Adenosine receptor involvement in a delayed phase of myocardial protection 24 hours after ischemic preconditioning

Abstract

Background: We previously reported a delayed phase of protection against infarction 24 hours after ischemic preconditioning in the rabbit. In the present study, we investigated the possibility that this 'second window of protection,' like the well-described early phase of protection in the rabbit, might be associated with adenosine receptor activation. Methods and Results: In the first series of experiments, we examined whether adenosine receptor blockade with 8-(p-sulfophenyl)-theophylline (SPT) during preconditioning could abolish the delayed protection against infarction 24 hours later. Open- chest rabbits were subjected to myocardial preconditioning (PC) with the four 5-minute coronary occlusions or they were sham operated on (SHAM). During these procedures, animals received either SPT (PC+SPT, n=6; and SHAM+SPT, n=6) or vehicle (PC+VEH, n=12; and SHAM+VEH, n=11). Twenty-four hours later, infarct development after a 30-minute coronary occlusion/120-minute reperfusion insult was assessed with triphenyltetrazolium staining. In vehicle-treated rabbits, the infarct-to-risk ratio (I/R) was reduced from 53.6±5.7% (SHAM+VEH) to 32.9±4.6% (PC+VEH) (P