The Role of δ2-Opioid Receptors in the Regulation of Tolerance of Isolated Cardiomyocytes to Hypoxia and Reoxygenation

Hypoxia (20 min) and reoxygenation (30 min) were simulated on isolated rat cardiomyocytes to evaluate the cytoprotective effect of selective δ2-opioid receptor agonist deltorphin II, opioid receptor antagonist naloxone methiodide, μ-opioid receptor antagonist CTAP, κ-opioid receptor antagonist nor-binaltorphimine, ε1-opioid receptor antagonist BNTX, and δ2-opioid receptors naltriben. Deltorphin II was administered 5 min before reoxygenation, antagonists were administered 10 min before reoxygenation. The cytoprotective effect of deltorphin II was assessed by the number of cardiomyocytes survived after hypoxia/reoxygenation, as well as by the lactate dehydrogenase content in the incubation medium. It has been established that the cytoprotective effect of deltorphin II occurs at a concentration of 64 nmol/liter and is associated with activation of δ2-opioid receptors.

Comparative Analysis of Infarct-Limiting Activity of Peptide and Non-Peptide δ- and κ-Opioid Receptor Agonists during Heart Reperfusion In Vivo

A comparative analysis of the infarct-limiting activity of δ- and κ-opioid receptors (OR) agonists was carried out on a model of coronary occlusion (45 min) and reperfusion (120 min) in male Wistar rats. We used selective δ2-OR agonist deltorphin II (0.12 mg/kg), δ-OR agonists BW373U86 and p-Cl-Phe DPDPE (0.1 and 1 mg/kg), selective agonists of δ1-OR DPDPE (0.1 and 0.969 mg/kg), κ1-OR U-50,488 (0.1 and 1 mg/kg), κ2-OR GR-89696 (0.1 mg/kg), and κ-OR ICI-199,441 (0.1 mg/kg). All drugs were administered intravenously 5 min before reperfusion. Deltorphin II, BW373U86 (1 mg/kg), p-Cl-Phe DPDPE (1 mg/kg), U-50,488 (1 mg/kg), and ICI-199,441 had a cardioprotective effect. The most promising compounds for drug development are ICI-199,441 and deltorphin II.

The Role of P2Y6 Receptors in the Mechanisms of the Neuroprotective Effect of Citicoline

Spontaneous bioelectrical activity of the brain and the duration of gasping were recorded in mice during modeling of global strangulation ischemia of the brain against the background of preventive administration of citicoline. The maximum neuroprotective effect of citicoline was observed when it was administered 60 min before the simulation of ischemia and was completely prevented by preliminary administration of a selective P₂Y₆ receptor antagonist MRS2578. The obtained experimental data attest to the leading role of receptor mechanisms in the implementation of neuroprotective activity of citicoline.

Role of PI3K, ERK1/2, and JAK2 Kinases in the Cardioprotective Effect of Deltorphin II during Cardiac Reperfusion

The signaling mechanism of the cardioprotective effect of deltorphin II was studied in models of coronary occlusion (45 min) and reperfusion (120 min) in male Wistar rats. We used the selective δ₂-opioid receptor agonist deltorphin II (0.12 mg/kg), which was administered intravenously 5 min before reperfusion, the PI3K inhibitor wortmannin (0.025 mg/kg), the ERK1/2 blocker PD-098059 (0.5 mg/kg), the inhibitor JAK2 AG490 (3 mg/kg). All kinase blockers were administered 10 min before reperfusion. The infarct-limiting effect of deltorphin II is associated with the activation of PI3K and ERK1/2 and does not depend on JAK2.

Decrease in Infarct-Limiting Effect of Chronic Normobaric Hypoxia in Rats with Induced Metabolic Syndrome Is Associated with Disturbances of Carbohydrate and Lipid Metabolism

We studied the infarct-limiting effect of adaptation to chronic normobaric hypoxia in rats with induced metabolic syndrome and the relationship between disturbances of adaptive cardioprotection and disorders of carbohydrate and lipid metabolism. Adaptation to chronic normobaric hypoxia was carried out for 21 days at 12% O₂ and 0.3% CO₂. The metabolic syndrome was modeled with a high-carbohydrate high-fat diet for 84 days with replacement of drinking water with a 20% fructose solution. The infarct size in rats exposed to chronic normobaric hypoxia was 38% smaller than in control animals. In rats with induced metabolic syndrome, hypertension, obesity, decreased glucose tolerance, increased serum triglyceride, and no infarction-limiting effect of chronic normobaric hypoxia were observed. Infarct size showed a direct correlation with impaired glucose tolerance and serum triglyceride levels. The study allows us to conclude that the lack of cardioprotection in chronic normobaric hypoxia in rats with induced metabolic syndrome is associated with impaired carbohydrate and lipid metabolism.

The Role of NO Synthase, MPT pore, and Protein Kinase A in the Cardioprotective Effect of the Opioid Receptor Agonist Deltorphin II

In male Wistar rats, coronary occlusion (45 min) and reperfusion (120 min) were modeled. Selective δ₂-opioid receptor agonist (deltorphin II, 0.12 mg/kg) was administered intravenously 5 min before reperfusion; NO synthase inhibitor (L-NAME, 10 mg/kg), MPT pore blocker (atractyloside, 5 mg/kg), and protein kinase A inhibitor (H-89, 10 μg/kg) were administered intravenously 10 min before reperfusion. Deltorphin II administered before reperfusion led to a 2-fold decrease in the infarct size. The infarct-limiting effect of deltorphin II was associated with blockade of MPT pore. Protein kinase A and NO synthase were not involved in the cardioprotective effect of deltorphin II.

The Role of NO Synthase in the Infarct-Limiting Effect of Urgent and Chronic Adaptation to Normobaric Hypoxia

We studied the role of NO synthase in the infarct-limiting effect of short-term (SNH) and chronic continuous normobaric hypoxia (CNH). In male Wistar rats, SNH (6 sessions of 10-min hypoxia 8% O2 and 10-min reoxygenation) or CNH (12% O2 for 21 days) was modeled. In 30 min after SNH or 24 h after CNH, the rats were subjected to coronary artery occlusion (45 min) and reperfusion (2 h). The following drugs were administered to rats: non-selective NO synthase inhibitor L-NAME (10 mg/kg), inhibitor of inducible NO synthase S-methylthiourea (3 mg/kg), and inhibitor of neuronal NO-synthase 7-nitroindazole (50 mg/kg). NO donor diethylenetriamine was administered intravenously in a dose 2 mg/kg. It was found that L-NAME and S-methylthiourea abolished the infarct-limiting effect of SNH and CNH. Diethylenetriamine increased cardiac tolerance to ischemia/reperfusion. It is believed that inducible NO synthase plays an important role in the cardioprotective effect of normobaric hypoxia.

The Role of Mitochondrial KATP Channels in the Infarct-Reducing Effect of Normobaric Hypoxia

We studied the role of K_ATP channels in the infarct-limiting effect of short-term normobaric hypoxia. Male Wistar rats were subjected to a 45-min coronary artery occlusion followed by a 120-min reperfusion. Normobaric hypoxia was simulated 30 min before coronary artery occlusion: 6 sessions of hypoxia (8% O₂, 10 min) and reoxygenation (21% O₂, 10 min). The following drugs were administered to rats: glibenclamide, 5-hydroxydecanoate, and HMR1098. It was found that normobaric hypoxia contributes to a decrease in myocardial infarct size by 36%. Preliminary administration of glibenclamide or 5-hydroxydecanoate eliminated the infarct-reducing effect of normobaric hypoxia. Activator of mitochondrial K_ATP channel diazoxide limited the infarct size. These findings suggest that mitochondrial K_ATP channels are involved into the cardioprotective effect of normobaric hypoxia.

The effect of age and a high-fat, high-carbohydrate diet on the development of arterial hypertension and kidney disease in the experiment

Aim. To identify the structural foundations of the pathogenesis of arterial hypertension and kidney disease associated with a high-fat, high-carbohydrate diet and age.

Materials and methods. The study was carried out on male Wistar rats aged 60 and 450 days. The animals were divided into 4 groups: group 1 (n = 14) – intact rats (60 days old) fed with a standard diet for 90 days; group 2 (n = 14) – rats (aged 60 days) receiving a high-fat, high-carbohydrate diet for 90 days; group 3 (n = 14) – intact rats (aged 450 days) receiving a standard diet for 90 days; group 4 (n = 14) – rats (aged 450 days) fed with a high-fat, high-carbohydrate diet for 90 days. Clinical and instrumental research methods, enzyme-linked immunosorbent assay, and immunohistochemistry and histology techniques were used in the study.

Results. Feeding 60-day-old animals with a high-fat, high-carbohydrate diet resulted in an increase in body weight and abdominal fat, a rise in systolic blood pressure, and moderately pronounced histologic changes in the kidneys. In intact 450-day-old rats, age-related changes prevailed: changes in the myocardial mass, an increase in TGF-β1, morphological changes in the renal tubules and glomeruli. In 450-day-old rats receiving a high-fat, highcarbohydrate diet, the most pronounced increase in both systolic and diastolic blood pressure, a significant rise in serum fibronectin, and destructive changes in the renal tissue were noted.

Conclusion. Functional and biochemical signs of arterial hypertension and morphological changes in the kidneys were the most pronounced in 450-day-old rats fed with a high-fat, high-carbohydrate diet.

Activation of Peripheral Opioid Kappa1 Receptor Prevents Cardiac Reperfusion Injury

The role of opioid kappa1 and kappa2 receptors in reperfusion cardiac injury was studied. Male Wistar rats were subjected to a 45-min coronary artery occlusion followed by a 120-min reperfusion. Opioid kappa receptor agonists were administered intravenously 5 min before the onset of reperfusion, while opioid receptor antagonists were given 10 min before reperfusion. The average value of the infarct size/area at risk (IS/AAR) ratio was 43 - 48% in untreated rats. Administration of the opioid kappa1 receptor agonist (-)-U-50,488 (1 mg/kg) limited the IS/AAR ratio by 42%. Administration of the opioid kappa receptor agonist ICI 199,441 (0.1 mg/kg) limited the IS/AAR ratio by 41%. The non-selective opioid kappa receptor agonist (+)-U-50,488 (1 mg/kg) with low affinity for opioid kappa receptor, the peripherally acting opioid kappa2 receptor agonist ICI 204,448 (4 mg/kg) and the selective opioid ?2 receptor agonist GR89696 (0.1 mg/kg) had no effect on the IS/AAR ratio. Pretreatment with naltrexone, the peripherally acting opioid receptor antagonist naloxone methiodide, or the selective opioid kappa2 receptor antagonist nor-binaltorphimine completely abolished the infarct-reducing effect of (-)-U-50,488 and ICI 199,441. Pretreatment with the selective opioid ? receptor antagonist TIPP[psi] and the selective opioid µ receptor antagonist CTAP did not alter the infarct reducing effect of (-)-U-50,488 and ICI 199,441. Our study is the first to demonstrate the following: (a) the activation of opioid kappa2 receptor has no effect on cardiac tolerance to reperfusion; (b) peripheral opioid kappa1 receptor stimulation prevents reperfusion cardiac injury; (c) ICI 199,441 administration resulted in an infarct-reducing effect at reperfusion; (e) bradycardia induced by opioid kappa receptor antagonists is not dependent on the occupancy of opioid kappa receptor.

Cardioprotective Effect of Opioids, Derivatives of Amide N-Methyl-2-(Pirrolidin-1-yl)Cyclohexyl-1-Amine, under Conditions of Ischemia/Reperfusion of the Heart

We performed a comparative analysis of infarction-limiting activity of analogues of opioid receptor agonist U-50488 under conditions of heart reperfusion in rats. Derivatives of amide N-methyl-2-(pyrrolidin-1-yl)cyclohexyl-1-amine were administered 5 min before reperfusion in a dose of 1 mg/kg, derivative II (opicor) was additionally used in a dose of 2 mg/kg. In a dose of 1 mg/kg, all derivatives of opioid U-50488 were ineffective and produced no infarction-limiting effect. Opicor in a dose of 2 mg/kg reduced the infarction size/area at risk ratio and improved the contractility parameters of the isolated heart. Opioid receptor antagonist naltrexone (5 mg/kg) abolished the infarction-limiting effect of opicor. Hence, the infarction-reducing effect of opicor is associated with activation of opioid receptors. We also demonstrated that the opioid (opicor) can improve cardiac contractility during the reperfusion period.

Comparative Analysis of Infarct Size Limiting Activity of κ-Opioid Receptor Agonists in In Vivo Reperfused Heart

A 45-min coronary artery occlusion followed by a 120-min reperfusion was performed in rats anesthetized with α-chloralose. The selective κ₁-opioid receptor (OR) agonist U-50,488 was administered intravenously in doses of 0.1 or 1 mg/kg. The selective κ₂-OR agonist GR-89696 was injected in a dose of 0.1 mg/kg. The selective κ₁-OR agonists ICI-199,441 and ICI-204,448 were employed in the doses of 0.1 and 4 mg/kg, respectively. These drugs were injected 5 min prior to reperfusion. U-50,488 exerted the cardioprotective effect in a dose of 1 mg/kg, but it produced no effect on infarct size in a dose of 0.1 mg/kg. ICI-199,441 reduced the reperfusion injury to the heart. The infarct size limiting effects of U-50,488 and ICI-199,441 were prevented by preliminary injection of naltrexone or nor-binaltorphimine. It is concluded that infarct size limiting effects of U-50,488 and ICI-199,441 were mediated via activation of κ₁-OR.

The involvement of protein kinases in the cardioprotective effect of chronic hypoxia

The purpose of this review is to analyze the involvement of protein kinases in the cardioprotective mechanism induced by chronic hypoxia. It has been reported that chronic intermittent hypoxia contributes to increased expression of the following kinases in the myocardium: PKCdelta, PKCalpha, p-PKCepsilon, p-PKCalpha, AMPK, p-AMPK, CaMKII, p-ERK1/2, p-Akt, PI3-kinase, p-p38, HK-1, and HK-2; whereas, chronic normobaric hypoxia promotes increased expression of the following kinases in the myocardium: PKCepsilon, PKCbetaII, PKCeta, CaMKII, p-ERK1/2, p-Akt, p-p38, HK-1, and HK-2. However, CNH does not promote enhanced expression of the AMPK and JNK kinases. Adaptation to hypoxia enhances HK-2 association with mitochondria and causes translocation of PKCdelta, PKCbetaII, and PKCeta to the mitochondria. It has been shown that PKCdelta, PKCepsilon, ERK1/2, and MEK1/2 are involved in the cardioprotective effect of chronic hypoxia. The role of other kinases in the cardioprotective effect of adaptation to hypoxia requires further research.

[Clinical Manifestation of Stressful Cardiomyopathy (Takotsubo Syndrome) and the Problem of Differential Diagnosis with Acute Myocardial Infarction]

The presented data show that tacotsubo syndrome (TS) is characterized by the absence of coronary artery obstruction, cardiac contractile dysfunction, apical ballooning, and heart failure, and in some patients, ST-segment elevation and prolongation of the QTc interval. Every tenth patient with TS develops ventricular arrhythmias. Most of TS patients have elevated markers of necrosis (troponin I, troponin Т, and creatine kinase МВ (CK-МВ), which are considerably lower than in patients with acute myocardial infarction (AMI) with ST-segment elevation. The level of N-terminal pro-B-type natriuretic peptide (NT-proBNP), in contrast, is considerably higher in patients with TS than with AMI. Differential diagnosis of TS and AMI should be based on a multifaceted approach using coronary angiography, echocardiography, analysis of ECG, magnetic resonance imaging, single-photon emission computed tomography, and measurement of troponins, CK-MB, and NT-proBNP.

Continuous Normobaric Hypoxia Improved Cardiac Bioenergetics after Ischemia/Reperfusion: Role of Opioid Receptors

We analyzed the role of opioid receptors in the conditioning effect of continuous normobaric hypoxia on bioenergetics of the heart subjected to ischemia/reperfusion injury. Male Wistar rats were adapted to a 21-day continuous normobaric hypoxia (12% pO₂). Then, the hearts were isolated and subjected to 45-min total ischemia followed by 30-min reperfusion. Damage to the myocardium was assessed by activity of creatine phosphokinase in the perfusate. Experiments on isolated mitochondria showed that ischemia/reperfusion injury decreased the respiration rate in state 3 (V₃), the ratio of added ADP and oxygen consumption in respiration state 3 (ADP/O ratio), the mitochondrial potential across the inner membrane (Δψ), and Ca²⁺ binding capacity of mitochondria. In addition, ischemia/reperfusion injury decreased myocardial ATP. Preventive continuous normobaric hypoxia pronouncedly moderated these adverse effects of reperfusion. It was found that its protective effects were related to activation of cardiac μ- and δ₂-opioid receptors.

The Role of Cardiac Opioid Receptors in the Cardioprotective Effect of Continuous Normobaric Hypoxia

We studied the role of opioid receptor subtypes in improvement of the functional state of the heart during reperfusion after adaptation to continuous normobaric hypoxia. To this end, male Wistar rats were subjected to continuous normobaric hypoxia (12% O₂). Then, the hearts were isolated and exposed to total 45-min ischemia followed by 30-min reperfusion. Opioid receptor antagonists were added to the perfusion solution prior to ischemia. It was found that continuous normobaric hypoxia reduced the release of creatine phosphokinase into the effluent, increased myocardial contractile force, and decreased the end-diastolic pressure during reperfusion; these positive effects were related to activation of cardiac δ₂- and μ-opioid receptors.

Cardioprotective properties of opioid receptor agonists in rats with stress-induced cardiac injury

The objectives of this study were to investigate the role of endogenous opioids in the mediation of stress-induced cardiomyopathy (SIC), and to evaluate which opioid receptors regulate heart resistance to immobilization stress. Wistar rats were subjected to 24 h immobilization stress. Stress-induced heart injury was assessed by 99mTc-pyrophosphate accumulation in the heart. The opioid receptor (OR) antagonists (naltrexone, NxMB - naltrexone methyl bromide, MR 2266, ICI 174.864) and agonists (DALDA, DAMGO, DSLET, U-50,488) were administered intraperitoneally prior to immobilization and 12 h after the start of stress. In addition, the selective micro OR agonists PL017 and DAMGO were administered intracerebroventricularly prior to stress. Finally pretreatment with guanethidine was used. Naltrexone did not alter the cardiac 99mTc-PP accumulation in stressed rats. NxMB aggravated stress-induced cardiomyopathy (P=0.005) (SIC). The selective micro OR agonist DALDA, which does not cross the blood-brain barrier, completely prevented (P=0.006) SIC. The micro OR agonist DAMGO exhibited weaker effect than DALDA. The selective delta ligand (DSLET) and kappa OR ligand (U-50,488) did not alter stress-induced 99mTc-pyrophosphate accumulation in the heart. Intracerebroventricular administration of the micro OR agonists aggravated SIC. Pretreatment with guanethidine abolished this effect (P=0.01). Guanethidine alone exhibited cardioprotective properties. A stimulation of central micro OR promotes an appearance of SIC. In contrast, stimulation of peripheral micro OR contributes to an increase in cardiac tolerance to stress.

[The Role of Reactive Oxygen Species in the Pathogenesis of Adipocyte Dysfunction in Metabolic Syndrome. Prospects of Pharmacological Correction]

It is established that oxidative stress induces insulin resistance of adipocytes, increases secretion leptin, IL-6, TNF-α by adipocytes. Adiponectin secretion by adipocytes is reduced after the action of reactive oxygen species. Metabolic syndrome contributes to oxidative stress in adipose tissue, on the one hand due to the activation of production of reactive oxygen species by adipocyte NADPH-oxidase, and on the other hand by reducing the antioxidant defense adipocytes. It is found that obesity itself can induce oxidative stress. Chronic stress, glucocorticoids, mineralocorticoids, angiotensin-II, TNF-α play an important role in the pathogenesis of oxidative stress of adipocytes. Metformin remains the cure for the treatment of insulin resistance. The positive results in the treatment of metabolic syndrome by losartan were obtained. Antioxidants and flavonoids exhibit a positive impact on the course of the experimental metabolic syndrome.

[Prospects for the Use of Cannabinoid Receptor Ligands for the Treatment of Metabolic Syndrome and Atherosclerosis: Analysis of Experimental and Clinical Data]

An antagonist of central cannabinoid CB1 receptors rimonabant causes weight loss in patients with obesity and metabolic syndrome, improves blood lipid parameters, increases the adiponectin level, decreases the rate of glucose and glycosylated hemoglobin in patients with diabetes mellitus type-2. However, rimonabant adverse effects include depression, anxiety, nausea, and dizziness which are apparently due to the blockade of central CB1 receptors. In mice with a high-calorie diet, we defined that the blockade of peripheral CB1 receptors prevents obesity, steatosis of the liver, improves lipid and carbohydrate metabolism. Experimental studies suggest that peripheral CB2 receptor agonists have antiatherogenic effect. To validate the expediency of clinical research of CB2 receptor agonists in patients with atherosclerosis the comparative analysis of antiatherogenic properties of cannabinoids should be performed. In addition, experiments are needed on the combination use of cannabinoids with well-known antiatherogenic agents, such as statins.

Myocardial Protection against Ischemic and Reperfusion Injuries (Experimental Study)

The effects of hypoxic, hyperoxic, and hypoxic-hyperoxic preconditioning were examined in the prospective study on narcotized and artificially ventilated rabbits. Under artificial circulation, acute myocardial ischemia was modeled by ligation of anterior descending coronary artery, which was followed by reperfusion. The degree of ventricular arrhythmias was assessed, and the ischemic area was evaluated in percent of the area at risk. Microscopic characterization of the myocardium was employed to assess the cardioprotective effect of hypoxic and/or hyperoxic preconditioning. According to Kruskal-Wallis test, the greatest resistance of the myocardium to ischemic and reperfusion injury was observed after hypoxic-hyperoxic preconditioning (H=42.459; p=0.009). The rabbits subjected to this type of preconditioning demonstrated the least damaged myocardium in comparison with nonconditioned controls.

Involvement of Autonomic Nervous System in Antiarrhythmic Effect of Intermittent Hypobaric Hypoxia

We studied the involvement of the autonomic nervous system in the antiarrhythmic effect of intermittent hypobaric hypoxia modeled by daily placing the rats into an altitude chamber at 405 mm Hg (5000 m above sea level). The antiarrhythmic effect of hypoxia was observed on the model of acute coronary occlusion/reperfusion in vivo, but not during simulation of total ischemia/reperfusion of the isolated myocardium. Intravenous injection of ganglionic blocker hexamethonium (30 mg/kg) 15 min prior to in vivo coronary occlusion modeling abolished the antiarrhythmic effect of intermittent hypobaric hypoxia, which suggests that this effect is mediated via activation of the autonomic nervous system.

[Prospects of Application of Remote Preconditioning at Heart Revascularization]

Remote ischemic preconditioning of the heart exerts anti-necrotic, antiarrhythmic, inotropic effects that have been demonstrated in clinical trials in cardiac surgery both in adults and children. However, so far there is no consensus between cardiologists regarding the impact of remote preconditioning on the incidence of intraoperative myocardial infarctions and mortality in the postoperative period. Until now there is no unanimity concerning choice of remote preconditioning protocol and timing of its application before cardiac surgery.

[Prospects of clinical application of pharmacological imitation of the phenomenon of ischaemic postconditioning of the heart]

Pharmacological imitation of the phenomenon of ischaemic postconditioning of the heart appears to exert a cardioprotective effect in the reperfusion period. It was determined that the protective effect may be carried out resulting from activation of the adenosine, opioid and bradykinin receptors. However, there is yet no common point of view concerning the question as to the activation of what subtypes of the receptors the cardioprotective effect of adenosine, opioids and bradykinin is associated with. The clinical findings strongly suggest that further studies are required, since the data obtained in the hitherto carried out trials are ambiguous, scarce, and sometimes yield contradicting results. Several clinical trials of adenosine have been conducted and in the majority of cases positive results were obtained. Adenosine administered in a dropwise manner was found to exert a cardioprotective effect. However, not all researchers succeeded in demonstrating this protective effect. Only one clinical trial was carried out with the opioid receptor agonist - morphine, yielding positive results, with morphine exerting a cardioprotective effect. Feasibility of the clinical application of bradykinin as a cardioprotector is not of current relevance because of its numerous side effects.

[The phenomenon of ischaemic postconditioning of the heart. Analysis of clinical data]

Data concerning the effectiveness of ischaemic postconditioning (IPost) in treatment of acute ST-segment elevation myocardial infarction (STEMI) are controversial. The authors of the majority of studies have reported an anti-apoptotic and infarct reducing effect of IPost. There is evidence that IPost reduces the microvascular obstruction zone, increases coronary flow reserve, and improves the pumping functions of the heart. At the same time, there are publications reporting that IPost does not influence the course of acute STEMI. It was established that IPost protects the heart from reperfusion injury occurring after cold cardioplegia in patients with tetralogy of Fallot.

CB-Receptor Agonist HU-210 Mimics the Postconditioning Phenomenon of Isolated Heart

CB receptor agonist HU-210 exhibits an infarction-limiting effect during in vitro reperfusion of the heart after focal ischemia. This effect is paralleled by a decrease in left-ventricular developed pressure and double product. In addition, HU-210 reduces end-diastolic pressure during the reperfusion period, which indirectly attests to reduced Ca²⁺ overload of cardiomyocytes.

Specific features of adaptation of rats to chronic cold treatment

Permanent exposure of rats to four-week cold treatment at +4ºC for 24 h/day resulted in increased weights of the brown adipose tissue, adrenals, and spleen and had no effect on the levels of cortisol and corticosterone in the blood serum. Similar data were observed after exposure of rats to intermittent four-week cold treatment at +4ºC for 8 h/day. After short-term exposure of rats to intermittent cold treatment at +4ºC for 1.5 h/day, all indices studied were similar to those observed in intact animals.

[INFARCT-LIMITING EFFECT OF ADAPTATION TO CONTINUOUS COLD EXPOSURE]

The experiments were performed on Wistar male rats, which were subjected to continuous cold exposure (+4 °C, 4 weeks). It has been established that this exposure is not a chronic stress. It has been shown that prolonged cold impact causes cold adaptation to cold and has the infarct-limi-ting effect.

[INVOLVEMENT OF 5-OPIOID RECEPTORS IN THE INCREASED RESISTANCE OF HEART AND MITOCHONDRIA TO IMPACT OF ISCHEMIA-REPERFUSION AFTER ADAPTATION TO CHRONIC CONTINUOUS HYPOXIA]

It was investigated the involvement of cardiac Ϭ-opioid receptors (OR) in increasing the resistance of the heart and myocardial mitochondria to ischemia-reperfusion after adaptation rats to chronic continuous normobaric hypoxia (CCNH). Rats were subjected to CCNH for 21 days at 12 % O2. It was evoked global ischemia (45 minutes) and reperfusion (30 minutes) of the isolated perfused heart. Adaptation to CCNH promoted a reduction of creatine kinase release from necrotic cardiomyocytes during reperfusion and improved reperfusion recovery of heart contractility. Mitochondrial respiratory and state of MPT pore were more resistant to ischemia-reperfusion in adapting rats. Perfusion of isolated hearts with TIPP(0) (30 nM/l, a selective Ϭ-OR-antagonist) or naltriben (1 nM/l, a selective 52-OR-antagonist) completely eliminated the cardioprotective effect of CCNH. BNTX (1 nM/l, a selective Ϭ-OR-antagonist) had no effect on the cardioprotective effect of CCNH. This data suggest that cardiac 52-OR involved in the increased resistance of the heart and mitochondria to ischemia-reperfusion after adaptation rats to CCNH.

[ROLE OF ENDOGENOUS OPIOID SYSTEM IN THE REGULATION OF FUNCTIONAL STATE OF HEART]

The cardiovascular effects of opioid peptides may be associated with activation of opioid receptors located on the sarcolemma of cardiomyocytes, on the cell membrane of ICA and endothelial cells, on sympathetic and parasympathetic nerve terminals in the heart and in the adrenals. The cardiovascular effects of opioids penetrating the blood-brain barrier may be the result of their impact on central opioid receptors.

Involvement of Protein Kinase C-δ in the Realization of Cardioprotective Effect of Ischemic Postconditioning

Experiments on isolated perfused rat heart modeled 45-min global ischemia followed by 30-min reperfusion. Ischemic postconditioning was modeled by 3 cycles of reperfusion (30 sec) and ischemia (30 sec). Cardiomyocyte necrosis was assessed by the level of creatine phosphokinase in the perfusate. Postconditioning reduced the release of creatine phosphokinase from the heart by 30%. The cardioprotective effect of ischemic postconditioning was eliminated after inhibition of protein kinase C with cheleritrin or after blockade of δ-isoform of protein kinase C with rottlerin. These findings attest to participation of protein kinase C-δ in the realization of the cardioprotective effect of postconditioning.

[INVOLVEMENT OF NITRIC OXIDE CYNTHASE IN THE EARLY PHASE OF THE HEART ISCHEMIC PRECONDITIONING]

Currently there is no single answer on the question of the participation of nitric oxide and NO-synthase (NOS) in the cardioprotection in the early phase of ischemic preconditioning (IP). In the present review the results of experimental studies indicate the involvement of NOS in the protective effect of IP and the literature data refuting this assumption. In addition, it was presented data on the increase of nitrates and nitrites (the stable metabolite of NO) in myocardial tissue after the IP, an increase in the expression of genes encoding NOS immediately after the IP, the data on the elimination of the protective effect of IP of NOS blockers and of imitation of IP affects IP by nitric oxide donors. It was exhibited a brief analysis of some of the studied mechanisms involving NO and NOS in cardioprotection at IP.

[SIGNIFICANCE OF OPIOID RECEPTORS IN THE CYTOPROTECTIVE ACTION OF CHRONIC HYPOXIA DURING ANOXIA-REOXYGENATION OF CARDIOMYOCYTES]

It was investigated the role of δ-, μ- и κ-opioid receptors (ORs) in the development of cytoprotective effect of chronic normobaric hypoxia (CNH) using anoxia/reoxygenation of isolated cardiomyocytes. Adaptation to CNH was achieved by the maintenance of rats for 21 days at atmosphere containing 12% O2. Anoxia/reoxygenation of isolated cardiomyocytes of intact rats evoked a death of 23% cells and enhancement of lactate dehydrogenase (LDH) release from cells. Anoxia/reoxygenation of isolated cardiomyocytes of adapting rats induced a death of only 2.5% cells and LDH release decreased by 25%. Preliminary incubation of cells with the OR blocker naloxone (300 nM) or the δ-OR antagonist TIPP(ψ) (30 nM) or the selective δ2-OR antagonist naltriben (1 nM) or the μ-OR antagonist CTAP (100 nM) 25 min prior to anoxia abolished adaptive enhancement of cell survival and a decrease in LDH release. The blocking of δ1-OR by BNTX (1 nM) or κ-OR by nor-binaltorphimine (3 nM) not affected on the cytoprotection at CNH. Consequently, cardiac cell δ2- and μ-opioid receptors are involved in the cytoprotective effect of chronic normobaric hypoxia.

[PROBLEM OF END EFFECTOR OF ISCHEMIC PRECONDITIONING OF THE HEART]

An analysis of the literature data performed by the authors shows that the main contenders for the role of the end effector of ischemic preconditioning of the heart are: (1) MPT pore (2) nexuses (3) cytoskeleton. Thus, almost all of the known intracellular molecular cascades eventually converge on MPT pore, on the components of the cytoskeleton and nexuses.

[PHENOMENON OF REMOTE PRECONDITIONING THE HEART AND ITS MAIN MANIFESTATIONS]

Remote ischemic preconditioning prevents reperfusion cardiomyocyte apoptosis and has the infarct-limiting effect which is maintained in the experiments on the isolated perfused heart. Remote preconditioning promotes to recovery the contractility of the heart during reperfusion, but did not affect the incidence of occlusion and reperfusion of ventricular arrhythmias. Remote preconditioning has a mild anti-inflammatory effect. Presented article is a review and formulated conclusions based on the published literature data.

[Main manifestations of the phenomenon of remote post-conditioning of the heart. Clinical application of post-conditioning]

It was determined that remote post-conditioning (RP) exerts infarction-limiting and antiapoptotic effects. The infarction-limiting effect of RP is associated with enhancement of autophagia of cardiomyocytes. It was determined that RP may be an effective method of preventing reperfusion contractile dysfunction of the heart. The problem of whether RP exerts an antiarrhythmic effect in cardiac ischaemia-reperfusion remains unsolved as yet. Limitation of leukocytic invasion may have direct relation to the cardioprotector effect of RP. Decreasing the level of anti-inflammatory cytokines and MCP-1 chemokine may contribute to limitation of leukocytic infiltration into the reperfusion zone. It was determined that RP provides a decrease in intensity of lipid peroxidation. Remote postconditioning prevents reperfusion damage to cardiomyocytes both in children and adults, but RP does not improve the clinical course of the postoperative period in patients with coronary bypass grafting. In children, RP improves the course of the postoperative period. What is the reason of such difference between children and adults remains unknown. It was shown that RP exerts an infarction-limiting effect in transcutaneous coronary interventions in patients with ST elevation myocardial infarction.

[Remote preconditioning phenomenon. prospects for use in pathology of lung and gastrointestinal tract]

The literature data on the effectiveness of remote ischemic preconditioning (RIP) in the prevention of lung injury are contradictory. Authors of some works argue that RIP prevents lung damage during surgical interventions, the authors of other publications claim that the RIP does not protect lung against pathological processes. It is obvious that there is an urgent need for multicenter, randomized trials aimed at studying RIP protective effects against pathological processes in lung. Also required is clinical evaluation of the effectiveness of RIP in the thromboembolism of pulmonary arteries, the transplantation of the lungs and intestinal infarction. Remote preconditioning prevents the intestine injury associated with abdominal aortic aneurysm repair. Experimental data indicate that RIP has the hepatoprotective effect during ischemia and reperfusion injury of liver, septic or haemorrhagic shock. The question of whether the DIP has a protective effect during ischemia-reperfusion of the pancreas remains open.

[PROSPECTS OF USING ADENOSINE, OPIOID AND BRADYKININ RECEPTOR AGONISTS FOR PHARMACOLOGICAL IMITATION OF HEART POSTCONDITIONING PHENOMENON.]

It is known that agonists of adenosine, opioid, and bradykinin receptors mimic the phenomenon of ischemic postconditioning. There is no commonly accepted notion of what adenosine receptor subtypes must be activated to increase cardiac resistance to reperfusion injury. Intravenous infusion of adenosine or intracoronary administration of adenosine produce infarct-limiting effect and contribute to a more complete restoration of coronary blood flow after recanalization of the infarct-related coronary artery. It was confirmed that opioids mimic the phenomenon of postconditioning. According to obtained data, the most promising compounds for the prevention of reperfusion injury of the heart are κ(1)- and δ(2)-opioid receptor agonists, as they produce the infarct-limiting effect, while not reducing the arterial pressure.

[Neuroprotective and nephroprotective effects of remote postconditioning: Prospects for clinical use]

The results of experimental and clinical studies strongly suggest that remote ischemic preconditioning (RIP) has no neuroprotective effect during cardiac surgery performed under extracorporeal circulation. Remote preconditioning (RP) has no neuroprotective effect in hemorrhagic stroke. A randomized multicenter study is needed to evaluate the efficiency RIP in patients with ischemic stroke. RP reduces the severity of ischemia/reperfusion kidney injury during transplantation. RIP has been established to prevent contrast-induced nephropathy. There is a need for a multicenter trial to evaluate the efficiency of RIP in patients with abdominal aortic aneurysm repair. Analysis of the presented data indicates that RIP fails to prevent cardiorenal syndrome in infants and children during cardiac surgery. The data available in the literature on the capacity of RIP to provide nephroprotective effect in patients after coronary artery bypass surgery are discordant and indicative of the advisability of a multicenter study.

[Ischaemic postconditioning of the heart. Analysis of experimental findings]

The data of publications regarding the influence of experimental atherosclerosis on the infarct-limiting effect of ischaemic postconditioning (IPost) are controversial. The presented information is suggestive that ageing removes or attenuates the infarct-limiting effect of postconditioning but does not influence the antiarrhythmic effect of IPost. The majority of experimental data report that streptozotocin-induced diabetes removes the infarct-limiting effect of IPost. The data concerning type 2 diabetes mellitus are controversial: some authors state that such diabetes completely levels the cardioprotecting effect of IPost; others tell that it only attenuates but does not remove the infarct-limiting effect of IPost. Postconditioning in rats with elevated arterial pressure prevents the appearance of reperfusion cardiac contractility dysfunction and exerts an infarct-limiting effect. Cardiac hypertrophy, postinfarction remodelling and dilatation cardiomyopathy do not influence the infarct-limiting and inotropic effect of postconditioning. According to the majority of publications, IPost enhances the inotropic and cardioprotecting effect of cardioplegia. The data of literature sources regarding the effect of gender on efficacy of IPost are limited.

[Chronic exposure to cold is adaptation without stress ]

It has been established that prolonged continuous cold exposure (+4°C for 24 hours/day, four weeks) causes an increase in brown fat weight, hypertrophy of the adrenal gland, spleen and did not affect cortisol and corticosterone levels in the blood serum in rats. Gastric ulcers were not observed in the rats. Chronic intermittent exposure to cold (+4°C, 8 hours/day, 4 weeks) promoted an increase in the weight of brown fat, spleen, kidneys and heart, stomach ulcers and an alteration of cortisol and corticosterone levels were did observed. Short-term intermittent exposure to cold (+4°C, 1.5 hours/day, 4 weeks) did not affect the weight of brown fat, but promoted an increases in the weight of body, spleen, kidneys and heart, stomach ulcers were not found, cortisol and corticosterone levels was not changed.

[CARDIOPROTRECTIVE EFFECT OF REMOTE POSTCONDITIONING: MECHANISMS AND POSSIBILITIES OF CLINICAL APPLICATION]

Experimental data indicate that postconditioning at a distance is an effective method for cardiac protection against reperfusion injury. Remote postconditioning prevents reperfusion necrosis and apoptosis of cardiomyocytes, decreases a probability of postinfarction remodeling of the heart. Cardioprotective effect of remote postconditioning depends on the release of tissue factor(s) increasing cardiac tolerance to long-term ischemia-reperfusion after transient ischemia. Clinical investigations show that postconditioning at a distance is an effective method for the prevention of reperfusion injury of the heart during coronary artery bypass surgery.

Effects of μ-Opioid Receptor Agonist DAMGO on Heart Contractility and Necrotic Injury to Cardiomyocytes during Ischemia and Reperfusion of Isolated Rat Heart

We studied the effects of μ-opioid receptor activation in vivo and in vitro on the tolerance of isolated perfused rat heart to global ischemia (45 min) and reperfusion (30 min). Stimulation of μ-receptors in vivo by intraperitoneal administration of μ-opioid receptor agonist DAMGO (0.1 mg/kg) reduced reperfusion release of creatinine phosphokinase and promoted aggravation of postischemic systolic and diastolic dysfunction of the isolated heart. Activation of μ-opioid receptors in vitro by addition of selective agonist DAMGO in a concentration of 170 nM to perfusion solution had no effect on necrotic death of cardiomyocytes and aggravated reperfusion stunning of the heart.