Specific bradycardic agents. 1. Chemistry, pharmacology, and structure-activity relationships of substituted benzazepinones, a-new class of compounds exerting antiischemic properties

Linked biaromatic compounds as cardioprotective agents

Cardiovascular diseases (CVDs) are widespread in the modern world, and their number is constantly growing. For a long time, CVDs have been the leading cause of morbidity and mortality worldwide. Drugs for the treatment of CVD have been developed almost since the beginning of the 20th century, and a large number of effective cardioprotective agents of various classes have been created. Nevertheless, the need for the design and development of new safe drugs for the treatment of CVD remains. Literature data indicate that a huge number of cardioprotective agents of various generations and mechanisms correspond to a single generalized pharmacophore model containing two aromatic nuclei linked by a linear linker. In this regard, we put forward a concept for the design of a new generation of cardioprotective agents with a multitarget mechanism of action within the indicated pharmacophore model. This review is devoted to a generalization of the currently known compounds with cardioprotective properties and corresponding to the pharmacophore model of biaromatic compounds linked by a linear linker. Particular attention is paid to the history of the creation of these drugs, approaches to their design, and analysis of the structure-action relationship within each class.

1-Isoindolinone scaffold-based natural products with a promising diverse bioactivity

Isoindolin-1-one or 1-isoindolinone framework is referred to phthalimidines or benzo fused γ-lactams of the corresponding γ-amino carboxylic acids and has been of prime interest for scientists for last several decades. 1-Isoindolinone framework is found in a wide range of naturally occurring compounds with diverse biological activities and therapeutic potential for various chronic diseases. Recent developments in synthetic methods for their procurement have opened a new era of 1-isoindolinone chemistry. This review aims to provide an alphabetical quick reference guide to only 1-isoindolinone based natural products and its variable fused, oxidized and reduced state skeleton with information for advanced chemotaxonomic analyses, cellular targets/pathways and diverse biological activities and future use for medicinal chemistry.

EC18 as a Tool To Understand the Role of HCN4 Channels in Mediating Hyperpolarization-Activated Current in Tissues

Hyperpolarization-activated cyclic nucleotide-gated (HCN) channels are membrane proteins encoded by four genes (HCN1-4) and widely distributed in the central and peripheral nervous system and in the heart. HCN channels are involved in several physiological functions, including the generation of rhythmic activity, and are considered important drug targets if compounds with isoform selectivity are developed. At present, however, few compounds are known, which are able to discriminate among HCN channel isoforms. The inclusion of the three-methylene chain of zatebradine into a cyclohexane ring gave a compound (3a) showing a 5-fold preference for HCN4 channels, and ability to selectively modulate I_h in different tissues. Compound 3a has been tested for its ability to reduce I_h and to interact with other ion channels in the heart and the central nervous system. Its preference for HCN4 channels makes this compound useful to elucidate the contribution of this isoform in the physiological and pathological processes involving hyperpolarization-activated current.

Synthesis of Polyheterocyclic Pyrrolo[3,4-b]pyridin-5-ones via a One-Pot (Ugi-3CR/aza Diels-Alder/N-acylation/aromatization/SN2) Process. A Suitable Alternative towards Novel Aza-Analogues of Falipamil

We describe the one-pot synthesis of twenty polyheterocyclic pyrrolo[3,4-b]pyridin-5-ones via a cascade process (Ugi-3CR/aza Diels-Alder/N-acylation/aromatization) in 20 to 95% overall yields, as well as four pharmacologically promising analogues via an improved cascade process (Ugi-3CR/aza Diels-Alder/N-acylation/aromatization/SN2): two piperazine-linked pyrrolo[3,4-b]pyridin-5-ones in 33 and 34%, and a couple of Falipamil aza-analogues in 30 and 35% overall yields. It is worth highlighting the good substrate scope found, because final products are furnished with alkyl, aryl, and heterocyclic substituents. The use of chain-ring tautomerizable isocyanides (as key reagents for the Ugi-type three component reaction) allowed for a rapid and efficient assembly of the polysubstituted oxindoles, which were used in situ toward the complex products, conferring features like robustness, sustainability, and the one-pot approach to this synthetic methodology.

Functional reversal of (-)-Stepholidine analogues by replacement of benzazepine substructure using the ring-expansion strategy

(-)-Stepholidine is an active ingredient of the Chinese herb Stephania and naturally occurring tetrahydroprotoberberine alkaloid with mixed dopamine receptor D1 agonistic and dopamine receptor D2 antagonistic activities. In this work, a series of novel hexahydrobenzo[4,5]azepino [2,1-a]isoquinolines were designed and synthesized as ring-expanded analogues of (-)-Stepholidine. Initial pharmacological assays demonstrated that a benzazepine replacement was associated with significant increase in selectivity and functional reversal at dopamine receptor D1 . Compound-(-)-15e (Ki  = 5.32 ± 0.01 nm) is more potent than (-)-Stepholidine (Ki  = 13 nm) and was identified as a selective dopamine receptor D1 antagonist (IC50  = 0.14 μm). Moreover, molecular modeling suggested that (-)-15e might exert its dopamine receptor D1 antagonistic activities through interacting with the transmembrane helix 7 of dopamine receptor D1 .

HCN Channels Modulators: The Need for Selectivity

Hyperpolarization-activated, cyclic nucleotide-gated (HCN) channels, the molecular correlate of the hyperpolarization-activated current (If/Ih), are membrane proteins which play an important role in several physiological processes and various pathological conditions. In the Sino Atrial Node (SAN) HCN4 is the target of ivabradine, a bradycardic agent that is, at the moment, the only drug which specifically blocks If. Nevertheless, several other pharmacological agents have been shown to modulate HCN channels, a property that may contribute to their therapeutic activity and/or to their side effects. HCN channels are considered potential targets for developing drugs to treat several important pathologies, but a major issue in this field is the discovery of isoform-selective compounds, owing to the wide distribution of these proteins into the central and peripheral nervous systems, heart and other peripheral tissues. This survey is focused on the compounds that have been shown, or have been designed, to interact with HCN channels and on their binding sites, with the aim to summarize current knowledge and possibly to unveil useful information to design new potent and selective modulators.

Development of 3,4-dihydroisoquinolin-1(2H)-one derivatives for the Positron Emission Tomography (PET) imaging of σ₂ receptors

σ₂ Receptors are promising biomarkers for cancer diagnosis given the relationship between the proliferative status of tumors and their density. With the aim of contributing to the research of σ₂ receptor Positron Emission Tomography (PET) probes, we developed 2-[3-[6,7-dimethoxy-3,4-dihydroisoquinolin-2(1H)-yl]propyl]-3,4-dihydroisoquinolin-1(2H)-one (3), with optimal σ₂ pharmacological properties and appropriate lipophilicity. Hence, 3 served as the lead compound for the development of a series of dihydroisoquinolinones amenable to radiolabeling. Radiosynthesis for compound 26, which displayed the most appropriate σ₂ profile, was developed and σ₂ specific binding for the corresponding [(18)F]-26 was confirmed by in vitro autoradiography on rat brain slices. Despite the excellent in vitro properties, [(18)F]-26 could not successfully image σ₂ receptors in the rat brain in vivo, maybe because of its interaction with P-gp. Nevertheless, [(18)F]-26 may still be worthy of further investigation for the imaging of σ₂ receptors in peripheral tumors devoid of P-gp overexpression.

Synthesis and biological activity of some 1,3-dihydro-2H-3-benzazepin-2-ones with a piperazine moiety as bradycardic agents

A series of 1,3-dihydro-2H-3-benzazepin-2-ones with a piperazine moiety were designed and synthesized by treating the common intermediate of 1,3-dihydro-7,8-dimethoxy-3-[3-(1-piperazinyl)propyl]-2H-3-benzazepin-2-ones with a variety of N-aryl-2-chloroacetamides and acyl chlorides. Their structures have been characterized by (1)H-NMR, MS, and elemental analysis. The title compounds were evaluated for their bradycardic activity in vitro. Most of the synthesized compounds exhibited some vasorelaxant activity and heart-rate-reducing activity with bradycardic potency.

3-(3-Chloro-prop-yl)-7,8-dimeth-oxy-1H-3-benzazepin-2(3H)-one at 125 K

In the title compound, C(15)H(18)ClNO(3), the seven-membered ring has a mirror plane passing through the methyl-ene C atom and bis-ecting the C=C bond. It adopts a bent conformation, inter-mediate between the boat and chair forms. Both meth-oxy groups are coplanar with the attached benzene ring [C-C-O-C = -0.5 (3) and 2.2 (3)°]. In the crystal structure, inversion-related mol-ecules are linked via C-H⋯O hydrogen bonds and π-π inter-actions involving the benzene ring [centroid-centroid distance = 3.6393 (12)Å].

3-(3-Chloro-prop-yl)-7,8-dimeth-oxy-2,3,4,5-tetra-hydro-1H-3-benzazepin-2-one at 125 K

In the title compound, C(15)H(20)ClNO(3), the seven-membered ring adopts a distorted boat-sofa conformation; the methyl-ene C atoms of this ring are coplanar with the benzene ring. Both meth-oxy groups are almost coplanar with the attached benzene ring [C-C-O-C = 6.5 (2) and -13.5 (3)°]. An intra-molecular C-H⋯O hydrogen bond is observed in the mol-ecular structure. In the crystal structure, a C-H⋯π inter-action involving the benzene ring is observed.

Design, synthesis and preliminary biological evaluation of zatebradine analogues as potential blockers of the hyperpolarization-activated current

A series of zatebradine analogues, differing in the basic moiety and in the methylene spacer, have been synthesized; their negative chronotropic activity has been determined in guinea pig atria. The most active compounds have been studied for their blocking properties on the hyperpolarization-activated current If (which is one of the main currents underlying automatic activity in the sinus node) measured on ventricular myocytes of old spontaneously-hypertensive rats (SHR) by means of the patch-clamp technique. The majority of the substances were able to block If, with one of them (15) being slightly more potent than zatebradine. Surprisingly one analogue (6), while showing good negative chronotropic activity, was found to inhibit If only at high concentration and to markedly reduce outward currents, suggesting for this substance a different mechanism of action responsible for the negative chronotropic effect.

Synthesis and pharmacological evaluation of N-acyl-1,2,3,4-tetrahydroisoquinoline derivatives as novel specific bradycardic agents

A series of N-acyl-1,2,3,4-tetrahydroisoquinoline derivatives were synthesized and evaluated for their bradycardic activities in isolated guinea pig right atria and in urethane-anesthetized rats. These efforts resulted in identification of the compound 8a, which exhibits potent bradycardic activity with minimal influence on mean blood pressure in urethane-anesthetized rats. Oral administration of compound 8a to conscious rats revealed increased potency and prolonged duration of action when compared to Zatebradine.

Synthesis and pharmacological evaluation of piperidinoalkanoyl-1,2,3,4-tetrahydroisoquinoline derivatives as novel specific bradycardic agents

A series of piperidinoalkanoyl-1,2,3,4-tetrahydroisoquinoline derivatives were synthesized, and their bradycardic activities were investigated in the isolated right atria of guinea pigs and in conscious rats. These efforts identified the achiral compound 2f, which exhibited potent and long-lasting bradycardic activity with minimal effects on mean blood pressure in conscious rats.

(+/-)-2-(3-Piperidyl)-1,2,3,4-tetrahydroisoquinolines as a new class of specific bradycardic agents

A series of (+/-)-2-(3-piperidyl)-1,2,3,4-tetrahydroisoquinolines were prepared and their bradycardic activities were examined in isolated guinea-pigs' right atria and in anesthetized rats. Modifications on the benzyl moiety of the parent compound, 1, led to the identification of compound 11e as a potent and specific bradycardic agent.

Cardiovascular hybrid drugs: new benzazepinone derivatives as bradycardic agents endowed with selective beta1-non-competitive antagonism

The synthesis and pharmacological profile of some hybrid compounds bearing both the benzazepinone moiety present in Zatebradine and typical beta-blocker aryloxypropanolamine groups are described. The new compounds proved to be endowed with negative chronotropic and inotropic activity and are weak vasorelaxant agents. The cardiodepressant action is probably due to selective beta(1)-noncompetitive reversible antagonism. Both enantiomers of the most active compound 5c were synthesized and they showed a different cardiovascular profile, that is (+)-(R)-enantiomer displays affinity for cardiac beta(1)-adrenoceptors, while (-)-(S)-enantiomer shows specificity for vessel smooth muscle.

Synthesis and pharmacological evaluation of 2-(3-piperidyl)-1,2,3,4-tetrahydroisoquinoline derivatives as specific bradycardic agents

Novel 1,2,3,4-tetrahydroisoquinoline derivatives bearing directly a cyclic amine at the 2-position were prepared and examined for their bradycardic activities in isolated right atria and in anesthetized rats. The structure-activity relationships (SAR) study revealed that the 2-(3-piperidyl)-1,2,3,4-tetrahydroisoquinoline skeleton is essential for the appearance of potent in vitro activity, and that the presence of at least one methoxy group at the 6- or 7-position of the 1,2,3,4-tetrahydroisoquinoline ring is important to exert potent in vitro activity. In vivo tests of selected compounds demonstrated that 2-(1-benzyl-3-piperidyl)-6,7-dimethoxy-1,2,3,4-tetrahydroisoquinoline (6c) exhibited potent bradycardic activity with negligible influence on mean blood pressure in rats, although its potency is a half of that of Zatebradine.

Parallel solid-phase synthesis of zatebradine analogues as potential I(f) channel blockers

The first solid-phase synthesis of zatebradine 1 and its analogues is reported. This has resulted in the preparation of compounds with increased ability to reduce the spontaneous beating of isolated guinea-pig atria in a concentration-dependent manner. One example, 8g, showed a maximum reduction of beating of 80% at 3 microM compared to a reduction of 40% at 3 microM with zatebradine 1.

Construction of bicyclic tetrahydroisoquinolinones by combination of an IMDAF-ring cleavage reaction of N-allyl-2-furan-2-yl-acetamides

The intramolecular Diels-Alder reaction of furanyl amides derived from 2-furylacetic acid has been examined. Substrates containing either an imide or tertiary amide linkage between the furan and the dienophile underwent smooth cycloaddition upon thermolysis. By varying the reaction conditions, either the primary cycloadduct or the ring-opened and acetylated product could be isolated in excellent yield. The stereochemical outcome of the IMDAF cycloaddition has the side arm of the tethered alkenyl group oriented syn with respect to the oxygen bridge. Semi-empirical AM1 calculations show that the exo-cycloadduct is 11 kcal lower in energy than the corresponding endo adduct and, presumably, some of this energy difference is reflected in the transition state for the cycloaddition. The IMDAF reaction of N-allyl-[2-(3,4-dimethoxyphenethyl)]-2-furanyl-2-yl-acetamide proceeded in 90% yield upon heating in xylene. The 4+2-cycloadduct undergoes ring-opening on treatment with base and the resulting alcohol was converted into the corresponding benzyl ether. Raney nickel reduction followed by Bischler-Napieralski cyclization furnished the tetracyclic skeleton of the berberine alkaloids.Key words: intramolecular, cycloaddition, Diels-Alder, furanylamide, heterocycle.

Role of zatebradine and propranolol in attenuation of tachycardia produced by dobutamine in pigs

BACKGROUND

Zatebradine is a new specific bradycardiac agent that selectively slows the depolarization in the pacemaker cells of the sinoatrial node. The purpose of our investigation was to determine whether the tachycardia induced by dobutamine can be attenuated by the administration of zatebradine. The results were compared with those produced by propranolol, which is used in the treatment of sinus tachycardia.

METHODS

Twelve pigs were anesthetized with sodium pentobarbital, intubated, and ventilated. After baseline hemodynamic measurements were obtained, dobutamine was administered until the heart rate reached 25% above baseline. Animals were randomized to one of two groups. Group I received zatebradine, 0.5 mg/kg i.v., and Group II received propranolol, 0.5 mg/kg i.v.

RESULTS

Dobutamine 10 micrograms.kg-1.min-1 increased the heart rate (FIR) by 25%, and increased mean arterial blood pressure (MAP) left ventricular (LV) dp/dt, and cardiac output (CO) (P < 0.05). Zatebradine decreased the HR to baseline (P < 0.05) without affecting left ventricular systolic pressure (LVSP), left ventricular end diastolic pressure (LVEDP), LV dP/dt, or CO. Stroke volume (SV) increased significantly (P < 0.05). Propranolol also reduced HR to baseline, but decreased LV dP/dt, LVSP, CO, and SV (P < 0.05).

CONCLUSION

Zatebradine effectively attenuates the tachycardia caused by dobutamine in anesthetized pigs, without reducing cardiac performance.

Mechanisms of block of a human cloned potassium channel by the enantiomers of a new bradycardic agent: S-16257-2 and S-16260-2

1. The effects of S-16257-2 (S57) and S-16260-2 (R60), the two enantiomers of a new bradycardic agent, were studied on human cloned K+ channels (hKv1.5) stably expressed in a mouse L cell line using the whole-cell configuration of the patch-clamp technique. 2. S57 and R60 did not modify the sigmoidal activation time course of the current but reduced the amplitude and increased the rate of the decay of the current during the application of depolarizing pulses. Both, S57 and R60 produced a concentration-dependent block of hKv1.5 channels with apparent KD values of 29.0 +/- 1.9 microM and 40.9 +/- 4.0 microM, respectively. Thus, S57 was 1.4 fold more potent than R60 in blocking hKv1.5 channels. 3. The blockade produced by S57 and R60 was voltage-dependent and increased steeply between -30 and 0 mV, which corresponded with the voltage range for channel opening. This result indicated that both enantiomers block the hKv1.5 channels, preferentially, when they are in the open state. Between 0 and +60 mV the blockade exhibited a shallow voltage-dependence which was described by an electrical distance of 0.18 +/- 0.002 and 0.19 +/- 0.004 for S57 and R60, respectively. 4. S57 and R60 also increased the rate of decline of the current during the application of depolarizing pulses. The time constant of such decline (tau Block) was faster in the presence of R60 than in the presence of S57 (16.2 +/- 1.5 ms vs. 24.0 +/- 2.6 ms; P < 0.01). The apparent association rate constants (k) were similar for S57 and R60 ((0.52 +/- 0.13) x 10(6) M-1 s-1 and (0.66 +/- 0.13) x 10(6) M-1 s-1, respectively), whereas the dissociation rate constant (l) was faster for R60 than for S57 (25.8 +/- 1.8 s-1 and 13.0 +/- 2.4 s-1, respectively). 5. Both enantiomers slowed the deactivation of the tail currents elicited upon repolarization to -40 mV, thus inducing a 'crossover' phenomenon. These results suggested that drug unbinding is required before hKv1.5 channels can close. 6. It is concluded that R60 and S57 produced a similar time- voltage- and state-dependent block of hKv1.5 channels that can be interpreted as open channel block by the charged form of each enantiomer. The main difference between R60 and S57 were linked to the apparent dissociation rate constants.

Addition of zatebradine, a direct sinus node inhibitor, provides no greater exercise tolerance benefit in patients with angina taking extended-release nifedipine: results of a multicenter, randomized, double-blind, placebo-controlled, parallel-group study. The Zatebradine Study Group

OBJECTIVES

We examined the antianginal and anti-ischemic effects of oral zatebradine, a direct sinus node inhibitor that has no blood pressure-lowering or negative inotropic effects in patients with chronic stable angina pectoris taking extended-release nifedipine.

BACKGROUND

Heart rate reduction is considered an important pharmacologic mechanism for providing anginal pain relief and anti-ischemic action in patients with chronic stable angina, suggesting a benefit for sinus node-inhibiting drugs.

METHODS

In a single-blind placebo run-in, randomized double-blind, placebo-controlled, multicenter study, patients already receiving extended-release nifedipine (30 to 90 mg once a day) were randomized to receive zatebradine (5 mg twice a day [n = 64]) or placebo (n = 60). All subjects had reproducible treadmill exercise-induced angina at baseline, and after randomization they performed a serial exercise test 3 h after each dose for 4 weeks.

RESULTS

Zatebradine reduced rest heart rate both at 4 weeks ([mean +/- SEM] 12.9 +/- 1.23 vs. 2.3 +/- 1.6 [placebo] beats/min, p < 0.0001) and at the end of comparable stages of Bruce exercise (16.7 +/- 1.2 vs. 3.4 +/- 1.2 [placebo] beats/min, p < 0.0001). Despite the significant effects on heart rate at rest and exercise, there were no additional benefits of zatebradine from placebo baseline in measurements of total exercise duration, time to 1-mm ST segment depression or time to onset of angina. Subjects taking zatebradine also had more visual disturbances as adverse reactions.

CONCLUSIONS

Zatebradine seems to provide no additional antianginal benefit to patients already receiving nifedipine, and it raises questions regarding the benefit of heart rate reduction alone as an antianginal approach to patients with chronic stable angina.

Semi-rigid analogues of the calcium antagonist verapamil: a molecular modelling study

In this work the rigid-analogue approach has been used to obtain information on the active conformation(s) of the calcium antagonist verapamil. A series of semi-rigid analogues of verapamil were synthesized and their biological activities evaluated on guinea-pig heart and aorta. These molecules were analysed by means of molecular modelling techniques. On the basis of the pharmacological profile and conformational analysis of these compounds, two different models for negative inotropic and negative chronotropic activity are proposed. The two actions seem to be due to conformations of the molecules which differ in the orientation of their phenylethylamino groups.

Zatebradine, a specific bradycardic agent, enhances the positive inotropic actions of dobutamine in ischemic myocardium

OBJECTIVES

This investigation determined whether attenuation of the tachycardia produced by dobutamine administration would improve perfusion and function distal to a severe coronary artery stenosis.

BACKGROUND

Tachycardia adversely affects perfusion and function distal to a coronary artery stenosis. It is not known whether a specific bradycardic agent can improve blood flow and function in an ischemic zone during administration of dobutamine.

METHODS

The effects of dobutamine (2, 5 and 10 micrograms/kg body weight per min) alone and in combination with zatebradine (0.5 mg/kg), a specific bradycardic agent, on hemodynamic status, segment shortening (ultrasound length transducers) and myocardial perfusion (microspheres) were studied in anesthetized dogs with severe left circumflex coronary artery stenosis.

RESULTS

A 50% reduction in left circumflex coronary artery blood flow (58 +/- 4 to 29 +/- 2 ml/min [mean value +/- SEM]) produced a decrease in systolic shortening in the ischemic zone. Only a dose of dobutamine that did not elevate heart rate (2 micrograms/kg per min) produced an increase in segment shortening in the ischemic zone. High doses of dobutamine (10 micrograms/kg per min) caused an increase in heart rate without improvement in function and a reduction in the subendocardial/subepicardial flow ratio (0.74 +/- 0.06 to 0.48 +/- 0.05). Zatebradine administered in the presence of dobutamine caused a decrease in heart rate, an increase in subendocardial/subepicardial blood flow ratio (0.48 +/- 0.05 to 0.78 +/- 0.09) and allowed an increase in ischemic zone segment shortening. When normalized for changes in heart rate, ischemic zone subendocardial flow increased by 123 +/- 41% (0.39 +/- 0.09 to 0.71 +/- 0.12 ml/100 g per beat). Atrial pacing abolished the effects of zatebradine.

CONCLUSIONS

The present data suggest that the perfusion-contraction matching that accompanies a decrease in heart rate results in enhancement of inotropic stimulation of an ischemic zone. The actions of zatebradine are related to an increase in subendocardial blood flow per beat that allows improvement of regional contractile function.

Use-dependent block of the pacemaker current I(f) in rabbit sinoatrial node cells by zatebradine (UL-FS 49). On the mode of action of sinus node inhibitors

BACKGROUND

Zatebradine (UL-FS 49) is a drug with a specific bradycardiac electrophysiological profile. It reduces heart rate by lengthening the duration of diastolic depolarization in the sinoatrial (SA) node. The ionic basis of this action, however, is not clarified.

METHODS AND RESULTS

We used the whole-cell patch-clamp technique to study the effects of zatebradine on ionic currents underlying diastolic depolarization of isolated rabbit SA node cells. Low concentrations of zatebradine simultaneously reduced diastolic depolarization rate and the pacemaker current I(f). The drug blocked the pacemaker current, I(f), in a use-dependent manner without causing a shift of its activation curve. At hyperpolarized potentials, unblock of I(f) occurred. Clinically relevant concentrations of the drug have little effect on the L-type calcium current or delayed rectifier potassium current.

CONCLUSIONS

This use-dependent block of the If channel can account for most of the pharmacological characteristics of zatebradine and is probably the mechanism of heart rate reduction caused by this agent. Thus, the sinus node inhibitor zatebradine belongs to a new class of "I(f) blockers" with possible advantages over currently available drugs for the treatment of ischemic heart disease.

Tedisamil (KC 8857) is a new specific bradycardic drug: does it also influence myocardial contractility? Analysis by the conductance (volume) technique in coronary artery disease

To determine whether inotropism influences the bradycardic action of tedisamil, hemodynamic assessment was performed in 13 patients with ischemic coronary artery disease including analysis of end-systolic pressure-volume relationships after an infusion of tedisamil, 0.3 mg/kg, at rest, and during paced tachycardia stress. Slope Emax fell by 14% at rest (13 patients) and by 10% during tachycardia (6/13 patients), whereas loops of end-systolic pressure-volume relationships moved rightward; all parameter changes indicated a lack of significant inotropism loss with tedisamil (p > 0.05). Although the mean heart rate decreased from 77.5 to 64.7 beats/min and QTc duration increased by 14% (p < 0.05), filling pressure and dp/dtmin remained unchanged and vascular resistance increased by 30%. Parameters of left ventricular pump function (ejection fraction, stroke volume, left ventricular efficiency) decreased slightly (between 3% and 13%), whereas left ventricular volumes increased (end-diastolic volume by 6%, end-systolic volume by 23%). The respective parameter changes during tachycardia were comparable in tendency, and angina could no longer be induced during postdrug pacing stress. We concluded that the bradycardic effects of tedisamil are selectively generated without impairing either ventricular pump function or contractility in a clinically relevant fashion, whereas the postdrug anginal threshold appears elevated. Thus tedisamil can be used safely in ischemic coronary artery disease.

Effect of zatebradine on contractility, relaxation and coronary blood flow

OBJECTIVES

The purpose of this study was to compare the effects of zatebradine on heart rate, contractility and relaxation with those of its structural analog verapamil. We used isoproterenol, a potent beta-agonist, to see how these effects were modulated by sympathetic activation. We also compared the effects of zatebradine and verapamil on coronary blood flow and coronary blood flow reserve.

BACKGROUND

Zatebradine, previously called UL-FS 49, is a new bradycardic agent believed to act selectively at the sinoatrial node.

METHODS

Isolated isovolumetric pig hearts were prepared and left ventricular pressure, its first derivative (dP/dt), tau and heart rate were measured both before and after administration of either 0.975 mg of zatebradine (Group I, n = 8) or 125 micrograms of verapamil (Group II, n = 8). After the effects of each drug reached a plateau, a continuous infusion of isoproterenol was started and measurements were obtained again and compared with a third group of measurements from control hearts infused with isoproterenol after receiving only saline solution (n = 8). We also assessed the effects of zatebradine and verapamil on coronary vascular tone by measuring flow in the left anterior descending coronary artery in intact anesthetized open chest pigs both before and after the intracoronary administration of these drugs (n = 8 for each). All preparations were atrially paced to negate any bradycardiac effects of the drugs.

RESULTS

In the group that received zatebradine, mean (+/- SE) heart rate decreased from 143 +/- 8 to 99 +/- 4 beats/min (p < 0.01) and there was no significant change in either peak left ventricular systolic pressure, dP/dt or tau. In contrast, verapamil produced a lesser decrease in heart rate (136 +/- 7 to 120 +/- 7 beats/min, p < 0.05) but produced substantial decreases in peak left ventricular pressure (100 +/- 3 to 45 +/- 4 mm Hg, p < 0.01) and dP/dt (68% decrease, p < 0.01) and an increase in tau (+26%, p < 0.05). Isoproterenol restored these variables toward normal values in the hearts treated with verapamil, although left ventricular systolic pressure and dP/dt were restored to control values only at the highest isoproterenol concentrations. In the hearts treated with zatebradine, isoproterenol significantly increased left ventricular pressure and contractility and decreased tau; however, heart rate remained unchanged at peak effect. Zatebradine had no effect on coronary blood flow and there was a 100% increase in flow with reactive hyperemia. Conversely, verapamil increased coronary flow by 100%, with no subsequent further increase by reactive hyperemia compared with control values.

CONCLUSIONS

Although structurally similar to verapamil, zatebradine is a highly specific bradycardic agent. It has little direct effect on left ventricular developed pressure, contractility, relaxation and coronary vascular tone. Furthermore, the bradycardic effect of zatebradine unlike that of verapamil, is not overcome by doses of isoproterenol that increase developed pressure and contractility and improve relaxation. Because of its highly specific bradycardic effect, this drug may potentially be useful in treating patients with ischemic heart disease or congestive heart failure.