Effects of DPI 201-106, a novel cardiotonic agent,on hemodynamics,cardiac electrophysiology and arrhythmias induced by programmed ventricular stimulation in dogs with subacute myocardial infarction: A comparative study with dobutamine

Summary DPI 201-106 (DPI), a novel and potent cardiotonic agent, exhibits its effects by prolonging the open state of Na⁺ channels, resulting in an increase in action potential duration, and thus, is supposed to share the class III antiarrhythmic activity. The effects of DPI on the hemodynamics, intraventricular conduction and refractoriness of heart, and the incidence of arrhythmias induced by programmed electrical ventricular stimulation (PES) were compared with (±)-dobutamine. Dogs which survived for 5 to 7 days after the induction of myocardial infarction were used as the model. The presence of sub-acute myocardial infarction caused by occluding the left anterior descending coronary artery elicited a mild left ventricular dysfunction represented by a significant decrease in peak LV dp/dt by about 20%.Both i.v. bolus injection of DPI (1, 3 and 5 mg/kg) and i. v. continuous infusion of dobutamine (3, 5 and 10 g/kg/min), which were administered in a cumulative manner, dose-dependently improved the hemodynamic parameters. At the higher doses of both DPI (3 and 5 mg/kg) and dobutamine (5 and 10 g/kg/min) the control values were reached or even exceeded. DPI dose-dependently increased the effective refractory period (ERP) of both non-infarcted and infarcted ventricular myocardia to a similar degree, but the conduction time showed a frequency-dependent increase in the infarcted myocardium to a greater degree than in the non-infarcted myocardium after DPI. In contrast, dobutamine decreased the ERP in both non-infarcted and infarcted myocardia, and slightly increased the difference of refractoriness between the non-infarcted and infarcted zones with no effect on the intraventricular conduction. In the PES study, DPI (3 and 5 mg/kg) produced a significant decrease in the incidence of ventricular tachycardia, whereas dobutamine (5 and 10 g/kg/min) tended to worsen the arrhythmias. These findings suggest that cardiotonic agents with a class III antiarrhythmic property such as DPI may be potentially useful for the management of heart failure accompanied by ischemic heart disease.Abbreviations DPI, DPI 201-106; PES programmed electrical ventricular stimulation - LV dp/dt the rate of rise of left ventricular pressure - ERP effective refractory period - RVOT right ventricular outflow tract - VT ventricular tachycardia - LAD left anterior discending coronary artery Send offprint requests to T. Uematsu at the above address     

DPI 201-106, a novel cardioactive agent. Combination of cAMP-independent positive inotropic,negative chronotropic,action potential prolonging and coronary dilatory properties

Summary The in vitro cardiac effects of DPI 201-106, a novel piperazinyl-indole, were investigated.DPI 201-106 produced concentration-dependent positive inotropic effects in guinea-pig and rat left atria, kitten, rabbit and guinea-pig papillary muscles and Langendorff perfused hearts of rabbits between 10^–7 and 3×10^–6 mol/l. During isometric twitches, contraction and relaxation phases were prolonged in guinea-pig left atria and right ventricular papillary muscles from kitten and guinea-pigs. Spontaneous sinus rate was decreased in right atria of guinea-pigs and rats. Coronary flow increased in rabbit isolated hearts. Functional refractory period was increased in left atria from guinea-pigs and rats with EC₅₀ values of 1.7 and 0.24 mol/l respectively.In electrophysiological measurements, DPI 201-106 prolonged the action potential duration (APD₇₀) in guinea-pig papillary muscles up to 70% and in rabbit atria up to 120% at 3 mol/l. Other action potential characteristics were not changed in guinea-pig papillary muscles but V _max was decreased in rabbit left atria. The electrophysiological as well as the positive inotropic effects were stereoselective with the activity residing in the S-enantiomer.DPI 201-106 increased the Ca²⁺-sensitivity of skinned fibres from porcine trabecular septomarginalis with an EC₅₀ of 0.2 nmol/l. DPI 201-106 did not change cAMP levels in guinea-pig atria and rabbit papillary muscles. Slow action potentials were not induced by DPI 201-106 in partially depolarized guinea-pig papillary muscles. Phosphodiesterase activity of rat hearts was not inhibited by DPI 201-106 at pharmacologically relevant concentrations. The presence of propranolol did not influence the inotropic potency of DPI 201-106 in guinea-pig atria.In conclusion, DPI 201-106 represents a novel type of positive inotropic agents with a synergistic sarcolemmal and intracellular mechanism of action.     

Cardiovascular actions of DPI 201-106, a novel cardiotonic agent

DPI 201-106 (4-[3-(4-diphenylmethyl-1-piperazinyl)-2-hydroxypropoxy]-1H-indole -2- carbonitrile) is characterized by a marked cardiotonic activity. The compound exerted positive inotropic effects in anesthetized and conscious dogs, pithed open-chest cats, and isolated hearts of cardiomyopathic hamsters and vanadate-treated guinea-pig atria. Left ventricular dP/dtmax was increased in anesthetized dogs after i.v. injection of 0.2 and 2 mg/kg DPI 201-106 (34 +/- 6 and 104 +/- 18%, respectively) and in unanesthetized dogs after oral doses of 2-8 mg/kg (22 +/- 3 to 50 +/- 5%, respectively). In most experiments, the compound lowered blood pressure and heart rate. Stroke work and left ventricular work were almost unaffected by DPI 201-106, and oxygen consumption and cardiac efficiency remained unchanged in open-chest dogs. Studies of the mechanism of action of DPI 201-106 lead to the conclusion that its positive inotropic effect is not explainable either by beta-stimulation or by liberation of catecholamines. This was shown in anesthetized dogs and pithed open-chest cats pretreated with propranolol and reserpine.     

Interaction of the cardiotonic agent DPI 201-106 with cardiac Ca2+ channels

The cardiotonic agent DPI 201-106 was investigated for its effects on (a) contractile force in guinea pig left atria, (b) membrane currents in isolated guinea pig cardiac myocytes, and (c) [3H]nitrendipine binding in guinea pig cardiac membranes. The compound elicited a positive inotropic effect in normally polarized (5.9 mM extracellular KCl) and a negative inotropic effect in partially depolarized (20 mM KCl) isolated, electrically stimulated left atria. This decrease in contractile force was probably caused by inactivation of the fast Na+ inward current and concomitant blockade of the inward Ca2+ current. The blocking effect on Ca2+ channels was directly shown in voltage-clamp experiments using isolated cardiocytes. Further evidence for interaction of DPI 201-106 with Ca2+ channels was obtained from the [3H]nitrendipine binding studies. Thus, Ca2+ antagonism contributes to the complex pharmacologic profile of DPI 201-106, and is probably responsible for the bradycardia and lowering of systemic vascular resistance observed in vivo.     

The inotropic agents DPI 201-106 and BDF 9148 differentially affect potassium currents of guinea-pig ventricular myocytes

The inotropic agents DPI 201-106 and BDF 9148 increase action potential duration (APD) of heart muscle. This effect can be explained by inhibition of inactivation of sodium current, which is affected by both agents to a similar extent (Ravens et al. 1991, Br J Pharmacol 104:1019–1023). However, as DPI 201-106 prolongs APD of guinea-pig ventricle to a larger extent than BDF 9148, other currents may also be involved. The aim of the present study was to measure the effects of DPI 201-106 and BDF 9148 on the inward rectifier I_K1, and the two components of the delayed rectifier, I_Ks and I_Kr. The methyl-for-carbonitrile-substituted derivative BDF 8784 was included to study structure-activity relationships. Single-electrode whole-cell voltage-clamp technique was used to measure membrane currents of guinea-pig ventricular myocytes. Only DPI 201-106 reduced I_K1 at potentials both negative and positive to the reversal potential. Three M of DPI 201-106 reduced I_Ks, whereas 1 M of BDF 9148 had no effect on this current. These concentrations were equieffective with respect to positive inotropic action (Ravens et al. 1991, Br J Pharmacol 104:1019–1023). BDF 9148 did however block I_Ks at higher concentrations, as did BDF 8784. It is concluded that block of outward current by DPI 201-106, but insignificant effects of BDF 9148, are responsible for the differential effects of these compounds on APD at equieffective concentrations with respect to inotropy. Correspondence to: U. Ravens at the above address     

Functional interaction between DPI 201-106, a drug that mimics congenital long QT syndrome, and sevoflurane on the guinea-pig cardiac action potential

1. Sevoflurane produces QT prolongation on the electrocardiogram, predominantly via inhibition of the slow delayed rectifier K(+) current. DPI 201-106 is an experimental drug that produces QT prolongation by reducing Na(+) channel inactivation, thereby mimicking congenital long QT syndrome type 3 (LQT3). The present study explores the electrophysiological consequences of administration of sevoflurane in the presence of impaired Na(+) channel activity. 2. We examined the effects of sevoflurane and DPI 201-106, alone and in combination, on the cardiac action potential of guinea-pig ventricular myocytes using standard microelectrode techniques. 3. Both sevoflurane and DPI-201-106 prolonged action potential duration, with the combination of the two drugs producing greater than additive effects. Similarly, instability and triangulation of the action potential waveform, measures of pro-arrhythmia, were more pronounced when both drugs were combined. 4. Sevoflurane treatment significantly alters cardiac action potential waveforms when administered in the presence of impaired Na(+) channel inactivation. These results indicate the potential for ventricular arrhythmia when sevoflurane is administered to LQT3 patients and suggests caution when using sevoflurane in this population.     

Cardiovascular effects of the novel cardiotonic agent DPI 201-106 in the anaesthetized rat

DPI 201-106 (4-[3-(4-diphenylmethyl-1-piperazinyl)-2-hydroxypropoxy]-1H-indole -2- carbonitrile) was given intravenously to anaesthetized male rats. DPI caused an increase in left ventricular dP/dt (LV dP/dt), giving a significant increase at 0.03 mumol/kg. At this dose DPI had no effect on either mean arterial pressure (MAP) or heart rate (HR). At higher doses, MAP decreased transiently. At 0.3 and 1 mumol/kg, HR was decreased. The results indicate that DPI produces positive inotropic and negative chronotropic effects in the anaesthetized rat.     

Mechanism of the vasodilator effects of the cardiotonic agent DPI 201-106

DPI 201-106 (DP) is a new cardiotonic agent. In experiment on cats anaesthetized with chloralose/urethane, it lowered blood pressure and caused peripheral vasodilatation at doses between 0.3 and 3 mg/kg, infused i.v. Furthermore, DPI lowered heart rate and increased coronary blood flow (measured with tracer microspheres). The mechanism of this vasodilator action was investigated in experiments in vitro using rabbit aorta. DPI inhibited depolarization-induced contraction. The effect was strongly dependent on the contact time. The pIC50 (-log IC50) values for 15 min, 1, and 2 h pretreatment were 4, 5.2, and 5.7, respectively. 45Ca2+ uptake into rabbit aorta was inhibited by DPI with pIC50 values of 4.3, 5.1, and 5.7, respectively, for the pretreatment periods indicated above. The excellent agreement between effects on tension development and calcium uptake suggests that the mechanism of vasodilatation observed in vivo is related to calcium antagonism.     

Interaction of DPI 201-106 with cardiac glycosides

The interaction of the cardiotonic agent DPI 201-106 (4-[3-(4-diphenylmethyl-1-piperazinyl(-2-hydroxypropoxy]-1H-indole -2- carbonitrile) with cardiac glycosides was investigated. In rabbit papillary muscles, all effects were normalized by using potentiating paired stimulation (PPS) as the 100% reference standard. Ouabain 1 microM alone increased the force of contraction (FC) by 66% +/- 6% (SEM) of PPS; 0.1 microM was ineffective. In the presence of 0.1 microM S-(-)-DPI 201-106, the active enantiomer of DPI 201-106, ouabain 0.1 and 1 microM increased FC by 41% +/- 11% and 119% +/- 19% of PPS, respectively. In anesthetized dogs, left ventricular dP/dtmax was increased by racemic DPI 201-106 0.2 mg/kg i.v. (+1987 +/- 660 mm Hg/s) and by ouabain 35 micrograms/kg i.v. (+560 +/- 40 mm Hg/s). The combined effect of DPI 201-106 and ouabain in similar doses was +2827 +/- 942 mm Hg/s. In digoxin-pretreated anesthetized cats, racemic DPI 201-106 was infused up to an accumulated dose of 12.22 mg/kg i.v. No signs of cardiotoxicity were observed in combination. In conclusion, the concomitant administration of DPI 201-106 and cardiac glycosides leads to enhanced positive inotropic effects in vitro and in vivo. The cardiotoxicity of glycosides was not increased by DPI 201-106.     

Cardiac and hemodynamic profile of the new cardiotonic agent, DPI 201-106, in the conscious dog

The cardiac and hemodynamic effects of increasing doses (0.1-3 mg/kg i.v.) of the novel cardiotonic agent, DPI 201-106 (DPI), were investigated over a 60 min period in conscious dogs chronically instrumented for the measurement of arterial pressure, heart rate, left ventricular pressure (LVP), LV (+) dP/dtmax and cardiac output. LV (+) dP/dtmax, cardiac output and stroke volume were significantly increased by DPI whereas the total peripheral resistance was significantly decreased. These effects were dose-dependent in intensity and in duration. The mean arterial pressure and heart rate remained unaffected, except by the 3 mg/kg dose, which increased them slightly. Autonomic blockade with hexamethonium, atropine and propranolol did not alter the positive inotropic properties of DPI but unmasked its intrinsic bradycardic effect. At equipotent positive inotropic doses, DPI (0.3 mg/kg), milrinone (40 micrograms/kg) and dobutamine (5 micrograms/kg per min) induced similar increases in cardiac output and similar decreases in total peripheral resistance, but only dobutamine and milrinone accelerated the heart rate, whereas ouabain (17.5 micrograms/kg) induced a strong rise in the total peripheral resistance and markedly lowered the heart rate and cardiac output. After coadministration of DPI and ouabain, LV (+) dP/dtmax was further increased whereas the ouabain-induced bradycardia, the rise in the total peripheral resistance and the decrease in cardiac output were reinforced, halved and unaltered, respectively. We conclude that (a) DPI exhibits potent and direct positive inotropic properties, associated with a peripheral vasodilating action, and almost no positive chronotropic effects, and (b) coadministration of DPI and ouabain results in synergistic positive inotropic effects.     

Interaction of DPI 201-106 with cardiac muscarinic receptors

The effects of the new cardiotonic compound, DPI 201-106, on muscarinic responses and muscarinic receptor binding were studied in the guinea pig heart. DPI 201-106 exerted a pronounced anticholinergic action in isolated auricles and a moderate one in papillary muscles, which resembled the pattern of a functional antagonism. However, in competition binding experiments, DPI 201-106 inhibited binding of the specific muscarinic antagonist [3H]NMS with equal potency in atrial and ventricular homogenates (apparent KI = 0.7 mumol/l in atria and 1.2 mumol/l in ventricles). At higher concentrations (greater than 3 mumol/l), DPI 201-106 slowed the dissociation of [3H]NMS from cardiac muscarinic receptors, indicating that DPI 201-106 affects in addition a site allosteric to the muscarinic receptor. It is concluded that DPI 201-106 is able to inhibit cholinergic responses in the heart, not only by a functional antagonism but also by direct interaction with muscarinic receptors.     

Pharmacological actions of APP 201-533, a novel cardiotonic agent

APP 201-533 [3-amino-6-methyl-5-phenyl-2(1H)-pyridinone] was investigated in vivo in anesthetized and unanesthetized dogs and pithed open-chest cats and in vitro in guinea pig atria and papillary muscles, skinned muscle fibers from pig hearts, and rat myocardium. Left ventricular dP/dt was increased in anesthetized dogs after intravenous injection of 0.2 and 2 mg/kg APP 201-533 (34 +/- 3 and 132 +/- 28%, respectively) and in unanesthetized dogs after oral doses of 1.5-7.5 mg/kg (34 +/- 11-138 +/- 43%). The substance induced moderate tachycardia. Large intraduodenal doses of APP 201-533 reduced afterload in anesthetized dogs. The compound does not seem to act either by stimulation of alpha- or beta-adrenoceptors or histamine receptors or by liberation of catecholamines. APP 201-533 up to 10(-5) M had no electrophysiological effect on normal action potentials in guinea pig papillary muscles. A phosphodiesterase-inhibiting activity (IC50 = 1.6 X 10(-4) M) may be responsible for the positive inotropic action. Another key to the mechanism of action may be based on our observation of a shift of the relationship between cardiac force and intracellular Ca2+ concentration. In contrast to amrinone and ouabain, APP 201-533 increases Ca2+ sensitivity of the myocardial contractile structures.     

Reversal of the cardiotonic and action-potential prolonging effects of DPI 201-106 by BDF 8784, a methyl-indol derivative.

1. We studied the interaction of the cardiotonic compound DPI 201-106 (4-[3'-(4'-benzhydryl-1'-piperazinyl)-2'-hydroxypropoxy]-1H-indole-2- carbonitrile; DPI) and its derivative BDF 8784 (2-methyl-4-[3'-(4'-benzhydryl- 1'-piperazinyl)-2'-hydroxypropoxy]-1H-indole; BDF) in isolated right ventricular papillary muscles of guinea-pig heart. 2. In contrast to the cardiotonic DPI, the methyl-indole derivative lacked a positive inotropic effect and even caused negative inotropic effects in concentrations above 1 microM. At 10 microM BDF significantly reduced the force of contraction and dV/dtmax, but did not affect action potential duration (APD). 3. Pretreatment of papillary muscles with BDF prevented the positive inotropic action of DPI in a concentration-dependent, but non-competitive fashion. At 10 microM, BDF prevented the inotropic effect of racemic DPI and shortened the DPI-induced prolongation of action potential duration. BDF similarly affected the inotropic and APD-prolonging effects of the sea anemone polypeptide ATX II. 4. In cardiac myocytes, DPI induced a tetrodotoxin (TTX)-sensitive, slowly inactivating inward current. The slow decay of this current was enhanced by BDF. In cells pretreated with BDF, DPI was not effective. BDF alone depressed the sodium and the calcium current. 5. In conclusion, the non-inotropic methyl-indole derivative BDF interacts with DPI noncompetitively at the sodium channels to abolish the inotropic and APD-prolonging effects of DPI, emphasizing the importance of the substituent in position 2 of the indole moiety for this effect.     

Removal of inactivation and blockade of cardiac Na+ channels by DPI 201-106 different voltage-dependencies of the drug actions

Summary The influence of the novel cardiotonic diphenylpiperazinylindole derivative. the racemic DPI 201-106. on cardiac Na⁺ channels was studied in conventional microelectrode experiments on papillary muscles of guinea pigs and in patch clamp experiments using inside-out patches excised from cultured neonatal rat cardiocytes. The maximal rate of rise (V _max) of Na⁺-dependent action potentials was taken as an estimate for INa. Racemic DPI (3 × 10^–6 mol/1) exerts a dual effect as it removes channel inactivation and may also block cardiac Na⁺ channels. Both drug actions proved highly voltage-dependent but a given change in membrane potential had a strictly different modulating influence on the two effects. The \0V _max depression induced by racemic DPI became attenuated due to hyperpolarization and finally tended to disappear at about -90 mV. while at the same time I _Na modification became increasingly accentuated. An increase in holding potential caused the non-decaying portion of the macroscopic I _Na to increase significantly. Resting inactivation remained operative in non-inactivating cardiac Na⁺ channels and showed a similar voltage-dependence as in normal Na⁺ channels. The differential voltage-dependencies of both DPI effects strongly suggest the existence of two binding sites for DPI.This work was supported by a grant of the Deutsche Forschungsgemeinschaft (Ko 778/2-1). Bonn, Federal Republic of Germany Send offprint requests to M. Kohlhardt at the above address     

Inotropic versus chronotropic, dromotropic, and coronary vasodilator actions of DPI 201-106, a novel positive inotropic agent, in the dog heart

Inotropic versus chronotropic, dromotropic, and vascular effects of DPI 201-106 were assessed in isolated, blood-perfused papillary muscle, sinoatrial (SA) node, and atrioventricular (AV) node preparations of dogs. DPI 201-106 was administered intraarterially. In paced papillary muscles the drug produced an increase in developed tension. In spontaneously beating papillary muscles the drug slightly decreased the beating rate. In SA node preparations the drug decreased sinus rate, and atrial standstill ensued from the highest dose. In AV node preparations the drug affected AV conduction only when administered into the AV node artery, and in high doses second- or third-degree AV block occurred. In all preparations the drug increased blood flow. DPI 201-106 at the dose that produced a 50% increase in the force of contraction of ventricular muscle increased coronary blood flow by 8.4%, AV conduction time by 7.6%, and decreased sinus rate by 2.6%, indicating its high selectivity for force. When infused into the AV node artery, the drug in high doses produced dose-dependent prolongations of both the AV nodal conduction time and the functional refractory period of the AV node, which were pronounced with elevation of the pacing rate. These effects of DPI 201-106 are very similar to those of calcium channel blockers.     

The role of sodium channels in the effects of the cardiotonic compound DPI 201-106 on contractility and membrane potentials in isolated mammalian heart preparations

The novel compound DPI 201-106 (4-3-(4-diphenyl-methyl-1-piperazinyl)-2-hydroxypropoxy-1H-indole-carbon itrile) prolonged the action potential duration (APD) and enhanced force of contraction in isolated papillary muscles of the guinea-pig. The effective concentration range was 0.1-3 mumol/l. These effects persisted upon removal of the compound, even after extensive washings. Both prolongation of APD and the positive inotropic effect were readily reversed or prevented after exposure to tetrodotoxin, 3 mumol/l. Slow action potentials of partially depolarized preparations in high potassium solution were hardly influenced by DPI 201-106 (1 mumol/l) or were depressed (3 mumol/l). In isolated myocytes DPI 201-106 induced a slowly decaying net inward current, that disappeared again after exposure to tetrodotoxin. With the exception of the lack of reversibility by washing, these effects were similar to the ones reported previously for the Anemonia sulcata polypeptide ATX II. ATX II and DPI 201-106 did not affect the post-rest contraction. The biphasic response in APD after a transient interruption of stimulation was accentuated by ATX II and became monophasic with DPI 201-106. It is concluded that the effects of DPI 201-106 are also mediated by an interaction with the Na channels, but DPI 201-106 and ATX II probably affect the channels in a different manner.     

Electrophysiological effects of EGIS-7229, a new antiarrhythmic agent, in isolated mammalian and human cardiac tissues

The cellular electrophysiological effects of EGIS-7229 (5-chlor-4-[N-(3,4-dimethoxy-phenyl-ethyl)-amino-propylamino]-3(2H)-pyridazinone fumarate), a novel antiarrhythmic agent, was studied using conventional microelectrode techniques in canine cardiac Purkinje fibers and papillary muscle preparations obtained from man, rabbits and guinea pigs. Low concentration of EGIS-7229 (3 μmol/l) selectively lengthened action potential duration (both APD₅₀ and APD₉₀) in all preparations. The effect of higher concentrations (30–100 μmol/l) of EGIS-7229 on action potential duration was variable depending on the preparation studied: in rabbit and human papillary muscles both APD₅₀ and APD₉₀ were lengthened, in canine Purkinje fibers APD₉₀ was lengthened but APD₅₀ was shortened, while in guinea pig papillary muscles both APD₅₀ and APD₉₀ were shortened by high concentrations of the drug. At these higher concentrations EGIS-7229 also decreased the maximum velocity of action potential upstroke (V _max) and depressed the plateau of action potentials without affecting the resting membrane potential or action potential amplitude. Both reduction of V _max and lengthening of APD were frequency dependent. The former effect was more prominent at higher pacing frequencies, while the latter was more pronounced at lower driving rates. In guinea pig papillary muscle, the time constant of recovery from V _max-block was 719 ± 33 ms (n = 18) and the rate of onset of the block was 1.81 ± 0.06 AP^–1 (n = 16) in the presence of 100 μmol/l EGIS-7229. EGIS-7229 had a complex action on refractoriness in guinea pig papillary muscles: ERP was lengthened at low concentrations (3 to 10 μmol/l), unchanged at 30 μmol/l and shortened at 100 μmol/l. The ratio of ERP/APD₉₀, however, was significantly increased at concentrations higher than 3 μmol/l. In canine Purkinje fiber, when the delayed rectifier K current (I_K) was blocked by d-sotalol (60 μmol/l) and APD was shortened back to its control value by additional application of nicorandil (15 μmol/l), APD was not affected by 3 μmol/l but was shortened by 30 μmol/l of EGIS-7229. 100 μmol/l EGIS-7229 shortened APD in guinea pig papillary muscle. This effect of EGIS-7229 was effectively prevented by nifedipine pretreatment (10 μmol/l). In this preparation, EGIS-7229 also decreased the V _max of the slow action potential, evoked in the presence of 20 mmol/l external K⁺ plus 0.5 mmol/l Ba²⁺. It is likely that EGIS-7229 at low concentrations blocks I_K in human, canine, rabbit and guinea pig cardiac preparations, but at higher concentrations also inhibits Ca and Na currents. Therefore, EGIS-7229 appears to carry mixed class III, IV and IB antiarrhythmic properties. Received: 8 July 1996 / Accepted: 23 October 1996     

Evidence for different receptor sites for the novel cardiotonic S-DPI 201-106, ATX II and veratridine on the cardiac sodium channel

DPI 201-106 (4-[3-(4-diphenylmethyl-1-piperazinyl)-2-hydroxypropoxy]-1 H-indole-2-carbonitrile, DPI) is a novel cardiotonic which prolongs the open state of the cardiac sodium channel. The interactions of the sea anemone toxin ATX II and of veratridine with the active enantiomer of (racemic) DPI, S-DPI, were investigated by making electrophysiologic measurements in guinea-pig papillary muscles. The prolongation of the action potential duration (APD) by S-DPI was potentiated in the presence of ATX II, suggesting that the two agents bound to different sites. Veratridine alone increased APD slowly over 4 h. S-DPI greatly accelerated and potentiated the effect of veratridine. Conversely, veratridine increased the efficacy of S-DPI but decreased its potency, both about 4-fold. All effects were TTX-sensitive. It is concluded that the three agents bind to different sites at the cardiac Na+ channel and that these sites are allosterically coupled.     

Pharmacological actions of DPN 205-734, a novel cardiotonic agent

DPN 205-734 [5-(4-cyanophenyl)-1,2-dihydro-6-methyl-2-oxopyridin-3-carbo nitrile] was investigated in vitro in Langendorff rabbit hearts, guinea pig and rabbit papillary muscles, and rat myocardium and in vivo in anesthetized and unanesthetized dogs, pithed open-chest cats, anesthetized rats, and cardiomyopathic hamsters. In vitro, this substance caused a concentration-dependent positive inotropic effect. Left ventricular dP/dtmax was increased in anesthetized dogs after intravenous injection of 0.02 and 0.2 mg/kg (35 +/- 10 and 130 +/- 13%, respectively) and in unanesthetized dogs after oral doses of 0.05-0.5 mg/kg (15 +/- 2 to 71 +/- 14%). DPN 205-734 lowered blood pressure and total peripheral resistance in several experimental models, indicating an afterload-reducing effect. It induced moderate tachycardia. The positive inotropic effect is not explainable by beta-stimulation as shown in pithed open-chest cats pretreated with propranolol. A phosphodiesterase-inhibiting activity (IC50 = 35.5 microM), measured in rat myocardium, may be primarily responsible for the positive inotropic action. In guinea pig papillary muscles partially depolarized with 22 mM K+, DPN 205-734 in a concentration of 1 microM restored slow action potentials, which were then blocked by carbachol. These actions can be explained by the increase in cardiac cyclic AMP level due to a phosphodiesterase-inhibiting effect. In rabbit papillary muscles the positive inotropic effect of DPN 205-734 (100 microM) was only moderately inhibited by carbachol (3 microM), suggesting an additional mechanism.     

The effect of a new inotropic agent, DPI 201-106, on systolic time intervals and the electrocardiogram in healthy subjects.

1. DPI 201-106 (DPI) is a novel inotropic agent, with Na+ channel agonistic action combined with a sensitization of contractile proteins to Ca++. In a double-blind trial in healthy volunteers (n = 20) cardiovascular effects (blood pressure, heart rate, ECG) of single oral doses were studied. In addition systolic time intervals (STIs) were assessed in 10 of these subjects. DPI plasma concentrations were measured by h.p.l.c. 2. Preejection period was shortened by 14 ms (P less than 0.01) and 30 ms (P less than 0.01) 1 h after 30 and 60 mg, respectively, suggesting a dose-dependent inotropic effect. Heart rate was slightly reduced after both doses. Mean blood pressure remained unchanged. 3. Corrected QT interval duration (QTc) was prolonged by a mean of 7 ms (NS) and 22 ms (P less than 0.001) 1 h after 30 and 60 mg, respectively. PQ and QRS intervals remained unaffected. 4. Peak plasma levels were attained at 1-2 h and the terminal elimination half-life was approximately 15 h. 5. It is concluded that DPI has positive inotropic and negative chronotropic properties which make it potentially useful for the treatment of heart failure.