Effects of nicorandil on coronary circulation and myocardial ischemia

Nicorandil for Periprocedural Myocardial Injury in Elective Percutaneous Coronary Intervention: A Meta-Analysis of 10 Randomized Controlled Trials

The clinical outcomes of nicorandil in percutaneous coronary intervention (PCI) are conflicting. We sought to evaluate the effects of nicorandil on periprocedural myocardial injury (PMI) in elective PCI. Eligible studies that reported the effect of nicorandil on PMI in elective PCI were obtained from PubMed, Web of Science, and Cochrane Library (up to October 28, 2019). The outcomes were PMI and major adverse cardiovascular and cerebrovascular events (MACCEs). Ten randomized controlled trials with 1304 patients undergoing elective PCI were evaluated. Nicorandil significantly reduced the incidence of PMI (odds ratio [OR] = 0.48; P = .0003); however, there was no significant difference in MACCEs (OR = 0.80; P = .45) between the 2 groups. Subgroup analyses showed that nicorandil significantly lowered the PMI risk when only patients with stable coronary artery disease (OR = 0.41; P = .0008) were considered and when nicorandil was administered intravenously (OR = 0.41; P = .0007) or orally (OR = 0.33; P = .0001). This meta-analysis suggests that nicorandil could reduce the incidence of PMI without increasing the occurrence of MACCEs in elective PCI. The effect of nicorandil in lowering the PMI risk is associated with the diagnosis of the patients and the route of nicorandil administration.

KATP Channels in the Cardiovascular System

KATP channels are integral to the functions of many cells and tissues. The use of electrophysiological methods has allowed for a detailed characterization of KATP channels in terms of their biophysical properties, nucleotide sensitivities, and modification by pharmacological compounds. However, even though they were first described almost 25 years ago (Noma 1983, Trube and Hescheler 1984), the physiological and pathophysiological roles of these channels, and their regulation by complex biological systems, are only now emerging for many tissues. Even in tissues where their roles have been best defined, there are still many unanswered questions. This review aims to summarize the properties, molecular composition, and pharmacology of KATP channels in various cardiovascular components (atria, specialized conduction system, ventricles, smooth muscle, endothelium, and mitochondria). We will summarize the lessons learned from available genetic mouse models and address the known roles of KATP channels in cardiovascular pathologies and how genetic variation in KATP channel genes contribute to human disease.

Effect of nicorandil in patients with heart failure: a systematic review and meta-analysis

BACKGROUND AND PURPOSE

It is unclear whether nicorandil, a metabolic therapeutic drug, can be applied clinically to therapy of heart failure (HF). This meta-analysis evaluated therapeutic effects of nicorandil on HF patients.

EXPERIMENTAL APPROACH

We performed a systematic review and meta-analysis of published studies evaluating effect of nicorandil on HF patients. Studies were stratified according to controlled versus uncontrolled designs and analyzed using random-effects meta-analysis models.

KEY RESULTS

We identified a total of 20 studies with a total of 1222 patients. In five randomized controlled studies, nicorandil treatment resulted in reduction in all-cause mortality and hospitalization for cardiac causes (HR: 0.35, P < 0.001) and improved cardiac pump function (SMD: 0.31, P = 0.02). In 15 observational studies, nicorandil therapy increases cardiac pump function (SMD: 0.75, P < 0.001), improves NYHA functional class (WMD: -1.33, P < 0.001), decreases PCWP (WMD: -6.86 mm Hg, P < 0.001), and pulmonary arterial pressure (SMD: -0.84, P < 0.001).

CONCLUSIONS AND IMPLICATIONS

The use of nicorandil in HF patients exerts substantial beneficial effects, suggesting that it may be an additional therapeutic agent for HF.

Nicorandil in patients with acute myocardial infarction undergoing primary percutaneous coronary intervention: a systematic review and meta-analysis

Background

Nicorandil, as an adjunctive therapy with primary percutaneous coronary intervention (PCI), had controversial benefits in cardioprotection in patients with acute myocardial infarction (AMI).

Methods and Results

We performed a systematic review of randomized controlled trials (RCTs) comparing treatment with nicorandil prior to reperfusion therapy with control (placebo or no nicorandil) in patients who suffered from AMI and performed primary PCI. PubMed, EMBASE and CENTRAL databases and other sources were searched without language and publication restriction. 14 trials involving 1680 patients were included into this meta-analysis. Nicorandil significantly reduced the incidence of thrombolysis in myocardial infarction (TIMI) flow grade ≤2 (risk ratio [RR], 0.57; 95% confidence interval [CI]: 0.42 to 0.79), the Timi frame count (TFC) (mean difference [MD], -5.19; 95% CI: -7.13 to -3.26), increased left ventricular ejection fraction (LVEF) (%) (MD, 3.08; 95% CI: 0.79 to 5.36), and reduced the incidence of ventricular arrhythmia (RR, 0.53; 95% CI: 0.37 to 0.76) and congestive heart failure (CHF) (RR, 0.41; 95% CI: 0.22 to 0.75). No difference in the pear creatine kinase (CK) value (MD, -290.19; 95% CI: -793.75 to 213.36) or cardiac death (RR, 0.39; 95% CI: 0.09 to 1.67) was observed.

Conclusions

Nicorandil prior to reperfusion is associated with improvement of coronary reflow as well as suppression of ventricular arrhythmia, and further improves left ventricular function in patients who suffered from AMI and underwent primary PCI. But the definite clinical benefits of nicorandil were not found, which may be due to the small sample size of the selected studies.

Multiplicity of effectors of the cardioprotective agent, diazoxide

Diazoxide has been identified over the past 50years to have a number of physiological effects, including lowering the blood pressure and rectifying hypoglycemia. Today it is used clinically to treat these conditions. More recently, another important mode of action emerged: diazoxide has powerful protective properties against cardiac ischemia. The heart has intrinsic protective mechanisms against ischemia injury; one of which is ischemic preconditioning. Diazoxide mimics ischemic preconditioning. The purpose of this treatise is to review the literature in an attempt to identify the many effectors of diazoxide and discuss how they may contribute to diazoxide's cardioprotective properties. Particular emphasis is placed on the concentration ranges in which diazoxide affects its different targets and how this compares with the concentrations commonly used to study cardioprotection. It is concluded that diazoxide may have several potential effectors that may potentially contribute to cardioprotection, including KATP channels in the pancreas, smooth muscle, endothelium, neurons and the mitochondrial inner membrane. Diazoxide may also affect other ion channels and ATPases and may directly regulate mitochondrial energetics. It is possible that the success of diazoxide lies in this promiscuity and that the compound acts to rebalance multiple physiological processes during cardiac ischemia.

Protective mechanism of nicorandil on rat myocardial ischemia-reperfusion

OBJECTIVES

To study the protective mechanism of nicorandil on myocardial ischemia-reperfusion injury.

METHODS

Fifty rats were randomly divided into five groups, four of which were operated on to produce myocardial ischemia-reperfusion. Nicorandil (5 mg/kg) was administrated by intravenous injection to three of the groups. The myocardial ultrastructure was observed by electron microscope. The expression levels of the antiapoptotic protein Bcl-2 and the pro-apoptotic protein Bax were detected by immunohistochemical staining with rhodamine 123. The mitochondrial membrane potential was detected by spectrophotometry.

RESULTS

The activity of lactate dehydrogenase (LDH) and malondialdehyde (MDA) content was decreased and the activity of superoxide dismutase (SOD) was increased in the three nicorandil groups, compared with those in the group without nicorandil (P < 0.01, P < 0.05). The positive staining level of the expressed Bcl-2 was increased and the expressed Bax was decreased (P < 0.01) in the three nicorandil groups, compared with those in the group without nicorandil. The mitochondrial inner membrane potential was increased in the three nicorandil groups compared with that in the group without nicorandil (P < 0.05).

CONCLUSION

A suitable level of nicorandil has a protective effect on rats' myocardial ischemia-reperfusion injury, and is mainly based on the opening of the mitochondrial KATP channel and the lowing of Ca overload.

Is the sarcolemmal or mitochondrial K(ATP) channel activation important in the antiarrhythmic and cardioprotective effects during acute ischemia/reperfusion in the intact anesthetized rabbit model?

The relative contributions of cardiomyocyte sarcolemmal ATP-sensitive K(+) (K(ATP)) and mitochondrial K(ATP) channels in the cardioprotection and antiarrhythmic activity induced by K(ATP) channel openers remain obscure, though the mitochondrial K(ATP) channels have been proposed to be involved as a subcellular mediator in cardioprotection afforded by ischemic preconditioning. In the present study, we sought to investigate the effects of administration of ATP-sensitive K(+) channel (K(ATP)) openers (nicorandil and minoxidil), a specific mitochondrial K(ATP) channel blocker (5-hydroxydecanoate (5-HD)) and a specific sarcolemmal K(ATP) channel blocker (HMR 1883; (1-[5-[2-(5-chloro-o-anisamido)ethyl]-2-methoxyphenyl]sulfonyl-3-methylthiourea) prior to coronary occlusion as well as prior to post-ischemic reperfusion on survival rate, ischemia-induced and reperfusion-induced arrhythmias and myocardial infarct size in anesthetized albino rabbits. The thorax was opened in the left 4th intercostal space and after pericardiotomy the heart was exposed. In Group I (n=88), occlusion of the left main coronary artery and hence, myocardial ischemia-induced arrhythmias was achieved by tightening a previously placed loose silk ligature for 30 min. In Group II (n=206), arrhythmias were induced by reperfusion following a 20-min ligation of the left main coronary artery. Both in Group I and Group II, intravenous (i.v.) administration of nicorandil (0.47 mg/kg), minoxidil (0.5 mg/kg), HMR 1883 (3 mg/kg)/nicorandil and HMR 1883 (3 mg/kg)/minoxidil before coronary artery occlusion increased survival rate (86%, 75%, 75% and 86% vs. 55% in the control subgroup in Group I; 75%, 67%, 67% and 75% vs. 46% in the control subgroup in Group II), significantly decreased the incidence and severity of life-threatening arrhythmias. In Group II, i.v. administration of nicorandil and minoxidil before coronary artery occlusion significantly decreased myocardial infarct size. However, i.v. administration of nicorandil or minoxidil before reperfusion did neither increase survival rate nor confer any antiarrhythmic or cardioprotective effects. The antiarrhythmic and cardioprotective effects of both nicorandil and minoxidil were abolished by pretreating the rabbits with 5-HD (5 mg/kg, i.v. bolus), a selective mitochondrial K(ATP) channel blocker but not by HMR 1883 (3 mg/kg). In the present study, higher levels of malondialdehyde (MDA) and lower levels of reduced glutathione (GSH) and superoxide dismutase (SOD) in necrotic zone of myocardium in all the 16 subgroups in Group II suggest little anti-free radical property of nicorandil and minoxidil. We conclude that intervention by intravenous administration of nicorandil and minoxidil (through the selective activation of mitochondrial K(ATP) channels) increased survival rate and exhibited antiarrhythmic and cardioprotective effects during coronary occlusion and reperfusion in anesthetized rabbits when administered prior to coronary occlusion. The cardiomyocyte mitochondrial K(ATP) channel may be a pharmacologically modulable target of cardioprotection and antiarrhythmic activity.

Nicorandil versus isosorbide dinitrate as adjunctive treatment to direct balloon angioplasty in acute myocardial infarction

OBJECTIVE

To compare the effects of nicorandil (a hybrid ATP sensitive potassium channel (K+(ATP) channel) opener/nitric oxide donor) with those of isosorbide dinitrate (ISDN) on myocardial microcirculation and cardiac function in patients with acute myocardial infarction (AMI) who had undergone reperfusion treatment by direct balloon angioplasty.

DESIGN

Double blind randomised study.

PATIENTS

60 patients with AMI in Killip class I.

INTERVENTIONS

Patients were assigned into two treatment groups: a nicorandil group (n = 30) and an ISDN group (n = 30). Each drug was infused intravenously at 6 mg/h for 72 hours starting at admission and was administered directly to the treated coronary artery immediately after angioplasty.

RESULTS

Compared with ISDN, nicorandil more frequently caused recovery of ST segment elevation just after reperfusion (15 of 27 (55.5%) in the nicorandil group v 5 of 26 (19.2%) in the ISDN group, p = 0.006). The nicorandil group had higher values of averaged peak velocity 40 minutes after reperfusion (mean (SD) 24.8 (13.3) cm/s v 16.0 (11.1) cm/s, p = 0.045) and higher values of regional wall motion of the infarcted area three weeks after onset of AMI (-1.78 (1.11) v -2.50 (1.04) SD/chord, p = 0.046).

CONCLUSIONS

A combination of nicorandil drip infusion starting before reperfusion and intracoronary injection immediately after reperfusion is more effective than a similarly performed infusion of ISDN in preserving myocardial microcirculation in the reperfused AMI area. The nicorandil regimen resulted in better left ventricular regional wall motion.

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.

Effect of mild hypothermia on nicorandil-induced vasodilation of pial arterioles in cats

OBJECTIVE

Nicorandil is characterized as hybrid between nitrates and potassium channel activators. Recent evidence suggested that mild hypothermia may alter cerebral vasodilation induced by a nitrate agent and potassium channel opener. However, the effect of mild hypothermia on nicorandil-induced vasodilation is not known. The present study was conducted to investigate whether mild hypothermia could alter nicorandil-induced cerebral vasodilation. In addition, the effects of mild hypothermia on cerebral vasodilation induced by nitroglycerin, a nitrate agent, and cromakalim, a selective adenosine 5'-triphosphate-sensitive potassium channel opener, were assessed in the same model.

DESIGN

Prospective, randomized, experimental study with repeated measures.

SETTING

Investigational animal laboratory.

SUBJECTS

Twenty-four cats.

INTERVENTIONS

Animals were anesthetized with pentobarbital. The cranial window technique, combined with microscopic video recording, was used to measure small (50-100 microm) and large (100-200 microm) pial arteriolar diameter in an experiment. Animals were assigned randomly to either a normothermic (37 degrees C) or a hypothermic (33 degrees C) group. Nicorandil, nitroglycerin, or cromakalim at concentrations of 10(-8), 10(-6), or 10(-4) mol/L was applied topically in the cranial window, and the diameter of pial arterioles was measured.

MEASUREMENTS AND MAIN RESULTS

Topical administration of nicorandil, nitroglycerin, and cromakalim significantly dilated both small and large pial arterioles in a dose-dependent manner during normothermia. Nicorandil-induced vasodilation of either large or small pial arterioles was not affected by hypothermia. However, hypothermia significantly attenuated nitroglycerine-induced vasodilation in both large and small pial arterioles and enhanced cromakalim-induced vasodilation in both large and small pial arterioles.

CONCLUSIONS

Nicorandil-induced vasodilation of cerebral pial arterioles was not affected by mild hypothermia. By contrast, mild hypothermia significantly attenuated nitroglycerin-induced vasodilation and enhanced cromakalim-induced vasodilation.

Potentiating effect of nicorandil on the adenosine A2 receptor-mediated vasodepression in rats: potential role for KATP channels

The effects of nicorandil on systemic blood pressure (SBP) and heart rate (HR) responses to adenosine were compared with those to N6-cyclopentyladenosine (CPA), a selective adenosine A1 receptor agonist, and 5'-(N-cyclopropyl)-carboxamidoadenosine (CPCA), a selective adenosine A2 receptor agonist, in anesthetized rats. When injected intravenously (i.v.), single bolus doses of CPCA (0.01-1.0 micrograms/kg), like adenosine (30 micrograms/kg), elicited dose-dependent decreases in SBP scarcely affecting HR, while CPA (0.03-1.0 micrograms/kg) produced only reduction of HR without influencing SBP. The enhancement of the vasodepressor response to CPCA, like adenosine, was induced by the i.v. infusion of either nicorandil (10 micrograms/kg per min) or cromakalim (0.1 micrograms/kg per min), but the response to CPA in HR remained unmodified during the infusion of nicorandil as well as cromakalim. After i.v. treatment with glibenclamide (20 mg/kg), and adenosine triphosphate (ATP)-sensitive K+ channel blocker, or 3,7-dimethyl-1-propargylxanthine (DMPX) (1 mg/kg), a selective antagonist of adenosine A2 receptor, not only CPCA action but also the enhancement of CPCA action by nicorandil and cromakalim were significantly attenuated. Similar results were obtained in the case of single bolus i.v. adenosine. The present result indicates that the augmentation of the adenosine action by nicorandil appears to be mediated by activation of ATP-sensitive K+ channels, closely linked with stimulation on A2 receptors by adenosine.

Salutary effect of adjunctive intracoronary nicorandil administration on restoration of myocardial blood flow and functional improvement in patients with acute myocardial infarction

Salutary effect of nicorandil, a K+ adenosine triphosphate channel opener, on restoration of myocardial blood flow and functional improvement after coronary revascularization was investigated in 20 patients with first anterior acute myocardial infarction. Ten patients received intracoronary administration of nicorandil (2 mg) after coronary revascularization; the other 10 patients received coronary revascularization only and served as control subjects. Myocardial contrast echocardiography and two-dimensional echocardiography were performed to assess microvascular integrity and regional function in the infarcted area. Nicorandil improved peak contrast intensity ratio (p < 0.001), calculated as the ratio of peak contrast intensity in the infarcted and noninfarcted areas, indicating the restoration of myocardial blood flow to the infarcted myocardium. Regional wall motion improved more significantly in 1 month in patients who received nicorandil (p < 0.01). Thus our results suggested the usefulness of intracoronary nicorandil administration after coronary revascularization for restoring blood flow and functional improvement in patients with acute myocardial infarction.

Effect of the potassium-channel opener nicorandil as an adjunct to cardioplegia on myocardial preservation in isolated rabbit hearts

We studied the effect of nicorandil on the hemodynamic, biochemical, and ultrastructural changes in rabbit hearts (n = 50) rendered cardioplegic with a single injection of Bretschneider's HTK solution over 30 min or 60 min at 37 degrees C or 15 degrees C, followed by reperfusion at 37 degrees C for 60 min. Particular attention was focused on the aspects of dose-response relationship, temperature sensitivity, and ischemic tolerance. Isolated hearts were prepared for modified Langendorff circulation using modified Krebs-Henseleit bicarbonate solution bubbled with a 95% O2(-5)% CO2 gas mixture, to which nicorandil (0, 0.1, 1, and 5 mM) was added. The optimal concentration of nicorandil was 1mM, which increased the recovery of left ventricular (LV) function, affecting coronary flow and the myocardial cyclic adenosine monophosphate, but not the myocardial concentrations of adenine nucleotide compounds or total calcium. These effects were abolished by the addition of glibenclamide to the HTK, but they were not diminished by a high potassium (K+) concentration of 20mM. The addition of nicorandil 1mM to the HTK at 15 degrees C did not improve the recovery of LV function. Our result suggested that nicorandil used adjunctly prevents LV functional depression after 30min, and possibly 60min of cardioplegia at 37 degrees C, and that this effect is not disturbed by a high K+ concentration up to 20 mM. However, nicorandil has temperature sensitivity whereby it loses its efficacy at 15 degrees C.

Pharmacologic myocardial preconditioning with monophosphoryl lipid A (MLA) reduces infarct size and stunning in dogs and rabbits

As the mechanism of ischemic preconditioning unfolds, various strategies for inducing pharmacologic preconditioning become apparent. Adenosine receptor agonists, KATP channel activators, and endothelial-neutrophil adhesion antagonists have enjoyed cardioprotective activity against ischemia/reperfusion injury in at least some preclinical models. Monophosphoryl lipid A (MLA), a structural derivative of the pharmacophore of endotoxin, enjoys an improved therapeutic index in relation to the parent biological product. MLA has found clinical application as a vaccine adjuvant and protects from sepsis and septic shock in the preclinical setting. In animal models of myocardial ischemia/reperfusion injury, pretreatment 12-24 hours prior to ischemia with a single IV bolus injection of MLA limits infarct size 50 to 75 percent in standard canine and rabbit models at doses of 10-35 micrograms/kg. Regional myocardial stunning following multiple 5-minute ischemic episodes as assessed by segment shortening is reduced in dogs pretreated 24 but not 1 hour prior to ischemia. Global cardiac function, as evaluated by pressure-volume constructs generated in dogs being weaned from cardiopulmonary bypass, recovers more quickly in animals pretreated with MLA. Cardiac protection in various models is associated with preservation of ATP during ischemia, induction of 5' nucleotidase and enhancement of calcium reuptake by SR during reperfusion. Limitation of infarct size by MLA in dogs and rabbits can be reversed by the administration of glibenclamide just prior to ischemia, suggesting a role for KATP channel opening during the first minutes of sustained ischemia. A clinical formulation of MLA (MPL-C) is currently undergoing clinical investigation in the Phase II setting in coronary artery bypass surgical patients. MLA may represent a novel means of inducing pharmacologic preconditioning, with potential for clinical application as a pretreatment before planned myocardial ischemia.

Cardioprotective effects of NIP-121, a novel ATP-sensitive potassium channel opener, during ischemia and reperfusion in coronary perfused guinea pig myocardium

We investigated the effect of NIP-121, a novel ATP-sensitive K+ channel opener, on myocardial damage during ischemia/reperfusion. The action potential and contractile force of coronary-perfused guinea pig right ventricular walls were recorded. The preparations were subjected to 30-min no-flow ischemia with or without NIP-121 or glibenclamide, followed by 60-min reperfusion. In untreated tissues, decreases in action potential duration (APD) and contractile force and an increase in resting tension were observed during the no-flow period. On reperfusion, transient arrhythmias were observed and resting or contractile force returned to <50% of preischemic values. NIP-121, at 0.3 microM, a concentration showing only a slight negative inotropic effect, caused a faster decrease in APD and contractile force but abolished the increase in resting tension (RT) during the no-flow period. On reperfusion, no arrhythmia was observed in NIP-121-treated preparations, and contractile force recovered to approximately 80% of the preischemic value. Glibenclamide 1 microM attenuated the decrease in APD but affected neither the decrease in contractile force nor the increase in RT during the no-flow period. On reperfusion, the incidence of arrhythmia was increased in glibenclamide-treated preparations, and the recovery of basal tension and contractile force was inhibited: Contractile force recovered to only approximately 15% of the preischemic value. NIP-121 was also shown to attenuate the decrease in tissue ATP during ischemia and reperfusion. We demonstrated that NIP-121 may have protective effects against myocardial injury during ischemia and reperfusion. Activation of ATP-sensitive K+ current may be an adaptive mechanism for cardioprotection under compromised blood flow.

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.

Antiischemic effects of nicorandil during coronary angioplasty in humans

The present study was undertaken on 10 patients with angina undergoing percutaneous transluminal coronary angioplasty. The angioplasty procedure consisted of two successive 30-second balloon inflations at 5 minute intervals. After the first inflation, nicorandil (0.1 mg/kg) was given intravenously over a 2-minute period. The second inflation was then performed 3 minutes after the completion of drug administration. Myocardial ischemia was measured as the magnitude of ST-segment elevation on the intracoronary electrocardiogram (intracoronary ECG) recorded from the guidewire. Nicorandil significantly reduced the magnitude of ST-segment elevation. Nicorandil did not change the heart rate-blood pressure product, nor the oxygen saturation of the blood sampled from the great cardiac vein, nor the velocity of coronary blood flow in those patients with no evidence of collaterals. These results favor the conclusion that nicorandil prolongs the intrinsic ability of cardiac myocyte to withstand oxygen deprivation. This salutary effect is possibly due to a direct cellular mechanism because nicorandil did not modify the peripheral and coronary hemodynamic parameters that govern myocardial oxygen consumption.

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)

Effects of nicorandil on regional perfusion and left ventricular function

Left ventricular function and regional perfusion were evaluated by two study designs in patient groups with stable ischemic coronary artery disease (CAD): (1) using conventional left ventricular angiographies and (2) applying myocardial contrast echocardiography. The aim of the studies was to establish the effects of sublingually or orally applied nicorandil (N) on pacing-induced myocardial ischemia (MIS). In the first angiographic study, in nine patients with ischemic CAD and with pacing-inducible MIS, the effect of N, 20 mg sublingually, on hemodynamics and regional wall motion (RWM) were studied. There were no parameter changes without MIS being induced when comparing measurements at the 7th and 14th minute after N application to control values (p > 0.05). In the 15th and 16th minutes after N, pacing-induced MIS could no longer be elicited but left ventricular pump function improved; comparing MIS with N versus MIS without N: ejection fraction improved by 21%, cardiac index by 37%, and RWM by 21%, while filling pressure fell by 41% and systemic vascular resistance fell by 29%. Thus, N-mediated "protection from ischemia" with rather improved hemodynamics and RWM corresponds with alterations that theoretically could have been expected after nitroglycerin given under the above conditions. In the second echocardiographic study, regional perfusion was assessed in 10 patients by intracoronary injection of a newly developed echo contrast medium (ECM) and measurement of ECM washout halftime (t1/2) over opacified myocardial regions of interest, which displayed wall motion abnormalities already at rest.(ABSTRACT TRUNCATED AT 250 WORDS)

Glibenclamide enhances but pinacidil reduces attenuation in sympathetic responsiveness after acute coronary artery occlusion

To investigate the role of ATP-sensitive K+ channels in modulating the efferent autonomic response following acute myocardial ischemia/infarction, we examined the effects of a blocker (glibenclamide) and an opener (pinacidil) of ATP-sensitive K+ channels on the time course and extent of the attenuation in efferent cardiac sympathetic responsiveness in anesthetized dogs. We measured the effective refractory periods (ERPs) at nonischemic sites basal and apical to the area of myocardial ischemia/infarction in the baseline state and during bilateral stimulation of the ansae subclaviae before and after each drug administration and 5, 30, 60, 120, and 180 minutes after latex injection of a diagonal branch of the left anterior descending coronary artery. Animals received either vehicle (n = 12), glibenclamide (0.3 mg.kg-1, n = 10), pinacidil (0.15 mg.kg-1 + 0.2 mg.kg-1 infusion, n = 10), or a combination of these two drugs (n = 9) intravenously. In another group of dogs receiving just pinacidil (n = 10), an intra-aortic balloon was inflated distal to the renal arteries to prevent pinacidil-induced hypotension. Another group of dogs received either high-dose glibenclamide (0.3 mg.kg-1 + 0.15 mg.kg-1, n = 4), low-dose glibenclamide (0.06 mg.kg-1, n = 4), medium-dose pinacidil (0.03 mg.kg-1 + 0.04 mg.kg-1 infusion, n = 4), or low-dose pinacidil (0.0075 mg.kg-1 + 0.01 mg.kg-1 infusion, n = 4). In all dogs, basal sites exhibited no attenuation of sympathetically induced shortening of the ERP throughout the period of acute myocardial ischemia/infarction. Cumulative attenuation in sympathetic responsiveness (shortening of ERP < or = 2 milliseconds induced by bilateral stimulation of the ansae subclaviae) at nonischemic test sites apical to the area of ischemia/infarction during a 3-hour period was greater in the glibenclamide group (26 of 44 sites, P = .008) and less in the pinacidil (2 of 44 sites, P = .002) and pinacidil-balloon (1 of 48 sites, P < .001) groups compared with the vehicle group (14 of 46 sites). Glibenclamide abolished the protective effect of pinacidil so that 10 of 45 sites had < 2-millisecond shortening during a 3-hour period in the glibenclamide + pinacidil group (P = .018 versus pinacidil group, P = .286 versus vehicle group). Such effects of glibenclamide and pinacidil on sympathetic attenuation were dose dependent. Maintaining the blood glucose level during glibenclamide administration did not affect the sympathetic attenuation after acute coronary artery occlusion.(ABSTRACT TRUNCATED AT 400 WORDS)

Mechanisms of vasodilation of cerebral vessels induced by the potassium channel opener nicorandil in canine in vivo experiments

BACKGROUND AND PURPOSE

Nicorandil, a potent antianginal agent characterized as a potassium channel opener, could produce cerebrovascular dilation in in vitro studies. Our aim was to investigate the pharmacologic response to the topical application of nicorandil on the vasomotor tone of pial vessels in vivo. To elucidate its mechanism, we also studied the inhibitory action of methylene blue and glibenclamide against nicorandil-induced vasodilation.

METHODS

In 14 dogs prepared with a parietal cranial window, we administered five different concentrations of nicorandil solution (10(-7), 10(-6), 10(-5), 10(-4), and 10(-3) mol/L) under the window and measured pial arterial and venular diameters. After pretreating pial vessels with either 10(-5) mol/L methylene blue or 10(-5) mol/L glibenclamide, we examined inhibitory action after the application of 10(-5) mol/L nicorandil. In additional experiments with 9 dogs, we evaluated the effects of nitroglycerin and cromakalim on pial vessels in the absence or presence of 10(-5) mol/L methylene blue and 10(-5) mol/L glibenclamide, respectively.

RESULTS

Nicorandil produced significant, concentration-dependent dilation of pial vessels (P < .05). Methylene blue blocked nicorandil-induced dilation, whereas glibenclamide only attenuated such action of nicorandil. Nitroglycerin and cromakalim also produced a concentration-dependent increase in pial arteriolar and venular diameters (P < .05), and those effects were blocked in the presence of methylene blue or glibenclamide, respectively.

CONCLUSIONS

Our in vivo study demonstrates that topical application of nicorandil dilates both pial arterioles and venules in a concentration-dependent manner and suggests that the mechanisms of such actions are most likely due to both cyclic GMP-mediated vascular smooth muscle dilation and the regulation of K+ flux.

Chronic gliclazide treatment affects basal and post-ischemic cardiac function in diabetic rats

1. A 6-week gliclazide treatment improved left ventricular developed pressure and left ventricular end-diastolic pressure, left ventricular pressure-rate products in isolated working hearts from streptozotocin-induced diabetic rats. 2. Post-ischemic recovery in heart rate, left ventricular developed pressure, left ventricular end-diastolic pressure, left ventricular pressure-rate products and cardiac work were also shown in gliclazide-treated diabetic rats. 3. Gliclazide treatment did not modify the degree of insulinopenia and hyperglycemia, nor the myocardial energy metabolism during ischemia-reperfusion. 4. The results suggest that the gliclazide treatment has a cardioprotective effect on basal and post-ischemic cardiac functions of chronic diabetes.

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.

Role of ATP-sensitive K+ channel current in ischemic arrhythmias

In acute myocardial ischemia slow conduction and short refractoriness both predispose to cardiac arrhythmias. Moreover, spatial dispersion in these parameters, in part determined by inhomogeneity in extracellular potassium concentration ([K+]0), which develops within minutes, is considered highly arrhythmogenic. The incidence and time distribution of ventricular arrhythmias is determined by these electrophysiological changes and by factors pertinent to the experimental model. In the initial phase of ischemia, glibenclamide, a potent blocker of ATP-sensitive K+ channels (K+ATP channels), reduces the rate of increase in [K+]0 and therefore, presumably, also the inhomogeneity in [K+]0. During this phase of ischemia glibenclamide has an antiarrhythmic effect, which may be based on a reduction in inhomogeneity in [K+]0. In addition, glibenclamide prolongs the action potential of ischemic myocardium. Although under ischemic conditions action potential duration is no longer a reliable parameter or refractoriness, glibenclamide-induced prolongation or refractoriness may play a role in the prevention of arrhythmias. In contrast, openers of K+ATP channels increase the incidence of ventricular arrhythmias or, in other models, the time course of onset is accelerated. They shorten the duration of the action potential in ischemic tissue. In the globally ischemic rabbit heart, initial changes in [K+]0 are not influenced by cromakalim. It is concluded that activation of the K+ATP channel current during early myocardial ischemia potentially contributes to the development of ventricular arrhythmias. Particularly, the direct electrophysiological effect of increased K+ current is considered arrhythmogenic.

ATP-sensitive K+ channels in cardiac ischemia: an endogenous mechanism for protection of the heart

The Role of ATP-sensitive K+ channels (KATP) in action potential shortening and protection of myocardium in ischemia were explored using isolated ventricular myocytes and arterially perfused right ventricular walls of guinea pigs. Conditions "simulating" some aspects of ischemia--(10.8 mM K+o, 6.9 pHo, 20 mM lactate, no glucose; 10 mM 2-deoxy-D-glucose; and either 1 mM cyanide or no O2 (bubbled with 95/5% N2/CO2)--caused a decline in action potential duration (APD) and the elaboration of time- and voltage-independent, steady-state outward conductance due to KATP, which could be inhibited with glibenclamide (50 microM) in myocytes studied via the perforated patch (nystatin) whole-cell technique. Right ventricular walls subjected to no-flow ischemia +/- glibenclamide (10 microM) to block, or +/- pinacidil (1 and 10 microM) to activate, KATP, respectively, exhibited varied ischemic injury. Glibenclamide caused a greater fall in resting membrane potential, inhibited the decline in APD, caused an early rise in resting tension, and inhibited recovery of contractile function upon reflow. Pinacidil caused a greater decline in APD, inhibited changes in resting tension, and improved recovery during reperfusion. These results indicate that KATP contributes to action potential shortening in isolated myocytes in simulated ischemia and intact myocardium in no-flow ischemia. Activation of this membrane current may be an important adaptive mechanism for protecting the myocardium when blood flow to the tissue is compromised.

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.

Clinical pharmacology of potassium channel openers

Opening of K+ channels in cell membranes with resulting increase in K+ conductance, shifts the membrane potential in a hyperpolarizing direction towards the K+ equilibrium potential. Hyperpolarization reduces the opening probability of ion channels involved in membrane depolarization and excitation is reduced. K+ channel openers are believed to hyperpolarize smooth muscle cells by a direct action on the cell membrane. The best known members of the group are cromakalim, nicorandil and pinacidil, but several new compounds are being evaluated. In addition, it has recently been shown that also clinically well-known drugs like, e.g. diazoxide and minoxidil exhibit K+ channel opening properties. Nicorandil and new compounds containing nitro groups have a dual mechanism of action, also activating guanylate cyclase, an effect that contributes to their cardiovascular effect profile. K+ channel openers have a wide range of effects. Some of their properties and actions are summarized, and their present applications and/or potential for future application, in e.g. hypertension, angina pectoris, asthma, bladder instability, and several other disorders are discussed. It is concluded that K+ channel openning represents an interesting pharmacological principle with many potential clinical applications. However, most available drugs do not seem to have a sufficient tissue selectivity to be useful therapeutic alternatives. Before the potential of the new members of the group on clinical trials can be properly evaluated, clinical experiences are needed.

Alterations in macrophage free radical and tumor necrosis factor production by a potassium channel activator

The potassium channel activator nicorandil, under evaluation for antianginal management, has been shown to decrease neutrophil respiratory burst. Since our laboratory has demonstrated that reactive oxygen species (ROS) increase tumor necrosis factor (TNF) production, we hypothesized that nicorandil might decrease TNF production from a lipopolysaccharide (LPS) challenge via reduction of respiratory burst. Macrophage viability and TNF production were determined after an 18-hr exposure to 5.0 micrograms/ml LPS and varying concentrations of nicorandil. Nicorandil was not toxic to macrophages below 12 mM (94 +/- 3% viability versus control) and decreased ROS and TNF production. Intracellular superoxide production decreased from 164 +/- 24 OD550 to 99 +/- 6 OD550 with 10 mM nicorandil and extracellular superoxide decreased from 3108 +/- 111 to 1760 +/- 210 nM. Hydrogen peroxide production was also decreased by 10 mM nicorandil. TNF production in response to 5 micrograms/ml LPS decreased from 6.8 +/- 0.6 to 2.7 +/- 0.4 ng/ml with 10 mM nicorandil. Northern and slot blot analyses demonstrate that nicorandil acts at a post-transcriptional site. These data imply that nicorandil decreases macrophage TNF production from an LPS challenge, possibly through a reduction in respiratory burst. Such compounds may prove useful in the treatment of conditions thought to be associated with free radical-lymphokine interactions such as ischemia-reperfusion injury, oxygen toxicity, adult respiratory distress syndrome, and septic shock.

ATP-regulated K+ channels protect the myocardium against ischemia/reperfusion damage

The role of ATP-regulated K+ channels in protecting the myocardium against ischemia/reperfusion damage was explored using glibenclamide and pinacidil to block and activate the channels, respectively. Electrical and mechanical activity of arterially perfused guinea pig right ventricular walls was recorded simultaneously via an intracellular microelectrode and a force transducer. The preparations were subjected to either 1) 20 minutes of no-flow ischemia with or without glibenclamide (1 and 10 microM) followed by reperfusion, or 2) 30 minutes of no-flow ischemia with or without pinacidil (1 and 10 microM) followed by reperfusion. No-flow ischemia for 20 minutes produced changes in electrical and mechanical activity that were completely reversed on reperfusion; resting membrane potential declined by 13 +/- 1.2 mV, action potential duration at 90% repolarization (APD90) decreased by 62%, and developed tension fell by greater than 95%, but resting tension did not change significantly. Glibenclamide (10 microM) had no effect on activity during normal perfusion, but during ischemia, resting membrane potential fell slightly further (17 +/- 1.8 mV) and APD90 declined by only 24%. Developed tension declined more slowly and to a lesser extent, but resting tension rose significantly between 10 and 20 minutes of ischemia. Reperfusion of glibenclamide-treated tissues elicited arrhythmias (extrasystoles and tachycardia), and the preparations failed to recover mechanical function. Glibenclamide at 1 microM produced qualitatively similar effects, albeit less severe. After 30 minutes of no-flow ischemia in untreated tissues, resting tension increased by approximately 130% during the no-flow period. Reperfusion caused arrhythmias (extrasystoles, tachyarrhythmias, and fibrillation) and failed to restore resting or developed tension to preischemic levels. Pinacidil at 1 microM did not affect electrical or contractile function, but at 10 microM it had a negative inotropic effect, decreasing APD90 and developed tension by 5% and 18%, respectively. Both concentrations of the drug caused a faster and greater decline in APD90 during the no-flow period. Resting tension did not change during 30 minutes of no-flow ischemia in the presence of pinacidil, and reperfusion led to 85% and complete recovery of electrical and mechanical activity at 1 and 10 microM, respectively. The data indicate that glibenclamide enhances whereas pinacidil reduces myocardial damage caused by ischemia/reperfusion. The results are consistent with the hypothesis that activation of ATP-regulated K+ channels during ischemia is an important adaptive mechanism for protecting the myocardium when blood flow to the tissue is compromised.

Cardiovascular and biological effects of K+ channel openers, a class of drugs with vasorelaxant and cardioprotective properties

Several new chemical entities (RP 52891, cromakalim and its derivatives) are potent and specific openers of vascular K+ channels. This mechanism is also shared, at least partially, by drugs such as minoxidil, diazoxide, pinacidil and nicorandil. The opening of plasmalemma K+ channels produces loss of cytosolic K+. This effect results in cellular hyperpolarization and functional vasorelaxation. In normotensive or hypertensive rats, K+ channel activators decrease aortic blood pressure (by producing a directly mediated fall in systemic vascular resistance) and reflexly increase heart rate. The former effect is not modified by specific blockers of classical vascular receptors but it is completely antagonized by the hypoglycemic sulphonylurea, glibenclamide, an established blocker of ATP-regulated K+ channels. K+ channel openers produce selective coronary vasodilatation and afford functional and biochemical protection to the ischemic myocardium. This salutary effect is mediated via cardiac K+ channel modulation and may result from an improved myocardial oxygen balance in the ischemic region. K+ channel openers increase plasma renin activity in animals as well as in man. However, only diazoxide, but not cromakalim or RP 52891, lowers plasma insulin concentration. The dose of glibenclamide entirely blocking the latter effect is over 50-fold smaller than that antagonizing the hypotensive and hyper-reninemic responses to diazoxide. In conclusion, K+ channel activators are potent vasorelaxant and cardioprotective agents possessing an original mechanism of action which is the opening of plasmalemma ATP-regulated K+ channels. Their clinical use as antihypertensive agents may be accompanied by undesirable effects (characteristic of peripheral vasodilators) which are likely to be attenuated or avoided by controlled release formulations. However, inasmuch as low doses of K+ channel openers may be sufficient to produce selective coronary artery dilatation and cardioprotection, these compounds could be of particular value in treating patients with coronary artery disease efficaciously and possibly without adverse cardiovascular effects.