title: δ-Opioid receptor (DOR) signaling and reactive oxygen species (ROS) mediate intermittent hypoxia induced protection of canine myocardium.
abstract: Intermittent, normobaric hypoxia confers robust cardioprotection against ischemia-induced myocardial infarction and lethal ventricular arrhythmias. δ-Opioid receptor (DOR) signaling and reactive oxygen species (ROS) have been implicated in cardioprotective phenomena, but their roles in intermittent hypoxia are unknown. This study examined the contributions of DOR and ROS in mediating intermittent hypoxia-induced cardioprotection. Mongrel dogs completed a 20 day program consisting of 5-8 daily, 5-10 min cycles of moderate, normobaric hypoxia (FIO2 0.095-0.10), with intervening 4 min room air exposures. Subsets of dogs received the DOR antagonist naltrindole (200 μg/kg, sc) or antioxidant N-acetylcysteine (250 mg/kg, po) before each hypoxia session. Twenty-four hours after the last session, the left anterior descending coronary artery was occluded for 60 min and then reperfused for 5 h. Arrhythmias detected by electrocardiography were scored according to the Lambeth II conventions. Left ventricles were sectioned and stained with 2,3,5-triphenyl-tetrazolium-chloride, and infarct sizes were expressed as percentages of the area at risk (IS/AAR). Intermittent hypoxia sharply decreased IS/AAR from 41 ± 5 % (n = 12) to 1.8 ± 0.9 % (n = 9; P < 0.001) and arrhythmia score from 4.1 ± 0.3 to 0.7 ± 0.2 (P < 0.001) vs. non-hypoxic controls. Naltrindole (n = 6) abrogated the cardioprotection with IS/AAR 35 ± 5 % and arrhythmia score 3.7 ± 0.7 (P < 0.001 vs. untreated intermittent hypoxia). N-acetylcysteine (n = 6) interfered to a similar degree, with IS/AAR 42 ± 3 % and arrhythmia score 4.7 ± 0.3 (P < 0.001 vs. untreated intermittent hypoxia). Without the intervening reoxygenations, hypoxia (n = 4) was not cardioprotective (IS/AAR 50 ± 8 %; arrhythmia score 4.5 ± 0.5; P < 0.001 vs. intermittent hypoxia). Thus DOR, ROS and cyclic reoxygenation were obligatory participants in the gradually evolving cardioprotection produced by intermittent hypoxia.
authors.affiliation: Institute of Cardiovascular and Metabolic Diseases, University of North Texas Health Science Center, Fort Worth, TX, USA.
authors.forename: Juan A
authors.initials: JA
authors.lastname: Estrada
authors.affiliation: Institute of Cardiovascular and Metabolic Diseases, University of North Texas Health Science Center, Fort Worth, TX, USA.
authors.forename: Arthur G
authors.initials: AG
authors.lastname: Williams
authors.affiliation: Institute of Cardiovascular and Metabolic Diseases, University of North Texas Health Science Center, Fort Worth, TX, USA.
authors.forename: Jie
authors.initials: J
authors.lastname: Sun
authors.affiliation: Institute of Cardiovascular and Metabolic Diseases, University of North Texas Health Science Center, Fort Worth, TX, USA.
authors.forename: Leticia
authors.initials: L
authors.lastname: Gonzalez
authors.affiliation: Institute of Cardiovascular and Metabolic Diseases, University of North Texas Health Science Center, Fort Worth, TX, USA.
authors.forename: H Fred
authors.initials: HF
authors.lastname: Downey
authors.affiliation: Institute of Cardiovascular and Metabolic Diseases, University of North Texas Health Science Center, Fort Worth, TX, USA.
authors.forename: James L
authors.initials: JL
authors.lastname: Caffrey
authors.affiliation: Institute of Cardiovascular and Metabolic Diseases, University of North Texas Health Science Center, Fort Worth, TX, USA. robert.mallet@unthsc.edu.
authors.forename: Robert T
authors.initials: RT
authors.lastname: Mallet
mesh_terms: D000111:Acetylcysteine; D000818:Animals; D001145:Arrhythmias, Cardiac / Q000378:metabolism / Q000517:prevention & control; D004285:Dogs; D005260:Female; D006400:Hematocrit; D000860:Hypoxia / Q000378:metabolism*; D019157:Ischemic Preconditioning, Myocardial / Q000379:methods*; D008297:Male; D009203:Myocardial Infarction / Q000378:metabolism / Q000473:pathology / Q000517:prevention & control*; D009206:Myocardium / Q000473:pathology; D009271:Naltrexone / Q000031:analogs & derivatives; D017382:Reactive Oxygen Species / Q000378:metabolism*; D017465:Receptors, Opioid, delta / Q000378:metabolism*
chemical_list: D017382:Reactive Oxygen Species; D017465:Receptors, Opioid, delta; D009271:Naltrexone; C055382:naltrindole; D000111:Acetylcysteine
keywords: Cardiac arrhythmias; Enkephalins; Myocardial infarction; N-acetylcysteine; Naltrindole