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

The alimentary tract is the main source of 5-hydroxytryptamine (5HT, serotonin) in the body, but the physiological role of this amine is as yet uncertain. Bulbring and Crema (1958) have shown that 5HT potentiates the peristaltic reflex when applied to the mucosal surface of the guinea-pig ileum in vitro. In man, intravenous injections of serotonin stimulate pressure waves in the jejunum and ileum (Hendrix, Atkinson, Clifton, and Ingelfinger, 1957) but inhibit the distal colon (Fink and Friedman, 1960). It is possible therefore that serotonin causes the alimentary symptoms of the carcinoid syndrome. In vitro, 5HT contracts human muscle strips from the small intestine but inhibits strips from the colon (Fishlock and Parks, 1963). The application of in vitro techniques to the study ofhuman alimentary muscle is an important advance, but cannot replace studies in vivo. We have therefore investigated the effect of 5-hydroxytryptamine both in vivo and in vitro on the stomach, small intestine, and colon. In addition, experiments were performed on strips of oesophageal muscle in vitro. We have also recorded the motility of the small intestine and colon in a patient with the carcinoid syndrome.