| Abstract: | Sequential histologic changes of the stomach during carcinogenesis induced by N-methyl-N'-nitro-N-nitrosoguanidine (MNNG; CAS: 70-25-7) were studied in susceptible ACI and resistant BUF strain rats. Rats were given MNNG at a concentration of 83 micrograms/ml in their drinking water for 32 weeks and then tap water and were sacrificed sequentially between weeks 1 and 57. In ACI rats, erosions, regenerative changes, focal and slightly atypical changes, and diffuse and severe atypical changes were observed sequentially in the pyloric region during the period of MNNG administration, where adenocarcinomas were observed after the cessation of MNNG treatment. In BUF rats, the main histologic changes induced by MNNG were erosions and hyperplasia of the glandular portion of pyloric glands at the margin of erosions. After the cessation of MNNG treatment, the hyperplasia of the pyloric glands subsided and was followed by atrophy of these glands. The results suggested that the responses of the gastric mucosa to MNNG in ACI and BUF rats were qualitatively different. |
