Role of cannabinoid receptors in the regulation of cardiac contractility during ischemia/reperfusion

We studied the effect of selective ligands of cannabinoid (CB) receptors on contractility of isolated Langendorff-perfused rat heart under conditions of 45-min total ischemia and 30-min reperfusion. Perfusion with a solution containing selective CB receptor agonist HU-210 for 10 min before ischemia increased the severity of reperfusion contractile dysfunction. This drug decreased left ventricular developed pressure and maximum rates of contraction and relaxation, but had no effect on heart rate and end-diastolic pressure. The negative inotropic effect of the drug was transitory and disappeared after 5-min reperfusion. Pretreatment with selective CB1 receptor antagonist SR141716A and selective CB2 receptor antagonist SR144528 had no effect on heart rate and myocardial contractility during reperfusion. Our results indicate that stimulation of CB receptors can increase the degree of reperfusion-induced cardiac contractile dysfunction. However, endogenous cannabinoids are not involved in the development of myocardial contractile dysfunction during ischemia/reperfusion of the isolated heart. __________ Translated from Byulleten’ Eksperimental’noi Biologii i Meditsiny, Vol. 142, No. 11, pp. 500–504, November, 2006     

Ganoderma lucidum extract in cardiac diastolic dysfunction and irreversible cardiomyocytic damage in ischemia and reperfusion of the isolated heart

We used a model of total 45-min ischemia and 30-min reperfusion of isolated rat heart by the Langendorf technique. The course administration (15 days) of Gonoderma lucidum extract attenuated reperfusion contracture and decreased creatine kinase levels in the venous effluent from rat isolated heart during reperfusion. However, the extract did not prevent a reperfusion decrease in pressure developed by the left ventricle, reduction in the heart rate, contraction and relaxation rates. The extract had no effect on the incidence of ventricular arrhythmia. We believe that Ganoderma lucidum extract is a drug which attenuates diastolic dysfunction and prevents irreversible cardiomyocyte damage during ischemia and heart reperfusion.     

The complex adaptogenic drug tonizid attenuates myocardial contractile dysfunction and prevents irreversible cardiomyocytic damages in ischemia and reperfusion of the isolated heart

A course administration of the complex plant adaptogenic drug tonizid was ascertained to increase murine exercise tolerance. In addition, the drug increased murine survival during hypobaric hypoxia (at an altitude of 10,500 m upon 20-min exposure). A model of total 35-min ischemia and that of 30-min reperfusion of the rat isolated heart were used by the Langendorff technique. The course administration of tonizid attenuated a reperfusion decrease in the left ventricular pressure and in the rate of contraction. However, tonizid did not prevent a reperfusion reduction in heart rate, a decrease in the rate of relaxation and an elevation of end diastolic pressure. Tonizid lowered the level of creatine kinase in the venous effluent from the isolated rat heart during reperfusion. At the same time, the plant adaptogen exerted no effect on the incidence of ventricular arrhythmias and coronary flow. It has been suggested that tonizid is an adaptogenic drug that attenuates contractile dysfunction and prevents irreversible cardiomyocytic damage during ischemia and reperfusion of the isolated heart.     

Activation of mu-opioid receptors and cardiomyocyte resistance to free radical damage

It has been found that after intravenous administration of selective agonist of mu-opioid receptors DAGO (0.1 mg/kg 15 min before heart excision) isolated rat heart becomes resistant to ischemia (45 min) and reperfusion (60 min) ex vivo. The in vivo pretreatment with DAGO prevented reperfusion injury of cardiac cells and decreased myocardial content of conjugated dienes during ischemia and reperfusion of the heart in vitro. In addition, similar mu-opioid receptor stimulation promotes a postischemic recovery of myocardial contractility in the postischemic period. However, this receptor activation does not affect heart tolerance to free radical damage during perfusion of isolated heart by a solution containing Fe(2+)-ascorbic acid.     

缺血后处理对抗大鼠离体心脏缺血再灌注损伤及其作用机制

目的： 研究缺血后处理（postconditioning）对抗大鼠离体心脏缺血再灌注损伤及其作用机制。方法：采用SD大鼠心肌缺血/再灌注模型，并于再灌注一开始即给予3次全心停灌30 s，再灌30 s处理作为缺血后预处理。记录心肌收缩功能指标，以Even’s blue-TTC法监测心肌梗死范围，并对心律失常严重程度进行定量分析。结果：缺血后处理组左室峰压（LVSP）、最大左室收缩速率（+dp/dt_max）以及心率明显高于缺血对照组。缺血后处理可明显缩小心肌梗死范围（22.97%±3.96% vs 缺血对照组 44.30%±13.61%，P<0.01）。观察复灌10 min时心律失常评分发现，缺血后处理组明显低于缺血对照组。缺血后处理组和缺血预处理组具有类似的心肌保护作用。5-HD组LVSP和+dp/dt_max低于缺血后处理组，心律失常评分增高，心肌梗死范围扩大。结论: 缺血后处理对大鼠缺血再灌注损伤具有心脏保护作用，其作用机制可能是部分通过激活线粒体ATP依赖性钾离子(mitoK_ATP)通道起作用。     

Efficiency of cardioplegic solutions containing L-arginine and L-aspartic acid

In experiments on rats we studied the effects of cardioplegic solutions with L-aspartic acid or L-arginine on functional recovery and metabolism of isolated working heart after 40-min normothermal global ischemia and 30-min reperfusion. After reperfusion of the hearts preventively protected with cardioplegic solution containing L-aspartic acid or Larginine, coronary flow decreased in comparison with the initial values. As a component of cardioplegic solution, L-arginine was less efficient in recovery of contractility and cardiac output of the hearts in comparison with L-aspartic acid. In hearts protected with L-aspartic acid, the postischemic levels of ATP and phosphocreatine were significantly higher, and the level of lactate was significantly lower than in hearts protected with Larginine. In comparison with L-arginine, L-aspartic acid is a more efficient component of cardioplegic solution in protection of the heart from metabolic and functional damages caused by global ischemia and reperfusion. __________ Translated from Byulleten’ Eksperimental’noi Biologii i Meditsiny, Vol. 141, No. 4, pp. 392–396, April, 2006     

Effect of Opiate Peptide Dalargin and Des-Tyr-Dalargin on Cardiac Pump Function during Ischemia-Reperfusion

Experiments on isolated perfused rat heart showed that nonselective micro- and delta-opiate receptor agonist dalargin decreased contractility of the intact heart, but had no effect on pump function of the ischemic myocardium. Dalargin analogue des-Tyr-dalargin not binding to opiate receptors decreased contractility of intact myocardium and isolated heart exposed to 45-min total ischemia. We hypothesize that the influence of dalargin is related to activation of cardiac delta-opiate receptors, while the inotropic effect of des-Tyr-dalargin is mediated by other receptors.     

Polymorphonuclear granulocytes induce myocardial dysfunction during ischemia and in later reperfusion of hearts exposed to low-flow ischemia

Polymorphonuclear granulocytes (PMNs) are known to contribute to reperfusion injury of the heart. However, whether PMNs compromise myocardial function of hearts exposed to a low-flow ischemia has not been determined. Moreover, not much is known about deleterious effects of PMNs at different times during ischemia and reperfusion. Isolated, working guinea pig hearts were subjected to 30 min of low-flow ischemia and reperfusion. Homologous PMNs were applied as 1-min boluses in the presence of thrombin during either ischemia or the first or fifth minute of reperfusion, and postischemic recovery of external heart work (REHW) and intracoronary PMN retention (PMNR) were quantified. In further experiments, the radical scavenger superoxide dismutase (SOD) was added. Compared with controls without PMNs (REHW, 92.4%), application of PMNs led to a significant loss of myocardial function, which was detected at all three examination times. Moreover, intracoronary PMNR increased significantly in comparison with that of controls with hearts not exposed to ischemia or reperfusion. On the other hand, addition of SOD significantly increased REHW. Intracoronary PMNR was not significantly changed by coapplication of SOD. We conclude that thrombin-stimulated PMNs applied at different times during ischemia and reperfusion significantly impaired cardiac function in hearts exposed to a low-flow ischemia.     

Polymerized human placenta hemoglobin given before ischemia protects rat heart from ischemia reperfusion injury

This study was to investigate whether polymerized human placenta hemoglobin (PolyPHb) given before ischemia protects in vivo rat heart function against ischemia/reperfusion (I/R) injury. Forty-five male Sprague-Dawley rats were randomly divided (n = 15 per group) into a sham group, control group (pretreatment with Lactated Ringer's solution), or PolyPHb group (pretreatment with 0.1 gHb/kg PolyPHb). Rat hearts were subjected to 30-min ischemia by occlusion of left anterior descending, followed by 2-hr reperfusion. As compared to the control group, PolyPHb preserved cardiac function and reduced cardiac troponin-I release and histopathological changes. Therefore, PolyPHb pretreatment provided a profound cardioprotective effect on the in vivo rat heart.     

Effect of semax and semax-heparin mixture on isolated heart activity after total ischemia in rats

Semax administered after 40-min total ischemia of isolated heart improved the recovery of heart rate and reduced myocardial contracture. When administered prior to ischemia, Semax exerted a negative effect on recovery of heart contractility. Semax-heparin mixture significantly improved the recovery of cardiac indices (end-diastolic pressure, heart rate, and relaxation rate) irrespective of administration schedule. Translated fromByulleten' Eksperimental'noi Biologii i Meditsiny, Vol. 128, No. 11, pp. 494–496, November, 1999     

Recovery of hypertrophied rat hearts after global ischemia and reperfusion at different perfusion pressures

The ability to resist transient ischemia was studied in isolated hearts of 18 months old spontaneously hypertensive (SHR) and Wistar-Kyoto (WKY) rats. Both types of hearts showed optimal performance during the preischemic period when perfused at a diastolic perfusion pressure of 8.0 (WKY) and 13.3 (SHR) kPa. Hemodynamic recovery of WKY hearts during reperfusion at 8.0 kPa, following 45 min global ischemia, was satisfactory. Coronary perfusion completely normalized, contractility (dP _lv/dt _max) was slightly depressed and cardiac output returned, on the average, to 40% of the preischemic values. In contrast, hemodynamic function of SHR hearts reperfused at 13.3 kPa was greatly depressed, as evidenced by almost complete abolition of cardiac output, severe reduction ofdP _lv/dt _max and persistent underperfusion of the endocardial layers. In addition, the postischemic release of lactate dehydrogenase was retarded and enhanced. The release patterns of degradation products of adenine nucleotides showed a shift to the endstage produets xanthine and uric acid. The enhanced vulnerability of the hypertrophied heart to ischemia was even more expressed when the SHR hearts were reperfused at 8.0 kPa. Postischemic function was characterized by electrical instability, loss of contractility and cardiac output, and noreflow in the endocardial layers. Persistent accumulation of lactate and degradation products of adenine nucleotides in the postischemic hearts are in line with the lack of reperfusion. The present results indicate that a detailed mechanistic explanation for the reduced ability to withstand ischemia of SHR cannot be based on differences in ATP content or an altered anaerobic glycolitic activity prior and during ischemia. It is suggested that a defect on the circulatory level, probably caused by enhanced reactivity of the coronary vessels towards ischemia-elicited factors, is responsible for the higher vulnerability of hypertrophied heart to an ischemia insult.Supported by Medigon/NWO (grant number 900516091)     

Relation between ischemic preconditioning and the duration of sustained ischemia.

It has been reported that repetitive brief periods of ischemia and reperfusion (ischemic preconditioning, IP) cause a significant reduction in the extent of myocardial necrosis or in the incidence of reperfusion arrhythmias in rat heart. However, recent reports have stated that IP effect is diminished or lost in the canine or bovine heart if ischemia (mostly regional) is sustained for 40 min or longer. The main objective of this study is to assess whether IP provides myocardial protection in prolonged sustained ischemia under the condition of global ischemia in isolated rabbit heart. The hearts were subjected to 10-60 min sustained ischemia (SI) followed by 60 min reperfusion with (IP heart) or without IP (ISCH heart). IP was induced by 4 cycles of 5 min global ischemia and 5 min reperfusion. Left ventricular function (LVF), extent of infarction (EI) and ultrastructural changes were examined. As a whole, the LVF began to recover on reperfusion but there was no significant difference in the functional parameters. However, extracellular Ca2+ concentration was lower in the ISCH hearts (p < 0.05) and the EI was significantly different between the hearts which had received 60 min SI (67% in the ISCH versus 32% in the IP heart, p < 0.01). Ultrastructural changes were homogeneous in the ISCH hearts and became irreversible in accordance with increase of the duration of ischemia, while these changes were heterogeneous and restricted in the IP heart. These results suggest that IP does not attenuate the postischemic dysfunction in prolonged ischemia but it can provide an infarct size-limiting effect and delay ultrastructural changes. This cardioprotective effect may be related to calcium homeostasis.     

Role of oxygen in postischemic myocardial injury

Myocardial function is dependent on a constant supply of oxygen from the coronary circulation. A reduction of oxygen supply due to coronary obstruction results in myocardial ischemia, which leads to cardiac dysfunction. Reperfusion of the ischemic myocardium is required for tissue survival. Thrombolytic therapy, coronary artery bypass surgery and coronary angioplasty are some of the treatments available for the restoration of blood flow to the ischemic myocardium. However, the restoration of blood flow may also lead to reperfusion injury, resulting in myocyte death. Thus, any imbalance between oxygen supply and metabolic demand leads to functional, metabolic, morphologic, and electrophysiologic alterations, causing cell death. Myocardial ischemia reperfusion (IR) injury is a multifactorial process that is mediated by oxygen free radicals, neutrophil activation and infiltration, calcium overload, and apoptosis. Controlled reperfusion of the ischemic myocardium has been advocated to prevent the IR injury. Studies have shown that reperfusion injury and postischemic cardiac function are related to the quantity and delivery of oxygen during reperfusion. Substantial evidence suggests that controlled reoxygenation may ameliorate postischemic organ dysfunction. In this review, we discuss the role of oxygenation during reperfusion and subsequent biochemical and pathologic alterations in reperfused myocardium and recovery of heart function.     

Cardioprotective Effect of Ischemic Postconditioning on the Model of Isolated Heart

Irreversible cardiomyocyte damage was induced by 45-min global ischemia followed by 30-min reperfusion in Langendorff-perfused isolated rat heart. Cell damage was assessed by the release of creatine phosphokinase into the perfusate. The hearts were subjected to the following postconditioning protocols: 1) three cycles of 10-sec reperfusion and 10-sec ischemia, total cycle time 20 sec; 2) six cycles of 10-sec reperfusion and 10-sec ischemia, total cycle time 20 sec; 3) three sessions of 20-sec reperfusion and 20-sec ischemia, total cycle time 40 sec; 4) 6 cycles of 20-sec reperfusion and 20-sec ischemia, total cycle time 40 sec; 5) 3 cycles of 30-sec reperfusion and 30-sec ischemia, total cycle time 60 sec. It was found that only postconditioning with a total cycle time of 40 sec or 60 sec prevents myocardial reperfusion injury.     

Role of ATP-sensitive K<Superscript>+</Superscript>-channels in antiarrhythmic and cardioprotective action of adaptation to intermittent hypobaric hypoxia

Mature Wistar rats were exposed to intermittent hypobaric hypoxia (5000 m, 6 h/day, 30 sessions). This mode of adaptation enhanced heart tolerance to the arrhythmogenic action of 45-min coronary occlusion, but does not affect the infarction size/risk area ratio. In some series, the rats were exposed to more severe intermittent hypobaric hypoxia (7000 m, 8 h/day, 6 weeks) followed by 20-min coronary occlusion and 3-h reperfusion one day after the last hypoxia session. In this case, adaptation reduced the infarction size/risk area ratio and enhanced cardiac tolerance to the arrhythmogenic effect of reperfusion, but had no effect on the incidence of ventricular arrhythmia during ischemia. We found that the cardioprotective and antiarrhythmic effects of adaptation to an altitude of 7000 m and the antiarrhythmic effect of 5000-m adaptation were mediated via activation of K_ATP channels. __________ Translated from Byulleten’ Eksperimental’noi Biologii i Meditsiny, Vol. 145, No. 4, pp. 395–398, April, 2008     

Postischemic reperfusion in the eyes of young and aged rats

The hemodynamic changes during postischemic reperfusion were investigated in the eyes of young (4 months) and aged (more than 18 months) rats using laser Doppler flowmetry, and histological changes in the retina were examined 6 h after the cessation of ischemia. During exposure to 80 mmHg of intraocular pressure, choroidal blood flow (ChBF) decreased to 40-50% of the baseline value. Marked hyperperfusion (186 +/- 9%) was observed 1 min after cessation of 30-min ischemia in young rats. The hyperperfusion was less (111 +/- 3%) after 120-min ischemia. Delayed hypoperfusion was not observed during 6 h of reperfusion after 120-min ischemia. In aged rats, the hyperperfusion after 30-min ischemia was less (130 +/- 17%) than that in young rats, and the ChBF decreased to 80% of the baseline value during 6 h of reperfusion after 120-min ischemia. Histological examination of the retina showed that exposure to 120-min ischemia caused microvacuolation in the inner and outer plexiform layers and vacuolar changes in the cytoplasms in the inner nuclear layer of both young and aged rats, suggesting edema formation in the retina. The thickness of the outer layers of the retina tended to increase after 120-min ischemia in young rats, whereas it decreased significantly in aged rats. These results suggest that 120-min ischemia with 40-50% of normal choroidal blood flow causes more severe damage than 30-min ischemia, and that the hemodynamic changes during reperfusion in aged rats are different from those in young rats.     

Reversibility of mild to moderate ischemic injuries in the isolated rat heart. A characterization by 31P-NMR and by physiological and ultrastructural indices.

We have studied cardiac function, metabolism, and ultrastructure during reperfusion after global ischemia of short duration (6 and 12 minutes) in isolated rat hearts. Our aim was to obtain more detailed information on the reversibility of changes following presumedly mild and moderate ischemic injuries by use of multiple time-based indices. In a modified Langendorff perfusion system, hearts were subjected to 24 minutes of control perfusion and 6 or 12 minutes of ischemia followed by 1.5 or 24 minutes of reperfusion. During the experiments we monitored left ventricular developed pressure (LVDP), heart rate, and coronary flow rate, and intracellular phosphocreatine (PCr), inorganic phosphate (P(i)), pH, and ATP by 31P nuclear magnetic resonance spectroscopy. The number of cells with sarcolemmal and nuclear injuries was counted. Our main findings during 24 minutes of reperfusion following 6 and 12 minutes of ischemia were 80% versus 53% recovery of LVDP at the end of reperfusion, an increased PCr, 80% versus 65% recovery of ATP, and a rapid versus slower recovery of pH. Ultrastructural examination revealed sarcolemmal and unclear abnormalities at the end of ischemia, these alterations being fully (rapidly versus more slowly) reversible during reperfusion. According to these findings, there was a dissociation between an essentially normal ultrastructure, and a depressed recovery of LVDP, reduced ATP, and an overshoot of PCr upon 24 minutes of reperfusion after 12 minutes of ischemia. This may indicate a postischemic dysfunction closely related to stunning.     

Remote preconditioning,perconditioning, and postconditioning: a comparative study of their cardioprotective properties in rat models

OBJECTIVE:

Ischemia reperfusion injury is partly responsible for the high mortality associated with induced myocardial injury and the reduction in the full benefit of myocardial reperfusion. Remote ischemic preconditioning, perconditioning, and postconditioning have all been shown to be cardioprotective. However, it is still unknown which one is the most beneficial. To examine this issue, we used adult male Wistar rat ischemia reperfusion models to compare the cardioprotective effect of these three approaches applied on double-sided hind limbs.

METHODS:

The rats were randomly distributed to the following five groups: sham, ischemia reperfusion, remote preconditioning, remote perconditioning, and remote post-conditioning. The ischemia/reperfusion model was established by sternotomy followed by a 30-min ligation of the left coronary artery and a subsequent 3-h reperfusion. Remote conditioning was induced with three 5-min ischemia/5-min reperfusion cycles of the double-sided hind limbs using a tourniquet.

RESULTS:

A lower early reperfusion arrhythmia score (1.50±0.97) was found in the rats treated with remote perconditioning compared to those in the ischemia reperfusion group (2.33±0.71). Meanwhile, reduced infarct size was also observed (15.27±5.19% in remote perconditioning, 14.53±3.45% in remote preconditioning, and 19.84±5.85% in remote post-conditioning vs. 34.47±7.13% in ischemia reperfusion, p<0.05), as well as higher expression levels of the apoptosis-relevant protein Bcl-2/Bax following global (ischemia/reperfusion) injury in in vivo rat heart models (1.255±0.053 in remote perconditioning, 1.463±0.290 in remote preconditioning, and 1.461±0.541 in remote post-conditioning vs. 1.003±0.159 in ischemia reperfusion, p<0.05).

CONCLUSION:

Three remote conditioning strategies implemented with episodes of double-sided hind limb ischemia/reperfusion have similar therapeutic potential for cardiac ischemia/reperfusion injury, and remote perconditioning has a greater ability to prevent reperfusion arrhythmia.     

降纤酶对离体大鼠工作心脏缺血再灌注损伤的作用

目的 :探讨降纤酶 ( Df)对心脏缺血再灌注损伤的作用。方法 :采用离体大鼠工作心脏缺血再灌注损伤模型 ,通过检测缺血再灌注损伤前后对照组、Df低剂量组及 Df高剂量组的心功能参数 ,观察Df的作用。结果 :Df可降低实验动物的室颤发生率 ,增强心肌收缩力 ( P<0 .0 5 ) ,防止冠脉流量下降 ( P<0 .0 5 )及左室内压下降 ( P<0 .0 1) ,促进压力最大上升速度的恢复 ( P<0 .0 5 )。结论 :Df对心脏缺血再灌注损伤具有显著的保护作用。     

Does nitric oxide generation contribute to the mechanism of remote ischemic preconditioning?

The protective effect of local or remote ischemic preconditioning (IPC) on subsequent 40-min ischemic and 120-min reperfusion myocardial damage was investigated. Preconditioned rats underwent one cycle of myocardial ischemia/reperfusion consisting of 5-min ischemia produced as a left coronary artery (LCA) occlusion and 5 min of reperfusion. Remote IPC was produced as 15 min of small intestinal ischemia with 15 min of reperfusion as well as 30 min of limb ischemia with 15 min of reperfusion. A marked protective action was afforded by both IPC protocols with a more significant effect of local (classic) ischemic preconditioning. Since the protective effect of remote IPC was not abolished by nitric oxide (NO) synthase inhibition with Nω-nitro- -arginine ( -NNA) it is concluded that NO generation may not be involved in the mechanism of remote IPC.