Localization of melatonin (Mel) and receptors (MT1 and MT2) in human gastrointestinal tract and pancreas assessed using immunohistochemistry.

Melatonin, MT1 and MT2 IR was strongest in the large intestine epithelium. At all levels of the gastrointestinal tract, the percentage of MT2-positive epithelial cells varied greatly between cases (from 5% to >75). Melatonin and MT2 and immunoreactivity (IR) is found in endocrine cells in the gut and pancreas. These cells are most plentiful in the small and large intestine. Melatonin IR was not assessed for plexus and vasculature. Nerve and vascular tissue showed both MT1 and MT2 IR although this was more frequent and stronger for MT2. Numbers of individuals where tissues were available for assessment is indicated under N. Percentage of individuals where tissue showed IR and the tissue type where IR was found is indicated (n). “na”: not applicable1Shown for cases where sufficient tissue was available for evaluation.2Serotonin IR is also negative for these sections.3Differences between expression in stomach (a), small intestine and appendix (b) and large intestine (c). Significance tested with the Kruskal-Wallis Test and the Mann Whitney U Test was used as a post-hoc test,*p**p***pns = not significant.Localization of melatonin (Mel) and receptors (MT1 and MT2) in human gastrointestinal tract and pancreas assessed using immunohistochemistry.