Leiomyomas and leiomyosarcomas of the kidney in 4-day-old BUF rats given methylazoxymethanol acetate intraperitoneally.

The effect of age and sex on the development of renal tumors was studied in inbred BUF male and female rats 4 days, 5, 8, 12, 24, or 52 weeks old. Methylazoxymethanol (MAM) acetate was injected ip (20 mg/kg body wt) once weekly for 9 weeks. Animals 52 weeks old died from hepatic and/or renal necrosis; however, animals of other ages survived 24-42 weeks. Female rats 4 days old were susceptible to the development of leiomyomas and leiomyosarcomas of the kidney, whereas 4-day-old male rats had a few leiomyomas. Adenomas and carcinomas of the kidney and nephroblastomas were not observed. It was concluded that the aglycone of cycasin, MAM, is important in the induction of leiomyosarcomas of the kidneys in 4-day-old rats.