title: Effect of theophylline on substrate metabolism during exercise.
abstract: We tested the hypothesis that adenosine is involved in regulating substrate metabolism during exercise. Seven trained cyclists were studied during 30 minutes of exercise at approximately 75% maximal oxygen uptake (VO2max). Lipid metabolism was evaluated by infusing [2H5]glycerol and [1-13C]palmitate, and glucose kinetics were evaluated by infusing [6,6-2H]glucose. Fat and carbohydrate oxidation were also measured by indirect calorimetry. The same subjects performed two identical exercise tests, but in one trial theophylline, a potent adenosine receptor antagonist, was infused for 1 hour before and throughout exercise. Theophylline did not increase whole-body lipolysis (glycerol rate of appearance [Ra]) or free fatty acid (FFA) release during exercise, but fat oxidation was lower than control values (9.5 +/- 3.0 v 18.0 +/- 4.2 micromol x min(-1) x kg(-1), P < .01). Glucose Ra was not affected by theophylline infusion, but glucose uptake was lower (31.6 +/- 4.1 v 40.4 +/- 5.0 micromol x min(-1) x kg(-1), P < .05) and glucose concentration was higher (6.4 +/- 0.6 v 5.8 +/- 0.4 mmol/L, P < .05) than in the control trial. Total carbohydrate oxidation (302.3 +/- 26.2 v 265.5 +/- 11.7 micromol x min(-1) x kg(-1), P < .06), estimated muscle glycogenolysis (270.7 +/- 23.1 v 225.1 +/- 9.7 micromol x min(-1) x kg(-1), P < .05), and plasma lactate concentration (7.9 +/- 1.6 v 5.9 +/- 1.1 mmol/L, P < .001) were also higher during the theophylline trial. These data suggest that adenosine may play a role in stimulating glucose uptake and restraining glycogenolysis but not in limiting lipolysis during exercise.
authors.affiliation: Metabolism Unit, Shriners Burns Institute, Galveston, TX 77550, USA.
authors.forename: C A
authors.initials: CA
authors.lastname: Raguso
authors.forename: A R
authors.initials: AR
authors.lastname: Coggan
authors.forename: L S
authors.initials: LS
authors.lastname: Sidossis
authors.forename: A
authors.initials: A
authors.lastname: Gastaldelli
authors.forename: R R
authors.initials: RR
authors.lastname: Wolfe
mesh_terms: D000328:Adult; D001786:Blood Glucose / Q000378:metabolism; D002395:Catecholamines / Q000097:blood; D004734:Energy Metabolism; D015444:Exercise / Q000502:physiology*; D005260:Female; D005934:Glucagon / Q000097:blood; D005947:Glucose / Q000008:administration & dosage / Q000378:metabolism; D005990:Glycerol / Q000008:administration & dosage / Q000097:blood; D006003:Glycogen / Q000378:metabolism; D006801:Humans; D007328:Insulin / Q000097:blood; D008297:Male; D009132:Muscles / Q000378:metabolism; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D058915:Purinergic P1 Receptor Antagonists; D013806:Theophylline / Q000494:pharmacology*
chemical_list: D001786:Blood Glucose; D002395:Catecholamines; D007328:Insulin; D010726:Phosphodiesterase Inhibitors; D058915:Purinergic P1 Receptor Antagonists; D006003:Glycogen; D005934:Glucagon; D013806:Theophylline; D005947:Glucose; D005990:Glycerol