Cl-IB-MECA [2-chloro-N⁶-(3-iodobenzyl)adenosine-5′-N- methylcarboxamide] reduces ischemia/reperfusion injury in mice by activating the A₃ adenosine receptor

We used pharmacological agents and genetic methods to determine whether the potent A₃ adenosine receptor (AR) agonist 2-chloro-N ⁶-(3-iodobenzyl)adenosine-5′-N-methylcarboxamide (Cl-IB-MECA) protects against myocardial ischemia/ reperfusion injury in mice via the A ₃AR or via interactions with other AR subtypes. Pretreating wild-type (WT) mice with Cl-IB-MECA reduced myocardial infarct size induced by 30 min of coronary occlusion and 24 h of reperfusion at doses (30 and 100 μg/kg) that concomitantly reduced blood pressure and stimulated systemic histamine release. The A₃AR-selective antagonist MRS 1523 [3-propyl-6-ethyl- 5[(ethylthio)carbonyl]-2-phenyl-4-propyl-3-pyridine-carboxylate], but not the A_2AAR antagonist ZM 241385 [4-{2-7-amino-2-(2-furyl)[1,2,4]triazolo- [2,3-a][1,3,5]triazin-5-ylamino]ethyl}phenol], blocked the reduction in infarct size provided by Cl-IB-MECA, suggesting a mechanism involving the A ₃AR. To further examine the selectivity of Cl-IB-MECA, we assessed its cardioprotective effectiveness in A₃AR gene "knock-out" (A₃KO) mice. Cl-IB-MECA did not reduce myocardial infarct size in A₃KO mice in vivo and did not protect isolated perfused hearts obtained from A₃KO mice from injury induced by global ischemia and reperfusion. Additional studies using WT mice treated with compound 48/80 [condensation product of p-methoxyphenethyl methylamine with formaldehyde] to deplete mast cell contents excluded the possibility that Cl-IB-MECA was cardioprotective by releasing mediators from mast cells. These data demonstrate that Cl-IB-MECA protects against myocardial ischemia/reperfusion injury in mice principally by activating the A₃AR.