Ultrastructural studies of endocrine cell populations showing an argentaffin reaction and/or serotonin immunoreactivity in the rat antral mucosa.

On the basis of staining results in closely related semi-thin sections from rat antral mucosa immunostained with polyclonal serotonin antibodies and silver-stained for the argentaffin reaction, respectively, three different cell populations could be distinguished. One of these cell populations showed both serotonin immunoreactivity and an argentaffin reaction, a second one serotonin immunoreactivity alone, and a third one only an argentaffin reaction. These cell populations were studied electron microscopically in ultra-thin sections located between the stained semi-thin sections. The cell population displaying an agentaffin reaction and serotonin immunoreactivity showed secretory granules of the enterochromaffin cell type. A similar granular appearance was observed in cells which only exhibited an argentaffin reaction. Serotonin immunoreactivity in the absence of an argentaffin reaction was evident in some G (gastrin) cells, and in some D1 and possibly also some D (somatostatin) cells; but not all the endocrine cells of the non-enterochromaffin type displayed serotonin immunoreactivity. The significance of the different reactions in the three cell populations is discussed.