Abstract
Various sources of cellular cholesterol ester were studied to determine the origin of the esters that accumulated in monkey smooth muscle cells exposed to hyperlipemic serum [in relation to atherosclerosis]. The movement of free cholesterol between the serum and the cells and its esterification by the smooth muscle cells were followed by a double-label procedure. Both uptake and efflux of free cholesterol were nearly linear over a 40-h period. Of the total cellular cholesterol ester .apprx. 1/3 was derived from the esterification of free cholesterol taken up from the hyperlipemic serum in the medium, and 1/3 originated from the esterification of the free cholesterol present in the cells at zero time. Cholesterol esters of the hyperlipemic serum accounted for the major portion of the final 1/3. The contribution to cellular cholesterol ester by cholesterol synthesized de novo by the cells was minimal. Maximal cellular cholesterol ester levels were achieved in the smooth muscle cells after 2 days of incubation in hyperlipemic serum, and additional repeated exposures to this serum produced little further ester accumulation. Cellular esterification of free cholesterol may be important to the increase in the cholesterol ester content of arterial cells exposed to hyperlipemic serum, since this process provided at least 60% of the total cholesterol esters accumulated.

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