Sequential observations on the appearance of neoplastic lesions in the liver and kidney after treatment with N-ethyl-N-hydroxyethylnitrosamine followed by partial hepatectomy and unilateral nephrectomy.

Sequential observations were carried out on the induction of preneoplastic lesions in the liver and the kidney. Rats were initially given N-ethyl-N-hydroxyethylnitrosamine (EHEN) in their drinking water (0.1%) for 3 days (Group 1), 1 week (Group 2) or 2 weeks (Group 3) or tap water (Group 4). Rats in Groups 1-3 were subjected to partial hepatectomy and unilateral nephrectomy (right side) 2 weeks after the end of EHEN treatment. Rats from these groups were killed in week 10, 20, 30 and 40 of the experiment. In the liver, the effect of EHEN in the induction of gamma-glutamyltranspeptidase (gamma-GT) positive foci and hyperplastic nodules (HN) was clearly dependent on the length of treatment. The preneoplastic lesions increased with the lapse of observation time. Changes measured as number of gamma-GT positive foci were 10-40 times greater than those measured as HN, especially among the small size range. Values for changes in Group 1 given 0.1% EHEN for 3 days were very low, indicating that this dose is close to the threshold. Two rats with hepatocellular carcinoma in Group 3 given EHEN for 2 weeks survived until week 40. In the kidney, tubular epithelial proliferations composed of cells with slightly basophilic cytoplasm and slightly atypical nuclei were tentatively named atypical cell foci (ACF). EHEN induced ACF, renal cell adenomas and renal cell carcinomas. The increase in the induction of ACF was dependent on the length of observation period but not on the length of treatment. Even though control rats (not treated with EHEN) also had ACF, their quantitative values were far less than the groups given EHEN and killed at week 40, indicating that a large number of ACF were induced by EHEN. Therefore, EHEN is good for experimental induction of preneoplastic lesions in the liver and kidney of rats. The experimental schedule for Groups 1 and 2 could be used as a shortterm screening test for promoters and the schedule for Group 3 as an assay for inhibitors.