Investigating the Signal Transduction Pathways Underlying Remote Ischemic Conditioning in the Porcine Heart

The mechanism underlying remote ischemic conditioning (RIC) remains unclear. We investigated whether RIC protects the heart through the activation of the adenosine receptor and the PI3K-Akt pathway at the onset of myocardial reperfusion. Domestic pigs (27-35 kg) were subjected to in situ left anterior descending coronary artery ischemia (60 min) followed by reperfusion (180 min) and randomised to the following: (1) Control- No additional intervention; (2) Remote ischemic preconditioning (RIPC)- Four-5 min cycles of lower limb ischemia/reperfusion were administered prior to myocardial ischemia; (3) RIPC + Wort or 8-SPT: Wortmannin (Wort 20 mu g/kg, a PI3K inhibitor) or 8-sulfophenyltheophylline (8-SPT 10 mg/kg, an adenosine receptor inhibitor) were administered intravenously 30 s before myocardial reperfusion to RIPC-treated animals; (4) Remote ischemic perconditioning (RIPerC)- Four-5 min cycles of lower limb ischemia/reperfusion were applied 1 min before myocardial reperfusion; (5) RIPerC + Wort or 8-SPT: Wort or 8-SPT were given 30 s before myocardial reperfusion to RIPerC-treated animals. Both RIPC and RIPerC reduced myocardial infarct size (13.3 +/- 2.2% with RIPC, 18.2 +/- 2.0% with RIPerC versus 48.8 +/- 4.2% in control:P < 0.05:N a parts per thousand yenaEuro parts per thousand 5/group). Wortmannin abolished the infarct-limiting effects of RIPC (33.2 +/- 6% with RIPC + Wort versus 13.3 +/- 2.2% with RIPC:P < 0.05:N a parts per thousand yenaEuro parts per thousand 5/group) but not RIPerC (18.0 +/- 3.4% with RIPerC + Wort versus 18.2 +/- 2.0% with RIPerC:P > 0.05:N a parts per thousand yenaEuro parts per thousand 5/group). 8-SPT did not influence the infarct-limiting effects of either RIPC or RIPerC. Western blot analysis confirmed Wortmannin-sensitive PI3K and Akt activation at myocardial reperfusion in RIPC-treated hearts. In the porcine heart, both RIPC and RIPerC both reduce myocardial infarct size and with RIPC but not RIPerC this cardioprotective effect is associated with the activation of the PI3K-Akt pathway at reperfusion.