title: Beta-endorphin immunoreactivity during high-intensity exercise with and without opiate blockade.
abstract: Nine highly fit men [mean (SE) maximum oxygen uptake, VO2max: 63.9 (1.7) ml x kg(-1) x min(-1); age 27.6 (1.6) years] were studied during two treadmill exercise trials to determine plasma beta-endorphin immunoreactivity during intense exercise (80% VO2max). A double-blind experimental design was used, and subjects performed the two exercise trials in counterbalanced order. Exercise trials were 30 min in duration and were conducted 7 days apart. One exercise trial was undertaken following administration of naloxone (1.2 3 cm3) and the other after receiving a placebo (0.9% NaCl saline; 3 cm3). Prior to each experimental trial, a flexible catheter was placed into an antecubital vein and baseline blood samples were collected. Thereafter, each subject received either a naloxone or placebo bolus injection. Blood samples were also collected after 10, 20 and 30 min of continuous exercise. beta-Endorphin was higher (P < 0.05) during exercise when compared to pre-exercise in both trials. However, no statistically significant difference was found (P> 0.05) between exercise time points within either experimental trial. beta-endorphin immunoreactivity was greater (P < 0.05) in the naloxone than in the placebo trial during each exercise sampling time point [10 min: 63.7 (3.9) pg x ml(-1) vs 78.7 (3.8) pg x ml(-1); 20 min: 68.7 (4.1) pg x ml(-1) vs (4.3) pg x ml(-1); 30 min: 71.0 (4.3) pg x ml(-1) vs 82.5(3.2) pg x ml(-1)]. These data suggest that intense exer induces significant increases in beta-endorphin that are maintained over time during steady-rate exercise. Exercise and naloxone had an interactive effect on beta-endorphin release that warrants further investigation.
authors.affiliation: Exercise Physiology Laboratory, University of Central Florida, College of Education, Orlando 32816-1250, USA. tangelop@maimi.ucf.edu
authors.forename: T J
authors.initials: TJ
authors.lastname: Angelopoulos
mesh_terms: D000328:Adult; D015444:Exercise / Q000502:physiology*; D006339:Heart Rate / Q000502:physiology; D006400:Hematocrit; D006801:Humans; D008297:Male; D009270:Naloxone / Q000008:administration & dosage*; D009292:Narcotic Antagonists / Q000008:administration & dosage*; D010100:Oxygen / Q000097:blood; D010101:Oxygen Consumption / Q000187:drug effects / Q000502:physiology; D001615:beta-Endorphin / Q000032:analysis / Q000097:blood* / Q000276:immunology
chemical_list: D009292:Narcotic Antagonists; D009270:Naloxone; D001615:beta-Endorphin; D010100:Oxygen