Comparison of binding and removal of remnants of triglyceride-rich lipoproteins of intestinal and hepatic origin by rat liver in vitro.

Chylomicrons were isolated from intestinal lymph and very low-density lipoproteins (VLDL) from the perfusate of isolated perfused livers. In vivo the initial phase of clearance of these particles was very rapid. Chylomicrons appeared to be cleared more quickly than VLDL (t1/2 = 3.7 +/- 1.4 vs. 10.6 +/- 4.0 min). Remnants were prepared from these particles in eviscerated rats and isolated using conditions under which contamination of particles from one organ by particles from the other organ was minimal. The removal of these remnant particles by isolated perfused livers was studied. VLDL remnants were removed more rapidly than the nascent VLDL. The removal of 125I-labeled VLDL remnants was inhibited by the presence of unlabeled VLDL remnants or chylomicron remnants in the perfusate. A 15- to 20-fold excess of either particle inhibited about 50% of the uptake of the labeled lipoprotein. The two types of remnants had comparable potency as competitors of uptake. Similarly, the two types of remnants inhibited uptake of a trace of labeled chylomicron remnants. The binding of these particles to rat liver plasma remnants. The binding of these particles to rat liver plasma membranes was also investigated. Both labeled chylomicron remnants and VLDL remnants bound specifically to the membranes, and either type of remnant displaced the binding of the other with equal potency. Taken together, these results indicate that chylomicron and VLDL remnants share the same hepatic removal mechanism and suggest that the rate of removal of a remnant is not a function of the organ of origin of the precursor lipoprotein.