Ultrastructural abnormalities in carcinogen-induced hepatocellular altered foci identified by resistance to iron accumulation.

Hepatocellular altered foci were induced in rat liver by cycles of feeding of N-2-fluorenylacetamide and were distinguished by their resistance to iron accumulation following production of hepatic siderosis by dietary administration of 8-hydroxyquinoline and ferrous gluconate. The foci were readily identified by their iron exclusion in plastic-embedded sections stained for iron. Sections from iron-free regions processed for electron microscopy permitted ultrastructural study of cells in foci identified by reduced cytoplasmic ferritin. Altered foci of the eosinophilic type produced by cyclic feeding of carcinogen for 16 weeks were composed of both normal-appearing hepatocytes and others with ultrastructural abnormalities, including increased agranular reticulum with associated glycogen particles, decreased rough endoplasmic reticulum with reduced length of cisternae, degranulated rough vesicles, altered and displaced Golgi complexes, and abnormal bile canaliculi. At 12 and 24 weeks after cessation of carcinogen exposure, cells in persistent eosinophilic foci continued to display ultrastructural abnormalities. They possessed increased rough endoplasmic reticulum with rather regular cisternal arrangement and relatively increased smooth endoplasmic reticulum. Golgi complexes were abnormal. Bile canaliculi were abnormal and occasionally increased in number. Nuclei displayed prominent nucleoli. Cells in a basophilic focus were characterized by the presence of numerous free polyribosomes diffusely scattered throughout the cytoplasm, distended rough endoplasmic reticulum with loss of parallel-stack and hypertrophic dilated Golgi complexes, and prominent marginated nucleoli. The finding that persistent foci continued to display ultrastructural abnormalities, some of which changed or progressed in the absence of further carcinogen exposure, suggests that the persistent iron-excluding foci are a permanently altered population.