title: beta-Endorphin and natural killer cell cytolytic activity during prolonged exercise. is there a connection?
abstract: This study was designed to test whether a single 50-mg dose of the opioid antagonist naltrexone hydrochloride, ingested 60 min before 2 h of moderate-intensity exercise (i.e., 65% peak O2 consumption), influenced the exercise-induced augmentation of peripheral blood natural killer cell cytolytic activity (NKCA). Ten healthy male subjects were tested on four occasions separated by intervals of at least 14 days. A rested-state control trial was followed by three double-blind exercise trials [placebo (P), naltrexone (N), and indomethacin] arranged according to a random block design. The indomethacin exercise trial is discussed elsewhere (S. G. Rhind, G. A. Gannon, P. N. Shek, and R. J. Shepherd. Med. Sci. Sports Exerc. 30: S20, 1998). For both the P and N trials, plasma levels of beta-endorphin were increased (P < 0.05) at 90 and 120 min of exercise but returned to resting (preexercise) levels 2 h postexercise. CD3(-)CD16(+)CD56(+) NK cell counts and NKCA were significantly (P < 0.05) elevated at each 30-min interval of exercise compared with correspondingly timed resting control values. However, there were no differences in NK cell counts or NKCA between P and N trials at any time point during the two trials. Changes in NKCA reflected mainly changes in NK cell count (r = 0.72; P < 0.001). The results do not support the hypothesis that the enhancement of NKCA during prolonged submaximal aerobic exercise is mediated by beta-endorphin.
authors.affiliation: Graduate Programme in Exercise Sciences, University of Toronto, Toronto M5S 1A1, Canada L2S 3A1.
authors.forename: G A
authors.initials: GA
authors.lastname: Gannon
authors.forename: S G
authors.initials: SG
authors.lastname: Rhind
authors.forename: M
authors.initials: M
authors.lastname: Suzui
authors.forename: J
authors.initials: J
authors.lastname: Zamecnik
authors.forename: B H
authors.initials: BH
authors.lastname: Sabiston
authors.forename: P N
authors.initials: PN
authors.lastname: Shek
authors.forename: R J
authors.initials: RJ
authors.lastname: Shephard
mesh_terms: D000328:Adult; D015703:Antigens, CD / Q000032:analysis; D015815:Cell Adhesion Molecules / Q000378:metabolism; D004311:Double-Blind Method; D006801:Humans; D007213:Indomethacin / Q000494:pharmacology; D007694:Killer Cells, Natural / Q000166:cytology / Q000276:immunology / Q000502:physiology*; D018655:Lymphocyte Count; D008297:Male; D009000:Monocytes / Q000166:cytology; D009271:Naltrexone / Q000031:analogs & derivatives / Q000097:blood / Q000494:pharmacology; D009292:Narcotic Antagonists / Q000494:pharmacology; D009490:Neurosecretory Systems / Q000502:physiology; D005082:Physical Exertion; D013997:Time Factors; D001615:beta-Endorphin / Q000097:blood*
chemical_list: D015703:Antigens, CD; D015815:Cell Adhesion Molecules; D009292:Narcotic Antagonists; C010410:6 beta-hydroxynaltrexone; D009271:Naltrexone; D001615:beta-Endorphin; D007213:Indomethacin