Substructural alterations of liver parenchymal cells induced by xenobiotics.

Xenobiotic-induced basic ultrastructural reactions of liver parenchymal cells as visualized with the basic method in ultrastructural research, the transmission electron microscopy, are described. There exists no "average hepatocyte", but even the normal liver is composed of a heterogeneous population of parenchymal cells revealing distinct ultrastructural and functional differences according to the intra-acinar location, circadian rhythms or metabolic and physiologic conditions. This liver cell heterogeneity is, as a rule, very much increased after acute or chronic exposure of the liver to any xenobiotic compound. Although most electron microscopic techniques are laborious and time consuming, electron microscopic research will play a growing role in analysing the response of the hepatocytes to drugs or other newly developed chemicals. There is no doubt that new methods and instrumental improvements will enable us to visualize more and more the primary site of action of any xenobiotic and the underlying molecular mechanisms in the hepatocytes followed by a sequence of events which lead to the manifestation of a complex reaction pattern composed of adaptation, injury, degeneration and reparation of the liver.