The incidence of myocardial infarction, as well as thrombosis, has been increasing recently in the consecutive autopsy cases over 40 years old in Kyushu University, but is still less frequent than those in the autopsy cases in Boston around 1960. Increased fat intake might play a significant role in the increasing frequency of myocardial infarction in Japanese. 2) In a nationwide cooperative study of atherosclerosis in young Japanese, atherosclerotic changes were observed to begin developing in childhood. Primary prevention of atherosclerosis should be initiated in the pediatric age group. We should pay more attention to subclinical atherosclerosis. Age, serum cholesterol, and blood pressure were significantly and positively correlated with SI and AI of aortas and coronary arteries. Serum cholesterol was more strongly correlated with the extent of fatty streaks than was mean blood pressure and vice versa with that of fibrous plaques. Atherosclerosis of cerebral arteries, however, showed a significant correlation only with the factor of mean blood pressure. Therefore the susceptibility to risk factors varies with the artery in the case of early lesions of atherosclerosis in young people. More attention should be paid to the fact that atherosclerosis is a multifactoral disease. 3) Deposition of fibrinogen in the intima might precede LDL deposition and possibly play a more important role than LDL in the development of atherosclerotic lesions in the cerebral arteries, especially in their early stage. 4) The proliferation of smooth muscle cells is stimulated by fibrin and later inhibited by FDP, as produced by fibrinolytic activity of smooth muscle cells. The metabolism of fibrin in the arterial wall may be of importance in the regulation of smooth muscle cell proliferation, and the coagulation-fibrinolysis system may play a significant role in atherosclerosis with the effect of other risk factors such as cholesterol and hypertension.
