Three‐dimensional Analysis of Glutathione S‐Transferase Placental Form‐positive Lesion Development in Early Stages of Rat Hepatocarcinogenesis

The development of glutathione S‐transferase placental form (GST‐P)‐positive lesions in the rat liver, from single cells to foci, and their locations within liver lobules were examined by a combined stereological approach for calculation of three‐dimensional (3‐D) data and by 3‐D computer graphics for reconstruction of lesions. Two weeks after initiation with diethylnitrosamine, the rats were divided into two groups. Animals in group 1 were given 2‐acetylaminofluorene, and animals in group 2 were given basal diet for 6 weeks. Partial hepatectomy (PH) was performed at week 3. The GST‐P‐positive single cells increased in number per liver after PH in group 1, but not in group 2, where a plateau level was maintained. The number of GST‐P‐positive foci per liver in group 2 also reached an almost constant low value after 4 weeks. In contrast, foci in group 1 increased greatly after PH. A 3‐D reconstruction, performed with a computer graphics system using up to 180 sections at 10 μm intervals, revealed the single cells to be distributed at random. Those that grew into foci were also not preferentially localized in any particular zone of the hepatic lobule. When foci within the same lobule came into contact, they underwent fusion. The present results thus indicate that only a small proportion of GST‐P‐positive single cells develops into foci, and that their growth is independent of zonal factors within individual lobules in early stages of rat hepatocarcinogenesis.