Rudi Grutzmann

The effects of nafazatrom in an acute occlusion-reperfusion model of canine myocardial injury

SummaryThe effects of the lipoxygenase enzyme inhibitor nafazatrom on infarct size, haemodynamics, and prostanoid release was studied in a canine occlusion-reperfusion model of ischaemic myocardial injury. Treatment was with 10 mg/kg nafazatrom i.d., starting before coronary occlusion, 2 h and 6 h thereafter, and was repeated in 6 h intervals. The left anterior descending (LAD) coronary artery was occluded for 6 h and reperfused for 42 h. Infarct size and anatomic area dependent on the occluded LAD were determined post mortem by the tetrazolium staining technique. Nafazatrom significantly reduced the extent of irreversible myocardial ischaemic damage whether it was expressed as g/100 g left ventricle (24 ± 4 vs. 46 ± 6 in controls;p<0.01; mean ± SEM) or as percentage of LAD risk region for infarcting (38 ± 8 vs. 65 ± 7% in controls;p<0.05). Nafazatrom did not affect peripheral haemodynamics but during drug vehicle treatment and LAD occlusion systemic blood pressure, left ventricular pressure anddP/dtmax decreased while filling pressure, heart rate, and the S-T segments of the ECG increased. The incidence of ventricular fibrillation was 8% during drug treatment and coronary ligature vs. 25% in controls (n.s.). During reperfusion, nafazatrom reduced the incidence of ventricular premature contractions and tachycardia. Ex vivo platelet aggregation in response to collagen was not inhibited by nafazatrom. Prostanoid release (thromboxane B2 and 6-keto-prostaglandin F1α as breakdown products of thromboxane A2 and prostacyclin, respectively) remained unaltered in vehicle controls but nafazatrom treatment elevated prostacyclin release significantly at 4 and 5 h during LAD occlusion. We conclude, that inhibition of 5-lipoxygenase by nafazatrom may promote endogenous prostacyclin release and reduce infiltration of reparatory white blood cells with deleterious release of arachidonic acid products contributing to extension of infarction. This mechanism may reduce ultimate ischaemic damage to the heart.