Neutrophil infiltration in ischemic porcine myocardium and protective effect of verapamil

Neutrophil infiltration in the ischemic porcine hearts was analyzed by spectrophotometrical assay of the neutrophil specific enzyme-myeloperoxidase (MPO). The results showed that neutrophil infiltration in the ischemic myocardium was increased with time. An increase of MPO activity per 1 g tissue from 1.3 +/- 0.8 to 4 +/- 3 IU was observed as early as 10 min after occlusion of the coronary artery. Three h after occlusion MPO activity increased to 8.4 +/- 1.3 IU, 7 times greater than that of normal tissue. One-h occlusion followed by 2-h reperfusion caused even higher neutrophil accumulation. MPO activity increased to 14 +/- 3 IU, 11 times greater than normal tissue. Pretreatment with verapamil to reperfusion hearts decreased MPO activity to 4.7 +/- 0.7 IU. In addition, verapamil completely eliminated the first episode of arrhythmia 5-10 min after occlusion. Our studies demonstrate that neutrophils can rapidly accumulate into the ischemic myocardium and suggest that the protective action of verapamil may in part due to its inhibition of neutrophil infiltration in the ischemic myocardium.