title: Opioid antagonism alters blood glucose homeostasis during exercise in humans.
abstract: In an attempt to clarify the role of endogenous opioid peptides in substrate mobilization and hormonal responses to dynamic exercise, eight trained cyclists completed exercise trials at 90% of maximal O2 consumption (VO2max) until exhaustion and at 70% VO2max for 90 min. Trials were conducted after intravenous administration of the opiate antagonist naloxone (NAL, 0.1 mg/kg bolus + 0.1 mg.kg-1.h-1) or volume-matched saline (SAL) at each intensity. Serum glucose was maintained at significantly higher levels at 60 and 90 min of exercise in the 70%-NAL than in the 70%-SAL trial and at all points during exercise and at 30 and 60 min of recovery in the 90%-NAL than in the 90%-SAL trial. The serum insulin response to exercise was not altered by NAL administration at either intensity. Serum C-peptide was approximately 50% higher at 60 and 90 min of exercise in the 70%-NAL than in the 70%-SAL trial but was significantly lower during exercise in the 90%-NAL than in the 90%-SAL trial. The plasma glucagon response to exercise at 70% VO2max was not altered by NAL administration but was significantly elevated in the 90%-NAL vs. the 90%-SAL trial. Plasma epinephrine was 50-150% (approximately 2-3 nM) higher during exercise from 30 to 90 min of exercise in the 70%-NAL than in the 70%-SAL trial and was higher at termination (4.9 +/- 2.1 vs. 2.7 +/- 1.7 nM) in the 90%-NAL than in the 90%-SAL trial, although the difference in the 90% trial was not statistically significant.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Human Performance Laboratory, Ball State University, Muncie, Indiana 47306.
authors.forename: M S
authors.initials: MS
authors.lastname: Hickey
authors.forename: S W
authors.initials: SW
authors.lastname: Trappe
authors.forename: A C
authors.initials: AC
authors.lastname: Blostein
authors.forename: B A
authors.initials: BA
authors.lastname: Edwards
authors.forename: B
authors.initials: B
authors.lastname: Goodpaster
authors.forename: B W
authors.initials: BW
authors.lastname: Craig
mesh_terms: D000328:Adult; D001642:Bicycling; D001786:Blood Glucose / Q000378:metabolism*; D002096:C-Peptide / Q000097:blood; D004723:Endorphins / Q000502:physiology*; D004837:Epinephrine / Q000097:blood*; D015444:Exercise / Q000502:physiology*; D005934:Glucagon / Q000097:blood; D006706:Homeostasis / Q000187:drug effects / Q000502:physiology*; D006801:Humans; D007328:Insulin / Q000097:blood; D008297:Male; D009270:Naloxone / Q000494:pharmacology*; D009638:Norepinephrine / Q000097:blood; D010101:Oxygen Consumption / Q000187:drug effects
chemical_list: D001786:Blood Glucose; D002096:C-Peptide; D004723:Endorphins; D007328:Insulin; D009270:Naloxone; D005934:Glucagon; D009638:Norepinephrine; D004837:Epinephrine