Induction of endometrial adenocarcinomas by a single intra-uterine administration of N-ethyl-N′-nitro-N-nitrosoguanidine to aged Donryu rats showing spontaneously persistent estrus

Induction of endometrial adenocarcinomas by a single intra-uterine administration of N-ethyl-N′-nitro-N-nitrosoguanidine (ENNG) to aged rats was examined. Donryu rats showing spontaneously persistent estrus were given a single intra-uterine administration of ENNG (20 mg/kg) at 10 months (44 weeks) of age. At the termination of the experiment (week 34 after the ENNG-treatment), 22% and 13% incidences of endometrial adenocarcinomas were observed in the experimental and control groups, respectively, the difference being without significance. No variation was found in the endocrine environment between experimental and non carcinogen-treated control animals throughout the experimental period. These results show that ENNG-treatment alone is not sufficient in aged rats for high induction of endometrial carcinomas. Comparison of the data with those from our previous studies, in which ENNG was given at a young age (10 weeks of age), indicates that young rats may be more sensitive than their old counterparts.