SINUSOIDAL ENDOTHELIAL ENDOCYTOSIS OF LOW-DENSITY LIPOPROTEIN-GOLD CONJUGATES IN PERFUSED LIVERS OF ETHINYL-ESTRADIOL TREATED RATS

Abstract

Endocytosis of low-density lipoproteins (LDL) conjugated to colloidal Au by the sinusoidal endothelium in perfused livers of 17.alpha.-ethynyl estradiol-treated rats was examined. After 15 min of perfusion, the Au9-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 Au 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. Apparently a specific endocytotic pathway for LDL is present in the sinusoidal endothelium in the estrogen-hypolipidemic state.