Background/Aims: Carcinoid patients show a hypertonic colonie motor response postprandially. Ondansetron reduces postprandial colonie tone in health. It was hypothesized that ondansetron, a selective 5HT3 antagonist, corrects the colonic motor response to eating in carcinoid diarrhea. Methods: The effects of ondansetron and placebo on fasting and postprandial colonic tone and motility in 10 patients with carcinoid diarrhea were compared using a manometry-barostat assembly positioned in the upper descending colon. Results: Fasting colonic tone and motility indices were similar in the placebo and ondansetron groups; ondansetron did not affect fasting motility. The placebo group showed a significant reduction in barostat balloon volume (signifying increased tone) from 207 ± 29 ml (mean ± SEM) during fasting to 106 ± 14 ml postprandially (P = 0.01). With ondansetron, a tonic colonie response was induced postprandially (198 ± 37 mL to 151 ± 30 mL; P = 0.053). However, the increment in tone in the ondansetron group (23% ± 7%) was significantly lower than in the placebo group (48% ± 5%; P = 0.02) and was similar to that observed in untreated healthy subjects (24% ± 3%). Postprandial manometric pressure activity increased significantly in the placebo group (P = 0.01); in the ondansetron group there was a trend (P = 0.09) to increased phasic activity. Conclusions: Ondansetron reduces the postprandial colonie hypertonic response in carcinoid diarrhea to levels previously reported in health; further clinical studies of this class of antagonists in carcinoid diarrhea appear warranted.
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