Serotonin: receptors and antagonists--summary of symposium.

Serotonin is a widely distributed amine, although 95% is found in the enterochromaffin cells of the gastrointestinal mucosa. Its effects are mediated via a large number of receptors differing in their physiological and pharmacological properties. Its principal actions are on the cardiovascular system, both directly and potentiating the effects of the vasoconstriction from noradrenaline, angiotensin and histamine; similarly it potentiates the effect of various platelet aggregating substances. There is evidence that 5-hydroxytryptamine releases endothelium-derived relaxing factor attenuating its direct constriction effect and in the human forearm an increase in flow is seen from serotonin. In the absence of endothelium as in atherosclerosis, vasoconstriction occurs. Serotonin antagonism may have useful therapeutic effects and ketanserin has undergone wide evaluation. There is evidence that ketanserin should be avoided with potassium-losing diuretics as an increased mortality has been reported with the combination.