A MORPHOMETRIC STUDY OF THE EPITHELIUM LINING THE RAT INTRAHEPATIC BILIARY TREE

Background/Aims: Morphological and functional heterogeneity of intrahe patic bile duct epithelial cells has been suggested irt situ and in is olated cholangiocytes. The aim of this study was to evaluate if: (a) b ile 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. Methods: Studies in situ were conducted on normal liver processed for light or electron microscopy. Data were al so obtained from preparations of intrahepatic biliary tree isolated fr om rat liver. The whole biliary tree was cut at different levels to ob tain bile ducts of different diameter. The diameter of ducts, the numb er of lining cells, the size and the area of individual cells, the nuc leo/cytoplasmic ratio, the volume density of mitochondria, endoplasmic reticulum, Golgi complex and lysosomes have been evaluated. Results: The diameter of intrahepatic bile ducts ranged from 5 to 100 mu m and the area of lining cells ranged from 8 to 100 mu m(2). A highly signif icant 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 a nd was not significantly different in ducts of different size. Rough e ndoplasmic reticulum was inconspicuous in the smallest ducts and incre ased only slightly in the largest. The inverse relationship between th e nucleo/cytoplasmic ratio and duct diameter was striking (r=-0.78, p< 0.001). All morphometric data were equivalent if bile ducts were evalu ated in situ or in isolated fragments. Taken together, the data allowe d bile ducts to be classified into 3 classes: <10, 10-50, and >50 mu m in diameter. Discussion: Our data show that (a) isolated bile ducts m aintain morphometric characteristics similar to the tissue in situ, (b ) a low grade of morphological heterogeneity is evident for intracellu lar organelles in ducts of different diameter and (c) the diameter of ducts, the number of lining cells and especially the nucleo/cytoplasmi c ratio may indicate the origin of fragments examined where functional studies are being considered.