Activation of intracisternal A particles in mouse liver by diethylnitrosamine.

Livers of 6- to 7-week-old male C3H/He, CBA, A, and BALB/c mice were examined by electron microscopy for the presence of intracisternal A particles (ICAP) after administration of diethylnitrosamine (DEN) in drinking water. In control mice, ICAP were extremely rare; they were found in the livers of only 2 mice (strains C3H/He and A; none in the other strains). By contrast, the treatment of mice with DEN greatly enhanced the appearance of ICAP in the liver cells of all strains. Within 2 weeks of the treatment, ICAP were found in 8-26% of liver cells examined in all mice and the number of ICAP/cell ranged from 3 to 12. Aside from mild disorganization of the rough endoplasmic reticulum, such as segmentation and vesiculation, liver cells of carcinogen-treated mice showed none of the consistent abnormalities that characterize the appearance of ICAP. The reactivation of ICAP (which are usually suppressed in adult mice) by DEN may become a useful marker for analysis of the sequential alterations of the liver that lead to the development of hepatoma during carcinogenesis.