Intimal thickening and lipid accumulation, which occur in atherosclerosis, were observed in fifteen human umbilical vessels. Quantification of lipid laden cells was done electron‐microscopically. Within 1 month after birth, lipid laden cells originating from macrophges were observed in the umbilical artery, while those originating from smooth muscle cells were seen in the umbilical artery and vein. Lipid droplet formation appeared to be independent and different in macrophages and smooth muscle cells; the latter cells were stimulated to produce lipid droplets by hypoxia and the former cells by blood component
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