Salutary action of nicorandil, a new antianginal drug, on myocardial metabolism during ischemia and on postischemic function in a canine preparation of brief, repetitive coronary artery occlusions: comparison with isosorbide dinitrate

Second-generation sulfonylureas preserve inhibition of mitochondrial permeability transition by the mitochondrial K+(ATP) opener nicorandil in experimental myocardial infarction

Openers of K+(ATP) channels protect the myocardium from I/R injury. Sulfonylureas are known as potent blockers of K(ATP) channels. We investigated whether 1) mitochondrial permeability transition pore may be involved in the protection afforded by the mitoK+(ATP) opener nicorandil and 2) whether sulfonylureas may prevent this beneficial effect. Anesthetized New Zealand White rabbits underwent 30 min of coronary artery occlusion, followed by 60 (isolated mitochondria) or 240 min (infarct size) of reperfusion. They received an administration of either saline (control) or nicorandil (0.5 mg kg(-1), i.v.) 15 min before ischemia. Each control and nicorandil group was divided in four subgroups pretreated by either saline, glibenclamide (Glib; 1 mg kg(-1)), gliclazide (Glic; 1 mg kg(-1)), or glimepiride (Glim; 5 microg kg(-1)) 10 min before this. Infarct size was assessed by triphenyltetrazolium chloride staining. Mitochondria were isolated from the area at risk for further assessment of the calcium retention capacity. Glibenclamide (35 +/- 8), but neither Glic (61 +/- 9) nor Glim (48 +/- 7), reversed the improvement in calcium retention capacity due to nicorandil (58 +/- 10 vs. 27 +/- 8 nmoles CaCl2 mg(-1) proteins in control). Infarct size reduction by nicorandil (32% +/- 6% vs. 65% +/- 6% of area at risk) was abolished by Glib (55 +/- 5) but not by Glic (37 +/- 3) or Glim (31 +/- 5). These data suggest that 1) the protective effect of nicorandil involves the inhibition of the mitochondrial permeability transition pore and 2) that unlike Glib, second-generation sulfonylureas preserve this cardioprotection.

Tissue protection mediated by mitochondrial K+ channels

Two distinct K+ uniporters have been described in mitochondria, ATP-sensitive and Ca2+-activated. Both are capable of protecting tissues against ischemia and other forms of injury when active. These findings indicate a central role for mitochondrial K+ uptake in tissue protection. This review describes the characteristics of mitochondrial K+ uniport, physiological consequences of this transport, forms of tissue damage in which K+ channels are implicated and possible mechanisms through which protection occurs.

Nicorandil induces late preconditioning against myocardial infarction in conscious rabbits

Nicorandil has been shown to induce an infarct-limiting effect similar to that induced by the early phase of ischemic preconditioning (PC). The goals of this study were to determine whether nicorandil induces a delayed cardioprotection that is analogous to the late phase of ischemic PC and, if so, whether nicorandil-induced late PC is associated with upregulation of cardioprotective proteins. Chronically instrumented, conscious rabbits received vehicle (intravenous normal saline; control group, n = 10), nicorandil (100 microg/kg bolus + 30 microg x kg(-1) x min(-1) i.v. for 60 min; nicorandil group, n = 10), or ischemic PC (6 cycles of 4-min coronary occlusion/4-min reperfusion; PC group, n = 8). Twenty-four hours later, rabbits underwent a 30-min coronary occlusion, followed by 3 days of reperfusion. Myocardial infarct size was significantly reduced in rabbits pretreated with nicorandil (27.5 +/- 5.3% of the risk region) or with ischemia (30.3 +/- 4.2%) versus controls (59.1 +/- 4.7%, P < 0.05 vs. both). Furthermore, the expression of cyclooxygenase-2 (COX-2) and Bcl-2 was significantly elevated (+38% and +126%, respectively; P < 0.05) in myocardium of rabbits given nicorandil 24 h earlier versus controls. We conclude that nicorandil induces delayed cardioprotection against myocardial infarction similar to that afforded by the late phase of ischemic PC, possibly by upregulating COX-2 and Bcl-2.

Effect of intracoronary nicorandil administration on preventing no-reflow/slow flow phenomenon during rotational atherectomy

A major limitation of the rotational atherectomy (RA) procedure is the occurrence of the no-reflow/slow flow phenomenon and the optimal strategy is still evolving. Recent clinical studies have demonstrated the beneficial effects of nicorandil, an adenosine triphosphate (ATP)-sensitive potassium channel opener, on no-reflow in patients with acute myocardial infarction. The purpose of this study was to evaluate the effect of nicorandil on no-reflow/slow flow phenomenon during RA procedures. Sixty-one patients who underwent RA of complex coronary lesions were randomly divided into 2 groups: (i) nicorandil cocktail (n=24 patients, 37 lesions) and (ii) verapamil cocktail (n=37 patients, 63 lesions). In each group, the drug cocktail mixed with pressurized saline was infused through the 4Fr Teflon sheath of the rotablator system during the RA procedure. In the nicorandil group, the drug cocktail consisted of 24 mg of nicorandil, 5 mg of nitroglycerin, and 10,000 U of heparin. In the verapamil group, the drug cocktail consisted of 10 mg of verapamil, 5 mg of nitroglycerin, and 10,000 U of heparin. Baseline and procedure characteristics did not differ between the 2 groups. RA was performed successfully, and death, Q-wave myocardial infarction, or emergency coronary artery bypass surgery did not occur in any patients. The no-reflow/slow flow phenomenon was observed in 11/63 (17.4%) lesions of the verapamil group, but in only 1/37 (2.7%) lesions of the nicorandil group (p=0.03). No untoward complications were observed during nicorandil infusion. These data indicate that the intracoronary continuous infusion of nicorandil during RA procedures is easy and safe, and prevents no-reflow/slow flow phenomenon more effectively than infusion of verapamil.

Nicorandil ameliorates posttransplant dysfunction in cardiac allografts harvested from non-heart-beating donors

OBJECTIVE

Warm ischemia is a major cause of cardiac allograft dysfunction in non-heart-beating donors (NHBDs). We evaluated the cardioprotective effects of nicorandil, an adenosine triphosphate-sensitive potassium channel opener, on the early posttransplant left ventricular (LV) function of hearts harvested from asphyxiated canine NHBDs.

METHODS

Hypoxic cardiac arrest was induced in 12 donor dogs. In 6, nicorandil was administered intravenously at 100 micrograms/kg + 25 micrograms/kg/min after respiratory arrest and hearts were preserved with nicorandil-supplemented cardioplegic solution (nicorandil group). The remaining 6 did not receive nicorandil at any time during the experiment (control group). Hearts were orthotopically transplanted after a mean myocardial ischemic time of 4 hours.

RESULTS

All 12 recipients were weaned from cardiopulmonary bypass without inotropic support. In the control group, posttransplant cardiac indices and left ventricular end-systolic pressure (LVESP) decreased significantly, while LV max-dP/dt and Tau increased over pretransplant values. No differences were seen in parameters between pretransplant and posttransplant values in the nicorandil group. Posttransplant cardiac indices, LVESP, and LV max + dP/dt were higher in the nicorandil group than in controls, while posttransplant LV max-dP/dt in the nicorandil group was lower.

CONCLUSIONS

Our results indicate that pretreatment with nicorandil during hypoxic perfusion before cardiac arrest and subsequent preservation with nicorandil-supplemented cardioplegia ameliorates early posttransplant LV dysfunction of hearts harvested from asphyxiated NHBDs.

Effect of ischemic preconditioning and mitochondrial KATP channel openers on chronic left ventricular remodeling in the ischemic-reperfused rat heart

The influence of ischemic preconditioning (IP) and mitochondrial ATP-sensitive potassium (mito-KATP) channel openers on chronic left ventricular (LV) remodeling remains unknown, so the effect of IP and mito-KATP channel openers on the LV pressure-volume curve was assessed in rats subjected to 30 min ischemia followed by a 3-week reperfusion. Infarct size was histologically determined at 3 weeks after reperfusion. The LV pressure-volume curve was significantly shifted left by IP, diazoxide and nicorandil compared with the controls. These effects were blocked by the selective mito-KATP channel blocker 5-hydroxydecanoate. The LV remodeling and the infarct size at 3 weeks after reperfusion correlated well, indicating that the reduction of LV remodeling in the ischemic-reperfused model was strongly influenced by attenuation of the ischemic injury. LV remodeling in the chronic phase is attenuated by IP and mito-KATP channel openers with concomitant reduction of infarct size.

Effects of nicorandil on myocardial function and metabolism in the post-ischaemic reperfused heart with or without inhalation anaesthetics

BACKGROUND

Nicorandil, which is an ATP-sensitive K channel opener, has been reported to protect the ischaemic myocardium. However, its interaction with inhalation anaesthetics on the ischaemic myocardium has not been well elucidated. So, we have investigated whether isoflurane or sevoflurane modify the effects of nicorandil on cardiac function and metabolism in the rat heart-lung preparation.

METHODS

Animals were allocated to 4 groups as follows: Control group, no drug; Nic group, nicorandil; Nic+Iso group, nicorandil and isoflurane; Nic+Sev group, nicorandil and sevoflurane. Seven minutes after the start of perfusion, nicorandil was administered and 10 min after the start of perfusion, the heart was rendered globally ischaemic for 10 min, and then the heart was reperfused for 10 min.

RESULTS

LVdP/dt max in the Nic group was higher than those in the other groups. Right atrial pressure in the Nic+Iso and Nic+Sev groups was significantly higher than in the Control and Nic groups. Myocardial ATP in the Nic group was higher than in the other groups. DHBA levels in the perfusate in the Nic and Nic+Iso groups were lower than those in the Control and Nic+Sev groups, but those in the Nic+Sev group were higher than those in the other groups.

CONCLUSIONS

Nicorandil improved post-ischaemic cardiac function and preserved high-energy phosphates. However, these beneficial effects of nicorandil were abolished by the combination with isoflurane or sevoflurane. In addition, sevoflurane increased hydroxyl radical formation in the post-ischaemic reperfused heart.

Animal models of cardiac disease: potential usefulness for studying health effects of inhaled particles

Cardiac disease is one of the major causes of morbidity and mortality worldwide and is the leading cause of death in the United States. Epidemiologic studies have shown a close association between morbidity and mortality from cardiac disease, primarily in persons already affected, and with modest increases in levels of air pollution. At present, no mechanisms are known by which inhaled air pollutants interact with the heart to cause death. Thus, animal models of cardiac disease are needed to study possible interactions between inhaled pollutants and the heart and the resultant morbidity and mortality. Very little research in animals has been conducted in this area, and appropriate animal models must be carefully selected. The purpose of this review is to examine several potential animal models and to discuss their advantages and disadvantages in the study of cardiac disease and air pollution.

Cardioprotective effect of intravenous nicorandil in patients with successful reperfusion for acute myocardial infarction

This study was designed to assess the cardioprotective effect of intravenous nicorandil, a potassium channel opener, in preventing reperfusion injury in acute myocardial infarction. Seventy patients were treated with placebo or nicorandil concomitant with reperfusion therapy in a prospective, randomized, double-blind fashion within 6 h after the onset of acute myocardial infarction. Nicorandil was administered before reperfusion as a 2-mg bolus iv injection followed by continuous infusion of 2-6 mg/h for the next 3 h. Thirty-six patients (17 in the placebo group, 19 in the nicorandil group) who demonstrated both complete occlusion of an infarct-related vessel before treatment and successful reperfusion were included in the final analysis. No significant changes in left ventricular ejection fraction were observed between the immediate and chronic phases in each group. In the analysis of regional ventricular function, the placebo group did not show any significant change in regional chord shortening (26.8+/-8.2 vs 24.3+/-7.3%, NS) or hypocontractile perimeter (36.4+/-28.2% vs 28.3+/-24.8%, NS) between immediate and chronic phase left ventriculograms. In contrast, in the nicorandil group, a significant increase in regional chord shortening (21.5+/-11.0% vs 25.8+/-11.3%, p<0.05) and a significant decrease in hypocontractile perimeter (33.3+/-19.6% vs 25.6+/-24.3%, p<0.05) were observed in the chronic phase left ventriculogram. Thus, nicorandil may be a useful adjunctive therapy for preserving myocardial contractile function in patients with acute myocardial infarction undergoing reperfusion therapy.

Nicorandil suppressed myocardial purine metabolism during exercise in patients with angina pectoris

To elucidate the effect of Nicorandil on myocardial energy metabolism and myocardial sympathetic activity, we administered Nicorandil orally to eight patients with angina pectoris prior to exercise testing. Arterial and coronary sinus levels of lactate, ammonia, hypoxanthine (HX), adrenaline and noradrenaline were measured during exercise in order to determine the irrespective myocardial extraction ratios (MER). Compared to placebo, Nicorandil increased the time to development of significant ST depression (322 vs 390 s) while decreasing the maximum amplitude of ST depression (0.244 vs 0.216 mV). Heart rate, systolic blood pressure, and the rate pressure product during exercise were not significantly affected. The MER of lactate, measured during exercise, was significantly higher after Nicorandil than placebo (13.6 vs 27.9). Similarly, the MERs of ammonia and HX were significantly higher after Nicorandil (-46.0 vs 7.4% and -47.0 vs 9.9% respectively). Nicorandil, had no apparent effect on myocardial sympathetic activity as the MERs of adrenaline and noradrenaline were essentially unaffected. We conclude that Nicorandil decreased myocardial ischaemia and suppressed myocardial accelerated purine metabolism (a marker of cellular energy metabolism) during exercise in patients with angina pectoris. This effect appears not to be related to myocardial sympathetic activity.

Electrophysiologic effects of potassium channel openers

Potassium-channel openers or activators have been introduced as a new class of antihypertensive and antianginal agents that act by increasing membrane conductance to potassium, mainly through augmentation of the ATP-sensitive potassium current. Recent in vitro studies have shown that K(+)-channel openers exert concentration-dependent effects on cardiac electrophysiology. A shortening of the cardiac action potential by acceleration of repolarization has been reported in multicellular preparations as well as in isolated myocytes. However, drug concentrations that affect the action potential duration of myocardial cells are considerably higher (10- to 100-fold) than those needed for effects on vascular smooth muscle cells. Studies in which mostly high concentrations of K(+)-channel openers were used have demonstrated that these drugs may accelerate automaticity and may promote reentrant activity. Particular interest has focused on the question whether opening of potassium channels may be potentially arrhythmogenic in the setting of acute myocardial ischemia. On the other hand, recent studies have shown that K(+)-channel openers are effective in suppressing polymorphic ventricular tachyarrhythmias induced by early afterdepolarizations and triggered activity in vivo. The clinical relevance of these experimental studies to the clinical situation is still unclear. Some K(+)-channel openers have been shown to produce electrocardiographic T-wave changes in patients in whom their effectiveness as antihypertensives was tested. However, this effect was not associated with adverse effects and has not been demonstrated for all compounds.(ABSTRACT TRUNCATED AT 250 WORDS)

In vitro protective effects of nicorandil on hypothermic injury to immature cardiac myocytes: comparison with nitroglycerin

The purpose of the present study was to evaluate the functional and biochemical effects of nicorandil and nitroglycerin on cardiac myocytes incubated under hypothermic conditions. Nicorandil is a coronary vasodilator with mixed nitrate-potassium channel agonist activity. Cardiac myocytes were isolated from neonatal rat ventricles and cultured for 4 days with MCDB 197 medium. Myocytes (12.5 x 10(5) myocytes/flask) were then incubated at 4 degrees C for 24 hours in media containing various concentrations of nicorandil (NRD) or nitroglycerin (NTG). After hypothermic incubation, CPK and LDH were measured. The myocytes were cultured for an additional 24 hours at 37 degrees C to evaluate the recovery of the myocyte beating rate. In the nicorandil group, 10(-4) M NRD showed a significant beating rate recovery compared to control (44.2% vs. 24.6%, respectively, as a percent of control; i.e., beating rate prior to hypothermic incubation). Nitroglycerin treatment had no effect on either beating rate recovery or release of CPK and LDH from myocytes. However, the release of CPK and LDH was significantly suppressed by 10(-4) M nicorandil compared to the control (10(-4) M NRD: 24.1, 257.2; control: 125.4 mIU/flask, 459.5 mIU/flask, respectively). Thus nicorandil showed an approximate two-fold recovery of myocyte functional activity after hypothermic incubation with only minor biochemical effects, and therefore may be suitable for cardiac preservation.

Effect of nicorandil on post-ischaemic contractile dysfunction in the heart: roles of its ATP-sensitive K+ channel opening property and nitrate property

1. This study aimed to characterize the effect of nicorandil (NC) on myocardial stunning and the role of ATP-sensitive K+ (KATP) channel opening property in its cardioprotective action. 2. In open-chest anaesthetized rabbits, myocardial stunning was induced by 10 min of coronary occlusion followed by 30 min of reperfusion. As an index of regional contractile function, systolic thickening fraction (TF) was measured by an epicardial Doppler sensor. The doses of NC (10 micrograms/kg per min) and nitroglycerin (TNG) (1 micrograms/kg per min) were selected not to lower the systemic blood pressure significantly. 3. In the untreated controls, TF at 30 min after reperfusion was 46.4 +/- 2.9% of the baseline value, indicating myocardial stunning. Both NC and TNG significantly improved post-ischaemic recovery of TF when administered during the pre-ischaemic and post-ischaemic periods (TF = 68.2 +/- 6.4%, 64.7 +/- 2.3%, respectively). However, when their infusion was restricted to a pre-ischaemic 10 min period, TF recovery was improved by NC, but not by TNG (63.4 +/- 7.9%, 40.9 +/- 6.2%, respectively). 4. Pretreatment with glibenclamide (GL; 0.3 mg/kg) did not influence the recovery of TF after the 10 min ischaemia (TF = 52.4 +/- 3.9% at 30 min after reperfusion). However, after the GL injection, a cardioprotective effect from nicorandil pretreatment was not detected (TF = 51.3 +/- 1.7%). 5. These results suggest that nicorandil protects the myocardium against stunning by opening the KATP channel when it is given before ischaemia, and that the nitrate property of nicorandil may also play a role during the reperfusion period in attenuation of post-ischaemic contractile dysfunction.

Protection by nicorandil against the dysfunction of the central vagal baroreflex system following transient global cerebral ischaemia in dogs

1. A possible cerebroprotective effect of nicorandil was investigated in a canine model of 5 min global cerebral ischaemia, and compared with protective effects of nitroglycerin and nicardipine. 2. Cerebral ischaemia was produced by occlusion of the left subclavian and the brachiocephalic arteries with preceding ligation of the intercostal arteries. The decrease in baroreflex sensitivity (BRS), measured by phenylephrine-induced reflex bradycardia, was used to assess the cerebroprotective effect. 3. Nicorandil (10 or 30 micrograms kg-1 min-1, i.v.), nitroglycerin (3 micrograms kg-1 min-1, i.v.) or nicardipine (0.3 micrograms kg-1 min-1, i.v.) were infused for 60 min just before ischaemia. Nitroglycerin and nicardipine decreased mean arterial blood pressure to an extent similar to that induced by the lower dose of nicorandil. Blood flow in the dorsal medulla oblongata was increased by nicorandil and nicardipine, but not by nitroglycerin. 4. Nicorandil at both doses and nitroglycerin prevented the post-ischaemic decrease in BRS. In these cases, bilateral vagotomy during the reperfusion period decreased BRS, indicating that the vagal component of BRS was protected from ischaemia. On the other hand, nicardipine failed to exert a cerebroprotective effect. 5. The present study suggests that nicorandil may possess a direct cerebroprotective effect and that its property as a nitrate might, at least in part, be important for the observed cerebral protection.

Anti-free-radical and neutrophil-modulating properties of the nitrovasodilator, nicorandil

The nitrovasodilator, nicorandil, is a clinically effective antianginal agent. We tested whether nicorandil may also possess anti-free-radical characteristics, since the nicotinamide moiety of its molecular structure is a known hydroxyl radical scavenger. In vitro production of hydroxyl radicals by hypoxanthine plus xanthine oxidase in the presence of iron produced a marked degradation of deoxyribose. Nicorandil and the structural analogs, nicotinic acid and nicotinamide, produced significant inhibition of deoxyribose breakdown at concentrations equipotent to the classical hydroxyl radical scavenger, mannitol. Nicorandil also produced a concentration-dependent inhibition of superoxide anion production by canine neutrophils that were activated with either phorbol myristate acetate (PMA) or opsonized zymosan. This inhibition could not be mimicked by the analog, nicotinamide. While equimolar concentrations of nitroglycerin produced less inhibition of superoxide anion generation in opsonized zymosan-activated neutrophils than that observed with nicorandil, nitroglycerin did not alter free-radical production in PMA-stimulated neutrophils. Glyburide, the ATP-sensitive potassium-channel blocker, did not reverse the action of nicorandil on neutrophils. Thus, nicorandil is a uniquely different nitrovasodilator with anti-free-radical and neutrophil-modulating properties.

EMD 52692 (bimakalim), a new potassium channel opener, attenuates luminol-enhanced chemiluminescence and superoxide anion radical formation by zymosan-activated polymorphonuclear leukocytes

We investigated the relationship of potassium channel activation on modulation of oxidative respiratory bursts in canine neutrophils. Generation of superoxide anion radicals in opsonized zymosan-activated cells was determined using the technique of ferricytochrome c reduction. Preincubation of cells with the selective potassium channel opener, EMD 52692 (1-100 microM), attenuated superoxide anion radical production. Furthermore, EMD 52692 also produced a concentration-dependent inhibition of luminol-enhanced chemiluminescence by activated neutrophils. Glyburide, a selective antagonist of ATP-sensitive potassium channels, prevented the modulatory effect of EMD 52692 on both superoxide anion generation and luminol-enhanced chemiluminescence. The results suggest that ATP-sensitive potassium channels may play a significant role in regulating oxygen-derived free radical production in neutrophil-induced tissue injury.

Suppression of sympathetic nervous system activity by nicorandil during exercise

1. Treadmill testing was done and plasma epinephrine and norepinephrine were measured during exercise and recovery in 21 patients with coronary artery disease given nicorandil. 2. Epinephrine levels during exercise did not change significantly with nicorandil, but the percent change in epinephrine with nicorandil tended to be lower during exercise. 3. Norepinephrine levels after exercise were suppressed with nicorandil (with, 424 +/- 15 pg/ml; without, 760 +/- 16, P less than 0.05). 4. Also, the percent change in norepinephrine with nicorandil was significantly decreased during exercise and recovery (with, 259 +/- 11%; without, 555 +/- 19, P less than 0.01). 5. Therefore, nicorandil suppressed the sympathetic nervous system hyper-response to exercise.

Pharmacology and therapeutic effects of nicorandil

Nicorandil, a nicotinamide derivative, is an orally efficacious antianginal drug possessing a nitrate moiety in its chemical structure. This drug is an effective and well-tolerated treatment for various types of angina pectoris. Its general efficacy is similar to that of nitrates, with several unique effects on the cardiovascular system. Nicorandil causes sustained dilation of both the arterial resistance and conductive vessels, thus markedly dilating the coronary artery and increasing coronary blood flow. In addition, nicorandil, unlike nitroglycerin or isosorbide dinitrate, possesses little hemodynamic effect on heart rate, blood pressure, or cardiac contractility with clinical doses yielding antianginal effects. The mechanism causing coronary vasodilation has not been completely clarified but appears to be associated partly with increases in c-GMP, as well as the hyperpolarization of the smooth muscle membrane. Nicorandil, in single oral doses of 10-30 mg, has been shown to be effective in chronic stable angina, as assessed objectively by increases in exercise duration and/or the time to onset of ST-segment depression during treadmill exercise. In open studies and controlled efficacy evaluations, nicorandil in daily oral doses of 15-40 mg demonstrated significant effectiveness in the treatment of various types of angina pectoris. Headaches due to vasodilation may occur, and some side effects occurred in 5.1-34% of patients receiving nicorandil, but were generally minor in nature. There was no depressant effect on atrioventricular conduction, which occurs frequently in patients treated with calcium antagonists of the verapamil and diltiazem type. Nicorandil may be effective even in patients with rest and effort angina who do not respond to combination therapy with calcium antagonists and oral nitrates. Thus, nicorandil appears to be a valuable addition to the arsenal of antianginal drugs due to its low incidence of serious side effects.

Effects of nicorandil on coronary circulation and myocardial ischemia

The effect of the new antianginal drug, nicorandil, was studied in several models of myocardial ischemia in anesthetized dogs. In animals subjected to an acute or chronic coronary artery occlusion, nicorandil produced increases in collateral perfusion when changes in aortic pressure were minimized. In a model of irreversible ischemia, nicorandil produced a marked (50%) decrease in myocardial infarct size. In several models of reversible ischemia-reperfusion injury, the "stunned myocardium," nicorandil was shown to enhance the recovery of systolic segment shortening after a brief period (15 to 30 minutes) of coronary occlusion. Other vasodilators such as nitroglycerin or nifedipine were not as efficacious as nicorandil. In a model of multiple (n = 3) coronary occlusion (5 minutes) with intermittent (30 minutes) reperfusion, nicorandil improved the recovery of systolic segment shortening during reperfusion and prevented the loss of adenosine triphosphate and tissue edema that occurred in untreated hearts. The beneficial effects of nicorandil on functional and metabolic recovery after recurrent ischemia was shown to be partially the result of an energy-sparing effect of nicorandil to reduce free fatty acid use during the ischemic period. Cyclooxygenase blockade with indomethacin did not block the beneficial effects of nicorandil in the stunned myocardium. These results suggest that nicorandil does not promote an increase of prostacyclin. Finally, nicorandil was found to inhibit superoxide anion production by human neutrophils stimulated by formyl-methionyl-leucyl-phenylalanine plus cytochalasin B. These results suggest that part of the beneficial actions of nicorandil may occur during reperfusion and may be the result of a reduction in oxygen free radical production.(ABSTRACT TRUNCATED AT 250 WORDS)

Nicorandil: animal pharmacology

Nicorandil, a nicotinamide derivative, is a recently developed, orally active antianginal drug with a cardioprotective activity, and its pharmacologic properties differ from those of conventional antianginal drugs. Nicorandil has the capacity to increase myocardial oxygen supply without increasing oxygen demand by reduction in preload and afterload. In isolated blood-perfused canine heart preparations, when injected into the sinus node, the atrioventricular node or the anterior septal arteries, nicorandil at dose levels doubling blood flow through the respective arteries has virtually no effect on sinus rate, atrioventricular conduction time or contractile force of ventricular muscle. This may indicate that nicorandil possesses a selective effect on the coronary vasculature rather than on the myocardium. Furthermore, the vasospasmolytic activity of nicorandil has been evidenced in in vivo and in vitro experiments. The precise mechanism by which nicorandil develops coronary vasodilating and vasospasmolytic effects remains to be elucidated, but it may be partly inferred by an increase in the potassium conductance in the membrane, a relation with cyclic guanosine monophosphate formation, or inhibition of intracellular calcium ion mobilization in the cell of coronary vascular smooth muscle. Nicorandil possesses a nitrate moiety in its chemical structure. However, it is noted that nicorandil unlike nitrates does not develop tolerance or cross tolerance to other conventional nitrates in terms of blood-pressure lowering effects and coronary vasodilating effects. Thus, nicorandil is likely to have highly beneficial properties in the treatment of angina pectoris.