European Journal of Applied Physiology

, Volume 86, Issue 1, pp 92–96 | Cite as

Beta-endorphin immunoreactivity during high-intensity exercise with and without opiate blockade

  • Theodore J. Angelopoulos
Original Article


Nine highly fit men [mean (SE) maximum oxygen uptake, \(\dot V{\rm O}_{{\rm 2max}} \) : 63.9 (1.7) ml·kg–1·min–1; age 27.6 (1.6) years] were studied during two treadmill exercise trials to determine plasma β-endorphin immunoreactivity during intense exercise (80% \(\dot V{\rm O}_{{\rm 2max}} \) ). 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 mg; 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. β-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. β-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·ml–1 vs 78.7 (3.8) pg·ml–1; 20 min: 68.7 (4.1) pg·ml–1 vs 83.8 (4.3) pg·ml–1; 30 min: 71.0 (4.3) pg·ml–1 vs 82.5 (3.2) pg·ml–1]. These data suggest that intense exercise induces significant increases in β-endorphin that are maintained over time during steady-rate exercise. Exercise and naloxone had an interactive effect on β-endorphin release that warrants further investigation.

β-Endorphin Naloxone Placebo Exercise Man 


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Copyright information

© Springer-Verlag 2001

Authors and Affiliations

  • Theodore J. Angelopoulos
    • 1
  1. 1.Exercise Physiology Laboratory, University of Central Florida, College of Education ED 214, Orlando, FL 32816-1250USA

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