EXPRESSION OF APOLIPOPROTEIN A-1 MESSENGER-RNA IN NORMAL INTRAHEPATICBILIARY TREE

Our previous study demonstrated that apolipoprotein A-1 (apo A-1) immu noreactive peptides were located diffusely in the cytoplasm, not only of human normal hepatocytes, but also of intrahepatic bile ducts and p eribiliary glands. It is important to determine whether the presence o f these immunoreactive peptides in intrahepatic biliary tree is caused by pinocytosis from the bile, or by intracellular protein synthesis. Thus, we investigated whether apo A-1 is synthesized by cells that lin e the biliary tree. Normal human liver samples obtained at surgery wer e used, and the expression and distribution of apo A-1 mRNA in normal human liver tissues were examined, using in situ hybridization histoch emistry with a S-35-labeled oligonucleotide probe specific for apo A-1 . On the autoradiogram, many silver grains were found to be distribute d uniformly in hepatocytes. In addition, an appreciable apo A-1 mRNA s ignal was also observed in both the surface epithelial lining of the b ile ducts and the epithelial cells of the peribiliary glands. In concl usion, these findings suggest that the apo A-1 found in bile is secret ed both by hepatocytes and by intrahepatic bile duct cells and peribil iary glands.