5‐HTP induced diarrhea as a carcinoid syndrome model in mice?

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Abstract
Summary—Serotonin (5‐HT) is present in the gastrointestinal tract and is probably one of the compounds responsible for diarrhea in patients presenting with carcinoid syndrome. Intraperitoneal administration of L‐5‐hydroxytryptophan (L‐5‐HTP) at doses of 25 to 100 mg/kg dramatically increase defecation in mice. In this new paradigm, counting fecal boli deposited is simple and the appraised or inhibition of diarrhea induced by ip 25 mg/kg of L‐5‐HTP is very clear, with a good reproducibility of scores. L‐5‐HTP needs to be metabolized into 5‐HT to be active; benserazide, an inhibitor of decarboxylase, antagonized the diarrhea induced by 5‐HT. Among the 5‐HT antagonists used in interaction with 5‐HT, only those of the 5‐HT3type (ondansetron, granisetron, tropisetron) and, to a lesser extent 5‐HT2type (ritanserin), decreased the diarrhea induced by 5‐HTP. The 5‐HT4receptor agonists from the benzamide family (metoclopramide and zacopride) increased defecation in mice but the effect failed to reach statistical significance.