CARDIOPROTECTIVE EFFECT OF IVABRADINE VERSUS CARVEDILOL IN RATS

CARDIOPROTECTIVE EFFECT OF IVABRADINE VERSUS CARVEDILOL IN RATS

El sayed A. Osman MD, Nasr N. Zaki MD, Samia M. M. Elshiaty MD, Hanan T. Emam MD and Fatma F. Hendawi

Department of pharmacology, Benha faculty of Medicine, Benha University, Egypt

ABSTRACT:  The discovery of the f-channel and its role in regulating pacemaker activity lead to the development of new pharmacological agents such as ivabradine, which target these f-channels causing a reduction in heart rate by inhibiting the /fcurrent. The aim of the present work was designed to evaluate the cardioprotective effect of ivabradine on experimentally- induced myocardial infarction and adrenaline-induced arrhythmia in rats. In addition, the present work studied the effect of ivabradine on isolated rabbit's aortic spiral strip and isolated rabbit's heart. Acute myocardial infarction in rats was induced by isoperameline (150mg/kg subcutenous injection, once) 24 rats were divided into the following groups: group (1) control normal rats, group (II) myocardial infarction – induced rats with no previous treatment, group (III) myocardial infarction – induced rats pretreated with ivabradine (10mg/kg/day) for one week and group (IV)) myocardial infarction – induced rats pretreated with carvedilol (1mg/kg/day) for one week. Electrophysiological, biochemical and histopathological parameters were estimated. pretreatment with either ivabradine or carvedilol show significant improvement in all these parameters with insignificant difference between them.  In the current work 20 rats were used to investigate the protective effects of ivabradine (10mg/kg) and carvedilol (1mg/kg) on adrenaline- induced arrhythmia in anaesthetized rats and the results revealed that both drugs had a prophylactive effect. Also data obtained in the present work pointed out that ivabradine in gradually increasing doses produce no significant effect on the isolated rabbit's aortic strip and basal myocardial contractility of isolated rabbit's heart. Both ivabradine and carvedilol have cardioprotective effect against acute MI as well as adrenaline- induced arrhythmia with no significant difference between them, also ivabradine has no effect on contractility of the heart. So, the choice of either drug in these disease states depend on which of them has low side effects.

Myocardial Infarction- Arrhythmia- Ivabradine – Carvedilol

INTRODUCTION Ivabradine is a selective and specific inhibitor of the sinus node If current. It offers clear therapeutic benefits to stable coronary patients including those already being treated with B-blockers or those with contraindication or intolerance to B-blockers. It specifically binds to the f-channels that are located in the membrane of the sinoatrial cells, in the pacemaker node ¹.                                                                                            

Ivabradine preserves both small and large coronary artery vasodilatation, whatever the level of exercise, thus ensuring adequate endocardial blood perfusion during exercise ².

Pure heart rate reduction with ivabradine results in improved left ventricular function and increased stroke volume, and thus preserved cardiac output 3.

Ivabradine exerts no significant effect on myocardial contractility, either at rest or during exercise ⁴.

Carvedilol is non selective beta blocker with α1-blocking activity decreasing heart rate, decreasing contractility, vasodilator and has antioxidant effect ⁵.          Heart rate reduction by both drugs through different mechanisms plays a role in the medical treatment of myocardial ischemia.

The present work was carried out to screen the cardioprotective effect of ivabradine and carvedilol on experimentally – induced       myocardial infarction and adrenaline-induced cardiac arrhythmia.

MATERIALS AND METHODS: 

This study was done in pharmacology department, Benha faculty of medicine, Benha university during February 2014.

Drugs and chemicals:

Ivabradine Hydrochloride (powder) [Servier, France]. Carvedilol (powder) [Marcyrl Pharmaceutical Industries, Egypt]. Isopernaline HcL (powder) [Sigma, U.S.A.]. Adrenaline Hydrochloride Tartrate (powder) [B.D.H, England]. Urethane (ethyl carbamat): (white crystals) [prolabo, Paris]. Hematoxylin & eosin stain [Biostain ready reagents, UK]. Formaline (solution) (neutral 10% formaline): El-Gomhoria Pharmaceutical Chemical Co., ARE.

In-vivo experiments:

Animals:

44 adult male albino rats (brought from Experimental Animal Breeding Farm, Helwan-Cairo) weighing 150-200gm. ,were used for in-vivo experiments. They have acclimatized for one week and were caged (6/ cage) in fully ventilated room (at room temperature). Rats were ad libitum access to water & balanced diet.

Experimental groups:

Model of experimentally induced myocardial infarction: 24 male rats weighing 150- 200 gm at the beginning of the study were used. After one week of acclimatization, rats were randomly subdivided into four groups to study the effect of ivabradine on myocardial infarction in comparison with carvedilol. Group (I): Control group: the rats of this group were given saline only by subcutaneous injection. Group (II): MI group: the rats of this group were given isoprenaline (150mg/kg) by subcutaneous injection⁶. Group (III): Ivabradine-treated group: the rats of this group were given ivabradine (10mg/kg/day) by gavage ⁷. For one week before subcutaneous injection of isoprenaline (150mg/kg).Group (IV): Carvedilol-treated group: the rats of this group were given Carvedilol (1mg/kg/day) by gavage ⁸. For one week before subcutaneous injection of isoprenaline (150mg/kg).

Experimentally induced myocardial infarction⁶.

The animals were anaesthetized with urethane in a dose of 1.5- 1.75 gm/kg body weight. Half of the dose was injected intraperitoneally, to induce rapid onset and the other half subcutaneously, to insure long maintenance of the anaesthetic effect.

After complete anaesthesia, the rats were led on their back. ECG records were done using needle electrodes. The four limb electrodes. The animals were then injected subcutaneously in the abdominal region with freshly prepared solution of the isoprenaline (150mg/kg) then the following parameters were measured:

Electrophysiological parameter: The four limbs electrodes were fixed to the animal's four limbs and records were done using the standard lead II at rate 25mm/min. the animals were then injected subcutaneously in the abdominal region with freshly prepared solution of the isoprenaline (150mg/kg). E.C.G. tracings were recorded immediately, 30 minutes, 1, 2 and 4 hours after isoprenaline injection. The use of lead II was more informative (in rats) than other leads ⁹.

Biochemical parameter: At the end of experiment after ECG records were done a blood sample of about 4 ml was withdrawn by heparinized cannula from right carotid artery¹⁰. The blood samples were centrifuged at 3000 rotation/minute and the sera were separated. Samples were stored at -20°C in dark containers and subjected to creatine phosphokinase-MB (CK-MB) and troponin-I measurement.

Histopathological examination:

After functional studies were completed, the chest was then rapidly opened and the heart was removed as a whole and was put into a buffered 4% formaline fixation solution and processed with paraffin wax for histopathological examination. Transverse sections (2-μm thick) of the LV free wall at the papillary muscle level were stained with hematoxylin and eosin then cardiac sections were examined for the presence of myocyte degenerative changes, infarct like necrosis¹⁰.

Model of experimentally adrenaline-induced arrhythmia¹¹:

20 male rats weighing 150- 200 gm were used. After complete anaesthesia, the rats were led on their back. ECG records were done using needle electrodes. Rats were randomly subdivided into two groups to study the effect of ivabradine on arrhythmia in comparison with carvedilol.

Group I: Ivabradine-adrenaline treated group:

i-Adrenaline was given I.V in rats in gradually increasing doses starting by 5ug/kg, then the dose was increased gradually by the same amount every 15 min. until arrhythmia (in the form of at least 3 consecutive ventricular ectopic beats) had occurred. The minimal arrhythmogenic dose of adrenaline was determined.

ii- Ivabradine was given I.V at dose of 10mg/kg¹².

iii- After 15 min., adrenaline was injected again beginning with the minimal arrhythmogenic dose and the dose was gradually increased every 15 min. until occurrence of arrhythmia again after ivabradine. The arrhythmogenic doses of adrenaline before and after ivabradine were compared statistically.

Group II:  Carvedilol-adrenaline treated group:

i- Adrenaline was given I.V in rats in gradually increasing doses starting by 5ug/kg, then the dose was increased gradually by the same amount every 15 min. until arrhythmia (in the form of at least 3 consecutive ventricular ectopic beats) had occurred. The minimal arrhythmogenic dose of adrenaline was determined.

ii-  Carvedilol was given I.V at dose of 1mg/kg ¹³.

iii- After 15 min., adrenaline was injected again beginning with the minimal arrhythmogenic dose and the dose was gradually increased every 15 min. until occurrence of arrhythmia again after carvedilol. The arrhythmogenic doses of adrenaline before and after carvedilol were compared statistically.

II- In-vitro experiments:

The following isolated preparations were used to investigate the possible effects and site of action of ivabradine:

1. Isolated perfused rabbit's heart¹⁴
2. Isolated perfused rabbit's aortic spiral strip¹⁵

Statistical Analysis:

All data were expressed as Mean + SEM. Difference between the groups were compared by student T-test  with  P- value < 0.05 selected as the level of statistical significance ¹⁶. SPSS version 16 was used for statistical analysis.

RESULTS:

In-vivo experiments:

Effect of ivabradine and carvedilol on myocardial infarction in rats:

T-wave voltage changes:

1- MI group:

The mean of T- wave voltage (mV) at 0 time (immediately before isoprenaline injection) was 0.29±0.02. After isoprenaline injection, the T wave voltage tend to be elevated reaching a maximum level after 4 hours with mean of 0.71±0.02 (mV), when this value was compared with the value of T-wave voltage at zero time it releaved a significant increase (p < 0.001) (Fig. 1)

2- Ivabradine-treated group:

The mean value of T-wave voltage at zero time was 0.36±0.03 (mV), after 4 hours the mean T-wave voltage was 0.42±0.03 mV. When this value was compared to corresponding value in MI group, there was a significant decrease (p < 0.001).(Fig. 2)

3- Carvedilol-treated group:

The mean value of T-wave voltage at zero time was 0.31±0.03 (mV), after 4 hours the mean T-wave voltage was 0.41±0.04 mV. When this value was compared to corresponding value in MI group, there was a significant decrease (p < 0.001).(Fig.3) Comparing the results of ivabradine-treated group to that of carvedilol-treated group, there was insignificant (p > 0.05) difference between them.

The effect on heart rate (HR):

1- MI group: The heart rate at the start of experiment (0 time) was 304.2±18.3 beat/min, while at 4 hours after isoprenaline injection, it was 461.7±13.1 beat/min. When both values were compared to each other, there was significant increase p < 0.001).(Fig.1)

2- Ivabradine-treated group:

The heart rate at the start of experiment (0 time) was 286.6±25.6 beat/min, while at 4 hours after isoprenaline injection, it was 330.8±15.8 beat/min. When these values were compared to the corresponding values of MI group, there was significant decrease (p<0.001).(Fig.2)

3- Carvedilol-treated group:

The heart rate at the start of experiment (0 time) was 298.3±14.2 beat/min, while at 4 hours after isoprenaline injection, it was 340.8±21.2 beat/min. When these values were compared to the corresponding values of MI group, there was significant decrease (p <0.001).(Fig.3)

Comparing the results of ivabradine-treated group to that of carvedilol-treated group, there was insignificant (p > 0.05) difference between them.

Serum level of CK-MB (Fig.4).

1- Control group:

The mean level of serum CK in normal rats was 589±15.5U/L.

2- MI group:

The mean serum CK level 4 hours after isoprenaline injection was 1495±30.9U/L. This level was highly significantly (p <0.001) increased when compared to mean value of CK level of normal rats.

3- Ivabradine-treated group:

The mean CK level was 845±61.9U/L at 4 hours after isoprenaline injection. When this value was compared to corresponding value in MI group, there was a significant decrease (p <0.001).

4- Carvedilol-treated group:

The mean CK level was 1019.7±54.8U/L at 4 hours after isoprenaline injection. When this value was compared to corresponding value in MI group, there was a significant decrease (p <0.001). Comparing the results of ivabradine-treated group to that of carvedilol-treated group, there was insignificant (P > 0.05) difference between them.

Serum level of Troponin-I (Fig.5).

1- Control group:

The mean level of serum troponin-I in normal rats was 0.24±0.06 ng/ml.

2- MI group:        

The mean serum troponin-I level 4 hours after isoprenaline injection was 1.97±0.270.4 ng/ml. This level was highly significantly (p<0.001) increased when compared to mean value of troponin-I level of normal rats.

3- Ivabradine-treated group:

The mean troponin-I level was 0.46±0.01 ng/ml at 4 hours after isoprenaline injection. When this value was compared to corresponding value in MI group, there was a significant decrease (p <0.001).

4- Carvidilol-treated group:

The mean troponin-I level was 0.54±0.13 ng/ml at 4 hours after isoprenaline injection. When this value was compared to corresponding value in MI group, there was a significant decrease (p <0.001).

Comparing the results of ivabradine-treated group to that of carvedilol-treated group, there was insignificant (p > 0.05) difference between them.

Histopathological examination:

Histopathological examination of the heart for detection of manefistation of acute ischemia and inflammation was done at the end of the experiment with comparison of signs of acute infarction (changes in cardiomyocyte bundles, nuclear shape) in different groups.

1-Control group:

There are interlacing bundles of cardiomyocytes with spindle shaped nucleus with abundant eosinophilic cytoplasm.(Fig 6).

2-MI group:

Isoprenaline induced acute ischemia and infarction in form of degenerative changes in cardiomyocyte bundles, nuclear shape.(Fig.7).

3- Ivabradine-treated group: There are little signs of infarction in form of slight atrophic cardiomyocytes.(Fig.8).

4- Carvedilol-treated group:

There are little signs of infarction in form of scatterd foci of necrotic areas.(Fig.9).

Effect of ivabradine and carvedilol on adrenaline-induced arrhythmia in rats (Fig.10).

1-Ivabradine-adrenaline treated group (Fig.11a-d).

In rats receiving adrenaline before injection of ivabradine, the mean minimal arrhythmogenic dose of adrenaline that could produce arrhythmia was 12±6ug/kg.

After restoration of normal rhythm and injection of ivabradine (10mg/kg IV) for 15 min., the mean dose of adrenaline that could produce arrhythmia after ivabradine was 1000±81.6ug/kg.

When the dose of adrenaline that could produce arrhythmia after ivabradine was compared to that dose of adrenaline that could produce arrhythmia before ivabradine injection, there was highly significant increase (p<0.001).

 2- Carvedilol-adrenaline treated group (Fig.12a-d).

In rats receiving adrenaline before injection of carvedilol, the mean minimal arrhythmogenic dose of adrenaline that could produce arrhythmia was 20±4.08ug/kg.

After restoration of normal rhythm and injection of carvedilol (1mg/kg IV) for 15 min., the mean dose of adrenaline that could produce arrhythmia after carvedilol was 1125±47.8ug/kg.

When the dose of adrenaline that could produce arrhythmia after carvedilol was compared to that dose of adrenaline that could produce arrhythmia before carvedilol injection, there was highly significant increase (p<0.001).

Comparing the results of ivabradine-adrenaline treated group to that of carvedilol-adrenaline treated group, there was insignificant (p> 0.05) difference between them.

1. In vitro experiments:
2. Effets on isolated perfused rabbit's heart: To show the effect of ivabradine on basal cardiac contractility in isolated rabbit heart, ivabradine was added in gradually increasing doses (2, 4, 8, 16, and 32ug). It was observed that ivabradine produced no change in the amplitude of contraction of isolated rabbit's heart (Fig.13)

2. Effect on isolated rabbit's aortic spiral strip:

Ivabradine added in gradually increasing doses (2, 4, 8, 16, and 32ug/25ml organ bath). It was observed that ivabradine produced no change on isolated rabbit's aortic spiral strip (Fig.14).

Also the drug had no effect on nor adrenaline precontracted isolated rabbit aortic strip (40ug/25ml organ bath) by increasing doses of the drug.(Fig.15)

DISCUSSION: The present study was designed to evaluate the cardioprotective effect of ivabradine and carvedilol on experimentally-induced  myocardial infarction and adrenaline-induced arrhythmia in rats.

 The cardioprotective effect of ivabradine and carvedilol on isoprenaline induced acute myocardial infarction in rats was investigated by ECG changes (T-wave and HR), biochemical changes (CK-MB and troponin-I) and histopathological changes of cardiac muscles.

 Myocardial infarction in rat was a result of disturbance in physiological balance between production of free radicals and antioxidative defense system ¹⁷.

 Some of the mechanisms proposed to explain isoprenaline induced damage to cardiac myocytes include hypoxia due to myocardial hyperactivity, coronary hypotension, calcium overload and hypertrophy, depletion of energy reserve and excessive production of free radicals ¹⁸.

 Panda and Naik¹⁹ documented that generation of highly cytotoxic free radicals through isoprenaline auto-oxidation stimulates lipid per-oxidation and causes irreversible damage to the myocardial membrane.

Regarding ECG changes, the results of the present study revealed that, the myocardial infarction group showed significant (P < 0.001) increase in T-wave voltage in all animals subjected to isoprenaline injection.

 These results are in agreement with those of Surawicz,²⁰ who reported that the "T" wave was elevated in rats immediately after coronary ischemia and remained elevated for 5 hours after ischemia. The ECG tracing showed sinus tachycardia in addition to the injury current in form of highly peaked T-wave. These results were in agreement with the observation of ²¹.

Similar results were obtained from ²² who proved marked increase of heart rate in isoprenaline injected rats with changes in ECG findings.

In the present study both ivabradine (10mg/kg/day) and carvedilol (1mg/kg/day) administration for one week produced significant decrease in T-wave voltage as well as heart rate with insignificant (p > 0.05) difference between them.

Du et al.,²³ demonstrated that oral treatment with ivabradine significantly reduced HR in a rat with sympathoadrenergic activation induced by b₁-agonist isoproterenol.

Same results were obtained by Vilaine ¹² in conscious Wistar rats after single or repeated oral dose of ivabradine. The author demonstrated that ivabradine selectively reduced the heart rate both at rest and during exercise by inhibiting the If pacemaker current of the sinus node without modification of myocardial contractility, atrioventricular conduction or ventricular repolarization offering great protection of regional myocardial contractility.

Ciobotaru et al.,²⁴ proved that ivabradine treatment for three months induced heart rate reduction in a rat model of MI with aortic banding.

Steg et al.,²⁵ reported that i.v ivabradine may be of potential value in ST-segment elevation myocardial infarction (STEMI), by allowing rapid heart rate control without affecting blood pressure or hemodynamics.

The results of the present study are in consistence with Mączewski and Mąckiewicz²⁶ who proved that ivabradine and metoprolol attenuated heart rate increase in a rat model of myocardial infarction (MI) with coronary artery ligation and also decreased mortality rate in both groups. Also ⁷showed that both metoprolol and ivabradine produced nearly comparable heart rate reduction either in early or late treatment in a model of MI.

The effects of either metoprolol or ivabradine once 15min after experimental occlusion of a coronary artery (CAO) and another time after 28 days of treatment in a rabbit model of MI were studied by ²⁵ who showed that ST displacement and the Q waves appeared in MI group had disappeared in ivabradine and metoprolol groups associated with significant reduction of heart rate and mortality rate.

Halkin et al.,²⁸ reported that β-blockers reduce the risk of re-infarction and death following acute myocardial infarction.

Cuculi et al.,²⁹ proved that patients with acute coronary syndrome pretreated with b-blockers and presented with MI should further receive their b-blocker if they are hemodynamically stable for its potential to prevent re-infarction and sudden cardiac death during the later period of the hospital stay. Patients without b-blocker pretreatment who are hemodynamically stable should start this therapy soon after presentation for MI, especially when there is tachycardia, hypertension or even with normotensive patient.

Fonarow ³⁰ reported that carvedilol has been proposed to ameliorate the adverse effects of ischemia and reperfusion by its properties involving antioxidation, inhibition of adhesion and activation of neutrophils, protection of endothelial function and direct vasodilation.

A study by Basu ³¹  investigated the effects of acute (intravenous) and long-term (oral medications for 6 months) treatment with carvedilol versus placebo in 151 patients with AMI. Carvedilol was found to significantly reduce cardiac events compared with placebo.

These data are in line with Svetlana et al., ³² who reported that the advantage of carvedilol over other beta blockers can also be found in the fact that the acute beta blockade in AMI can cause a deeper ischemia caused by neurohormonal activation and vascular constriction through the non-blocked alpha-receptors. With the simultaneous beta and alpha blockade carvedilol improves the subendocardial flow and reduces the myocardial ischemia. With its antiischemic effect carvedilol reduces the seriousness and the number of anginal attacks, increases the threshold for the effort-induced ischemia and improves the functional capacity of the coronary patient. ³²

The biochemical parameters studied in the present work revealed elevation in the level of serum creatine kinase MB-isoform (CK-MB) and troponin-I in MI group.

Myocardium contains an abundant amount of diagnostic marker enzymes for MI and once metabolically damaged it releases its intracellular contents into the extracellular fluid³³. Hence, the serum levels of these markers enzymes reflect the alterations in membrane integrity and/or permeability. ³⁴

During myocardial infarction, damaged heart tissue releases cardiac enzymes such as creatine kinase (CK). CK is found in the heart muscle, liver, skeletal muscles, and in the brain. CK-MB is a subtype of CK that is found only in heart muscle. Low level of the enzyme is normally found in the blood stream. Assay of MB isoenzyme of CK (CK-MB) activity in blood to obtain the magnitude and persistence of elevations is useful in estimating the extent of infarction ³⁵.

Initial studies demonstrated that the distribution of CK was found to correlate with the distribution of reduced blood flow in heart of rabbit. Also, it was found to be correlated to ST-segment elevation that histologically demonstrates necrosis and with electron microscopic changes associated with cell death ³⁶.

CK is an enzyme that catalyzes the transphosphorylation of ADP to ATP. CK is an intracellular enzyme which controls the concentration of ATP in such a way that it is retained in the cell at a constant level. This action of CK is extremely important if very high ATP turnover rate in the heart is considered ³⁷.

 Lefer et al., ³⁸ has found that serum CK correlates with myocardial CK depletion in cats with acute myocardial infarction.

The obtained data are in harmony with previous studies concluded that infarction leads to cardiac abnormalities and increase in the level of CK-MB ³⁹.

Troponin is a protein released from myocytes when irreversible myocardial damage occurs. It is highly specific to cardiac tissue and accurately diagnoses myocardial infarction with a history of ischaemic pain or ECG changes reflecting ischaemia. Cardiac troponin level is dependent on infarct size, thus giving clinicians an idea of the prognosis following an infarct ⁴⁰.

In the year of 2000, Cardiac troponin replaced CK-MB as the biomarker of choice for diagnosing a myocardial infarction ⁴¹.

The preseant study show that in both ivabradine and carvedilol groups of rats, the serum CK-MB and troponin-I levels 4 hours after isoprenaline injection was significantly decreased (P< 0.001) compared to MI group with insignificant (P > 0.05) difference between them.

The results of the present study are in keeping with results achieved in the clinical trial done in patients with early phases of reperfused anterior myocardial infarction with impaired left ventricular function done by Fasullo et al.,⁴² who demonstrated the beneficial effect of ivabradine and metoprolol with significant reduction of serum cardiac enzyme creatine kinase. Same results were obtained by Gerd Heusch et al.,⁴³ in patients with heart failure accompanying acute anterior wall MI, ivabradine effectively controls heart rate preventing excessive sinus tachycardia, reduces infarct size and troponin-I level probably secondary to control of heart rate.

Nageh et al.,⁴⁴; Cavallini et al.,⁴⁵ and Okmen et al.,⁴⁶ reported that the serum level of troponin I and CK-MB increase considerably after percutaneous coronary interventions (PCI) in patients who undergo elective PCI. This observation may suggest some degrees of myocardial injury during PCI.

Moloudiet al.,⁴⁷demonstrated that administering 12.5 mg carvedilol prior to PCI prevented the rise of troponin I and CK-MB after the process considerably, with its effect most pronounced at 24 hours after PCI.

Histopathological study indicated that in ivabradine and carvedilol groups there are little signs of acute infarction (changes in cardiomyocyte bundles, nuclear shape and nuclear cytoplasm) compared to MI group. Isoprenaline, a potent synthetic catecholamine produced ‘‘infarct-like’’ lesions in the heart of experimental rats, which were similar to those found in acute myocardial infarction (AMI) and sudden death in man. ⁴⁸

Upaganlawar et al.,¹⁸ demonstrated that isoprenaline elicited cardiac damage evidenced by focal confluent necrosis of muscle fibers with inflammatory cell infiltration, and edema with fragmentation of muscle fibers.

In agreement with the present study Heusch et al.,⁴⁹ demonstrated that ivabradine pretreatment in anaesthetized pigs subjected to 90min controlled left anterior descending coronary artery hypoperfusion and 120min reperfusion significantly reduced the infarct size.

This was referred to the antioxidative effects of ivabradine. The in-vivo effects of ivabradine were absent at a dose that did not lower heart rate that correlates the HR reduction with corresponding anti-atherosclerotic effects and decrease oxidative stress ⁵⁰. These results may, in part, explain the significant decrease of myocardial infarction (MI) size observed in patients treated with ivabradine ⁵¹.

As far as comparing the efficacy of different β-blockers in preventing LV remodeling after AMI, Tang ⁵² reported an effective attenuation of LV remodeling by carvedilol and improvement of hemodynamics and LV function after AMI in rats. Metoprolol exhibited similar benefits regarding hemodynamics, LV dilatation and function, but not LV hypertrophy. Therefore, in instances where the use of β-blockers is indicated such as during the peri- and post-MI period, carvedilol may be superior to other medications in the same class. Yuejin et al.,⁸ added that Cilazapril, carvedilol and their combination are all effective in preventing LV remodeling after AMI in rats, and in improving haemodynamics and LV function, with the combination therapy being superior to monotherapy in all respects.

Same results were obtained by Svetlana et al.,³² in the group of AMI patients, treated with carvedilol the frequency of serious cardiac events (reinfarctions, unstable angina, urgent revascularization) was reduced for 42%, which was a significantly larger percentage compared to the placebo-treated group.

Beta-blocker therapy has been found to produce significant reductions in the risk of sudden cardiac death after MI ⁵³.

In the current work, the protective effects of ivabradine (10mg/kg) and carvedilol (1mg/kg) in adrenaline-induced arrhythmia in anaesthetized rats were investigated. The results revealed that both ivabradine and carvedilol had a prophylactic effect against adrenaline-induced arrythmias.

The result of this study is in consistence with Koncz et al.,⁵⁴ who studied the effects of ivabradine on maximum rate of depolarization (V_max), repolarization and spontaneous depolarization using micro-electrode technique and by applying patch-clamp technique in large animal (dog) to examine action potential characteristics and ionic currents respectively. Ivabradine exerted decrease in the amplitude of spontaneous diastolic depolarization, reduction in spontaneous rate of firing of action potentials and produced a concentration- and frequency-dependent (V_max) block in dog Purkinje fibers and ventricular muscle.

In agreement with the present study Vaillant et al.,⁵⁵ reported that in a model of myocardial ischaemia which induced in pigs by complete and brief (1-min) occlusion of the proximal left anterior descending coronary artery. Repeated abrupt coronary occlusions were performed at 15-min intervals. Ventricular fibrillation threshold (VFT) determinations were performed at the end of each coronary occlusion, before and after i.v. administration of ivabradine (0.25mg/kg).VFT was significantly increased in ivabradine treated animals, this increase in VFT was explained by an increase in duration of monophasic action potential, and reduction of the hypoxic area.

Luminita and Roxana ⁵⁶ considered the ivabradine efficacy and safety profile, the heart rate reduction in the early postoperative period after coronary surgery in patients with conduction abnormalities or left ventricular dysfunction with ivabradine therapy emerged as the best treatment.

In agreement with the present study in case of inappropriate sinus tachycardia (IST) which characterized by paroxysmal tachycardia originating in the sinus nodal area. Zellerhoff et al.,⁵⁷ demonstrated that ivabradine appears effective and safe in patients with symptomatic inappropriate sinus tachycardia.

The same results were obtained by Mackiewicz et al.,⁵⁸ who reported that potential mechanisms of ivabradine as antiarrhythmic agent in acute MI in rat include prevention of diastolic Ca²⁺ leak from sarcoplasmic reticulum and upregulation of If current in left ventricle.

The result of this study is in consistence with Fu Siong et al.,⁵⁹ who found that ivabradine, which is licensed for chronic stable angina and chronic heart failure, may be useful in the clinical setting to prevent reperfusion arrhythmias if given early enough during the course of acute ischaemia-infarction before primary percutaneous coronary interventions (PCI), and may also be protective against reperfusion arrhythmias in unstable angina and coronary vasospasm.

There is also evidence suggesting that beta blocker administration is associated with a better prognosis in patients with sustained ventricular tachyarrhythmias and in patients successfully resuscitated from cardiac arrest ⁶⁰. The protective effect of beta blockers may be exerted via their anti-adrenergic effects; some authors believe that additional mechanisms are involved including a possible membrane-stabilizing effect ^61.

Storstein ⁶² added that carvedilol exerts a weak blockade of the slow-type calcium channel. As a class, calcium channel-blockers inhibit the inwardly directed Ca²⁺ current, delaying conduction through the atrial and atrioventricular nodes. The ability to depress this particular calcium-ion current is the basis for use of carvedilol in the management of supraventricular arrhythmias, ischemia and reperfusion-induced arrhythmias.

Takusagawa et al., ⁶³ reported that carvedilol has the inhibitory effect against reperfusion arrhythmias in rats and suggest that the mechanism of action of this compound is related to the combined effects of beta-blocking and antioxidant. Also ⁶⁴ demonstrated the beneficial effect of carvedilol on arrhythmias when taken with an ACE inhibitor.  As, carvedilol significantly reduced supraventricular arrhythmias and atrial flutter or fibrillation.  Also, carvedilol significantly reduced 'any ventricular arrhythmia' by 63% and 'malignant ventricular arrhythmias' by 70%. Morover, treatment with carvedilol lead to an increase in time to first occurrence of atrial flutter or fibrillation and first malignant ventricular arrhythmia.

Same results were obtained by Carol et al.,⁶⁵ in a 6-month, randomized, placebo-controlled study of 168 patients with heart failure due to ischemic etiology or idiopathic dilated cardiomyopathy, carvedilol administered at 12.5-50mg twice daily lead to reduced ventricular arrhythmia activity and improved ventricular function.

The results of current work are similar to those of Acikel et al.,⁶⁶ in a randomized clinical trial of 110 patients investigating the efficacy of carvedilol compared with metoprolol succinate in preventing postoperative  atrial fibrillation in the first 3 days after coronary artry bypass graft, 20 patients (36%) in the metoprolol group and 9 patients (16%) in the carvedilol group developed AF.

The data of the present work revealed that ivabradine in gradually increasing doses produced no effect on the amplitude of spontaneous contractions of isolated perfused rabbit's heart.

Same result was obtained by Berdeaux ⁶⁷ who reported that selective inhibition of if current by ivabradine was found to reduce heart rate both at rest and during exercise in experimental animals, without any inotropic effects or effect on left ventricular systolic function or coronary vasomotor activity. Also Savelieva ⁶⁸ reported that ivabradine reduces the heart rate without altering myocardial contractility or other hemodynamics.

The present results showed that ivabradine produced no effect on nor adrenaline induced contractions in isolated rabbit's aortic spiral strip.This result is consistent with that obtained by Drouin et al.,⁶⁹ who showed that 3-months treatment of young dyslipidaemic mice with ivabradine had a protective effect on endothelial function with no effect on lipid profile. On the other hand, acute ivabradine treatment had no effect on endothelial dysfunction. One of the possible explanations is that chronic treatment with ivabradine potently inhibits vascular oxidative stress. The authors excluded the endothelial protective effects of ivabradine to be secondary to the reduction of heart rate.

CONCLUSION: We can assume that both ivabradine and carvedilol have cardioprotective effect against acute MI as well as adrenaline-induced arrhythmia with no significant difference between both drugs. The present experimental study supports the concept that increased heart rate is deleterious to the cardiovascular system. So, the choice of either drug in these disease states depend on which of them has low side effects.

ACKNOWLEDGMENT: thanks to all members of department of pharmacology, Benha faculty of medicine, Benha University.

REFERENCES:

1. Canet E, Lerebours G and Vilaine JP (2011): Innovation in coronary artery disease and heart failure: clinical benefits of pure heart rate reduction with ivabradine. Ann N Y Acad Sci., 1222: 90-99.
2. Cargnoni A, Ceconi C, Stavroula G and Ferrari R (2006): Heart rate reduction by pharmacological if current inhibition. Adv Cardiol., 43:31-44.
3. Mulder P, Barbier S, Chagraoui A, Richard V, Henry JP, Lallemand F, Renet S, Lerebours G, Mahlberg-Gaudin F and Thuillez C (2004): Long-term heart rate reduction induced by the selective if current inhibitor ivabradine improves left ventricular function and intrinsic myocardial structure in congestive heart failure. Circulation. 109:1674-1679.
4. Vilaine JP, Bidouard JP, Lesage L, Reure H and Péglion JL (2003): Anti-ischemic effects of ivabradine, a selective heart rate reducing agent, in exercise-induced myocardial ischemia in pigs. J Cardiovasc Pharmacol., 42(5):688-696.
5. Chen and Chow M.S. (1997): Focus on carvedilol: a novel beta-adrenergic blocking agent for the treatment of congestive heart failure. Formulary 32(8): 795-805.
6. Nirmala, C. and Puvanakrishnan, R. (1994): Isoproterenol Induced myocardial infarction in rats: functional and biochemical alteration. Med. Sci. Res., 22:575-7.
7. Ulu N, Henning RH, Goris M, Schoemaker RG and Van Gilst WK (2009): Effects of ivabradine and metoprolol on cardiac angiogenesis and endothelial dysfunction in rats with heart failure. J Cardiovasc Pharmacol., 53:9-17.
8. Yuejin Yang, Yida Tang, Yingmao Ruan, Yongli Li, Yanwen Zhou, Runlin Gao, Jilin Chen, Zaijia Chen. (2002): Comparative effects of cilazapril, carvedilol and their combination in preventing from left ventricular remodelling after acute myocardial infarction in rats Journal of Renin-Angiotensin-Aldosterone System 2002 3: 31
9. Chan M., Soter D. and Ko W.W. (1987): Effect of morphine on cardiovascular responses to acute myocardial infarction in rats. Br J Pharmacol. Mar; 90(3):537-43.
10. Yamamoto K., Masuyamaa T., Sakataa Y., Manoa T., Nishikawaa N., KondoH. and Akehi N. (2000): Roles of renin–angiotensin and endothelin systems in development of diastolic heart failure in hypertensive hearts Cardiovascular Research 47; 274–283
11. Mouille P., Schmitt H., Heymol G. and Gautur E. (1976): Cardiovasculer and beta adrenergic blocking effect of timolol.Eur.J.Pharmacol., 35:235.
12. Vilaine JP (2006): The discovery of the selective If current inhibitor ivabradine. A new therapeutic approach to ischemic heart disease. Pharmacolo Res., 53:424-434.
13. Cice G, Tagliamonte E, Ferrara L, et al.(2000): Efficacy of carvedilol on complex ventricular arrhythmias in dilated cardiomyopathy: double-blind, randomized, placebo-controlled study. Eur Heart J. 21(15): 1259–64
14. H. (1952): Practical Pharmacology. Blackwell Scientific Publications; P35-37.
15. Furchgott R.F. and Bhadrakom S. (1953): Reactions of strips of rabbit aorta to epinephrine, isoproterenol, sodium nirite and other drugs. J. Pharmacol. Exp. Ther. 142: 39 – 58.
16. Hill ,B.A. (1971): Principles of medical stastics 9^th London: limited publication, 147-283
17. Srivastava S, Chandrasekar B, Gu Y, Luo J, Hamid T, Hill BG and Prabhu SD (2007): Downregulation of CuZn-superoxide dismutase contributes to beta-adrenergic receptor-mediated oxidative stress in the heart. Cardiovasc Res., 74: 445-455.
18. Upaganlawar A, Gandhi H and Balaraman R (2010): Effect of vitamin E alone and in combination with lycopene on biochemical and histopathological alterations in isoproterenol-induced myocardial infarction in rats. J Pharmacol Pharmacother., 1(1): 24-31.
19. Panda VS and Naik SR (2008): Cardioprotective activity of Ginkgo biloba Phytosomes in isoproterenol-induced myocardial necrosis in rats: A biochemical and histoarchitectural evaluation. Exp Toxicol Pathol., 60:397-404.
20. Surawicz, B. (1974): Clinical significant of primary T-wave abnormalities. In Schalnt, R.C. and Hurst J.W. (eds.): Advances in electrocardiography, New York, Grune and Stratton PP. 377- 421.
21. El-Hawary M.B.I., Mareie A., El-Brairy A., Isaak Z., Moktar S. and Khalil A. (1988): Estimation of isoprenaline induced myocardial infarction area by histochemical methods and its correlation with serum CPK level. Med. J. Cairo Univ. 56 (2), 65:79
22. Hagar HH (2002): Folic acid and vitamin b12 supplementation attenuates isoprenaline-induced myocardial infarction in experimental hyperhomo-cysteinemic rats. Pharmacol Res., 46(3): 213-219.
23. Du XJ, Feng X, Gao XM, Tan TP, Kiriazis H and Dart AM (2004): If channel inhibitor ivabradine lowers heart rate in mice with enhanced sympatho-adrenergic activities. Br J Pharmacol., 142:107-112.
24. Ciobotaru V, le Heimburger M, Louedec L, Heymes C, Clapier RV, Bedossa P, Escoubet B, Michel JB, Mercadier JJ and Logeart D (2008): Effect of long-term heart rate reduction by If current inhibition on pressure overload-induced heart failure in rats. J Pharmacol Exp Therap., 324:43-49.
25. Steg PG, Lopez-de-Sà E, Schiele F, Hamon M, Meinertz T,Goicolea J, Werdan K, Lopez-Sendon JL(2013): Safety of intravenous ivabradine in acute ST-segment elevation myocardial infarction patients treated with primary percutaneous coronary intervention: a randomized, placebo-controlled, double-blind, pilot study European Heart Journal: Acute Cardiovascular Care .0(0) 1–10
26. Mączewski M and Mąckiewicz U (2008): Effect of metoprolol and ivabradine on left ventricular remodelling and Ca²⁺ handling in the post-infarction rat heart. Cardiovas Res., 79:42-51.
27. Langenbach MR, Schmitz-Spanke S, Brockert M, Schepan M, Pomblum VJ, Gams E, Zirngibl H and Schipke JD (2006): Comparison of a beta-blocker and an If current inhibitor in rabbits with myocardial infarction. J Cardiovasc Surg., 47(6):719-25.
28. Halkin A, Grines CL, Cox DA, Garcia E, Mehran R, Tcheng JE, et al. (2004): Impact of intravenous beta-blockade before primary angioplasty on survival in patients undergoing mechanical reperfusion therapy for acute myocardial infarction. Journal of the American College of Cardiology. 43(10):1780.
29. Cuculi F, Radovanovic D, Pedrazzini G, Regli M, Urban P, Stauffer JC and Erne P (2010): Is pretreatment with beta-blockers beneficial in patients with acute coronary syndrome? Cardiology. 115(2):91-7.
30. Fonarow GC. (2009): Role of carvedilol controlled-release in cardiovascular disease. Expert Rev Cardiovasc Ther. 7(5): 483–98
31. Basu S, Senior R, Raval U, et al. (1997): Beneficial effects of intravenous and oral carvedilol treatment in acute myocardial infarction: a placebo-controlled, randomized trial. Circulation .96(1): 183–91
32. Svetlana A, Milan P, Miloj T, Aleksandar S,užica J, Slobodan I (2001): The Advantages of carvedilol in coronary artery disease. Medicine and Biology Vol.8, No 1, pp. 11 – 18
33. Suchalatha S and Shyamala Devi CS (2004): Protective effect of Terminalia chebula against experimental myocardial injury induced by isopro-terenol. Indian J Exp Biol., 42:174-178
34. Wang SB, Tian S, Yang F, Yang HG, Yang XY and Du GH (2009): Cardioprotective effect of salvianolic acid A on isoproterenol-induced myocardial infarction in rats. Europ J Pharmacol., 615:125-132.
35. Sobel BE (1992): Acute myocardial infarction. In: J.B. Wyngarden, L.H. Smith Jr. and J.C. Bennett, Editors, Textbook of Medicine (19th ed.), Saunders, W.B., Philadelphia pp. 304-318.
36. Marzo A, Ghirardi P and Croce G. (1972): Pharmacokinetics of creatinol-o-phosphate. Clin Ter. 1972 Sep 15;62(5):419-30
37. Marzo A. and Ghirardi P. (1979-b): Creatinine phosphokinase, role in metabolic process Arzneimittelforshcung, 29 (11):147.
38. Lefer A.M., Cohn G.R. and Osman C.H. (1977): Effect of timolol on acute myocardial ischemia in cats. Eur. J. of Pharmacol., 41:379.
39. Eisenman, A. (2006): "Troponin assays for the diagnosis of myocardial infarction and acute coronary syndrome: where do we stand?". Expert Rev Cardiovasc Ther., 4: 509–14.
40. Antman EM, Tanasijevic MJ, Thompson B and Schactman M et al. (1996): Cardiac-specific troponin I levels to predict the risk of mortality in patients with acute coronary syndromes. N Engl J Med.5:1342-1349.
41. Alpert J.S., Thygesen K., Antman E. and Bassand J.P. (2000): "Myocardial infarction redefined--a consensus document of The Joint European Society of Cardiology/American College of Cardiology Committee for the redefinition of myocardial infarction". J Am Coll Cardiol. 36: 959–969.
42. Gerd Heusch, Andreas Skyschally and Rainer Schulz (2011): Cardioprotection by Ivabradine Through Heart Rate Reduction and Beyond. J cardiovasc. pharmacol ther.Vol. 16 no. 3-4 281-284
43. Nageh T, Sherwood RA, Harris BM, Byrne JA, Thomas MR. (2003): Cardiac troponin T and I and creatine kinase-MB as markers of myocardial injury and predictors of outcome following percutaneous coronary intervention. International journal of cardiology. 92(2):285–93.
44. Cavallini C, Savonitto S, Violini R, Arraiz G, Plebani M, Olivari Z, et al. (2005): Impact of the elevation of biochemical markers of myocardial damage on long-term mortality after percutaneous coronary intervention: results of the CK-MB and PCI study. European heart journal. 26(15):1494–8.
45. Okmen E, Cam N, Sanli A, Unal S, and Tartan Z, Vural M. (2006): Cardiac troponin I increase after successful percutaneous coronary angioplasty: predictors and long-term prognostic value. Angiology. 57(2):161–9.
46. Moloudi A, Sabzi F,Rashidi Sh (2012): Suppression of Myocardial Injury Markers following Percutaneous Coronary Interventions by Pre-treatment with Carvedilol. Int Cardiovasc Res J.; 6(3):88-91.
47. Karthikeyan K, Bai BR and Devaraj SN (2007): Cardioprotective effect of grape seed proantho-cyanidins on isoproterenol-induced myocardial injury in rats. Int. J. Cardiol., 115:326-333.
48. Heusch G, Skyschally A, Gres P, Caster PV, Schilawa D and Schulz R (2008): Improvement of regional myocardial blood flow and function and reduction of infarct size with ivabradine: protection beyond heart rate reduction. Eur Heart J., 29: 2265-75.
49. Custodis F, Baumhäkel M, Schlimmer N, List F, Gensch C, Böhm M and Laufs U (2008): Heart rate reduction by ivabradine reduces oxidative stress, improves endothelial function, and prevents atherosclerosis in apolipoprotein e–deficient mice. Circulation. 117:2377-2387.
50. Fox K, Ford I, Steg PG, Tendera M and Ferrari R (2008): Ivabradine for patients with stable coronary artery disease and left ventricular systolic dysfunction (BEAUTIFUL): a randomised, double-blind, placebo-controlled trial. The Lancet. 372 (9641): 807-816.
51. Tang YD. (2001): Comparative effects of carvedilol and metoprolol in preventing from left ventricular remodeling after acute myocardial infarction in rats [in Chinese]. Zhongguo Yi Xue Ke Xue Yuan Xue Bao .23(5): 476–80
52. Hjalmarson A., Kneider M. and Waagstein F. (1997): The role of beta-blockers in left ventricular dysfunction and heart failure. Drugs. 54(4):501-10.
53. Koncz I, Szél T, Bitay M, Cerbai E, Jaeger K, Fülöp F, Jost N, Virág L, Orvos P, Tálosi L, Kristóf A, Baczkó I, Papp JG and Varró A (2011): Electrophysiological effects of ivabradine in dog and human cardiac preparations: Potential anti-arrhythmic actions. Eur J Pharmacol., 668 (3): 419-26.
54. Vaillant F, Dehina L, Mazzadi A, Descotes J, Chevalier P, Tabib A, Bui-Xuan B, Riera C, Belhani D and Timour Q (2011): Heart rate reduction with ivabradine increases ischaemia-induced ventricular fibrillation threshold: role of myocyte structure and myocardial perfusion. Resuscitation. 82(8):1092-9.
55. Luminita I. and Roxana E. (2012): Ivabradine Versus Beta-Blockers in Patients with Conduction Abnormalities or Left Ventricular Dysfunction Undergoing Coronary Artery Bypass Grafting, Perioperative Considerations in Cardiac Surgery, Prof. Cuneyt Narin (Ed.), ISBN: 978-953-51-0147-5,
56. Zellerhoff S1, Hinterseer M, Felix Krull B, Schulze-Bahr E, Fabritz L, Breithardt G, Kirchhof P, Kääb S.(2010): Ivabradine in patients with inappropriate sinus tachycardia. Naunyn Schmiedebergs Arch Pharmacol. 382(5-6):483-6.
57. Mackiewicz, U., Gerges, J. Y.; Chu S., Duda M., Dobrzynski H., Lewartowski B.and  Mączewski M. (2014): Ivabradine Protects Against Ventricular Arrhythmias in Acute Myocardial Infarction in the Rat.Journal of Cellular Physiology,Volume 229, Number 6, 1 June 2014, pp. 813-823(11).
58. Fu Siong Ng, Iqbal T. Shadi, Nicholas S. Peters, and Alexander R. Lyona (2013): Selective heart rate reduction with ivabradine slows ischaemia-induced electrophysiological changes and reduces ischaemia–reperfusion-induced ventricular arrhythmias. J Mol Cell Cardiol. 59(100): 67–75.
59. Reiter MJ and Reiffel JA (1998): Importance of beta blockade in the therapy of serious ventricular arrhythmias. Am J Cardiol., 82:9I-19I..
60. Coram WM, Olson RW, Beil ME, Cabot CF and Weiss GB (1987): Effects of metoprolol, alone and in combination with lidocaine, on ventricular fibrillation threshold: comparison with atenolol, propranolol, and pindolol. J Cardiovasc Pharmacol., 9(5):611-21.
61. Storstein L. (1993): Carvedilol: clinical experience in arrhythmias. Cardiology. 82 Suppl. 3: 29–33.
62. Takusagawa M., Komori S. and Motsumura K.(2000): The inhibitory effects of carvedilol against arrhythmia induced by coronary reperfusion in anesthetized rats. J. Cardiovasc. Pharmacol. Ther. vol 5 no.2 105-112
63. McMurray J, Køber L, Robertson M, et al.(2005): Antiarrhythmic effect of carvedilol after acute myocardial infarction: results of the Carvedilol Post-Infarct Survival Control in Left Ventricular Dysfunction (CAPRICORN) trial. J Am Coll Cardiol. 45(4): 525–30.
64. Carol Chen-S., Louis S. II, Yahya M., Wen-Shi S., Waqas Q., Justin D., Rodeo A., Tova G., Umesh K. G., Louis S., Giuseppe F. and Tiziano M. S. (2012): A Critical Review of the Use of Carvedilol in Ischemic Heart Disease Am J Cardiovasc Drugs.12(6):391-401.
65. Acikel S, Bozbas H, Gultekin B, et al. (2008): Comparison of the efficacy of metoprolol and carvedilol for preventing atrial fibrillation after coronary bypass surgery. Int J Cardiol. 126(1): 108–13.
66. Berdeaux A (2007): Perclinical results with I (f) current inhibition by ivabradine. Drugs; 67 (Suppl) 2: 25-33.
67. Savelieva I and Camm AJ (2008): If Inhibition with ivabradine: electrophysiological effects and safety. Drug Safety. 31: 95-107.
68. Drouin A, Gendron ME, Thorin E, Gillis MA, Mahlberg-Gaudin F and Tardif JC (2008): Chronic heart rate reduction by ivabradine prevents endothelial dysfunction in dyslipidaemic mice. Br J Pharmacol., 154: 749-757.
    

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    El sayed A. Osman MD, Nasr N. Zaki MD, Samia M. M. Elshiaty MD, Hanan T. Emam MD and Hendawi FF. Cardioprotective Effect of Ivabradine versus Carvedilol in Rats. Int J Pharm Sci Res 2015; 6(5): 1862-76.doi: 10.13040/IJPSR.0975-8232.6(5).1862-76.

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