Cannabinoid Receptor Antagonists SR141716 and SR144528 Exhibit Properties of Partial Agonists in Experiments on Isolated Perfused Rat Heart

We studied the effect of selective cannabinoid receptor ligands on contractility of isolated Langendorff-perfused rat heart. It was found that 10-min perfusion of rat heart with a solution containing selective agonist of CB1 and CB2 receptors HU-210 (10 nM) decreased left ventricular developed pressure and maximum rates of contraction and relaxation. However, HU-210 had no effect on heart rate and end-diastolic pressure. Treatment with selective CB1 receptor antagonist SR141716 (1 µM) and selective CB2 receptor antagonist SR144528 (1 µM) decreased left ventricular developed pressure and maximum rates of contraction and relaxation, but had no effect on heart rate and end-diastolic pressure. Ten-minute perfusion of rat heart with a solution containing selective agonist of CB1 and CB2 receptors HU-210 (10 nM) decreased cAMP concentration in the heart. CB receptor antagonists had little effect on cAMP concentration in the heart. The negative inotropic effect of HU-210 and CB receptor antagonists is probably mediated by activation of CB1 receptors. It can be hypothesized that the decrease in heart cAMP concentration is related to stimulation of CB2 receptors. Our results suggest that selective CB receptor antagonists SR141716 and SR144528 in a final concentration of 1 µM exhibit properties of partial CB receptor agonists.__________Translated from Byulleten’ Eksperimental’noi Biologii i Meditsiny, Vol. 139, No. 5, pp. 512–516, May, 2005     

Delta-opioid receptor activation prevents appearance of irreversible damages of cardiomyocytes and exacerbates myocardial contractility dysfunction during ischemia and reperfusion

It is shown that prestimulation of cardiac delta-opioid receptors (OR) by selective agonists (DPDPE and TAN-67) decreases creatine kinase levels in the coronary effluent of isolated rat heart during 45-min global ischemia and 30-min reperfusion. This effect was completely abolished by pretreatment with a delta-antagonist naltrindole or a non-selective agonist naloxone. It was found that preactivation of cardiac delta-OR exacerbates reperfusion contractility dysfunction of the heart. This effect was also eliminated by opioid receptor antagonists. It is suggested that stimulation of cardiac delta-OR prevents irreversible cardiac cell damage but exacerbates contractility dysfunction during ischemia and reperfusion in vitro.     

Negative chronotropic effect of cannabinoids and their water-soluble emulsion is related to activation of cardiac CB1 receptors

Intravenous injection of cannabinoids dissolved in cremophore EL:ethanol:NaCl mixture and water-soluble emulsion of the same cannabinoids caused identical negative chronotropic effects in chloralose-narcotized rats. Selective CB1 and CB2 receptor antagonist HU-210 also induced a negative chronotropic effect in rats, while pre-injection of CB1 receptor antagonist SR 141716A completely abolished this effect of HU-210. Selective CB2 receptor antagonist SR 144528 had no effect on HU-210-induced bradycardia. Preinjection of ganglioblocker hexamethonium also did not abolish the negative chronotropic effect of HU-210 and ACPA. Perfusion of isolated rat heart with Krebs-Henseleit solution containing HU-210 in a final concentration of 100 nM reduced heart rate. It was shown that the negative chronotropic effect of cannabinoids is mediated through activation of cardiac CB1 receptors. __________ Translated from Byulleten’ Eksperimental’noi Biologii i Meditsiny, Vol. 142, No. 10, pp. 433–436, October, 2006     

Activation of μ-opiate receptors as a factor of regulation of heart resistance to ischemia-reperfusion and oxidative stress

Intravenous injection of the selective μ-opiate receptor agonist DAMGO (0.1 mg/kg, 15 min before isolation of the heart) improved resistance of isolated perfused rat heart to ischemia (45 min) and reperfusion (60 min) damages.In vivo administration of DAMGO prevented reperfusion-induced damages to cardiomyocytes and decreased the content of conjugated dienes in the myocardium during ischemia-reperfusionin vitro. Furthermore, stimulation of μ-opiate receptors promoted recovery of myocardial contractility during reoxygenation, but had no effect on heart resistance to free radical-induced damages during perfusion of isolated heart with a solution containing Fe²⁺ and ascorbic acid. Translated fromByulleten’ Eksperimental’noi Biologii i Meditsiny, Vol. 130, No. 8, pp. 163–167, August, 2000     

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.     

Activation of μ-opiate receptors as a factor of regulation of heart resistance to ischemia-reperfusion and oxidative stress

Intravenous injection of the selective μ-opiate receptor agonist DAMGO (0.1 mg/kg, 15 min before isolation of the heart) improved resistance of isolated perfused rat heart to ischemia (45 min) and reperfusion (60 min) damages.In vivo administration of DAMGO prevented reperfusion-induced damages to cardiomyocytes and decreased the content of conjugated dienes in the myocardium during ischemia-reperfusionin vitro. Furthermore, stimulation of μ-opiate receptors promoted recovery of myocardial contractility during reoxygenation, but had no effect on heart resistance to free radical-induced damages during perfusion of isolated heart with a solution containing Fe²⁺ and ascorbic acid.     

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.     

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.     

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.     

Involvement of central and peripheral cannabionoid receptors in the regulation of heart resistance to arrhythmogenic effects of epinephrine

Intravenous injection of the selective cannabinoid receptor agonist HU-210 in doses of 0.05 and 0.25 mg/kg increased heart resistance to arrhythmogenic effects of epinephrine, while intracerebroventricular infusion of this substance had no effect on the incidence of epinephrine-induced arrhythmia. The selective antagonist of type I cannabinoid receptors SR141716A in a dose of 3 mg/kg and ganglion blocker hexamethonium in a dose of 10 mg/kg did not modify the antiarrhythmic effect of HU-210. This effect of HU-210 is probably related to activation of type II peripheral cannabinoid receptors. Translated fromByulleten’ Eksperimental’noi Biologii i Meditsiny, Vol. 130, No. 11, pp. 552–554, November, 2000     

Effect of sarcolemmal anion transport system blockers on the development of ischemia-induced myocardial edema and recovery of contractile function during reperfusion

Subtotal 30-min ischemia leads to myoglobin release and increases water content in the heart. Reperfusion partially restores the developed pressure. Addition of furosemide (a Na⁺, K⁺, 2Cl⁻-sumport blocker) or NMA (inhibitor of Na⁺/H⁺-exchange) to perfusate decreases myocardial water content, reduces myoglobin loss, and completely restores myocardial contractile function. The low-rate perfusion of isolated heart and its reperfusion with solutions containing DIOA (inhibitor of K⁺, Cl⁻-co-transport) or IAA-94 (Cl⁻ channel blocker) increases water accumulation and myoglobin release from the myocardium, and deteriorated its contractile function during reperfusion. Translated fromByulleten' Eksperimental'noi Biologii i Meditsiny, Vol. 127, No. 4, pp. 400–403, April, 1999     

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     

Modulation of the balance between cannabinoid CB(1) and CB(2) receptor activation during cerebral ischemic/reperfusion injury

Cannabinoid receptor activation has been shown to modulate both neurotransmission (CB(1)) and neuroinflammatory (CB(2)) responses. There are conflicting reports in the literature describing the influence of cannabinoid receptor activation on ischemic/reperfusion injury. The goal of this study was to evaluate how changing the balance between CB(1) and CB(2) activation following cerebral ischemia influences outcome. CB(1) and CB(2) expression were tested at different times after transient middle cerebral artery occlusion (MCAO) in mice by real-time RT-PCR. Animals subjected to 1 h MCAO were randomly assigned to receive different treatments: a CB(1) antagonist, a CB(2) antagonist, a CB(2) agonist, a CB(1) antagonist plus CB(2) agonist, a CB(2) antagonist plus CB(2) agonist or an equal volume of vehicle as control. Cerebral blood flow was continuously monitored during ischemia; cerebral infarction and neurological deficit were tested 24 h after MCAO. Cerebral CB(1) and CB(2) mRNA expression undertook dynamic changes during cerebral ischemia. The selective CB(1) antagonist significantly decreased cerebral infarction by 47%; the selective CB(2) antagonist increased infarction by 26% after 1 h MCAO followed by 23 h reperfusion in mice. The most striking changes were obtained by combining a CB(1) antagonist with a CB(2) agonist. This combination elevated the cerebral blood flow during ischemia and reduced infarction by 75%. In conclusion, during cerebral ischemia/reperfusion injury, inhibition of CB(1) receptor activation is protective while inhibition of CB(2) receptor activation is detrimental. The greatest degree of neuroprotection was obtained by combining an inhibitor of CB(1) activation with an exogenous CB(2) agonist.     

Activation of type II cannabinoid receptors improves myocardial tolerance to arrhythmogenic effects of coronary occlusion and reperfusion

Preliminary intravenous injection of cannabinoid receptor agonist HU-210 (0.05 mg/kg) reduced the incidence of ventricular arrhythmias during 10-min coronary occlusion and 10-min reperfusion in chloralose-anesthetized rats. Preliminary injection of type I cannabinoid receptor antagonist SR 141716A (3 mg/kg) had no effect on the antiarrhythmic effect of HU-210, while type II cannabinoid receptor antagonist SR 144528 (1 mg/kg) completely abolished the effect of HU-210. Preconditioning with glibenclamide (0.3 mg/kg), an inhibitor of ATP-dependent K⁺-channels, did not affect the antiarrhythmic activity of HU-210. These findings suggest that antiarrhythmic effect of HU-210 is mediated through activation of type II cannabinoid receptors rather than activation of K⁺-channels.     

Effect of uridine derivatives on myocardial stunning during postischemic reperfusion of rat heart

Uridine and uridine-5’-monophosphate prevent myocardial stunning during postischemic reperfusion of isolated rat heart. Uridine-5’-diphosphate does not prevent postischemic myocardial dysfunction, while uridine-5’-triphosphate aggravates it. Translated fromByulleten' Eksperimental'noi Biologii i Meditsiny, Vol. 130, No. 10, pp. 411–414, October, 2000     

Cardioprotective effect of κ<Subscript>1</Subscript>-opioid receptor activation and role of cAMP in its realization

The cardioprotective and antiarrhythmic effects of a selective κ₁-opioid receptor agonist U-50,488 were studied during experimental 45-min total ischemia and 30-min reperfusion of isolated rat heart. The opioid had no effect on the incidence and type of reperfusion arrhythmias. U-50,488 in a concentration of 0.1 μM inhibited reperfusion-induced release of creatine phosphokinase and decreased cAMP concentration in the myocardium by 2 times. These parameters remained unchanged after treatment with U-50,488 in a concentration of 1 μM. The cardioprotective effect of U-50,488 was probably associated with a decrease in cAMP concentration in heart cells. U-50,488 in a concentration of 1 μM produced no cardioprotective effect, which can be explained by its interaction with an unknown non-opioid receptor in cardiomyocytes. __________ Translated from Byulleten’ Eksperimental’noi Biologii i Meditsiny, Vol. 143, No. 1, pp. 28–31, January, 2007     

Cannabinoid CB2 receptor activation reduces mouse myocardial ischemia-reperfusion injury: involvement of cytokine/chemokines and PMN

In this study, we have assessed the activation of the cannabinoid CB2 receptor (CB2-R) in a model of mouse myocardial ischemia/reperfusion (I/R). The results show that treatment of animals with WIN55212-2, a CB1/CB2-R agonist, given 30 min before induction of I/R, significantly reduced the extent of infarct size (IS) in the area at risk, as measured 2.5 h later, with almost a 51% inhibition observed at the dose tested of 3.5 mg/kg intraperitoneally (i.p.). The protective effect of WIN55212-2 was almost abolished by the selective CB2-R antagonist AM630 (1 mg/kg i.p.) and not affected by the selective CB1-R antagonist AM251 (3 mg/kg i.p.). The CB2-R antagonist administered alone produced a slight but significant (P<0.05) increase in IS compared with vehicle alone. The protection afforded by WIN55212-2 was paralleled by lower values of myeloperoxidase activity and interleukin-1beta and of the CXC chemokine ligand 8 into the injured tissue. In conclusion, we demonstrate for the first time that exogenous and endogenous CB2-R activation reduces the leukocyte-dependent myocardial damage associated with an I/R procedure.     

Anandamide enhances expression of heat shock protein 72 to protect against ischemia–reperfusion injury in rat heart

Anandamide (AEA), one of endocannabinoids, has been reported to exhibit a cardioprotective ability to limit the damage produced by ischemia–reperfusion injury. AEA reportedly enhanced heat shock protein 72 (HSP72) and HSP25 expression in lungs to protect against lung inflammation. This study tested the hypothesis that intravenously injected AEA would induce HSP72 in the heart and thus render cardioprotection against ischemia–reperfusion injury in rats. Cardiac expression of HSPs was quantitatively evaluated in rats by Western blot analysis. That intravenously injected AEA 1 mg/kg in vivo induced expression of HSP72, which peaked at 24 h after administration. The enhancement of HSP72 by AEA was blocked by cannabinoid 2 (CB₂) receptor antagonist AM630, but not cannabinoid 1 (CB₁) receptor antagonist AM251. Therefore, the rats were induced with a 30-min coronary occlusion followed by a 120-min reperfusion in vivo at 24 h after administration of drugs or vehicle, and then the infarct size was measured. AEA reduced myocardial infarct size compared to control group. Pretreatment with AM630 but not AM251 abolished the infarct size-limiting effect of AEA. Further study demonstrated pretreatment with phosphatidylinositol 3-kinase (PI3K) inhibitor wortmannin, Akt inhibitor MK-2206 and AM630 attenuated phosphorylation of Akt and AEA-induced HSP72 expression. The results suggest that AEA is cardioprotective against ischemia–reperfusion insult through its induction of HSP72, which might be mediated by the PI3K/Akt signaling pathway. These effects were mediated by CB₂ but not CB₁ receptors.     

Dimethyl amiloride,a Na<Superscript>+</Superscript>–H<Superscript>+</Superscript> exchange inhibitor,and its cardioprotective effects in hemorrhagic shock in in vivo resuscitated rats

Stimulation of the Na⁺–H⁺ exchanger plays an important role in the pathway of myocardial dysfunction and injury following hemorrhagic shock. Inhibition of the Na⁺–H⁺ exchanger appears to be a new pharmacological tool for myocardial protection. Despite the extensive research that has been done on the role of the Na⁺–H⁺ exchanger in ischemia reperfusion, little is known about the role of the exchanger following hemorrhagic shock. The purpose of this study was to examine the protective effects of blocking the cardiac Na⁺–H⁺ exchanger, using 20 μM dimethyl amiloride (DMA), a specific Na⁺–H⁺ exchanger blocker, on myocardial contractile function after ex vivo perfusion of isolated rat heart following 1 h of hemorrhagic shock. Sprague–Dawley rats were assigned to hemorrhage + DMA, hemorrhage, sham hemorrhage + DMA and sham hemorrhage groups (n = 6 per group). Hearts were perfused with a balanced salt solution for 60 min. In the DMA treated group, 20 μM DMA was added for the first 5 min of the 60-min ex vivo heart resuscitation. The results showed that inhibition of the Na⁺–H⁺ exchanger for 5 min on ex vivo perfusion of the isolated hearts following hemorrhagic shock using 20 μM DMA improved myocardial contractile function. Blocking the Na⁺–H⁺ exchanger on ex vivo perfusion of isolated hearts using 20 μM DMA has protective effects on myocardial contractile function.