Endocrine cells in the anal canal.

Endocrine cells are normal inhabitants of the anal canal. While numerous endocrine cells are distributed throughout anal ducts and crypts, few are dispersed in the anal transitional zone. All these cells were characterized as serotonin-storing cells, and this endocrine profile is quite distinctive from that of adjacent mucosae. Rectal epithelium contains serotonin, somatostatin, enteroglucagon, BPP and HPP immunoreactive cells; endocrine cells are lacking in the pectinal folds and perianal skin. It is suggested that this distinctive hormonal profile may be regarded as a specific marker of this anal territory. The same pattern is found in the fetal transitional lining of anal canal. Evidence of serotonin-storing cells in the transitional epithelium of anal glands and crypts and in the ATZ epithelium, reinforces the homology between these linings and urothelium. The presence of a similar fetal epithelium implies that ATZ epithelium in adults is not necessarily metaplastic. All derivatives of the cloaca may therefore share the same endocrine profile.