Rapid transport of fatty acids from rat liver endothelial to parenchymal cells after uptake of cholesteryl ester-labeled acetylated LDL.

Acetylated low-density lipoprotein (acetyl-LDL) radiolabeled in the oleate moiety of cholesteryloleate was injected into rats. Isolation of the various liver cell types at different times after acetyl-LDL injection by a low-temperature procedure allowed the intrahepatic metabolism of the oleate moiety to be followed in vivo. The cholesteryloleate radioactivity is rapidly cleared from the circulation and at 5 min after injection recovered into parenchymal and endothelial liver cells, mainly as cholesteryloleate ester. At longer time intervals after injection, the amount of cholesteryl esters associated with the endothelial cells was sharply decreased and the [14C]oleate was redistributed within the liver and mainly recovered in the parenchymal cells. The cholesteryl ester initially directly taken up by the parenchymal cells was also rapidly hydrolysed but, in contrast to the endothelial cells, the [14C]oleate remained inside the cells and was incorporated into triacylglycerols and phospholipids. The 14C radioactivity in parenchymal cells taken up between 5 and 30 min after injection of the cholesteryl [14C]oleate-labeled acetyl-LDL (transported as oleate from endothelial cells), followed a similar metabolic route as the amount which was directly associated to parenchymal cells. The data indicate that the liver and, in particular, the liver endothelial cell has the full capacity to rapidly catabolize modified lipoproteins. In this catabolism, the liver functions as an integrated organ in which fatty acids, formed from cholesteryl esters in endothelial cells, are rapidly transported to parenchymal cells, indicating the concept of metabolic cooperation between the various liver cell types.