ALBERT

Notes: Summary The African rodent Mastomys spontaneously develops gastric argyrophil carcinoids. The tumor cells showed a varying degree of argyrophilia. The most strongly argyrophilic cells showed an OPT-induced fluorescence suggesting the presence of histamine. In addition, electron microscopy showed that these strongly argyrophil cells contained numerous cytoplasmic granules, similar to the endocrine-like cells in the oxyntic gland area of the rat and mouse stomach. The bulk of tumor cells, however, were weakly argyrophil, conceivably due to the scarcity of cytoplasmic granules. These granules resembled those of many polypeptide hormone-producing tumors, such as bronchial carcinoids and medullary thyroid carcinoma. Chemical analysis revealed the presence of histamine and histidine decarboxylase in extracts from tumor tissue. These observations agree with previous findings of numerous histamine-containing (OPT-fluorescent), argyrophilic, endocrine-like cells in the oxyntic mucosa of the rat and mouse stomach. In search for the parent cell of the gastric carcinoid of the Mastomys, histofluorescence techniques, in combination with light and electron microscopy, were used. 1. The OPT-method for the fluorescence microscopic demonstration of histamine revealed a small population of fluorescent cells scattered in the epithelium of the oxyntic and pyloric mucosa. 2. The fluorescent cells were argyrophilic after silver-staining according to Grimelius. In the pyloric gland area, however, most of the argyrophilic cells were non-fluorescent. 3. The Falck-Hillarp fluorescence technique revealed that the argyrophil cells had the capacity to accumulate dopamine after injecting animals with the precursor DOPA. This was also true for the tumor cells. 4. The pyloric gland area was rich in 5-hydroxytryptamine-containing endocrine-like cells as revealed by their formaldehyde-induced fluorescence and by the positive argentaffin staining of their cytoplasmic granules at the electron microscopic level. 5. Ultrastructurally, the epithelium of the oxyntic gland area contained scattered endocrine-like cells with numerous cytoplasmic granules. Based on the morphology of their cytoplasmic granules, at least two different cell types could be distinguished, probably representing two types of histamine-containing cells. It is suggested that a common progenitor of the two types of histamine-containing argyrophil endocrine-like cells in the oxyntic gland area of the Mastomys stomach represents the parent cell of the tumor.