MYOCARDIAL SALVAGE EFFICACY OF THE THROMBOXANE RECEPTOR ANTAGONIST IFETROBAN IN FERRETS AND DOGS

The effect of the thromboxane A(2) (TXA(2))/ prostaglandin endoperoxide (TP) receptor antagonist ifetroban (EMS-180291) on infarct size (IS) resulting from coronary occlusion/reperfusion was determined in anesthetized dogs and ferrets. In dogs, ifetroban (1 + 1 mg/ kg/h, intravenously, i.v.) or vehicle administration was initiated 10 min before left circumflex coronary artery (LCX) occlusion. In ferrets, the left anterior descending coronary artery (LAD) was occluded; after 75 min, a continuous infusion of ifetroban (0.3 + 0.3 mg/kg/h i.v.) or vehicle was started. After 90-min ischemia in both species, the LCX or LAD occlusion was released; reperfusion was continued for 5 h, at which time IS was determined. Regional myocardial blood flow (RMBF) before and during occlusion and during reperfusion were measured with radioactive microspheres. Ifetroban significantly decreased the extent of infarction to 39 +/- 5% of the area at risk (AAR) from 64 +/- 5% in dogs and to 15 +/- 2% of the left ventricle as compared with a control of 22 +/- 2% in ferrets. The protective effect of ifetroban in both species occurred with no increase in collateral BF or treatment-related alterations in peripheral hemodynamic status. Ifetroban, at the doses that reduced IS in ferrets, inhibited 99% of platelet TP receptors throughout the experiment, as measured by inhibition of the ex vivo platelet shape change response to U-46,619, a TP receptor agonist. Thus, doses of ifetroban causing profound TP receptor blockade also salvaged jeopardized myocardium in dogs and ferrets without changing collateral BF or peripheral hemodynamics.