Role of macrophages in lipid metabolism.

One of the cells involved in lipid metabolism and thought to have adrenergic receptors is the macrophage. Low-density lipoprotein (LDL), once modified, can bind to modified LDL receptors on the macrophage. After binding to these receptors, LDL is internalized by a mechanism that is not controlled by feedback inhibition. This unregulated uptake results in massive cholesterol ester accumulation in atherosclerotic plaques. Macrophages secrete apolipoprotein E, a process that appears to be regulated by the cholesterol content of the macrophage, as well as by lipoprotein lipase. Macrophages are also thought to have receptors for high-density lipoprotein (HDL) on their surface, receptors that may play a key role in reverse cholesterol transport of cholesterol esters from the cells. Studies are being conducted to determine the effects of alpha 1-adrenergic activation on lipoprotein metabolism in these cells.