Cyclooxygenase-2 does not mediate late preconditioning induced by activation of adenosine A(1) or A(3) receptors

Recent studies have demonstrated that the adenosine A(1) receptor agonist 2 -chloro-N-6-cyclopentyladenosine (CCPA) and the adenosine A(3) receptor ago nist N-6-(3-iodobenzyl) adenosine-5'-N-methyluronamide (IB-MECA) produce a delayed phase of protection against infarction similar to the late phase of ischemic preconditioning (PC). However, the mechanism for adenosine A(1) o r A(3) receptor-induced late PC remains unknown. The goal of this study was to determine whether the delayed cardioprotective effects of adenosine A(1 ) or A(3) receptors are mediated by cyclooxygenase-2(COX-2), which is an ob ligatory mediator of ischemic PC. We found that COX-2 protein expression (W estern blotting) did not increase 24 h after the administration of either C CPA (100 mug/kg iv) or IB-MECA (300 mug/kg iv) compared with controls. To p robe the role of constitutive COX-2 expression, conscious rabbits were subj ected to 30-min coronary occlusion followed by 72-h reperfusion. Twenty-fou r hours before the occlusion, the rabbits were pretreated with CCPA (100 mu g/kg iv) or IB-MECA (300 mug/kg iv). Both CCPA and IB-MECA resulted in a ma rked (similar to 47%) reduction in infarct size vs. controls [36.2 +/-4.0% of the risk region (n = 9), 31.2 +/-4.7% (n = 9), and 59.5 +/-3.8% (n = 9), respectively; P < 0.05], similar to that induced by the late phase of isch emic PC [31.8<plus/minus>3.2% (n = 9)]. The selective COX-2 inhibitor N-(2- [cyclohexyloxy]4-nitrophenyl)methanesulfonamide (NS-398, 5 mg/kg), which ab olished the protective effect of ischemic late PC, failed to block the prot ection of either CCPA or IB-MECA, indicating that COX-2 does not mediate th e delayed protection of either CCPA or IB-MECA [CCPA + NS-398, 29.1 +/-3.4% (n = 7); IB-MECA + NS-398, 34.9 +/-2.9% (n = 8)]. NS-398 in itself did not affect infarct size [54.9 +/-3.7% (n = 9)]. Taken together, these results demonstrate that, in contrast to ischemia-induced late PC, the mechanisms o f adenosine A(1) or A(3) receptor-induced late PC is independent of COX-2.