A morphometric study of the epithelium lining the rat intrahepatic biliary tree

Morphological and functional heterogeneity of intrahepatic bile duct epithelial cells has been suggested in situ and in isolated cholangiocytes. The aim of this study was to evaluate if: (a) bile ducts, when isolated, maintain morphometric parameters similar to ducts in situ, (b) cellular organelles show heterogeneity in ducts of different size, and (c) some features permit different classes of bile ducts to be distinguished.

Studies in situ were conducted on normal liver processed for light or electron microscopy. Data were also obtained from preparations of intrahepatic biliary tree isolated from rat liver. The whole biliary tree was cut at different levels to obtain bile ducts of different diameter. The diameter of ducts, the number of lining cells, the size and the area of individual cells, the nucleo/cytoplasmic ratio, the volume density of mitochondria, endoplasmic reticulum, Golgi complex and lysosomes have been evaluated.

The diameter of intrahepatic bile ducts ranged from 5 to 100 micrograms and the area of lining cells ranged from 8 to 100 micrograms2. A highly significant linear relationship existed between duct diameter and bile duct epithelial cell area (r = 0.97, p < 0.001) or number of lining cells (r = 0.96, p < 0.001). The volume density of mitochondria ranged from 7.58 +/- 2.0% of cytoplasmic volume in the smallest isolated bile ducts to 8.50 +/- 2.7% in the largest (p = NS). The volume density of lysosomes was low and was not significantly different in ducts of different size. Rough endoplasmic reticulum was inconspicuous in the smallest ducts and increased only slightly in the largest. The inverse relationship between the nucleo/cytoplasmic ratio and duct diameter was striking (r = -0.78, p < 0.001). All morphometric data were equivalent if bile ducts were evaluated in situ or in isolated fragments. Taken together, the data allowed bile ducts to be classified into 3 classes: < 10, 10-50, and > 50 micrograms in diameter.

Our data show that (a) isolated bile ducts maintain morphometric characteristics similar to the tissue in situ, (b) a low grade of morphological heterogeneity is evident for intracellular organelles in ducts of different diameter and (c) the diameter of ducts, the number of lining cells and especially the nucleo/cytoplasmic ratio may indicate the origin of fragments examined where functional studies are being considered.