A Possible Vagal Adrenergic Release of Serotonin from Enterochromaffin Cells in the Cat

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Abstract
The intracellular concentrations of serotonin (5-HT) in enterochromaffin cells (EC) in the cat small intestine have been studied by a cytofluorimetric method before and after long-lasting efferent vagal nerve stimulation in the neck. Such stimulation induces a decrease of 5-HT in EC of the gut as observed previously. Pretreatment with atropine could not block this decrease, suggesting a noncholinergic mechanism. Pre-treatment with a β-blocking agent, propranolol, or bilateral removal of the superior cervical ganglia could, however, block this 5-HT decrease. Pretreatment with an α-blocking agent, phenoxybenzamine, caused an increase in the 5-HT content of EC both with and without nerve stimulation; the reason for this is obscure. The results indicate, that vagal nerve stimulation induces a neurogenic 5-HT release from EC in the gut, and that adrenergic fibres, originating in the superior cervical ganglia, mediate this release probably via a β-receptor mechanism. Whether or not an α-receptor mechanism is also involved cannot be judged at present.