Regional hypothermia reduces myocardial necrosis even when instituted after the onset of ischemia

Previously, we observed that reducing myocardial temperature in the risk region before coronary artery occlusion caused a profound reduction in infarct size. It is unknown whether lowering myocardial temperature after ischemia has already begun, or just before reperfusion, is also effective in reducing infarct size. This study tests the hypothesis that reducing myocardial temperature locally, after coronary occlusion, reduces infarct size.Methods: Anesthetized rabbits received 30 min of coronary artery occlusion and three hours of reperfusion. Myocardial temperature in the risk zone was monitored. Rabbits were randomly assigned to one of three groups: group 1, topical myocardial cooling starting 10 min after coronary occlusion (n=11); group 2, cooling starting 25 min after coronary occlusion (n=11); or group 3, control, no intervention (n=10).Results: Hemodynamic parameters and regional myocardial blood flow were equivalent in all groups. Risk zone temperature was similar in all groups at occlusion. The cooling maneuver produced a rapid reduction in temperature in the risk region. In group 1, myocardial temperature was reduced an average of 6.3°C between 10 and 15 min of coronary artery occlusion; myocardial temperature in group 2 was reduced an average of 5.9°C between 25 and 30 min of coronary artery occlusion. Cooling was maintained until 15 min of reperfusion. Myocardial temperature in group 3 remained within 0.3°C of baseline during coronary artery occlusion and into reperfusion. Core temperature was similar in all groups. Although the ischemic risk region was comparable in all groups, early cooling (group 1) resulted in a significant reduction in infarct size, expressed as a fraction of the risk region, compared with the control group (0.23±0.04 vs. 0.44±0.04 of the risk region); however, cooling just before reperfusion (group 2) failed to modify infarct size compared with the controls (0.43±0.04 and 0.44±0.04 of the risk region, respectively).Conclusion: These results support our hypothesis that reducing myocardial temperature reduces infarct size. However, it is important the reduction in temperature be produced as early as possible following coronary artery occlusion.     

RISK信号转导通路与肾缺血后处理的心肌保护作用

目的通过在体兔心肌缺血再灌注模型,研究再灌注损伤补救酶(RISK)信号转导通路是否参与肾缺血后处理对急性心肌缺血再灌注损伤的保护作用。方法32只兔随机分为4组,每组8只。对照组:结扎冠状动脉前降支1h,再灌注5h。实验A组于再灌注同时对左侧肾动脉行结扎30s、开通30s的3次反复循环,余同对照组;实验B组于再灌注15min后对左侧肾动脉行结扎30s、开通30s的3次反复循环,余同对照组;药物组于再灌注前5min耳缘静脉注射磷脂酰肌醇3激酶(PI3K)抑制剂LY294002(0.3mg/kg),余同实验A组。分别于再灌注3h、再灌注5h取兔血,测定各组血超氧化物歧化酶(SOD)和丙二醛(MDA)的水平。实验终末,取结扎血管支配部位心肌进行免疫组化处理,观察心肌组织蛋白激酶B(Akt)和内皮一氧化氮合酶(eNOS)含量以及心肌组织结构的变化。结果实验A组血SOD含量高于其它组(P<0.01),MDA含量低于其它组(P<0.01),实验A组心肌组织Akt和eNOS含量明显高于其它组(P<0.01);其余组间各项观察指标无显著差异。结论RISK信号转导通路参与肾缺血后处理对急性心肌缺血再灌注损伤的保护作用;肾缺血后处理必须在心肌再灌注后数分钟内立刻进行才能发挥其心肌保护作用。     

What is the Required Reperfusion Period for Assessment of Myocardial Infarct Size Using Triphenyltetrazolium Chloride Staining in the Rat?

Measurements of infarct size by use of tripenyltetrazoliumchloride (TTC) is a widely accepted method used to delineate the extent of myocardial necrosis following coronary occlusion and reperfusion in various animal experiments. There is controversy, however, regarding the optimal reperfusion time for estimating the maximally infarcted area by TTC staining in the rat. We tested six different reperfusion times following 90 minutes of regional myocardial ischemia. Group 1 had 5 minutes of reperfusion (n=6), group 2 had 30 minutes of reperfusion (n=6), group 3 had 1 hour of reperfusion (n=6), group 4 had 2 hours of reperfusion (n=6), group 5 had 3 hours of reperfusion (n=6), group 6 had 4.5 hours of reperfusion (n=6). Risk areas, measured by the use of blue dye, were similar among the 6 study groups. Infarct size as a percent of risk area was 57±11% in group 1, 74±7% in group 2, 61±9% in group 3, 71±5% in group 4, 70±5% in group 5, and 64±9% in group 6 (x±standard error [SE]). There was no signifcant difference in infarct size between the groups. However, prior to 60 minutes of reperfusion, patches of pink and white areas were observed within the risk regions, indicating a more difficult assessment of proper delineation of outer regions of necrotic tissue. For acute assessment of infarct size, reperfusion for 60 minutes or more is optimal because the infarct does appear homogeneous at that time and does not become larger with longer reperfusion periods.     

The protective effects of cromakalim and pinacidil on reperfusion function and infarct size in isolated perfused rat hearts and anesthetized dogs

Summary The direct myocardial protective effects of intracoronary infusions of cromakalim and pinacidil were determined in an anesthetized canine model of coronary occlusion and reperfusion. The left circumflex coronary artery was occluded for 90 minutes and reperfused for 5 hours, at which time the infarct size was determined. Cromakalim (0.1 g/kg/min) or pinacidil (0.09 g/kg/min) were infused into the left circumflex coronary artery starting 10 minutes preischemia. Cromakalim significantly reduced infarct size as a percent of the left ventricular area at risk (25±5%) compared with vehicle controls (55±7%). Pinacidil did not reduce infarct size at an equimolar dose, but at the higher dose also significantly reduced infarct size. Collateral blood flow was not significantly altered by either drug, though reperfusion flow was significantly higher in cromakalim-treated animals, particularly in the subepicardial region. When the same dose of cromakalim was given starting 2 minutes before the initiation of reperfusion, no significant beneficial effect of cromakalim was observed. In another study, isolated buffer-perfused rat hearts were subjected to 25 minutes of global ischemia and 30 minutes of reperfusion. These hearts were treated with 7 M cromakalim, either starting 10 minutes before ischemia or only during reperfusion, and its effect on reperfusion function and LDH release were determined. Cromakalim pretreatment (both when given throughout the experiment and when not present in the reperfusion buffer) resulted in significant improvements in the reperfusion function. Reperfusion contracture and LDH were also significantly reduced with this treatment. When given only during reperfusion, cromakalim did not reduce the severity of ischemia when compared with vehicle controls. Thus, both cromakalim and pinacidil reduce ischemic/reperfusion injury, though the timing of treatment may be important.     

Acute ethanol does not protect against ischemic/ reperfusion injury in rabbit myocardium

Moderate use of alcohol has shown protective effects in coronary artery disease, while excessive use has been associated with cardiomyopathy and hypertension. Since alcohol is a vasodilator, we postulated that it might have protective effects when administered acutely in the setting of ischemia/reperfusion. Therefore, we studied the acute effects of alcohol on myocardial infarction in a rabbit model. Anesthetized, open chest rabbits were subjected to a 30 minute coronary artery occlusion followed by 4 hours of reperfusion. Rabbits were randomized to a control group (n = 20), receiving an infusion of 10 ml normal saline, intravenously, over 10 minutes via a Harvard pump, or an alcohol group (n = 20), receiving a diluted solution of 100% ethanol (1 ml/kg diluted in normal saline to 10 ml total solution) infused in a similar fashion. This infusion regimen resulted in an average blood alcohol level of 110 mg/dl (range 77–129) tested in five rabbits within the study. Ten minutes after infusion, a marginal branch of the circumflex artery was occluded. Regional myocardial blood flow during coronary occlusion and reperfusion was measured using radioactive microspheres. Myocardial ischemic area at risk (AR) was assessed by blue dye injection and myocardial necrosis (AN) by triphenyltetrazolium chloride (TTC) staining. The mean regional coronary blood flow in ischemic tissue was 0.04 ± 0.01 ml/min/g in the control group versus 0.03 ± 0.01 ml/min/g in the experimental group (p = NS) and averaged 1.74 ml/min/g (control) to 1.98 ml/min/g (alcohol) in the nonischemic tissue. All rabbits received comparable ischemic insult: Collateral blood flow and AR were similar in both groups. An overall analysis showed no significant reduction in infarct size (expressed as the percent of necrotic tissue within the area at risk) in the alcohol group (23 ± 3%) compared with the control group (27 ± 4%). In conclusion, alcohol did not reduce infarct size in the rabbit model.     

Effects of late coronary artery reperfusion on left ventricular remodeling persist for 10 weeks after experimental rat myocardial infarction and are associated with improved survival

Objective: To test the hypothesis that coronary artery reperfusion performed too late to reduce infarct size improves survival by altering left ventricular remodeling and preventing progressive left ventricular dilation.Background: Several clinical trials have suggested that late coronary artery reperfusion without infarct size reduction is associated with a survival benefit. Although the mechanism is not known, survival benefits could be related to decreased infarct expansion associated with late coronary artery reperfusion. Decreased infarct expansion results in decreased left ventricular volume, and the resulting decreased wall stress could prevent or attenuate progressive left ventricular dilation and improve survival.Methods: Rats (n=84) were randomized to undergo sham operation, permanent left coronary artery ligation, or 2 hours of left coronary artery ligation followed by reperfusion. Ten weeks later, hemodynamic measurements were made before and after volume loading. The rats were killed, the hearts were removed, and passive pressurevolume curves were obtained. The hearts were fixed at a constant pressure and analyzed morphometrically.Results: When examined 10 weeks after experimental myocardial infarction, late reperfusion's effects on left ventricular remodeling resulted in reduced left ventricular volume when compared to hearts with infarcts supplied by a permanently occluded coronary artery (1.9 ± 0.1 ml/kg vs. 2.1 ± 0.2 ml/ kg; p < 0.01). Although there was a trend toward less thinning (0.95 ± 0.13 mm vs. 1.00 ± 0.10 mm; p=NS) and less expansion (2.3 ± 0.4 vs. 2.8 ± 0.9; p=NS) in reperfused hearts compared to hearts with a permanently occluded coronary artery, changes in infarct shape 10 weeks after infarction were not significantly different. Reperfusion's beneficial effects on remodeling of noninfarcted myocardium were associated with improved survival. Mortality was higher in the permanently occluded rats than in the reperfused rats (35% vs. 12%; p < 0.05).Conclusion: Late coronary artery reperfusion has a beneficial effect on remodeling of noninfarcted myocardium that results in reduced left ventricular volume in rat hearts examined 10 weeks after infarction. These beneficial effects on left ventricular remodeling are associated with improved survival.     

Cardioprotective effect of MCI-186 (3-methyl-1-phenyl-2-pyrazolin-5-one) during acute ischemia-reperfusion injury in rats

MCI-186 (3-methyl-1-phenyl-2-pyrazolin-5-one), a free radical scavenger, has the ability to stimulate prostacyclin release and to inhibit the lipoxygenase pathway in the arachidonic acid cascade. The authors investigated the cytoprotective effect of MCI-86 in a reperfusion model of myocardial ischemia. Rats were subjected to occlusion of the left coronary artery for ten minutes followed by reperfusion for twenty-four hours. The loss of myocardial creatine kinase activity (CK) from the left ventricular free wall (LVFW) twenty-four hours after the induction of myocardial ischemia was used as an index of ischemic damage. Administration of MCI-186 (3 mg/kg IV) significantly blunted the depletion of LVFW-CK activity when compared with vehicle (MCI-186 vs vehicle, 31.5 ± 1.1 vs 26.5 ± 1.2 U/mg protein, respectively,p<0.01). In another group of rats that underwent coronary artery occlusion—reperfusion, infarct size was measured by planimetry on histologic sections of serial slices of the left ventricle and was found to be 20.0 ± 1.3% of the left ventricle in vehicle-treated rats and 10.7 ± 1.3% in MCI-186 (3 mg/kg)-treated rats (p<0.01). These results indicate the potential usefulness of MCI-186 in myocardial ischemia-reperfusion injury.This study was supported in part by a Grant-in-aid for Scientific Research from the Japanese Ministry of Education in 1992     

Time Window for the Contribution of the δ-opioid Receptor to Cardioprotection by Ischemic Preconditioning in the Rat Heart

The present study aimed to examine (1) whether the role of the opioid receptor in ischemic preconditioning (PC) is consistent regardless of the duration of ischemic insult and (2) which opioid receptor subtype contributes to PC. In the first series of experiments, the effects of PC, a nonselective opioid receptor antagonist (naloxone), and their combination on the infarct size after various durations of ischemia were assessed. In anesthetized, open-chest rats, the coronary artery was occluded for 20, 30, or 40 minutes to induce infarction and was reperfused for 3 hours, PC was performed with two cycles of 5-minute ischemia followed by 5-minute reperfusion before the sustained ischemia. At 25 minutes before the ischemia, naloxone was injected alone or in combination with subsequent PC. Infarct size was determined by tetrazolium staining and was expressed as a percentage of the risk area size (%IS/RA). In the second series of experiments, the effects of a -receptor selective antagonist, naltrindole (NTI), and a -receptor selective antagonist, nor-binaltrophimine (nor-BNI), on PC before 30-minute coronary occlusion were assessed. In untreated controls, %IS/RA was 53.1 ± 3.2 after 20 minutes, 67.9 ± 3.9 after 30 minutes, and 87.8 ± 2.0 after 40 minutes of ischemia, respectively. PC significantly reduced %IS/RA after 20, 30, and 40 minutes of ischemia to 3.1 ± 0.8, 12.8 ± 1.1, and 42.1 ± 4.3, respectively (P < 0.05 vs. each control). Naloxone (6 mg/kg) partially attenuated the protection afforded by PC when the sustained ischemia was 30 minutes (%IS/RA = 27.4 ± 4.5; P < 0.05 vs. PC), but this inhibitory effect of naloxone was not detected when the duration of the ischemia was 20 or 40 minutes. NTI (10 mg/kg) also attenuated infarct size limitation by PC after 30 minutes of ischemia (%IS/RA = 25.6 ± 3.7), but nor-BNI (10 mg/kg) failed to modify infarct size limitation by PC (%IS/RA = 13.3 ± 3.2). The present results suggest that activation of the opioid -receptor partly contributes to preconditioning against infarction in the rat and that there may be a time window (at around 30 minutes after the onset of ischemia) for this opioid receptor–mediated protective mechanism.     

Pyrroloquinoline Quinone (PQQ) Decreases Myocardial Infarct Size and Improves Cardiac Function in Rat Models of Ischemia and Ischemia/Reperfusion

Summary As pyrroloquinoline quinone (PQQ) is a redox cofactor in mammals, we asked if it is cardioprotective. Rats were subjected to 2 h of left anterior descending (LAD) coronary artery ligation without reperfusion (model 1, ischemia). In model 2 (ischemia/reperfusion), rats were subjected to 17 or 30 min of LAD occlusion and 2 h of reperfusion. PQQ (15–20 mg/kg) was given i.p., either 30 min before LAD occlusion (Pretreatment) or i.v. at the onset of reperfusion (Treatment). In model 1, PQQ reduced infarct size (10.0 ± 1.5 vs 19.1 ± 2.1%, P < 0.01). In model 2, either PQQ Pretreatment or Treatment also reduced infarct size (18.4 ± 2.3 and 25.6 ± 3.5% vs 38.1 ± 2.6%, P < 0.01). PQQ resulted in higher LV developed pressure and LV (+)dP/dt after 1–2 h of reperfusion (P < 0.05), and fewer ventricular fibrillation episodes. PQQ dose (5–20 mg/kg) was inversely related to infarct size. PQQ reduced myocardial tissue levels of malondialdehyde (MDA), an indicator of lipid peroxidation (316 ± 88 vs 99 ± 14 nmol/g, P < 0.01). PQQ given either as Pretreatment or as Treatment at the onset of reperfusion is highly effective in reducing infarct size and improving cardiac function in a dose-related manner in rat models of ischemia and ischemia/reperfusion. The optimal dose in this study, which exhibited neither renal nor hepatic toxicity, was 15 mg/kg, but lower doses may also be efficacious. We conclude that PQQ, which appears to act as a free radical scavenger in ischemic myocardium, is a highly effective cardioprotective agent.This study was supported by the Charitable Leadership Foundation     

Late coronary artery reperfusion has additive beneficial effects on infarct expansion when combined with early angiotensin converting enzyme inhibitor therapy post myocardial infarction

Background: Individually, late coronary artery reperfusion and early angiotensin converting enzyme (ACE) inhibitor therapy prevent infarct expansion post myocardial infarction (MI). Objectives: To examine the effect of late reperfusion on infarct expansion when added to early ACE inhibitor therapy post MI. Methods: Rats were randomized into two groups: Reperfusion group: rats underwent coronary artery occlusion followed by reperfusion 2 hours after MI, a time too late to reduce infarct size. A control group: rats underwent permanent coronary artery occlusion followed by a sham operation 2 hours after MI. All rats received enalapril (2.0 ± 0.2 mg/kg) daily in drinking water, started immediately after the second operation. Rats were sacrificed 2 weeks after coronary occlusion. Hearts were arrested and fixed at a constant pressure, then sectioned and photographed for morphometric analysis. Results: Infarct size was similar in the reperfusion and control groups (23 ± 2 vs 26 ± 2%, p = NS). Septal thickness was also similar in both groups (1.8 ± 0.1 vs 1.8 ± 0.1 mm, p = NS). There was a trend towards thicker infarcts in the reperfusion group compared to the control group (0.84 ± 0.06 vs 0.72 ± 0.05 mm, p = 0.1). Compared to early ACE inhibition alone, late reperfusion combined with early ACE inhibition limited infarct expansion (expansion index, 1.13 ± 0.12 vs 1.44 ± 0.14, p < 0.05), prevented left ventricular (LV) dilation (LV volume, 0.30 ± 0.02 vs 0.39 ± 0.03 ml, p < 0.01) and prevented LV hypertrophy (LV weight, 0.71 ± 0.18 vs 0.77 ± 0.20 gm, p < 0.05). Conclusions: Late coronary artery reperfusion prevents infarct expansion, LV dilation and hypertrophy even when added to early ACE inhibitor therapy post MI. This suggests that late reperfusion may be beneficial in patients with acute MI treated with early ACE inhibitor therapy.     

肾脏缺血后处理对兔急性缺血再灌注心肌细胞凋亡和Bcl-2、Bax蛋白表达的影响

目的研究肾脏缺血后处理对兔急性缺血再灌注心肌细胞凋亡的影响,并探讨其保护机制。方法24只新西兰大白兔随机分为3组,每组8只。（1）缺血再灌注组（IR组）：结扎左冠状动脉前降支1h,再灌注6h。（2）肾脏缺血后处理组（RI-Post组）：操作同IR组,在再灌注即刻用动脉血管夹反复夹闭左侧肾动脉（阻断30S,再通30S,重复3次）,再灌注6h。（3）药物干预组（MI组）：结扎左冠状动脉前降支1h,再灌注前10min给予蛋白激酶C抑制剂-GF109203X（O．05mg／kg）耳缘静脉注射持续10min,再灌注即刻行RI-Post组操作,最后心肌再灌注直至6h。实验结束,采用Tunel法检测24只兔梗死区的心肌细胞凋亡,用免疫组化法检测Bax和Bcl-2蛋白在心肌细胞中的表达水平。结果肾脏缺血后处理组与对照组和药物干预组比较,心肌细胞凋亡指数明显减少（P〈0．05）,Bcl-2表达明显增多（P〈0．01）,Bax表达明显减少（P〈0．05）;而药物干预组与对照组相比各检测指标无明显差别（P〉0．05）。结论肾脏缺血后处理可减少急性缺血再灌注后心肌细胞凋亡,并影响Bcl-2、Bax蛋白的表达,从而对缺血心肌产生保护作用,其保护机制可能与激活蛋白激酶C有关。     

Local beta-adrenergic blockade does not reduce infarct size after coronary occlusion and reperfusion: A study of coronary venous retroinfusion of metoprolol

Summary Previous studies have demonstrated pronounced ischemic zone myocardial concentrations of metoprolol following coronary venous retroinfusion in pigs with coronary artery ligation. The effect of coronary venous retroinfusion of metoprolol on myocardial infarct size was studied in 16 pentobarbital-anesthetized open-chest pigs undergoing 60-minute occlusion of the left anterior descending coronary artery followed by 3 hours of reperfusion. Pigs in the experimental group (n=8) were given 0.4 mg/kg (1.0 mg/ml) of metoprolol via the anterior interventricular vein over a period of 5 minutes, beginning immediately after coronary occlusion followed by 0.2 mg/kg/hr intravenously. Control pigs (n=8) received the same volume of saline as the treated group. The risk area and the necrotic area were assessed by monastral blue dye and triphenyl tetrazolium chloride staining, respectively. Metoprolol did not influence hemodynamics. Plasma concentrations of metoprolol were within therapeutic levels. The administration of the beta-blocker resulted in a trend toward reduced norepinephrine concentrations, both in the aorta and coronary vein after coronary occlusion, but it did not prevent norepinephrine overflow following reperfusion. Infarct size expressed as a percentage of the risk area was 77±11% in the control group and 75±12% (mean ± SD; NS) in the treated group. Thus, metoprolol retroinfusion did not reduce infarct size and did not prevent catecholamine overflow after reperfusion. It is concluded that the beneficial effects of metoprolol in acute infarction are probably unrelated to local beta-adrenergic blockade, at least in the pig, an animal with a paucity of coronary collateral blood flow.     

Adrenomedullin limits reperfusion injury in experimental myocardial infarction

Adrenomedullin (AM) is a vascular–derived polypeptide that exerts numerous actions in cardiovascular homeostasis. Recent studies have demonstrated a cytoprotective action of exogenously applied or genetically over–expressed AM in experimental myocardial infarction. The present studies were undertaken to test the hypothesis that AM exerts its effects through direct augmentation of NO generation in the myocardium during early reperfusion. Rat isolated hearts underwent 35 min left coronary artery occlusion followed by 120 min reperfusion. Infarct size (as percentage of ischaemic riskzone) was determined by Evans’ blue and tetrazolium double staining. AM 1 nM administered 5 min prior to and during the first 15 min of ischaemia did not significantly influence infarct size. However, the same concentration of AM given during the last 5 min ischaemia and first 15 min of reperfusion significantly limited infarct size (AM reperfusion 15.9 ± 3.5% vs control 31.4 ± 2.1%, P < 0.01). AM at reperfusion improved coronary flow and LV contractility. The protective effects of adrenomedullin were abolished in the presence of the NO synthase inhibitor, L–NAME 100 µM (infarct size 24.6 ± 5.7%, P > 0.05 vs control). AM treatment at reperfusion was associated with augmented phosphorylation of the pro–survival kinase, Akt, determined by immunoblotting of tissue sampled 30 min following reperfusion. These studies provide the first evidence that AM exerts its cytoprotective action specifically during early reperfusion through a NO–dependent mechanism.     

The effect of β-adrenergic blockade on infarct size following experimental coronary occlusion

Summary The effect of Pindolol on myocardial infarct size was studied in 10 open chest dogs. In each animal a sequential occlusion and reperfusion of 2 medium-sized branches of the left coronary artery was performed in the same heart. After occlusion and reperfusion of the control artery the initial dose of Pindolol (0.25 mg/kg body weight) was administered. Thereafter the test artery was occluded, followed by a maintenance dose of Pindolol (0.3 mg/kg body weight).The drug caused a significant decrease in LVP and LV-dp/dt but no change in heart rate. MVO₂ also decreased significantly. Regional myocardial blood flow was measured with the tracer microsphere method. Collateral flow in the perfusion area of the control artery was 11.2±5.9% and in the area of the test artery 10.0±4.4% of normal. No change in the endo/epi ratio as a result of treatment was observed.The area of infarction (p-nitroblue tetrazolium-reaction) was divided by the area of perfusion (angiography). Infarct size, expressed as the percentage of the perfusion area. was 48.2±22.2% in the region of the control artery and 43.0±23.9% in the region of the test artery. The difference was statistically not significant.With 1 table     

Post-Ischemic Treatment with Dipyruvyl-Acetyl-Glycerol Decreases Myocardial Infarct Size in the Pig

The beneficial effects of pyruvate in organ reperfusion injury have been documented, however the therapeutic use of pyruvate has been hindered by the lack of an appropriate delivery method. Pyruvic acid is unstable and high rates of sodium pyruvate infusion are toxic. Dipyruvyl-acetyl-glycerol (DPAG) ester was developed as a novel method for intravenous pyruvate delivery at a high rate without sodium overload. We tested the ability of DPAG to reduce myocardial infarct size when administered after severe myocardial ischemia in an anesthetized open-chest pig model of ischemia-reperfusion injury. Ischemia was induced by total occlusion of the distal 2/3 of the left anterior descending coronary artery for one hour, followed by two hours of reperfusion. Animals were either untreated (n = 7), or treated with intravenous DPAG (8.0 mg/kg^–1 · min^–1, n = 8) during the two hours of reperfusion. Infarct size was measured on blinded samples using tetrazolium staining. The DPAG treated group had elevated pyruvate levels (0.82 ± 0.07 mM) and reduced infarct size (20.1 ± 4.2% of the volume at risk, compared to 30.8 ± 4.6% in the untreated animals (p < 0.05)), with no difference in blood pressure or heart rate between groups. In conclusion, an intravenous infusion of DPAG safely increases arterial pyruvate concentration and reduces myocardial infarct size following myocardial ischemia.     

Effects of coronary venous retroinfusion of lipo-prostaglandin E1 on myocardial infarct size in pigs

The coronary venous system is an alternate route for drug delivery to the acutely ischemic myocardium when the coronary arterial blood flow is impeded. This study was designed to determine the effect of retrograde infusion of lipid microsphere containing prostaglandin E₁ (lipo-PGE₁), which is believed to prevent rapid destruction of PGE₁, on myocardial infarct size after acute myocardial ischemia and reperfusion. Twenty-one open-chest porcine models were subjected to 45 minutes of left anterior descending coronary artery (LAD) occlusion followed by 4 hours of reperfusion. Group A (n=7), the control group, was given, into the great cardiac vein, 4 ml of vehicle dissolved in 36 ml of saline for 5 minutes starting before the onset of reperfusion. In group B (n=7), 20 µg/4ml of lipo-PGE₁ was administered into the great cardiac vein in the same manner as in group A. Group C (n=7) was treated the same as group B, but lipo-PGE₁ was injected into the inferior vena caval vein. Infarct size, expressed as a percentage of area at risk, was significantly smaller in group B (56.1±12.6%) than groups A (79.4±11.4%) and C (83.0±11.1%) (p<0.05). The results of this study indicate that retrograde infusion of lipo-PGE₁ is an effective treatment for the prevention of myocardial reperfusion injury in the experimental model.Presented at the 37th Annual World Congress, International College of Angiology, Helsinki, Finland, July 1995.     

Prevention of the “no reflow” phenomenon in the canine heart by mioflazine

Summary The effects of oral pretreatment with mioflazine (2.5 mg·kg^–1) on regional myocardial reflow, infarct size reduction and hemodynamic recovery were studied in 24 anesthetized open-chest dogs undergoing 90 minutes of acute left anterior descending coronary artery (LAD) occlusion followed by 150 minutes of reperfusion.Regional myocardial blood flow was measured with tracer microspheres, and infarct size was determined by triphenyl tetrazolium chloride staining. Pretreatment with mioflazine resulted in a reduced diastolic aortic pressure (p<0.05) and an elevated cardiac output and LV dpdt max (p<0.05). These effects persisted throughout the experiment. In control animals (n=12) a hyperemic reflow response was found in the perfusion area of the LAD during the first minutes of reperfusion. After 150 min of reperfusion, however, the viable myocardium of the LAD area became underperfused, and almost no reflow was found in the infarcted zones.In the animals pretreated with mioflazine (n=12) the hyperemic response persisted throughout the reperfusion phase and the no-reflow phenomenon was prevented. Infarct size (expressed as percentage of perfusion area) tended to be smaller in this group: 23.7±12.4% versus 33.7±19.2% (p>0.05).Left atrial pressure increased during LAD occlusion in both groups but normalized completely in the drug-pretreated animals (p<0.05).It is concluded that pretreatment with mioflazine prevents the no-reflow phenomenon after reperfusion of an evolving infarction, tends to reduce infarct size and improves hemodynamic recovery.In part supported by a grant from I.W.O.N.L.     

Fentanyl,Na-pentobarbital and halothane influence myocardial infarct size

Summary We investigated the effects of three anesthetics on the size of myocardial infarction and on blood flow distribution within the myocardial wall. Myocardial infarcts were induced in 34 dogs by ligating a coronary artery for 90 minutes, and permitting reflow for 90 minutes. The anesthetics used were fentanyl, Na-pentobarbital, and halothane. Under halothane the mean blood pressure (BP) during coronary artery ligation was 113±2/82±2 mm Hg and the heart rate (HR) was 135±2/min. Under fentanyl, the BP was 143±3/91±2 mm Hg and HR 99±3/min. Under Na-pentobarbital, BP was 141±2/104±2 mm Hg and HR 146±2/min. A higher mean BP combined with a slower HR, as seen under fentanyl, was associated with the smallest infarct (24±8%). Low BP and higher HR, as seen under halothane, was associated with the largest infarct (51±5%). Na-pentobarbital, with a higher BP but also a faster HR, resulted in an infarct size of 32±5%. We conclude that a higher mean BP combined with a slower HR might favor the preservation of a larger mass of vulnerable myocardial tissue in a totally occluded coronary artery.Supported by: Department of Anesthesiology, The George Washington University Medical Center and in part by the National Institute of Health grant #2 507 RR 5359 19.     

Atrial Natriuretic Peptide Reduces the Severe Consequences of Coronary Artery Occlusion in Anaesthetized Dogs

The aim of the present study was to examine the effects of atrial natriuretic peptide (ANP) on the responses to coronary artery occlusion. In chloralose-urethane anaesthetised mongrel dogs either saline (controls) or human synthetic ANP was infused intravenously (10 g kg^–1 + 0.1 g kg^–1 min^–1), starting 30 min before and continuing 10 min during a 25 min occlusion of the left anterior descending coronary artery (LAD). ANP infusion resulted in a fall in mean arterial blood pressure (by 17 ± 2 mmHg, p < 0.05), a transient (max. at 5 min) increase in coronary blood flow (by 24 ± 5 ml min^–1, P < 0.05), and a reduction in coronary vascular resistance (by 0.27 ± 0.05 mmHg ml^–1, p < 0.05). When the LAD coronary artery was occluded, there was a less marked elevation in left ventricular end-diastolic pressure (LVEDP) in the ANP-treated dogs than in the controls (9.0 ± 0.9 versus 12.2 ± 0.8 mmHg, p < 0.05). Compared to the controls, ANP reduced the number of ventricular premature beats (VPBs, 26 ± 12 versus 416 ± 87, p < 0.05), the number of episodes of ventricular tachycardia per dogs (VT, 0.7 ± 0.3 versus 12.4 ± 4.2, p < 0.05), and the incidences of VT (45% versus 100%, p < 0.05) and ventricular fibrillation (VF 18% versus 57%, p < 0.05) during occlusion. Reperfusion of the ischaemic myocardium at the end of the occlusion period led to VF in all the control dogs (survival from the combined ischaemia-reperfusion insult was therefore 0%), but VF following reperfusion was much less in the dogs given ANP (survival 64%; p < 0.05). The severity of myocardial ischaemia, as assessed from changes in the epicardial ST-segment and the degree of inhomogeneity, was significantly less marked in dogs given ANP. We conclude that ANP protects the myocardium from the consequences of myocardial ischaemia resulting from acute coronary artery occlusion and reperfusion in anaesthetized dogs.     

Adenosine A1 Agonist at Reperfusion Trial (AART): Results of a Three-Center, Blinded, Randomized, Controlled Experimental Infarct Study

Adenosine A₁ receptor agonists given prior to myocardial ischemia limit ischemic injury in several species. However, the ability of adenosine receptor agonists to limit infarct size when given at reperfusion has proved controversial. We designed a three-center experimental study using a blinded, randomized treatment protocol to test the hypothesis that adenosine A₁ receptor activation during early reperfusion can attenuate lethal reperfusion injury, thereby reducing infarct size. Sixty anesthetized rabbits (20 in each laboratory) underwent 30 minutes coronary artery occlusion followed by 120 minutes reperfusion. The selective adenosine A₁ receptor agonist GR79236 (10.5 g/kg, a dose shown to limit infarction in this model when given before ischemia) or vehicle were administered IV 10 minutes before reperfusion. Infarct size was assessed by tetrazolium staining and, after the randomization code was revealed, data from the three laboratories were pooled for statistical analysis. Infarct size was not modified by administration of GR79236. In the vehicle-treated group, the infarct-to-risk ratio was 28.9 ± 2.7% (n = 24) compared with 31.9 ± 2.6% (n = 26) in the GR79236-treated group (not significant). Risk zone volume was similar in the two groups (1.06 ± 0.05 cm³ vs 1.00 ± 0.05 cm³, respectively). A modest reduction in rate-pressure product was noted following the administration of GR79236, but this effect was transient. The same dose of GR79236 was found to limit infarct size when given prior to coronary artery occlusion. We conclude that A₁ receptor activation does not modify lethal reperfusion injury in myocardium.