997-91 Glycogen Loading In Vivo Reverses Decreased Function After Ischemic Preconditioning In Vitro

We recently observed that glycogen loading of the heart in vivo improves ischemia tolerance to the same extent as ischemic preconditioning (IP). We have now tested the hypothesis that glycogen loading is beneficial in a protocol where IP per se is not effective. We perfused hearts from fed animals with bicarbonate buffer containing glucose (10mM). Five min IP with 5min preconditioning-reperfusion (IP5/5) or 10 min normoxic perfusion (Control, C) were preceded by a 15min stabilization period and followed by 15min global. no flow ischemia witl 30min of reperfusion. Glycogen loaded hearts came from fasted animals, were perfused with buffer containing glucose (10mM). lactate (10mM) and insulin (10mU/ml) and were subjected to the same protocol as IP5/5. Cardiac power and heart rate were assessed continuously. Postischemic recovery was assessed by postischemic power as % of preischemic power. Hearts were freeze-clamped for metabolites.ResultsGlycogen levels in vivo were higher in the glycogen loaded hearts than in C (140±4.5 vs. 70±6.6 μmol/g dry). IP5/5 did not improve postischemic recovery compared to C (68.5±3.7% vs. 71.4±3.5% of preischemic power, n=9 each). However, glycogen loading of this group resulted in a full return of cardiac power post ischemia (101±6.1%, n=8). Levels of glucose6-phosphate (G-6-P), pyruvate, and lactate were not different in IP5/5 and C and returned to preischemic levels with reperfusion. Glycogen loaded hearts maintained elevated G-6-P and lactate levels with reperfusion.ConclusionsGlycogen loading improves ischemia tolerance where IP fails to do so. Thus, glycogen or glycogen breakdown may playa crucial role in myocardial protection