Adenosine A 1 Receptor Activation Induces Delayed Preconditioning in Rats Mediated by Manganese Superoxide Dismutase

Abstract

Background —We have previously described a second window of protection against infarction in rabbits 24 to 72 hours after adenosine A 1 receptor (A 1 R) activation. In this study, we examined the potential role of the mitochondrial antioxidant manganese superoxide dismutase (Mn-SOD) as a potential end effector in mediating this protection. Methods and Results —Rats were treated with an intravenous bolus of the A 1 R agonist 2-chloro- N 6 -cyclopentyladenosine (CCPA, 75 μg/kg) or saline vehicle. They were also given a 5 mg/kg IV infusion of a 22-mer phosphorothioate oligodeoxynucleotide (ODN) with sequence antisense to the initiation site of rat Mn-SOD mRNA. Sense ODN and scrambled ODN were used as controls. Twenty-four hours later, hearts were isolated and perfused with buffer at constant pressure and subjected to 35 minutes of regional ischemia and 2 hours of reperfusion. Treatment with CCPA compared with saline vehicle (control) significantly reduced infarct size, expressed as percentage of myocardium at risk (22.3±3.3% versus 42.1±3.8%, respectively; P =0.001). This protection was completely abolished by prior treatment with antisense ODN, which had no effect on its own. Neither sense ODN nor scrambled ODN had an effect on the CCPA-induced delayed cardioprotection. In separate animals, 24 hours after the same treatment, hearts were assayed for Mn-SOD content and activity. CCPA treatment induced a significant increase in myocardial Mn-SOD content and activity compared with the control condition; this increase was abolished by pretreatment with antisense ODN. Conclusions —This is the first study to show that transient A 1 R activation induces delayed cardioprotection in the rat. These results strongly suggest an important role for mitochondrial Mn-SOD as a potential end effector of this protection.