Immunohistochemical localization of motilin in endocrine non-enterochromaffin cells of the small intestine of humans and monkey.

Motilin-immunoreactive cells in the human and monkey duodenum and upper jejunum were investigated by immunofluorescence (IF) and peroxidase-antiperoxidase (PAP) techniques using antibodies against synthetic 13-norleucine motilin and synthetic porcine motilin. Contrary to previous reports, we have demonstrated that motilin-immunoreactive cells are a distinct cell population that does not correspond to 5-hydroxytryptamine-containing enterochromaffin (EC-) cells. EC-cells, indentified by formaldehyde-induced fluorescence (FIF) or by argentaffinity (AA), do not react with either antisera. EC-cells of the monkey, utilizing one method (PAP), reacted to one antiserum very weakly. This reaction was also suppressed by absorption with 13-norleucine motilin. It is suggested that the EC-cells of the monkey contain either a very small amount of motilin or another peptide that exhibits a part of the amino acid sequence of motilin. The discrepancy between these results and those of other authors can be explained by the different reactivity of the antisera used.