CI-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 A 3 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 3 AR 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 mu g/ kg) that concomitantly reduced blood pressure and stimulated systemic histamine release. The A(3)AR-selective antagonist MRS 1523 [3-propyl-6-ethyl-5[(ethylthio) carbonyl]-2-phenyl-4-propyl-3-pyridine-carboxylate], but not the A(2A)AR 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 3 AR. To further examine the selectivity of Cl-IB-MECA, we assessed its cardioprotective effectiveness in A(3)AR gene " knock-out" (A(3)KO) mice. Cl-IB-MECA did not reduce myocardial infarct size in A 3 KO mice in vivo and did not protect isolated perfused hearts obtained from A 3 KO 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 A(3)AR.