Coronary endothelial dysfunction from ischemia and reperfusion: effect of reactive oxygen metabolite scavengers

Using anesthetized mongrel dogs exposed to 60 min of ligation of the left anterior descending coronary artery followed by 60 min of reperfusion, we examined the effect of superoxide dismutase (SOD) and dimethylthiourea (DMTU) on evidence of endothelial injury in coronary rings studied in vitro. In 13 dogs treated with saline rings from the normal left circumflex coronary artery (LCF) relaxed by 98 +/- 4% when exposed to 10(-5) M acetylcholine whereas rings from the left anterior descending coronary artery (LAD) relaxed by 79 +/- 7% (p less than 0.05). In the same rings maximum relaxation with the ionophore A23187 was 107 +/- 5% versus 87 +/- 8% (p less than 0.05) for the LCF and the LAD, respectively. Comparisons of concentration-response curves through a range of doses of both acetylcholine and A23187 revealed significant differences for both vasodilators between the LCF and the LAD (p less than 0.01 for each). Nine dogs were treated with bovine SOD infused in the left atrium the last 20 min of ligation and throughout reperfusion (140 units/kg/min) and six other dogs were treated with DMTU 500 mg/kg i.v. given the last 30 min of the ligation period. Neither SOD nor DMTU prevented endothelial injury in the LAD. Despite pretreatment with these agents, there were significant reductions in maximum relaxation and in total concentration-response curves in the LAD as compared with the results in rings from the LCF with both acetylcholine and A23187. There were normal responses to nitroprusside in both the LCF and LAD in all three experimental groups.(ABSTRACT TRUNCATED AT 250 WORDS)     

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.     

褐毛甘西鼠尾注射液对大鼠在体心肌缺血再灌注损伤的保护作用

本实验与丹参进行对比研究云南产鼠尾草属药物褐毛甘西鼠尾对急性心肌缺血再灌注损伤的保护作用。采用结扎大鼠冠脉左前降支方法造成心肌缺血再灌注模型,测定再灌注60 min后血清中CK、LDH、SOD、GSH-Px和MDA含量。实验结果显示:该药可以显著降低心肌缺血再灌注后血清CK、LDH和MDA含量,升高血清SOD和GSH-Px活力(P<0.01,P<0.05)。表明褐毛甘西鼠尾对在体缺血/再灌注心肌有保护作用。     

Catecholamine release and ventricular arrhythmias during coronary occlusion and reperfusion in the dog

In anesthetized dogs, 60-min occlusions of either the proximal (n = 14), distal (n = 8) left circumflex (LCX), or left anterior descending (LAD, n = 10) arteries were followed by reperfusion. Coronary sinus and aortic norepinephrine and epinephrine plasma concentrations were measured. The ventricular arrhythmias were ventricular premature depolarizations (VPDs), unsustained ventricular tachycardia (VT) (greater than or equal to 3 and less than 20 VPDs), sustained VT (greater than or equal to 20 VPDs), and ventricular fibrillation (VF). A gradual twofold increase (p less than 0.05) in myocardial norepinephrine overflow followed occlusion in all three groups. The increases in the amounts of norepinephrine released in the coronary sinus blood during reperfusion were significant and proportional to the size of the occluded area: proximal LCX, from 0.236 +/- 0.038 to 1.528 +/- 0.490 ng/mL of plasma (p less than 0.001); LAD, from 0.180 +/- 0.027 to 0.795 +/- 0.286 ng/mL (p less than 0.05); distal LCX, from 0.215 +/- 0.039 to 0.404 +/- 0.110 ng/mL (p less than 0.05). Aortic epinephrine concentrations were significantly increased only by LAD occlusion; at 15 min, the value had increased to 0.187 +/- 0.053 ng/mL from an initial value of 0.069 +/- 0.029 ng/mL (p less than 0.001). Two phases of ventricular arrhythmias followed both occlusion and reperfusion. Phase 1 postocclusion was characterized by VPDs and phase 2 by VPDs and unsustained VT. Sustained VT was seen only in phase 1 postreperfusion, whereas unsustained VT was seen in phase 2. VF was seen in 50, 35, and 25% of the dogs with proximal LCX, LAD, and distal LCX occlusion and reperfusion.(ABSTRACT TRUNCATED AT 250 WORDS)     

Chronic exercise training preserves prostaglandin-induced dilation of epicardial coronary artery during development of heart failure in awake dogs

Although it has been shown that long-term exercise training preserves endothelium-mediated nitric oxide vasodilator function in chronic heart failure (CHF), whether exercise training exerts similar beneficial effects on endothelial/prostaglandin-mediated vasodilator capacity in coronary circulation during the development of CHF has not been determined. Fifteen mongrel dogs were surgically instrumented for measurement of left ventricular pressure, aortic pressure, coronary blood flow and left circumflex coronary artery diameter. Dogs (n = 5) who underwent 4 weeks of cardiac pacing (210 b/min for 3 weeks and 240 b/min for the 4th week) developed CHF as characterized by significant reduction in left ventricular systolic pressure, mean arterial pressure and left ventricular dP/dt, increases in left ventricular end-diastolic pressure and heart rate, as well as clinical signs of CHF. Endothelial prostaglandin-mediated vasodilation of the epicardial coronary artery was impaired, as manifested by an attenuated arachidonic acid (AA)-induced dilation of the artery (epicardial artery diameter increased by: 0.78 +/- 0. 84% in CHF versus 4.6 +/- 0.89% in normal, P < 0.05); however, prostacyclin (PGI(2))-induced and nitroglycerin-induced vasodilation of the coronary circulation were not altered. In contrast, dogs (n = 6) with cardiac pacing plus daily exercise training (4.4 +/- 0.3 km/h, 2 h/day) only developed mild cardiac dysfunction, and the response of the epicardial coronary artery diameter to AA was preserved (epicardial artery diameter increased by 4.2 +/- 0.98% from baseline, P 0.05 compared to its respective control). Thus, long-term exercise training preserves endothelial/prostaglandin-mediated dilation of epicardial coronary artery during development of CHF.     

Difference in the relation between infarct and occluded bed in pentobarbital-anesthetized and conscious dogs

The relationship between myocardial infarct size (IS) and occluded bed size (OBS) in pentobarbital-anesthetized (A, n = 16) and conscious (C, n = 20) dog models were compared. IS and OBS (postmortem coronary arteriography) were measured by computerized planimetry of weighed left ventricular (LV) rings 7 days after permanent left anterior descending (LAD, n = 19) or circumflex (LC, n = 17) coronary artery occlusion. For both A and C groups, IS was directly related to OBS (p less than 0.001) and no infarcts developed for small occluded beds. For either LAD or LC subgroups, infarcts were larger in A than C dogs (49 +/- 18 vs. 30 +/- 19% OBS, p less than 0.025), with greater slope of the linear regression between IS and OBS (p less than 0.001) and less epicardial sparing on topographic mapping (p less than 0.05). Although postocclusion mean arterial and left atrial pressures were similar in A and C groups, heart rates were greater in the A dogs, both pre- (125 vs. 88 beats/min, p less than 0.001) and post-occlusion (151 vs. 108 beats/min, p less than 0.001). Endocardial flows (radioactive microspheres) in infarct centers and margins were less in A than C dogs. Also, endocardial/epicardial (endo/epi) flow ratios in all regions were less in A than C dogs, both pre- and post-occlusion. Increasing heart rate in 10 other C dogs with LAD occlusion to that of the A group (151 beats/min) by right ventricular pacing resulted in larger infarcts with greater slope of the linear regression and less endo/epi flow ratios, as in the A group.(ABSTRACT TRUNCATED AT 250 WORDS)     

Cardioprotection by adenosine A2A agonists in a canine model of myocardial stunning produced by multiple episodes of transient ischemia

We sought to determine whether administration of a very low, nonvasodilating dose of a highly selective adenosine A(2A) receptor agonist (ATL-193 or ATL-146e) would be cardioprotective in a canine model of myocardial stunning produced by multiple episodes of transient ischemia. Twenty-four anesthetized open-chest dogs underwent either 4 (n=12) or 10 cycles (n=12) of 5-min left anterior descending coronary artery (LAD) occlusions interspersed by 5 or 10 min of reperfusion. Left ventricular thickening was measured from baseline through 180 min after the last occlusion-reperfusion cycle. Regional flow was measured with microspheres. In 12 of 24 dogs, A(2A) receptor agonist was infused intravenously beginning 2 min prior to the first occlusion and continuing throughout reperfusion at a dose below that which produces vasodilatation (0.01 microg x kg(-1) x min(-1)). Myocardial flow was similar between control and A(2A) receptor agonist-treated animals, confirming the absence of A(2) receptor agonist-induced vasodilatation. During occlusion, there was severe dyskinesis with marked LAD zone thinning in all animals. After 180 min of reperfusion following the last cycle, significantly greater recovery of LAD zone thickening was observed in A(2A) receptor agonist-treated vs. control animals in both the 4-cycle (91 +/- 7 vs. 56 +/- 12%, respectively; P<0.05) and the 10-cycle (65 +/- 9 vs. 8 +/- 16%, respectively; P<0.05) occlusion groups. The striking amount of functional recovery observed with administration of low, nonvasodilating doses of adenosine A(2A) agonist ATL-193 or ATL-146e supports their further evaluation for the attenuation of postischemic stunning in the clinical setting.     

高氧液预处理对兔心肌缺血再灌注损伤的影响

目的:研究高氧液预处理对兔心肌缺血再灌注损伤的影响。方法:雄性新西兰白兔32只,随机分为4组(n=8),结扎-开放冠状动脉左前降支(LAD)建立心肌缺血再灌注模型。假手术组(Sham组)只穿线环绕LAD不结扎;吸氧组(OX组)结扎前30 min经鼻吸纯氧2L/min;在结扎LAD前30 min分别静脉注射HO 10 ml/kg(HO1组)、20 ml/kg(HO2组)。于结扎LAD前即刻(T0,基础值)、开放LAD前即刻(T1)、再灌注60 min(T2)及再灌注120 min(T3)时记录HR和MAP,于T3时抽取动脉血样3 ml,测定血清肌酸激酶(CK)、肌钙蛋白I(cTNI)的活性和IL-6和TNF-α的浓度,并测定心肌梗死范围。结果:I/S组与T0时比较,T 1-3时各组HR、MAP进行性下降(P<0.05);三组间HR、MAP比较差异无统计学意义(P>0.05)。与Sham组比较,I/S组血清CK、cTNI、IL-6和TNF-α含量明显升高(P 0.01);与OX组比较,HO2组上述酶及炎症因子浓度显著下降(P<0.01),心肌梗死范围减小(P<0.05)。结论:高氧液预处理可减轻兔心肌缺血再灌注损伤,机制可能与其抑制炎性反应有关。     

Coronary smooth muscle reactivity to muscarinic stimulation after ischemia-reperfusion in porcine myocardial infarction.

This study tested whether ischemia-reperfusion alters coronary smooth muscle reactivity to vasoconstrictor stimuli such as those elicited by an adventitial stimulation with methacholine. In vitro studies were performed to assess the reactivity of endothelium-denuded infarct-related coronary arteries to methacholine (n = 18). In addition, the vasoconstrictor effects of adventitial application of methacholine to left anterior descending (LAD) coronary artery was assessed in vivo in pigs submitted to 2 h of LAD occlusion followed by reperfusion (n = 12), LAD deendothelization (n = 11), or a sham operation (n = 6). Endothelial-dependent vasodilator capacity of infarct-related LAD was assessed by intracoronary injection of bradykinin (n = 13). In vitro, smooth muscle reactivity to methacholine was unaffected by ischemia-reperfusion. In vivo, baseline methacholine administration induced a transient and reversible drop in coronary blood flow (9.6 +/- 4.6 to 1.9 +/- 2.6 ml/min, P < 0.01), accompanied by severe left ventricular dysfunction. After ischemia-reperfusion, methacholine induced a prolonged and severe coronary blood flow drop (9.7 +/- 7.0 to 3.4 +/- 3.9 ml/min), with a significant delay in recovery (P < 0.001). Endothelial denudation mimics in part the effects of methacholine after ischemia-reperfusion, and intracoronary bradykinin confirmed the existence of endothelial dysfunction. Infarct-related epicardial coronary artery shows a delayed recovery after vasoconstrictor stimuli, because of appropriate smooth muscle reactivity and impairment of endothelial-dependent vasodilator capacity.     

A3 adenosine receptor agonist IB-MECA reduces myocardial ischemia-reperfusion injury in dogs

We examined the effect of the A3 adenosine receptor (AR) agonist IB-MECA on infarct size in an open-chest anesthetized dog model of myocardial ischemia-reperfusion injury. Dogs were subjected to 60 min of left anterior descending (LAD) coronary artery occlusion and 3 h of reperfusion. Infarct size and regional myocardial blood flow were assessed by macrohistochemical staining with triphenyltetrazolium chloride and radioactive microspheres, respectively. Four experimental groups were studied: vehicle control (50% DMSO in normal saline), IB-MECA (100 microg/kg iv bolus) given 10 min before the coronary occlusion, IB-MECA (100 microg/kg iv bolus) given 5 min before initiation of reperfusion, and IB-MECA (100 microg/kg iv bolus) given 10 min before coronary occlusion in dogs pretreated 15 min earlier with the ATP-dependent potassium channel antagonist glibenclamide (0.3 mg/kg iv bolus). Administration of IB-MECA had no effect on any hemodynamic parameter measured including heart rate, first derivative of left ventricular pressure, aortic pressure, LAD coronary blood flow, or coronary collateral blood flow. Nevertheless, pretreatment with IB-MECA before coronary occlusion produced a marked reduction in infarct size ( approximately 40% reduction) compared with the control group (13.0 +/- 3.2% vs. 25.2 +/- 3.7% of the area at risk, respectively). This effect of IB-MECA was blocked completely in dogs pretreated with glibenclamide. An equivalent reduction in infarct size was observed when IB-MECA was administered immediately before reperfusion (13.1 +/- 3.9%). These results are the first to demonstrate efficacy of an A3AR agonist in a large animal model of myocardial infarction by mechanisms that are unrelated to changes in hemodynamic parameters and coronary blood flow. These data also demonstrate in an in vivo model that IB-MECA is effective as a cardioprotective agent when administered at the time of reperfusion.     

Effects of yohimbine and desipramine on cardiac noradrenaline release and ventricular arrhythmias during acute coronary artery occlusion and reperfusion in anesthetized dogs

Effects of yohimbine (YHMB, an alpha 2-antagonist) and desipramine (DMI, a neuronal uptake inhibitor) were compared on cardiac noradrenaline (NA) release either upon left ansa subclavia nerve stimulation during acute occlusion of the left anterior descending coronary artery (LAD) or upon subsequent LAD reperfusion without stimulation in anesthetized dogs. In control dogs, before LAD occlusion, coronary sinus (CS) NA output increased from 5.4 +/- 1.0 to 26.8 +/- 4.0 ng/min (p less than 0.05) upon stimulation (2 Hz, 30 s). The response to stimulation remained unchanged 25 min after LAD occlusion. During reperfusion 60 min after occlusion, the output of CS-NA and lactate increased from 6.1 +/- 0.8 to 51.3 +/- 19.4 ng/min (p less than 0.05) and from 2.7 +/- 0.5 to 6.7 +/- 1.3 mg/min (p less than 0.05), respectively. In dogs treated with YHMB, the stimulation-induced increase in NA output was potentiated at least fourfold (p less than 0.05) either before or during LAD occlusion, but not during reperfusion. In dogs receiving DMI, stimulation-induced CS-NA output was enhanced to a similar extent (approximately twofold, p less than 0.05) either before or during occlusion, while reperfusion-induced NA output was markedly potentiated by approximately ninefold (p less than 0.05). Maximum dP/dt of left ventricular pressure remained unchanged upon reperfusion in all groups. The total arrhythmic ratio in the drug-treated groups did not significantly differ from the ratio in control dogs upon either stimulation or reperfusion. The data suggest that an abrupt increase in NA output upon reperfusion may result from a washout of NA locally accumulated in the ischemic and (or) peri-ischemic region during the preceding occlusion period, and that NA thus released does not have substantial hemodynamic effects. The results indicate that in the presence of YHMB or DMI, the potentiated increase in NA release in response to either nerve stimulation during LAD occlusion or to reperfusion without stimulation did not aggravate ventricular arrhythmia, most probably owing to the antiarrhythmic properties of these substances.     

白鲜皮水提物对大鼠心肌缺血再灌注损伤的保护作用

目的研究白鲜皮水提物对大鼠心肌缺血再灌注损伤的保护作用。方法 Wistar大鼠随机分为假手术组,模型组,阳性药组(地奥心血康)及白鲜皮低、中、高剂量组(白鲜皮水提物0.128、0.64、1.28 g/kg),每组6只。结扎冠状动脉左前降支制备大鼠心肌缺血再灌注损伤模型,观察给药后大鼠心电图ST段的改变,测量心肌梗死面积,观察大鼠心肌组织病理形态,检测大鼠血清CK,SOD活性、MDA含量。结果白鲜皮中、高剂量组给药后能明显减少心肌梗死面积,明显降低缺血30 min和再灌注120 min时ST段的抬高,并能降低大鼠血清中MDA含量,升高SOD活性,减少因缺血导致的心肌组织病理损害。结论白鲜皮水提物对大鼠心肌缺血再灌注损伤具有保护作用,其作用机制可能与保护心肌细胞功能、提高心肌抗氧化能力、清除氧自由基有关。     

Effect of desflurane-induced preconditioning following ischemia-reperfusion on nitric oxide release in rabbits

Nitric oxide (NO) is the mediator of ischemic preconditioning against myocardial infarction. Desflurane produces anesthetic preconditioning to protect the myocardium against infarction. In the model of myocardial ischemia-reperfusion injury in rabbits, we evaluated desflurane-induced ischemic preconditioning and studied its mechanism of NO synthesis. Thirty-two male adult New Zealand white rabbits were anesthetized with intravenous (IV) 30 mg/kg pentobarbital followed by 5 mg/kg/hr infusion. All rabbits were subjected to 30 minutes (min) long lasting left anterior descending coronary artery (LAD) occlusion and three hours (hr) of subsequent reperfusion. Before LAD occlusion, the rabbits were randomly allocated into four groups for preconditioning treatment (eight for each group). The control group did not receive any preconditioning treatment. The desflurane group received inhaled desflurane 1.0 MAC (minimal end-tidal alveolar concentration) for 30 min that was followed by a 15 min washout period. The L-NAME-desflurane group received L-NAME (NG-nitro-L-arginine methyl ester; non-selective Nitric Oxide Synthetase (NOS) inhibitor) 1 mg/kg IV 15 min before 1.0 MAC inhaled desflurane for 30 min. The L-NAME group received L-NAME 1 mg/kg IV. Infarct volume, ventricular arrhythmia, plasma lactate dehydrogenase (LDH), creatine kinase (CK) activity and myocardial perfusion were recorded simultaneously. We have found that hemodynamic values of the coronary blood flow before, during, and after LAD occlusion were not significantly different among these four groups. For the myocardial ischemia-reperfusion injury animals, the infarction size (mean +/- SEM) in the desflurane group was significantly reduced to 18 +/- 3% in the area at risk as compared with 42 +/- 7% in the control group, 35 +/- 6 in the L-NAME group, and 34 +/- 4% in the L-NAME-desflurane group. The plasma LDH, CK levels, and duration of ventricular arrhythmia were also significantly decreased in the desflurane group during ischemia-reperfusion injury. Our results indicate that desflurane is an anesthetic preconditioning agent, which could protect the myocardium against the ischemia-reperfusion injury. This beneficial effect of desflurane on the ischemic preconditioning is probably through NO release since L-NAME abrogates the desflurane preconditioning effect.     

The intermediary metabolite pyruvate attenuates stunning and reduces infarct size in in vivo porcine myocardium

The intermediary metabolite pyruvate has been shown to exert significant beneficial effects in in vitro models of myocardial oxidative stress and ischemia-reperfusion injury. However, there have been few reports of the ability of pyruvate to attenuate myocardial stunning or reduce infarct size in vivo. This study tested whether supraphysiological levels of pyruvate protect against reversible and irreversible in vivo myocardial ischemia-reperfusion injury. Anesthetized, open-chest pigs (n = 7/group) underwent 15 min of left anterior descending coronary artery (LAD) occlusion and 3 h of reperfusion to induce stunning. Load-insensitive contractility measurements of regional preload recruitable stroke work (PRSW) and PRSW area (PRSWA) were generated. Vehicle or pyruvate (100 mg/kg i.v. bolus + 10 mg x kg(-1) x min(-1) intra-atrial infusion) was administered during ischemia and for the first hour of reperfusion. In infarct studies, pigs (n = 6/group) underwent 1 h of LAD ischemia and 3 h of reperfusion. Group I pigs received vehicle or pyruvate for 30 min before and throughout ischemia. In group II, the infusion was extended through 1 h of reperfusion. In the stunning protocol, pyruvate significantly improved the recovery of PRSWA at 1 h (50 +/- 4% vs. 23 +/- 3% in controls) and 3 h (69 +/- 5% vs. 39 +/- 3% in controls) reperfusion. Control pigs exhibited infarct sizes of 66 +/- 1% of the area at risk. The pyruvate I protocol was associated with an infarct size of 49 +/- 3% (P < 0.05), whereas the pyruvate II protocol was associated with an infarct size of 30 +/- 2% (P < 0.05 vs. control and pyruvate I). These findings suggest that pyruvate attenuates stunning and decreases myocardial infarction in vivo in part by reduction of reperfusion injury. Metabolic interventions such as pyruvate should be considered when designing the optimal therapeutic strategies for limiting myocardial ischemia-reperfusion injury.     

Acetaminophen and myocardial infarction in dogs

The hypothesis that acetaminophen can reduce necrosis during myocardial infarction was tested in male dogs. Two groups were studied: vehicle- (n=10) and acetaminophen-treated (n=10) dogs. All dogs were obtained from the same vendor, and there were no significant differences in their ages (18 +/- 2 mo), weights (24 +/- 1 kg), or housing conditions. Selected physiological data, e.g., coronary blood flow, nonspecific collateral flow, epicardial temperature, heart rate, systemic mean arterial pressure, left ventricular developed pressure, the maximal first derivative of left ventricular developed pressure, blood gases, and pH, were collected at baseline and during regional myocardial ischemia and reperfusion. There were no significant differences in coronary blood flow, nonspecific collateral flow, epicardial temperature, heart rate, systemic mean arterial pressure, or blood gases and pH between the two groups at any of the three time intervals, even though there was a trend toward improved function in the presence of acetaminophen. Infarct size, the main objective of the investigation, was markedly and significantly reduced by acetaminophen. For example, when expressed as a percentage of ventricular wet weight, infarct size was 8 +/- 1 versus 3 +/- 1%(P <0.05) in vehicle- and acetaminophen-treated hearts, respectively. When infarct size was expressed as percentage of the area at risk, it was 35 +/- 3 versus 13 +/- 2% (P <0.05) in vehicle- and acetaminophen-treated groups, respectively. When area at risk was expressed as percentage of total ventricular mass, there were no differences in the two groups. Results reveal that the recently reported cardioprotective properties of acetaminophen in vitro can now be extended to the in vivo arena. They suggest that it is necessary to add acetaminophen to the growing list of pharmaceuticals that possess cardioprotective efficacy in mammals.     

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.     

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.     

Hypoxic conditioning suppresses nitric oxide production upon myocardial reperfusion

Physiologically modulated concentrations of nitric oxide (NO) are generally beneficial, but excessive NO can injure myocardium by producing cytotoxic peroxynitrite. Recently we reported that intermittent, normobaric hypoxia conditioning (IHC) produced robust cardioprotection against infarction and lethal arrhythmias in a canine model of coronary occlusion-reperfusion. This study tested the hypothesis that IHC suppresses myocardial nitric oxide synthase (NOS) activity and thereby dampens explosive, excessive NO formation upon reperfusion of occluded coronary arteries. Mongrel dogs were conditioned by a 20 d program of IHC (FIO(2) 9.5-10%; 5-10 min hypoxia/cycle, 5-8 cycles/d with intervening 4 min normoxia). One day later, ventricular myocardium was sampled for NOS activity assays, and immunoblot detection of the endothelial NOS isoform (eNOS). In separate experiments, myocardial nitrite (NO(2)(-)) release, an index of NO formation, was measured at baseline and during reperfusion following 1 h occlusion of the left anterior descending coronary artery (LAD). Values in IHC dogs were compared with respective values in non-conditioned, control dogs. IHC lowered left and right ventricular NOS activities by 60%, from 100-115 to 40-45 mU/g protein (P < 0.01), and decreased eNOS content by 30% (P < 0.05). IHC dampened cumulative NO(2)(-) release during the first 5 min reperfusion from 32 +/- 7 to 14 +/- 2 mumol/g (P < 0.05), but did not alter hyperemic LAD flow (15 +/- 2 vs. 13 +/- 2 ml/g). Thus, IHC suppressed myocardial NOS activity, eNOS content, and excessive NO formation upon reperfusion without compromising reactive hyperemia. Attenuation of the NOS/NO system may contribute to IHC-induced protection of myocardium from ischemia-reperfusion injury.     

Effects of recombinant human extracellular-superoxide dismutase type C on myocardial infarct size in pigs.

The efficacy of human extracellular-superoxide dismutase type C (EC-SOD C) to limit infarct size after ischemia and reperfusion was explored and compared to that of EC-SOD C combined with catalase (CAT) and to that of CAT alone. EC-SOD C binds to heparan sulphate proteoglycan on the cell surfaces. Thirty-two pigs were subjected to 45 min of myocardial ischemia followed by 4 h of reperfusion. Control pigs (group A; n = 8) received 300 mL of saline into the great cardiac vein during a 30-min period started 5 min prior to reperfusion; pigs in group B (EC-SOD C; n = 8) got 16.6 mg of EC-SOD C; pigs in group C (EC-SOD C + CAT; n = 8) got 16.6 mg of EC-SOD C together with 150 mg of CAT. Pigs in group D (CAT; n = 8) received 150 mg of CAT. In groups B, C, and D, the drug was dissolved in saline and infused into the great cardiac. Infarct size expressed as percent of area at risk was smaller in groups B (14.5 +/- 16.7%) and C (40.8 +/- 13.3%) than in groups A (78.8 +/- 8.6%) and D (67.2 +/- 18.6%; p less than .05). Creatine kinase (CK) activity in ischemic myocardium was higher in groups B (1740 +/- 548 U/g) and C (1729 +/- 358 U/g) than in groups A (1184 +/- 237 U/g) and D (1251 +/- 434 U/g; p less than .05). There was an inverse relation (r = -.83) between infarct size and CK content. The EC-SOD C infusions resulted in only minimal increases in plasma SOD activities. In conclusion, the presence of SOD on the cell surfaces is of importance in the prevention of reperfusion injury rather than circulating SOD.     

The effect of an adenosine and lidocaine intravenous infusion on myocardial high-energy phosphates and pH during regional ischemia in the rat model in vivo

We have previously shown that an intravenous infusion of adenosine and lidocaine (AL) solution protects against death and severe arrhythmias and reduces infarct size in the in vivo rat model of regional ischemia. The aim of this study was to examine the relative changes of myocardial high-energy phosphates (ATP and PCr) and pH in the left ventricle during ischemia-reperfusion using 31P NMR in AL-treated rats (n = 7) and controls (n = 6). The AL solution (A: 305 microg.(kg body mass)-1.min-1; L: 608 microg.(kg body mass)-1.min-1) was administered intravenously 5 min before and during 30 min coronary artery ligation. Two controls died from ventricular fibrillation; no deaths were recorded in AL-treated rats. In controls that survived, ATP fell to 73% +/- 29% of baseline by 30 min ischemia and decreased further to 68% +/- 28% during reperfusion followed by a sharp recovery at the end of the reperfusion period. AL-treated rats maintained relatively constant ATP throughout ischemia and reperfusion ranging from 95% +/- 6% to 121% +/- 10% of baseline. Owing to increased variability in controls, these results were not found to be significant. In contrast, control [PCr] was significantly reduced in controls compared with AL-treated rats during ischemia at 10 min (68% +/- 7% vs. 99% +/- 6%), at 15 min (68% +/- 10% vs. 93% +/- 2%), and at 20 min (67% +/- 15% vs. 103% +/- 5%) and during reperfusion at 10 min (56% +/- 22% vs. 99% +/- 7%), at 15 min (60% +/- 10% vs. 98% +/- 7%), and at 35 min (63% +/- 14% vs. 120% +/- 11%) (p < 0.05). Interestingly, changes in intramyocardial pH between each group were not significantly different during ischemia and fell by about 1 pH unit to 6.6. During reperfusion, pH in AL-treated rats recovered to baseline in 5 min but not in controls, which recovered to only around pH 7.1. There was no significant difference in the heart rate, mean arterial pressure, and rate-pressure product between the controls and AL treatment during ischemia and reperfusion. We conclude that AL cardioprotection appears to be associated with the preservation of myocardial high-energy phosphates, downregulation of the heart at the expense of a high acid-load during ischemia, and with a rapid recovery of myocardial pH during reperfusion.