Histopathological and ultrastructural study on extramedullary hematopoietic foci in early stage of 3'-methyl-4-(dimethylamino)azobenzene hepatocarcinogenesis.

A quantitative analysis was performed on the extramedullary hematopoietic foci which appeared in the liver during the early stages of hepatocarcinogenesis with 3'-methyl-4-(dimethylamino)azobenzene in rats. The frequency in the appearance of the foci reached a maximum at around 3 weeks of azo-dye feeding. Since the liver in this period has been known to show deviation of various characteristics toward fetal liver, an intimate correlation of the appearance of the foci and fetal character of the liver was suggested. Histologically the hematopoietic foci were always observed in the sinusoidal space of original hepatocytes adjacent to the oval cell proliferating area. Ultrastructurally the cells of the foci were identified as erythroblasts and were found in the space of Disse as seen in the hematopoiesis in fetal liver.