Postconditioning reduces infarct size via adenosine receptor activation by endogenous adenosine

Abstract Objective: This study tested the hypothesis that brief cycles of iterative ischemiaa??reperfusion at onset of reperfusion (termed bpostconditioningQ, post-con) delays washout of intravascular adenosine and thereby increases endogenous adenosine receptor (AR) activation during the early moments of reperfusion (R). Methods: Isolated mouse hearts were subjected to 20 min global ischemia (I) and 30 min R with or without post-con (3 or 6 cycles of 10 s R I). Intravascular purines in coronary effluent were analyzed by HPLC. To assess the functional role of endogenous AR activation in postcon, an open-chest rat model of myocardial infarction was employed. Rats were randomly divided into 11 groups: control, no intervention at R; post-con, three cycles of 10 s R followed by 10 s LCA re-occlusion immediately upon R. In the following interventions, drugs (or vehicle) were administered 5 min before R in the absence or presence (F) of post-con. Vehicle (DMSO b300 cl/kg); 8-SPT (non-selective AR antagonist, 10 mg/kg) F post-con; DPCPX (A1AR antagonist, 0.1 mg/kg) F post-con; ZM241385 (A2AAR antagonist, 0.2 mg/kg) F postcon; MRS1523 (A3AR antagonist, 2 mg/kg) F post-con. Results: In isolated mouse hearts, post-con reduced diastolic pressure during both early (26F3* vs. 37F3 mmHg at 5 min) and late (22F3* vs. 34F3 mmHg at 30 min) R. Post-con also hastened the early recovery of contractile function (developed pressure 39F6* vs. 16F2 mmHg at 5 min R), although differences did not persist at 30 min R. Importantly, post-con was associated with reduced adenosine washout (58F5* vs. 155F16 nM/min/g) at 2 min R suggesting greater retention time of intravascular adenosine. In rats, post-con significantly attenuated infarct size compared to control (40F3 vs. 53F2 * in control), an effect that was unaltered by DPCPX (42F2 ) but was abrogated by 8-SPT (50F2 ), ZM241385 (49F3 ) or MRS1523 (52F1 ) (Pb0.02). Conclusion: These data suggest that post-con involves endogenous activation of A2A and A3 but not A1AR subtypes. This activation may be linked to the delay in the washout of intravascular adenosine during the early minutes of R during which post-con is applied.