Opening the calcium-activated potassium channel participates in the cardioprotective effect of puerarin

The aim of the present study was to determine whether the effective cardioprotection conferred by puerarin against ischemia and reperfusion is mediated by the calcium-activated potassium channel. Hearts isolated from male Sprague-Dawley rats were perfused on a Langendorff apparatus and subjected to 30 min of global ischemia followed by 120 min of reperfusion. The production of formazan, which provides an index of myocardial viability, was measured by absorbance at 550 nm, and the level of lactate dehydrogenase (LDH) in the coronary effluent was determined. Pretreatment with puerarin at 0.24 mmol/l for 5 min before ischemia increased myocardial formazan content and reduced LDH release during reperfusion. Administration of paxilline (1 micromol/l), an antagonist of the calcium-activated potassium channel, attenuated the protective effects of puerarin. In isolated ventricular myocytes, pretreatment with puerarin prevented simulated ischemia and reperfusion injury, hydrogen peroxide-induced cell death and the release of reactive oxygen species. Paxilline and chelerythrine (a protein kinase C inhibitor) both attenuated the effects of puerarin. These findings indicate that puerarin protects the myocardium against ischemia and reperfusion injury via opening the calcium-activated potassium channel and activating protein kinase C.

Ischemic preconditioning in solid organ transplantation: from experimental to clinics

This study reviews the current understanding of ischemic preconditioning (IP) in experimental and clinical setting, and the mechanisms that mediate the complex processes involved as a tool to protect against ischemia and reperfusion (I/R) injury, but is not intended as a complete literature review of preconditioning. IP has been mainly elucidated in cardiac ischemia. Recent reports confirm the efficacy of pre- and postconditioning in cardiac surgery and percutaneous coronary interventions in humans. IP utilizes endogenous as well as distant mechanisms in skeletal muscle, liver, lung, kidney, intestine and brain in animal models to convey varying degrees of protection from I/R injury. Specifically, preconditioned tissues exhibit altered energy metabolism, better electrolyte homeostasis and genetic reorganization, as well as less oxygen-free radicals and activated neutrophils release, reduced apoptosis and better microcirculatory perfusion. To date, there are few human studies, but recent trials suggest that human liver, lung and skeletal muscle acquire protection after IP. Present data address the potential therapeutic application of IP in the prevention of I/R damage specially aimed at clinical transplantation. IP is ubiquitous but more research is required to fully translate these findings to the clinical arena.

Survivin mediates the anti-apoptotic effect of delta-opioid receptor stimulation in cardiomyocytes

Survivin is known to be essential for cell division and to inhibit apoptosis during embryonic development and in adult cancerous tissues. However, the cardiovascular role of survivin is unknown. We observed that in cardiomyocytes cultured under conditions of serum and glucose deprivation (DEPV), the levels of survivin, Bcl-2 and extracellular signal-regulated kinase (ERK) were positively correlated with the anti-apoptotic action of a delta-opioid receptor agonist, [D-Ala2, D-Leu5]-enkephalin acetate (DADLE). By contrast, Bax translocation, mitochondrial membrane damage and reactive oxygen species (ROS) production were inversely correlated with the changes of survivin and Bcl-2. The use of RNA interference (RNAi) targeting survivin increased DEPV-induced cardiomyocyte apoptosis, whereas the anti-apoptotic effect of DADLE was blunted by survivin RNAi. Moreover, survivin transfection and overexpression provided protection against DEPV-induced cardiomyocyte apoptosis. Inhibition of ERK prevented the DADLE-induced decrease in apoptosis and Bax translocation, and increase in survivin and Bcl-2. DADLE-induced increase in survivin was also blunted by phosphoinositol 3-kinase (PI 3-kinase) inhibition. In conclusion, the present study provides the first direct evidence of an anti-apoptotic role of survivin mediating the anti-apoptotic effect of delta-opioid receptor activation in cardiomyocytes. ERK and PI 3-kinase were found to be upstream regulators of survivin. Mitochondrial membranes as well as ROS, Bcl-2 and Bax were also involved in this anti-apoptotic action.

Delta opioid receptors stimulation with [D-Ala2, D-Leu5] enkephalin does not provide neuroprotection in the hippocampus in rats subjected to forebrain ischemia

It has been reported that delta opioid agonists can have neuroprotective efficacy in the central nervous system. This study was conducted to test the hypothesis that a delta opioid receptor (DOR) agonist, [D-Ala2, D-Leu5] enkephalin (DADLE), can improve neuron survival against experimental forebrain ischemia in rats. Using male rats (n=125), intraperitoneal injection of DADLE (0, 0.25, 1, 4, 16 mg kg-1) was performed 30 min before ischemia. Ten minutes interval forebrain ischemia was provided by the bilateral carotid occlusion combined with hypotension (35 mm Hg) under isoflurane (1.5%) anesthesia. All animals were neurologically and histologically evaluated after a recovery period of 1 week. As histological evaluation, percentages of ischemic neurons in the CA1, CA3, dentate gyrus (DG) were measured. During the recovery period, 27 rats died because of apparent upper airway obstruction, seizure, or unidentified causes. There were no differences in the motor activity score among the groups. Ten minutes forebrain ischemia induced approximately 75, 20, and 10% neuronal death in the CA1, CA3, and DG, respectively. Any doses of DADLE did not attenuate neuronal injury in the hippocampus after ischemia. Pre-ischemic treatment of DORs agonism with DADLE did not provide any neuroprotection to the hippocampus in rats subjected to forebrain ischemia.

Mechanism by which activation of delta-opioid receptor reduces the severity of postresuscitation myocardial dysfunction

OBJECTIVE

Postresuscitation myocardial dysfunction has been recognized as a leading cause of early death after initially successful cardiopulmonary resuscitation. We have previously demonstrated that opening adenosine triphosphate (ATP)-sensitive K (KATP) channels or activation of delta-opioid receptors minimized the severity of postresuscitation myocardial dysfunction and increased the duration of postresuscitation survival. In the present study, we investigated the potential mechanism of myocardial protection following delta-opioid receptor activation in a rat model of cardiac arrest and cardiopulmonary resuscitation.

DESIGN

Randomized prospective animal study.

SETTING

Animal research laboratory.

SUBJECTS

Male Sprague-Dawley rats.

INTERVENTIONS

Ventricular fibrillation was induced in 24 Sprague-Dawley rats. Mechanical ventilation and precordial compression were initiated after 8 mins of untreated ventricular fibrillation. Defibrillation was attempted after 6 mins of cardiopulmonary resuscitation. The animals were randomized to four groups: a) pentazocine (0.3 mg/kg), a delta-opioid receptor agonist; b) pentazocine pretreated with KATP channel blocker, glibenclamide (0.3 mg/kg), administered 45 mins before induction of ventricular fibrillation; c) glibenclamide pretreated alone 45 mins before induction of ventricular fibrillation; and d) placebo. Pentazocine or saline placebo was injected into the right atrium after 5 mins of untreated ventricular fibrillation.

MEASUREMENTS AND MAIN RESULTS

Postresuscitation myocardial function, as measured by the rate of left ventricular pressure increase at 40 mm Hg, left ventricular end-diastolic pressure, and cardiac index, was significantly improved in pentazocine-treated animals. This was associated with significantly prolonged duration of survival. Except for ease of defibrillation, the beneficial effects of pentazocine were abolished by pretreatment with the KATP channel blocker glibenclamide.

CONCLUSIONS

The postresuscitation myocardial protective effects provided by activation of delta-opioid receptor may be mediated via opening KATP channels.

nPKCepsilon and NMDA receptors participate in neuroprotection induced by morphine pretreatment

Morphine pretreatment induces ischemic tolerance in neurons, but it remains uncertain whether novel protein kinase C epsilon isoform (nPKCepsilon) and N-methyl-D-aspartate (NMDA) receptors are involved in this neuroprotection. The present study examined this issue. Hippocampal slices from adult BALB/C mice were incubated with morphine at 0.1-10.0 muM in the presence or absence of various antagonists for 30 minutes and then kept in morphine- and antagonist-free buffer for 30 minutes before being subjected to oxygen-glucose deprivation for 20 minutes. After recovery in oxygenated artificial fluid for 5 hours, assessment of slice injury was done by determination of the intensity of slice stain after they were incubated with 2% 2,3,5-triphenyltetrazolium chloride for 30 minutes and extracted by organic solvent for 24 hours. At designated periods, slices were preserved for immunoblot analysis to observe effects of morphine pretreatment on membrane translocation and total protein expression of nPKCepsilon and phosphorylation of NR1 subunits of NMDA receptors. The neuroprotection induced by morphine pretreatment was partially blocked by chelerythrine (a nonselective PKC blocker), epsilonv(1-2) (a selective nPKCepsilon antagonist), MK-801 (a noncompetitive NMDA receptor blocker), chelerythrine combined with MK-801, and epsilonv(1-2) with MK-801. Morphine pretreatment significantly inhibited nPKCepsilon membrane translocation and phosphorylation of NR1 subunits of NMDA receptors during reperfusion injury. However, epsilonv(1-2) blocked these effects induced by morphine pretreatment. These findings suggested that nPKCepsilon and NMDA receptors might participate in neuroprotection induced by morphine pretreatment, and NMDA receptors might be downstream targets of nPKCepsilon.

Isoflurane and other commonly used anaesthetics do not protect the isolated buffer perfused mouse heart from ischemia-reperfusion injury

1. Some anaesthetic agents such as barbiturates and opioids possess cardioprotective properties in rats, rabbits, dogs and pigs. The purpose of this study was to evaluate the effects of some commonly used anaesthetic agents (pentobarbital, isoflurane and a mixture of midazolam, fentanyl and fluanisone) on the tolerance of the isolated mouse heart to ischaemia-reperfusion injury. 2. The isolated, Langendorff-perfused hearts were subjected to 45 min of global ischaemia followed by 60 min of reperfusion. Left ventricular pressures, heart rate and coronary flow were measured and infarct size was determined using triphenyltetrazolium staining. 3. There were no differences in haemodynamic variables during reperfusion between groups. Infarct size was not influenced by the choice of anaesthesia. 4. None of the anaesthesia protocols exerted significant protective effects on the ischaemic-reperfused isolated mouse heart performance. In mice, isoflurane as well as pentobarbital, opioids and benzodiazepines may be safely used for anaesthesia without a risk of protective side-effects in isolated mouse heart studies.

Activation of ERK and suppression of calcineurin are interacting mechanisms of cardioprotection afforded by δ-opioid receptor activation

The aim of this study was to examine possible interactions of ERK and calcineurin in cardioprotection afforded by delta-opioid receptor stimulation. Infarction was induced in rat hearts by 20-min coronary occlusion and reperfusion. Tissue ERK level and calcienurin activity were determined by immunoblotting and an assay using a phosphopeptide substrate, respectively. Administration of a delta-opioid receptor agonist, D-Ala2-D-Leu5-enkephalin (DADLE, 1 mg/kg), before ischemia increased the phospho-ERK levels during ischemia and reduced infarct size (as percentage of risk area, %IS/AR) from 47.7 +/- 2.3% to 23.2 +/- 2.5%. This protection was abolished by 10 mg/kg of natrindole hydrochloride (NTI), a delta-opioid receptor antagonist. PD98059, a MEK1/2 inhibitor, abolished both ERK1/2 activation and infarct size limitation by DADLE. Calcineurin inhibitors, cyclosporine-A (5 mg/kg) and FK506 (3.5 mg/kg), reduced %IS/AR (27.4 +/- 4.4% and 29.9 +/- 3.4%, respectively). The protective effects of these calcineurin inhibitors were inhibited by PD98059, and the combination of DADLE with cyclosporine-A or FK506 did not afford further cardioprotection. DADLE significantly suppressed myocardial calcineurin activity, and this effect was inhibited by NTI. Suppression of calcineurin activity by FK506 was associated with modest activation of ERK1/2. These results suggest that suppression of calcineurin and activation of ERK1/2 are interacting mechanisms involved in cardioprotection by delta-opioid receptor activation.

Effect of modulating cardiac A1adenosine receptor expression on protection with ischemic preconditioning

Activation of A1adenosine receptors (A1ARs) may be a crucial step in protection against myocardial ischemia-reperfusion (I/R) injury; however, the use of pharmacological A1AR antagonists to inhibit myocardial protection has yielded inconclusive results. In the current study, we have used mice with genetically modified A1AR expression to define the role of A1AR in intrinsic protection and ischemic preconditioning (IPC) against I/R injury. Normal wild-type (WT) mice, knockout mice with deleted (A1KO−/−) or single-copy (A1KO+/−) A1AR, and transgenic mice (A1TG) with increased cardiac A1AR expression underwent 45 min of left anterior descending coronary artery occlusion, followed by 60 min of reperfusion. Subsets of each group were preconditioned with short durations of ischemia (3 cycles of 5 min of occlusion and 5 min of reperfusion) before index ischemia. Infarct size (IF) in WT, A1KO+/−, and A1KO−/−mice was (in % of risk region) 58 ± 3, 60 ± 4, and 61 ± 2, respectively, and was less in A1TG mice (39 ± 4, P < 0.05). A strong correlation was observed between A1AR expression level and response to IPC. IF was significantly reduced by IPC in WT mice (35 ± 3, P < 0.05 vs. WT), A1KO+/−+ IPC (48 ± 4, P < 0.05 vs. A1KO+/−), and A1TG + IPC mice (24 ± 2, P < 0.05 vs. A1TG). However, IPC did not decrease IF in A1KO−/−+ IPC mice (63 ± 2). In addition, A1KO−/−hearts subjected to global I/R injury demonstrated diminished recovery of developed pressure and diastolic function compared with WT controls. These findings demonstrate that A1ARs are critical for protection from myocardial I/R injury and that cardioprotection with IPC is relative to the level of A1AR gene expression.

Attenuation of post-ischemia reperfusion injury by thaliporphine and morphine in rat hearts

Pretreatment with thaliporphine before ischemia affords cardioprotective effects against reperfusion injury via antioxidant activity. This study evaluated whether thaliporphine administered at a certain period after myocardial ischemia conferred the same cardioprotection and assessed its possible new mechanism. The left main coronary artery of anaesthetized rats was occluded for 1 h and then reperfused for 2 h. Thaliporphine was administered at 10 min before reperfusion. Controls received saline only. Morphine, a nonselective opioid receptor agonist, was used as reference compound at 0.3 mg/kg. Thaliporphine at 0.05 and 0.5 mg/kg were found to reduce the infarct size. Recovery of cardiac function was higher in thaliporphine (0.5 mg/kg) group, as assessed by a significant improvement in the rates of pressure development (+dp/dt (max)). This compound also reduced plasma creatine kinase and cardiac MPO activity. These protective effects afforded by thaliporphine were diminished by the opioid receptor antagonists (naloxone or naltrexone) and by the mitochondrial K(ATP) blocker 5HD. In comparison, morphine reduced infarct size and MPO activity in the myocardium but produced slightly improvement in cardiac function after ischemia-reperfusion. These results demonstrate that reperfusion therapy with thaliporphine protect cardiac injury through further mechanism via activation of opioid receptor and opening of mitochondrial K(ATP) channels as morphine but with stronger activity.

Role of protein kinase C in intestinal ischemic preconditioning

INTRODUCTION

Tissue protection by ischemic preconditioning (IPC) has been previously characterized in organs such as the heart and involves at least in part PKC activation. It is not yet clear whether such preconditioning against ischemia/reperfusion (I/R) injury operates in the intestine, and, if so, whether IPC involves protein kinase C (PKC).

MATERIALS AND METHODS

IPC of the small intestine in male Sprague Dawley rats was induced by 10-min superior mesenteric artery (SMA) clamp followed by 120-min reperfusion. Sham-operated control or IPC rats were then rechallenged with 20-min SMA clamp. Histological injury to jejunal mucosa was assessed by microscopic examination and Parks' injury score (Grade 0-4; 0 = no damage). PKC activity was determined by immunoprecipitation of specific isoforms followed by in vitro kinase assay using mucosal scrapings of the harvested jejunum. Data were expressed as mean +/- SEM and analyzed by one-way ANOVA with multiple comparison tests.

RESULTS

Ten-minute SMA clamp led to epithelial damage that was fully reversed by 120-min reperfusion. Activity of several PKC isoforms (PKCalpha, -delta, -epsilon) increased after 10-min ischemia. Epithelial injury associated with 20-min SMA clamp was attenuated by prior IPC. The protective effect of IPC on intestinal mucosa was prevented when animals were pretreated with the conventional (c) and novel (n) PKC inhibitor Go6850, but not with Go6976 (selective cPKC inhibitor), rottlerin (selective PKCdelta inhibitor), or saline control.

CONCLUSIONS

Brief mesenteric ischemia induces a reversible epithelial injury in rats associated with activation of several PKC isoforms. Injury induced by mesenteric ischemia is reduced by brief ischemic preconditioning, an effect that is abolished by nonselective PKC inhibition but not by a selective inhibitor of cPKC or PKCdelta. The results suggest that activation of nPKC isoform(s), especially PKCepsilon during and following ischemic insults (IPC), may play an important role in protection against I/R injury in the intestine.

Remifentanil mimics cardioprotective effect of ischemic preconditioning via protein kinase C activation in open chest of rats

AIM

To examine whether the protective effect of remifentanil preconditioning (RPC) on postischemic hearts is mediated by protein kinase (PKC) activation in comparison with ischemic preconditioning (IPC).

METHODS

Male Sprague-Dawley rats were anesthetized and their chests were opened. The experiment was performed with chelerythrine (CHE, 2 mg/kg), GF109203X (0.05 mg/kg) protein kinase C (PKC) inhibitors administered before RPC (remifentanil 6 microg x kg(-1) x min(-1) x 3 cycle) or IPC, respectively. Infarct size (IS), as a percentage of the area at risk (AAR), was determined by triphenyltetrazolium staining.

RESULTS

In groups subjected to IPC and RPC the IS/AAR were significantly reduced (IS/AAR from 52.7%+/-5.5% to 12.9%+/-3.4%, P<0.01 vs CON and 16.2%+/-6.4%, P<0.01 vs CON), respectively. CHE and GF, both PKC inhibitors, administered 5 min before RPC or IPC completely abolished the cardioprotective effect of RPC (IS/AAR: CHE+RPC 51.2%+/-5.0%, GF+RPC 53.6%+/-6.1%, P>0.05 vs CON) or IPC (CHE+IPC 53.7%+/-4.3%, GF+IPC 54.1%+/-6.2%, P>0.05 vs CON). The difference was not significant in any of the hemodynamic parameters between control and treatment groups during ischemia and reperfusion.

CONCLUSION

Remifentanil confers myocardial protection against ischemic injury through a mechanism that is similar to IPC and involves PKC activation.

Involvement of uracil nucleotides in protection of cardiomyocytes from hypoxic stress

Cardiomyocytes express one or more subtypes of P2 receptors for extracellular nucleotides. P2 purinoceptors, which are activated by nucleotides, are classified as P2X or P2Y: P2X receptors are ligand-gated intrinsic ion channels, and P2Y receptors are G protein-coupled receptors. Extracellular pyrimidine and purine nucleotides are released from the heart during hypoxia. Although the cardioprotective effects of purines acting via purinoceptors were studied intensively, the physiological role of uracil nucleotide-responsive P2Y2, P2Y4, P2Y6, and P2Y14 receptors is still unclear, especially in the cardiovascular system. This study revealed that uridine-5'-triphosphate (UTP) protected cultured rat cardiomyocytes during hypoxia and explored the UTP signaling pathway leading to this cardioprotection. We found that UTP, but not UDP or uridine, significantly reduced cardiomyocyte death induced by hypoxia. Incubation with UTP for 1 h, before exposure to hypoxic conditions, protected the cells 24 h later. The cardioprotective effect of UTP was reduced in the presence of the P2 antagonist suramin. In addition, UTP caused a transient increase of [Ca2+]i in cardiomyocytes. Pyridoxal-5'-phosphate-6-azophenyl-2,4-disulfonate (PPADS) or Reactive blue 2 (RB-2), other antagonists of P2 receptors, abolished the [Ca2+]i elevation caused by UTP. We used various inhibitors of the Ca2+ signaling pathway to show that UTP elevated levels of [Ca2+]i, originating from intracellular sources, via activation of phospholipase C and the IP3 receptor. Interestingly, these inhibitors of the Ca2+ signaling pathway did not prevent the immediate protective effect caused by UTP. Although mitochondrial KATP channels are involved in other preconditioning mediator pathways, the involvement of these channels in the cardioprotective effect induced by UTP was ruled out, because 5-hydroxydecanoic acid (5-HD), a specific inhibitor of these channels, did not prevent the protection.

Ischemic preconditioning, insulin, and morphine all cause hexokinase redistribution

Association of hexokinase (HK) with mitochondria preserves mitochondrial integrity and is an important mechanism by which cancer cells are protected against hypoxic conditions. Maintenance of mitochondrial integrity also figures prominently as a major characteristic of many cardioprotective manipulations. In this study, we provide evidence that cardioprotective interventions may promote HK redistribution from the cytosol to the mitochondria in the heart. Isolated Langendorff-perfused rat hearts (n = 6/group) were subjected to normoxic perfusion (control, Con), three 5-min ischemia-reperfusion periods (ischemic preconditioning, IPC), 1 U/l insulin (Ins), or 1 microM morphine (Mor). Hearts were immediately homogenized and centrifuged to obtain whole cell, cytosolic, and mitochondrial fractions. HK, lactate dehydrogenase (LDH), and citrate synthase (CS) enzyme activities were determined. No change in LDH or CS present in the cytosol fraction relative to whole cell activity was observed with any of the cardioprotective interventions. By contrast, HK present in the cytosol fraction relative to whole cell activity decreased significantly (P < 0.05) with all cardioprotective interventions, from 0.58 +/- 0.03 (Con) to 0.46 +/- 0.04 (IPC), 0.41 +/- 0.01 (Ins), and 0.45 +/- 0.02 (Mor). In addition, HK relative to CS activity in the mitochondrial fraction increased significantly with cardioprotection, from 0.15 +/- 0.001 (Con) to 0.21 +/- 0.002 (IPC), 0.18 +/- 0.003 (Ins), and 0.21 +/- 0.005 (Mor). Our novel data suggest that well-known cardioprotective interventions share a common end-effector mechanism of cytosolic HK translocation. Association of HK with mitochondria may promote inhibition of the mitochondrial permeability transition pore and thereby reduce cell death and apoptosis.

Met5-enkephalin-induced cardioprotection occurs via transactivation of EGFR and activation of PI3K

Our previous studies indicated that opioid-induced cardioprotection occurs via activation of mitochondrial ATP-sensitive K(+) (K(ATP)) channels. However, other elements of the Met(5)-enkephalin (ME) cardioprotection pathway are not fully characterized. In the present study, we investigated the role of tyrosine kinase, MAPK, and phosphatidylinositol 3-kinase (PI3K) signaling in ME-induced protection. Ca(2+)-tolerant, adult rabbit cardiomyocytes were isolated by collagenase digestion and subjected to simulated ischemia for 180 min. ME was administered 15 min before the 180 min of simulated ischemia; blockers were administered 15 min before ME. Cell death was assessed by trypan blue as a function of time. The epidermal growth factor receptor (EGFR) kinase inhibitor AG-1478 (250 nM) blocked ME-induced protection, but the inactive analog AG-9 (100 microM) did not. Treatment with herbimycin (1 microM) completely eliminated ME-induced protection. To verify that ME activates EGFR and to determine the involvement of Src, Western blotting of EGFR was performed after ME administration with and without herbimycin A. ME resulted in herbimycin-sensitive robust phosphorylation of EGFR at Tyr(992) and Tyr(1068). Administration of the selective MAPK inhibitor PD-98059 (10 nM) and the specific MEK1/2 inhibitor U-0126 (10 microM) also inhibited ME-induced cardioprotection. ME-induced ERK1/2 phosphorylation was significantly reduced by PD-98059, the EGFR kinase inhibitor PD-153035 (10 microM), and chelerythrine (2 microM). The PI3K inhibitor LY-294002 (20 microM) abrogated ME-induced protection, and ME-induced Akt phosphorylation at Ser(473) was suppressed by LY-294002, PD-153035, and chelerythrine. We conclude that ME-induced cardioprotection is mediated via Src-dependent EGFR transactivation and activation of the PI3K and MAPK pathways.

Long-term infusion of Met5-enkephalin fails to protect murine hearts against ischemia-reperfusion injury

Recently, we reported that exogenous administration of Met(5)-enkephalin (ME) for 24 h reduces infarct size after ischemia-reperfusion in rabbits. In the present study, we tested whether ME-induced cardioprotection is exhibited in murine hearts and whether chronic infusion of this peptide can render hearts tolerant to ischemia. Barbiturate-anesthetized open-chest mice (C57BL/6J) were subjected to regional myocardial ischemia-reperfusion (45 min of occlusion and 20 min of reperfusion). Mice received saline vehicle or ME for 24 h or 2 wk before undergoing regional myocardial ischemia-reperfusion or for 24 h followed by a 24-h delay before regional myocardial ischemia-reperfusion. Infarct size was measured with propidium iodide and is expressed as a percentage of the area at risk. Infarcts were smaller after infusion of ME for 24 h than with vehicle control: 49.2 +/- 9.0% vs. 22.2 +/- 3.2% (P < 0.01). In contrast, administration of ME for 2 wk failed to elicit cardioprotection: 36.5 +/- 9.1% and 41.4 +/- 8.2% for control and ME, respectively (P = not significant). When a 24-h delay was imposed between the end of drug treatment and the onset of the ischemic insult, cardioprotection was lost: 38.5 +/- 6.1% and 42.8 +/- 6.6% for control and ME, respectively (P = not significant). Chronic sustained exogenous infusion of the endogenously produced opioid peptide ME is associated with loss of the cardioprotection that is observed with 24 h of infusion. Furthermore, in this in vivo murine model, ME failed to induce delayed tolerance to myocardial ischemia-reperfusion.

Remifentanil limits infarct size but attenuates preconditioning-induced infarct limitation

OBJECTIVES

We investigated the influence of the narcotic anesthetic remifentanil on irreversible myocardial ischemic injury.

METHODS

New Zealand White rabbits were anesthetized with propofol (0.7-1.8 mg.kg.min) and then subjected to 30 min regional myocardial ischemia and 3 h reperfusion (CON). Some animals also underwent ischemic preconditioning, elicited by either one (IP1) or two (IP2) cycles of 5 min ischemia and 5 min reperfusion, and/or remifentanil, administered either as a transient infusion mimicking the preconditioning protocol (RP2, 10 microg x kg x min) or as a continuous infusion (R, 3-10 microg x kg x min). Rabbits were randomly assigned to experimental groups. Infarct size was assessed with tetrazolium. Results are reported as mean+/-SD.

RESULTS

Non-preconditioned infarct size was approximately 50% of the area-at-risk (49.6+/-20.1% CON). Both one and two cycles of ischemic preconditioning markedly reduced infarct size (49.6+/-20.1% CON versus 18.6+/-8.6% IP and versus 7.5+/-7.6% IP2; both p<0.001). Preconditioning with remifentanil modestly reduced infarct size (49.6+/-20.1% CON versus 29.3+/-8.5% RP2; p<0.01). However, sustained administration of remifentanil did not provide protection (49.6+/-20.1% CON versus 43.9+/-16.2% R), and it attenuated the protection offered by preconditioning (49.6+/-20.1% CON versus 35.6+/-20.7% R+IP1, p=NS; and versus 14.5+/-14.5% R+IP2; p<0.05).

CONCLUSION

Transient pre-ischemic administration of remifentanil modestly reduces infarct size in propofol-anesthetized rabbits, but continuous administration of remifentanil increases the threshold for ischemic preconditioning-induced infarct limitation.

Morphine mimics the antiapoptotic effect of preconditioning via an Ins(1,4,5)P3 signaling pathway in rat ventricular myocytes

Morphine has cardioprotective effects against ischemic-reperfusion injuries. This study investigates whether morphine could mimic the antiapoptotic effect of preconditioning using a model of cultured neonatal rat cardiomyocytes subjected to metabolic inhibition (MI). To quantify MI-induced apoptosis, DNA fragmentation and mitochondrial cytochrome c release levels were measured by ELISA. MI-dependent DNA fragmentation was prevented by both Z-VAD-fmk (20 microM), a pan-caspase inhibitor, and cyclosporine A (CsA; 5 microM), a mitochondrial pore transition blocker, added during MI (36% and 54% decrease, respectively). MI-dependent cytochrome c release was not blocked by Z-VAD-fmk but was decreased (38%) by CsA during MI. Metabolic preconditioning (MIP) and preconditioning with morphine (1 microM) were also assessed. MI-dependent DNA fragmentation and cytochrome c release were prevented by MIP (40% and 45% decrease, respectively) and morphine (34% and 45%, respectively). The antiapoptotic effect of morphine was abolished by naloxone (10 nM), a nonselective opioid receptor antagonist, or xestospongin C (XeC, 400 nM), an inhibitor of inositol (1,4,5)-trisphosphate [Ins(1,4,5)P(3)]-mediated Ca(2+) release. Ca(2+) preconditioning, induced by increasing extracellular Ca(2+) from 1.8 to 3.3 mM, mimicked the antiapoptotic effect of morphine on DNA fragmentation (24% decrease) and cytochrome c release (57% decrease). This effect mediated by extracellular Ca(2+) was also abolished by XeC. Measurements of intracellular Ca(2+) concentration using fura-2 microspectrofluorimetry showed that morphine induces Ins(1,4,5)P(3)-dependent Ca(2+) transients abolished by 2-aminoethoxydiphenyl borate (2-APB), a cell-permeable Ins(1,4,5)P(3) antagonist. These results suggest that morphine preconditioning prevents simulated ischemia-reperfusion-induced apoptosis via an Ins(1,4,5)P(3) signaling pathway in rat ventricular myocytes.

The effects of the delta-opioid agonist SNC80 on hind-limb motor function and neuronal injury after spinal cord ischemia in rats

Recent investigation suggested neuroprotective efficacy of a delta-opioid agonist in the brain. We investigated the effects of intrathecal treatment with a delta-opioid agonist (SNC80) on spinal cord ischemia (SCI) in rats. SCI was induced with an intraaortic balloon catheter. The animals were randomly allocated to one of the following five groups: 1) SNC80 before 9 min of SCI (SNC-9; n = 12), 2) vehicle before 9 min of SCI (V-9; n = 12), 3) SNC80 before 11 min of SCI (SNC-11; n = 10), 4) vehicle before 11 min of SCI (V-11; n = 12), or 5) sham (n = 12). SNC80 (400 nmol) or vehicle was administered 15 min before SCI. Forty-eight hours after reperfusion, hind-limb motor function was assessed by using the Basso, Beattie, Bresnahan (BBB) scale (0 = paraplegia; 21 = normal) and histological assessment of the L4 and L5 spinal segments was performed. BBB scores in the SNC-9 group were higher compared with those in the V-9 group (P < 0.05), whereas there were no differences in BBB scores between the SNC-11 and V-11 groups. There were significantly more normal neurons in the SNC-9 and SNC-11 groups than in the V-9 and V-11 groups (P < 0.05). The results indicate that intrathecal treatment with the delta-opioid agonist SNC80 can attenuate hind-limb motor dysfunction and neuronal injury after SCI in rats.

Selective Inhibition of Inward Rectifier K + Channels (Kir2.1 or Kir2.2) Abolishes Protection by Ischemic Preconditioning in Rabbit Ventricular Cardiomyocytes

Volume regulatory Cl- channels are key regulators of ischemic preconditioning (IPC). Because Cl- efflux must be balanced by an efflux of cations to maintain cell membrane electroneutrality during volume regulation, we hypothesize that I(K1) channels may play a role in IPC. We subjected cultured cardiomyocytes to 60-minute simulated ischemia (SI) followed by 60-minute of simulated reperfusion (SR) and assessed percent cell death using trypan blue staining. Ischemic preconditioning (10-minute SI/10-minute SR) significantly (P<0.0001) reduced the percent cell death in nontransfected cardiomyocytes [IPC(CM) 18.0+/-2.1% versus control (C(CM)) 48.3+/-1.0%]. IPC protection was not altered by overexpression of the reporter gene (enhanced green fluorescent protein, EGFP). However, overexpression of dominant-negative Kir2.1 or Kir2.2 genes using adenoviruses (AdEGFPKir2.1DN or AdEGFPKir2.2DN) encoding the reporter gene EGFP prevented IPC protection [both IPC(CM)+AdEGFPKir2.1DN 45.8+/-2.3% (mean+/-SEM) and IPC(CM)+AdEGFPKir2.2DN 47.9+/-1.4% versus IPC(CM); P<0.0001] in cultured cardiomyocytes (n=8 hearts). Transfection of cardiomyocytes with AdEGFPKir2.1DN or AdEGFPKir2.2DN did not affect cell death in control (nonpreconditioned) cardiomyocytes (both C(CM)+ AdEGFPKir2.1DN 45.8+/-0.7% and C(CM)+AdEGFPKir2.2DN 46.2+/-1.3% versus C(CM); not statistically significant). Similar effects were observed in both cultured (n=5 hearts) and freshly isolated (n=4 hearts) ventricular cardiomyocytes after I(K1) blockade with 20 micromol/L BaCl2 plus 1 micromol/L nifedipine (to prevent Ba2+ uptake). Nifedipine alone neither protected against ischemic injury nor blocked IPC protection. Our findings establish that I(K1) channels play an important role in IPC protection.

Brief apnea induces myocardial ischemic tolerance by an opioid-insensitive mechanism

BACKGROUND

Intermittent brief "preconditioning" (PC) ischemia has been shown to render the heart resistant to a subsequent sustained ischemic insult, in part through an opioid-dependent mechanism. Using the rabbit model, we tested the hypothesis that intermittent in vivo apnea elicits a cardioprotective response similar to that achieved with conventional PC ischemia. In addition, we sought to determine if infarct size reduction seen in this model was stimulated via opioid receptor activation.

METHODS

Anesthetized, intubated rabbits (n=35) were randomized to receive three 4.5-min bouts of apnea interspersed with 5 min normal ventilation or time-matched standard ventilation (controls). Upon completion of the in vivo PC/control period, the hearts were excised and assessed for ischemic tolerance on a modified Langendorff apparatus (40 min global ischemia+2h reperfusion). To assess the contribution of opioid receptor stimulation, two additional control and PC groups received the nonspecific opioid antagonist naloxone (10 mg/kg) prior to the in vivo intervention phase. Infarct size (delineated by tetrazoliam staining and expressed as a percentage of the left ventricle [LV]) was compared among the four groups by ANOVA.

RESULTS

Infarct size was significantly reduced in hearts that received antecedent apneic PC when compared with controls (63+/-5% vs. 34+/-8%) of the LV, respectively; P<.05). Pretreatment with naloxone had no significant effect on infarct size in nonpreconditioned hearts (80+/-6%) and did not inhibit the protective effects of apnea-induced PC (52+/-10% in naloxone+PC group).

CONCLUSIONS

Intermittent apnea evokes significant myocardial ischemic tolerance through an opioid-insensitive mechanism.

Effect of exogenous kappa-opioid receptor activation in rat model of myocardial infarction

The involvement of opioid receptor activation during ischemia-reperfusion is somewhat controversial. While it is generally accepted that activation of the delta-opioid receptor (DOR) is cardioprotective, and may indeed be an important mediator of ischemic preconditioning, the role of the kappa-opioid receptor (KOR) is less well understood. To this end, we examined three different KOR agonists and their effects upon infarct size and arrhythmia development. Male Sprague-Dawley rats were subjected to 30 minutes of occlusion followed by 90 minutes of reperfusion. Opioid receptor agonists were administered 10 minutes before the onset of ischemia, while the opioid antagonists were given 20 minutes before occlusion. Untreated rats exhibited an infarct size (IS/AAR%) of 52.4 +/- 2.7%. Pretreatment with the DOR agonist, BW373U86, limited infarct development to 37.2 +/- 1.8%, which was reversed by the selective DOR antagonist, BNTX. All three KOR agonists studied, U50,488, ICI 204,448, and BRL 52537 significantly reduced infarct size to levels comparable to that of BW373U86. The infarct-sparing effects of U50,488 and ICI 204,448 were abolished by the selective KOR antagonist, nor-BNI. Nor-BNI failed to inhibit the cardioprotective effects of BRL 52537. Furthermore, U50,488 and BRL 52537, but not ICI 204,448, significantly reduced the incidence of arrhythmias. These effects were not blocked by nor-BNI. These data demonstrate that KOR activation provides a similar degree of infarct size reduction as DOR activation. KOR agonists also reduced arrhythmogenesis; however, these responses appear to be independent of KOR activation.

Relative contribution of endogenous opioids to myocardial ischemic tolerance1

BACKGROUND

Opioid preconditioning by exogenous opioids experimentally protects the myocardium against ischemia/reflow injury. Additionally, endogenous opioid peptides released during ischemia also enhance ischemic tolerance. Promiscuous opioid receptor agonists conceal the differential contribution of the mu, delta, and kappa opioid subtypes. This study compared the impact of selective delta and kappa opioid receptor antagonists on postischemic functional and metabolic recovery. Also measured were changing levels of peptides dynorphin B and met-enkephalin during ischemia/reflow injury.

MATERIALS AND METHODS

Using the rabbit Langendorff model, the functional recovery of control hearts (following 2 h of global ischemia) was compared to hearts pretreated with delta antagonist NTB (1 microM) or kappa antagonist, nor-BNI (1 microM). Measures included percentage of return of isovolumetric developed pressure (LVDP), myocardial oxygen consumption (MVO(2)) and coronary flow (CF). In additional studies, untreated hearts were harvested at baseline, following ischemia, or following 5 or 45 min of reflow. Tissue concentrations of met-enkephalin and dynorphin B were measured by RIA.

RESULTS

After 45 min of reflow, hearts pretreated with either NTB or nor-BNI showed impaired functional recovery by a decrease in LVDP (P < 0.05); however, MVO(2) or CF were unaffected. RIA data shows that baseline levels of both peptides are similar and increase significantly during ischemia, but reflow dynorphin levels drop far below baseline, while met-enkephalin returns to baseline.

CONCLUSION

Antagonism of both delta and kappa opioid receptor subtypes equally contributes to impaired left ventricular function, independent of altered perfusion or metabolic rate. Endogenous kappa-receptor agonists may contribute primarily during ischemia or early reflow, since low late reflow dynorphin content did not correlate with altered functional recovery.

Exogenous NO triggers preconditioning via a cGMP- and mitoKATP-dependent mechanism

Exogenous nitric oxide (NO) triggers a preconditioning-like effect in heart via a pathway that is dependent on reactive oxygen species. This study examined the signaling pathway by which the NO donor S-nitroso-N-acetylpenicillamine (SNAP, 2 microM) triggers its anti-infarct effect. Isolated rabbit hearts experienced 30 min of regional ischemia and 120 min of subsequent reperfusion. Infarct size was determined by triphenyltetrazolium chloride staining. Infarct size was reduced from 30.5 +/- 3.0% of the risk zone in control hearts to 10.2 +/- 2.0% in SNAP-treated hearts. Bracketing the SNAP infusion with either the guanylyl cyclase blocker 1H-[1,2,4]oxadiazole[4,3-a]quinoxalin-1-one (2 microM) or the mitochondrial ATP-sensitive K(+) (mitoK(ATP)) channel blocker 5-hydroxydecanoate (200 microM) completely blocked the infarct-sparing effect of SNAP (34.3 +/- 3.8 and 32.2 +/- 1.6% infarction, respectively). Pretreatment of hearts with 8-(4-chlorophenylthio)-guanosine 3',5'-cyclic monophosphate (10 microM), which is a cell-permeable cGMP analog that activates protein kinase G, mimicked the preconditioning effect of SNAP by reducing infarct size to 7.5 +/- 1.1% of the risk zone. This salutary effect was abolished by either the free radical scavenger N-(2-mercaptopropionyl)glycine (1 mM) or 5-hydroxydecanoate (100 microM; 28.9 +/- 2.7 and 33.6 +/- 5.0% infarction of the risk zone, respectively). To confirm these functional data and the effect of SNAP on the guanylyl cyclase-protein kinase G signaling pathway, cGMP levels were measured. SNAP increased the level from 0.18 +/- 0.04 to 0.61 +/- 0.14 pmol/mg of protein (P < 0.05). These data suggest that exogenous NO triggers the preconditioning effect by initiating a cascade of events including stimulation of guanylyl cyclase to make cGMP, activation of protein kinase G, opening of mitoK(ATP) channels, and, finally, production of reactive oxygen species.

Morphine-Tolerant Mice Exhibit a Profound and Persistent Cardioprotective Phenotype

Background— Morphine and other opioids continue to be used as the major treatment for acute pain both before and after surgery. In this regard, much research has focused on the mechanisms of morphine tolerance and dependence in the central nervous system; however, few studies have examined the effect of morphine on peripheral organs, such as the heart, in morphine-tolerant animals. Here, we examine the effect of tolerance to the analgesic effect of morphine on ischemic tolerance in mice after prolonged morphine exposure and withdrawal.

Methods and Results— Male C57/BL6 mice were implanted subcutaneously with either placebo or morphine pellets (25 or 75 mg). After prolonged exposure to and/or withdrawal from morphine or placebo, the hearts were excised and subjected to 25 minutes of ischemia and 45 minutes of reperfusion. Morphine-tolerant mice exhibited a markedly improved functional recovery compared with placebo and mice subjected to acute morphine. Lactate dehydrogenase release was also significantly reduced. The protection observed was equieffective 48 hours after withdrawal of pellet, whereas the onset of protection preceded analgesic tolerance.

Conclusions— These data demonstrate that chronic exposure to morphine unexpectedly results in a profound and persistent cardioprotective phenotype.

Sustained exogenous administration of Met5-enkephalin protects against infarction in vivo

The opioid antagonist naloxone abolishes infarct limitation by myocardial ischemic preconditioning, suggesting that one or more endogenous opioid peptides can mediate cardiac protection against ischemic damage. We tested the hypothesis that the naturally occurring opioid peptide Met5-enkephalin (ME) modulates myocardial infarct size in vivo. Experiments were conducted in barbiturate-anesthetized open-chest rabbits subjected to regional myocardial ischemia-reperfusion. ME was administered via osmotic minipump for 24 h. Infarct size was assessed with tetrazolium and is expressed as a percentage of the area at risk. Exogenous ME reduced the amount of the risk zone infarcted by approximately 60% compared with saline-treated controls. ME-induced protection was sensitive to opioid receptor blockade with naloxone [NAL 50 +/- 2% vs. ME + NAL 39 +/- 3%, P = not significant (NS)] and also to blockade of sarcolemmal and mitochondrial ATP-sensitive K+ (KATP) channels [5-hydroxydecanoate (5-HD) 33 +/- 3% vs. ME + 5-HD 43 +/- 8%, P = NS; and HMR-1098 60 +/- 3% vs. ME + HMR-1098 54 +/- 7%, P = NS]. We conclude that ME limits ischemic injury in vivo by an opioid receptor-mediated mechanism that involves both sarcolemmal and mitochondrial KATP channels.

Comparison of three different A1 adenosine receptor antagonists on infarct size and multiple cycle ischemic preconditioning in anesthetized dogs

A(1) adenosine receptor (AR) antagonists are effective diuretic agents that may be useful for treating fluid retention disorders including congestive heart failure. However, antagonism of A(1)ARs is potentially a concern when using these agents in patients with ischemic heart disease. To address this concern, the present study was designed to compare the actions of the A(1)AR antagonists CPX (1,3-dipropyl-8-cyclopentylxanthine), BG 9719 (1,3-dipropyl-8-[2-(5,6-epoxynorbornyl)]xanthine), and BG 9928 (1,3-dipropyl-8-[1-(4-propionate)-bicyclo-[2,2,2]octyl]xanthine) on acute myocardial ischemia/reperfusion injury and ischemic preconditioning (IPC) in an in vivo dog model of infarction. Barbital-anesthetized dogs were subjected to 60 min of left anterior descending coronary artery occlusion followed by 3 h of reperfusion, after which infarct size was assessed by staining with triphenyltetrazolium chloride. IPC was elicited by four 5-min occlusion/5-min reperfusion cycles produced 10 min before the 60-min occlusion. Multiple-cycle IPC produced a robust reduction ( approximately 65%) in infarct size; this effect of IPC on infarct size was not abrogated in dogs pretreated with any of the three AR antagonists. Surprisingly, in the absence of IPC, pretreatment with CPX or BG 9928 before occlusion or immediately before reperfusion resulted in significant reductions ( approximately 40-50%) in myocardial infarct size. However, treatment with an equivalent dose of BG 9719 had no similar effect. We conclude that the A(1)AR antagonists BG 9719, BG 9928, and CPX do not exacerbate cardiac injury and do not interfere with IPC induced by multiple ischemia/reperfusion cycles. We discuss the possibility that the cardioprotective actions of CPX and BG 9928 may be related to antagonism of A(2B)ARs.

HL-1 myocytes exhibit PKC and K ATP channel-dependent delta opioid preconditioning 1,2 1This was presented at the annual meeting of the Association for Academic Surgery, Boston, MA, November 7–9, 2002. 2The present study was supported by a grant from the National Institutes of Health-NHLBI, HL58781

BACKGROUND

Opioid preconditioning protects the myocardium against ischemia/reperfusion (IR) injury. By enhancing cardiomyocyte viability, opioids can enhance cardiac function and recovery from IR injury during acute cardiac care. The myocyte model HL-1 is an immortalized, mouse atrial cell line that expresses functional delta-opioid receptors. The HL-1 myocyte may be useful for IR injury research exploring opioid cardioprotection.

MATERIALS AND METHODS

In study I, microplates of HL-1 were subjected to 10 min pre-treatment with either basal media, delta-opioid agonist DADLE(10uM), or DADLE(10uM) + delta-antagonist naltrindole (10uM). Study II treatment groups included PKC inhibitor chelerythrine (2uM), K(ATP) channel closer glybenclamide (100uM), or mitochondrial K(ATP) channel opener diazoxide (100uM) administered in various combinations followed by DADLE (10uM) or control. Microplates were subjected to normal oxygen/substrate conditions or ischemic (<1% 0(2)) and substrate deficient (10 uM 2-Deoxyglucose versus 10 mM glucose) conditions, then reperfused with normal oxygen and glucose-containing media. Microplate supernatants were subjected to lactate dehydrogenase (LDH) assay.

RESULTS

Compared to untreated control, the LDH assay showed significant reduction in opioid-only pretreated groups at all time points. These effects were attenuated with delta-opioid antagonist co-administration. Co-administration of non-selective K(ATP) channel closer glybenclamide and DADLE abolished DADLE cytoprotection, while selective mitochondrial K(ATP) opener diazoxide mimicked DADLE cytoprotection Co-administration of chelerythrine and DADLE significantly reduced chelerythrine cytotoxicity.

CONCLUSION

Delta-opioid preconditioning of HL-1 myocytes significantly decreased necrosis from in vitro simulated ischemia/reperfusion as measured by LDH release; this effect was reversed by delta-antagonist naltrindole. Cytoprotection was PKC and K(ATP) channel-dependent. HL-1 myocytes exhibit opioid-induced cytoprotection from IR injury, and present a novel model of pharmacologic preconditioning.

Bimodal delta-opioid receptors regulate vagal bradycardia in canine sinoatrial node

Methionine-enkephalin-arginine-phenylalanine (MEAP) introduced into the interstitium of the canine sinoatrial (SA) node by microdialysis interrupts vagal bradycardia. In contrast, raising endogenous MEAP by occluding the SA node artery improves vagal bradycardia. Both are blocked by the same delta-selective antagonist, naltrindole. We tested the hypothesis that vagal responses to intranodal enkephalin are bimodal and that the polarity of the response is both dose- and opioid receptor subtype dependent. Ultralow doses of MEAP were introduced into the canine SA node by microdialysis. Heart rate frequency responses were constructed by stimulating the right vagus nerve at 1, 2, and 3 Hz. Ultralow MEAP infusions produced a 50-100% increase in bradycardia during vagal stimulation. Maximal improvement was observed at a dose rate of 500 fmol/min with an ED50 near 50 fmol/min. Vagal improvement was returned to control when MEAP was combined with the delta-antagonist naltrindole. The dose of naltrindole (500 fmol/min) was previously determined as ineffective vs. the vagolytic effect of higher dose MEAP. When MEAP was later reintroduced in the same animals at nanomoles per minute, a clear vagolytic response was observed. The delta1-selective antagonist 7-benzylidenenaltrexone (BNTX) reversed the vagal improvement with an ED50 near 1 x 10-21 mol/min, whereas the delta2-antagonist naltriben had no effect through 10-9 mol/min. Finally, the improved vagal bradycardia previously associated with nodal artery occlusion and endogenous MEAP was blocked by the selective delta1-antagonist BNTX. These data support the hypothesis that opioid effects within the SA node are bimodal in character, that low doses are vagotonic, acting on delta1-receptors, and that higher doses are vagolytic, acting on delta2-receptors.

Activation of delta- and kappa-opioid receptors by opioid peptides protects cardiomyocytes via KATP channels

To examine the receptor specificity and the mechanism of opioid peptide-induced protection, we examined freshly isolated adult rabbit cardiomyocytes subjected to simulated ischemia. Cell death as a function of time was assessed by trypan blue permeability. Dynorphin B (DynB) and Met5-enkephalin (ME) limitation of cell death (expressed as area under the curve) was sensitive to blockade by naltrindole (NTI, a delta-selective antagonist) and 5'-guanidinyl-17-(cyclopropylmethyl)-6,7-dehydro-4,5alpha-epoxy-3,14-dihydroxy-6,7-2',3'-indolomorphinan (GNTI dihydrochloride, a kappa-selective antagonist): 85.7 +/- 2.7 and 142.9 +/- 2.7 with DynB and DynB + NTI, respectively (P < 0.001), 94.1 +/- 4.2 and 164.5 +/- 7.3 with DynB and DynB + GNTI, respectively (P < 0.001), 111.9 +/- 7.0 and 192.1 +/- 6.4 with ME and ME + NTI, respectively (P < 0.001), and 120.2 +/- 4.3 and 170.0 +/- 3.3 with ME and ME + GNTI, respectively (P < 0.001). Blockade of ATP-sensitive K+ channels eliminated DynB- and ME-induced protection: 189.6 +/- 5.4 and 139.0 +/- 5.4 for control and ME, respectively (P < 0.001), and 210 +/- 5.9 and 195 +/- 6.1 for 5-HD and ME + 5-HD, respectively (P < 0.001); 136.0 +/- 5.7 and 63.4 +/- 5.4 for control and ME, respectively (P < 0.001), and 144.6 +/- 4.5 and 114.6 +/- 7.7 for HMR-1098 and ME + HMR-1098, respectively (P < 0.01); 189.6 +/- 5.4 and 139.0 +/- 5.4 for control and ME, respectively (P < 0.001), and 210 +/- 5.9 and 195 +/- 6.1 for 5-HD and ME + 5-HD, respectively (P < 0.001); and 136.0 +/- 5.7 and 63.4 +/- 5.4 for control and ME, respectively (P < 0.001), and 144.6 +/- 4.5 and 114.6 +/- 7.7 for HMR-1098 and ME + HMR-1098, respectively (P < 0.01). We conclude that opioid peptide-induced cardioprotection is mediated by delta- and kappa-receptors and involves sarcolemmal and mitochondrial ATP-sensitive K+ channels.

Activation of peripheral delta opioid receptors eliminates cardiac electrical instability in a rat model of post-infarction cardiosclerosis via mitochondrial ATP-dependent K+ channels

The effects of the selective delta-1 (delta(1)) opioid receptor agonist, DPDPE, and the selective delta(2) opioid receptor agonist, DSLET, have been studied on the ventricular fibrillation threshold (VFT) in rats with an experimental post-infarction cardiosclerosis (CS). It has been found that CS induced a significant decrease in VFT. This CS-induced decrease in VFT was significantly reversed by intravenous administration of DPDPE (0.1 mg/kg) 10 min before VFT measurement. On the contrary, intravenous injection of DSLET (0.5 mg/kg) exacerbated the CS-induced cardiac electrical instability. Pretreatment with the selective delta opioid receptor antagonist, ICI 174,864 (0.5 mg/kg), completely abolished the changes in VFT produced by both DPDPE and DSLET. Previous administration of a nonselective peripherally acting opioid receptor antagonist, naloxone methiodide (5 mg/kg) also completely reversed the antifibrillatory action of DPDPE. Naloxone methiodide and ICI 174,864 alone had no effect on VFT. Pretreatment with the nonselective K(ATP) channel blocker, glibenclamide (0.3 mg/kg), or with the mitochondrial selective K(ATP) channel blocker, 5-hydroxydecanoic acid (5-HD, 5 mg/kg), completely abolished the DPDPE-induced increase in cardiac electrical stability. Glibenclamide and 5-HD alone had no effect on VFT. These results demonstrate that the delta opioid receptor plays an important role in the regulation of electrical stability in rats with post-infarction cardiosclerosis. We propose that peripheral delta(1) opioid receptor stimulation reverses CS-induced electrical instability via mitochondrial K(ATP) channels. On the contrary, delta(2) opioid receptor stimulation may exacerbate the CS-induced decrease in VFT. Further studies are necessary to determine the delta opioid receptor subtype which mediates the antifibrillatory effect of DPDPE and pro-fibrillatory effect of DSLET.

Role of kappa-opioid receptor activation in pharmacological preconditioning of swine

Pharmacological preconditioning with kappa-opioid receptor agonists is proarrhythmic and exerts antipreconditioning effects in rats. In swine, it is unknown whether kappa-opioid receptor stimulation plays a role in pharmacological preconditioning. Swine were preconditioned with 1) saline (controls), 2) [d-Ala(2),d-Leu(5)]enkephalin (DADLE), 3) morphine, 4) pentazocine, 5) norbinaltorphimine (nor-BNI), 6) DADLE + nor-BNI, 7) morphine + nor-BNI, or 8) pentazocine + nor-BNI before occlusion (45 min) and reperfusion (180 min) of the left anterior descending coronary artery. Infarct size to area at risk (IS), regional (systolic shortening) and global (pressures and flows) myocardial function, and arrhythmia occurrence were assessed. Only DADLE + nor-BNI preconditioning significantly decreased infarct size compared with controls (47 +/- 13 vs. 65 +/- 5%, P < 0.05); morphine preconditioning was not cardioprotective with or without kappa-opioid receptor blockade (nor-BNI). DADLE preconditioning significantly increased ischemia-induced arrhythmias relative to controls, whereas pentazocine-preconditioned animals (n = 2) experienced intractable ventricular fibrillation during ischemia. kappa-Opioid receptor blockade with DADLE or pentazocine preconditioning alleviated proarrhythmic effects. These results suggest that kappa-opioid receptor activation during pharmacological preconditioning is proarrhythmic in swine.

COX-2-derived prostacyclin mediates opioid-induced late phase of preconditioning in isolated rat hearts

Opioids confer biphasic (early and late) cardioprotection against myocardial infarction by opening mitochondrial ATP-sensitive K(+) channels. It is unknown whether cyclooxygenase-2 (COX-2), which mediates ischemia-induced late preconditioning, also mediates opioid-induced cardioprotection. Isolated perfused rat hearts were subjected to 20 min of global ischemia followed by 20 min of reperfusion. BW-373U86 (BW), a delta-opioid receptor agonist, was administered 1, 12, or 24 h before death. Recovery of left ventricular developed pressure (LVDP) after ischemia-reperfusion improved when BW was administered 1 or 24 h before ischemia (control: 57 +/- 8, BW 1 h: 75 +/- 5, BW 24 h: 85 +/- 6%) but not when it was administered 12 h before (60 +/- 5%). Levels of 6-keto-PGF(1alpha) (a stable metabolite of PGI(2)) in coronary effluent after 20 min of reperfusion were higher with 24-h BW pretreatment than in controls (1,053 +/- 92 vs. 724 +/- 81 pg/ml), whereas 6-keto-PGF(1alpha) levels at baseline did not differ. Administration of a selective COX-2 inhibitor, NS-398, abolished the late phase of cardioprotection (recovery of LVDP, 53 +/- 8%) and attenuated the increase in PGI(2) (706 +/- 138 pg/ml) but did not block the early phase of cardioprotection. The selective COX-1 inhibitor SC-560 did not affect either phase of protection. Western immunoblotting revealed upregulation of PGI(2) synthase protein 24 h after BW administration without changes in COX-1 and COX-2 protein levels. In conclusion, the late (but not the early) phase of delta-opioid receptor-induced preconditioning is mediated by COX-2. A functional coupling between COX-2 and upregulated PGI(2) synthase appears to underlie this cardioprotective phenomenon in the rat.

Delta-opioid receptor-induced late preconditioning is mediated by cyclooxygenase-2 in conscious rabbits

Although activation of delta-opioid receptors is known to induce both early and late preconditioning (PC) against myocardial infarction, the mechanisms for this salubrious effect are unclear. Furthermore, it is unknown whether delta-opioid receptors can also induce late PC against myocardial stunning. By using conscious rabbits (n = 120) in this study, we found that the delta-opioid receptor agonist (+/-)-4-[(alpha-R*)-alpha-[(2S*,5R*)-4-allyl-2,5-dimethyl-1-piperazinyl]-3-hydroxybenzyl]-N,N-diethylbenzamide (BW-373U86) induced late PC against myocardial stunning 24 h after treatment and that this effect was abolished by the selective cyclooxygenase-2 (COX-2) inhibitors N-[2-(cyclohexyloxy)4-nitrophenyl]methanesulfonamide (NS-398) and celecoxib. This protective effect was also abrogated by the selective delta(1)-opioid receptor antagonist 7-benzylidenenaltrexone, indicating that the delta(1)-opioid receptor is necessary for BW-373U86-induced late PC. BW-373U86 did not induce early PC against stunning. In addition, BW-373U86 induced late PC against infarction, which was blocked by NS-398. At 24 h after BW-373U86 administration, myocardial COX-2 protein expression and PGE(2) and 6-keto-PGF(1alpha) levels were significantly increased. These results demonstrate that activation of delta-opioid receptors induces late PC against both stunning and infarction via a COX-2-dependent mechanism.

Myocardial protection by anesthetic agents against ischemia-reperfusion injury: an update for anesthesiologists

PURPOSE

The aim of this review of the literature was to evaluate the effectiveness of anesthetics in protecting the heart against myocardial ischemia-reperfusion injury.

SOURCE

Articles were obtained from the Medline database (1980-, search terms included heart, myocardium, coronary, ischemia, reperfusion injury, infarction, stunning, halothane, enflurane, desflurane, isoflurane, sevoflurane, opioid, morphine, fentanyl, alfentanil sufentanil, pentazocine, buprenorphine, barbiturate, thiopental, ketamine, propofol, preconditioning, neutrophil adhesion, free radical, antioxidant and calcium).

PRINCIPAL FINDINGS

Protection by volatile anesthetics, morphine and propofol is relatively well investigated. It is generally agreed that these agents reduce the myocardial damage caused by ischemia and reperfusion. Other anesthetics which are often used in clinical practice, such as fentanyl, ketamine, barbiturates and benzodiazepines have been much less studied, and their potential as cardioprotectors is currently unknown. There are some proposed mechanisms for protection by anesthetic agents: ischemic preconditioning-like effect, interference in the neutrophil/platelet-endothelium interaction, blockade of Ca2+ overload to the cytosolic space and antioxidant-like effect. Different anesthetics appear to have different mechanisms by which protection is exerted. Clinical applicability of anesthetic agent-induced protection has yet to be explored.

CONCLUSION

There is increasing evidence of anesthetic agent-induced protection. At present, isoflurane, sevoflurane and morphine appear to be most promising as preconditioning-inducing agents. After the onset of ischemia, propofol could be selected to reduce ischemia-reperfusion injury. Future clinical application depends on the full elucidation of the underlying mechanisms and on clinical outcome trials.

Role of delta-opioid receptor agonists on infarct size reduction in swine

Opioids are involved in cardiac ischemic preconditioning. Important species differences in cellular signaling mechanisms, antiarrhythmic, and antistunning effects have been described. The role of the delta-opioid receptor activation in swine remains unknown. Forty minutes before a 45-min occlusion and 180-min reperfusion of the left anterior descending coronary artery, open-chest, pentobarbital-anesthetized swine received either 1) saline (controls); 2) [D-Ala(2),D-Leu(5)]enkephalin (DADLE); 3) [D-Pen(2,5)]enkephalin (DPDPE); 4) deltorphin-D, a novel delta(2)-opioid agonist; or 5) ischemic preconditioning (IP). Assessed were 1) infarct size to area at risk (IS, triphenyltetrazolium staining), 2) regional and global myocardial function (sonomicrometry, ventricular pressure catheters), and 3) arrhythmias (electrocardiogram analyses). It was found that DPDPE and deltorphin-D pretreatment reduced IS from 64.7 +/- 5 to 36.5 +/- 6% and 27.4 +/- 11% (P < 0.01), respectively, whereas DADLE had no effect (66.8 +/- 3%). Both IP and DADLE had a proarrhythmic effect (P < 0.01). However, no differences in global or regional myocardial function or arrhythmia scores were observed between groups. This suggests that delta-receptor-specific opioids provide cardioprotection in swine.

Complementary role of extracellular ATP and adenosine in ischemic preconditioning in the rat heart

Although adenosine is an important mediator of ischemic preconditioning (IPC), its relative contribution to IPC remains unknown. Because adenosine is formed through the hydrolysis of ATP, the present study investigated the role of ATP and adenosine in IPC. Isolated and buffer-perfused rat hearts underwent IPC by three cycles of 5-min ischemia and 5-min reperfusion before 25 min of global ischemia. The rate-pressure product (RPP) 30 min after reperfusion was taken as an endpoint of functional protection. Interstitial fluid (ISF) adenine nucleotides and adenosine were measured by cardiac microdialysis techniques. Inhibition of IPC-induced recovery of RPP was partial by the adenosine receptor antagonist 8-(p-sulfophenyl)theophylline (SPT; 100 microM) or by the structurally distinct P2Y purinoceptor antagonists suramin (300 microM) or reactive blue (RB; 10 microM) but was additive when SPT was given with suramin or RB. The P2X antagonist pyridoxal-phosphate-6-azophenyl-2',4'-disulfonic acid tetrasodium (50 microM) had no effect on functional protection. The improved functional recovery was not significantly affected by an ecto-5'-nucleotidase inhibitor, alpha,beta-methylene adenosine diphosphate (AMP-CP; 100 microM), alone but was inhibited by AMP-CP plus SPT, suramin, or RB. ISF ATP and adenosine increased temporarily by 10-fold during IPC. AMP-CP augmented the increase in ISF ATP associated with the decrease in ISF adenosine. There was a reciprocal correlation between the ISF concentration of ATP and adenosine in preconditioned hearts. In addition, there was a significant correlation between ISF adenosine and ATP and the inhibitory potency of SPT and suramin or RB against functional protection conferred by IPC. These results suggest that extracellular ATP and adenosine play a complementary role in IPC through P2Y purinoceptors and adenosine receptors, respectively.

Preconditioning - endogenous defence mechanisms of the heart

The term 'preconditioning' refers to the paradoxical phenomenon that pretreatment with a potential noxious stress-stimulus can increase cellular tolerance to subsequent noxious stress-stimuli. This was first described in an experimental model in dogs in which short-lasting periods of myocardial ischemia resulted in reduced infarction during a subsequent long-lasting coronary artery occlusion. Similar observations have also been made in other species and in other organs. During the last few years, the term preconditioning has been expanded to include pretreatment with other physical stress-stimuli or pharmacological agents that can increase cellular resistance to injury. The phenomenon probably represents a general adaptive response to cellular stress, but mechanisms involved are not fully clarified. This review focuses on preconditioning in the heart. Firstly, we want to address the observation that activation of endogenous defence mechanisms can increase cellular tolerance to several potentially noxious stimuli. Based on results from experimental research, we will give an overview of intracellular mechanisms that is currently in focus. Secondly, we want to address the potential role of preconditioning in clinical practice. We will present results from studies in patients with coronary artery disease and discuss possible clinical implications. Results show that the phenomenon probably exists in the human myocardium. In the future, this might be exploited in patients with acute coronary syndromes, especially since advanced techniques are now available for acute revascularization. Additionally, identification of possible mechanisms involved may influence the choice of medical treatment in high-risk patients with stable coronary artery disease. Preconditioning can also be exploited during elective surgical procedures. This should be of great interest, as the extent of elective surgery in patients at high-risk for coronary events is increasing. In this respect it is important to note that opioid-receptors are probably involved in preconditioning in humans. The last part of this review will address the possible relation between preconditioning and different anesthetic agents and sedatives.

Transient arterial occlusion raises enkephalin in the canine sinoatrial node and improves vagal bradycardia

The C-terminal proenkephalin sequence, Methionine-enkephalin-arginine-phenylalanine (MEAP), is abundant in the myocardium and when delivered into the sinoatrial (SA) node by microdialysis, the peptide had significant vagolytic activity. The study that follows was conducted to determine if an increase in endogenous nodal MEAP could be demonstrated during reduced nodal blood flow and was endogenous MEAP similarly vagolytic. Microdialysis probes were placed in the canine SA node and perfused at 5 microl per min. The SA node artery was occluded and released four times at 10-min intervals. The intermittent occlusions were followed by one or two prolonged occlusions (30 min). Vagally mediated bradycardia was compared before, during, and after occlusion of the artery. An increase in recovered MEAP (70-220 fmol) was recorded during each of the initial 10-min occlusions. MEAP returned to baseline during each subsequent 10-min reperfusion. There was a sustained increase in MEAP (110-150 fmol) during longer occlusions. Contrary to the hypothesis, the increased MEAP during arterial occlusion was coincident with improved vagal bradycardia. The improvement in vagally mediated bradycardia was highly reproducible and was observed again during a second 30-min occlusion. The improved vagal function was reversed or reduced, respectively, when naltrindole or glibenclamide was included in the microdialysis inflow during arterial occlusion. Although these observations suggested that opioid receptors and ATP-sensitive K+ channels might have been involved, only a single dose of each agent was practical. Therefore, the specificity of these two responses remains to be confirmed. In summary, the recovery of endogenous opioids from the sinoatrial node increased during reduced arterial perfusion of the node. Contrary to expectations, the increase in recovered endogenous opioids was accompanied byimproved rather than impaired vagal bradycardia.

Myocardial protection by ischemic preconditioning and delta-opioid receptor activation in the isolated working rat heart

OBJECTIVE

delta-Opioid receptors are involved in the cardioprotective effect of ischemic preconditioning. This study was designed (1) to assess the protective capacities of ischemic preconditioning and the synthetic delta-opioid receptor agonist D-Ala(2)-D-Leu(5) enkephalin (DADLE) in a functionally oriented experimental model of ischemia and reperfusion and (2) to assess whether the effects of both protective measures are similarly blocked by naloxone, a nonspecific delta-opioid receptor antagonist.

METHODS

Sixty-four isolated working rat hearts were subjected to 45 minutes of hypothermic ischemia at 30 degrees C followed by 25 minutes of normothermic reperfusion. Rats were pretreated with DADLE (1 mg/kg body weight intravenously), naloxone (3 mg/kg body weight intravenously), or a combination thereof within 60 minutes before onset of isolated heart perfusion. During the preischemic perfusion period, 8 hearts per group were preconditioned by one cycle of 5 minutes of normothermic global ischemia and subsequent reperfusion whereas another 8 served as nonpreconditioned controls. The postischemic functional recovery of hearts and their creatine kinase leakage were determined.

RESULTS

Pretreatment with DADLE and ischemic preconditioning improved the postischemic recovery of aortic flow when compared with nonpreconditioning (57.7% +/- 4.0% and 60.8% +/- 4.3% vs 40.0% +/- 4.2% of preischemic baseline value, P <.001). Combined pretreatment with DADLE before ischemic preconditioning afforded additional aortic flow recovery compared with pretreatment with DADLE alone (68.6% +/- 3.3% vs 57.7% +/- 4.0% of preischemic baseline value; P =.038). With combined pretreatment, early postischemic creatine kinase release was lower than control in hearts without pretreatment (0.48 +/- 0.11 vs 0.80 +/- 0.12 IU/5 minutes per heart; P =.001). Naloxone abolished the beneficial functional effects of pretreatment with DADLE and ischemic preconditioning.

CONCLUSIONS

Pharmacologic activation of delta-opioid receptors affords improvement of functional protection in isolated working rat hearts similar to that conferred by classic ischemic preconditioning. The combination of both pretreatments reduces ischemic cellular damage and further adds to postischemic functional recovery. These changes are reversed by naloxone, an observation providing evidence that ischemic preconditioning involves signaling through opioid receptors.

Naloxone blocks transferred preconditioning in isolated rabbit hearts

We have shown that the cardioprotective benefits of ischemic preconditioning (PC) can be transferred from PC to virgin acceptor hearts via coronary effluent transfusion, implicating the presence of hormonal preconditioning factor(s). Using isolated buffer-perfused rabbit hearts, our aims were to: (1) determine whether the protective factor(s) could be concentrated and recovered by reverse phase chromatography and (2) whether opioid receptor activation contributes to this transferred cardioprotection. Material released into the coronary effluent during PC ischemia/reperfusion or normoxic perfusion was concentrated by reverse phase chromatography. In phase one, hearts received no intervention (controls), PC ischemia, concentrate generated from normoxic hearts (normoxic acceptors) or concentrate from PC hearts (PC acceptors). All hearts underwent 40 min of global ischemia, and area of necrosis (AN) was delineated by tetrazolium staining. In phase two, three additional groups of hearts (control, PC and PC acceptors) received the opioid antagonist naloxone (2 microM) throughout the intervention phase. Treatment with normoxic concentrate had no effect on infarct size: (AN: normoxic acceptors 39+/-8%; control 42+/-8%). In contrast, treatment with PC concentrate evoked cardioprotection equivalent to that afforded by conventional PC (AN 19+/-5% and 21+/-6% respectively P<0.05 v control). Naloxone had no effect on infarct size in controls, and did not inhibit preconditioning. However, naloxone abrogated the protection achieved by transfer of PC concentrate (AN: 44+/-7%). These results indicate that PC concentrate evokes a cardioprotective effect via a mechanism requiring an intact opioid receptor system.

Late preconditioning is blocked by racemic ketamine, but not by S(+)-ketamine

Racemic ketamine blocks K(ATP) channels in isolated cells and abolishes short-term cardioprotection against prolonged ischemia. We investigated the effects of racemic ketamine and S(+)-ketamine on ischemic late preconditioning (LPC) in the rabbit heart in vivo. A coronary occluder was chronically implanted in 36 rabbits. After recovery, the rabbits divided into four groups (each n = 9). LPC was induced in conscious rabbits by a 5-min coronary occlusion. Twenty-four hours later, the animals were instrumented for measurement of left ventricular systolic pressure (LVSP, tip manometer), cardiac output (CO, ultrasonic flowprobe) and myocardial infarct size (triphenyltetrazolium staining). All rabbits were then subjected to 30-min coronary occlusion and 2 h reperfusion. Controls underwent the ischemia-reperfusion program without LPC. To test whether racemic ketamine or S(+)-ketamine blocks the cardioprotection induced by LPC, the drugs (10 mg/kg) were given 10 min before the 30-min ischemia. Hemodynamic values were not significantly different between groups during the experiments (baseline: LVSP, 94 +/- 3 mm Hg [mean +/- SEM] and CO, 243 +/- 9 mL/min; coronary occlusion: LVSP, 93% +/- 4% of baseline and CO, 84% +/- 4%; after 2 h of reperfusion: LVSP, 85% +/- 4% and CO, 83% +/- 4%). LPC reduced infarct size from 44% +/- 3% of the area at risk in controls to 22% +/- 3% (P = 0.002). Administration of racemic ketamine abolished the cardioprotective effects of LPC (44 +/- 4%, P = 0.002). S(+)-ketamine did not affect the infarct size reduction induced by LPC (26 +/- 6%, P = 0.88).

IMPLICATIONS

Racemic ketamine, but not S(+)-ketamine, blocks the cardioprotection induced by ischemic late preconditioning in rabbit hearts in vivo. Thus, the influence of ketamine on ischemic late preconditioning is most likely enantiomer specific, and the use of S(+)-ketamine may be preferable in patients with coronary artery disease.

Effects of kappa-opioid receptor activation on myocardium

Kappa-opioid receptor stimulation of the heart transiently increases twitch amplitude and decreases Ca2+-dependent actomyosin Mg2+-ATPase activity through an undetermined mechanism. One purpose of the present study was to determine if the increase in twitch amplitude is due to changes in myofilament Ca2+ sensitivity. We also wanted to determine if kappa-opioid receptor activation alters maximum actin-myosin ATPase activity and Ca2+ sensitivity of tension in a way consistent with protein kinase A or protein kinase C (PKC) action. Rat hearts were treated with U50,488H (a kappa-opioid receptor agonist), phenylephrine plus propranolol (alpha-adrenergic receptor stimulation), isoproterenol (a beta-adrenergic receptor agonist), or phorbol 12-myristate 13-acetate (PMA, receptor independent activator of PKC) or were untreated (control), and myofibrils were isolated. U50,488H, phenylephrine plus propranolol, and PMA all decreased maximum Ca2+-dependent actomyosin Mg2+-ATPase activity, whereas isoproterenol treatment increased maximum Ca2+-dependent actomyosin Mg2+- ATPase activity. Untreated myofibrils exposed to exogenous PKC-epsilon, but not PKC-delta, decreased maximum actomyosin Mg2+-ATPase activity. Langendorff-perfused hearts treated with U50,488H, phenylephrine plus propranolol, or isoproterenol had significantly higher ventricular ATP levels compared with control hearts. PKC inhibitors abolished the effects of U50,488H on Ca2+-dependent actomyosin Mg2+-ATPase activity and myocardial ATP levels. U50,488H and PMA treatment of isolated ventricular myocytes increased Ca2+ sensitivity of isometric tension compared with control myocytes at pH 7.0. The U50,488H-dependent increase in Ca2+ sensitivity of tension was retained at pH 6.6. Together, these findings are consistent with the hypotheses that 1) the positive inotropy associated with kappa-opioid receptor activation may be due in part to a PKC-mediated increase in myofilament Ca2+-sensitivity of tension and 2) the kappa-opioid receptor-PKC pathway is a modulator of myocardial energy status through reduction of actomyosin ATP consumption.

Role of endogenous opioids in ischemic preconditioning but not in short-term hibernation in pigs

Endogenous opioids are involved in ischemic preconditioning (IP) in several species. Whether or not opioids are important for IP and short-term myocardial hibernation (STMH) in pigs is currently unknown. In 34 enflurane-anesthetized pigs, the left anterior descending coronary artery was flow constantly perfused. Subendocardial blood flow (Endo), infarct size (IS; percent area at risk), and the free energy change of ATP hydrolysis (DeltaG) were determined. After 90-min severe ischemia and 120-min reperfusion, IS averaged 28.3 +/- 5.4% (means +/- SE) (n = 8; Endo: 0.047 +/- 0.009 ml. min(-1) x g(-1)). IP by 10-min ischemia and 15-min reperfusion reduced IS to 9.9 +/- 3.8% (P < 0.05, n = 8; Endo: 0.044 +/- 0.009 ml. min(-1) x g(-1)). After naloxone (1 mg/kg iv followed by 2 microg x kg(-1) x min(-1)), IS averaged 25.8 +/- 7.0% (n = 6; Endo: 0.039 +/- 0.008 ml x min(-1) x g(-1)) without and 24.7 +/- 4.7% (n = 6; Endo: 0.044 +/- 0.006 ml x min(-1) x g(-1)) with IP. At 5-min moderate ischemia in the presence of naloxone, Endo decreased from 0.90 +/- 0.07 to 0.28 +/- 0.03 ml x min(-1) x g(-1)and DeltaG decreased from -58.6 +/- 1.0 to -52.6 +/- 0.4 kJ/mol. Prolongation of ischemia to 90 min did not alter Endo, but DeltaG recovered toward control values (57.7 +/- 1.1 kJ/mol), and the myocardium remained viable. These responses are identical to those of nonnaloxone-treated pigs. Endogenous opioids are involved in IP but not in STMH in pigs.

Essential activation of PKC-delta in opioid-initiated cardioprotection

Stimulation of the delta(1)-opioid receptor confers cardioprotection to the ischemic myocardium. We examined the role of protein kinase C (PKC) after delta-opioid receptor stimulation with TAN-67 or D-Ala(2)-D-Leu(5)-enkephalin (DADLE) in a rat model of myocardial infarction induced by a 30-min coronary artery occlusion and 2-h reperfusion. Infarct size (IS) was determined by tetrazolium staining and expressed as a percentage of the area at risk (IS/AAR). Control animals, subjected to ischemia and reperfusion, had an IS/AAR of 59.9 +/- 1.8. DADLE and TAN-67 administered before ischemia significantly reduced IS/AAR (36.9 +/- 3.9 and 36.7 +/- 4.7, respectively). The delta(1)-selective opioid antagonist 7-benzylidenenaltrexone (BNTX) abolished TAN-67-induced cardioprotection (54.4 +/- 1.3). Treatment with the PKC antagonist chelerythrine completely abolished DADLE- (61.8 +/- 3.2) and TAN-67-induced cardioprotection (55.4 +/- 4.0). Similarly, the PKC antagonist GF 109203X completely abolished TAN-67-induced cardioprotection (54.6 +/- 6.6). Immunofluorescent staining with antibodies directed against specific PKC isoforms was performed in myocardial biopsies obtained after 15 min of treatment with saline, chelerythrine, BNTX, or TAN-67 and chelerythrine or BNTX in the presence of TAN-67. TAN-67 induced the translocation of PKC-alpha to the sarcolemma, PKC-beta(1) to the nucleus, PKC-delta to the mitochondria, and PKC-epsilon to the intercalated disk and mitochondria. PKC translocation was abolished by chelerythrine and BNTX in TAN-67-treated rats. To more closely examine the role of these isoforms in cardioprotection, we utilized the PKC-delta selective antagonist rottlerin. Rottlerin abolished opioid-induced cardioprotection (48.9 +/- 4.8) and PKC-delta translocation without affecting the translocation of PKC-alpha, -beta(1), or -epsilon. These results suggest that PKC-delta is a key second messenger in the cardioprotective effects of delta(1)-opioid receptor stimulation in rats.