An ultrastructural study of spontaneous and phenobarbitone-induced nodules in the mouse liver.

Male C3H/He mice were given 0 (control) or 85 mg/kg/day phenobarbitone (PB) in the diet. At 40, 60 and 93 weeks, groups of mice were killed and the ultrastructure of spontaneous and PB-induced liver nodules was examined. Treated mice showed typical centrilobular hypertrophy and eosinophilic nodules which may be considered as an end stage lesion. The nodule cells were similar in appearance to those in areas of centrilobular hypertrophy except for the presence of convoluted membranes which are considered to be indicative of proliferation. The incidence of carcinoma was not increased by PB treatment. The carcinomas from control and treated animals differed in their ultrastructure in that increased levels of smooth endoplasmic reticulum (SER) were seen in the carcinomas of the PB animals. The presence of SER proliferation in the carcinomas of PB animals suggests that carcinoma may respond to the enzyme-inducing effects of PB.