ABSENCE OF ATHEROSCLEROSIS EVOLUTION IN THE CORONARY ARTERIAL SEGMENTCOVERED BY MYOCARDIAL TISSUE IN CHOLESTEROL-FED RABBITS

The evolution of atherosclerotic lesions is suppressed in the intima o f the human coronary artery, beneath myocardial bridges. To elucidate the mechanism of the protective effect, we investigated morphological changes using the rabbit coronary artery as a model. Rabbits fed a 1%- cholesterol diet were killed at intervals up to 20 weeks. Two short se gments of the left coronary arteries running in the epicardial adipose tissue (Epi-LAD) and subsequently running in the myocardium (MyoLAD) were compared morphologically. The intima of the EpiLAD had flat endot helial cells with a polygonal shape, and demonstrated raised atheroscl erotic lesions with increase in serum cholesterol level. In contrast, the intima of the MyoLAD was free of atherosclerotic lesions throughou t the study, and the endothelial cells were spindle-shaped and engorge d. While ferritin particles reached only the surroundings of the inter nal elastic lamina in the MyoLAD, they permeated into the media of the EpiLAD. We suggest that myocardial bridges suppress coronary atherosc lerosis by an alteration of endothelial permeability, which may be due to changes in haemodynamic force tending towards a higher shear stres s. The data provide an insight into the relationship between haemodyna mics and the development of coronary atherosclerosis.