Role of adenosine and glycogen in ischemic preconditioning of rat hearts

Abstract We tested whether ischemic preconditioning of the rat heart is mediated by reduced glycogenolysis during ischemia, an event triggered by adenosine A 1 receptor activation. Rat hearts ( n =40) were studied with [ 31 P] and [ 13 C] nuclear magnetic resonance (NMR) spectroscopy, using the Langendorff perfusion technique (5.5 mM [1- 13 C]glucose, 10 U/l insulin). In parallel experiments, hearts ( n =43) were freeze-clamped at different time-points throughout the protocol. They were subjected to either ischemic preconditioning (PC), PC in the presence of 50 μM adenosine receptor antagonist, 8-( p -sulfophenyl)-theophylline (SPT), or intermittent infusion of 0.25 μM adenosine A 1 receptor agonist, 2-chloro- N 6 -cyclopentyladenosine (CCPA). After 30 min ischemia and reperfusion, recovery of heart rate×pressure product was improved in hearts treated with preconditioning (33±13%) or CCPA (58±14%) compared with the SPT and ischemic control (IC) groups, which both failed to recover ( P 13 C]glycogen ( P 13 C]glycogen decreased by 25 and 47%, respectively ( P P 13 C]glycogen utilization during the first 15 min of ischemia (in μmol/min g wwt) was not statistically different between IC (0.42±0.03), PC (0.30±0.04), and CCPA (0.38±0.05) hearts, but was reduced in SPT hearts (0.24±0.05; P