Abstract 1144: Diazoxide and Ischemic Preconditioning Enhance Phosphorylation of GSK-3β During Myocardial Ischemia in Pigs
Introduction: Phosphorylation at serine-9 residue (Ser9) and subsequent inactivation of GSK-3β via the Akt/PI3-Kinase pathway was recently shown to play an important role in the protection and enhanced cell survival afforded by ischemic preconditioning (PC) in isolated rat hearts.
Hypothesis: We assessed the hypothesis that cardioprotective doses of PC or pharmacological preconditioning with diazoxide alter GSK-3β phosphorylation in an in vivo swine model subsequently exposed to regional ischemia.
Methods: Barbital-anesthetized open-chest pigs underwent 15 min complete occlusion of the left anterior descending coronary artery, a period that produces minimal necrosis. Hearts treated with PC were subjected to two cycles of 5 min ischemia and 10 min reflow prior to test ischemia. Pharmacologically preconditioned hearts were infused with a cardioprotective dose of diazoxide (3.5 mg/kg, 1 ml/min i.v.) prior to occlusion. Proteins were extracted from transmural ischemic and nonischemic regions of left ventricular tissue. Western blot analysis was performed on three groups of hearts (n=5 each group) subjected to control (no pretreatment), PC, or diazoxide treatment.
Results: Both PC and diazoxide caused a significant and consistent increase in GSK-3β phosphorylation in subepicardial, midmyocardial, and subendocardial ischemic regions compared to time-matched control tissue. These studies provide the first evidence linking PC and diazoxide treatment to GSK-3β phosphorylation in an intact large animal model.
Conclusion: These data are consistent with a cardioprotective role for inactivation of GSK-3β by these interventions, and indicate that the protective cellular mechanism may be in place during the period of sustained ischemia and prior to final reperfusion. Pharmacological modulation of GSK-3β activity could have utility for protecting the myocardium against ischemic injury.