Myocardial reperfusion injury. Platelet-activating factor stimulates polymorphonuclear leukocyte hydrogen peroxide production during myocardial reperfusion.

To study the roles of platelet-activating factor, polymorphonuclear leukocytes, and oxygen free radicals in myocardial reperfusion injury, we subjected 10 sheep to 90 minutes of mid-left anterior descending coronary artery followed by 6 hours of reperfusion. Stainings with gentian violet and tetratriphenyl ammonium chloride demonstrated 20% +/- 3% of the left ventricular mass at risk for ischemia, of which 75% +/- 10% underwent infarction. Coronary sinus blood was assayed for platelet-activating factor and neutrophil hydrogen peroxide production before and during coronary occlusion and during reperfusion. Platelet-activating factor was isolated by column chromatography and lipid extraction and quantified by radioimmunoassay. Neutrophil hydrogen peroxide production was measured by a 2',7'-dichlorofluorescein flow-cytometric assay. Platelet-activating factor was elevated to 899 +/- 210 pg/ml at 15 minutes of reperfusion, compared with the preocclusion level of 271 +/- 55 pg/ml and coronary occlusion level of 359 +/- 64 pg/ml (p less than 0.05; analysis of variance). Neutrophil hydrogen peroxide production, measured on a relative fluorescence scale, was also elevated to a level of 141 +/- 27 at 1 hour of reperfusion, compared with the preocclusion level of 103 +/- 6 and the coronary occlusion level of 114 +/- 13 (p less than 0.01; analysis of variance). Both of these parameters returned toward baselines at the end of 6 hours of reperfusion. Histologic examination revealed infiltration of polymorphonuclear leukocytes into the interstitium of the reperfused myocardium. Neutrophils isolated from unoperated and healthy sheep demonstrated a graded dose response in hydrogen peroxide production when stimulated by purified platelet-activating factor in vitro. These findings suggest that platelet-activating factor is released in the coronary circulation and is a mediator of oxygen free radical production in polymorphonuclear leukocytes during myocardial reperfusion.