Effects of increased heart work on release of norepinephrine and ventricular arrhythmias following reperfusion in the isolated rat heart.

The influence of increasing left atrial pressures (0.5, 1.0, and 2.0 kPa) on the incidence of ventricular arrhythmias and the liberation of prelabeled norepinephrine (3H-NE) was investigated in the isolated working rat heart. Acute regional myocardial ischemia (30 min) was produced by ligature of the left main coronary artery with subsequent release of the ligature to achieve reperfusion, which consistently provoked ventricular arrhythmias. The magnitude of regional ischemia was measured by microspheres, and the efflux of 3H-labeled NE compounds was measured in the coronary effluent. Our data show that an increase in atrial pressure enhanced reperfusion arrhythmias, but the magnitude of NE release was not directly related to the occurrence of arrhythmias. It is proposed that increased heart work has an arrhythmogenic effect by enhancing the severity of regional ischemia.     

Effect of repeated regional myocardial ischemia in the rat heart on reperfusion arrhythmias and release of norepinephrine.

We tested the hypothesis that repetitive regional myocardial ischemia in the rat could decrease reperfusion ventricular arrhythmias, possibly acting by diminished release of norepinephrine. Isolated perfused working rat hearts were pre-labeled with tritiated norepinephrine (NE3H). The efflux of 3H-labeled compounds was measured in the effluent coronary flow. Each heart was subjected to two consecutive periods of regional myocardial ischemia induced by ligature of the left coronary artery. The duration of the first ischemic period was 5 or 10 min and that of the second was 10 min. Serious rhythm disturbances did not occur during the first period of ischemia but did after reperfusion. The amount of NE3H liberated during the reperfusion period was more marked after an initial ischemic period of 10 min than after 5 min of ischemia. Reperfusion arrhythmias were of little importance after 5 min of ischemia but developed in a sustained pattern when reperfusion followed 10 min of ischemia. After 5 min of ischemia, the mean duration of reperfusion arrhythmias was 12.8 +/- 10.4 s during the first 3 min of reperfusion, but after 10 min of ischemia the mean duration of serious rhythm disturbances was 149.7 +/- 16.7 s. Reperfusion after the second 10-min occlusion increased the release of NE3H. In series 5-10, the percentage of NE3H compared with the total radioactivity was a mean of 71.4 +/- 3.3% during the 5 min of ligature, 79.0 +/- 5.3% during the first 3 min of reperfusion. During the 10-10 series in which the ligature was maintained for 10 min, the percentage of NE3H compared with the total radioactivity was 70.6 +/- 5.1%, 81.1 +/- 8.7% during the first 3 min of reperfusion. These results show no reduction of any catecholamine release or of reperfusion arrhythmias by repetitive regional ischemia and provide no evidence for any preconditioning effect after short periods of regional ischemia. The antiarrhythmic effects of repetitive myocardial ischemia such as preconditioning previously reported may depend on the exact protocols used.     

Effect of oligomer procyanidins on reperfusion arrhythmias and lactate dehydrogenase release in the isolated rat heart

The antiarrhythmic effect of an oral 3-week-pretreatment with oligomer procyanidins derived from Vitis vinifera was investigated on the isolated perfused heart after global no-flow ischemia (procyanidin-treated group: n = 9, control group: n = 13). Hearts were perfused with a modified Krebs-Henseleit solution in which the K+ content was reduced to 3.0 mmol/l in order to lower the fibrillation threshold. Monophasic action potentials in addition to ECG were recorded. The durations of ischemia and reperfusion were 20 and 30 min, respectively. Arrhythmias including ventricular fibrillation (VF), ventricular tachycardia (VT), flutter (Fl) and bradycardia were evaluated. During the reperfusion, irreversible VF occurred in most of control hearts. The incidence of VF (percentage of the hearts in which VF occurred) was lowered by oligomer procyanidins from 84.6 to 55.6 %, and the duration of the episodes of VF (expressed as percentage relative to the total duration) was significantly shortened from 76.1 +/- 27.9 % to 36.6 +/- 40.6 % (p = 0.036). Simultaneously, the percentage of duration of normal sinus rhythm (NSR) increased from 19.5 +/- 30.3 % to 46.2 +/- 35.9 % (n.s.). VF occuring in the procyanidin-treated hearts could be reversed in two hearts within few minutes to a stage of "reversible arrhythmias" consisting of short episodes (1 to 60 s) of either Fl or VT or bradycardia or NSR alternating with each other. LDH (lactate dehydrogenase) release in the first drops appearing from the reperfused heart was significantly reduced in the procyanidin-treated rats (66.7 +/- 36.2 mU/min, n = 8) in comparison to controls (159.7 +/- 79.0 mU/min, n = 10; p = 0.010). These results demonstrate an antiarrhythmic and cytoprotective effect of oral pretreatment with oligomer procyanidins under the given experimental conditions.     

双乙酰香茶菜甲素抗离体大鼠工作心脏缺血再灌注损伤的作用

目的：观察双乙酰香茶菜甲素（ＤＡＡＡ）对心肌缺血再灌注损伤的作用．方法：离体大鼠心脏停灌４０ｍｉｎ，再灌２５ｍｉｎ，造成心肌缺血再灌注损伤模型．结果：ＤＡＡＡ０１３，０２５，０５０ｍｍｏｌ·Ｌ－１对再灌注所致心功能低下有心脏保护作用，降低室颤发生率及乳酸脱氢酶（ＬＤＨ），丙二醛（ＭＤＡ）的生成量．ＤＡＡＡ０２５ｍｍｏｌ·Ｌ－１改善心肌超微结构．结论：ＤＡＡＡ抗心肌缺血再灌注损伤的作用与其抗脂质过氧化损伤有关．     

Involvement of the renin-angiotensin system in ischemic damage and reperfusion arrhythmias in the isolated perfused rat heart.

We have investigated the contribution of the renin-angiotensin system to the damage caused by 40-min global ischemia in the isolated rat heart. A converting enzyme inhibitor, enalaprilat (70 nM), an angiotensin II receptor antagonist, compound 89 (2 microM), and an inhibitor of rat renin, CGP 44099A (20 nM), given before ischemia reduced the median duration of ventricular fibrillation on reperfusion to a similar extent (5.53, 5.72, and 5.14 min, respectively, compared to 13.98 min in the control group) but had no effect on creatine phosphokinase release (22.2 +/- 2.6, 22.1 +/- 6.8, and 24.1 +/- 3.6, IU/30 min, respectively, compared to 19.9 +/- 1.9 IU/30 min) or recovery or left ventricular developed pressure (67 +/- 6, 73 +/- 7 and 71 +/- 6%, respectively, compared to 66 +/- 3% after 30 min reperfusion). The increase in coronary resistance and left ventricular diastolic pressure on reperfusion was not affected by any of the agents. All three agents also tended to reduce the duration of ventricular fibrillation when given only on reperfusion. We conclude that angiotensinogen is present in the rat heart and it is converted to angiotensin I by a renin or a renin-like aspartic proteinase. The angiotensin I is converted to angiotensin II by converting enzyme. The angiotensin II formed is an important mediator of postreperfusion ventricular fibrillation in the isolated rat heart but does not contribute to the reduction in mechanical function produced by global ischemia in this preparation.     

Comparison of the effect of antidepressant drugs on arrhythmias in the isolated rat heart subjected to myocardial ischaemia and reperfusion

Rat isolated hearts were perfused according to the Langendorff's method. The hearts were prelabelled with 3H-noradrenaline (3H-NA) and the left coronary artery was occluded during 10 min. The liberation of 3H-NA and the development of ventricular arrhythmias were investigated during ischaemia and the following reperfusion period. In control preparations, reperfusion was followed by ventricular fibrillation and a sudden release of radioactivity in the coronary effluent. Antidepressants such as imipramine, metapramine, mianserin and nomifensine prevented reperfusion arrhythmias in a concentration-dependent manner and caused bradycardia. Amineptine, however, was ineffective in preventing reperfusion arrhythmias even in a high concentration, this agent did not decrease heart rate. Nevertheless none of the antidepressants changed the rate of liberation of 3H-NA during the ligation and reperfusion periods. A quinidine like action seems the most appropriate explanation for the cardiac effects of these antidepressant drugs.     

Effects of nicainoprol on reperfusion arrhythmia in the isolated working rat heart and on ischemia and reperfusion arrhythmia and myocardial infarct size in the anesthetized rat

The effect of the novel antiarrhythmic agent nicainoprol on coronary occlusion and reperfusion arrhythmia was investigated in isolated working rat hearts and in anesthetized rats. In isolated working rat hearts nicainoprol (10(-6) M, 5 X 10(-6) M and 10(-5) M) induced concentration-related protection against reperfusion arrhythmia without changing the cardiodynamics, with the exception of a decrease in heart rate at the highest concentration. Enzyme levels (lactate dehydrogenase and creatine kinase) in the coronary venous effluent, and cardiac tissue concentrations of glycogen, lactate, ATP and creatine phosphate were not affected by nicainoprol. Given to anesthetized rats, nicainoprol (5 and 10 mg/kg i.v.) reduced dose dependently in the early post occlusion (0-30 min) period, the percentage of animals with premature ventricular complexes (PVCs) and ventricular tachycardia while completely preventing the occurrence of ventricular fibrillation. In the reperfusion period no animal treated with 5 mg/kg and 12% of the rats treated with 10 mg/kg showed PVCs (the only form of arrhythmia observed in this period) versus 60% of the control rats. Both doses of nicainoprol induced a decrease in heart rate, blood pressure and myocardial oxygen consumption. The ratio of infarct mass to ventricular mass was significantly reduced by 20% at a dose of 5 mg/kg and by 28% at the dose of 10 mg/kg. Nicainoprol could be useful in the prevention and treatment of arrhythmias associated with acute myocardial infarction.     

Salicylate reduces ventricular dysfunction and arrhythmias during reperfusion in isolated rat hearts.

Recent studies have shown the ability of salicylic acid (SA) to trap hydroxyl radicals (OH.) generated during reperfusion in ischemic myocardium. Since OH. is implicated in the pathogenesis of reperfusion injury, we examined the effect of SA on reperfusion-induced arrhythmias and postischemic ventricular dysfunction. Isolated rat hearts perfused by the Langendorff technique were preperfused with Krebs-Henseleit buffer containing SA for 10 min. Hearts were then made ischemic for 30 min, followed by 30 min of reperfusion. In a separate group, SA was administered only at the onset of reperfusion. The left ventricular contractile functions, left ventricular developed pressure (LVDP) and its first derivative (LV dP/dt), coronary flow (CF), and creatine kinase (CK) release were determined before and after ischemia. Epicardial electrocardiogram (ECG) was also recorded to analyze the incidence of ventricular tachycardia (VT) and ventricular fibrillation (VF). SA improved LVDP, LV dp/dt, and CF recovery and reduced CK release compared to the control group. The incidence of VT and VF during reperfusion was also significantly reduced by SA. Analysis of tissue thiobarbituric acid-reactive products indicates that SA decreased oxidative stress during reperfusion. In conclusion, these results suggest that SA reduces myocardial reperfusion injury and attenuates ventricular arrhythmias by trapping OH. radicals upon reperfusion in isolated rat hearts.     

Local release of myocardial norepinephrine during acute ischemia: an experimental study in the isolated perfused rat heart

The appearance of an early ischemia-induced local release of myocardial norepinephrine (NE) was examined in the isolated Langendorff-perfused rat heart prelabeled with [3H]NE. Either glucose or lactate was used as the perfusion substrate. Ischemia for a 60-min period was produced by global flow reduction (by 90%) or left coronary artery ligation followed by a 15-min reperfusion period. During the first 20 min of ischemia both the concentration of [3H]NE and the fraction of total 3H representing nonmetabolized [3H]NE were increased in the coronary venous effluent. This early increase in [3H]NE concentration was most pronounced in hearts with global ischemia perfused with lactate as substrate (from 19 +/- 2 to 524 +/- 76 fmol/ml/g after 20 min of ischemia). The quantity of [3H]NE released was then further increased during the 60-min period of ischemia. Reperfusion of the ischemic myocardium was associated with a marked outflow of [3H]NE and [3H]NE metabolites, primarily representing a washout from the ischemic tissue. Under the present experimental conditions the ischemia-induced release of NE was attenuated by glucose, probably owing to an ongoing glycolytic ATP formation. This effect was most pronounced during global low-flow ischemia. It is concluded that ischemia is associated with a local release of myocardial NE. In the nonworking Langendorff heart preparation, clear evidence of such a local release was already obtained after 10-20 min of ischemia.     

氟卡胺对豚鼠工作心脏缺血复灌诱发心率失常的影响

用离体豚鼠工作心脏模型研究了抗心律失常药物氟卡胺诱发心律失常的初步机理。结果发现，氟卡胺在１，１０μｍｏｌ·Ｌ－１范围内对缺血复灌诱发的心律失常有明显的保护作用。但１００μｍｏｌ·Ｌ－１的氟卡胺对此模型诱发的心律失常不但无对抗作用，反而能加重和诱发心律失常。当氟卡胺１００μｍｏｌ·Ｌ－１同时加入ｌμｍｏｌ·Ｌ－１维拉帕米对此模型诱发的心律失常表现出明显的对抗作用，作用强于维拉帕米和氟卡胺单独使用。提示大剂量氟卡胺由于较强的抑制了心肌细胞钠、钾电流，从而使钙通道活性过高而产生心律失常。     

不同浓度的L-精氨酸在心肌缺血再灌注损伤中的不同效应

目的 观察L-精氨酸-一氧化氮途径（L-Arg-NO)是否对心肌再灌注损伤有影响，以及不同浓度的L-精氨酸（L-Arg)的不同效应，方法 将48只雄性SD大鼠随机分为6组。缺血对照组，1mM组，3mM组，10mM组，30mM组，100mM组，进行离体心脏灌流实验观察缺血前及再灌注后左心功能，冠脉流出液中乳酸脱氢酶，心肌TP含量，结果 1mM组，3mM组再灌注后心功能指标，心肌酶溢出量，心肌组织ATP含量，以及心肌细胞超微结构均较对照组为佳。10mM组，30mM组再灌注后心功能恢复率，心肌组织ATP含量，电镜超微结构与对照组相比无明显差异。100mM组再灌注后心肌酶溢出量较对照组明显增高。结论 （1）在缺血前予1mM,3mM的L-Arg能减轻再灌注损伤；（2）而给予高于3mM的L-Arg并不能减轻再灌注损伤，100mM组甚至加重了再灌注损伤，说明L-Arg在缺血再灌注损伤中发挥双重作用。     

Effect of clonidine on cardiac norepinephrine spillover in isolated rat heart

The purpose of this study is to determine the effect of clonidine on cardiac norepinephrine spillover utilizing an isolated rat heart preparation with attached cardiac sympathetic nerves. Following a 20-minute stabilization period, the sympathetic ganglion for each heart preparation was electrically stimulated with 10V and 2 Hz for 30 seconds (S1: 60 pulses). Heart rate, left ventricular developed pressure, and coronary perfusion pressure was allowed to return to baseline and the perfusate was randomly switched to Krebs buffer containing one of two treatments: placebo or clonidine (1 microM). After 10 minutes of treatment, the sympathetic ganglion was again electrically stimulated with 10V and 2 Hz for 30 seconds (S2: 60 pulses). The perfusate exiting the heart before, during, and after each electrical stimulation was collected for the determination of cardiac norepinephrine spillover. Clonidine administration significantly reduced cardiac norepinephrine spillover by approximately 50% (P < 0.05) and was associated with a 36% reduction in heart rate (P < 0.05). These findings provide evidence that clonidine can directly suppress NE spillover from cardiac sympathetic nerve terminals. Thus, suppression of cardiac NE by clonidine may be due to stimulation of presynaptic alpha2-adrenergic receptors or imidazoline subtype I receptors located on cardiac sympathetic nerve terminals. Results from our study demonstrate a reduction in cardiac NE spillover by clonidine and provide additional evidence that it can directly suppress peripheral sympathetic activity in that our results were obtained utilizing an isolated perfused heart preparation with attached cardiac sympathetic nerves devoid of any CNS input.     

Beneficial effects of streptokinase on left ventricular function after myocardial reoxygenation and reperfusion following global ischemia in the isolated rabbit heart

To determine the effect of streptokinase on the ischemic myocardium independent of its effects on the occluding thrombus, the isolated rabbit heart, perfused with Krebs-Henseleit solution, was subjected to a 45-min period of ischemia--83% reduction in myocardial (perfusion) flow--plus anoxia (95% N2 and 5% CO2), followed by restoration of perfusion and reoxygenation. Streptokinase, 75 or 150 IU/min, was infused starting 15 min before reperfusion and continuing for 30 min after reperfusion. Compared with the control group, streptokinase was associated during reperfusion with a significant dose-dependent greater restoration or smaller depression of ventricular function, dP/dt, and developed pressure. To determine if streptokinase effects were mediated during the ischemic or reperfusion phase, the high streptokinase dose was administered in either the last 30 min of the ischemia or the first 30 min of reperfusion. The improvement in recovery of left ventricular function was primarily in the group having streptokinase administered only during the ischemic period. Thus, streptokinase affects the ischemic myocardium so that there is an acceleration in the recovery of ventricular function or a reduction of the impairment in ventricular function during myocardial reperfusion.     

Effect of nitric oxide and nitroxide SOD-mimic on the recovery of isolated rat heart following ischemia and reperfusion

Nitric oxide synthesized from L-arginine in cells has important salutary physiological roles, but can also exert deleterious effects. Nitric oxide (NO) can ameliorate post-ischemic reperfusion myocardial injury, yet formation from NO and O(2)z*(-) of peroxynitrite and its downstream toxic products, such as *OH, *NO(2) and CO(3)*(-), can ultimately exacerbate reperfusion damage. Nitroxide stable radicals, such as 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (TPL), unlike SOD, readily penetrate cells and catalytically remove intracellular O(2)*(-). Hence, nitroxides by virtue of catalytic removal of O(2)*(-) would be expected to diminish the adverse effect of NO and lower post-ischemic reperfusion cardiac damage. We show that post-ischemic recovery of hemodynamic functions of isolated perfused rat hearts treated with L-arginine or TPL alone did not differ from that of the control hearts. However, the recovery of hearts treated with the combined regimen of L-arginine and TPL was significantly improved, e.g. the Work Index=(left ventricular developed pressure x heart rate) recovered to 92+/-1.6% (L-arginine and TPL) vs. 59.4+/-5.4% (Control), 60+/-2.9% (L-arginine) and 53.3+/-4.3% (TPL) of the pre-ischemic value; mean+/-SEM, N=10, P<0.001. The enhanced recovery of hemodynamic function of hearts treated with L-arginine and TPL was accompanied by an increased recovery of oxygen consumption during the reperfusion. The combined regimen of L-arginine and TPL reduces the negative effects of NO by either inhibiting the production of ONOO(-) or through reaction with CO(3)z.rad;(-) and *NO(2) radicals formed during the decomposition of peroxynitrite in the presence of bicarbonate, thus promoting cardioprotection following post-ischemic reperfusion.     

Endothelin release by capsaicin in isolated working rat heart.

Capsaicin (1 nM-1 microM) induced a concentration-dependent decrease in heart rate, coronary flow, aortic flow, left ventricular developed pressure and its first derivative, dP/dt(max) in isolated working rat heart. The effect of 10 nM capsaicin was mimicked by 0.1 nM endothelin. PD142893 (200 nM), a non-selective endothelin receptor blocking agent antagonized the effect of either endothelin (0.1 nM) or capsaicin (10 nM). We conclude that the majority of the effects of capsaicin in the rat heart are mediated by neural endothelin release.     

Effect of enalaprilat on bradykinin and des-Arg9-bradykinin release following reperfusion of the ischaemic rat heart.

1. The release of bradykinin (BK) and its metabolite, des-Arg9-bradykinin (des-Arg9-BK), was studied following reperfusion of a globally ischaemic rat heart. 2. BK-like immunoreactivity increased from 13 +/- 3 (preischaemic value) to 48 +/- 12 fmol min-1 g-1 (P < 0.05, n = 14) 30 s after reperfusion. No difference in BK release was found between control hearts and hearts pretreated with the angiotensin converting enzyme (ACE or kininase II) inhibitor, enalaprilat (50 ng ml-1). 3. No significant change in des-Arg9-BK-like immunoreactivity during reperfusion was observed in control hearts. In contrast, des-Arg9-BK-like immunoreactivity rose from 44 +/- 15 to 177 +/- 61 fmol min-1 g-1 (P < 0.05, n = 7) 30 s after reperfusion in enalaprilat-treated hearts. 4. In conclusion, BK is released upon reperfusion of the globally ischaemic rat heart. ACE inhibitors, through the inhibition of kininase II, increase the formation of the active metabolite, des-Arg9-BK.     

Effect of dimethylsulfoxide on isolated rat heart and lacticodehydrogenase release

Isolated perfused rat hearts were submitted to different concentrations of dimethylsulfoxide (DMSO). Mechanical and cellular electrical activities, electrogram and perfusate lacticodehydrogenase (LDH) activity were recorded.     

8,14-二氢萨鲁塔里啶碱对缺血心脏舒张功能的保护作用

采用离体大鼠工作心脏缺血模型，观察８，１４－二氢萨鲁塔里啶碱（ＤＨＳ）对心脏舒张功能和对冠脉流出液中肌酸磷酸激酶释放的影响，结果表明，ＤＨＳ可使缺血后－ｄＰ／ｄｔｍａｘ降低，ＬＶＥＤＰ和Ｔ值的增加均显著低于对照组；并使缺血后ＬＶＳＰ、＋ｄＰ／ｄｔｍａｘ的下降百分率减低。说明ＤＨＳ对缺血大鼠心脏的舒张功能有明显保护作用，可改善收缩功能。ＤＨＳ可显著降低缺血后ＣＰＫ的释放，提示其对膜代谢损伤有一定保护作用。