Thromboxane A₂-induced Myocardial Infarction Part II

Male albino rabbits were fed a one percent cholesterol containing pellets for 3 months and the same number of the age-matched rabbits served as controls.As described in Part I, various combinations of 15-30μg of prostaglandin H2 and 1-5mg of protein of microsome obtained from cow platelets were injected through the indwelling catherter. ECG, blood pressure and pulse rate were monitored before and after injection continuously for 20 minutes and timely until death and/or 48 hours after the experiment.In this series of experiments, the normal control group showed no changes related to myocardial infarction. These rabbits were killed 48 hours after the completion of experiment. In one rabbit given a dose of 30μg of PGH2 and 5mg of protein of microsome there was an ST elevation in V1-3 at 3 minutes after the injection, however, recovery was rapid.On the contrary, in the cholesterol-fed group, all rabbits exhibited typical ST elevation in II, III, aVF and/or precordial leads at 3-5 minutes after injection of TXA2 with a sattistically significant decrease in blood perssure and heart rate. All these rabbits died within 48 hours except one given ninimum dose of 15μg of PGH2 and 1mg protein. In 2 rabbits, Q waves were observed. Histological and histochemical studies, using HE, Haematoxyling basic fuchsin-picric acid stain, phosphorylase, LDH and SDH staining, confirmed an ischemic state in left ventricle and/or septal walls of the heart in these cholesterol-fed rabbits. Microthrombi were frequently detected in the small coronary vessels, mainly at the endocardial area of the myocardium. Such findings were not evident in the control group.These data clearly demonstrated that thromboxane A2 produces fatal damage in the myocardium following total occlusion of the coronary sclerotic vessels.