Dose‐dependent Induction of Both Pepsinogen‐altered Pyloric Glands and Adenocarcinomas in the Glandular Stomach of C3H Mice Treated with N‐Methyl‐N‐nitrosourea

The dose‐response relation for the appearance of pepsinogen isozyme 1 (Pg l)‐altered pyloric glands (PAPG) and the related induction of adenocarcinomas were examined in male C3H mice given N‐methyl‐N‐nitrosourea (MNU) in their drinking water at the concentration of 120 ppm (group 1), 60 ppm (group 2), 30 ppm (group 3) or 0 ppm (group 4) for 30 weeks and then normal tap water. Animals were killed at weeks 10, 30 and 42. Adenomatous hyperplasias and adenocarcinomas were noted from week 30 and their induction was dose‐dependent at week 42. Almost all cells of pyloric gland cell type in those lesions had little or no immunohistochemically demonstratable Pg 1 content, as was also the case for the cells in PAPG, whose numbers per 100 normal‐appearing pyloric glands were found to be MNU dose‐dependent at all experimental time points. The numbers of PAPG at week 10 significantly correlated with the incidences of adenomatous hyperplasias and adenocarcinomas at week 42. Investigation of proliferation by immunohistochemical detection of bromodeoxyuridine (BrdU) labeling in the PAPG at week 10 demonstrated elevation (P <0.05) as compared to normal pyloric glands. Intestinal metaplasia was not a feature in the present experiment and the results suggest that in mice, PAPG might be a preneoplastic lesion involved in gastric chemical carcinogenesis.