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Heterogeneity of Rabbit Aortic Endothelial Cells, with Special Reference to Phagocytosis

Heterogeneity of aortic endothelial cells with regard to phagocytotic ability was examined by injecting India ink into normal rabbits. Light and electron microscopic analyses revealed that particles of India ink were phagocytosed in the endothelial cells, which in turn were localized at the distal side of the orifice of aortic branches, especially those of brachiocephalic, left calvicular, and dor sal intercostal arteries. No remarkable differences were found ultrastructurally between phagocytosing and nonphagocytosing endothelial cells. Ingested India ink particles were present within phagosomes of the endothelial cells for several hours after injection; the particles eventually accumulated in the subendothelial space twenty-four hours after injection. These results indicate that an active transport system of large molecules via the phagocytotic processes is present in endothelial cells located at the distal sides of the orifice of aortic branches. These regions are known to develop initial atherosclerotic lesions in hypercholesterolemic animals. Thus, a possible corre lation between phagocytotic ability of endothelial cells and development of atherosclerosis is suggested.