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.