Single GST-P positive liver cells--putative initiated hepatocytes.

Immunohistochemical investigation of liver tissue 48 h after single doses of the hepatocarcinogens diethylnitrosamine (DEN), dimethylnitrosamine, aflatoxin B1 and methylazoxymethanol acetate revealed the generation of a population of single glutathione S-transferase placental form (GST-P) positive hepatocytes. Yield was carcinogen dose dependent. Although the mixed function enzyme inducers sodium phenobarbital (PB), methylcholanthrene (Mech), polychlorinated biphenyls (PCB) and isosafrole (IS) did not in themselves induce comparable single cell lesions, their application prior to DEN caused significant alteration in the resultant numbers of GST-P positive hepatocytes observed. While PB and IS were associated with decreased yield, Mech and PCB, in contrast, brought about an increase. The results gained from investigation of the effects of 3-aminobenzamide administration and partial hepatectomy carried out at different times after carcinogen treatment also pointed to an 'initiated' character for the lesions and suggest that GST-P may be a useful marker for analyzing factors relevant to the initiation stage of hepatocarcinogenesis. Thus the interplay between carcinogen metabolism, DNA adduct formation and repair, toxicity and proliferation may be assessable in terms of numbers of enzyme-altered solitary hepatocytes.