Postconditioning reduces infarct size via adenosine receptor activation by endogenous adenosine

Abstract

Objective: This study tested the hypothesis that brief cycles of iterative ischemia–reperfusion at onset of reperfusion (termed “postconditioning”, 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 post-con, 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 (±) of post-con. Vehicle (DMSO 1AR antagonist, 0.1 mg/kg) ± post-con; ZM241385 (A_2AAR antagonist, 0.2 mg/kg) ± post-con; MRS1523 (A₃AR antagonist, 2 mg/kg) ± post-con. Results: In isolated mouse hearts, post-con reduced diastolic pressure during both early (26 ± 3* vs. 37 ± 3 mmHg at 5 min) and late (22 ± 3* vs. 34 ± 3 mmHg at 30 min) R. Post-con also hastened the early recovery of contractile function (developed pressure 39 ± 6* vs. 16 ± 2 mmHg at 5 min R), although differences did not persist at 30 min R. Importantly, post-con was associated with reduced adenosine washout (58 ± 5* vs. 155 ± 16 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 (40 ± 3% vs. 53 ± 2%* in control), an effect that was unaltered by DPCPX (42 ± 2%) but was abrogated by 8-SPT (50 ± 2%), ZM241385 (49 ± 3%) or MRS1523 (52 ± 1%) (PConclusion: These data suggest that post-con involves endogenous activation of A_2A 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.