Enhanced expression and localization of heme oxygenase-1 during recovery phase of porcine stunned myocardium

Myocardial adaptation to ischemia involves up-regulated expression of a number of genes implicated in conferring cytoprotection. We have previously shown that myocardial ischemia followed by reperfusion leads to a co-ordinated expression of mRNAs encoding heme oxygenase-1 (HO-1) and ubiquitin in pigs. HO-1 participates in biological reaction leading to the formation of the antioxidant, bilirubin and the putative cellular messenger, carbon monoxide. In the present study, we examined the expression and cellular localization of HO-1 in the heart during myocardial stunning in anesthetized pigs. After thoracotomy, the LAD was occluded for 10 min and reperfused for 30 min (group I, n = 4), again occluded for 10 min and reperfused for 30 min (group II, n = 6), 90 min (group III, n = 4), 210 min (group IV, n = 5) and for 390 min (group V, n = 4). Myocardial tissue specimens were collected in 10% formalin as well as in liquid nitrogen and processed for immunohistochemistry and mRNA expression analysis, respectively. In the distribution territory of the LAD (experimental, E), systolic wall thickening was significantly decreased (39 ± 6%) as compared to that of the area perfused by left circumflex coronary artery (LCx, control) in group I and remained depressed in all subsequent groups. Northern blot analysis revealed that the expression of a single mRNA species of 1.8 kb encoding HO-1 was significantly induced in E as compared to control in groups II and III with maximum mRNA levels in group II (1.9 ± 0.4 fold vs. control). Immunoreactive HO-1 was localized in the cytoplasm of cardiomyocytes as well as in the perivascular regions in all groups. Semiquantitative analysis of HO-1 staining showed significantly enhanced levels of HO-1 in perivascular region in E as compared to respective controls derived from groups III and IV. These results suggest that myocardial adaptive response to ischemia involves up-regulation of HO-1 in cells of perivascular region indicating that this enzyme may participate in regulating vascular tone via CO and thereby, contributing in pathophysiologically important defense mechanism(s) in the heart.     

Role of nucleoside transport and purine release in a rabbit model of myocardial stunning

Previously, we have demonstrated the role of nucleoside transport and purine release in post-ischemic reperfusion injury (myocardial stunning) in several canine models of ischemia. Since rabbits are deficient of xanthine oxidase, it is not known whether selective blockade of purine release is beneficial in a rabbit model of coronary artery occlusion and reperfusion (stunning). Therefore, we determined the hemodynamic and metabolic correlates in response to myocardial stunning in the presence or absence of selective nucleoside transport blocker (p-nitrobenzylthioinosine, NBMPR) and adenosine deaminase inhibitor (erythro-9-(2-hydroxy-3-nonyl)adenine, EHNA).Sixty adult anaesthetized rabbits were surgically prepared for hemodynamic measurements. After stabilization period, the left anterior descending coronary artery was occluded for 15 min and reperfused for 30 min. Transmural myocardial biopsies were obtained from the ischemic LAD area and from the non-ischemic posterior (circumflex, CFX) segment of the myocardium.Rabbits (n = 60) were randomly assigned to either the control or the EHNA/NBMPR-treated group (n = 30 each). Each group was further divided to either functional or metabolic groups (n = 15 each subgroup). Each animal received intravenously 30 ml of either a vehicle solution or 100 M EHNA and 25 M NBMPR 10 min before ischemia.Although administration of EHNA/NBMPR did not affect the heart rate, it did cause mild hypotension (about 20-30%). Fifteen minutes of LAD occlusion resulted in significant ATP depletion and concomitant accumulation of nucleosides in both groups (p < 0.05 vs. baseline and non-ischemic CFX segment). AMP was higher in the LAD compared to the CFX segment. Significant accumulation of adenosine was observed in the treated group compared to the control group.It is concluded that EHNA/NBMPR induced site specific entrapment of adenosine of nucleoside transport in the rabbit heart, in vivo.     

Effect of ethanol on myocardial infarct size in a canine model of coronary artery occlusion-reperfusion

This study was conducted to determine if elevated blood alcohol prior to acute coronary artery occlusion affects myocardial infarct size in an in vivo canine model. Seven pentobarbital anesthetized open-chest dogs received 10 min Iv infusion of ethanol (0.08 g/kg/min). Ten min after ethanol, the left anterior descending coronary artery (LAD) was occluded distal to its first major branch for 60 min. The LAD was then reperfused for 5 h. Following electrically induced ventricular fibrillation, the area at risk of infarction was delineated with dye. The area of infarction was identified by staining with triphenyl tetrazolium chloride. Eleven untreated control experiments were also conducted. Mean blood ethanol concentration was 155 ± 26 mg/dl just prior to LAD occlusion and 47 ± 3 mg/dl after 4 h reperfusion. Ethanol infusion had no effect on systemic hemodynamic variables during ischemia. In ethanol treated animals, the area at risk was 19.7 ± 3.0% of the left ventricle, and the infarct size was 20.9 ± 4.8% of the area at risk. In control experiments, the area at risk was 23.0 ± 4.1% of the left ventricle (p > 0.05), and the infarct size was 21.6 ± 3.8% of the area at risk (p > 0.05). Collateral blood flow to ischemic region did not differ between the two groups, and the relationships between infarct size and collateral flow were similar for control and untreated hearts. Acute ethanol exposure prior to coronary artery occlusion and subsequent reperfusion does not affect myocardial infarct size in the heart of the anesthetized dog.     

Comparison of the effects of prostaglandins E1 and A1 on coronary occlusion induced arrhythmia.

The present study compares the effects of PGE1 and PGA1 on ventricular arrhythmias following coronary artery occlusion. The left anterior descending coronary artery (LAD) was occluded abruptly in 55 cats anesthetized with alpha-chloralose. Lead II of the ECG along with arterial blood pressure were monitored for one hour after occlusion. Either vehicle or prostaglandin was infused into the left atrium (LA) or femoral vein (IV) 15 min prior to and for 1 hour after LAD occlusion at a rate of 0.15 ml/min. Prostaglandin was infused at either a high dose (1.0 microgram/kg/min) or a low dose (0.1 microgram/kg/min). Infusion of either PGE1 or PGA1 produced a marked fall in blood pressure and heart rate which returned toward control before occlusion. Abrupt occlusion of the LAD produced ventricular arrhythmia in all cats ranging from ventricular premature beats to ventricular fibrillation (VF). The control animals had a 38% incidence of VF. VF occurred in 75% of the animals in which PGE1 was administered into the LA at either the high or low dose while the occurrence in those administered PGA1 was 67% and 50%, respectively. Intravenous administration of the high dose of PGE1 or PGA1 resulted in VF in 13% and 67% of the animals after LAD occlusion, respectively. These data indicate that the IV administration of PGE1 may protect the heart from VF while the infusion of PGE1 or PGA1 into the LA may enhance VF after LAD occlusion.     

Protective effects of Curcuma longa on ischemia-reperfusion induced myocardial injuries and their mechanisms

The present study was undertaken to evaluate the cardioprotective potential of Curcuma longa (Turmeric) in the ischemia-reperfusion (I/R) model of myocardial infarction (MI). Wistar rats were divided into three groups and received saline orally (sham, control I/R group) and Curcuma longa 100 mg/kg (CL-100 treated group) respectively for one month. On the 31st day, rats of the control I/R and Cl treated groups were subjected to 45 min of occlusion of the LAD coronary artery and were thereafter reperfused for 1 h. I/R resulted in significant cardiac necrosis, depression in left ventricular function, decline in antioxidant status and elevation in lipid perodixation in the control I/R group as compared to sham control. Myocardial infarction produced after I/R was significantly reduced in the Cl treated group. Cl treatment resulted in restoration of the myocardial antioxidant status and altered hemodynamic parameters as compared to control I/R. Furthermore, I/R-induced lipid peroxidation was significantly inhibited by Cl treatment. The beneficial cardioprotective effects also translated into the functional recovery of the heart. Cardioprotective effect of Cl likely results from the suppression of oxidative stress and correlates with the improved ventricular function. Histopathological examination further confirmed the protective effects of Cl on the heart.     

Cardioprotection by HO-4038, a novel verapamil derivative, targeted against ischemia and reperfusion-mediated acute myocardial infarction

Many cardiac interventional procedures, such as coronary angioplasty, stenting, and thrombolysis, attempt to reintroduce blood flow (reperfusion) to an ischemic region of myocardium. However, the reperfusion is accompanied by a complex cascade of cellular and molecular events resulting in oxidative damage, termed myocardial ischemia-reperfusion (I/R) injury. In this study, we evaluated the ability of HO-4038, an N-hydroxypiperidine derivative of verapamil, on the modulation of myocardial tissue oxygenation (Po(2)), I/R injury, and key signaling molecules involved in cardioprotection in an in vivo rat model of acute myocardial infarction (MI). MI was created in rats by ligating the left anterior descending coronary artery (LAD) for 30 min followed by 24 h of reperfusion. Verapamil or HO-4038 was infused through the jugular vein 10 min before the induction of ischemia. Myocardial Po(2) and the free-radical scavenging ability of HO-4038 were measured using electron paramagnetic resonance spectroscopy. HO-4038 showed a significantly better scavenging ability of reactive oxygen radicals compared with verapamil. The cardiac contractile functions in the I/R hearts were significantly higher recovery in HO-4038 compared with the verapamil group. A significant decrease in the plasma levels of creatine kinase and lactate dehydrogenase was observed in the HO-4038 group compared with the verapamil or untreated I/R groups. The left ventricular infarct size was significantly less in the HO-4038 (23 +/- 2%) compared with the untreated I/R (36 +/- 4%) group. HO-4038 significantly attenuated the hyperoxygenation (36 +/- 1 mmHg) during reperfusion compared with the untreated I/R group (44 +/- 2 mmHg). The HO-4038-treated group also markedly attenuated superoxide production, increased nitric oxide generation, and enhanced Akt and Bcl-2 levels in the reperfused myocardium. Overall, the results demonstrated that HO-4038 significantly protected hearts against I/R-induced cardiac dysfunction and damage through the combined beneficial actions of calcium-channel blocking, antioxidant, and prosurvival signaling activities.     

ST段抬高性和非ST 段抬高性急性心肌梗死患者的冠状动脉病变特点比较

目的:比较ST段抬高性和非ST段抬高性急性心肌梗死患者的冠状动脉病变特点。方法:选取100例在我院接受24h动态心电图和冠状动脉造影检查的急性心肌梗死患者,根据心电图结果分为观察组和对照组各50例。对照组为ST段抬高性心肌梗死(STEMI)患者,观察组为非ST段抬高性心肌梗死(NSTEMI)患者,比较两组患者冠状动脉病变的差异。结果:对照组LAD(左前降支)闭塞血管比例(52.00%)显著高于观察组(18.00%),差异具有统计学意义(P0.05)。对照组LCX(回旋支)闭塞血管比例(8.00%)显著低于观察组(50.00%),差异具有统计学意义(P0.05)。对照组RCA(右冠脉主干)闭塞血管比例(40.00%)和观察组(30.00%)比较,差异无统计学意义(P0.05)。对照组单支病变比例(46.00%)明显高于观察组(12.00%),对照组三支病变比例(20.00%)明显低于观察组(48.00%)比较,差异均具有统计学意义(P0.05)。对照组二支及正常血管比例与观察组比较,差异均无统计学意义(P0.05)。对照组罪犯血管狭窄程度在76%-90%、91%-99%及完全闭塞的比例与观察组比较差异均具有统计学意义(P0.05)。罪犯血管狭窄程度在50%及50%-75%时,两组差异无统计学意义(P0.05)。两组并发症发生情况比较,差异无统计学意义(P0.05)。结论:1NSTEMI罪犯血管闭塞以LCX多见,STEMI罪犯血管闭塞以LAD多见;2NSTEMI以三支血管病变较多见,STEMI以单支病变较多见。     

Biochemical mechanism(s) of stunning in conscious dogs

The mechanism(s) underlying contractile dysfunction in cardiac stunning is not completely understood. The expression and/or the phosphorylation state of cardiac Ca(2+) homoeostasis-regulating proteins might be altered in stunning. We tested this hypothesis in a well-characterized model of stunning. Conscious dogs were chronically instrumented, and the left anterior descending artery (LAD) was occluded for 10 min. Thereafter, reperfusion of the LAD was initiated. Tissues from reperfused LAD (stunned) and Ramus circumflexus (control) areas were obtained when left ventricular regional wall thickening fraction had recovered by 50%. Northern and Western blotting revealed no differences in the expression of the following genes: phospholamban, calsequestrin, sarco(endo)plasmic reticulum Ca(2+)-ATPase 2a, and the inhibitory subunit of troponin I (TnI). However, the phosphorylation state of TnI and phospholamban were reduced in the LAD area. Fittingly, cAMP levels were reduced by 28% (P < 0.05). It is concluded that the contractile dysfunction in cardiac stunning might be mediated in part by decreased levels of cAMP and subsequently a reduced phosphorylation state of phospholamban and TnI.     

Exercise training improves endothelium-mediated vasorelaxation after chronic coronary occlusion.

The present study evaluated combined effects of chronic coronary occlusion and exercise training on endothelial function. Gradual occlusion was produced by placement of an ameroid constrictor around the proximal left circumflex (LCX) coronary artery of female swine. Two months after placement of the ameroid, animals were restricted to their pens or exercise trained for 16 wk. Epicardial arteries (>500 microm ID) were isolated from the collateral-dependent LCX coronary artery distal to the occlusion and the nonoccluded left anterior descending (LAD) coronary artery. Bradykinin- and ADP-mediated relaxation of LCX and LAD coronary arteries was enhanced after exercise training. Inhibition of nitric oxide synthase with N(G)-nitro-L-arginine methyl ester decreased bradykinin- and ADP-mediated relaxation in LCX and LAD myocardial regions. Importantly, combined inhibition of effects of endothelium-derived hyperpolarizing factor with increased extracellular K(+) (20-30 mM) and nitric oxide synthase completely abolished coronary LAD and LCX relaxation to bradykinin. Our data indicate that exercise training improves endothelium-mediated relaxation of arteries isolated after chronic coronary artery occlusion, likely as a result of enhanced production of nitric oxide and endothelium-derived hyperpolarizing factor.     

Heme oxygenase-1 and the ischemia-reperfusion injury in the rat heart

Carbon monoxide (CO) is a signaling gas produced intracellularly by heme oxygenase (HO) enzymes using heme as a substrate. During heme breakdown, HO-1 and HO-2 release CO, biliverdin, and Fe(2+). In this study, we investigated the effects of manipulation of the HO-1 system in an in vivo model of focal ischemia-reperfusion (FIR) in the rat heart. Male Wistar albino rats, under general anesthesia and artificial ventilation, underwent thoracotomy, the pericardium was opened, and a silk suture was placed around the left descending coronary artery; ischemia was induced by tightening the suture and was monitored for 30 min. Subsequently, the ligature was released to allow reperfusion lasting for 60 min. The first group of rats was sham operated and injected intraperitoneally (i.p.) with saline. The second group underwent FIR. The third group was treated ip 18 hr before FIR with hemin (4 mg/kg). The fourth group was pretreated ip 24 hr before FIR and 6 hr before hemin with zinc protoporphyrin IX (ZnPP-IX, 50 microg/kg). Specimens of the left ventricle were taken for determination of HO expression and activity, infarct size, malonyldialdehyde (MDA) production, and tissue calcium content. FIR led to a significant increase in the generation of MDA and notably raised tissue calcium levels. Induction of HO-1 by hemin significantly decreased infarct size, incidence of reperfusion arrhythmias, MDA generation, and calcium overload induced by FIR. These effects were prevented by the HO-1 inhibitor ZnPP-IX. The present experiments show that the concerted actions of CO, iron, and biliverdin/bilirubin modulate the FIR-induced myocardial injury.     

Heme oxygenase-1-derived bilirubin ameliorates postischemic myocardial dysfunction

Bilirubin is a potent antioxidant generated intracellularly during the degradation of heme by the enzyme heme oxygenase. The purpose of this study was to determine the role of increased cardiac bilirubin in protection against postischemic myocardial dysfunction. Rat hearts were isolated and perfused according to the Langendorff technique to evaluate the recovery of myocardial function after 30 min of global ischemia and 60 min of reperfusion. We found that upregulation of the inducible isoform of heme oxygenase (HO-1) by treatment of animals with hemin 24 h before ischemia ameliorated myocardial function and reduced infarct size (tetrazolium staining) on reperfusion of isolated hearts. Tin protoporphyrin IX, an inhibitor of heme oxygenase activity, completely abolished the improved postischemic myocardial performance observed after hemin-mediated HO-1 induction. Likewise, cardiac tissue injury was exacerbated by treatment with tin protoporphyrin IX. Increased cardiac HO-1 expression and heme oxygenase activity were associated with enhanced tissue bilirubin content and an increased rate of bilirubin release into the perfusion buffer. Furthermore, exogenously administered bilirubin at concentrations as low as 100 nanomolar significantly restored myocardial function and minimized both infarct size and mitochondrial damage on reperfusion. Our data provide strong evidence for a primary role of HO-1-derived bilirubin in cardioprotection against reperfusion injury.     

Inhibition of myocardial injury by ischemic postconditioning during reperfusion: comparison with ischemic preconditioning

Ischemic preconditioning (Pre-con) is an adaptive response triggered by a brief ischemia applied before a prolonged coronary occlusion. We tested the hypothesis that repetitive ischemia applied during early reperfusion, i.e., postconditioning (Post-con), is cardio-protective by attenuating reperfusion injury. In anesthetized open-chest dogs, the left anterior descending artery (LAD) was occluded for 60 min and reperfused for 3 h. In controls (n = 10), there was no intervention. In Pre-con (n = 9), the LAD was occluded for 5 min and reperfused for 10 min before the prolonged occlusion. In Post-con (n = 10), at the start of reperfusion, three cycles of 30-s reperfusion and 30-s LAD reocclusion preceded the 3 h of reperfusion. Infarct size was significantly less in the Pre-con (15 +/- 2%, P < 0.05) and Post-con (14 +/- 2%, P < 0.05) groups compared with controls (25 +/- 3%). Tissue edema (% water content) in the area at risk was comparably reduced in Pre-con (78.3 +/- 1.2, P < 0.05) and Post-con (79.7 +/- 0.6, P < 0.05) versus controls (81.5 +/- 0.4). Polymorphonuclear neutrophil (PMN) accumulation (myeloperoxidase activity, Deltaabsorbance.min-1.g tissue-1) in the area at risk myocardium was comparably reduced in Post-con (10.8 +/- 5.5, P < 0.05) and Pre-con (13.4 +/- 3.4, P < 0.05) versus controls (47.4 +/- 15.3). Basal endothelial function measured by PMN adherence to postischemic LAD endothelium (PMNs/mm2) was comparably attenuated by Post-con and Pre-con (15 +/- 0.6 and 12 +/- 0.6, P < 0.05) versus controls (37 +/- 1.5), consistent with reduced expression of P-selectin on coronary vascular endothelium in Post-con and Pre-con. Endothelial function assessed by the maximal vasodilator response of postischemic LAD to acetylcholine was significantly greater in Post-con (104 +/- 6%, P < 0.05) and Pre-con (109 +/- 5%, P < 0.05) versus controls (71 +/- 8%). Plasma malondialdehyde (microM/ml), a product of lipid peroxidation, was significantly less at 1 h of reperfusion in Post-con (2.2 +/- 0.2, P < 0.05) versus controls (3.2 +/- 0.3) associated with a decrease in superoxide levels revealed by dihydroethidium staining in the myocardial area at risk. These data suggest that Post-con is as effective as Pre-con in reducing infarct size and preserving endothelial function. Post-con may be clinically applicable in coronary interventions, coronary artery bypass surgery, organ transplantation, and peripheral revascularization where reperfusion injury is expressed.     

Comparison of the effects of prostaglandins E1 and A1 on coronary occlusion induced arrhythmia

The present study compares the effects of PGE₁ and PGA₁ on ventricular arrhythmias following coronary artery occlusion. The left anterior descending coronary artery (LAD) was occluded abruptly in 55 cats anesthetized with α-chloralose. Lead II of the ECG along with arterial blood pressure were monitored for one hour after occlusion. Either vehicle or prostaglandin was infused into the left atrium (LA) or femoral vein (IV) 15 min prior to and for 1 hour after LAD occlusion at a rate of 0.15 ml/min. Prostaglandin was infused at either a high dose (1.0 μg/kg/min) or a low dose (0.1 μg/kg/min). Infusion of either PGE₁ or PGA₁ produced a marked fall in blood pressure and heart rate which returned toward control before occlusion. Abrupt occlusion of the LAD produced ventricular arrhythmia in all cats ranging from ventricular premature beats to ventricular fibrillation (VF). The control animals had a 38% incidence of VF. VF occurred in 75% of the animals in which PGE₁ was administered into the LA at either the high or low dose while the occurrence in those administered PGA₁ was 67% and 50%, respectively. Intravenous administration of the high dose of PGE₁ or PGA₁ resulted in VF in 13% and 67% of the animals after LAD occlusion, respectively. These data indicate that the IV administration of PGE₁ may protect the heart from VF while the infusion of PGE₁ or PGA₁ into the LA may enhance VF after LAD occlusion.     

Evaluation of BM-573, a novel TXA2 synthase inhibitor and receptor antagonist, in a porcine model of myocardial ischemia-reperfusion

AIMS: To investigate whether BM-573 (N-tert-butyl-N'-[2-(4'-methylphenylamino)-5-nitro-benzenesulfonyl]urea), an original combined thromboxane A2 synthase inhibitor and receptor antagonist, prevents reperfusion injury in acutely ischemic pigs. METHODS: Twelve animals were randomly divided in two groups: a control group (n = 6) intravenously infused with vehicle, and a BM-573-treated group (n = 6) infused with BM-573 (10 mg kg(-1) h(-1)). In both groups, the left anterior descending (LAD) coronary artery was occluded for 60 min and reperfused for 240 min. Either vehicle or BM-573 was infused 30 min before LAD occlusion and throughout the experiment. Platelet aggregation induced by arachidonic acid ex vivo measured was prevented by BM-573. RESULTS: In both groups, LAD occlusion decreased cardiac output, ejection fraction, slope of stroke work--end-diastolic volume relationship, and induced end-systolic pressure-volume relationship (ESPVR) rightward shift, while left ventricular afterload increased. Ventriculo-arterial coupling and mechanical efficiency decreased. In both groups, reperfusion further decreased cardiac output and ejection fraction, while ESPVR displayed a further rightward shift. Ventriculo-arterial coupling and mechanical efficiency remained impaired. Area at risk, evidenced with Evans blue, was 33.2+/-3.4% of the LV mass (LVM) in both groups, and mean infarct size, revealed by triphenyltetrazolium chloride (TTC), was 27.3+/-2.6% of the LVM in the BM-573-treated group (NS). Histological examination and immunohistochemical identification of desmin revealed necrosis in the anteroseptal region similar in both groups, while myocardial ATP dosages and electron microscopy also showed that BM-573 had no cardioprotective effect. CONCLUSIONS: These data suggest that BM-573 failed to prevent reperfusion injury in acutely ischemic pigs.     

Substance P distribution and effects in the canine epicardial coronary arteries

Substance P (SP), a vasoactive neuropeptide detected in animal and human hearts has been reported to increase coronary blood flow in animals. However, no data are available on SP effects on epicardial coronary arteries, the site of coronary disease. To determine the amount and distribution of SP and its action in the large coronary vessels, we studied two groups of dogs. One group was anesthetized for collecting three 1 cm segments of the circumflex coronary artery (CX) and left anterior descending artery (LAD) through a left thoracotomy. These segments represented proximal (I), middle (II), and distal (III) portions of the two arteries. Concentrations (ng/g) of SP-like immunoreactivity (SP-LI) were determined by radioimmunoassay. SP-LI was present in LAD (I: 1.17 +/- 0.20, II: 1.08 +/- 0.36, III: 1.14 +/- 0.25) and CX (I: 1.44 +/- 0.38, II: 1.51 +/- 0.47, III: 0.70 +/- 0.20). SP differences among segments of LAD and segments I and II of CX were not significant, but there was a significant difference between segment III of CX and the others. In the second group of closed chest anesthetized dogs, we examined the effects of intracoronary SP infusion before and during administration of serotonin (5HT). LAD and CX artery responses (% area change) to SP and to SP plus 5HT were examined using quantitative coronary angiography. Intracoronary 133Xe in saline provided coronary flow data. SP infusion produced significant vasodilation in segment II (15% area increase) and III (17%) during the highest dose (1 microgram/min). The three SP doses infused with 5HT (0.05 mg/min) did not produce vasodilation, although LAD segment III constriction from 5HT was abolished during the highest dose of SP infusion. The presence of SP, and its dilatory effect on the coronary arteries, suggests a role in maintaining vasodilator tone in the coronary arteries.     

Metabolic protection of the reperfused canine endocardium by the thromboxane synthetase inhibitor, dazoxiben

This study investigated whether dazoxiben, a thromboxane synthesis inhibitor, could reverse regional contractile dysfunction and protect against adenine nucleotide loss in the "stunned myocardium". Hearts from anesthetized dogs were "stunned" by 15 min of left anterior descending coronary artery occlusion followed by 3 hr of reperfusion. Left ventricular segment shortening (%SS) and regional myocardial blood flow (RMBF) were measured by sonomicrometry and the radioactive microsphere technique, respectively. Local coronary venous blood was withdrawn and thromboxane A2 and prostacyclin measured by radioimmunoassay. Transmural biopsies from the reperfused and nonischemic areas were taken at 3 hr following reperfusion for tissue metabolite analysis. During ischemia, %SS, RMBF and area at risk were decreased to similar levels in both control and dazoxiben-treated hearts indicating equivalent degrees of flow deprivation. During reperfusion, %SS recovered only partially and was not significantly improved by dazoxiben. Dazoxiben augmented peak prostacyclin production (123 +/- 31% vs. 292 +/- 49% of preocclusion values) following reperfusion, while it completely blocked thromboxane A2 production. Dazoxiben attenuated the decline in endocardial ATP (69 +/- 5% vs. 92 +/- 9% normalized to the nonischemic zone) and total adenine nucleotides. The results indicate that dazoxiben may elicit a cardioprotective effect on energy metabolism in the reperfused heart, but this is dissociated from any improvement in regional contractile function.     

Investigating the dual nature of endothelin-1: ischemia or direct arrhythmogenic effect?

Endothelin-1 (ET-1) is a potent vasoconstrictor peptide, which may also elicit severe ventricular arrhythmias. The aims of our study were to compare the effects of total left anterior descending coronary artery (LAD) occlusion to intracoronary (ic.) ET-1 administration and to investigate the pathomechanism of ET-1 induced arrhythmias in 3 groups of anesthetized, open-chest mongrel dogs. In group A (n=10) a total LAD occlusion was carried out for 30 min, followed by a 60 min reperfusion period. In groups B and C ET-1 was administered into LAD for 30 min at a rate of 30 pmol/min (n=6) and 60 pmol/min (n=8). Epi- and endocardial monophasic action potential (MAP) recordings were performed to detect electrophysiologic changes and ischemia Blood samples for lactate measurements were collected from the coronary sinus (CS) and from the femoral artery. Infrared imaging was applied to follow epimyocardial heat emission changes. At the end of the ET-1 infusion period coronary blood flow (CBF) was reduced significantly in groups B and C (deltaCBF30MIN B: 21+/-2%, p<0.05; C: 35+/-2%, p<0.05), paralleled by a significant epimyocardial temperature decrease in group C (deltaT30MIN: -0.65+/-0.29 degrees C, p<0.05). Two dogs died of ventricular fibrillation (VF) in the reperfusion period in group A. Ventricular premature contractions and non-sustained ventricular tachycardic episodes appeared in group B, whereas six dogs died of VF in group C. Significant CS lactate level elevation indicating ischemia was observed only in group A from the 30th min occlusion throughout the reperfusion period (control vs. 30 min: 1.3+/-0.29 vs. 2.2+/-0.37 mmol/l, p<0.05). Epi- and endocardial MAP durations (MAPD90) and left ventricular epicardial (LV(EPI)) upstroke velocity decreased significantly in group A in the occlusion period. ET-1 infusion significantly increased LV(EPI) MAPD90 in group B and both MAPD90-s in group C. In conclusion, ischemic MAP and CS lactate changes were observed only in group A. Although ET-1 reduced CBF significantly in groups B and C, neither MAP nor lactate indicated ischemic alterations. ET-1 induced major ventricular arrhythmias appeared before signs of myocardial ischemia developed, though reduced CBF presumably contributed to sustaining the arrhythmias.     

Cardioprotective effect induced by brief exposure to nitric oxide before myocardial ischemia-reperfusion in vivo.

Administration of nitric oxide (NO) donors during ischemia and reperfusion protects from myocardial injury. However, whether administration of an NO donor during a brief period prior to ischemia protects the myocardium and the endothelium against ischemia-reperfusion injury in vivo is unknown. To study this possibility anesthetized pigs were subjected to 45-min ligation of the left anterior descending coronary artery (LAD) followed by 4h of reperfusion. In initial dose-finding experiments, vehicle or three different doses of the NO donor S-nitroso-N-acetyl-D,L-penicillamin (SNAP; 0.1; 0.5; 2.5 micromol) were infused into the LAD for 3 min starting 13 min during ischemia. Only the 0.5 micromol dose of SNAP reduced infarct size (from 85+/-3% of the area at risk in the vehicle group to 63+/-3% in the SNAP-treated group; p<0.01). There were no significant differences in hemodynamics in the vehicle and SNAP groups during ischemia-reperfusion. Endothelium-dependent dilatation of coronary microvasculature induced by substance P was larger in the SNAP group than in the vehicle group. Myeloperoxidase activity was lower in the ischemic/reperfused myocardial area of pigs given SNAP (4.97+/-0.61 U/g) than in vehicle-treated pigs (8.45+/-0.25 U/g; p<0.05). It is concluded that intracoronary administration of the NO donor SNAP for a brief period before ischemia reduces infarct size, attenuates neutrophil accumulation, and improves endothelial function. These results suggest that NO exerts a classic preconditioning-like protection against ischemia-reperfusion injury in vivo in a narrow concentration range.     

Pyruvate provides cardioprotection in the experimental model of myocardial ischemic reperfusion injury

The present study was designed to evaluate the cardioprotective potential of pyruvate and to characterize the mechanism underlying the protection. Wistar albino rats were randomly divided into three groups. Two groups were administered saline orally (sham, ischemia-reperfusion (I-R) control group) and animals of third group received pyruvate (500 mg/kg) for 4 weeks. On the 29th day, animals of the I-R control and pyruvate treated groups underwent 45 min of occlusion of the left anterior descending (LAD) coronary artery and were thereafter reperfused for 60 min. In the I-R control group, a significant cardiac necrosis, depressed mean arterial pressure (MAP) and heart rate (HR), decline in myocardial antioxidant status and elevation in lipid peroxidation were observed as compared to sham control. Pyruvate treatment restored the myocardial antioxidant status and favorably modulated the altered MAP as compared to I-R control. Furthermore, I/R-induced lipid peroxidation was significantly inhibited by pyruvate treatment. These beneficial cardioprotective effects translated into significant improvement in MAP. Histopathological examination and restored specific myocardial injury marker CK-MB isoenzyme activity further confirmed protective effects of pyruvate. In conclusion, our study has demonstrated that the beneficial effect of pyruvate likely results from improved MAP and suppression of oxidative stress.     

The role of heme oxygenase-related carbon monoxide and ventricular fibrillation in ischemic/reperfused hearts

Reperfusion-induced ventricular fibrillation (VF) and heme oxygenase (HO)-related carbon monoxide (CO) production in isolated ischemic/reperfused rat hearts were studied by gas chromatography. Hearts were subjected to 30 min ischemia followed by 2 h reperfusion, and the expression of HO-1 mRNA (about 4-fold) was observed in ischemic/reperfused-nonfibrillated hearts. In fibrillated hearts, the reduction (about 75%) in HO-1 mRNA expression was detected. These changes in HO-1 mRNA expression were reflected in tissue CO production. Thus, in the absence of VF, CO production was increased about 3.5-fold, while in the presence of VF, CO production was under the detectable level in comparison with the control group. Our results suggest that the stimulation of HO-1 mRNA expression may lead to the prevention of reperfusion VF via an increase in endogenous CO production. To prove this, hearts were treated with 1 microM of N-tert-butyl-alpha-phenylnitrone (PBN) as an inducer of HO-1. PBN treatment resulted in about 20 times increase in HO-1 mRNA expression, and even a higher production rate in endogenous CO. HO protein level and enzyme activity followed the same pattern, as it was observed in HO-1 mRNA expression, in fibrillated and nonfibrillated myocardium. Five mM/l of zinc-protoporphyrin IX (ZnPPIX) significantly blocked HO enzyme activity and increased the incidence of VF, therefore the application of ZnPPIX led to a significant reduction in HO-1 mRNA and protein expression. Our data provide direct evidence of an inverse relationship between the development of reperfusion-induced VF and endogenous CO production. Thus, interventions that are able to increase tissue CO content may prevent the development of reperfusion-induced VF.