Changes of endothelin-1 and big endothelin-1 levels and action potential duration during myocardial ischemia-reperfusion in dogs with and without ventricular fibrillation

Myocardial ischemia-reperfusion is associated with increased production of endothelin-1 (ET-1). Moreover, exogenous ET-1 has arrhythmogenic properties. Our aim was to investigate the correlation between endogenous ET-1, big ET-1 levels and epicardial monophasic action potential duration during myocardial ischemia-reperfusion in anesthetized dogs. Thirty-minute myocardial ischemia was followed by a 90-minute reperfusion period in 18 mongrel dogs. The total incidence of ventricular fibrillation (VF) during ischemia and reperfusion was 11.1% and 33.3%, respectively. During ischemia, the monophasic action potential duration at 90% repolarization (MAPD90) decreased significantly (control versus ischemia, 30 minutes, 224.7 +/- 7.1 ms versus 173.8 +/- 7.6 ms; P < 0.05), while during reperfusion a significant prolongation of MAPD90 was observed (ischemia, 30 minutes versus reperfusion, 30 minutes, 173.8 +/- 7.6 ms versus 249.7 +/- 9.9 ms, P < 0.05). During reperfusion ET-1 and big ET-1 levels increased significantly in the coronary sinus and femoral artery (control versus reperfusion, 90 minutes: coronary sinus ET-1, 15.1 +/- 1.4 fmol/mL versus 22.3 +/- 1.1 fmol/mL; big ET-1, 14.7 +/- 1.9 fmol/mL versus 27.4 +/- 2.3 fmol/mL; P < 0.05). The ET-1 concentration increased to a higher level during ischemia in dogs with VF compared with dogs surviving ischemia-reperfusion (non-VF versus VF: control, 15.1 +/- 1.3 versus 15.2 +/- 1.3; ischemia, 30 minutes, 17.6 +/- 1.2 fmol/mL versus 22 +/- 1.6 fmol/mL; P < 0.05), demonstrating a trend of correlation between endothelin levels and development of VF (P = 0.07). ET-1 and big ET-1 levels increased during reperfusion and in the VF group during ischemia; however, there was no correlation between endothelin levels and MAPD90.     

Edaravone prevented deteriorated cardiac function after myocardial ischemia-reperfusion via inhibiting lipid peroxidation in rat

Edaravone (3-methyl-1-phenyl-2-pyrazolin-5-one) has potent effects in the brain as a free radical scavenger in ischemia-reperfusion as well as in ischemic injuries. However, whether this free radical scavenger prevents deterioration of cardiac function and lethal ventricular arrhythmias after ischemia-reperfusion in rat heart is not clear. We aimed to assess whether free radical scavenging by edaravone maintains cardiac function and suppresses life-threatening ventricular tachyarrhythmia after myocardial ischemia-reperfusion. Twenty-nine 7-week-old male Sprague-Dawley rats had acute myocardial ischemia induced by ligation of the left coronary artery for 5 minutes followed by reperfusion. Eleven were treated by intravenous injection of edaravone at 3 mg/kg 2 minutes after coronary ligation, and 18 were left untreated. The index of systolic function (contractility; end-systolic elastance, Ees) and hemodynamics were measured by pressure-volume relationships every 5 minutes before ligation to 25 minutes after reperfusion. Blood levels of malondialdehyde (MDA) and the ischemic areas were also measured 25 minutes after reperfusion. There were no differences in the ischemic areas between the groups. Lethal reperfusion tachyarrhythmia was observed in 5 untreated rats but not in those having edaravone treatment. Ees was significantly greater in the edaravone-treated than in untreated rats from 5 to 25 minutes after reperfusion (1789 +/- 866 in untreated versus 2809 +/- 273 mm Hg/mL in edaravone-treated rats at 25 minutes, P < 0.001). MDA level was significantly lower in edaravone-treated than in untreated rats (1.44 +/- 0.29 nmol/L in edaravone-treated versus 1.90 +/- 0.28 nmol/L in untreated group, P < 0.05). The results suggest that edaravone treatment before reperfusion prevented lethal reperfusion ventricular tachyarrhythmias and deteriorated cardiac function with ischemia and ischemia-reperfusion injuries through inhibiting lipid peroxidation in terms of scavenging for free radicals.     

Post-ischemic cardioprotection by A2A adenosine receptors: dependent of phosphatidylinositol 3-kinase pathway

Activation of myocardial A2A adenosine receptors during reperfusion has been shown to be cardioprotective. The intracellular mechanisms underlying this protection remain unknown. To understand the beneficial effects of activated A2A adenosine receptors in such a state, we investigated whether the enzymes phosphatidylinositol 3-kinase (PI3K) and caspase-3 can account for this post-ischemic cardioprotective effect in an anesthetized rabbit model of myocardial infarction (30 minutes ischemia; 5 hours reperfusion). Administration of the A2A agonist CGS21680 (0.2 microg/kg/min) 5 minutes before reperfusion began (Early) reduced infarct size expressed as a percentage of the area at risk (25.7 +/- 5.3% versus 46.5 +/- 5.3% for the control group; * P < 0.05). Treatment with the A2A agonist 5 minutes after the onset of reperfusion (Late) had no effect on infarct size (38.2 +/- 6.2%). In the presence of a selective inhibitor of PI3K (LY294002), the beneficial effects of CGS21680 on infarct size was no longer observed (43.9 +/- 7.9%). After 5 hours of reperfusion, higher PI3K activity in the ischemic region was observed in the Early group compared with the other experimental groups. Caspase-3 activity was not observed in these different groups. In another set of experiments, PI3K activity was significantly higher during the first 15 minutes of reperfusion in the Early group as compared with the Control group. Caspase-3 activity increased rapidly during the first 15 minutes of reperfusion in the Control group and remained stable in the Early group. These results indicated that post-ischemic cardioprotection afforded by A2A adenosine receptor activation is PI3K-dependent and modulate rapidly other signaling pathways such as caspase-3.     

Pioglitazone mimics preconditioning in the isolated perfused rat heart: a role for the prosurvival kinases PI3K and P42/44MAPK

Ischemic preconditioning, the most powerful protection against infarction, activates PI3Kinase (PI3K)/AKT and P42/44MAPK. Pioglitazone, a thiazolidinedione and PPARgamma receptor agonist used in Type II diabetes treatment, has been shown to activate these kinase cascades. We therefore hypothesized that pioglitazone could protect the myocardium when given prior to myocardial ischemia/reperfusion injury. Langendorff perfused rat hearts underwent 40 minutes of stabilization then 35 minutes of regional ischemia and 120 minutes of reperfusion (control) or Pioglitazone (1, 2, 5, and 10 microM)-given before ischemia. Additional groups underwent the same protocol but with either PI3K inhibitors (15 microM LY294002 or 100 nM wortmannin) or P42/44MAPK inhibitors (10 microM U0126 or 10 microM PD98059) given either during stabilization or at reperfusion. Infarct size was determined as a percentage of risk zone (I/R%). Pioglitazone (2 microM) significantly reduced I/R% compared with control (25.4 +/- 3.1 versus 47.3 +/- 3.4; P < 0.05). This protection was abolished by PI3K inhibitors (pioglitazone+LY294002 46.5 +/- 5.0, pioglitazone + wortmannin 48.8 +/- 4.6 versus pioglitazone alone 25.4 +/- 3.1; P < or = 0.05) but not by P42/44MAPK inhibitors (pioglitazone+U0126 30.7 +/- 5.7, pioglitazone + PD98059 28.5 +/- 6.3 versus pioglitazone alone 25.4 +/- 3.1; P < or = 0.05) given in stabilization. However when the inhibitors were given at reperfusion, the protection was abrogated by blocking either pathway (pioglitazone+LY294002 49.8 +/- 3.1, pioglitazone+U0126 48.7 +/- 3.7 versus pioglitazone alone 25.4 +/- 3.1; P < or = 0.05). In conclusion pioglitazone induced significant protection against ischemia/reperfusion injury when administered prior to ischemia. This protection appears to involve PI3K and P42/44MAPK.     

Effects of a new angiotensin converting enzyme inhibitor, enalapril, in acute and chronic left ventricular failure in dogs

Enalapril (MK-421) is a new angiotensin converting enzyme inhibitor which effectively lowers elevated blood pressure and might also be useful in heart failure. Enalapril was infused into six awake dogs 2 hours after left circumflex coronary artery embolization (acute failure group) and into six other awake dogs two to six months after coronary embolization (chronic failure group). In the acute failure group 2 hours after embolization, increased left ventricular end-diastolic pressure and reduced cardiac output remained unchanged during enalapril infusion. In the chronic failure group, increased left ventricular end-diastolic pressure also remained unchanged during enalapril infusion, but cardiac output, which had fallen to 131.8 +/- 11.9 (S.D.) from 165.8 +/- 17.9 ml/min/kg (P less than 0.01) by two to six months in this group rose during enalapril infusion to 154.5 +/- 27.7 ml/min/kg (P less than 0.05). Heart rate and blood pressure were not changed during enalapril in either group, but stroke volume rose (26.0 +/- 5.9 to 29.2 +/- 6.9 ml, P less than 0.01) and systemic vascular resistance fell (58.5 +/- 10.3 to 39.3 +/- 4.3 units, P less than 0.01) during enalapril only in the chronic failure group. Plasma renin activity after embolization was slightly but not significantly higher in the acute failure group. Thus, enalapril appears to be an arterial vasodilator in dogs with chronic but not acute left ventricular failure.     

A selective inhibitor of Na+/Ca2+ exchanger, SEA0400, preserves cardiac function and high-energy phosphates against ischemia/reperfusion injury

The Ca2+ overload by Ca2+ influx via Na+/Ca2+ exchanger (NCX) is a critical mechanism in myocardial ischemia/reperfusion injury. We investigated protective effects of a novel selective inhibitor of NCX, SEA0400, on cardiac function and energy metabolism during ischemia and reperfusion. Langendorff-perfused rat hearts were exposed to 35 minutes global ischemia and 40 minutes reperfusion. Using 31P nuclear magnetic resonance spectroscopy, cardiac phosphocreatine (PCr), ATP, and pHi were monitored. SEA0400 did not change the basic cardiac function, but improved the recovery of left ventricular developed pressure (LVDP) after reperfusion (27.6 +/- 4.9 mm Hg in control, 101.2 +/- 19.3 mm Hg in 0.1 microM, and 115.5 +/- 13.3 mm Hg in 1 microM SEA0400, means +/- SE, n = 6, P < 0.05). SEA0400 reduced left ventricular end-diastolic pressure and increased coronary flow after reperfusion. SEA0400 improved the recoveries of cardiac phosphocreatine and ATP after reperfusion, but did not affect pHi. There were significant linear correlations between left ventricular developed pressure and cardiac phosphocreatine (r = 0.79, P < 0.05), and left ventricular developed pressure and ATP (r = 0.80, P < 0.05). However, SEA0400 increased the incidence and duration of reperfusion ventricular arrhythmias. SEA0400 added only after reperfusion also improved both the contractile function and energy metabolism. It is concluded that the selective inhibition of NCX may be effective to preserve high-energy phosphates and to improve cardiac function after reperfusion, but may not be able to prevent fatal arrhythmias.     

Benidipine reduces myocardial infarct size involving reduction of hydroxyl radicals and production of protein kinase C-dependent nitric oxide in rabbits

Japanese white rabbits underwent 30 minutes of ischemia and 48 hours of reperfusion. Benidipine (3 or 10 microg/kg, i.v.) was administered 10 minutes before ischemia with and without pretreatment with L-NAME (10 mg/kg, i.v., a NOS inhibitor), chelerythrine (5 mg/kg, i.v., a PKC blocker) or 5-HD (5 mg/kg, i.v. a mitochondrial KATP channel blocker), genistein (5 mg/kg, i.v. a protein tyrosin kinase blocker). SNAP (2.5 mg/kg/min x 70 minutes, i.v., an NO donor) was also administered 10 minutes before ischemia. Benidipine significantly reduced the infarct size in a dose-dependent manner (3 microg/kg: 29.0 +/- 2.7%, n = 8, 10 microg/kg: 23.0 +/- 2.4%, n = 10) compared with the control (41.6 +/- 3.3%, n = 10). This effect was completely blocked by L-NAME (39.9 +/- 3.6%, n = 8) and chelerythrine (35.5 +/- 2.4%, n = 8) but not by 5-HD (23.0 +/- 2.4%, n = 10) or genistein (24.6 +/- 3.1%, n = 10). SNAP also reduced the infarct size (24.6 +/- 3.1%, n = 8). Benidipine significantly increased the expression of eNOS mRNA at 30 minutes after reperfusion and significantly increased the expression of eNOS protein at 3 hours after reperfusion in the ischemic area of the left ventricle. Benidipine and SNAP significantly decreased myocardial interstitial 2,5-DHBA levels, an indicator of hydroxyl radicals, during ischemia and reperfusion. Benidipine increased myocardial interstitial NOx levels, which effect was blocked by chelerythrine, during 0 to 30 minutes and 150 to 180 minutes after reperfusion. Benidipine reduces the infarct size through PKC-dependent production of nitric oxide and decreasing hydroxyl radicals but not through involving protein tyrosine kinase or mitochondrial KATP channels in rabbits.     

Protective effect of FR183998, a Na+/H+ exchange inhibitor, against postischemic injury after normothermic and prolonged hypothermic ischemia in isolated perfused rat hearts.

Inhibition of Na+/H+ exchanger has been reported to protect hearts from ischemia and reperfusion injury. However, the effect of Na+/H+ exchange inhibition on hypothermic ischemic injury has not been extensively studied and the results are inconsistent. The purpose of this study was to investigate whether inhibition of Na+/H+ exchange with FR183998 (5-(2,5-dichlorothiphen-3-yl)-3-[(2-dimethylaminoethyl)carbamoyl]benzoylguanidine dihydrochloride), a potent Na+/H+ exchange inhibitor, would show protective effects against postischemic cardiac dysfunction after hypothermic as well as normothermic ischemia and furthermore, after hypothermic cardioplegic arrest in isolated rat hearts. FR183998 (3.2 x 10(-8)-3.2 x 10(-7) M) improved post-ischemic recovery of left ventricular developed pressure and suppressed the increase of left ventricular end diastolic pressure in a dose-dependent manner, after not only 45 min of normothermic ischemia but also 6 h of hypothermic ischemia. Furthermore, FRI 83998 (10(-7)-10(-6) M) significantly reduced creatine kinase release during reperfusion after 3 h of hypothermic ischemia with cardioplegia. These results indicate that FR183998 has a potent protective effect on postischemic cardiac dysfunction after normothermic and hypothermic ischemia, and also on reperfusion injury after hypothermic cardioplegic arrest, suggesting that its effect would be additive to cardioplegia.     

Preconditioning effects of levosimendan in a rabbit cardiac ischemia-reperfusion model

The preconditioning effects of levosimendan were investigated on ischemia-reperfusion induced morphological and functional cardiac damage. Langendorff-perfused rabbit hearts were reserved as controls or subjected either to global myocardial ischemic preconditioning or to perfusion with levosimendan (0.1 micromol/l) for two 5-minute cycles. After a washout period, all hearts were then subjected to 30 minutes of global ischemia and 120 minutes of drug-free reperfusion. Intraventricular pressure and coronary flow were measured, and infarct size determined after nitroblue-tetrazolium staining on completion of the experiments. Levosimendan pretreatment resulted in a significantly smaller elevation from the preischemic level in left ventricular end-diastolic pressure during reperfusion (37 +/- 17 mm Hg) compared with controls (56 +/- 14 mm Hg) and ischemia-preconditioned hearts (53 +/- 34 mm Hg). The left ventricular developed pressure-representing the functional recovery of the heart after ischemia-that was significantly improved by levosimendan pretreatment (38 +/- 6% vs 16 +/- 5% in controls, P < 0.05). In addition, contractility and relaxability parameters (+dP/dt and -dP/dt, respectively) were better preserved in the levosimendan hearts. The volume of infarcted myocardium after global ischemia-reperfusion was significantly (P < 0.05) decreased by both ischemic preconditioning (38 +/- 2%) or levosimendan pretreatment (45 +/- 2%) versus controls (52 +/- 2%). The results of this study suggest that levosimendan pretreatment is capable of decreasing infarct size in an ischemia-reperfusion model and improving recovery of cardiac function following ex vivo global ischemia.     

Serine protease inhibitor nafamostat given before reperfusion reduces inflammatory myocardial injury by complement and neutrophil inhibition

Animal data strongly support a role for inflammation in myocardial ischemia reperfusion injury. Attempts at cardioprotection by immunomodulation (such as with the specific C5 antibody pexelizumab) in humans have been disappointing. We hypothesized that a broader spectrum antiinflammatory agent might yield successful cardioprotection. The serine protease inhibitor nafamostat (FUT-175), which is already in clinical use, is a potent antiinflammatory synthetic serine protease inhibitor with anticomplement activity that we tested in a well-established rabbit model of 1 hour of myocardial ischemia followed by 3 hours of reperfusion. Compared to vehicle-treated animals, nafamostat (1 mg/kg of body weight) administered 5 minutes before reperfusion significantly reduced myocardial injury assessed by plasma creatine kinase activity (38.1 +/- 6.0 versus 57.9 +/- 3.7I U/g protein; P < 0.05) and myocardial necrosis (23.6 +/- 3.1% versus 35.7 +/- 1.0%; P < 0.05) as well as myocardial leukocyte accumulation (P < 0.05). In parallel in vitro studies, Nafamostat was a significantly more potent broad spectrum complement suppressor than C1 inhibitor. Nafamostat appears to have capability as an inhibitor of both complement pathways and as a broad-spectrum antiinflammatory agent by virtue of its serine protease inhibition. Administration of nafamostat before myocardial reperfusion after ischemia produced significant, dose-dependent cardioprotection. Reduced leukocyte accumulation and complement activity seem involved in the mechanism of this cardioprotective effect.     

Similarities between ischemic preconditioning and 17beta-estradiol mediated cardiomyocyte KATP channel activation leading to cardioprotective and antiarrhythmic effects during ischemia/reperfusion in the intact rabbit heart

The aims of our present work were to assess whether treatment with either ischemic preconditioning (IPC) or 17beta-estradiol or both combined produce proarrhythmic or antiarrhythmic effects, and whether opening of the sarcolemmal or mitochondrial KATP channels is relatable to this effect; to assess biochemically the effects of IPC and/or 17beta-estradiol on oxidant stress and antioxidant defenses in the myocardium; to examine the effects of nitric oxide (NO) synthase inhibitor, Nomega-nitro-L-arginine methyl ester (L-NAME) pretreatment in rabbits treated with either IPC or 17beta-estradiol (because 17beta-estradiol evoked NO release has been implicated in KATP activation and IPC); and examine the effects of ischemic preconditioning and 17beta-estradiol on myocardial energy metabolism during ischemia and reperfusion in a well-standardized model of reperfusion arrhythmias in anesthetized adult male New Zealand White rabbits (n = 124) subjected to 30 minutes occlusion of the left coronary artery followed by 120 minutes of reperfusion. Pretreatment with either 17beta-estradiol (10 microg/kg, i.v.) or one cycle of ischemic preconditioning prior to the period of coronary occlusion offers significant infarct size reduction (18.6 +/- 2.2% and 19.4 +/- 1.9%, respectively versus 40.1 +/- 3.9% in saline control and 39.2 +/- 3.2% in vehicle control groups; P < 0.01) and antiarrhythmic effects. Both 17beta-estradiol and ischemic preconditioning treatment significantly attenuated the incidence of life-threatening arrhythmias like sustained VT (13% and 13%, respectively versus 100% in saline control and 100% in vehicle control groups; P < 0.001) and other arrhythmias (25% and 25%, respectively versus 100% in saline control and 100% in vehicle control groups; P < 0.001), and were quite effective in increasing the number of animals that survived without developing any arrhythmia during ischemia and reperfusion. 5-hydroxydecanoate(5-HD; 5 mg/kg, i.v.) alone offered no cardioprotective and antiarrhythmic activities. Pretreatment with 5-HD but not HMR 1883 (3 mg/kg, i.v.) abolished the beneficial effects of 17beta-estradiol and ischemia preconditioning on reperfusion-induced arrhythmias and cardioprotection suggesting that such effects have been achieved via the selective activation of cardiomyocyte mitochondrial KATP channels rather than sarcolemmal KATP channels. The reduced reperfusion arrhythmic incidence and durations induced by estrogen was not significantly altered by ICI 182 720 (2.5 mg/kg, i.v.). The lack of effect of ICI 182 720 on antiarrhythmic and infarct-limiting effects of 17beta-estradiol and ischemic preconditioning suggest that these favorable effects are rapid, direct, and non-genomic effects. This study demonstrates similarities between 17beta-estradiol and ischemic preconditioning of the rabbit myocardium in terms of cardioprotection, antiarrhythmic, and metabolic activities. Ischemic preconditioning and 17beta-estradiol appear to share a final common effector; the mitochondrial KATP channel.     

Beneficial effect of sodium nitroprusside after coronary artery bypass surgery: pump function correlates inversely with cardiac release of proinflammatory cytokines

The authors studied the relationship between cardiac cytokine release and pump function and whether low-dose application of sodium nitroprusside (SNP) improves cardiac performance during coronary artery bypass graft (CABG) creation. Cardiac reperfusion and application of nitric oxide have an influence on cytokine release. However, the functional consequences are unclear. Patients with CABGs (n = 30) with severely compromised left ventricular ejection fraction (<40%) were treated with either SNP (0.5 microg/kg/min) or placebo for the first 60 minutes of reperfusion after cardiac arrest. Interleukin (IL)-6, IL-8, and tumor necrosis factor (TNF)-alpha were determined in blood samples from the radial artery and coronary sinus during reperfusion (5, 35, and 75 minutes). Hemodynamic measurements were performed before and after cardiopulmonary bypass and at the end of surgery. In all patients, the cardiac index at the end of surgery correlated negatively with levels of TNF-alpha at 5 minutes (r = 0.398; P < 0.05), IL-8 at 35 minutes (r = 0.394; P < 0.05), and IL-6 at 75 minutes of reperfusion (r = 0.421; P < 0.025). Sodium nitroprusside improved the cardiac index immediately after reperfusion (4.4 L/min/m2 +/- 0.3 vs. 3.7 L/min/m2 +/- 0.1; P = 0.014) and at the end of surgery (3.8 L/min/m2 +/- 0.3 vs. 3.0 L/min/m2 +/- 0.2; P = 0.023). The negative correlation between cardiac index and transcardiac cytokines suggests that reducing cardiac inflammatory reaction improves postischemic cardiac function. This was achieved by treating CABG patients with the nitric oxide donor SNP at a dosage without vasodilatory action.     

The calcium antagonist nisoldipine improves the functional recovery of reperfused myocardium only when given before ischemia.

It is unclear whether the protective effects of calcium antagonists on reperfused myocardium are secondary to increased blood flow during ischemia (anti-ischemic action) or reperfusion (Gregg phenomenon), or are mediated through altered calcium kinetics in ischemic or reperfused myocardium. To study the effect of the calcium antagonist nisoldipine on the functional recovery of stunned myocardium, 32 enflurane-anesthetized dogs were subjected to 15 min of occlusion of the left circumflex coronary artery and subsequent 4 h of reperfusion. Eight dogs served as placebo controls (group I), and eight dogs received nisoldipine (5 micrograms/kg i.v.) before occlusion (group II), eight dogs at 10 min of occlusion (group III), and eight dogs at 4 min of reperfusion (group IV). The mean aortic pressure was kept constant with an intra-aortic balloon, and the heart rate did not change. In group I, posterior systolic wall thickening (WT, sonomicrometry) decreased from 18.3 +/- 2.4% (mean +/- SD) during control conditions to -3.0 +/- 2.0% at 13 min of occlusion. At 10 min of reperfusion, WT was 1.7 +/- 3.9% and did not recover further (-1.2 +/- 3.7% at 4 h of reperfusion). Posterior transmural blood flow (BF, colored microspheres) decreased from 1.42 +/- 0.43 ml/min/g during control conditions to 0.26 +/- 0.08 ml/min/g at 13 min of occlusion. BF was 2.07 +/- 0.93 ml/min/g at 10 min and 0.95 +/- 0.31 ml/min/g at 4 h of reperfusion. In groups III and IV, the WT and BF were not different from those in group I throughout the experimental protocol. In group II, however, the WT, although similar to the WT of group I before and during ischemia, recovered from 2.7 +/- 4.3% at 10 min to 11.8 +/- 6.0% at 4 h of reperfusion (p less than 0.05 vs. groups I, III, and IV). The BF in group II decreased from 2.52 +/- 0.66 ml/min/g after administration of nisoldipine to 0.22 +/- 0.14 ml/min g at 13 min of occlusion. The BF was 1.31 +/- 0.51 ml/min/g at 10 min and 1.33 +/- 0.43 ml/min/g at 4 h of reperfusion. Nisoldipine exerts no beneficial effect when given immediately before or after the onset of reperfusion. The improved functional recovery of reperfused myocardium in dogs pretreated with nisoldipine cannot be attributed to an increased regional myocardial blood flow during ischemia or reperfusion. The better myocardial recovery, therefore, appears to be related to an attenuated myocardial calcium overload during the first few minutes of ischemia.     

Hemodynamic effects of combined sildenafil and L-arginine during acute pulmonary embolism-induced pulmonary hypertension

Sildenafil attenuates acute pulmonary embolism-induced pulmonary hypertension. However, the hemodynamic effects of sildenafil in combination with other vasodilators during acute pulmonary embolism have not been examined yet. In the present study, we examined the hemodynamic effects of combined sildenafil (0.25 mg/kg, i.v.) and L-arginine (100, 200, 500, and 1000 mg/kg/h, i.v.) in an anesthetized dog model of acute pulmonary embolism. Plasma nitrite/nitrate (NO(x)) and cGMP concentrations were determined using an ozone-based chemiluminescence assay and a commercial enzyme immunoassay, respectively. We found that L-arginine alone did not attenuate acute pulmonary embolism-induced pulmonary hypertension. However, significant decreases in mean pulmonary artery pressure were observed 30, 45, 60, and 75 min after the administration of sildenafil alone or after the combined administration of sildenafil and L-arginine (all P < 0.05). No significant differences among groups were observed in the respiratory parameters. While L-arginine significantly increased NO(x) concentrations, cGMP concentrations increased only when sildenafil was administered (all P < 0.05). These results suggest that while sildenafil attenuates acute pulmonary embolism-induced pulmonary hypertension, L-arginine does not enhance the beneficial hemodynamic effects of sildenafil. In addition, these findings suggest that stimulation of NO synthesis with L-arginine during acute pulmonary embolism does not produce beneficial effects.     

Effects of the cardioselective KATP channel blocker HMR 1098 on cardiac function in isolated perfused working rat hearts and in anesthetized rats during ischemia and reperfusion

It has been argued that activation of KATP channels in the sarcolemmal membrane of heart muscle cells during ischemia provides an endogenous cardioprotective mechanism. In order to test whether the novel cardioselective KATP channel blocker HMR 1098 affects cardiac function during ischemia, experiments were performed in rat hearts during ischemia and reperfusion. Isolated perfused working rat hearts were subjected to 30 min of low-flow ischemia in which the coronary flow was reduced to 10% of its control value, followed by 30-min reperfusion. In the first set of experiments the hearts were electrically paced at 5 Hz throughout the entire protocol. At the end of the 30-min ischemic period the aortic flow had fallen to 44 +/- 2% (n=8) of its nonischemic value in vehicle-treated hearts, whereas in the presence of 0.3 micromol/l and 3 micromol/l HMR 1098 it had fallen to 29 +/- 7% (n=5, not significant) and 8 +/- 2% (n=12, P<0.05), respectively. Glibenclamide (3 micromol/l) reduced the aortic flow to 9.5 +/- 7% (n=4, P<0.05). In control hearts the QT interval in the electrocardiogram shortened from 63 +/- 6 ms to 36 +/- 4 ms (n=10, P<0.05) within 4-6 min of low-flow ischemia. This shortening was completely prevented by 3 micromol/l HMR 1098 (60 +/- 5 ms before ischemia, 67 +/- 6 ms during ischemia, n=9, not significant). When rat hearts were not paced, the heart rate fell spontaneously during ischemia, and HMR 1,098 (3 micromol/l) caused only a slight, statistically non-significant reduction in aortic flow during the ischemic period. In order to investigate whether HMR 1098 shows cardiodepressant effects in a more pathophysiological model, the left descending coronary artery was occluded for 30 min followed by reperfusion for 60 min in anesthetized rats. Treatment with HMR 1098 (10 mg/kg i.v.) had no statistically significant effects on mean arterial blood pressure and heart rate during the control, ischemia and reperfusion periods. At the end of the reperfusion period, aortic blood flow was slightly reduced by HMR 1098, without reaching statistical significance (two-way analysis of ANOVA, P=0.15). Myocardial infarct size as a percentage of area at risk was not affected by HMR 1098 (vehicle: 75 +/- 3%, HMR 1098: 72 +/- 2%, n=7 in each group). In conclusion, cardiodepressant effects of HMR 1098 were observed only in isolated perfused working rat hearts which were continuously paced during global low-flow ischemia. In the model of anesthetized rats subjected to regional ischemia, HMR 1098 had no significant effect on cardiac function or infarct size.     

Antiarrhythmic effects of the angiotensin converting enzyme inhibitor perindoprilat in a pig model of acute regional myocardial ischemia.

Previous studies on the possible antiarrhythmic effects of angiotensin converting enzyme (ACE) inhibitors during early ischemia in pigs have been inconclusive or negative; however, proof of adequate ACE inhibition was not provided. Perindoprilat, 0.06 mg/kg, i.v., was administered 30 min prior to ligation of the anterior descending coronary artery (CAL) in anesthetised open-chest pigs. Plasma ACE activity was decreased by 95.0 +/- 1.9% when measured 5 min before CAL. Within 5 min of CAL, the ventricular fibrillation threshold (VFT) in the control group was decreased from 11.8 +/- 1.9 to 7.2 +/- 1.2 mA (p less than 0.01). Perindoprilat prevented the fall in the VFT and the increase in left ventricular end-diastolic pressure caused by CAL. Perindoprilat decreased arterial pressure. Cardiac output (thermodilution) was decreased by 23 +/- 3% after CAL in the control group and by only 10 +/- 5% (p less than 0.05) in the perindoprilat group (both versus pre-CAL values). In the control group cyclic AMP was increased from 0.97 +/- 0.04 (pre-CAL) to 1.16 +/- 0.04 nmol/g (p less than 0.05) in the central ischemic zone 20 min after CAL. Perindoprilat prevented this increase in cyclic AMP. Twenty minutes after CAL blood flow (microsphere method) in the nonischemic zone of the perindoprilat group was increased, whereas blood flow in the central ischemic zone was decreased compared to the control group. However, levels of tissue metabolites (ATP, phosphocreatine, lactate) measured in drill biopsies in the same zones of the two groups were similar.(ABSTRACT TRUNCATED AT 250 WORDS)     

Enhanced Na+/H+ exchange during ischemia and reperfusion impairs mitochondrial bioenergetics and myocardial function

Inhibition of Na+/H+ exchange (NHE) during ischemia reduces cardiac injury due to reduced reverse mode Na+/Ca2+ exchange. We hypothesized that activating NHE-1 at buffer pH 8 during ischemia increases mitochondrial oxidation, Ca2+ overload, and reactive O2 species (ROS) levels and worsens functional recovery in isolated hearts and that NHE inhibition reverses these effects. Guinea pig hearts were perfused with buffer at pH 7.4 (control) or pH 8 +/- NHE inhibitor eniporide for 10 minutes before and for 10 minutes after 35- minute ischemia and then for 110 minutes with pH 7.4 buffer alone. Mitochondrial NADH and FAD, [Ca2+], and superoxide were measured by spectrophotofluorometry. NADH and FAD were more oxidized, and cardiac function was worse throughout reperfusion after pH 8 versus pH 7.4, Ca2+ overload was greater at 10-minute reperfusion, and superoxide generation was higher at 30-minute reperfusion. The pH 7.4 and eniporide groups exhibited similar mitochondrial function, and cardiac performance was most improved after pH 7.4+eniporide. Cardiac function on reperfusion after pH 8+eniporide was better than after pH 8. Percent infarction was largest after pH 8 and smallest after pH 7.4+eniporide. Activation of NHE with pH 8 buffer and the subsequent decline in redox state with greater ROS and Ca2+ loading underlie the poor functional recovery after ischemia and reperfusion.     

Mildronate, a novel fatty acid oxidation inhibitor and antianginal agent, reduces myocardial infarct size without affecting hemodynamics

Mildronate is a fatty acid oxidation inhibitor approved as an antianginal drug in parts of Europe. We carried out the first study to determine whether a 10-day course of mildronate could reduce myocardial infarct size (IS) during acute myocardial ischemia. Sprague Dawley rats received 200 mg/kg/d of mildronate (treated group, n = 16) or sterile water (control group, n = 14) subcutaneously for 10 days before ischemia-reperfusion. Rats were then subjected to 45 minutes of left coronary artery occlusion and 2 hours of reperfusion. The 2 groups had identical areas at risk: treated 38 +/- 3%; controls 38 +/- 2%. The amount of necrosis was smaller in the mildronate group at 16 +/- 2% of the left ventricle versus controls, 22 +/- 2% (P = 0.05); and for any amount of risk >25%, necrosis was smaller in the treated group (P = 0.0035). Myocardial IS (% of risk zone) was 43+/-3% in the mildronate-treated rats, and 57+/-4% in controls (P = 0.004). During occlusion, there were no differences between the 2 groups in heart rate (216 +/- 12 bpm, mildronate and 210 +/- 9 bpm, control), in mean arterial pressure (60 +/- 2 mm Hg, mildronate and 64 +/- 3 mm Hg, control) or in the frequency of arrhythmias. Our study for the first time demonstrated that a 10-day treatment with mildronate reduced myocardial IS in an experimental model of acute myocardial ischemia, without any effect on hemodynamics.     

The impact of acute myocardial ischemia on the ventricular defibrillation threshold during chronic oral azimilide therapy

The effects of chronic oral azimilide therapy on the ventricular defibrillation threshold (DFT) during ischemia are unknown. The effects of azimilide on defibrillation efficacy under ischemic condition were investigated in a closed-chest animal model. Azimilide (20 mg/kg/d) was administered orally for 7 days to 10 pigs (20 to 25 kg). The control group (no treatment) comprised 15 pigs. A 2-lead defibrillation system was used. Each shock was delivered after 8 seconds of ventricular fibrillation. A step-up and step-down protocol was used to calculate mean DFT before and 10 minutes after coronary artery occlusion using an angioplasty balloon in the left descending artery. The basal DFT of the azimilide group did not differ from controls (20.8 +/- 4.8 versus 18.8 +/- 2.8; P = 0.33). After ischemia, the mean DFT of the azimilide-treated animals was similar to controls (21.8 +/- 5.2 versus 23.2 +/- 3.8 J; P = 0.54), despite significant lengthening of ventricular repolarisation (428.2 +/- 51.8 versus 494.1 +/- 46.6 msec; P = 0.005) and significant prolongation of the ventricular fibrillation cycle length (85.1 +/- 13 versus 104.7 +/- 24 msec; P < 0.04). Chronic oral azimilide treatment does not affect the DFT at baseline or during acute myocardial ischemia.     

The potential benefits of 1.5% hetastarch as a cardioplegia additive

INTRODUCTION: Myocardial edema is a clinically relevant problem found in post-ischemic reperfused hearts. The objective of this study was to understand the effects of hetastarch-supplemented cardioplegia on post-ischemic edema and cardiac function. MATERIALS AND METHODS: Swine hearts were arrested with either St. Thomas Hospital cardioplegia with (n=6) or without (n=7) 1.5% hetastarch. Following hypothermic global ischemia, hearts were crystalloid reperfused in a four-chamber isolated working mode. RESULTS: Hetastarch decreased myocardial water content gains after three hours of reperfusion (control versus hetastarch, hour 0: 67+/-5% versus 67+/-3%, NS; hour 3: 82+/-2% versus 78+/-1%, p=0.1). Post-ischemic control group left ventricular end-diastolic pressures were elevated after 1h (in mm Hg, hour 0: 13+/-2, hour 1: 19+/-3, hour 2: 19+/-3, hour 3: 20+/-2) but remained stable (<16 mm Hg) in the hetastarch group. Post-reperfusion creatine phosphokinase perfusate levels in the hetastarch treated hearts were decreased (control: 1.6 IU/l/g versus hetastarch: 0.6 IU/l/g, p=0.15). DISCUSSION/CONCLUSIONS: Hetastarch treatment delayed myocardial edema development and attenuated myocardial creatine kinase efflux, thereby preserving diastolic function.