Protective effect of preconditioning on ischemic heart and characterization of adenosine receptors in ischemic rabbit heart

Aim: To assess the role of adenosine receptors in the cardioprotective effect of preconditioning and the characterization of adenosine receptors in heart. Methods: In 18 anesthetized rabbits, myocardial ischemia was induced by occlusion of left descending coronary artery. ST segment elevation in epicardial electrogram was used as a criterion of acute ischemic injury. Myocardial adenosine receptors were measured using [³H]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 of the ventricular myocytes prepared from ischemic-preconditioning group, 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 the [³H]adenosine was not different in the 3 groups (K(d) being 181 ± 18, 169 ± 21, and 196 ±24 nmol · L^-1, respectively). Conclusion: Activation of adenosine receptors along with an increase in adenosine receptor density during ischemic-preconditioning provides the basis for adenosine to exert its protective effect on the ischemic heart.