Three-dimensional arrangement of ductular structures formed by oval cells during hepatocarcinogenesis.

The three-dimensional arrangement of ductular structures formed by oval cells in rats fed 2-acetylaminofluorene (2-AAF) was studied by scanning electron microscopy (SEM) of biliary tract casts and light microscopy of sections of liver injected with india ink via the biliary tract. Both resin and india ink were well injected up to bile ductules, and the findings of each method correlated with each other. By the second week after 2-AAF administration, a few oval cells appeared in the periportal areas forming ductular structures which connected with the portal bile ducts. At the 4th week, increased ductular structures occupied two thirds of the lobule and formed networks communicating with each other, and with the portal bile ducts. At the 8th week, such ductular structures were compressed around hyperplastic nodules and appeared like a basket in biliary casts examined by SEM. Although a histochemical study of gamma-glutamyl transpeptidase revealed activity both on the luminal side of the ductular structures and hepatocytes in hyperplastic nodules, no transition was observed between these two cell populations. These results suggest that oval cells have characteristics more similar to those of biliary epithelia than of hepatocytes, and have no relation to the development of hyperplastic nodules.