Glycogen turnover and anaplerosis in preconditioned rat hearts

Using (13)C NMR, we tested the hypothesis that protection by preconditioning is associated with reduced glycogenolysis during ischemia. Preconditioned rat hearts showed improved postischemic function and reduced ischemic damage relative to ischemic controls after 30 min stop-flow ischemia and 30 min reperfusion (contractility: 30+/-10 vs. 2+/-2%; creatine kinase release: 41+/-4 vs. 83+/-15 U/g; both P<0.05). Preconditioning decreased preischemic [(13)C]glycogen by 24% (a 10% decrease in total glycogen), and delayed ischemic [(13)C]glycogen consumption by 5-10 min, reducing ischemic glycogenolysis without changing acidosis relative to controls. Upon reperfusion, glycogen synthesis resumed only after preconditioning. Glutamate (13)C-isotopomer analysis showed recovery of Krebs cycle activity with higher anaplerosis than before ischemia (23+/-4 vs. 11+/-3%, P<0.05), but in controls reperfusion failed to restore flux. Compared to control, preconditioning before 20 min ischemia increased contractility (86+/-10 vs. 29+/-14%, P<0.05) and restored preischemic anaplerosis (13+/-3 vs. 39+/-9%, P<0.05). Preconditioning is associated with reduced glycogenolysis early during ischemia. However, protection does not rely on major variations in intracellular pH, as proposed earlier. Our isotopomer data suggest that preconditioning accelerates metabolic and functional recovery during reperfusion by more efficient/active replenishment of the depleted Krebs cycle.