Immunoelectron cytochemical localization of motilin and substance P in rabbit bile duct enterochromaffin (EC) cells.

Using an immunoreactive technique the two peptides, motilin and Substance P, have been localized at the ultrastructural level in enterochromaffin (EC) cells. Motilin occurs in cells containing a mixed population of biconcave and round secretory granules whereas Substance P is found in cells with exclusively round granules. These observations confirm the existence of at least two functionally and morphologically different types of EC cell in rabbit bile duct, both of which contain 5-hydroxytryptamine. Classification of the endocrine cells of the gut on a purely morphological basis is clearly impossible, however.