EFFECT OF POSTLATHYRITIC MEDIAL SCAR ON PROGRESSION OF EXPERIMENTAL ATHEROSCLEROSIS IN RATS

A hyperlipemic diet containing increasing concentrations of butter was fed for 16 weeks to weanling rats which were previously damaged in utero with β-aminopropionitrile (BAPN-high-fat group). The same dietary regimen was employed in a group of normal weanling rats (high-fat controls). Aortas from both groups of animals were examined by light and electron microscopy. In the BAPN-high-fat group, relatively advanced aortic lesions were often observed and included intimal and inner medial changes which were either absent or inconspicuous in high-fat control rats. These lesions revealed the following characteristic components: (1) proliferation of medial smooth muscle cells, often in association with extracellular lipid deposits; (2) abundant protein-like material, mainly between endothelium and its abnormal basement membrane; (3) numerous, seemingly phagocytic, endothelial cells with fatty changes (endothelial foam cells) similar to those seen in macrophages; (4) accumulation of lipid bodies with structural features of phospholipids in extracellular spaces and in membrane-bound vacuoles of macrophages and endothelial foam cells; and (5) degenerative changes of many macrophages. These findings indicate that the presence of a postlathyritic medial scar (Balis et al., 1966) accelerates or modifies the evolution of atheromatous lesions. The findings further suggest that some macrophages originate from phagocytic endothelial cells. The possible role of macrophages in the accumulation of extracellular fat is discussed. © 1968.