Motor responses of human gastrointestinal tract to 5-hydroxytryptamine in vivo and in vitro

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EDITORIAL SYNOPSIS This paper reports studies on the effects of serotonin on gastrointestinal motility in vivo and on muscle strips in vitro. Serotonin stimulates upper and lower small intestinal motility but inhibits activity in the stomach and colon. This effect is apparently a direct one on the smooth muscle. These studies fit in well with the observed effect in man in the carcinoid syndrome, as patients with increased urinary excretion of 5HIAA have been shown to have hypermotility of the small intestine and hypomotility of the colon.