title: Adenosine exerts a glycogen-sparing action in contracting rat skeletal muscle.
abstract: The role of adenosine in regulating glycogen breakdown during electrically induced muscle contractions was investigated in isolated rat hindquarters perfused with a standard medium either lacking or containing 100 microU/ml insulin and/or 1.67 nM isoprenaline. Nonselective A1/A2-adenosine receptor antagonism via caffeine enhanced (P < 0.05) glycogen breakdown in contracting fast-oxidative (FO) fibers by 40%, provided they were exposed to both insulin and isoprenaline. Combined A1/A2-receptor antagonism by 8-cyclopentyl-1,3-dipropylxanthine (CPDPX) plus 3,7-dimethyl-1-proparglyxanthine (DMPX) fully reproduced (P < 0.05) this stimulatory effect. Furthermore, CPDPX plus DMPX also enhanced (P < 0.05) glycogenolysis during contractions in soleus but not in white gastrocnemius muscle. In contrast, CPDPX or DMPX alone did not affect glycogenolysis in either fiber type. Muscle adenosine 3',5'-cyclic monophosphate concentration during contractions was increased (P < 0.05) by CPDPX plus DMPX in both fiber types, whereas glycogen synthase fractional activity was depressed (P < 0.05). Phosphorylase activity was not changed by CPDPX plus DMPX. It is concluded that adenosine exerts a glycogen-sparing action in oxidative skeletal muscle exposed to both insulin and beta-adrenergic stimulation during contraction, presumably via stimulation of glycogen synthase activity.
authors.affiliation: Department of Kinesiology, Faculty of Physical Education and Physiotherapy, Katholieke Universiteit Leuven, Belgium.
authors.forename: L
authors.initials: L
authors.lastname: Vergauwen
authors.forename: E A
authors.initials: EA
authors.lastname: Richter
authors.forename: P
authors.initials: P
authors.lastname: Hespel
mesh_terms: D000241:Adenosine / Q000494:pharmacology*; D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism; D004338:Drug Combinations; D006003:Glycogen / Q000378:metabolism*; D006006:Glycogen Synthase / Q000378:metabolism; D008297:Male; D009119:Muscle Contraction; D018482:Muscle, Skeletal / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D010762:Phosphorylase a / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D013805:Theobromine / Q000031:analogs & derivatives / Q000494:pharmacology; D014970:Xanthines / Q000494:pharmacology
chemical_list: D004338:Drug Combinations; D014970:Xanthines; D002110:Caffeine; C057837:3,7-dimethyl-1-propargylxanthine; D006003:Glycogen; C051360:1,3-dipropyl-8-cyclopentylxanthine; D000242:Cyclic AMP; D010762:Phosphorylase a; D006006:Glycogen Synthase; D000241:Adenosine; D013805:Theobromine