Uptake of C 14 -1-Palmitic Acid-P 32 -Phospholipid Labeled Chylomicrons By Perfused Liver and Liver Slices. ∗

Abstract

Summary

Liver slices from post absorptive dogs and fed rats were incubated for up to 3 hours with chylomicrons containing C¹⁴-palmitate and P³²-phospholipid suspended in phosphate buffer. The ratio of P³²/C¹⁴ in the liver slices was in most instances higher than that of the substrate chylomicrons. Re-incubation of the dog liver slices with buffer or nonlabeled chylomicrons showed some release of C¹⁴ and P³². Cyanide failed to inhibit lipid uptake by dog liver tissue, but lowered temperatures reduced the uptake. Dog liver slices deactivated by heating took up chylomicron P³² but the C¹⁴ uptake was greatly diminished from normal. Separation of chylomicrons into different size classes by centrifugation in sucrose gradients showed that the smaller particles are relatively richer in P³² than the larger chylomicrons. Evidence indicates, however, that the high P³²/C¹⁴ ratios in the liver slice are probably not caused by preferential uptake of small chylomicron particles. The perfused rat liver took up the two labels in nearly the same proportion as present in the circulating chylomicrons. Apparently chylomicrons were taken up as intact particles including their phospholipid envelope. It is suggested that adsorption of chylomicron lipid on the liver slice may account for much of the “uptake” and throws some doubt on the validity of experiments with tissue slices for the study of chylomicron transport into the liver.