The cardioprotective effect of preconditioning is associated with
glycogen depletion and attenuation of intracellular
acidosis during subsequent prolonged
ischemia. This study determined the effects of increasing 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 depletion before prolonged
ischemia. Anesthetized rats underwent a single episode of preconditioning lasting 1.25, 2.5, 5, or 10 minutes or multiple 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 45 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 and
phthalocyanine blue dye.
Glycogen levels were determined by an enzymatic assay in selected rats from each group before prolonged
ischemia. We found that increasing preconditioning
ischemia time resulted in
glycogen depletion and
infarct size reduction that could both be described by exponential functions. Furthermore,
infarct size reduction correlated with
glycogen depletion before prolonged
ischemia (r = 0.98; p < 0.01). These findings suggest a role for
glycogen depletion in reducing ischemic injury in the preconditioned heart.