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.

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Prostaglandins (PGs) are hydroxy-fatty acids widely distributed in animal and human tissues and biologically active in minute amounts. Despite the vast literatureltheir physiological role remains unclear. They are present in the gastrointestinal tract and although comparatively little is known about the function of these PGs912, there is some evidence that they may be concerned in some physiological and pathological processes affecting the gut. This review examines the present state of knowledge about PGs in relation to the gastrointestinal tract. Chemical Structure and Synthesis The PGs are derived from 'prostanoic acid'. They are unusual amongst biological compounds in that they contain no nitrogen, but consist of a C20 molecule with a five-membered ring between C8 and C12 (figs 1 and 2)1" 1-15. Many naturally occurring PGs have been isolated, but the gastrointestinal effects of only PGE1, PGE2, and PGF2,, and to a lesser extent PGA, and PGFc, have been studied. Although the F type PGs differ from prostaglandins of the E type solely in having a hydroxyl instead of a ketone group at the C9 position, their biological properties are markedly different.

EDITORIAL COMMENT Near maximal infusions of pentagastrin were found to have no consistent effect upon motility except in the gastric antrum. The results suggest that gastrin is not directly concerned in the mediation of the gastro-colic reflex.