Brief Antecedent Ischemia Enhances Recombinant Tissue Plasminogen Activator–Induced Coronary Thrombolysis by Adenosine-Mediated Mechanism

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Abstract
Background—Clinical studies have implicated preinfarct angina (brief antecedent ischemia/reperfusion [I/R]) as a predictor of more rapid thrombolysis and lower rates of reocclusion. However, the effects of antecedent ischemia on the efficacy of thrombolysis have not been rigorously assessed. Using a canine model of coronary thrombosis, we aimed to (1) reproduce these clinical findings and (2) determine whether release of adenosine (a potent inhibitor of platelet aggregation via stimulation of platelet A2receptors) during brief I/R contributes to this improved patency.Methods and Results—To address our first objective, we compared the time required to achieve lysis with recombinant tissue plasminogen activator and patency during the first 2 hours after lysis in dogs in which 1-hour thrombotic occlusion was preceded by brief I/R (10-minute coronary occlusion/10-minute reperfusion) versus 20-minute uninterrupted perfusion (controls). Time to lysis was accelerated in the I/R group versus the control group (11±1 versus 35±6 minutes,P=0.004). In addition, the duration of subsequent reocclusion was reduced (17±12 versus 30±11 minutes), and the area of the flow-time profile (normalized to baseline flow×120 minutes) was increased (64±12% versus 35±7%,P=0.04) in the I/R cohort. The protocol was then repeated, but all dogs were pretreated with the adenosine A2/A1antagonist CGS 15943 (CGS, 1.5 mg/kg). Time to lysis (38 versus 39 minutes) and subsequent patency were comparable in the CGS+control group versus the CGS+I/R group.Conclusions—Brief antecedent I/R enhances the efficacy of coronary thrombolysis in this canine model, which is due, at least in part, to an adenosine-mediated mechanism.

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