N-NITROSOMETHYLUREA-INDUCED CARCINOGENESIS IN THE PROGENY OF MALE-RATS OF DIFFERENT AGES

Three-month-old male and 3-month-old female LIO rats as well as 25-mon th-old males and 3-month-old females were mated and at the age of 3 mo nths their progeny were exposed to a single intravenous injection of N -nitrosomethylurea (MNU) at the dose of 20 mg/kg of body weight or sol vent. Animals were under observation during 18 months after injection of the carcinogen. There was no significant difference in spontaneous tumor incidence between progeny of young and old male rats. At the sam e time, the susceptibility to the carcinogenic effect of NMU in the ma le and female progeny of old males was slightly but significantly incr eased in comparison to the progeny of young males. Mesenchymal kidney tumors were discovered in the NMU-treated male progeny of old males bu t not in the male progeny of young male rats. In females, the incidenc e of mesenchymal kidney tumors in the NMU-treated progeny of young and old males was 7% and 20%, respectively, and the mean survival times o f these tumor-bearing rats was 4 months shorter in the last group. The data obtained are in agreement with the observation on germ-line tran sgeneration transmission of predisposition to carcinogenesis.