PROTECTIVE EFFECT OF PRECONDITIONING ON ISCHEMIC HEART AND CHARACTERIZATION OF ADENOSINE RECEPTORS IN ISCHEMIC RABBIT HEARTS

AIM: To assess the role of adenosine receptors in the cardioprotective effect of preconditioning and the characterization of adenosine recep tors in heart, METHODS: In 18 anesthetized rabbits, myocardial ischemi a was induced by occlusion of left descending coronary artery. ST segm ent elevation in epicardial electrogram was used as a criterion of acu te ischemic injury. Myocardial adenosine receptors were measured using [H-3]adenosine ligand. RESULTS: After 60-min ischemia, epicardial ST segment elevation was higher in ischemia group (13.9 +/- 0.6 mV) than in the ischemic preconditioning group (3.1 +/- 0.5 mV). In membranes o f the ventricular myocytes prepared from ischemic-preconditioning grou p, the density of adenosine receptors was higher than that of ischemia and sham ischemia groups (B-max being 602 +/- 40, 348 +/- 28, and 335 +/- 30 pmol/g protein, respectively). Affinity of the receptors for t he [H-3]adenosine was not different in the 3 groups (K-d being 181 +/- 18, 169 +/- 21, and 196 +/- 24 nmol . L(-1), respectively). CONCLUSIO N: Activation of adenosine receptors along with an increase in adenosi ne receptor density during ischemic-preconditioning provides the basis for adenosine to exert its protective effect on the ischemic heart.