Effect of age on the induction of endometrial lesions by a single intra-uterine administration of N-ethyl-N'-nitro-N-nitrosoguanidine in F344 rats.

A total of 54 10-week-old or 49 10-month-old female F344 rats were given a single intrauterine administration of 20 mg/kg N-ethyl-N'-nitro-N-nitrosoguanidine (ENNG) dissolved in polyethylene glycol (PEG) via the vagina using a non-laparotomy approach. Control animals (32 10-week-old or 29 10-month-old rats) were given PEG alone in the same manner. The animals were killed at 15 and 18 months of age, respectively. One animal in the young treated group presented an endometrial adenocarcinoma (incidence: 2.1%), although the incidence and degree of endometrial hyperplasias were significantly increased in both groups of treated animals, as compared to corresponding controls. Histologically, many of these lesions were polypous glandular hyperplasias (adenomatous polyps) with stromal proliferation. The incidence and grade of proliferative lesions in the young treated group were slightly higher than those in the old treated group. ENNG administration did not appear to affect the hormonal situation in treated animals. These results indicate that young animals may be more sensitive to ENNG than aged ones for induction of endometrial lesions, although ENNG-treatment alone is not sufficient for early and high induction of carcinomas even in young rats of this strain.