Postischemic cell death in reperfused porcine hearts is not attenuated by the spin trap agent PBN during early reperfusion

Summary Ischemic, reperfused porcine hearts were used to investigate whether the spin trap agent PBN (N-tert-butyl-alpha-phenylnitrone) attenuates postischemic cell death by scavenging of free radicals. The left anterior descending coronary artery (LAD) was ligated distally in 16 pigs for 45 min and then reperfused for 3 h. PBN (coronary concentration approximately 1 mM) was infused into the LAD of eight pigs during the first 45 min of reperfusion. Electron spin resonance spectroscopy (ESR) was performed to identify free radical adducts in the reperfused coronary venous blood. Regional systolic shortening (SS%) was determined by sonomicrometry. Infarct size was evaluated as the percentage of infarcted (tetrazolium stain) to ischemic (dye technique) myocardium. The transmural ultrastructural degree of myocardial injury as well as myocardial ATP levels were assessed at the end of the experiment.Intracoronary treatment with PBN during early reperfusion did not attenuate myocardial damage. Infarct sizes (control group 59±19%, treated group 55±14%), transmural ultrastructural alterations, myocardial ATP concentrations (control group 1.8±0.3 mol/mg frozen weight, treated group 1.7±0.4 mol/mg) and regional systolic shortening at the end of the experiments (control group –1±5%, treated group –2±6% did not differ significantly. Furthermore, under various experimental conditions of spin trapping, free radical adducts could not be identified in coronary venous blood during early reperfusion. The results suggest that the spin trap agent PBN (1 mM) does not affect postischemic cell death in porcine hearts.This study was supported by the Deutsche Forschungsgemeinschaft (KL 724/1-2) and the SFB 330-Organprotektion, Göttingen (A8)     

Stuttering reperfusion of ischemic myocardium does not exacerbate myocardial infarction: Evidence against lethal cell reperfusion injury in the rabbit

In the clinical setting of acute myocardial infarction, coronary reperfusion may occur intermittently. Whether this intermittent or stuttering reperfusion exacerbates reperfusion cell injury is not known. To investigate whether stuttering reperfusion affects the development of necrosis, anesthetized male rabbits were randomized to either control or stuttering-reperfusion groups. The control rabbits underwent 40 minutes of continuous left anterior descending (LAD) occlusion followed by 3 hours of continuous reperfusion. The stuttering-reperfusion rabbits were occluded for the same 40 minutes but were reperfused for 1 minute at 37, 39, and 41 minutes into the occlusion period. Each of these brief reperfusion periods was followed by 1 minute of occlusion. After 40 minutes of occlusion (43 minutes after initial occlusion), the stuttering-reperfusion group was continuously reperfused for 3 hours. Regional myocardial blood flow was measured during occlusion and 30 minutes after final reperfusion in both groups. Area at risk (AR, %LV) was delineated by in vivo blue dye injection and the area of necrosis (AN) by in vitro tetrazolium staining.Results There was no difference in AR blood flow between groups, Ischemic blood flow (ml/min/g) was 0.05 ± 0.02 in the control group and 0.09 ± 0.04 in stuttering-reperfusion group. After reperfusion, blood flow in the ischemic area was 1.36 ± 0.13 in control and 1.87 ± 0.40 in stuttering-reperfusion rabbits. The AN expressed as a percentage of the AR was 43 ± 8 in the control rabbits and 36 ± 6 in the stuttering-reperfusion rabbits. Stuttering-reperfusion did not augment the development of necrosis compared with the control group.Conclusion Reperfusing the myocardium in a stuttering fashion had no effect on the amount of necrosis and did not contribute to lethal cell reperfusion injury in this model.     

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.     

Effect of spontaneous reperfusion on myocardial infarct size

The effect of perfusion of the infarct artery on myocardial infarct size was studied in 39 patients who had not received interventive therapy. At predischarge coronary angiography, 19 patients had subtotal and 20 total occlusion of the infarct artery. The early ST-segment elevation recorded on a 12-lead electrocardiogram was used as an index of the amount of initially jeopardized myocardium. Infarct size was estimated by peak serum creatine kinase and, at discharge, by a QRS score, sigma Q and sigma R on a 12-lead electrocardiogram, and by radionuclide global and infarct segment left ventricular ejection fraction. Despite a similar degree of initial ischemia (sigma ST), infarct size was smaller in the 11 patients with anterior infarction and subtotal occlusion than in the 9 patients with anterior infarction and total occlusion when measured by peak serum creatine kinase (2114 +/- 1192 U/l vs. 3653 +/- 1059 U/l, p less than 0.02), QRS score (5.0 +/- 2.7 vs. 9.6 +/- 3.5, p less than 0.01), sigma Q (3.25 +/- 2.74 mV vs. 5.92 +/- 3.56 mV, p less than 0.10), sigma R (4.36 +/- 1.25 mV vs. 2.16 +/- 0.91 mV, p less than 0.001), global left ventricular ejection fraction (45.0 +/- 12.2% vs. 33.4 +/- 6.7%, p less than 0.05), and infarct segment ejection fraction (40.4 +/- 8.2% vs. 30.3 +/- 5.4%, p less than 0.05). In the inferior infarct patients, both the degree of initial ischemia and final infarct size were similar in the 8 patients with subtotal and in the 11 patients with total occlusion.(ABSTRACT TRUNCATED AT 250 WORDS)     

R56865 is antifibrillatory in reperfused ischemic guinea-pig hearts,even when given only during reperfusion

Summary R56865 was previously characterized as an inhibitor of Na and Ca overload that has beneficial effects during ischemia and reperfusion. An isolated guinea-pig heart preparation was subjected to 60 minutes of ischemia and 60 minutes of reperfusion. R56865 was given before ischemia and with the onset of reperfusion, applying different dosing schedules, including an initial loading dose. R56865 below 0.1 µmol/l had no cardiodepressant effects in normoxic hearts and at 0.1 µmol/l reduced left ventricular pressure marginally. The onset of ischemic contracture was delayed only at this concentration. R56865 given before ischemia potently inhibits delayed sustained fibrillation occurring during reperfusion in the concentration range between 0.01 µmol/l and 0.1 µmol/l. Analysis of cellular Na⁺, K⁺, and Ca²⁺ concentrations revealed that R56865 substantially improves the ionic homeostasis of myocardial cells. Most importantly, the compound also reduced the incidence of delayed sustained fibrillation when given at the onset of reperfusion. R56865 was most effective when fast equilibration of drug with tissue was achieved by giving an initial loading dose. In particular, the cellular Na⁺ and Ca²⁺ contents were improved using this dosing scheme. The results are compatible with the classification of R56865 as an inhibitor of Na⁺ and Ca²⁺ overload.     

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.     

Ultrastructural evaluation of postischemic cell death (lethal reperfusion injury) in porcine hearts

This study investigated whether reperfusion results in an increase of ultrastructurally determined myocardial injury in pig hearts. The left anterior descending coronary artery (LAD) was distally occluded in 12 pigs for 35–45 minutes and then reperfused for 3 hours. At the end of ischemia, as well as after 3 hours of reperfusion, one transmural biopsy was removed from the center of the risk region and subdivided into four specimens, representing the subendocardial (I), subendo-midmyocardial (II), subepi-midmyocardial (III), and subepicardial layers (IV). The degree of injury was assessed by electronmicroscopy and was scored as reversible (1), an almost equal mixture of reversible and irreversible (2), and totally irreversible (3) damage. In addition, infarct size was determined as the ratio of infarcted (tetrazolium stain) to ischemic (dye technique) myocardium. Infarct sizes ranged from 29.3% to 93% (mean 61.2%). The scores of injury of the four tissue layers before and after reperfusion did not differ significantly: layer I, 2.4 ± 0.8/2.3 ± 0.9; layer II, 2.2 ± 0.9/2.0 ± 0.9; layer III, 1.8 ± 0.9/2.0 ± 0.9; and layer IV, 1.6 ± 0.9/1.3 ± 0.6. The means of the four layers were almost identical at the end of ischemia (2.1 ± 0.8) and after 3 hours of reperfusion (2.0 ± 0.6). A linear regression analysis with 95% confidence limits of the score values before and after reperfusion indicated that maximally 25% of a mean final infarct size of about 50% may be due to lethal reperfusion injury. This study suggests that cell death in regional ischemia and reperfusion occurs predominantly during ischemia and not during reperfusion.     

Effects of the superoxide radical scavenger superoxide dismutase,and of the hydroxyl radical scavenger mannitol,on reperfusion injury in isolated rabbit hearts

Summary Hydroxyl radical formation, secondary to superoxide radical generation, has been advocated as the actual mechanism of oxygen radical-mediated damage in biological systems. The present study was designed to compare the efficacy of administration of the hydroxyl radical scavenger mannitol vs. that of the superoxide radical scavenger superoxide dismutase (SOD) in reducing myocardial reperfusion injury, and to test whether combined treatment with both agents would confer better tissue protection compared with either intervention alone. Rabbit hearts perfused within a ³¹P nuclear magnetic resonance (³¹P-NMR) spectrometer were subjected to 30 minutes of total global ischemia at 37°C. At reflow, 12 hearts in each group received either (a) a bolus of standard perfusion buffer, followed by 45 minutes of reperfusion (controls); (b) the superoxide radical scavenger recombinant human SOD (h-SOD, as a 60,000 U bolus followed by a 100 U/ml infusion for 15 minutes); (c) the hydroxyl radical scavenger mannitol (50 mM bolus followed by 15 minutes of 50 mM infusion); or (d) a combination of both agents. All treated hearts were switched to standard buffer for the remaining 30 minutes of reperfusion. Treatment with h-SOD alone was associated with a significant improvement in the recovery of cardiac contractility and coronary flow, as well as of ATP content, compared to control hearts. In contrast, mannitol treatment resulted in a small, nonsignificant improvement in these parameters. The addition of mannitol to h-SOD did not result in further significant improvement of contractility and ATP recovery compared to h-SOD alone. These data demonstrate that under our experimental conditions significant protection against reperfusion injury can be achieved by the administration of h-SOD alone, without the need for additional hydroxyl radical scavenger therapy with mannitol. These results do not exclude that significant tissue protection may be achieved by different doses of mannitol or by other agents. However, they suggest that under definite experimental conditions prevention of hydroxyl radical formation, rather than attempts to minimize hydroxyl radical toxicity, might be a more efficient method to prevent oxygen radical-mediated reperfusion injury in isolated hearts.     

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.     

Temporal and spatial development of infarcts in porcine hearts

Summary We investigated the temporal and spatial development of infarcts in porcine hearts to evaluate the time-dependent beneficial effect of reperfusion on infarct size. The left anterior descending coronary artery (LAD) was occluded in 17 pigs for different periods of time followed by 4 hours of reperfusion. Transmural needle biopsies subdivided into subendocardial and subepicardial halves were taken from the ischemic apex after 60 min of ischemia to determine the tissue concentrations of ATP and NAD. The myocardium-at-risk was assessed with a fluorescent dye injected into the right atrium at the end of the experiments, just after the LAD had been reoccluded. The excised hearts were cut into slices parallel to the heart basis. The ischemic myocardium was measured by planimetry of the nonfluorescent areas whereas the infarcted tissue was determined with the NBT stain and related to the area-at-risk. Ischemic cell death started in the jeopardized left ventricular subendocardial septum after about 30 min of ischemia. The further progress involved the right subendocardial septum and the subendocardium of the left anterior free wall. Already after 75 min of ischemia most of the myocytes-at-risk were irreversibly injured.Infarctions reached their final extent after 90–120 min of ischemia. These results indicate that in hearts without a significant collateral blood flow reperfusion can only reduce infarct size if its initiated within 60–75 min of ischemia. Like in canine hearts infarctions progress from the ischemic subendocardium towards the outer layers.This study was supported by a grant from SFB 89 Kardiologie, Göttingen     

Use of the QRS scoring system in the early estimation of myocardial infarct size following reperfusion

While the QRS scoring system has been established as a convenient tool for estimating infarct size in nonreperfused patients during the chronic stage of myocardial infarction, its applicability to reperfused patients in the acute stage has not been established. To investigate whether infarct size could be estimated by the QRS scoring system soon after reperfusion, we evaluated QRS scores obtained serially 6 hours to 1 month after reperfusion, total creatine kinase release, and left ventricular ejection fraction in 126 patients with acute myocardial infarction who underwent successful reperfusion therapy. A significant correlation was observed between the QRS score obtained after 6 hours and that obtained after 1 month (r = .89). The QRS scores obtained after 6 hours and 1 month were significantly correlated with total creatine kinase release (r = −.65 and r = −.75, respectively) and left ventricular ejection fraction (r = .62 and r = .76, respectively). Thus, the QRS scoring system can be used as a simple and economical method for estimation of infarct size soon after reperfusion.     

Postconditioning cardioprotection against infarct size and post-ischemic systolic dysfunction is influenced by gender

Whether cardioprotection by postconditioning (PostC) is gender dependent is not clear. We studied the effect of PostC in terms of both infarct size (IS) and post-ischemic systolic dysfunction (PSD) reduction. Isolated male and female rat hearts were subjected to 10- or 30-min of global ischemia and 120-min of reperfusion, with or without PostC (i.e., 5 cycles of 10-s reperfusion/ischemia immediately after the ischemia). Surprisingly, after 10-min ischemia, IS and PSD were greater in female than male hearts (IS: 21 ± 2% Vs. 11 ± 2%; P < 0.01), while PostC attenuated IS and PSD in female hearts only. After 30-min ischemia IS was smaller in female than male hearts (52 ± 2% Vs. 61 ± 3%; P < 0.05), whereas PSD was similar in these two groups. PostC reduced IS in both genders, though the effect was smaller (P < 0.05) in females. Yet, PostC reduced PSD in female, but not in male hearts. Contracture development paralleled IS in all groups. To check the effects of buffer perfusion over heart function, additional hearts underwent 150-min buffer perfusion only. Contractile function of these hearts was not significantly affected over time. In conclusion IS, contracture and PSD are differently affected by gender, depending on ischemia duration. Yet, reduction of IS induced by PostC depends on the extension of IS induced by index-ischemia. While in female hearts reduction of PSD paralleled IS reduction, in male it does not occur. Results suggest that improvement of systolic function is mainly due to the anti-necrotic rather than to the anti-stunning effect exerted by PostC. Returned for 1. Revision: 20 August 2008 1. Revision received: 6 October 2008 Returned for 2. Revision: 20 October 2008 2. Revision received: 24 October 2008     

Hypothermia during reperfusion does not reduce myocardial infarct size in pigs

We previously described a method for regional myocardial cooling that reaches the target temperature within 4 min. The present study evaluated whether this method for regional myocardial cooling during reperfusion reduces myocardial infarct size (IS) in 75-kg pigs. Myocardial infarction was induced by inflation of an angioplasty balloon in the left anterior descendent artery for 45 min followed by 3 h reperfusion. First, 15 pigs were randomized to regional myocardial cooling during reperfusion (n = 8) or control (n = 7). As further control experiments, systemic hypothermia was induced prior to ischemia (n = 3) and during reperfusion (n = 3). IS and area at risk (AAR) were evaluated in vivo by single photon emission cardiac tomography (SPECT) and by standard histochemical staining. Regional cooling during reperfusion did not reduce IS/AAR as assessed by histochemistry (cooling: 0.71 +/- 0.8; control: 0.68 +/- 0.10; p = ns) and SPECT (cooling: 0.90 +/- 0.20; control: 0.88 +/- 0.32; p = ns). Systemic hypothermia during ischemia reduced IS/AAR (histochemistry: 0.09 +/- 0.11; SPECT: 0.25 +/- 0.22; p < 0.001 and p = 0.01 vs control, respectively). Induction of systemic hypothermia during reperfusion had no significant effect on IS/AAR (histochemistry: 0.63 +/- 0.07; SPECT: 0.74 +/- 0.09; p = ns vs control for both comparisons). In conclusion, hypothermia during ischemia is strongly myocardioprotective while hypothermia during reperfusion does not reduce myocardial infarct size in human-sized pigs.     

Reduction of infarct size in vivo with ischemic preconditioning: Mathematical evidence for protection via non-ischemic tissue

Summary We constructed a mathematical model of ischemic preconditioning based on experimental data obtained from rat hearts. In this animal model of low collateral blood flow, we found that infarct size in preconditioned hearts, expressed as a percentage of area at risk, increased as the size of the area at risk increased (r=0.76, p=0.0007). In contrast, infarct size in control hearts appeared independent of changes in area at risk. Similarly, the lateral distance between the edge of the area at risk and the edge of the area of necrosis did not vary with risk region in control hearts, but in preconditioned hearts, lateral distance decreased as the size of the area at risk increased (r=–0.67, p=0.0046). We used these findings to develop a simple model which provided mathematical relationships between lateral distance and area at risk and between infarct size and area at risk for both control and preconditioned hearts that were consistent with the experimental data. These relationships led us to propose that in preconditioned hearts 1) a protective substance may be produced or activated throughout the heart, and 2) that the protective substance may be transported by diffusion. If we assumed uniform production of protective substance in an amount proportional to the size of the ischemic and non-ischemic areas, we were able to derive, using a simple diffusion model, relationships between the above variables that were consistent with our mathematical model and with the experimental data. Although our model does not identify the protective substance, its implications provide ideas for additional crucial experiments that may enhance our understanding of ischemic preconditioning.List of abbreviations used A_N area of necrosis - A_N/A_R area of necrosis expressed as a fraction of the area at risk - A_R area at risk - C concentration of protective substance; C₁ inside the area at risk, C₂ outside the area at risk - d diffusion distance - LV left ventricle - m amount of protective substance supplied to the area at risk - s lateral distance between the edge of the infarct and the edge of the area at risk - t thickness of the area at risk - w width of the area at risk     

Left ventricular unloading during reperfusion does not limit myocardial infarct size

To determine whether venting the left ventricle during coronary reperfusion limits myocardial infarct size, we studied paced (200 beats/min) Langendorff rabbit hearts, perfused with blood from a support rabbit. A left coronary artery was occluded for 60 minutes, followed by 2 hours of reperfusion. Four experimental conditions, as follows, were used: In group 1 (control), the hearts contracted isovolumetrically on a fluid-filled balloon in the left ventricle during both occlusion and reperfusion. In group 2, the balloon was present only during occlusion, and the heart was vented during reperfusion. Hearts in group 3 were vented during occlusion and developed pressure during reperfusion. In group 4, the left ventricle was vented during occlusion and reperfusion. Perfusion pressure (91.2 +/- 0.9 mm Hg) and coronary flow (0.88 +/- 0.03 ml/min/g) were not different between groups. Left ventricular pressures (mean of all groups) were 87.3 +/- 1.5 mm Hg systolic and 6.5 +/- 0.6 mm Hg diastolic. Infarcted myocardium was assessed by triphenyl tetrazolium staining and expressed as a percentage of the area at risk, as measured by fluorescent particles. Venting during both ischemia and reperfusion (n = 10) did result in significantly smaller infarcts than in the unvented controls (n = 10), that is, 13 +/- 5% vs. 41 +/- 6%, respectively. Venting only during reperfusion (n = 10) or occlusion (n = 11) did not significantly limit infarct size (57 +/- 6% and 32 +/- 5%, respectively), as compared with controls. Thus, the clinically feasible intervention of left ventricular venting during reperfusion was not cardioprotective.     

Comparative study on the effects of intracoronary nicorandil and nitroglycerin in ischaemic, reperfused porcine hearts

The direct cardioprotective properties of nitroglycerin andnicorandil were compared in regionally ischaemic (45 min), reperfused(24 h) porcine hearts. Intracoronary treatments, which werestarted 15 min prior to occlusion of the distal left anteriordescending coronary artery (LAD), were continuously administeredfor 105min. The following equi-hypotensive drug dosages wereused in nine pigs each; nitroglycerin 6 fig. kg^–1 x minbefore ischaemia and during 45 min of reperfusion, 0.6 µg.kg^–1x min during ischaemia; nicorandil 5 fig. kg^–1x min before ischaemia and during 45 min of reperfusion, and0.5 fig. kg^–1 x min during ischaemia. Nine control animalswere treated with isotonic sodium hydrochloride solution (1ml. min^–1). Despite comparable effects on blood pressure, intracoronarynicorandil, in contrast to intracoronary nitroglycerin, didnot increase heart rate. Although neither drug affected coronaryblood flow significantly, nicorandil substantially reduced regionalmyocardial oxygen consumption before coronary artery occlusion( – 37±22%, P=0003 vs control group, P=0.01 vsnitroglycerin treatment). Infarct sizes (tetrazolium method)after 45 min of ischaemia and 24 h of reperfusion were significantlydecreased by nicorandil (control group 76.9 ± 19%, nicorandilgroup 49.3 ± 24%, P=0.012)whereas nitroglycerin exhibiteda borderline effect (62.5 ± 15%, P=0.054). Both treatmentsresulted in improved regional systolic shortening of the reperfusedsegment at the end of the experiments but this was not significant.At these drug dosages the direct cardioprotective action ofnicorandil is slightly superior to nitroglycerin. This may beascribed to its K-channel opening property associated with reducedregional myocardial oxygen consumption before the onset of ischaemia.     

Acute treatment with vitamin E does not protect the regionally ischemic,reperfused porcine heart

Summary Thirty pigs were randomly assigned to a blind treatment with vitamin E or placebo. Ten animals each received 0.5g d-alpha tocopherol intravenously before ischemia (group 1) or before reperfusion (group 2). Ten control pigs were treated with a lipid emulsion as placebo. The left anterior descending coronary artery was distally ligated for 45 min followed by 3 days of reperfusion. Infarct size was determined as ratio of infarcted (tetrazolium stain) to ischemic myocardium (dye technique). Regional systolic shortening was assessed by sonomicrometry. Myocardial and plasma concentrations of vitamin E were determined by high-performance liquid chromatography. Global hemodynamic parameters and estimated left ventricular oxygen consumption did not differ among the three groups. Intravenous treatment with vitamin E raised the plasma levels of this vitamin from 1 ± 0.3 mg/l (control group) to 21 ± 6 mg/l before ischemia, to 4 ± 2 mg/l before reperfusion and to 2 ± 0.6 mg/l at the end of the experiments in group 1. In group 2, vitamin E plasma levels increased from 1 ± 0.3 mg/l to 24 ± 13 mg/l before reperfusion and to 2 ± 0.6 mg/l after 3 days of reperfusion. At the end of the experiments, myocardial vitamin E concentrations amounted to 4.2 ± 0.7 ng/mg fresh weight (control group), 9.7 ± 2.1 ng/mg (group 1), and to 8.7 ± 1.4 ng/mg (group 2). The increase in vitamin E plasma concentration was not associated with a cardioprotective effect. Infarct sizes of the three groups (group 1: 68 ± 12%, group 2: 66 ± 15%, control group: 69 ± 8%) were almost identical. Furthermore, recovery of systolic shortening was not improved by the acute vitamin E treatment. Mean systolic shortening of the reperfused segment amounted to 4% in the two treatment groups and 3% in the control group after 3 days of reperfusion. These results suggest that an acute increase in vitamin E plasma concentration before ischemia or during the early phase of reperfusion does not protect the ischemic, reperfused porcine heart.This study was supported by a grant from the Deutsche Forschungsgemeinschaft, KL 724     

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.     

洛伐他汀预处理的延迟性心肌保护作用及其机制

目的探究洛伐他汀在大鼠心脏急性缺血/再灌注中的延迟性心肌保护作用及其机制。方法SD大鼠24只随机分为3组（每组8只）:模型对照组（C）;Lovastatin组（L）,洛伐他汀直接灌胃两周15mg/（kg·d）;Lovastatin复合LNAME组（N）,洛伐他汀15mg/（kg·d）直接灌胃2周同时腹腔注射LNAME30mg/（kg·d）;2周后建立在体急性缺血/再灌注心脏模型,监测缺血/再灌注前后血流动力学各项指标,同时观察各组血脂水平及其血浆中MDA、SOD、LDH以及CK的变化情况。结果L组和N组较C组心率显著减慢（P<0.01）,缺血/再灌注心律失常消失和再灌注时-dp/dtmax下降显著改善（P<0.05）;各项血脂指标不变的情况下,洛伐他汀显著减少再灌注时血浆中MDA生成和LDH及CK的释放（P<0.01）,并且提高心肌组织SOD活性（P<0.05）。结论Lovastatin对在体大鼠心脏急性缺血/再灌注时具有非降脂外的延迟性心肌保护作用。NO合酶途径是其心脏保护作用的诸多途径之一。     

Intracoronary trimetazidine does not improve recovery of regional function in a porcine model of repeated ischemia

Summary We evaluated the effect of trimetazidine (TMZ) on recovery of regional cardiac function in anesthetized open-chest pigs, subjected to fifteen 2-minute occlusions of the left anterior descending coronary artery, separated by 2 minutes of reperfusion and a 120-minute recovery period. Regional myocardial function was evaluated by sonomicrometry-derived segment lengthening and the area enclosed by the left ventricular pressure-segment length loop (external work, EW) in animals, which received either an intracoronary infusion of TMZ (33 µg/kg/min, n=6) or saline (1 ml/min, n=7), starting 15 minutes before the first occlusion and ending 2 minutes after the 15th occlusion. In addition, myocardial malondialdehyde production to evaluate oxygen free radical production, oxygen consumption, and the ATP, ADP, and AMP content, as well as the energy charge, were determined at regular time intervals.In control pigs the sequences of occlusion-reperfusion did not affect systemic hemodynamics, except for the LVdP/dt_max, which decreased by 11% during the interventions and did not recover during the following reperfusion period of 2 hours (78% of baseline, p<0.05). Systolic segment length shortening and EW were increased at the end of the first occlusion-reperfusion cycle, decreased gradually during the remainder of the occlusion-reperfusion periods, and did not improve during the recovery period. Energy charge and myocardial blood flow were not impaired, but oxygen consumption was decreased during the recovery period. The malondialdeyde data did not provide evidence for production of oxygen free radicals. TMZ decreased LVdP/dt_max by 6% (p<0.05) and caused a twofold increase in postsystolic segment shortening (p<0.05) before the first occlusion, but did not influence the hemodynamic responses, the changes in regional cardiac function, and the metabolic events produced by repetitive regional ischemia.