Gut endocrine cells in rat stomach carcinoma induced by N-methyl-N'-nitro-N-nitrosoguanidine

Gut endocrine cells in a total of 18 gastric adenocarcinomas in inbred Wistar rats induced by N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) and gastrin or serotonin, were examined histologically, ultrastructurally, and immunohistochemically for gastrin, somatostatin, calcitonin, glicentin, and serotonin. A large number of argyrophil cells were observed in 17 tumors (94.4%) and 14 tumors (77.8%) had argentaffin cells. Immunohistochemically, C-terminal fragment of gastrin (G17) immunoreactivity was observed in 15 (82.2%) out of the 18 tumors, but 3 G17-positive tumors had no G 34 immunoreactive cells in rats treated with MNNG plus gastrin. Serotonin immunoreactivity was detected in 14 tumors (77.8%). Somatostatin immunoreactivity was detected in 7 of the 11 tumors (63.6%) in rats treated with MNNG plus gastrin whereas no tumor in rats treated with MNNG plus serotonin had somatostatin, the difference of the incidence being significant (P less than 0.05). One endocrine cell carcinoma which consisted mainly of serotonin-producing cells was observed in a rat treated with MNNG plus serotonin. Calcitonin and glicentin immunoreactivity was not demonstrated in any tumors. Ultrastructurally, three types of endocrine granule were found in the tumor cells. These data suggest that hormonal environment in stomach carcinogenesis may influence the expression of endocrine cells within the tumors.