Gut , 1960 , 1 , 44 . SEROTONIN , BANANAS , AND DIARRHOEA

"Is 5-hydroxytryptamine (5-H.T.) Nature's remedy for constipation?" This speculation (Collier, 1958) about a possible r6le for 5-H.T. was prompted by the following observations: it is present in the intestinal mucosa in higher concentration than in any other tissue of the body; it causes isolated pieces of intestine to contract; and when given to mice by injection (Erspamer, 1952) or by mouth it increases the amount of faeces passed, "as a much larger dose of senna does" (Collier, 1958). Bulbring and Lin (1958) have also recently shown that 5-H.T. stimulates peristalsis when introduced into the lumen of the isolated guinea-pig intestine. These observations lend some support to the view that 5-H.T. may be concerned in the regulation of bowel function in some animals, and, by inference, in man, especially as diarrhoea is a prominent symptom of the carcinoid syndrome. We have, therefore, tried to obtain further evidence about the relationship between 5-H.T. and bowel function in man in two separate studies. As very little is known about the fate of 5-H.T. or its effect on intestinal motility when given by mouth, we observed the effects of feeding large amounts of it in the form of bananas to a group of normal subjects and measured its excretion in the urine as 5-hydroxyindoleacetic acid (5-H.I.A.A.). Anderson, Ziegler, and Doeden (1958) noted that monkeys excreted much more 5-H.I.A.A. when bananas were added to their diet, and Waalkes, Sjoerdsma, Creveling, Weissbach, and Udenfriend (1958) showed that this was because bananas contain large amounts of serotonin. This surprising finding was of further interest because bananas have enjoyed a traditional reputation in the treatment of coeliac disease and other bowel disorders. In our second