The combined SEM and TEM observations of morphological changes in endothelial cells of the aorta induced by Anitschkow's procedure, i.e, one-shot treatment of rabbits with cholesterol (1g/kg p.o.), were subjects of the present investigation. (1) In the SEM analysis of the luminal surface of thoracic aorta, the appearance of vertical lines at regular intervals of 0.6 to 1.8μ and and depths of 0.2 to 0.3μ and of crater-like structures was observed after administration of cholesterol (p<0.01, p<0.01). PDC pretreatment reduced the appearance of both changes (p<0.01, p<0.01). The crater-like structures appeared predominantly on or close to the boundaries of endothelial cells and, on the basis of TEM observation done concomitantly, the majority of such structures were reasonably considered to reprsent blebs, while the vertical lines were considered to represent the active contraction of endothelial cells. (2) In the TEM analysis, the appearance of subendothelial edema was reconfirmed to be induced by one-shot treatment of rabbits with cholesterol (p<0.05). In such animals an unevenness of endothelial cells, accompanied by relatively strong indentations and occasionally pinches (p<0.001), which represent the active contraction of endothelial cells, 6) seen. It was also shown that the formation of blebs, especially of large ones with a diameter over 1μ, can be induced by the above mentioned challenge (p<0.01, p<0.01). Also, the sticking of platelets to blebs and the formation of fibrin by such platelets were often observed. All such changes were inhibited by PDC pretreatment (10mg/kg p.o.). (3) The characteristic response of endothelial cells of the artery to cholesterol, which was shown in the present observations, seemed to result from the active contraction of their contractile proteins.8) Such a response has been proposed as the trigger-mechanism in atherogenesis, and possibly in thrombogenesis.
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