Role of beta 1- and beta 2-adrenoceptor subtypes in preconditioning against myocardial dysfunction after ischemia and reperfusion

Comparison of Cardioprotective Potential of Cannabidiol and β-Adrenergic Stimulation Against Hypoxia/Reoxygenation Injury in Rat Atria and Ventricular Papillary Muscles

BACKGROUND

Hypoxia is one of the most significant pathogenic factors in cardiovascular diseases. Preclinical studies suggest that nonpsychoactive cannabidiol (CBD) and β-adrenoceptor stimulation might possess cardioprotective potential against ischemia-reperfusion injury. The current study evaluates the influence of hypoxia-reoxygenation (H/R) on the function of atria and ventricular papillary muscles in the presence of CBD and the nonselective β-adrenoceptor agonist isoprenaline (ISO).

METHODS

The concentration curves for ISO were constructed in the presence of CBD (1 µM) before or after H/R. In chronic experiments (CBD 10 mg/kg, 14 days), the left atria isolated from spontaneously hypertensive (SHR) and their normotensive control (WKY) rats were subjected to H/R following ISO administration.

RESULTS

Hypoxia decreased the rate and force of contractions in all compartments. The right atria were the most resistant to hypoxia regardless of prior β-adrenergic stimulation. Previous β-adrenergic stimulation improved recovery in isolated left atria and right (but not left) papillary muscles. Acute (but not chronic) CBD administration increased the effects of ISO in left atria and right (but not left) papillary muscles. Hypertension accelerates left atrial recovery during reoxygenation.

CONCLUSIONS

H/R directly modifies the function of particular cardiac compartments in a manner dependent on cardiac region and β-adrenergic prestimulation. The moderate direct cardioprotective potential of CBD and β-adrenergic stimulation against H/R is dependent on the cardiac region, and it is less than in the whole heart with preserved coronary flow. In clinical terms, our research expands the existing knowledge about the impact of cannabidiol on cardiac ischemia, the world's leading cause of death.

Role of cardiac β1-adrenergic and A1-adenosine receptors in severe arrhythmias related to Parkinson's disease

AIMS

Although reduced life expectancy in Parkinson's Disease (PD) patients has been related to severe cardiac arrhythmias due to autonomic dysfunctions, its molecular mechanisms remain unclear. To investigate the role of cardiac β1-Adrenergic (β1AR) and A1-Adenosine (A1R) receptors in these dysfunctions, the pharmacological effects of stimulation of cardiac β1AR (isoproterenol, ISO), in the absence and presence of cardiac β1AR (atenolol, AT) or A1R (1,3-dipropyl-8-cyclopentyl xanthine, DPCPX) blockade, on the arrhythmias induced by Ischemia/Reperfusion (CIR) in an animal PD model were studied.

METHODS

PD was produced by dopaminergic lesions (confirmed by immunohistochemistry analysis) caused by the injection of 6-hydroxydopamine (6-OHDA, 6 μg) in rat striatum. CIR was produced by a surgical interruption for 10 min followed by reestablishment of blood circulation in the descendent left coronary artery. On the incidence of CIR-Induced Ventricular Arrhythmias (VA), Atrioventricular Block (AVB), and Lethality (LET), evaluated by Electrocardiogram (ECG) analysis, the effects of intravenous treatment with ISO, AT and DPCPX (before CIR) were studied.

RESULTS

VA, AVB and LET incidences were significantly higher in 6-OHDA (83%, 92%, 100%, respectively) than in control rats (58%, 67% and 67%, respectively). ISO treatment significantly reduced these incidences in 6-OHDA (33%, 33% and 42%, respectively) and control rats (25%, 25%, 33%, respectively), indicating that stimulation of cardiac β1AR induced cardioprotection. This response was prevented by pretreatment with AT and DPCPX, confirming the involvement of cardiac β1AR and A1R.

CONCLUSION

Pharmacological modulation of cardiac β1AR and A1R could be a potential therapeutic strategy to reduce severe arrhythmias and increase life expectancy in PD patients.

Pharmacological modulation of b-adrenoceptors as a new cardioprotective strategy for therapy of myocardial dysfunction induced by ischemia and reperfusion

Purpose:

To evaluate the cardioprotective response of the pharmacological modulation of β-adrenergic receptors (β-AR) in animal model of cardiac ischemia and reperfusion (CIR), in spontaneously hypertensive (SHR) and normotensive (NWR) rats.

Methods:

CIR was induced by the occlusion of left anterior descendent coronary artery (10 min) and reperfusion (75 min). The SHR was treated with β-AR antagonist atenolol (AT, 10 mg/kg, IV) 5 min before CIR, and NWR were treated with β-AR agonist isoproterenol (ISO, 0.5 mg/kg, IV) 5 min before CIR.

Results:

The treatment with AT increased the incidence of VA, AVB and LET in SHR, suggesting that spontaneous cardioprotection in hypertensive animals was abolished by blockade of β-AR. In contrast, the treatment with ISO significantly reduced the incidence of ventricular arrhythmia, atrioventricular blockade and lethality in NWR (30%, 20% and 20%, respectively), suggesting that the activation of β-AR stimulate cardioprotection in normotensive animals. Serum CK-MB were higher in SHR/CIR and NWR/CIR compared to respective SHAM group (not altered by treatment with AT or ISO).

Conclusion:

The pharmacological modulation of β-AR could be a new cardioprotective strategy for the therapy of myocardial dysfunctions induced by CIR related to cardiac surgery and cardiovascular diseases.

β-Adrenergic signaling, monoamine oxidase A and antioxidant defence in the myocardium of SHR and SHR-mtBN conplastic rat strains: the effect of chronic hypoxia

The β-adrenergic signaling pathways and antioxidant defence mechanisms play important roles in maintaining proper heart function. Here, we examined the effect of chronic normobaric hypoxia (CNH, 10% O2, 3 weeks) on myocardial β-adrenergic signaling and selected components of the antioxidant system in spontaneously hypertensive rats (SHR) and in a conplastic SHR-mtBN strain characterized by the selective replacement of the mitochondrial genome of SHR with that of the more ischemia-resistant Brown Norway strain. Our investigations revealed some intriguing differences between the two strains at the level of β-adrenergic receptors (β-ARs), activity of adenylyl cyclase (AC) and monoamine oxidase A (MAO-A), as well as distinct changes after CNH exposure. The β2-AR/β1-AR ratio was significantly higher in SHR-mtBN than in SHR, apparently due to increased expression of β2-ARs. Adaptation to hypoxia elevated β2-ARs in SHR and decreased the total number of β-ARs in SHR-mtBN. In parallel, the ability of isoprenaline to stimulate AC activity was found to be higher in SHR-mtBN than that in SHR. Interestingly, the activity of MAO-A was notably lower in SHR-mtBN than in SHR, and it was markedly elevated in both strains after exposure to hypoxia. In addition to that, CNH markedly enhanced the expression of catalase and aldehyde dehydrogenase-2 in both strains, and decreased the expression of Cu/Zn superoxide dismutase in SHR. Adaptation to CNH intensified oxidative stress to a similar extent in both strains and elevated the IL-10/TNF-α ratio in SHR-mtBN only. These data indicate that alterations in the mitochondrial genome can result in peculiar changes in myocardial β-adrenergic signaling, MAO-A activity and antioxidant defence and may, thus, affect the adaptive responses to hypoxia.

Delta Opioid Receptors and Cardioprotection

The opioid receptor family, with associated endogenous ligands, has numerous roles throughout the body. Moreover, the delta opioid receptor (DORs) has various integrated roles within the physiological systems, including the cardiovascular system. While DORs are important modulators of cardiovascular autonomic balance, they are well-established contributors to cardioprotective mechanisms. Both endogenous and exogenous opioids acting upon DORs have roles in myocardial hibernation and protection against ischaemia-reperfusion (I-R) injury. Downstream signalling mechanisms governing protective responses alternate, depending on the timing and duration of DOR activation. The following review describes models and mechanisms of DOR-mediated cardioprotection, the impact of co-morbidities and challenges for clinical translation.

Remote Postconditioning Induced by Trauma Protects the Mouse Heart against Ischemia Reperfusion Injury. Involvement of the Neural Pathway and Molecular Mechanisms

PURPOSE

Abdominal superficial surgical incision elicits cardioprotection against myocardial ischemia reperfusion (I/R) injury in mice. This cardioprotective phenomenon, termed remote preconditioning of trauma (RPCT), results in an 80 to 85 % reduction in cardiac infarct size. We evaluated cardioprotection and the molecular mechanisms of remote postconditioning of trauma (RPostCT) in a murine I/R injury model.

METHODS

Mice were analyzed using a previously established I/R injury model. An abdominal superficial surgical incision was made 45 min after myocardial ischemia at the end of coronary occlusion, and infarct size was determined 24 h after reperfusion.

RESULTS

The results indicated that a strong cardioprotective effect occurred during RPostCT (56.94 ± 2.71 % sham vs. 15.58 ± 2.16 % RPostCT; the mean area of the infarct divided by the mean area of the region at risk; p ≤ 0.05; n = 10). Furthermore, pharmacological intervention revealed neurogenic signaling involvement in the beneficial effects of RPostCT via sensory and sympathetic thoracic nerves. Pharmacological experiments in transgenic mice demonstrated that bradykinin receptors, β-adrenergic receptors (AR), and protein kinase C were implicated in the cardioprotective effects of RPostCT.

CONCLUSIONS

RPostCT significantly decreased myocardial infarction size via neurogenic transmission and various signaling pathways. This study describes a new cardiac I/R injury prevention method that might lead to the development of therapies that are more clinically relevant for myocardial I/R injury.

Drug Signature-based Finding of Additional Clinical Use of LC28-0126 for Neutrophilic Bronchial Asthma

In recent decades, global pharmaceutical companies have suffered from an R&D innovation gap between the increased cost of a new drug’s development and the decreased number of approvals. Drug repositioning offers another opportunity to fill the gap because the approved drugs have a known safety profile for human use, allowing for a reduction of the overall cost of drug development by eliminating rigorous safety assessment. In this study, we compared the transcriptional profile of LC28-0126, an investigational drug for acute myocardial infarction (MI) at clinical trial, obtained from healthy male subjects with molecular activity profiles in the Connectivity Map. We identified dyphilline, an FDA-approved drug for bronchial asthma, as a top ranked connection with LC28-0126. Subsequently, we demonstrated that LC28-0126 effectively ameliorates the pathophysiology of neutrophilic bronchial asthma in OVA_LPS-OVA mice accompanied with a reduction of inflammatory cell counts in the bronchoalveolar lavage fluid (BALF), inhibition of the release of proinflammatory cytokines, relief of airway hyperactivity, and improvement of histopathological changes in the lung. Taken together, we suggest that LC28-0126 could be a potential therapeutic for bronchial asthma. In addition, this study demonstrated the potential general utility of computational drug repositioning using clinical profiles of the investigational drug.

The Cardioprotective Effects of Late-Phase Remote Preconditioning of Trauma Depends on Neurogenic Pathways and the Activation of PKC and NF-κB (But Not iNOS) in Mice

BACKGROUND

A superficial abdominal surgical incision elicits cardioprotection against cardiac ischemia-reperfusion (I/R) injury in mice. This process, called remote preconditioning of trauma (RPCT), has both an early and a late phase. Previous investigations have demonstrated that early RPCT reduces cardiac infarct size by 80% to 85%. We evaluated the cardioprotective and molecular mechanisms of late-phase RPCT in a murine I/R injury model.

METHODS

Wild-type mice, bradykinin (BK) 2 receptor knockout mice, 3M transgenic mice (nuclear factor κB [NF-κb] repressor inhibitor of nuclear factor of kappa light polypeptide gene enhancer in B-cells inhibitor alpha [IκBα((S32A, S36A, Y42F))]), and inducible nitric oxide synthase (iNOS) knockout mice were analyzed using a previously established I/R injury model. A noninvasive abdominal surgical incision was made 24 hours prior to I/R injury and the infarct size was determined at 24 hours post-I/R injury.

RESULTS

The results indicated that a strong cardioprotective effect occurred during late-phase RPCT (58.42% ± 1.89% sham vs 29.41% ± 4.00% late RPCT, mean area of the infarct divided by the mean area of the risk region; P ≤ .05; n = 10). Furthermore, pharmacological intervention revealed the involvement of neurogenic signaling in the beneficial effects of late RPCT via sensory and sympathetic thoracic nerves. Pharmacological experiments in transgenic mice-implicated BK receptors, β-adrenergic receptors, protein kinase C, and NF-κB but not iNOS signaling in the cardioprotective effects of late RPCT.

CONCLUSION

Late RPCT significantly decreased myocardial infarct size via neurogenic transmission and various other signaling pathways. This protective mechanism differentiates late and early RPCT. This study describes a new cardiac I/R injury prevention method and refines the concept of RPCT.

Silymarin Constituent 2,3-Dehydrosilybin Triggers Reserpine-Sensitive Positive Inotropic Effect in Perfused Rat Heart

2,3-dehydrosilybin (DHS) is a minor flavonolignan component of Silybum marianum seed extract known for its hepatoprotective activity. Recently we identified DHS as a potentially cardioprotective substance during hypoxia/reoxygenation in isolated neonatal rat cardiomyocytes. This is the first report of positive inotropic effect of DHS on perfused adult rat heart. When applied to perfused adult rat heart, DHS caused a dose-dependent inotropic effect resembling that of catecholamines. The effect was apparent with DHS concentration as low as 10 nM. Suspecting direct interaction with β-adrenergic receptors, we tested whether DHS can trigger β agonist-dependent gene transcription in a model cell line. While DHS alone was unable to trigger β agonist-dependent gene transcription, it enhanced the effect of isoproterenol, a known unspecific β agonist. Further tests confirmed that DHS could not induce cAMP accumulation in isolated neonatal rat cardiomyocytes even though high concentrations (≥ 10 μM) of DHS were capable of decreasing phosphodiesterase activity. Pre-treatment of rats with reserpine, an indole alkaloid which depletes catecholamines from peripheral sympathetic nerve endings, abolished the DHS inotropic effect in perfused hearts. Our data suggest that DHS causes the inotropic effect without acting as a β agonist. Hence we identify DHS as a novel inotropic agent.

Anti-arrhythmic effect of acupuncture pretreatment in the rats subjected to simulative global ischemia and reperfusion--involvement of intracellular Ca2+ and connexin 43

BACKGROUND

The previous study showed that the cardiac arrhythmias induced by myocardial ischemia and reperfusion were attenuated by the pretreatment of acupuncture; however, the related mechanism is not understood. The present study was therefore designed to determine whether intracellular Ca(2+) ([Ca(2+)]i) and connexin 43 (Cx43) are involved in the mediation of the anti-arrhythmic effect of electro-acupuncture (EA) pretreatment in the rats subjected to simulative global ischemia and reperfusion (SGIR).

METHODS

SGIR was made in the isolated heart by a low flow perfusion followed by a flow restoration. Four groups of animals are involved in the present study, including normal control group, SGIR group, EA group and EA plus 18 beta-glycyrrhetinic acid (EAG) group. For EA pretreatment, bilateral Neiguan acupoints (PC6) of the rats were stimulated for 30 min once a day in 3 consecutive days. Cx43 antagonist was given to the rats in EAG group 30 minutes before the EA pretreatment. The resting [Ca(2+)]i concentration, calcium oscillation, the contents of total Cx43 and non-phosphrylated Cx43 and arrhythmia score were compared among different groups.

RESULTS

In EA group, the arrhythmic score, the resting [Ca(2+)]i concentration and the number of [Ca(2+)]i oscillations were all significantly less than those in SGIR group (all P < 0.05), and interestingly, after EA pretreatment, the contents of nonphosphated Cx43 in the EA group were significantly lower than that in SGIR group respectively (P < 0.05). However, when the rats were treated with Cx43 antagonist prior to the EA pretreatment, the protection effects induced by EA pretreatment were reversed.

CONCLUSIONS

The results showed that EA pretreatment could produce anti-arrhythmic effect in the rats subjected to SGIR. The anti-arrhythmic effect of EA pretreatment may be due at least partially to the inhibition of SGIR-induced calcium overload and [Ca(2+)]i oscillations, reduction of non-phosphorylated Cx43 and the enhancement of the corresponding phosphorylated Cx43 in the cardiac cells.

The mechanism of beta-adrenergic preconditioning: roles for adenosine and ROS during triggering and mediation

The aim of this study was to investigate the mechanism of beta-adrenergic preconditioning (BPC). The roles of adenosine and its receptor subtypes, the generation of oxygen free radicals (ROS) and activation of the K(ATP) channels as well as the phosphoinositide-3-kinase (PI(3)K)/PKB/Akt and extracellular signal-regulated kinase (ERK) signal transduction pathways during the triggering and mediation phases were evaluated. Using the isolated working rat heart, BPC was elicited by administration of denopamine (beta1 adrenergic receptor agonist, 10(-7) M), isoproterenol (beta1/beta2 adrenergic receptor agonist, 10(-7) M) or formoterol (beta2 adrenergic receptor agonist, 10(-9) M) for 5 min followed by 5 min washout. Index ischaemia was 35 min regional ischaemia and infarct size determined using the tetrazolium method. The role of adenosine was studied using adenosine deaminase and selective antagonists as well as the PI(3)K and ERK inhibitors, wortmannin and PD98,059, bracketing the triggering and mediating phases. Involvement of ROS, PKC, the mitochondrial K(ATP) channels, release of endogenous opioids and bradykinin was studied by administration of N-acetyl cysteine (NAC), bisindolylmaleimide, the K(ATP) channel blocker 5-hydroxydecanoate (5-HD), naloxone or HOE140, respectively. Activation of PKB/Akt and ERKp44/p42 during triggering and reperfusion was determined by Western blot. Preconditioning with all three beta-adrenergic receptor agonists caused a reduction in infarct size and an improvement in postischaemic function. BPC preconditioning with isoproterenol, denopamine or formoterol was abolished by the adenosine A3 receptor antagonist MRS1191 during both the triggering and mediation phases. Isoproterenol-induced preconditioning (beta1/beta2 PC) was attenuated by MRS1754, an adenosine A(2B) receptor antagonist, during the triggering phase and abolished during reperfusion. The mediation phase of beta1/beta2 PC was also abolished by ZM241385, an adenosine A(2A) antagonist. The free radical scavenger NAC caused a significant attenuation of cardioprotection induced by isoproterenol when administered during both trigger and mediation phases, while being effective during the trigger phase with denopamine and during reperfusion in formoterol preconditioned hearts. The mitochondrial K(ATP) channel blocker, 5-HD, was without effect on beta1/beta2 PC during both triggering and mediation phases. BPC in rat hearts is dependent on activation of the A(3) adenosine receptors by endogenously produced adenosine and production of free radicals during the triggering and mediation phases while the A(2A) and A(2B) adenosine receptors participate mainly during reperfusion. The mitochondrial K(ATP) channels do not contribute to cardioprotection at any stage. Activation of ERK and PI3K/PKB/Akt during the triggering and reperfusion phases is associated with cardioprotection.

Peripheral nociception associated with surgical incision elicits remote nonischemic cardioprotection via neurogenic activation of protein kinase C signaling

BACKGROUND

Although remote ischemic stimuli have been shown to elicit cardioprotection against ischemia/reperfusion injury, there is little known about the effects of nonischemic stimuli. We previously described a remote cardioprotective effect of nonischemic surgical trauma (abdominal incision) called remote preconditioning of trauma (RPCT). In the present study, we elucidate mechanisms underlying this phenomenon.

METHODS AND RESULTS

We used a murine model of myocardial infarction to evaluate ischemia/reperfusion injury, and either abdominal surgical incision, or application of topical capsaicin, to elicit cardioprotection. We show that the cardioprotective effect of RPCT is initiated by skin nociception, and requires neurogenic signaling involving spinal nerves and activation of cardiac sensory and sympathetic nerves. Our results demonstrate bradykinin-dependent activation and repression, respectively, of PKCepsilon and PKCdelta in myocardium after RPCT, and we show involvement of the K(ATP) channels in cardioprotection. Finally, we show that topical application of capsaicin, which selectively activates C sensory fibers in the skin, mimics the cardioprotective effect of RPCT against myocardial infarction.

CONCLUSIONS

Nontraumatic nociceptive preconditioning represents a novel therapeutic strategy for cardioprotection with great potential clinical utility.

Lack of cardioprotection from subcutaneously and preischemic administered liraglutide in a closed chest porcine ischemia reperfusion model

Background

Glucagon-like peptide 1 (GLP1) analogues are promising new treatment options for patients with type 2 diabetes, but may have both potentially beneficial and harmful cardiovascular effects. This may also be the case for the analogues of GLP1 for clinical use. The present study examined the effect of treatment with Liraglutide, a long-acting GLP1 analogue, on myocardial ischemia and reperfusion in a porcine model.

Methods

Danish Landrace Pigs (70–80 kg) were randomly assigned to Liraglutide (10 μg/kg) or control treatment given daily for three days before ischemia-reperfusion. Ischemia was induced by balloon occlusion of the left anterior descending artery for 40 minutes followed by 2.5 hours of reperfusion. The primary outcome parameter was infarct size in relation to the ischemic region at risk. Secondary endpoints were the hemodynamic parameters mean pulmonary pressure, cardiac output, pulmonary capillary wedge pressure as measured by a Swan-Ganz catheter as well as arterial pressure and heart rate.

Results

The infarct size in relation to ischemic risk region in the control versus the Liraglutide group did not differ significantly: 0.46 ± 0.14 and 0.54 ± 0.12) (mean and standard deviation (SD), p = 0.21). Heart rate was significantly higher in the Liraglutide group during the experiment, while the other hemodynamic parameters did not differ significantly.

Conclusion

Liraglutide has a neutral effect on myocardial infarct size in a porcine ischemia-reperfusion model.

Antiarrhythmic effect of acupuncture pretreatment in rats subjected to simulative global ischemia and reperfusion--involvement of adenylate cyclase, protein kinase A, and L-type Ca2+ channel

Our previous study showed that electro-acupuncture (EA) pretreatment protects the heart from injury of ischemia. The present study explored further whether adenylate cyclase (AC), protein kinase A (PKA), and L-type Ca(2+) channel, the beta(1)-AR signaling components modulating intracellular Ca(2+) ([Ca(2+)](i)), are involved in the mediation of the antiarrhythmic effect of EA pretreatment in the rats from which the hearts were subsequently isolated and subjected to simulative global ischemia and reperfusion (SGIR). SGIR was performed by perfusing the isolated heart at a low flow followed by normal perfusion. Adult rats were randomized into four groups, namely, normal control (NC), SGIR, EA, and NC plus EA (NCEA) groups. The rats in the EA and NCEA groups were given EA pretreatment at bilateral Neiguan points (PC6) for 30 min once a day in 3 consecutive days before the hearts were isolated and perfused. The arrhythmia score and the response of [Ca(2+)](i) to the activators of AC, PKA, and L-type Ca(2+) channel in single ventricular myocyte isolated from the hearts subjected to SGIR were compared among the groups. The results showed that the arrhythmia score was significantly higher in the SGIR group as compared with the NC and NCEA groups. The SGIR-enhanced arrhythmia score was significantly attenuated in the EA group. More interesting, EA pretreatment also attenuated the SGIR-enhanced response of [Ca(2+)](i) to the activators of AC, PKA, and the L-type Ca(2+) channel in the myocytes isolated from the hearts subjected to SGIR. In conclusion, EA pretreatment can produce an antiarrhythmic effect in the rat of SGIR. AC, PKA and the L-type Ca(2+) channel are involved in the mediation of the antiarrhythmic effect of EA pretreatment.

Activation of peripheral delta2 opioid receptors increases cardiac tolerance to ischemia/reperfusion injury Involvement of protein kinase C, NO-synthase, KATP channels and the autonomic nervous system

AIMS

This study aims to investigate the role of peripheral delta(2) opioid receptors in cardiac tolerance to ischemia/reperfusion injury and to examine the contribution of PKC, TK, K(ATP) channels and the autonomic nervous system in delta(2) cardioprotection.

MAIN METHODS

Deltorphin II and various inhibitors were administered in vivo prior to coronary artery occlusion and reperfusion in a rat model. The animals were monitored for the development of arrhythmias, infarct development and the effects of selected inhibitors.

KEY FINDINGS

Pretreatment with peripheral and delta(2) specific opioid receptor (OR) antagonists completely abolished the cardioprotective effects of deltorphin II. In contrast, the selective delta(1) OR antagonist 7-benzylidenenaltrexone (BNTX) had no effect. The protein kinase C (PKC) inhibitor chelerythrine and the NO-synthase inhibitor L-NAME (N-nitro-L-arginine methyl ester) also reversed both deltorphin II effects. The nonselective ATP-sensitive K+ (K(ATP)) channel inhibitor glibenclamide and the selective mitochondrial K(ATP) channel inhibitor 5-hydroxydecanoic acid only abolished the infarct-sparing effect of deltorphin II. Inhibition of tyrosine kinase (TK) with genistein, the ganglion blocker hexamethonium and the depletion of endogenous catecholamine storage with guanethidine reversed the antiarrhythmic action of deltorphin II but did not change its infarct-sparing action.

SIGNIFICANCE

The cardioprotective mechanism of deltorphin II is mediated via stimulation of peripheral delta(2) opioid receptors. PKC and NOS are involved in both its infarct-sparing and antiarrhythmic effects. Infarct-sparing is dependent upon mitochondrial K(ATP) channel activation while the antiarrhythmic effect is dependent upon TK activation. Endogenous catecholamine depletion reduced antiarrhythmic effects but did not alter the infarct-sparing effect of deltorphin II.

Activation of beta-adrenoceptors mimics preconditioning of rat-isolated atria and ventricles against ischaemic contractile dysfunction

The effects of ischaemia and reoxygenation on cardiac contractile function can be abrogated by ischaemic preconditioning (IPC). We tested whether beta-adrenoceptor agonists could mimic IPC and whether IPC was dependent on beta-adrenoceptor activation in rat-isolated cardiac tissues. Paced left atria and right ventricular strips were set-up in Krebs solution and isometric developed tension recorded. Ischaemia was simulated by replacing with hypoxic glucose-free Krebs solution for 30 min. IPC and isoprenaline (10(-7) M) preconditioning for 10 min were examined. Developed tension post-reoxygenation was expressed as a percentage of the pre-ischaemic baseline. Recovery at 15 min was significantly increased by IPC in atria (47 +/- 4.0% vs. 29.3 +/- 1.7%, p < 0.05) and ventricles (39.0 +/- 5.2% vs. 22.4 +/- 2.8%, p < 0.05). At 60 min, isoprenaline-treated atria recovery (75.8 +/- 16.6%) was significantly (p < 0.05) greater than controls (47.9 +/- 2.3%). Propranolol (10(-6) M) abolished both effects. Therefore, both IPC and beta-adrenoceptor agonist-induced improvement of contractile recovery was propranolol-sensitive and beta-adrenoceptor-mediated.

Advanced-glycation end products (AGEs) derived from glycated albumin suppress early beta1-adrenergic preconditioning

Ischemic heart disease in diabetic patients might be linked to the accumulation of advanced-glycation end products (AGEs). In ischemic rat hearts, expression of receptor for AGEs and its ligands is significantly enhanced and involved in cardiac ischemia/reperfusion (I/R) injury even in the absence of diabetes. It has recently been reported that diabetic human myocardium cannot be protected by preconditioning. In this context, our hypothesis was that beta1-adrenergic preconditioning might be altered in the presence of AGEs. Using an isolated non-working rat heart model, this study investigated the effect of AGEs on cardioprotection induced by transient beta1-adrenoceptor (beta1-AR) stimulation with xamoterol (Xa). After 6-hydroxydopamine (6-OHDA) pre-treatment and a 20-min stabilization period, hearts were perfused at constant pressure for 20 min, then subjected to 40 min of global ischemia and 30 min of reperfusion (I/R, Ctrl); and exposed to 0.01 microm Xa for 5 min framed with or without 15.2 microm albumin (Alb) or glycated albumin (Gly Alb). The main endpoints were the mean coronary flow (MCF), the left ventricular end-diastolic pressure (LVEDP), rate-pressure product (RPP) and creatine kinase (CK) release and necrosis area. XA induced an increase in the MCF after I/R (t = 85 min), a protective effect on the LVEDP, an improvement in RPP, a decrease of CK release during reperfusion and a reduction of necrotic area. The beneficial effects induced by Xa during reperfusion were suppressed by the administration of Gly Alb during Xa infusion, whereas Alb did not hamper Xa-induced protection. These results suggest that AGEs suppress the cardioprotection resulting from the activation of beta1-ARs and thus might contribute to cardiovascular damages seen in diabetic patients.

Acupuncture pretreatment protects heart from injury in rats with myocardial ischemia and reperfusion via inhibition of the beta(1)-adrenoceptor signaling pathway

Our previous study showed that a cardioprotective effect was produced by pretreatment with acupuncture at bilateral Neiguan acupoints (PC6) and the effect of EA was diminished by propranolol, a nonspecific antagonist of beta-adrenoceptors (beta-ARs) which are the most powerful cardiac receptors, indicating an involvement of beta-ARs. The present study explored further the signaling mechanism underlying the cardioprotective effect of acupuncture pretreatment in rats subjected to myocardial ischemia and reperfusion (MIR). Myocardial ischemia was achieved by ligating the left anterior descending coronary artery and reperfusion by releasing the ligation. Adult rats were divided into three groups, namely, a normal control (NC) group, a group subjected to ischemia and reperfusion (IR) only, and a group given electro-acupuncture (EA) before IR. For EA, bilateral Neiguan points (PC6) of the rats were stimulated for 30 min once a day for 3 consecutive days. The ST segment of ECG, the ratio of infarct size over risk zone, and the contents of beta(1)-adrenoceptor (beta(1)-AR), Gsalpha protein and cAMP in ischemic myocardium were compared among the three groups. IR increased the elevation of ECG ST segment, myocardial infarct size, contents of beta(1)-AR, Gsalpha protein and cAMP. These effects were attenuated by EA pretreatment at bilateral Neiguan acupoints. In conclusion, the present results indicate that EA produces cardioprotective effect against IR which may be mediated via the beta(1)-AR-Gs-protein-cAMP pathway.

beta1-Adrenoreceptor activation contributes to ischemia-reperfusion damage as well as playing a role in ischemic preconditioning

Protein kinase A (PKA) activation has been implicated in early-phase ischemic preconditioning. We recently found that during ischemia PKA activation causes inactivation of cytochrome-c oxidase (CcO) and contributes to myocardial damage due to ischemia-reperfusion. It may be that beta-adrenergic stimulation during ischemia via endogenous catecholamine release activates PKA. Thus beta-adrenergic stimulation may mediate both myocardial protection and damage during ischemia. The present studies were designed to determine the role of the beta(1)-adrenergic receptor (beta(1)-AR) in myocardial ischemic damage and ischemic preconditioning. Langendorff-perfused rabbit hearts underwent 30-min ischemia by anterior coronary artery ligation followed by 2-h reperfusion. Occlusion-reperfusion damage was evaluated by delineating the nonperfused volume of myocardium at risk and volume of myocardial necrosis after 2-h reperfusion. In some hearts ischemic preconditioning was accomplished by two 5-min episodes of global low-flow ischemia separated by 10 min before coronary occlusion-reperfusion. Orthogonal electrocardiograms were recorded, and coronary flow was monitored by a drip count. Three hearts from each experimental group were used to determine mitochondrial CcO and aconitase activities. Two-hour reperfusion after occlusion caused an additional decrease in CcO activity vs. that after 30-min occlusion alone. Blocking the beta(1)-AR during occlusion-reperfusion reversed CcO activity depression and preserved myocardium at risk for necrosis. Similarly, mitochondrial aconitase activity exhibited a parallel response after occlusion-reperfusion as well as for the other interventions. Furthermore, classic ischemic preconditioning had no effect on CcO depression. However, blocking the beta(1)-AR during preconditioning eliminated the cardioprotection. If the beta(1)-AR was blocked after preconditioning, the myocardium was preserved. Interestingly, in both of the latter cases the depression in CcO activity was reversed. Thus the beta(1)-AR plays a dual role in myocardial ischemic damage. Our findings may lead to therapeutic strategies for preserving myocardium at risk for infarction, especially in coronary reperfusion intervention.

Inhibition of myocardial apoptosis by ischaemic and beta-adrenergic preconditioning is dependent on p38 MAPK

INTRODUCTION

Apoptosis occurring during ischaemia /reperfusion contributes independently to tissue damage, and involves activation of the stress-kinase, p38 MAPK during reperfusion. Ischaemic preconditioning (IPC) protects against ischaemia/reperfusion mediated necrosis and apoptosis. The role of p38 MAPK in the protective effect of preconditioning against apoptosis is unknown. Pharmacologic preconditioning with isoproterenol (beta-PC) also protects against necrosis, but it is not known whether it protects against apoptosis.

AIM

The aim of the study was to investigate whether the protective effect of IPC against apoptosis is related to activation of p38 MAPK and whether beta-PC also protects against apoptosis.

MATERIALS AND METHODS

Isolated perfused rat hearts were used to study the effect of ischaemia and reperfusion on apoptosis and infarct size. Ischaemic preconditioning was elicited by 3 x 5 min global ischaemia, and beta-PC by 5 min isoproterenol 10(-7) M. For infarct size hearts were subjected to regional ischaemia for 35 min followed by 120 min reperfusion. Infarct size was determined by the tetrazolium staining technique, and expressed as percentage of area at risk. For markers of apoptosis hearts were subjected to global ischaemia of 25 min plus 30 min reperfusion. Apoptosis was determined by Western blot using antibodies against caspase-3 and PARP. p38 MAPK activation was inhibited by SB203580 (1 microM) administration 10 min prior to commencing ischaemia, and bracketing the IPC and beta-PC preconditioning protocols. p38 MAPK was activated by administration of anisomycin (5 microM) 10 min prior to index ischaemia in one protocol, and 10 min during reperfusion in non-preconditioned as well as IPC and beta-PC hearts. Results were analysed using ANOVA and a Newman-Keuls post-hoc test.

RESULTS

In the apoptosis model using global ischaemia, IPC and beta-PC both resulted in a significant decrease in p38 MAPK activation at the end of reperfusion when compared to non-preconditioned hearts. This was accompanied by a significant decrease in apoptosis as measured with both caspase-3 activation and PARP cleavage. Inhibiting p38 MAPK by administration of SB203580 10 min prior to ischaemia resulted in a significant reduction in both markers of apoptosis. Bracketing the triggering phase of either IPC or beta-PC with SB203580 resulted in attenuated p38 MAPK activation during reperfusion and did not abolish the protective effect of IPC or beta-PC against apoptosis. Activating p38 MAPK with anisomycin prior to ischaemia resulted in a reduction of markers of apoptosis, whereas activation of p38 MAPK with anisomycin during reperfusion did not exacerbate apoptosis in any groups, exept for an increase in PARP cleavage in IPC hearts. In the model of regional ischaemia, IPC and beta-PC reduced infarct size significantly, and to the same extent as inhibition of p38 MAPK by administration of SB203580 10 min prior to ischaemia. Bracketing the triggering phase of either IPC or beta-PC did not abolish the reduction in infarct size. Activating p38 MAPK during reperfusion was accompanied by an increase in infarct size only in IPC hearts, but not in beta-PC hearts.

CONCLUSION

These results indicate that (1) Both IPC and beta-PC elicit protection against apoptosis and necrosis, (2) activation of p38 MAPK is not a trigger of preconditioning against apoptosis and necrosis and (3) activation of p38 MAPK during reperfusion increases necrosis only if ischaemia is used to precondition hearts, but not with pharmacologic preconditioning with isoproterenol.

Cardiac myosin binding protein C phosphorylation is cardioprotective

Cardiac myosin binding protein C (cMyBP-C) has three phosphorylatable serines at its N terminus (Ser-273, Ser-282, and Ser-302), and the residues' phosphorylation states may alter thick filament structure and function. To examine the effects of cMyBP-C phosphorylation, we generated transgenic mice with cardiac-specific expression of a cMyBP-C in which the three phosphorylation sites were mutated to aspartic acid, mimicking constitutive phosphorylation (cMyBP-C(AllP+)). The allele was bred into a cMyBP-C null background (cMyBP-C((t/t))) to ensure the absence of endogenous dephosphorylated cMyBP-C. cMyBP-C(AllP+) was incorporated normally into the cardiac sarcomere and restored normal cardiac function in the null background. However, subtle changes in sarcomere ultrastructure, characterized by increased distances between the thick filaments, indicated that phosphomimetic cMyBP-C affects thick-thin filament relationships, and yeast two-hybrid data and pull-down studies both showed that charged residues in these positions effectively prevented interaction with the myosin heavy chain. Confirming the physiological relevance of these data, the cMyBP-C(AllP+:(t/t)) hearts were resistant to ischemia-reperfusion injury. These data demonstrate that cMyBP-C phosphorylation functions in maintaining thick filament spacing and structure and can help protect the myocardium from ischemic injury.

Cardioprotective effects of acute and chronic opioid treatment are mediated via different signaling pathways

A 5-day exposure to morphine exerts a profound cardioprotective phenotype in murine hearts. In the present study, we examined mechanisms by which morphine generates this effect, exploring the roles of Gi and Gs proteins, PKA, PKC, and β-adrenergic receptors (β-AR) in acute and chronic opioid preconditioning. Langendorff-perfused hearts from placebo, acute morphine (AM; 10 μmol/l)-, or chronic morphine (CM)-treated mice (75-mg pellet, 5 days) underwent 25-min ischemia and 45-min reperfusion. After reperfusion, placebo-treated hearts exhibited marked contractile and diastolic dysfunction [rate-pressure product (RPP), 40 ± 4% baseline; end-diastolic pressure (EDP), 33 ± 3 mmHg], whereas AM hearts showed significant improvement in recovery of RPP and EDP (60 ± 3% and 23 ± 4 mmHg, respectively; P < 0.05 vs. placebo). Furthermore, CM hearts demonstrated a complete return of diastolic function and significantly greater recovery of contractile function (83 ± 3%, P < 0.05 vs. both placebo and AM). Pretreatment with Gi protein inhibitor pertussis toxin abolished AM protection while partially attenuating CM recovery ( P < 0.05 vs. placebo). Treatment with Gs inhibitor NF-449 did not affect AM preconditioning yet completely abrogated CM preconditioning. Similarly, PKA inhibition significantly attenuated the ischemia-tolerant state afforded by CM, whereas it was ineffective in AM hearts. PKC inhibition with chelerythrine was ineffective in CM hearts while completely abrogating AM preconditioning. Moreover, whereas β1-AR blockade with CGP-20712A failed to alter recovery in CM hearts, the β2-AR antagonist ICI-118,551 significantly attenuated postischemic recovery. These data describe novel findings whereby CM preconditioning is mediated by a PKC-independent pathway involving PKA, β2-AR, and Gs proteins, whereas AM preconditioning is mediated via Gi proteins and PKC.

A preliminary study on the cardioprotection of acupuncture pretreatment in rats with ischemia and reperfusion: involvement of cardiac beta-adrenoceptors

The purpose of this study was to determine the cardioprotective effects of the repetitive pretreatment of acupuncture in rats with myocardial ischemia and reperfusion (MIR). Experimental MIR was produced by ligating and reperfusing the left anterior descending coronary artery in the rats. The elevated ST segments of electrocardiogram (ECG), cardiac arrhythmias, and ratio of infarct size/risk zone were compared among the normal control (NC), ischemia and reperfusion (IR), electro-acupuncture (EA), electro-acupuncture plus propranolol (EAP), and EA at nonacupoint (EAN) groups. Before the experiment, EA was applied at bilateral Neiguan acupoints (PC6) in the forelimbs in EA and EAP groups for 30 min once a day for 3 consecutive days. In the EAN group, the same EA treatment was administered at bilateral nonacupoints in the hind limbs. In the EAP group, propranolol, a nonspecific antagonist of beta-adrenoceptors, was administered intraperitoneally 15 min before each EA pretreatment. The results showed that the elevated ST segment of ECG, cardiac arrhythmia score, and ratio of infarct size/risk zone were significantly attenuated in the EA group when compared with those in the IR group (P < 0.05), indicating a cardioprotection of EA pretreatment. When propranolol was given before each EA pretreatment in the EAP group, the cardioprotective effect of EA pretreatment was abolished, showing an involvement of beta-adrenoceptors in mediating the effect of EA pretreatment. There was no significant cardioprotective effect observed in the EAN group. The results suggest that pretreatment may be a better way to apply acupuncture in the prevention and treatment of coronary heart disease.

Beta1-Adrenergic receptor antagonism abrogates cardioprotective effects of intermittent hypoxia

Adaptation to hypoxia lessens myocardial ischemic injury. This study tested whether hypoxia-induced beta-adrenergic activity mobilizes mechanisms that protect myocardium during subsequent ischemia and reperfusion. Dogs were intermittent hypoxia conditioned (IHC) by a 20 days program of 5-8 daily, 5-10 min cycles of normobaric hypoxia (FIO2 = 9.5-10%), or sham conditioned with normoxic air, and metoprolol (beta1-adrenoceptor antagonist) was administered throughout the IHC program. Twenty-four hours after the last IHC session, the left anterior descending coronary artery (LAD) was occluded for 60 min, and then reperfused for 5 h. Area at risk (AAR) and infarct size (IS) were measured. IHC lowered IS/AAR from 38+/-6% in sham-conditioned dogs to 1.1+/-0.3%, and eliminated ventricular tachycardia (VT) and fibrillation (VF) that occurred in 14 of 17 non-conditioned dogs. Metoprolol blunted IHC-evoked cardioprotection (IS/AAR=27+/-3%), and VT and/or VF occurred in 5 of 6 dogs. Metoprolol did not exacerbate ischemic injury in sham-conditioned dogs (IS/AAR=38+/-2%). Neither IHC nor metoprolol affected hematocrit or LAD collateral blood flow. A single IHC session failed to protect ischemic myocardium (IS/AAR = 36+/-8%), and protection was incomplete after 10 days of IHC (IS/AAR = 13+/-5%), suggesting that de novo protein synthesis was required for protection. Thus, episodic beta1-adrenergic activation during IHC evokes progressive development of powerful resistance to myocardial ischemia.

Apomorphine-induced myocardial protection is due to antioxidant and not adrenergic/dopaminergic effects

Apomorphine (Apo), a dopaminergic agonist used for treatment of Parkinson disease, is a potent antioxidant. In addition to its antioxidative effects, the dopaminergic and adrenergic effects of Apo were studied. Isolated perfused rat hearts were exposed to 25 min of no-flow global ischemia (37 degrees C) and 60 min of reperfusion (I/R, control). Drugs were introduced for the first 20 min of reperfusion. The LVDP of the control group recovered to 54.6 +/- 3.3%. Apo-treated hearts had significantly improved recovery (61.6 +/- 5%, p < 0.05). The recovery of the work index LVDP x HR was even bigger: 67.8 +/- 3.7% (Apo treatment) vs 41.7 +/- 4.6% (control, p < 0.001). Haloperidol, a dopaminergic antagonist, did not affect the recovery with Apo. Propranolol, a beta-adrenergic blocker, initially inhibited the effect of Apo. However, the recovery of the combined group (Apo + propranolol) increased and reached significance (LVDP, p < 0.05 vs control group) after cessation of propranolol perfusion. At 60 min of reperfusion this group was superior to Apo-treated hearts (LVDP, p < 0.05). Propranolol (without Apo) did not improve the hemodynamic recovery. The same pattern of recovery applies also to the recovery of the +dP/dt during the reperfusion. L-DOPA was less effective than Apo. I/R caused significant increase in carbonylation of proteins. Apomorphine inhibited the increase in carbonylation. Haloperidol did not affect this beneficial effect of Apo. L-DOPA significantly decreased the carbonylation of proteins. We conclude that the antioxidative effect of Apo is its main mechanism of cardioprotection.

beta 2-Adrenergic stimulation is involved in the contractile dysfunction of the stunned heart

Endogenous catecholamines released during myocardial ischemia have been considered both to aggravate cell injury and exacerbate arrhythmias and to exert a protective action on the post-ischemic contractile function. The present work was addressed to look for evidence to explain this controversy. The effects of cardiac catecholamine depletion and of alpha- and beta-adrenoceptor (AR) blockade on the post-ischemic contractile dysfunction, as well as its possible relationship with cardiac oxidative stress, were studied in isolated and perfused rat hearts submitted to 20 min of ischemia and 30 min of reperfusion (stunning). Catecholamine depletion improves the contractile recovery in the stunned heart. This mechanical effect was associated with decreased levels of lipid peroxidation. A similar enhancement of the contractile function during reperfusion was detected after the simultaneous blockade of alpha 1- and beta-ARs with prazosin plus propranolol. To ascertain which specific AR pathway was involved in the effects of catecholamines on the stunned heart, selective AR blockers, prazosin (alpha 1-blocker), atenolol (beta 1-blocker), ICI 118,551 (beta 2-blocker) and selective inhibitors of Gi-PI3K pathway (pertussis toxin and wortmannin) were alternatively combined. The results indicate that catecholamines released during ischemia exert a dual action on the contractile behavior of the stunned heart: a deleterious effect, related to the activation of the beta 2-AR-Gi-PI3K-pathway, which was counteracted by a beneficial effect, triggered by the stimulation of alpha 1-AR. Neither the depression nor the enhancement of the post-ischemic contractile recovery were related with the increase in ROS formation induced by endogenous catecholamines.

H-89, a Non-Specific Inhibitor of Protein Kinase A, Promotes Post-Ischemic Cardiac Contractile Recovery and Reduces Infarct Size

Myocardial ischemia is associated with increased production of cyclic adenosine monophosphate (cAMP), with potentially deleterious effects. We hypothesized that the ischemia-induced activation of cAMP-dependent protein kinase A (PKA), could beneficially be inhibited by a PKA-inhibitor N-(2-[p-bromocinnamylamino]ethyl)-5-isoquinoline-sulfonamide (H-89). H-89 when given to isolated perfused rat hearts before 30 minutes of global ischemia-reperfusion improved postischemic function and decreased infarct size. In another series, H-89 administered prior to preconditioning by 10 minutes of transient global ischemia decreased PKA activity (measured at the end of the preconditioning protocol) and augmented postischemic mechanical recovery. H-89 given for 5 minutes before the 10 minutes of transient ischemia further decreased infarct size from 13.4 +/- 1.0% (preconditioning alone) to 7.0 +/- 0.93 (P < 0.01). In a third series, forskolin (0.3 muM, 5 minutes, 10 minutes washout prior to ischemia) increased PKA activity and reduced infarct size. Prior H-89 decreased PKA activity after 5 minutes of forskolin and further reduced infarct size versus forskolin alone. In conclusion, three procedures increased postischemic recovery and reduced infarct size: H-89; preconditioning by transient ischemia; or forskolin as a preconditioning-mimetic. PKA-inhibition by H-89 further decreased infarct size beyond preconditioning or forskolin. Despite the reservation that H-89 could be non-selective in its actions, we propose H-89 as a candidate cardioprotective agent.

The role of β‐Adrenergic Receptor Signaling in Cardioprotection

This study examines the role of the beta2-adrenergic receptor (beta2-AR) in cardioprotection. The beta2-AR couples to Gs and Gi proteins. Gs activates PKA, which phosphorylates the receptor and switches beta2-AR coupling from Gs to Gi. Prior to 20 min of global ischemia, mouse hearts were either perfused for 30 min without treatment (control), treated with 10 nmol/L of isoproterenol (ISO) for 5 min followed by 5 min washout, or preconditioned with 4 cycles of 5 min ischemia and 5 min reflow (PC). Recovery of left ventricular developed pressure (LVDP) and infarct size were measured. Intermittent ISO treatment improved post-ischemic recovery of LVDP (58.5+/-4.8% vs. 22.0+/-6.3% in control) and reduced infarct size (31.0+/-2.4% vs. 53.0+/-4.6% in control). The Gi inhibitor pertussis toxin blocked the ISO-induced improvement in postischemic LVDP and infarct size. To test the role of beta2-AR in PC, we studied mice lacking beta2-AR (beta2-AR-/-) and found that PC had no effect on postischemic LVDP or infarct size in beta2-AR-/-. To test whether PKA is required for the PC and ISO-induced protection, hearts were treated with the PKA inhibitors PKI and H-89. We found that PKI and H-89 blocked the PC- and ISO-induced improvement in postischemic LVDP and infarct size. These data show an important role for beta2-AR in cardioprotection and support the novel hypothesis that preconditioning involves switching of beta2-AR coupling from Gs to Gi.

The roles of alpha- and beta-adrenoceptor stimulation in myocardial ischaemia

beta-Adrenoceptor (AR) ligands have been the mainstay of cardiovascular therapy for decades, with beta-AR antagonist being used for hypertension, angina and myocardial infarction and adrenaline in use for cardiopulmonary resuscitation for nearly 100 years. Ischaemia of the heart through coronary artery occlusion causes cell injury and death through necrosis and apoptosis. Reperfusion of the ischaemic myocardium results in cardiac dysfunction and infarction. Stimulation of alpha- and beta-ARs in the ischaemic heart have variable and inconsistent effects depending on when the agonist is applied. This review describes the different effects of stimulation of the three established beta-AR subtypes (beta(1)-, beta(2)- and beta(3)-ARs) either before ischaemia (preconditioning) or during ischaemia and reperfusion of the heart (postconditioning). Brief periods of ischaemia preceding a major ischaemic episode can have a protective effect against post-ischaemia-reperfusion damage, known as ischaemic preconditioning. This review considers the role of endogenous catecholamines released during preconditioning and the nature of the adrenoceptor subtypes that mediate these effects. The clinical significance of this to the use of beta-AR antagonists is considered. The transduction pathways and effects on apoptosis of the cardioprotective and deleterious effects of AR activation are considered. This commentary reviews the literature and attempts to bring together a unified synopsis of the effects of adrenoceptor stimulation in myocardial ischaemia and the potential clinical relevance.