Effect of Sodium/Hydrogen Exchange Inhibition on Myocardial Infarct Size after Coronary Artery Thrombosis and Thrombolysis

This study examines the cardioprotective effects of Na+/H+ exchange inhibition with BIIB-722 or ischemic preconditioning after occlusive thrombus formation and subsequent thrombolysis for reperfusion. Coronary artery thrombosis was induced by vessel wall electrolytic injury. Thrombotic occlusion was maintained for 60 or 90 min in 4 different groups: (1) control; (2) Na+/H+ exchange inhibitor, BIIB-722 (3 mg/kg) before occlusion; (3) BIIB-722 (0.75 mg/kg) before reperfusion; (4) ischemic preconditioning (4 × 5 min). Thrombolysis with intracoronary recombinant tissue plasminogen activator produced reperfusion in 6.3 ± 1.4 min (average for 68 dogs). After restoration of blood flow, vessel patency was maintained for 4 h with the glycoprotein IIb/IIIa receptor antagonist, BIBU 52ZW. BIIB-722, administered before (26.9 ± 3.6%) or after (22.0 ± 2.3%) 60-min ischemia or preconditioning (18.4 ± 2.8%), produced comparable and significant reductions in infarct size (percent of area at risk) compared to controls (47.2 ± 2.0%). After 90 min of ischemia, BIIB-722 administered before occlusion (37.3 ± 1.1%) and ischemic preconditioning (35.0 ± 4.8%) provided significant cardioprotection compared to control (45.9 ± 1.8%). BIIB-722 was not cardioprotective when administered during occlusion (48.0 ± 2.4%). The results indicate that Na+/H+ exchange inhibition and preconditioning provide a comparable degree of cardioprotection against 60 min of regional ischemia. However, when the regional ischemic period is extended to 90 min, the degree of cardioprotection is markedly reduced. Further studies incorporating clinically relevant events such as thrombosis and thrombolysis are required before one can conclude that Na+/H+ exchange inhibition is effective against more prolonged myocardial ischemia.