The vagal release of 5-hydroxytryptamine from enterochromaffin cells in the cat

Enterochromaffin cells (EC) from the cat duodenum were studied before and after electrical efferent stimulation of the cervical vagi by means of electron microscopy and fluorescence histochemistry according to the Hillarp-Falck technique. From the same animals portal blood plasma was assayed for serotonin (5-HT) at various stages of the nerve stimulation. Within 15 min after the onset of vagal nerve stimulation there was a more than twofold increase of the portal 5-HT levels, which returned to normal after cessation of stimulation. There was also a pronounced reduction in the fluorescence intensity of EC demonstrating a lowered intracellular 5-HT level. Ultrastructurally there was evidence for basal exocytosis as well as for a release of osmiophilic material from the EC directly into the gut lumen after nerve stimulation. Together, these observations strongly suggest a vagally induced 5-HT release from EC in the cat.