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(Circulation. 1998;97:1282-1289.)
© 1998 American Heart Association, Inc.

Basic Science Reports

Ischemic Preconditioning in the Intact Rat Heart Is Mediated by ₁- But Not µ- or -Opioid Receptors

Jo El J. Schultz, PhD; Anna K. Hsu, BS; ; Garrett J. Gross, PhD

From the Department of Pharmacology and Toxicology, Medical College of Wisconsin, Milwaukee.

Correspondence to Garrett J. Gross, PhD, Department of Pharmacology and Toxicology, Medical College of Wisconsin, 8701 Watertown Plank Rd, Milwaukee, WI 53226.

	Abstract

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Background—Our laboratory has previously shown that -opioid receptors are involved in the cardioprotective effect of ischemic preconditioning in the rat heart. However, this class of receptors consists of two subtypes, ₁ and ₂, and µ- or -opioid receptors may also exist in the heart. Therefore, the purpose of the present study was to test the hypothesis that ischemic preconditioning is mediated through stimulation of one or both -opioid receptor subtypes.

Methods and Results—Anesthetized, open chest, male Wistar rats were assigned to 1 of 14 groups. All animals were subjected to 30 minutes of occlusion and 2 hours of reperfusion. Ischemic preconditioning was elicited by three 5-minute occlusion periods interspersed with 5 minutes of reperfusion. Two doses of 7-benzylidenenaltrexone (BNTX; 1 and 3 mg/kg IV), a selective ₁-opioid receptor antagonist, or naltriben (NTB; 1 and 3 mg/kg IV), a selective ₂-opioid receptor antagonist, were given before ischemic preconditioning. To test for a role of µ-opioid receptors, rats were pretreated with ß-funaltrexamine (ß-FNA; 15 mg/kg SC), an irreversible µ-opioid receptor antagonist, 24 hours before ischemic preconditioning or given the µ-opioid receptor agonist D-Ala,²N-Me-Phe,⁴glycerol⁵-enkephalin (DAMGO) as three 5-minute infusions (1, 10, and 100 µg/kg per infusion IV, respectively) interspersed with 5-minute drug-free periods before the prolonged ischemic and reperfusion periods (lowDAMGO, medDAMGO, and hiDAMGO, respectively). The involvement of -opioid receptors was tested by administering one of two doses of nor-binaltorphimine (nor-BNI; 1 and 5 mg/kg IV) before ischemic preconditioning. Infarct size (IS) as a percent of the area at risk (AAR) was measured by triphenyltetrazolium stain. Ischemic preconditioning markedly reduced IS/AAR (14±4%, P<.05) compared with control (55±4%). NTB, ß-FNA, and nor-BNI were unable to block the cardioprotective effect of ischemic preconditioning. In addition, DAMGO had no effect on IS/AAR. However, the high dose of BNTX (3 mg/kg IV) significantly attenuated the cardioprotective effect of ischemic preconditioning (39±5%; P<.05 versus control and ischemic preconditioning).

Conclusions—These results indicate that ₁-opioid receptors play an important role in the cardioprotective effect of ischemic preconditioning in the rat heart.

Key Words: receptors • ischemia • myocardial infarction • signal transduction • heart diseases

	Introduction

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The idea of multiple opioid receptors is an accepted concept, and a number of subtypes for each class of opioid receptors has been identified.^{1 2 3 4} Through biochemical and pharmacological methods, the µ-, -, and -opioid receptors have been characterized.^{3 5} Pharmacologically, it is well known that -opioid receptors consist of two subtypes, ₁ and ₂.^{6 7 8}

Opioid receptor activation has been implicated to elicit a protective effect during situations of stress produced by hypoxia, ischemia, cold, or acidic environments,^{9 10 11 12 13 14 15 16 17 18 19 20} and the -opioid receptor has been demonstrated to play a major role in this protection.^{13 14 15 18} Mayfield and D'Alecy^{14 15} showed, using DPDPE (selective ₁-opioid receptor agonist) and BNTX (selective ₁-opioid receptor antagonist), that the ₁-opioid receptor mediated the adaption or increased survival time of mice to hypoxic environments. Furthermore, Chien et al¹³ demonstrated that the time before organ transplantation was increased significantly from a 6-hour window to a 48-hour window after the administration of a synthetic -opioid receptor agonist, DADLE. Recently, our laboratory showed that -opioid receptors were involved in the cardioprotective effect of ischemic preconditioning (PC) in the intact rat heart.¹⁸ We demonstrated that administration of naltrindole, a nonselective -opioid receptor antagonist, attenuated the cardioprotective effect of ischemic PC and morphine.¹⁸ However, the role of the specific -opioid receptor subtype (₁ and ₂) as well as a role for µ- and -opioid receptors in the cardioprotective effect of ischemic PC remains unknown. Therefore, the focus of the present study was to determine the role of these four opioid receptor subtypes in mediating the cardioprotective effect of ischemic PC in the intact rat heart.

	Methods

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This study was performed in accordance with the guidelines of the Animal Care Committee of the Medical College of Wisconsin, which is accredited by the American Association of Laboratory Animal Care.

General Surgical Preparation
Male Wistar rats weighing 350 to 450 g were used. The rats were anesthetized by intraperitoneal administration with the long-acting thiobutabarbital inactin (100 mg/kg IV). A tracheotomy was performed and the rat was intubated with a cannula connected to a rodent ventilator (model 683, Harvard Apparatus) and ventilated with room air at 65 to 70 breaths/min. Atelectasis was prevented by maintaining a positive end-expiratory pressure of 5 to 10 mm of H₂O. Arterial pH, PCO₂, and PO₂ were monitored at baseline, at 15 minutes of occlusion, and at 15, 60, and 120 minutes of reperfusion by a blood gas analyzer (AVL 995, Automatic Blood Gas System) and maintained within a normal physiological range (pH 7.35 to 7.45; PCO₂ 25 to 40 mm Hg; PO₂ 80 to 110 mm Hg) by adjusting the respiratory rate and/or tidal volume (2 to 4 mL/100 g). Body temperature was monitored (Yellow Springs Instruments, Tele-Thermometer) and maintained at 37±1°C (mean±SEM) by use of a heating pad.

The right carotid artery was cannulated to measure blood pressure and heart rate with a Gould PE50 or Gould PE23 pressure transducer, which was connected to a Grass (model 7) polygraph. The right jugular vein was cannulated to infuse saline or drugs. A left thoracotomy was performed 15 mm from the sternum to expose the heart at the fifth intercostal space. The pericardium was removed and the left atrial appendage was moved to reveal the location of the left coronary artery. The vein descending along the septum of the heart was used as the marker for the left coronary artery. A ligature (6–0 prolene), along with a snare occluder, was placed around the vein and left coronary artery close to the place of origin. After surgical preparation, the rat was allowed to stabilize for 15 minutes before the various interventions.

Drugs
Inactin, (-)-trans-(1S,2S)-U-50488H, nor-binaltorphimine (nor-BNI) and [D-Pen,² D-Pen⁵]-enkephalin (DPDPE) were purchased from Research Biochemicals International. 7-benzylidenenaltrexone (BNTX), naltriben (NTB), and ß-funaltrexamine (ß-FNA) were generously donated as gifts from Dr Hiroshi Nagase, Toray Industries, Inc, Kanagawa, Japan. D-Ala,²N-Me-Phe,⁴glycerol⁵-enkephalin (DAMGO) was purchased from Bachem Bioscience, Inc. 2,3,5-triphenyltetrazolium chloride (TTC) was purchased from Sigma Chemical Co. Inactin, NTB, and DAMGO were dissolved in 0.9% saline. BNTX and DPDPE were dissolved in distilled water and brought up to volume with saline. ß-FNA, U-50488H, and nor-BNI were dissolved in distilled water. TTC was dissolved in a 100 mmol/L phosphate buffer.

Study Groups and Experimental Protocols
All protocols contained control (group I) and three 5-minute ischemic PC (group II) groups. The control group was subjected to 30 minutes of occlusion and 2 hours of reperfusion. Ischemic PC was elicited by three 5-minute occlusion periods interspersed with 5 minutes of reperfusion before the prolonged occlusion and reperfusion periods. Fig 1 represents the experimental protocol designed to demonstrate the specific (₁ or ₂) opioid receptor involved in the cardioprotective effect of ischemic PC. In group III, BNTX (3 mg/kg IV) was given 10 minutes before the long occlusion period in nonpreconditioned animals. Groups IV and V showed a dose-response effect of BNTX to antagonize ischemic PC (1 and 3 mg/kg IV; lowBNTX+PC and hiBNTX+PC, respectively). In group VI, NTB (1 mg/kg IV) was administered 10 minutes before the 30 minutes of occlusion in nonpreconditioned animals. In groups VII and VIII, NTB (1 and 3 mg/kg IV, respectively) was given as a bolus 10 minutes before ischemic PC or as an infusion starting 60 minutes before ischemic PC and continuing for 50 minutes (lowNTB+PC and hiNTB+PC, respectively). A slow infusion of the high dose of NTB was necessary because this dose produced a marked hypotensive effect when rapidly administered.

View larger version (20K): [in this window] [in a new window]   Figure 1. Protocol used to determine which -opioid receptor subtype mediates the cardioprotective effect of ischemic preconditioning (PC). Groups consist of I, control (CON); II, ischemic PC elicited by three 5-minute occlusion periods interspersed with 5 minutes of reperfusion; III, BNTX (3 mg/kg IV), a selective 1-opioid receptor antagonist, given 10 minutes before the 30 minutes of occlusion; IV, lowBNTX+PC, BNTX (1 mg/kg IV) given 10 minutes before ischemic PC; V, hiBNTX+PC, BNTX (3 mg/kg IV) given 10 minutes before ischemic PC; VI, NTB, naltriben (1 mg/kg IV), a 2-opioid receptor antagonist, given 10 minutes before the 30 minutes of occlusion; VII, lowNTB+PC, NTB (1 mg/kg IV) given 10 minutes before ischemic PC; and VIII, hiNTB+PC, naltriben (3 mg/kg IV) infused for 50 minutes before ischemic PC.

Because µ- and -opioid receptors have been implicated in many cardiovascular physiological and pathophysiological responses,^{21 22 23 24} several pharmacological antagonists and one agonist were used to determine if these two opioid receptors were involved in ischemic PC in the intact rat heart (Fig 2). In group IX, animals were pretreated 24 hours before ischemic PC with ß-funaltrexamine (ß-FNA; 15 mg/kg SC), an irreversible µ-opioid receptor antagonist (ß-FNA+PC). To test if stimulating the µ-opioid receptor mimicked ischemic PC, groups X through XII consisted of three 5-minute infusions (1, 10, and 100 µg/kg per infusion IV, respectively) of DAMGO, a selective µ-opioid receptor agonist, interspersed with 5-minute drug-free periods before the prolonged ischemic and reperfusion periods (lowDAMGO, medDAMGO, hiDAMGO, respectively). Last, to test if -opioid receptors mediated the cardioprotective effect of ischemic PC, a dose-response effect of nor-binaltorphimine (nor-BNI), a -opioid receptor antagonist, was studied. In groups XIII (low nor-BNI+PC) and XIV (hi nor-BNI+PC), nor-BNI (1 and 5 mg/kg IV, respectively) was given 15 minutes before ischemic PC. In previous studies, we have shown that saline or distilled water had no effect on infarct size in rat hearts.^{16 17}

View larger version (26K): [in this window] [in a new window]   Figure 2. Protocol to demonstrate a role of µ- and -opioid receptors in ischemic preconditioning (PC). Groups consist of I, control (CON); II, three 5-minute ischemic PC; IX, ß-funaltrexamine (15 mg/kg SC), an irreversible µ-opioid receptor antagonist, given 24 hours before ischemic PC (ß-FNA+PC); X through XII, DAMGO, a µ-opioid receptor agonist, given as three 5-minute DAMGO infusions (1 µg/kg per infusion, lowDAMGO; 10 µg/kg per infusion, medDAMGO; 100 µg/kg per infusion, hiDAMGO); XIII, nor-binaltrophimine (1 mg/kg IV; norBNI), a -opioid receptor antagonist, given 15 minutes before ischemic PC (lownorBNI+PC); and XIV, nor-binaltrophimine (5 mg/kg IV) given 15 minutes before ischemic PC (hi norBNI+PC).

Specificity of the Opioid Receptor Agonist and Antagonists
To demonstrate that the effect of the antagonists and agonists occurred at a specific opioid receptor, BNTX, and NTB, the ₁- and ₂-opioid receptor antagonists, respectively, ß-FNA, the irreversible µ-opioid receptor antagonist, nor-BNI, the -opioid receptor antagonist, DAMGO, the µ-opioid receptor agonist, DPDPE, the -opioid receptor agonist, and U-50488H, the -opioid receptor agonist, were used. DAMGO produced a transient hypotensive effect during infusion of the three doses (1, 10, and 100 µg/kg IV) studied. Therefore, animals that were pretreated with ß-FNA (group 9 from Fig 2) were subjected to a dose response of DAMGO (3, 30, and 300 µg/kg IV) before ischemic PC to test the specificity of ß-FNA for the µ-opioid receptor. Similarly, a dose response of DAMGO (3, 30, and 300 µg/kg IV) was studied with BNTX or NTB (groups III and VI from Fig 1) in which either -opioid receptor antagonist was given and then a DAMGO dose response was performed before the long occlusion period to demonstrate the lack of effect of BNTX and NTB for the µ-receptor and their specificity for the ₁-(BNTX) and ₂-(NTB) opioid receptor.

In addition, specificity of the ₁-, ₂-, and -antagonists to their respective opioid receptors was further demonstrated with a - and -opioid receptor agonist. A dose response of DPDPE (1, 3, and 10 mg/kg IV), the -opioid receptor agonist, was performed and a transient decrease in blood pressure was observed. BNTX (3 mg/kg IV), the ₁-opioid receptor antagonist, was given 10 minutes before the next DPDPE dose response. Similarly, a dose response of U-50488H (1, 5, and 10 mg/kg IV), the -opioid receptor agonist, was performed followed by the administration of nor-BNI (5 mg/kg IV), the -opioid receptor antagonist, 15 minutes before the next U-50488H dose response.

Pretreatment for 24 hours with ß-FNA resulted in a complete blockade of the vascular response to DAMGO, whereas neither BNTX nor NTB had any effect on the response to DAMGO (data not shown). The decrease in blood pressure caused by DPDPE was antagonized by BNTX but not by NTB (data not shown). In addition, hypotensive responses to U-50488H were blocked by nor-BNI (data not shown). These data demonstrate that the doses of opioid antagonists used are specific for their respective receptors.

Determination of Infarct Size
After each experiment, the left coronary artery was reoccluded and Patent blue dye was injected into the venous catheter to stain the normally perfused region of the heart. The rat was euthanized with 15% KCl through the arterial catheter. The heart was excised and the left ventricle removed and sliced into five cross-sectional pieces. This procedure allowed for visualization of the normal, nonischemic region and the area at risk (AAR). The AAR was separated from the normal area with the use of a dissecting scope (Cambridge Instruments). Both tissue regions (nonischemic and AAR) were incubated at 37°C for 15 minutes in a 1% 2,3,5-triphenyltetrazolium stain in 100 mmol/L phosphate buffer (pH 7.4). TTC was used as an indicator to separate out viable and nonviable tissue.²⁵ The tissue was stored overnight in a 10% formaldehyde solution. The following day, the infarcted tissue was separated from the AAR by use of the dissecting scope. The different regions (nonischemic, AAR, and infarct) were determined by gravimetry, and infarct size (IS) was calculated as a % of the AAR (IS/AAR).

Exclusion Criteria
A total of 107 animals were assigned to the present study. Animals were excluded from the study because of unacceptable blood gases, intractable ventricular fibrillation (VF), or hypotension (mean arterial blood pressure <30 mm Hg). Three animals in the control group, two in the ischemic PC group, two animals in the hiBNTX+PC group, one in the hiDAMGO group, and four animals in the ß-FNA+PC group were excluded because of intractable ventricular fibrillation. In addition, three animals in the hiNTB+PC group and one animal in the low nor-BNI+PC group were excluded because of hypotension. A total of 91 animals completed the study.

Statistical Analysis of the Data
All values are expressed as mean±SEM. One-way ANOVA was used to determine differences among groups for IS and AAR. Differences between groups in hemodynamics at various time points were compared by use of two-way ANOVA for time and treatment with repeated measures and Fisher's least significant difference test if significant F ratios were obtained. Statistical differences were considered significant if the probability value was <.05.

	Results

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Hemodynamics
Tables 1 and 2 summarize the mean±SEM values for the hemodynamic parameters of heart rate (HR), mean arterial blood pressure (MBP), and rate-pressure product (RPP) analyzed at baseline, 30 minutes of occlusion, and 2 hours of reperfusion. In Table 1, HR, MBP, and RPP at baseline were not significantly different among the groups. However, at 30 minutes of occlusion, the MBP in the lowBNTX+PC group was significantly higher compared with control, but by 2 hours of reperfusion, no differences in MBP were found between groups. In addition, RPP at 30 minutes of occlusion was significantly higher in the ischemic PC, BNTX, lowBNTX+PC, and hiBNTX+PC groups; however, the RPP at 2 hours of reperfusion was not significantly different in any of these groups. The HR in the NTB group was significantly lower at 2 hours of reperfusion, but there was no significant difference in MBP or RPP.

View this table: [in this window] [in a new window]   Table 1. Hemodynamic Data Obtained in the Presence of Specific -Opioid Receptor Subtype Antagonists

View this table: [in this window] [in a new window]   Table 2. Hemodynamic Data Obtained in the Presence of µ- and -Opioid Receptor Agonists or Antagonists

Table 2 shows that the baseline HR in the ischemic PC group was significantly lower than control; however, HR in this group was not significantly different from control at 30 minutes of occlusion or 2 hours of reperfusion. The hiDAMGO group had a significantly lower HR compared with control at 2 hours of reperfusion. The medDAMGO and ß-FNA+PC groups had a significantly lower MBP at 30 minutes of occlusion and 2 hours of reperfusion. In addition, MBP at 2 hours of reperfusion was significantly lower in the hiDAMGO and low nor-BNI+PC groups. RPP at 30 minutes of occlusion was significantly lower in the medDAMGO and ß-FNA+PC groups. However, there were no significant differences in RPP among the groups at 2 hours of reperfusion.

Infarct Size and Area at Risk
₁- and ₂-Opioid Receptors
Left ventricular (LV) weight, AAR, and IS weights are shown in Table 3. The LV and AAR weights were not significantly different between groups. Infarct size was significantly smaller in the ischemic PC, lowBNTX+PC, and both NTB+PC groups. The IS/AAR data for the individual rat hearts are depicted in Fig 3 as well as the mean±SEM for each group. The control group had an average IS/AAR of 53.2±2.9%. Ischemic PC markedly reduced infarct size to 14.1±5.1% (P<.05 versus control). The low dose of the selective ₁-receptor antagonist BNTX (1 mg/kg IV) did not attenuate the effect of ischemic PC (19.0±3.4%; P<.05), whereas the high dose of BNTX (3 mg/kg IV) significantly attenuated the cardioprotective effect of ischemic PC (38.7±5.4%; P<.05 versus control and ischemic PC). Similarly, a dose response to NTB, a ₂-opioid receptor antagonist, was performed. Neither dose (1 and 3 mg/kg IV) of NTB inhibited the cardioprotective effect of ischemic PC (24.4±6.5% and 18.1±2.5%, respectively). BNTX or NTB alone had no effect on infarct size in nonpreconditioned groups.

View this table: [in this window] [in a new window]   Table 3. Infarct Size Data in the Presence of BNTX and NTB, Specific -Opioid Receptor Subtype Antagonists

View larger version (15K): [in this window] [in a new window]   Figure 3. Infarct sizes in rat hearts subjected to control (CON); ischemic preconditioning (PC) elicited by three 5-minute occlusion periods interspersed with 5 minutes of reperfusion; BNTX (3 mg/kg IV), a selective 1-opioid receptor antagonist, given 10 minutes before the 30 minutes of occlusion; lowBNTX+PC, BNTX (1 mg/kg IV) given 10 minutes before ischemic PC; hiBNTX+PC, BNTX (3 mg/kg IV) given 10 minutes before ischemic PC; NTB, naltriben (1 mg/kg IV), a 2-opioid receptor antagonist, given 10 minutes before the 30 minutes of occlusion; lowNTB+PC, NTB (1 mg/kg IV) given 10 minutes before ischemic PC; and hiNTB+PC, naltriben (3 mg/kg IV) infused for 50 minutes before ischemic PC. , Infarct sizes from individual hearts; , group mean infarct size; mean±SEM, with *P<.05 vs control and *§P<.05 vs control and ischemic PC.

µ- and -Opioid Receptors
The results shown in Table 4 indicate that there were no significant differences in LV and AAR weights between the groups. Also, the results in Table 4 demonstrate that the IS weights in ischemic PC, ß-FNA+PC–treated animals, and low and hi nor-BNI+PC groups were significantly lower compared with control. In addition, the results in Fig 4 show the infarct sizes of the individual rat hearts and the mean±SEM for each group. The average IS/AAR in the control group was 54.7±3.7%. Ischemic PC significantly reduced IS/AAR (12.0±3.2%; P<.05 versus control). Twenty-four–hour pretreatment (15 mg/kg SC) with ß-FNA, an irreversible µ-opioid receptor antagonist, did not abolish the cardioprotective effect of ischemic PC (8.0±1.7%; P<.05 versus control). Furthermore, three doses (1, 10, and 100 µg/kg per 5-minute infusion IV) of DAMGO, a selective µ-opioid receptor agonist, did not mimic the cardioprotective effect of PC (53.9±4.3%, 52.9±4.7%, and 52.0±8.1%, respectively). Finally, two doses (1 and 5 mg/kg IV) of nor-BNI, a -opioid receptor antagonist, given 15 minutes before ischemic PC did not block its protective effect (20.2±5.1% and 20.2±2.5%, respectively).

View this table: [in this window] [in a new window]   Table 4. Infarct Sizes in Rat Hearts Treated With µ- or -Opioid Receptor Agonists and Antagonists

View larger version (14K): [in this window] [in a new window]   Figure 4. Infarct sizes in rat hearts subjected to control (CON); three 5-minute ischemic preconditioning (PC); ß-funaltrexamine (15 mg/kg SC), an irreversible µ-opioid receptor antagonist, given 24 hours before ischemic PC (ß-FNA+PC); DAMGO, a µ-opioid receptor agonist, given as three 5-minute DAMGO infusions (1 µg/kg per infusion, lowDAMGO; 10 µg/kg per infusion, medDAMGO; 100 µg/kg per infusion, hiDAMGO); nor-binaltrophimine (1 mg/kg IV; norBNI), a -opioid receptor antagonist, given 15 minutes before ischemic PC (lownorBNI+PC) and nor-binaltrophimine (5 mg/kg IV) given 15 minutes before ischemic PC (hinorBNI+PC). Open circles indicate infarct sizes from individual hearts. Filled circles in each group indicate the average infarct size; mean±SEM with *P<.05 vs control.

	Discussion

Top Abstract Introduction Methods Results Discussion References

 
The class of -opioid receptors consists of two subtypes, ₁ and ₂.^{6 7 8} There are a number of pharmacological agents available to distinguish these two subtypes of -opioid receptor.⁵ BNTX, a nonpeptidic ₁-opioid receptor antagonist, and NTB, a nonpeptidic ₂-opioid receptor antagonist, were used in the present study to clarify the role of these two subtypes to mediate the cardioprotective effect of ischemic PC. A number of studies have demonstrated the selectivity and specificity of BNTX and NTB toward its respective opioid receptor.^{26 27 28} Dose responses of both BNTX and NTB were performed in the present study, and the results demonstrate that the high dose (3 mg/kg IV) of BNTX but not the low dose (1 mg/kg IV) partially abolished the protective effect of ischemic PC. Conversely, neither dose of NTB (1 or 3 mg/kg IV) blocked ischemic PC. Our results demonstrating that BNTX at the low dose (1 mg/kg) did not block the cardioprotective effect of ischemic PC confirm the results obtained by Mayfield and D'Alecy.¹⁵ This group observed that 1 mg/kg of BNTX did not decrease the hypoxic survival time of mice; however, at a higher dose of BNTX (10 mg/kg), the hypoxic survival time was significantly decreased.¹⁵ Similarly, we observed that the cardioprotective effect of ischemic PC in the rat was blocked at a higher dose of BNTX (3 mg/kg). BNTX (3 mg/kg IV) and NTB (1 mg/kg IV) in combination when given 10 minutes before ischemic PC did not have an additive effect to block the cardioprotective effect (data not shown). In fact, the IS/AAR observed when the combination of BNTX and NTB was given was no larger than the IS/AAR observed when BNTX alone was given before ischemic PC. This observation further suggests that ischemic PC in the rat heart is predominantly mediated by the ₁-opioid receptor. Overall, these data demonstrate that the ₁-opioid receptor is the important -opioid receptor subtype involved in the cardioprotective effect of ischemic PC in the rat. Further studies with selective ₁-opioid receptor agonists are necessary to demonstrate that stimulating this -opioid receptor produces a cardioprotective effect to reduce infarct size in the rat heart.

Involvement of µ- and -opioid receptors were studied with the use of the µ-receptor agonist DAMGO, the irreversible µ-receptor antagonist ß-FNA, and the -receptor antagonist nor-BNI. Many studies have provided evidence that DAMGO and ß-FNA are selective for the µ-opioid receptor,^{29 30} and nor-BNI is selective for -opioid receptors.^{31 32} We demonstrated that ß-FNA (15 mg/kg SC) when administered 24 hours preceding ischemic PC did not block its cardioprotective effect. Similarly, DAMGO at any of the doses studied did not mimic the cardioprotection induced by brief periods of ischemia. Previously, we showed that morphine reduced infarct size and elicited a cardioprotective effect in the rat heart, indicating that this cardioprotection may involve µ-opioid receptors.¹⁷ However, our laboratory recently showed that naltrindole, a nonselective -opioid receptor antagonist, abolished the cardioprotective effect of morphine, demonstrating that its protection is mediated by a -opioid receptor.¹⁸ It is known that morphine has high affinity for the µ-opioid receptor; however, morphine has also been shown to interact with the - and -opioid receptors.^{3 22 33} In addition, a number of investigators have demonstrated that cross-talk can occur between µ- and -opioid receptors.^{34 35 36 37} Therefore, we used a more selective µ-opioid receptor agonist, DAMGO, to further demonstrate and clarify the role, if any, of µ-opioid receptors in the cardioprotective effect of ischemic PC in the rat. The present results clearly suggest that the µ-opioid receptor does not mediate ischemic PC. The lack of µ-opioid receptor activity in the cardioprotective effect of ischemic PC has also been supported by a number of functional and receptor binding studies in ventricular myocytes, indicating an absence of this particular opioid receptor in this tissue.^{33 38 39 40 41} In addition, the hypoxic conditioning study by Mayfield and D'Alecy¹⁵ showed that ß-FNA (48-hour pretreatment with 1 to 20 mg/kg SC) did not decrease hypoxic survival time in mice, indicating that the µ-opioid receptor was not involved.

The role of -opioid receptors in the protective effect of ischemic PC was tested by the use of nor-BNI, a selective -opioid receptor antagonist. Two doses of nor-BNI (1 and 5 mg/kg IV) were tested. Neither dose of nor-BNI abolished ischemic PC, suggesting that -opioid receptors are not involved in cardioprotection in the rat. As with the BNTX and NTB combination, there was no additive effect to block ischemic PC in the rat when BNTX (3 mg/kg IV) and nor-BNI (1 mg/kg IV) were given together (data not shown). In support of the lack of involvement of the -opioid receptor in ischemic PC, Xia et al⁴² demonstrated that antiarrhythmic effect of ischemic PC in the isolated rat heart may be due to a decreased affinity of -opioid receptor binding by U69593, a highly selective -agonist, during reperfusion. Also, Mayfield and D'Alecy¹⁵ were unable to decrease hypoxic survival time of mice with nor-BNI (1 to 20 mg/kg SC) when animals were subjected to hypoxic preconditioning. Furthermore, Niroomand et al⁴³ indicated that -opioid receptors may not be present on canine cardiac sarcolemma because the -agonist U50488H did not inhibit adenylate cyclase activity.

In summary, our results indicate that the beneficial effect of brief periods of ischemia are partially mediated by the ₁-opioid receptor. BNTX, the ₁-opioid receptor antagonist, attenuated the cardioprotection, whereas NTB, the ₂-opioid receptor antagonist, did not inhibit ischemic PC. Neither µ- nor -opioid receptors seem to be involved in eliciting cardioprotection in the rat heart because antagonists to these two receptors did not prevent PC and DAMGO, a selective µ-opioid receptor agonist, did not mimic ischemic PC. Also, combinations of the ₂- or -antagonist with BNTX did not produce an additive inhibition of ischemic PC in comparison to the results with BNTX alone, suggesting that ischemic PC in the rat occurs primarily through activation of ₁-opioid receptors.

The results of this study suggest that there may be significant clinical potential for stimulating ₁-opioid receptors with regard to treating cardiac ischemia in patients with coronary artery disease; however, more studies need to be performed to demonstrate a universal role for ₁-opioid receptors in ischemic PC in all species. Opioids have been used clinically to manage pain after surgery. The demonstration that opioid receptors, most notably ₁, which not only have analgesic properties but may have the potential to protect the myocardium during cardiac surgical interventions, suggests a possible new pharmacological approach for the treatment of patients with acute myocardial infarction.

	Acknowledgments

 
This study was supported by NIH grant HL-08311 and an Advanced Predoctoral fellowship from the PhMRA Foundation, Inc. The investigators would like to acknowledge James M. Fujimoto, PhD, for his helpful suggestions in designing the present study, Hiroshi Nagase, PhD, from Toray Industries, Inc, for his generous donations of the opioid receptor antagonists BNTX, NTB, and ß-FNA, and Jeannine Moore for her excellent technical assistance.

Received August 21, 1997; revision received October 14, 1997; accepted October 31, 1997.

	References

Top Abstract Introduction Methods Results Discussion References

 
1. Lord JAH, Waterfield AA, Hughes J, Kosterlitz HW. Endogenous opioid peptides: multiple agonists and receptors. Nature. 1977;267:495–500.[Medline] [Order article via Infotrieve]

2. Miller RJ. Multiple opiate receptors for multiple opioid peptides. Med Biol. 1982;60:1–6.[Medline] [Order article via Infotrieve]

3. Paterson SJ, Robson LE, Kosterlitz HW. Classification of opioid receptors. Br Med Bull. 1983;39:1–36.[Free Full Text]

4. Goldstein A, James IF. Multiple opioid receptors: criteria for identification and classification. Trends Pharmacol Sci. 1984;5:503–505.

5. Dhawan BN, Cesselin F, Raghubir R, Reisine T, Bradley PB, Portoghese PS, Hamon M. International union of pharmacology XII: classification of opioid receptors. Pharmacol Rev. 1996;48:567–592.[Medline] [Order article via Infotrieve]

6. Jiang Q, Takemori AE, Sultana M, Portoghese PS, Bowen WD, Mosberg HI, Porreca F. Differential antagonism of opioid delta antinociception by [D-Ala,² Leu,⁵ Cys⁶]enkephalin and naltrindole 5-isothiocyanate: evidence for delta receptor subtypes. J Pharmacol Exp Ther. 1991;257:1069–1075.[Abstract/Free Full Text]

7. Mattia A, Vanderah T, Mosberg HI, Porreca F. Lack of antinociceptive cross-tolerance between [D-Pen,² D-Pen⁵]enkephalin and [D-Ala²]deltorphin II in mice: evidence for delta receptor subtypes. J Pharmacol Exp Ther. 1991;258:583–587.[Abstract/Free Full Text]

8. Sofuoglu M, Portoghese PS, Takemori AE. Differential antagonism of delta opioid agonists by naltrindole and its benzofuran analog (NTB) in mice: evidence for delta opioid receptor subtypes. J Pharmacol Exp Ther. 1991;257:676–680.[Abstract/Free Full Text]

9. Arrigo-Reina R, Ferri S. Evidence for an involvement of the opioid peptidergic system in the reaction to stressful condition. Eur J Pharmacol. 1980;64:85–88.[Medline] [Order article via Infotrieve]

10. Ferri S, Arrigo-Reina R, Candeletti S, Costa S, Murari G, Speroni E, Scoto G. Central and peripheral sites of action for the protective effect of opioids on the rat stomach. Pharmacol Res Commun. 1983;15:409–418.[Medline] [Order article via Infotrieve]

11. Ferri S, Speroni E, Candeletti S, Cavicchini E, Romualdi P, Govoni P, Marchini M. Protection by opioids against gastric lesions caused by necrotizing agents. Pharmacology. 1988;36:140–144.[Medline] [Order article via Infotrieve]

12. Mayfield KP, D'Alecy LG. Role of endogenous opioid peptides in the acute adaptation to hypoxia. Brain Res. 1992;582:226–231.[Medline] [Order article via Infotrieve]

13. Chien S, Oeltgen PR, Diana JN, Salley RK. Extension of tissue survival time in multiorgan block preparation with a delta opioid DADLE ([D-Ala,² D-Leu⁵]-enkephalin). J Thorac Cardiovasc Surg. 1994;107:964–967.[Free Full Text]

14. Mayfield KP, D'Alecy LG. Delta-1 opioid agonist acutely increases hypoxic tolerance. J Pharmacol Exp Ther. 1994;268:683–688.[Abstract/Free Full Text]

15. Mayfield KP, D'Alecy LG. Delta-1 opioid receptor dependence of acute hypoxic adaptation. J Pharmacol Exp Ther. 1994;268:74–77.[Abstract/Free Full Text]

16. Schultz JJ, Rose E, Yao Z, Gross GJ. Evidence for involvement of opioid receptors in ischemic preconditioning in rat hearts. Am J Physiol. 1995;268:H2157–H2161.[Abstract/Free Full Text]

17. Schultz JJ, Hsu AK, Gross GJ. Morphine mimics the cardioprotective effect of ischemic preconditioning via a glibenclamide-sensitive mechanism in the rat heart. Circ Res. 1996;78:1100–1104.[Abstract/Free Full Text]

18. Schultz JJ, Hsu AK, Gross GJ. Ischemic preconditioning and morphine-induced cardioprotection involve the delta ()-opioid receptor in the intact rat heart. J Mol Cell Cardiol. 1997;29:2187–2195.[Medline] [Order article via Infotrieve]

19. Chien GL, Van Winkle DM. Naloxone blockade of myocardial ischemic preconditioning is stereoselective. J Mol Cell Cardiol. 1996;28:1895–1900.[Medline] [Order article via Infotrieve]

20. Miki T, Downey J. Opioid receptors participate in ischemic preconditioning in rabbits. J Mol Cell Cardiol. 1996;28:A187. Abstract.

21. Holaday JW. Cardiovascular effects of endogenous opiate systems. Ann Rev Pharmacol Toxicol. 1983;23:541–594.[Medline] [Order article via Infotrieve]

22. Martin WR. Pharmacology of opioids. Pharmacol Rev. 1983;35:283–323.[Abstract]

23. Wong TM, Lee AYS, Tai KK. Effects of drugs interacting with opioid receptors during normal perfusion or ischemia and reperfusion in the isolated rat heart: an attempt to identify cardiac opioid receptor subtype(s) involved in arrhythmogenesis. J Mol Cell Cardiol. 1990;22:1167–1175.[Medline] [Order article via Infotrieve]

24. Siren A-L, Feuerstein G. The opioid system in circulatory control. News Physiol Sci. 1992;7:26–30.[Abstract/Free Full Text]

25. Klein HH, Puschmann S, Schaper J, Schaper W. The mechanism of the tetrazolium reaction in identifying myocardial infarction. Virchows Arch. 1981;393:287–297.

26. Portoghese PS, Sultana M, Nagase H, Takemori AE. A highly selective ₁-opioid receptor antagonist: 7-benzylidenenaltrexone. Eur J Pharmacol. 1992;218:195–196.[Medline] [Order article via Infotrieve]

27. Takemori AE, Sultana M, Nagase H, Portoghese PS. Agonist and antagonist activities of ligands derived from naltrexone and oxymorphone. Life Sci. 1992;50:1491–1495.[Medline] [Order article via Infotrieve]

28. Sofuoglu M, Portoghese PS, Takemori AE. 7-benzylidenenaltrexone (BNTX): a selective 1 opioid receptor antagonist in the mouse spinal cord. Life Sci. 1993;52:769–775.[Medline] [Order article via Infotrieve]

29. Takemori AE, Larson DL, Portoghese PS. The irreversible narcotic antagonistic and reversible agonistic properties of the fumarate methyl ester derivative of naltrexone. Eur J Pharmacol. 1981;70:445–451.[Medline] [Order article via Infotrieve]

30. Ward SJ, Portoghese PS, Takemori AE. Pharmacological characterization in vivo of the novel opiate, ß-Funaltrexamine. J Pharmacol Exp Ther. 1982;220:494–498.[Abstract/Free Full Text]

31. Portoghese PS, Lipkowski AW, Takemori AE. Bimorphinans as highly selective, potent opioid receptor antagonists. J Med Chem. 1987;30:238–239.[Medline] [Order article via Infotrieve]

32. Portoghese PS, Lipkowski AW, Takemori AE. Binaltorphimine and nor-Binaltorphimine, potent and selective -opioid receptor antagonists. Life Sci. 1987;40:1287–1292.[Medline] [Order article via Infotrieve]

33. Ela C, Barg J, Vogel Z, Hasin Y, Eilam Y. Distinct components of morphine effects on cardiac myocytes are mediated by the and opioid receptors. J Mol Cell Cardiol. 1997;29:711–720.[Medline] [Order article via Infotrieve]

34. Jiang Q, Mosberg HI, Porreca F. Modulation of the potency and efficacy of mu-mediated antinociception by delta agonists in the mouse. J Pharmacol Exp Ther. 1990;254:683–689.[Abstract/Free Full Text]

35. Schoffelmeer ANM, Yao Y-H, Gioannini TL, Hiller JM, Ofri D, Roques BP, Simon EJ. Cross-linking of human [¹²⁵I]ß-endorphin to opioid receptors in rat striatal membranes: biochemical evidence for the existence of a mu/delta opioid receptor complex. J Pharmacol Exp Ther. 1990;253:419–426.[Abstract/Free Full Text]

36. Sheldon RJ, Nunan L, Porreca F. Differential modulation by [D-Pen,² D-Pen⁵]-enkephalin and dynorphin A-(1–17) of the inhibitory bladder motility effects of selected mu agonists in vivo. J Pharmacol Exp Ther. 1989;249:462–469.[Abstract/Free Full Text]

37. Traynor JR, Elliott J. -Opioid receptor subtypes and cross-talk with µ-receptors. Trends Pharmacol Sci. 1993;14:84–86.[Medline] [Order article via Infotrieve]

38. Krumins SA, Faden AI, Feuerstein G. Opiate binding in rat hearts: modulation of binding after hemorrhagic shock. Biochem Biophys Res Commun. 1985;127:120–128.[Medline] [Order article via Infotrieve]

39. Ventura C, Bastagli L, Bernardi P, Caldarera CM, Guarnieri C. Opioid receptors in rat cardiac sarcolemma: effect of phenylephrine and isoproterenol. Biochim Biophys Acta. 1989;987:69–74.[Medline] [Order article via Infotrieve]

40. Ventura C, Spurgeon H, Lakatta EG, Guarnieri C, Capogrossi MC. and Opioid receptor stimulation affects cardiac myocyte function and Ca²⁺ release from an intracellular pool in myocytes and neurons. Circ Res. 1992;70:66–81.[Abstract/Free Full Text]

41. Zimlichman R, Gefel D, Eliahou H, Matas Z, Rosen B, Gass S, Ela C, Eilam Y, Vogel Z, Barg J. Expression of opioid receptors during heart ontogeny in normotensive and hypertensive rats. Circulation. 1996;93:1020–1025.[Abstract/Free Full Text]

42. Xia Q, Zhang W-M, Shen Y-L, Wong TM. Decreased affinity of -receptor binding during reperfusion following ischaemic preconditioning in the rat heart. Life Sci. 1996;58:1307–1313.[Medline] [Order article via Infotrieve]

43. Niroomand F, Mura RA, Piacentini L, Kubler W. Opioid receptor agonists activate pertussis toxin-sensitive G proteins and inhibit adenylyl cyclase in canine cardiac sarcolemma. Naunyn Schmiedebergs Arch Pharmacol. 1996;354:643–649.[Medline] [Order article via Infotrieve]

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				R. M. Fryer, A. K. Hsu, J. T. Eells, H. Nagase, and G. J. Gross Opioid-Induced Second Window of Cardioprotection : Potential Role of Mitochondrial KATP Channels Circ. Res., April 16, 1999; 84(7): 846 - 851. [Abstract] [Full Text] [PDF]

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