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 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 (Bmax 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 (Kd 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.