Cardiac Injury by Activated Leukocytes: Effect of Cyclooxygenase and Lipoxygenase Inhibition Evaluated by Electron Microscopical Morphometry

Leukocytes can take part in an inflammatory response in the heart after myocardial infarction or cardio-thoracic surgery. To investigate the injurious mechanism of activated polymorphonuclear leukocytes (PMN), isolated rat hearts were perfused with phorbol 12-myristate 13-acetate (PMA) activated PMN (3 ×106/ml) alone for 10 min, in combination with a mixture of oxygen free radical scavengers (superoxide dismutase +catalase +thiourea) or in combination with ibuprofen (IBU), a cyclooxygenase inhibitor or diethylcarbamazine (DCM), a lipoxygenase inhibitor or BW 755C, a dual inhibitor of cyclooxygenase and lipoxygenase and an oxygen free radical scavenger. After 30 min of recovery, the hearts were perfusion-fixed with glutaraldehyde for electron microscopical examination. Based on examination of 25 micrographs per heart obtained by a random sampling procedure and on morphometric methods, volume fractions (Vv) of mitochondria (mito), altered mitochondria (alt mito), myofilament, and cellular edema were measured as fractions of myocyte volume. The most important finding was that Vv(alt mito /myocyte) was 0.09 ±0.16 and 0.02 ±0.04 in the hearts receiving PMN +PMA alone and when scavengers were added, respectively, whilst no changes in mitochondrial ultrastructure was observed after addition of IBU, BW 755C or DCM. Vv(mito /myocyte) was for PMN +PMA alone: 0.33 ±0.04, +scavengers: 0.29 ±0.02, +IBU:0.29 ±0.02, +BW 755C: 0.23 ±0.03*, +DCM: 0.28 ±0.02 (mean ± , *P<0.05 compared to PMN +PMA). Capillary wall volume (cap wall) as a fraction of the whole capillary was also quantified. Vv(cap wall /cap) was for PMN +PMA alone: 0.26 ±0.06, +scavengers: 0.22 ±0.03, +IBU: 0.19 ±0.04*, +BW755C: 0.21 ±0.03, +DCM: 0.15 ±0.04* (*P<0.05). These results further strengthen the notion that activated PMN are intravascularly active. In addition to exerting a cardiodepressive effect the present study shows that activated PMN can induce structural changes in the heart through the combined action of oxygen free radicals and arachidonic acid metabolites.