Spontaneous occurrence of gamma-glutamyl transpeptidase-positive hepatocytic foci in 105-week-old Wistar and 72-week-old Fischer 34 male rats.

Spontaneous hepatic changes in old male rats of Wistar and F344 inbred strains were studied histochemically. gamma-Glutamyl transpeptidase-positive hepatocytic foci and cholangiolar proliferation associated with fibrosis and inflammatory infiltration were common findings in the old rats of both strains. Histochemical properties of the hepatocytes of the foci were similar to those of hyperplastic foci seen in early stages of liver carcinogenesis due to various chemical carcinogens. The incidence of the foci was 2.52/cm2 of the histochemically stained sections in 105-week-old male Wistar and F344 rats, and the presence of other spontaneous neoplastic and nonneoplastic changes was revealed.