CHYLOMICRON REMNANT UPTAKE BY ENTEROCYTES IS RECEPTOR-DEPENDENT

During glyceryl trioleate absorption in the rat, mucosal triacylglycer ol (TG) fatty acids have been shown to consist of only 71% exogenous o leate. Chylomicron remnants are enriched with endogenous TG fatty acid s, compared with their parent chylomicrons, which consist primarily of exogenous TG; fatty acids. Because enterocytes have the apolipoprotei n B-100/E receptor, this study was directed at determining whether the cells can take up and metabolize chylomicron remnants and, if so, whe ther this was receptor mediated. Isolated enterocytes were incubated w ith purified H-3-labeled chylomicron remnants. The remnants were shown to be taken up by the basolateral membrane, not the apical membrane. Remnant uptake was proportional to time and number of enterocytes, and saturation kinetics were observed. Nonradiolabeled remnants, human lo w-density lipoprotein (LDL), anti-LDL receptor antibody, and receptor- associated protein, an LDL-related receptor inhibitor, were all shown to compete for or reduce H-3-remnant uptake. Remnants taken up by the enterocytes could not be removed on incubation with excess human LDL. Uptake was shown to be greatest in the villus tips of the proximal int estine. These studies suggest that enterocytes take up chylomicron rem nants by a receptor-mediated process from their basolateral membranes and that the remnants could provide a source of endogenous TG fatty ac ids for the enterocytes.