, reorganization of the ECM and the myocytes occurs, contributing to loss of heart function. In certain pathological circumstances, the ECM is modulated such that the structure of the tissue becomes damaged. The matrix metalloproteinases (MMPs) are a family of enzymes that degrade molecules of the ECM. The present experiments were performed to define the time-course, isozyme subtypes, and cellular source of increased MMP expression that occurs following MI in an experimental rabbit model. Heart tissue samples from infarcted and sham animals were analyzed over a time-course of 1-14 days. By zymography, it was demonstrated that, unlike the sham controls, MMP-9 expression was induced within 24 hours following MI. MMP-3 expression, also absent in sham controls, was induced 2 days after MI. MMP-2 expression was detected in both the sham and infarcted samples and was modestly up-regulated following MI. Tissue inhibitor of metalloproteinase-1 (TIMP-1) expression was evaluated and shown to be down-regulated following MI, inverse of MMP-9 and MMP-3 expression. Further, MMP-9 and MMP-3 expression was detected by immunohistochemistry in myocytes within the infarct. Additional studies were conducted in which cultured rat cardiac myocytes were exposed to a hypoxic environment (2% O2) for 24 hours and the media analyzed for MMP expression. MMP-9 and MMP-3 were induced following exposure to hypoxia. It is speculated that the net increase in proteolytic activity by myocytes is a contributing factor leading to myocyte misalignment and slippage. Additional studies with a MMP inhibitor would elucidate this hypothesis.

Pharmacology of SB-273779, a nonpeptide calcitonin gene-related peptide 1 receptor antagonist.

Calcitonin gene-related peptide (CGRP), a potent vasodilatory and cardiotonic peptide, has a potential role for CGRP in diverse physiologic and pathophysiologic situations such as congestive heart failure, diabetes, migraine, and neurogenic inflammation. Although a peptide CGRP receptor antagonist, CGRP(8-37,) is available, its utility presents significant limitations for these indications. Here, we describe the properties of SB-(+)-273779 [N-methyl-N-(2-methylphenyl)-3-nitro-4-(2-thiazolylsulfinyl)nitrobenzanilide], a selective nonpeptide antagonist of CGRP(1) receptor. SB-(+)-273779 inhibited (125)I-labeled CGRP binding to SK-N-MC (human neuroblastoma cells) and human cloned CGRP(1) receptor with K(i) values of 310 +/- 40 and 250 +/-15 nM, respectively. SB-(+)-273779 also inhibited CGRP (3 nM)-activated adenylyl cyclase in these systems with IC(50) values of 390 +/-10 nM (in SK-N-MC) and 210 +/-16 nM (recombinant human CGRP receptors). Prolonged treatment (>30 min) of SK-N-MC cells with SB-(+)-273779 followed by extensive washing resulted in reduction in maximum CGRP-mediated adenylyl cyclase activity, suggesting that this compound has irreversible binding characteristics. In addition, SB-(+)-273779 antagonized CGRP-mediated 1) stimulation of intracellular Ca(2+) in recombinant CGRP receptors in HEK-293 cells, 2) inhibition of insulin-stimulated [(14)C]deoxyglucose uptake in L6 cells, 3) vasodilation in rat pulmonary artery, and 4) decrease in blood pressure in anesthetized rats. SB-(+)-273779 tested at 3 microM had no significant affinity for calcitonin, endothelin, angiotensin II, and alpha-adrenergic receptors under standard ligand binding assays. SB-(+)-273779 also did not inhibit forskolin and pituitary adenylate cyclase-activating polypeptide. These results suggest that SB-(+)-273779 is a valuable tool for studying CGRP-mediated functional responses in complex biological systems.

Vasodilatory effect of adrenomedullin in mouse aorta.

Human adrenomedullin (AM) and human calcitonin gene-related peptide (CGRP) produced a concentration-dependent relaxation in mouse aorta, precontracted with noradrenaline. EC(50) values for AM and CGRP were 9.8 +/- 2.4 and 4.2 +/- 0.1 nmol/l, respectively. AM-mediated vasorelaxation was partially (3-fold) shifted by AM(22-52), the C-terminal AM fragment, but not by CGRP(8-37), a selective CGRP1 antagonist. Both AM(22-52) and CGRP(8-37) failed to inhibit CGRP-mediated vasorelaxation of mouse aorta rings. Binding of rat [(125)I]AM to these membranes was specific. Both human AM and AM(22-52) displaced rat [(125)I]AM binding in a concentration-dependent manner with IC(50) values of 12.0 +/- 4 and 19.4 +/- 8 nmol/l, respectively. In contrast, both human CGRP and CGRP(8-37) were weak in displacing [(125)I]AM binding. Very little specific binding was observed with [(125)I]CGRP. In conclusion, the data presented here demonstrate that the mouse aorta displays AM receptors that mediate vasorelaxation.

Cardiac loading conditions modify the ventricular repolarization in conscious dogs with heart failure.

Changes in myocardial loading conditions influence the ventricular action potential via mechanoelectric feedback, a mechanism impaired in pathology. In vivo the QT interval of the electrocardiogram which reflects the action potential duration allows appropriate determination of its modifications. The effects of changes in cardiac loading conditions (load reduction with trinitrin; volume loading with Plasmion) on regional function and ventricular local electrogram were investigated in conscious dogs before (control) and after 4 weeks of rapid pacing (dilated cardiomyopathy, DCM). In controls both interventions increased heart rate. Trinitrin increased end-diastolic wall thickness (EDWth, P<0.001) and reduced absolute QT interval duration (P<0.05). Plasmion decreased EDWth (P<0.001) and increased left ventricular end diastolic pressure (LVEDP, P<0.001) without QT interval alteration. However, the corrected QT interval was unchanged in both interventions. In DCM, trinitrin did not change the QT interval. Plasmion increased LVEDP (P<0.01) and prolonged QT and corrected QT intervals (P<0.01) despite the tachycardia. In controls the changes in cardiac loading conditions did not modify the QT interval, suggesting intact endogenous regulation of repolarization. The impaired adaptation observed in DCM contributed to an increase in QT interval following volume loading. In this model, a prolonged repolarization after abrupt volume loading may result from enhanced or disclosed mechanoelectric feedback.

Influence of sympathetic heart rate modulation on RT interval rate adaptation in conscious dogs.

The objective was to test if changes in autonomic tone still influenced the RT-RR relationship when full RT adaptation is completed, when heart rate is controlled, and when beat-to-beat variability is abolished by atrial pacing. Eight dogs (8-11 kg) were chronically instrumented with atrial pacing electrodes. Digital ECG (1,000 Hz, 12 bits) were recorded from healthy conscious dogs during spontaneous sinus rhythm and during atrial pacing. The protocol was repeated before and after atenolol (2 mg/kg), prazosin (0.5 mg/kg), or atenolol + prazosin. A vocal incitation was used as sympathetic stimulation. Beat-to-beat quantitative analysis of the RT interval (from QRS apex to end of T wave) was correlated with the preceding RR by linear regression. In spontaneous rhythm, atenolol increased RR (P < 0.001), RT (P < 0.001), and short-term heart rate variability (P < 0.01) and decreased RT-RR slopes (P < 0.001). Prazosin did not significantly modify any parameter. Sympathetic stimulation decreased RR (P < 0.001), RT (P < 0.05), and short-term heart rate variability (P < 0.01) and increased RT-RR slopes (P < 0.001). In atrial pacing, the RT-RR slopes were steeper during pacing than during spontaneous rhythm but were not modified by pharmacological manipulation of the autonomic nervous system. During sinus rhythm the RT-RR relationship is increased by sympathetic stimulation and decreased by beta-blockade. When heart rate modulation and the effects of the time delay in RT rate adaptation are abolished by atrial pacing, the influence of autonomic tone on RT rate adaptation disappears.

Electrophysiological characterization of BRL-32872 in canine Purkinje fiber and ventricular muscle. Effect on early after-depolarizations and repolarization dispersion.

Amongst the different pharmacological approaches to the treatment of cardiac arrhythmias, compounds with multiple electrophysiological activities appear to exhibit a reduced adverse effect profile. BRL-32872 (N-(3,4-dimethoxyphenyl)-N-[3[[2-(3,4-dimethoxyphenyl) ethyl] propyl]-4-nitrobenzamide hydrochloride) is a typical example of an antiarrhythmic agent with combined K(+) and Ca(2+) blocking actions. In this study, we investigated the effects of BRL-32872 on early after-depolarizations and on dispersion of repolarization. Action potentials were recorded either in canine cardiac Purkinje fibers alone or in preparations containing both ventricular muscle and the attached Purkinje fibers. In Purkinje fibers, BRL-32872 (0. 3-10 microM) induced a bell-shaped concentration-dependent increase in action potential duration. At 90% of repolarization, the action potential was prolonged at concentrations up to 1 microM and was shortened when the concentration of BRL-32872 was further increased. In all 17 experiments, BRL-32872 did not cause early after-depolarizations in Purkinje fibers. On the contrary, BRL-32872 (3 microM) systematically suppressed early after-depolarizations induced by clofilium (4-chloro-N, N-diethyl-N-heptylbenzenebutanaminium tosylate, 1 microM), a selective inhibitor of the delayed rectifier K(+) current. A similar effect was observed once with 1 microM BRL-32872, a concentration able to prolong Purkinje fiber action potentials. Simultaneous recording of action potentials in ventricular and Purkinje preparations showed that increasing concentrations of BRL-32872 (0. 3-10 microM) induced a limited increase in the difference of repolarization time between the two tissues. The selective K(+) channel inhibitor E-4031 (N-(4-(1-[2-(6-methyl-2-pyridyl) ethyl]-4-piperidyl)-carbonyl] phenyl) methanesulfonamide dihydrochloride dihydrate) exhibited a significant concentration-dependent increase in dispersion of repolarization. We conclude from the present results that the Ca(2+) blocking activity of BRL-32872 (i) prevents the occurrence of early after-depolarizations associated with action potential prolongation and (ii) limits an excessive increase in action potential duration heterogeneity. These electrophysiological features might represent the basis for antiarrhythmic compounds with reduced proarrhythmic profile.

Impaired endothelium-dependent relaxation by adrenomedullin in monocrotaline-treated rat arteries.

The effects of adrenomedullin were evaluated in isolated vascular rings from rats treated with monocrotaline (60 mg/kg, s.c.) causing pulmonary hypertension and right ventricular hypertrophy within 3 to 4 weeks. Sham animals (NaCl-treated rats) were used for comparison. The relaxing effects of adrenomedullin (10(-8) M) and acetylcholine (10(-6) M) were determined in thoracic aorta and pulmonary artery rings precontracted with phenylephrine (10(-7) M). In sham animals, adrenomedullin caused significant vasorelaxation of aorta and pulmonary artery although of different amplitude (24 +/- 3% and 40 +/- 2%, respectively). A greater relaxation was observed in response to acetylcholine. Monocrotaline-treated rats exhibited a reduction in adrenomedullin relaxation in pulmonary artery (54 and 68% loss of effect, at 3 and 4 weeks, respectively, P < 0.01 vs. sham) and comparable reductions in acetylcholine responses. The decrease in adrenomedullin relaxing effect was less pronounced in aorta than in pulmonary artery, suggesting a distinct tissue sensitivity to monocrotaline. In contrast, the relaxing effect of acetylcholine on aorta was decreased at 4 weeks (36% reduction, P < 0.01 vs. sham). In this model, the adrenomedullin-induced relaxation of the pulmonary artery was impaired due to a severe endothelial dysfunction which may contribute partly to the evolving pathophysiological process.

Comparative affinities of adrenomedullin (AM) and calcitonin gene-related peptide (CGRP) for [125I] AM and [125I] CGRP specific binding sites in porcine tissues.

We have investigated the binding characteristics of rat [125I] adrenomedullin (AM) and human [125I] calcitonin gene-related peptide (CGRP) to membranes prepared from a number of porcine tissues including atrium, ventricle, lung, spleen, liver, renal cortex and medulla. These membranes displayed specific, high affinity binding for [125I] rat AM and [125I] human CGRP. Porcine lung displayed the highest density of binding sites for radiolabeled AM and CGRP followed by porcine renal cortex. Competition experiments performed with [125I] rat AM indicated that the rank order of potencies of various peptides for inhibiting [125I] rat AM binding to various tissues were rat AM > or = human AM > or = human AM(22-52) > h alpha CGRP > or = h alpha CGRP(8-37) >>>> sCT except spleen, atrium, renal cortex and renal medulla where rAM and hAM were 20-300 fold more potent than hAM (22-52). When the same experiments were performed using [125I] h alpha CGRP as the radioligand, the rank order potencies for various peptides were rAM = hAM > h alpha CGRP > h alpha CGRP(8-37) in most of the tissues except in spleen and liver where h alpha CGRP was the most potent ligand. In lung, h alpha CGRP was almost as potent as rAM and hAM in displacing [125I] h alpha CGRP binding. These data suggest the existence of distinct CGRP and AM specific binding sites in contrast to previous reports that showed that both peptides interact differently in rat tissues.

Synthesis, electrophysiological properties and analysis of structural requirements of a novel class of antiarrhythmic agents with potassium and calcium channel blocking properties.

Class III antiarrhythmic agents have been shown to prevent reentrant arrhythmias but also to be responsible for initiating arrhythmias characterised by afterdepolarizations and triggered activities. By combining potassium and calcium channel antagonistic actions, as with BRL-32872 (1), it might be possible to reduce the incidence of proarrhythmias albeit retaining antiarrhythmic efficacy. In the present study we synthesised and tested for their electrophysiological activity in guinea pig papillary muscle a wide panel of analogues of BRL-32872. Some qualitative relationships between compound structure and the inhibitory effect on the rapidly activating component of the delayed rectifier potassium current and/or the L-type calcium current will be presented. New derivatives depicting bell-shaped dose-response curves on action potential duration may therefore represent novel agents for improved antiarrhythmic therapy.

Combined potassium and calcium channel blocking activities as a basis for antiarrhythmic efficacy with low proarrhythmic risk: experimental profile of BRL-32872.

In the search for novel antiarrhythmic agents, compounds with a diversity of electrophysiological actions have been suggested to result in treatments with potentially improved efficacy but with reduced proarrhythmic risk. To test this hypothesis, the antiarrhythmic versus proarrhythmic profile of BRL-32872, a novel agent with combined potassium and calcium channel blocking activity, was assessed in two different in vivo models of ventricular arrhythmia. Furthermore, the effects of potassium and calcium channel antagonists given either alone or in combination were assessed in the same models. Dogs with myocardial infarction received intravenously either vehicle, BRL-32872, the class III antiarrhythmic agent, E-4031, verapamil or a combination of E-4031 with verapamil (n = 8 per group). Ventricular tachyarrhythmias were induced by programmed electrical stimulation (PES). BRL-32872 (0.1, 0.3, 1.0 mg/kg) significantly increased QTc interval (from 387 +/- 10 to 462 +/- 19 msec.sec-1/2 at 1.0 mg/kg, P < .01). Ventricular effective refractory periods were increased in normal and infarcted areas (P < .01). Similar effects were observed with E-4031 (0.1, 0.3, 1.0 mg/kg). Verapamil (0.03, 0.1, 0.3 mg/kg) reduced heart rate, mean arterial pressure and, to a lesser extent, (+)dP/dtmax. Verapamil did not change QTc interval and ventricular effective refractory periods, but increased PR interval (P < .001). PES-induced tachyarrhythmias were not changed by vehicle or increasing doses of verapamil. E-4031 reduced the severity of arrhythmias from sustained ventricular tachycardia (VT) to nonsustained VT (7 dogs at 1.0 mg/kg, P = .013 vs. vehicle). BRL-32872 (0.1 and 0.3 mg/kg) suppressed the induction of sustained VT in six dogs (P = .02 vs. vehicle). In the presence of BRL-32872, 1.0 mg/kg, five dogs became noninducible to PES (P = .013 vs. vehicle). Combination of E-4031 (0.1 mg/kg) with verapamil provided a degree of protection that was similar to that observed with BRL-32872. In a second model, the proarrhythmic potential of BRL-32872 was assessed in anesthetized rabbits sensitized to develop torsades de pointes (TdP). BRL-32872 was compared with the class III antiarrhythmic agents, E-4031, dofetilide, clofilium and RP-58866. The pure class III antiarrhythmic agents induced TdP in 50 to 90% of the rabbits, and prolonged QT interval by 20 to 50%. BRL-32872 (10 micrograms/kg/min) increased QT interval by 35 +/- 5%, but did not promote TdP. In additional experiments, verapamil reduced the incidence of TdP induced by E-4031. These results show that BRL-32872 is a potent antiarrhythmic compound in a model of PES-induced arrhythmias and induces fewer proarrhythmic events than typical class III antiarrhythmic agents. The effects observed with BRL-32872 suggest that a compound with a combination of potassium (class III) and calcium (class IV) channel antagonistic properties might constitute a novel antiarrhythmic agent with reduced proarrhythmic risk.

Antifibrillatory effects of BRL-32872 in anesthetized Yucatan minipigs with regional myocardial ischemia.

The antifibrillatory potential of BRL-32872, a novel antiarrhythmic compound with K+ and Ca2+ channel blocking activities, was examined in a minipig model of ischemia-induced arrhythmia. The effects of intravenous (i.v.) BRL-32872 (0.3 and 1.0 mg/kg, n = 8), dofetilide (0.3 mg/kg, n = 8), and flecainide (2.0 mg/kg, n = 8), were investigated on the incidence of ventricular fibrillation (VF) during a 20-min occlusion of the left anterior descending coronary artery (LAD). Ischemia-induced VF occurred in 6 of 9 vehicle-treated pigs. BRL-32872 reduced the incidence of ischemic VF to 13% at 0.3 mg/kg (p < 0.05) and to 0% at 1.0 mg/kg (p < 0.01). Dofetilide also prevented the occurrence of VF (0%, p < 0.01) In contrast, flecainide did not reduce the incidence of VF (63%). Indeed, flecainide shortened the time to onset of VF from 17 +/- 1 min in the vehicle group to 10 +/- 1 min (p < 0.001). The antifibrillatory effects of BRL-32872 and dofetilide were associated with a prolongation of QT interval on ECG. Flecainide did not prolong repolarization, but slowed the ventricular conduction velocity, as shown by significant increases in PR and QRS intervals. During early reperfusion, 1 of 8 surviving pigs in each group treated with BRL-32872 and 4 of 8 in the dofetilide group developed VF. This study demonstrated an antifibrillatory effect of BRL-32872 associated with prolonged ventricular repolarization and showed enhanced efficacy over dofetilide on reperfusion arrhythmias which is most likely a consequence of its Ca2+ blocking activity.

Electrophysiological effect of BRL-32872, a novel antiarrhythmic agent with potassium and calcium channel blocking properties, in guinea pig cardiac isolated preparations.

The effects of N-(3,4-dimethoxyphenyl)-N-[3[[2-(3,4-dimethoxyphenyl) ethyl] propyl]-4-nitrobenzamide hydrochloride (BRL-32872), a novel antiarrhythmic agent, were studied in guinea pig cardiac preparations using standard microelectrode and patch-clamp techniques. In papillary muscle, BRL-32872 did not change resting membrane potential and maximum rate of depolarization but prolonged action potential duration (APD) by 24% +/- 2% at 1.0 microM. When the concentration was increased to 3.0 and 10.0 microM, the effect on APD was not further enhanced, and a bell-shaped dose-response curve resulted. Patch-clamp experiments in isolated myocytes showed that BRL-32872 inhibited the rapidly activating component of the delayed rectifier potassium current (EC50 = 0.028 microM) and the L-type calcium current (EC50 = 2.8 microM) but had a limited effect on the inward rectifier potassium current. In papillary muscles stimulated at 300, 500, 1000 and 2000 msec, the effect of BRL-32872 in prolonging APD did not vary (P = .717). By contrast, N-(4-(1-[2-(6-methyl-2-pyridyl)ethyl]-4-piperidyl)- carbonyl]phenyl)methanesulfonamide dihydrochloride dihydrate (E-4031), a pure class III antiarrhythmic agent, increased APD more at slower than at faster stimulation rates (P = .001), which illustrated the reverse frequency-dependence of this agent. Among the 35 experiments performed with BRL-32872, only one fiber showed early afterdepolarizations (EADs), and these, which occurred at 1.0 microM, were suppressed at higher concentration (3.0 microM). Moreover, EADs induced by E-4031 were suppressed by BRL-32872 (3.0 microM).(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of zatebradine, a specific bradycardic agent, on ischemia-induced arrhythmias in anesthetized rabbits.

The effects of the specific bradycardic agent, zatebradine (UL-FS 49), on ventricular arrhythmias occurring during an acute ischemia were compared to those of verapamil. Anesthetized rabbits were submitted to a ligation of the left circumflex coronary artery for 20 min. Zatebradine (150 and 750 micrograms/kg, i.v.) dose-dependently reduced heart rate, but changed neither the left ventricular pressure nor the (+)dp/dtmax. In comparison, verapamil (150 and 750 micrograms/kg, i.v.) reduced heart rate, systemic blood pressure, left ventricular pressure and (+)dp/dtmax. The incidence of ventricular premature beats occurring during acute ischemia was changed neither by zatebradine nor by verapamil. Ventricular fibrillation, occurring in 36% of the saline-treated rabbits, was reduced to 18% in the presence of 750 micrograms/kg of zatebradine and 0% with verapamil (750 micrograms/kg, p < 0.05). The action of zatebradine on ischemia-induced ventricular fibrillation, albeit limited, was completely reversed by atrial pacing to the predrug heart rate. To further investigate the mechanisms involved in the antiarrhythmic potential of both zatebradine and verapamil, their electrophysiological actions were compared in canine Purkinje fibers. Both zatebradine and verapamil induced a dose-dependent increase in action potential duration (APD) measured at 90% repolarization. The APDs measured during the plateau level (APD30) and at 50% of the repolarization (APD50) were shortened by verapamil and increased by zatebradine showing that at the concentrations used, zatebradine did not exhibit any calcium antagonistic activity when compared to verapamil. The results of the present study suggest that the specific bradycardic agent zatebradine showed a beneficial action mainly because of its anti-ischemic properties. However, the present studies performed in anesthetized rabbits suggest that in this species pure reduction in heart rate is not sufficient to entirely prevent ischemic arrhythmias.

Actions and interactions of E-4031 and tedisamil on reperfusion-induced arrhythmias and QT interval in rat in vivo.

The effects of the Ito blocker, tedisamil (0.1, 1.0, and 3.0 mg/kg, IV), and the IK blocker, E-4031 (0.1, 1.0, and 3.0 mg/kg, IV), on the incidence and duration of reperfusion-induced arrhythmias were compared in the anesthetized rat (n = 12 per group). Reperfusion arrhythmias were evaluated after a 5 minute occlusion period of the left main coronary artery. In the absence of any pronounced effect on blood pressure, tedisamil and E-4031 reduced heart rate in a dose-dependent manner. During the preischemic period, QTc interval was increased by tedisamil but was not changed by E-4031. Both compounds increased the QTc interval during the ischemic period and also during the reperfusion. E-4031 was unable to reduce the incidence and duration of reperfusion-induced ventricular arrhythmias after 5 minutes of coronary artery occlusion. Tedisamil dose-dependently reduced the duration of reperfusion arrhythmias and their incidence. In a second set of experiments, the combination of tedisamil (1.0 mg/kg) with E-4031 (1.0 mg/kg) was administered. The electrocardiographic action of this combination was similar to that observed with tedisamil given alone. However, with the combination the incidence of fibrillation was reduced from 83% in the control group to 8% in the treated group (p < 0.001), and the mortality was reduced from 67% to 0% (p < 0.001), that is, to a greater extent than with tedisamil (1.0 mg/kg) alone. The results show that the blockade of Ito by tedisamil allows a reduction of reperfusion-induced mortality and that a specific IK blocker (E-4031) is devoid of antifibrillatory action in the anesthetized rat.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of glibenclamide on ventricular arrhythmias and cardiac function in ischaemia and reperfusion in isolated rat heart.

OBJECTIVE: The aim was to investigate the effects of glibenclamide, a specific blocker of the ATP sensitive potassium channel, on the incidence of ventricular arrhythmias and the functional changes occurring during myocardial ischaemia and reperfusion. METHODS: Hearts (n = 10 per group) were obtained from male Wistar rats, weight 250-300 g. The study was performed in isolated Langendorff perfused rat hearts subjected to ligation of the left coronary artery and reperfusion. Because of the occurrence of arrhythmias, cardiac function was not evaluated during reperfusion. Glibenclamide (1 or 10 microM) was added to the perfusion solution before the coronary artery occlusion, during ischaemia or after reperfusion. In some experiments the incidence of various durations of ischaemia (5, 10, 15, and 30 min) was evaluated. RESULTS: During the preischaemic period, glibenclamide induced a marked reduction in coronary flow, with a slight decrease in heart rate and left ventricular pressure. The ischaemia induced decrease in left ventricular pressure was markedly attenuated when glibenclamide was given before ischaemia. Thus the isovolumetric left ventricular pressure measured after 15 min ischaemia, which represents 59(SEM 6)% of the preischaemic value in the control group, was increased to 82(9) and 94(8)% in presence of glibenclamide (1 and 10 microM, p < 0.05 respectively). The effect was less pronounced when glibenclamide was added to the perfusion fluid during the ischaemic period. None of the hearts showed ventricular fibrillation during the ischaemic period. Glibenclamide (1 and 10 microM) did not reduce the incidence of reperfusion induced ventricular fibrillation. However, a defibrillatory action was observed since glibenclamide reduced the duration of ventricular fibrillation during reperfusion. CONCLUSIONS: Glibenclamide may increase the probability of spontaneous termination of ventricular fibrillation and facilitate the restoration of the myocardial function during regional ischaemia.

Comparative effects of a potassium channel blocking drug, UK-68,798, and a specific bradycardic agent, UL-FS 49, on exercise-induced ischemia in the dog: significance of diastolic time on ischemic cardiac function.

The effects of N-]4-(2-(2-[4-(methanesulphonamide)phenoxy]-N- methylethylamino)ethyl)phenyl]methanesulphonamide, free base (UK-68,798) (30 and 100 micrograms/kg i.v.), a class III antiarrhythmic with potassium channel blocking activity, on regional ventricular function during exercise-induced ischemia in conscious dogs were compared to those of 1,3,4,5-tetrahydro-7,8-dimethoxy-3-[3-(]2-ad3,4- dimethoxyphenyl]ethyl)methylamino)propyl]-2H-3-benzazepin-2-one, hydrochloride (UL-FS 49) (500 micrograms/kg, i.v.), a specific bradycardic agent. Studies were performed in chronically instrumented dogs trained to run on a motor-driven treadmill. After stenosis of the left anterior descending coronary artery, dogs were submitted to a submaximal exercise. UK-68,798 did not change the resting heart rate, but reduced exercise heart rate by 6.5 and 13.5% at 30 and 100 micrograms/kg, respectively (P less than .05). In a normal area, both doses of UK-68,798 slightly increased regional function. In an ischemic area, the lower dose of UK-68,798 (30 micrograms/kg) was without effect. At the higher dose (100 micrograms/kg), the ischemic dysfunction was worsened, because the percent systolic shortening was reduced from 22.6 +/- 2.6% in the control exercise to 11.1 +/- 5.6% in the presence of UK-68,798 (P less than .05). UL-FS 49 (500 micrograms/kg) reduced heart rate before and during exercise. At rest, UL-FS 49 slightly increased systolic shortening in normal and ischemic areas. In the ischemic area, UL-FS 49 reversed the exercise-induced dysfunction. Before and during exercise, UL-FS 49 (500 micrograms/kg) prolonged diastolic time significantly more than UK-68,798 (100 micrograms/kg; P less than .05).(ABSTRACT TRUNCATED AT 250 WORDS)

Ischemia and reperfusion-induced arrhythmias in rabbits with chronic heart failure.

The incidence of ventricular arrhythmias occurring during acute myocardial ischemia and reperfusion was studied in anesthetized rabbits with chronic heart failure. Cardiac failure was induced by volume and pressure overload and was characterized by marked hypertrophy (84%) and lower systolic aortic blood pressure (112 +/- 3 mmHg) than in controls (124 +/- 2 mmHg, P less than 0.01). During the first 20 min postcoronary artery ligation, the incidence and duration of ventricular fibrillation were greater in the heart failure group (76% and 485 +/- 77 s, respectively) compared with the control group (27% and 86 +/- 37 s, respectively, P less than 0.01). Reperfusion-induced arrhythmias after various ischemic durations were also more frequent in the heart failure group than in the control group. Papillary muscles taken from rabbits with heart failure showed a reduced diastolic potential and a prolonged action potential duration (APD90) compared with the control group (by 7 and 46%, respectively), but there was no change in maximum upstroke velocity. The present study established that rabbits with pronounced morphological signs of chronic heart failure have an enhanced susceptibility to ischemia and reperfusion-induced arrhythmias. As already described in situations of uncomplicated cardiac hypertrophy, a delay in the repolarization process could represent an arrhythmogenic mechanism in this model.