Enterochromaffin-like cell carcinoids of gastric mucosa in rats after life-long inhibition of gastric secretion.

Small intramucosal tumours in the oxyntic area of the rat stomach were observed in an oncogenicity study with omeprazole. The tumours could be defined as carcinoids of enterochromaffin-like (ECL) cell origin. ECL cells occur exclusively in oxyntic mucosa and respond to the trophic hormone gastrin with a proliferation that becomes exaggerated in old rats. Inhibition of gastric acid secretion is known to induce hypergastrinaemia in rats. According to the common concept of endocrine cells, a sustained hormonal stimulation with gastrin may induce a continuous gradient between hyperplasia and neoplasia of the ECL cells. The tumours found are thus to be regarded as hormone-induced endocrine tumours of the ECL cells in the stomach. The ECL-cell tumours of the rats in the oncogenicity study appeared to belong to the low-malignancy type of carcinoids and did not make their appearance until the end-life period of the study. The sex and species differences observed may be explained by inherent differences in gastrin response, spontaneous ECL cell density or in responsiveness to gastrin-stimulated ECL cell proliferation between sexes and species.