Opioid Antagonism, Perceived Exertion and Tolerance to Exercise-Thermal Stress

• Published in: International journal of sports medicine 1992-05, Vol.13 (4), p.326-331
• Main Authors: Hickey, M. S., Franke, W. D., Herbert, W. G., Walberg-Rankin, J., Lee, J. C.
• Format: Article
• Language: English
• Subjects: Adult; Analysis of Variance; Biological and medical sciences; Forearm - blood supply; Fundamental and applied biological sciences. Psychology; Hemodynamics; Hot Temperature - adverse effects; Humans; Male; Naloxone - administration & dosage; Naloxone - antagonists & inhibitors; Oxygen Consumption; Physical Exertion - physiology; Receptors, Opioid - drug effects; Receptors, Opioid - physiology; Vertebrates: body movement. Posture. Locomotion. Flight. Swimming. Physical exercise. Rest. Sports
• ISSN: 0172-4622; 1439-3964
• DOI: 10.1055/s-2007-1021275

Abstract In an attempt to investigate the physiological responses to opioid receptor blockade during exercise in the heat, five male volunteers completed two bouts of stationary cycling at 70% V̇O 2 max in a hot (33 °C765% RH) environment. Exercise was conducted following the administration of either naloxone or saline (4 mg i. v.) five minutes prior to exercise. A second 4 mg dose was administered at 25 minutes of exercise. Performance time was 11% shorter (p = 0.06), and RPE response was significantly higher at test termination on naloxone. No drug effect was observed on rectal or mean skin temperature during exercise. Forearm blood flow (FBF) was higher on naloxone, while exercise heart rates were lower on the drug versus saline. No significant changes were observed in estimated mean arterial pressure or gross sweat responses to exercise. Plasma immunoreactive β-endorphin was significantly elevated in the naloxone trial only. Thus, while opioids may play some hemodynamic role during exercise in the heat, it appears that opioid mediation of the perceived stress of exercise contributes more to an individual's thermal tolerance. Additionally, the results suggest that perceptual and hemodynamic/cardiovascular responses that may be mediated by these peptides are dissociable phenomena.