PRECONDITIONING ISCHEMIA TIME DETERMINES THE DEGREE OF GLYCOGEN DEPLETION AND INFARCT SIZE-REDUCTION IN RAT HEARTS

The cardioprotective effect of preconditioning is associated with glyc ogen depletion and attenuation of intracellular acidosis during subseq uent prolonged ischemia. This study determined the effects of increasi ng preconditioning ischemia time on myocardial glycogen depletion and on infarct size reduction. In addition, this study determined whether infarct size reduction by preconditioning correlates with glycogen dep letion before prolonged ischemia. Anesthetized rats underwent a single episode of preconditioning lasting 1.25, 2.5, 5, or 10 minutes or mul tiple episodes cumulating in 10 (2 x 5 min) or 20 minutes (4 x 5 or 2 x 10 min) of preconditioning ischemia time, each followed by 5 minutes of reperfusion. Then both preconditioned and control rats underwent 4 5 minutes of ischemia induced by left coronary artery (LCA) occlusion and 120 minutes of reperfusion. After prolonged ischemia, infarct size was determined by dual staining with triphenyltetrazolium chloride an d phthalocyanine blue dye. Glycogen levels were determined by an enzym atic assay in selected rats from each group before prolonged ischemia. We found that increasing preconditioning ischemia time resulted in gl ycogen depletion and infarct size reduction that could both be describ ed by exponential functions. Furthermore, infarct size reduction corre lated with glycogen depletion before prolonged ischemia (r = 0.98; p < 0.01). These findings suggest a role for glycogen depletion in reduci ng ischemic injury in the preconditioned heart.