Myogenic foam cells in explants of fatty dots and streaks from rabbit aorta. Morphological studies

Present studies indicate that in explants of early atherosclerotic lesions removed from aortae of young rabbits on a 1% hypercholesterolemic diet for four and seven weeks respectively, myogenic foam cells (MCF's) were capable of emigrating into the culture medium and maintained their ability to produce microfibrils, elastic tissue elements, and collagen fibrils. In explants of the smallest lesions (fatty dots and small streaks) the MFC's divided prior to, or while emigrating. At the interphase between the primary tissue and the culture medium they contained in intracytoplasmic vacuoles fragments of elastic tissue and extraneous substances which were reminiscent of cellular debris. It is possible that this phenomenon represents a true phagocytic property of the MFC's. All formed extracellular connective tissue components were also produced by the emigrated MFC's in the tissue surrounding the cellular outgrowth. In the large fatty streaks cell division was observed at the interphase between the tissue and culture medium, but not within the substance of the explant; here cellular necrosis was prominent. The fat inclusions in the MFC's of explants and the outgrowth had the appearance of conglomerateds of unorganized, and only at times concentric, membranous profiles rather than that of homogeneous droplets observed by electron microscopy in these cells in tissue sections. In the outgrowth from explants of normal aortic areas adjacent to the lesions a moderate number of smoot muscle cells contained fat inclusions; these were almost totally absent in cells of the primary aortic cultures from normal aortae. It is conceivable that the migratory and phagocytic properties of the MFC's observed in the present study relate to some aspects of regression of atherosclerotic lesions; this, however, remains highly speculative at present.