Differential localisation of substance P and motilin.

: Motilin, and Substance P, have previously been shown to be present in enterochromaffin (EC) cells in the gut mucosa. By comparing a specific immunofluorescence stain for Substance P with an immunoperoxidase reaction for motilin, applied sequentially to the same tissue section, it is possible to demonstrate that the two peptides are present in different cells. It is concluded that a) at least two different types of EC cells must exist and b) these results provide further evidence for the neuroectodermal origin of the gastrointestinal APUD cells. Studies of the degranulation pattern of EC cells could help to elucidate the role of amines in the mechanism of storage and secretion of different peptides under normal and pathological conditions.