Immunofluorescent localization of secretin in the canine duodenum.

The endocrine polypeptide (APUD) cells responsible for the production and storage of secretin have been demonstrated, in canine duodenum, by the application of an indirect immunofluorescence technique, using anti-pure porcine secretin, to carbodiimide-fixed cryostat sections. The cells are identified, by the use of parallel cytochemical and ultrastructural preparations, as the small granular S cells. These are essentially restricted to the transitional zone of the duodenal mucosa, with whose lumen their apical projections probably always make contact. There is no need to alter the title of the cells since S can now stand for secretin instead of for small.