ENDOGENOUS ADENOSINE ATTENUATES MYOCARDIAL STUNNING BY ANTIADRENERGICEFFECTS EXERTED DURING ISCHEMIA AND NOT DURING REPERFUSION

The effect of adenosine receptor blockade and adrenergic blockade on m yocardial stunning [left anterior descending coronary artery (LAD) occ luded for 10 min and reperfused for 180 min] was studied in 38 open-ch est cats. A control group (Control) was compared with two other groups in which adenosine receptors were blocked by 8-phenyltheophylline (7. 5 mg/kg) before reperfusion (8-PT-R) or before ischemia (8-PT-I). Grou p A, in which adrenergic receptors were blocked (doxazosin 200 mu g/kg + propranolol 1 mg/kg), was compared with group A + 8-PT-I, in which both adenosine and adrenergic receptors were blocked before coronary a rtery occlusion. Regional systolic function assessed by sonomicrometry in the LAD perfused area recovered less in 8-PT-I (55 +/- 5% recovery ) as compared with Control (87 +/- 9%) and 8-PT-R (89 +/- 8%), which i ndicates that adenosine receptor blockade during ischemia increases st unning. Functional recovery was similar in Control, group A (96 +/- 5% ), and group A + 8-PT-I (87 +/- 5%), which demonstrates that if adrene rgic receptors are blocked, adenosine receptor blockade during ischemi a does not increase stunning. These results may indicate that the card ioprotective effects of endogenous adenosine are mediated through anti adrenergic effects exerted during coronary artery occlusion.