PRAOMYS (MASTOMYS) NATALENSIS - A MODEL FOR GASTRIC CARCINOID FORMATION

The gastric carcinoid tumors of Praomys (Mastomys) natalensis have bee n reviewed with respect to histogenesis, development, biochemistry, an d morphological properties. Multicentric gastric carcinoids frequently develop in the oxyntic mucosa of aging Mastomys. The development of t hese tumors can be significantly enhanced by drug-induced hypergastrin emia, e.g., histamine2-receptor blockade. Spontaneous and drug-induced gastric carcinoids are endocrine in nature, as evidenced by their arg yrophilic staining properties and chromogranin A content. They are als o rich in histidine decarboxylase activity and produce large amounts o f histamine, although other hormones, such as peptide YY and enteroglu cagon, have also been demonstrated in these tumors. Ultrastructurally, gastric carcinoids are composed of tumor cells with typical secretory granules resembling those of enterochromaffin-like (ECL) cells. A clo se examination of the gastric carcinoids in Mastomys reveals striking similarities with gastric carcinoids developing in humans suffering fr om chronic atrophic gastritis type A or from the Zollinger-Ellison syn drome in combination with multiple endocrine neoplasia type 1 (MEN-1). Both these conditions are associated with hypergastrinemia and a high er risk for developing multi-centric gastric carcinoids of ECL-cell or igin. The Mastomys tumor model therefore appears to be a significant e xperimental model in which induction and formation of gastric carcinoi d tumors can be studied.