Sinusoidal endothelial endocytosis of low density lipoprotein-gold conjugates in perfused livers of ethinyl-estradiol treated rats.

We examined endocytosis of low-density lipoproteins (LDL) conjugated to colloidal gold by the sinusoidal endothelium in perfused livers of 17 alpha-ethinyl estradiol-treated rats. After 15 min of perfusion, the gold-LDL was randomly bound at the endothelial surface, but internalized only at coated pits. Uptake of the conjugate was to electron-lucid vacuoles. After 1 h of perfusion, there was a progressive accumulation of gold in organelles resembling lysosomes, with further accumulation seen at 2 h perfusion. Uptake of the conjugate was equivalent to the rate of 125I-LDL and competitively inhibited by a 20-fold excess of free LDL. These results suggest that a specific endocytotic pathway for LDL is present in the sinusoidal endothelium in the estrogen-hypolipidemic state.