title: Exercise enhances myocardial ischemic tolerance via an opioid receptor-dependent mechanism.
abstract: Exercise increases serum opioid levels and improves cardiovascular health. Here we tested the hypothesis that opioids contribute to the acute cardioprotective effects of exercise using a rat model of exercise-induced cardioprotection. For the standard protocol, rats were randomized to 4 days of treadmill training and 1 day of vigorous exercise (day 5), or to a sham exercise control group. On day 6, animals were killed, and global myocardial ischemic tolerance was assessed on a modified Langendorff apparatus. Twenty minutes of ischemia followed by 3 h of reperfusion resulted in a mean infarct size of 42 +/- 4% in hearts from sham exercise controls and 21 +/- 3% (P < 0.001) in the exercised group. The cardioprotective effects of exercise were gone by 5 days after the final exercise period. To determine the role of opioid receptors in exercise-induced cardioprotection, rats were exercised according to the standard protocol; however, just before exercise on days 4 and 5, rats were injected subcutaneously with 10 mg/kg of the opioid receptor antagonist naltrexone. Similar injections were performed in the sham exercise control group. Naltrexone had no significant effect on baseline myocardial ischemic tolerance in controls (infarct size 43 +/- 4%). In contrast, naltrexone treatment completely blocked the cardioprotective effect of exercise (infarct size 40 +/- 5%). Exercise was also associated with an early increase in myocardial mRNA levels for several opioid system genes and with sustained changes in a number of genes that regulate inflammation and apoptosis. These findings demonstrate that the acute cardioprotective effects of exercise are mediated, at least in part, through opioid receptor-dependent mechanisms that may include changes in gene expression.
authors.affiliation: Department of Emergency Medicine, University of Iowa Hospitals and Clinics, 200 Hawkins Drive, Iowa City, IA 52242-1009, USA. eric-dickson@uiowa.edu
authors.forename: Eric W
authors.initials: EW
authors.lastname: Dickson
authors.forename: Christopher P
authors.initials: CP
authors.lastname: Hogrefe
authors.forename: Paula S
authors.initials: PS
authors.lastname: Ludwig
authors.forename: Laynez W
authors.initials: LW
authors.lastname: Ackermann
authors.forename: Lynn L
authors.initials: LL
authors.lastname: Stoll
authors.forename: Gerene M
authors.initials: GM
authors.lastname: Denning
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000235:genetics; D004195:Disease Models, Animal; D015870:Gene Expression; D007249:Inflammation / Q000235:genetics / Q000378:metabolism; D008297:Male; D017202:Myocardial Ischemia / Q000150:complications / Q000235:genetics / Q000378:metabolism / Q000473:pathology / Q000517:prevention & control*; D015428:Myocardial Reperfusion Injury / Q000209:etiology / Q000235:genetics / Q000378:metabolism / Q000473:pathology / Q000517:prevention & control*; D009206:Myocardium / Q000378:metabolism* / Q000473:pathology; D009271:Naltrexone / Q000494:pharmacology; D009292:Narcotic Antagonists / Q000494:pharmacology; D018847:Opioid Peptides / Q000235:genetics / Q000378:metabolism*; D005082:Physical Exertion; D011498:Protein Precursors / Q000235:genetics / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D011957:Receptors, Opioid / Q000235:genetics / Q000378:metabolism*; D013997:Time Factors
chemical_list: D009292:Narcotic Antagonists; D018847:Opioid Peptides; D011498:Protein Precursors; D012333:RNA, Messenger; D011957:Receptors, Opioid; D009271:Naltrexone