Background: 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.
Methods and results: 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 μg/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 ≥ 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 ≥ 5/group) but not RIPerC (18.0 ± 3.4% with RIPerC + Wort versus 18.2 ± 2.0% with RIPerC:P > 0.05:N ≥ 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.
Conclusions: 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.