HYPOXIA PRECONDITIONS RABBIT MYOCARDIUM BY AN ADENOSINE RECEPTOR-MEDIATED MECHANISM

OBJECTIVES: To test the ability of hypoxia without reoxygenation to pr econdition myocardium and to test a possible involvement of adenosine reception in that response. DESIGN: Isolated rabbit hearts were perfus ed with oxygenated Krebs-Henseleit buffer. Control hearts underwent 30 min regional ischemia followed by 2 h reperfusion. A second group rec eived 10 min global perfusion with hypoxic buffer (PO2=33+/-3 mmHg) im mediately before coronary occlusion. A third group was subjected to a similar protocol as group 2, with the adenosine receptor blocker 8-(p- sulfophenyl) theophylline (SPT) (100 mu M) added to the buffer immedia tely before and throughout hypoxia. At the end of reperfusion the area at risk for infarction was determined by fluorescent particles while infarction size was measured by triphenyltetrazolium staining. RESULTS : Hearts without hypoxic perfusion preceding ischemia experienced 38.2 +/-2.4% infarction. The hypoxic group, despite a longer total period o f oxygen deprivation, had only 21.0+/-4.2% infarction (P less than or equal to 0.05). SPT blocked the protection (42.1+/-6.9% infarction). C ONCLUSIONS: Hypoxia without subsequent reoxygenation before ischemia p rotected the heart from infarction, indicating that reoxygenation may not be the critical feature of reperfusion typically employed in an is chemic preconditioning protocol. Because adenosine receptor blockade a bolishes the protection from hypoxic perfusion, the mechanism of this protection may be similar to that seen with ischemic preconditioning.