Failure of glycogen depletion to improve left ventricular function of the rabbit heart after hypothermic ischemic arrest.

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Abstract
We tested the hypothesis that depletion of glycogen prior to myocardial ischemia diminishes lactate buildup and improves functional recovery on reperfusion in the isolated rabbit heart. Cardiac glycogen was reduced either by substituting N2 for O2 in the perfusate or by perfusion with substrate-free solution, before the onset of ischemia. Hearts were subjected to either 30 minutes of normothermic (37 degrees C) or 60 minutes of hypothermic (4 degrees C) ischemia followed by 30 minutes of reperfusion with oxygenated Krebs-Henseleit buffer. Function was assessed by measuring peak left ventricular pressure at end-diastolic pressures ranging from 0 to 20 mm Hg. N2 perfusion for 15 minutes lowered myocardial glycogen by 60% and decreased ATP and phosphocreatine (p less than 0.001). Glycogen depletion did not decrease lactate accumulation during ischemia, but it impaired recovery with reperfusion (-46%, p less than 0.05). N2 perfusion for 5 minutes also reduced glycogen by 60%, but energy-rich phosphates were not reduced and functional recovery was still impaired (-40%, p less than 0.05). Perfusion with substrate-free medium diminished glycogen by 33% (p less than 0.05). Although lactate accumulation was significantly reduced (-45%, p less than 0.05), recovery following reperfusion was not improved. The results suggest that preservation of glycogen stores, but not the prevention of lactate buildup during ischemia, is beneficial for the recovery of function with reperfusion.