Vagal influence on serotonin concentration in enterochromaffin cells in the cat

The intracellular concentrations of 5-HT in enterochromaffin cells of the jejunum, midgut and ileum of the cat have been estimated by a cytofluorimetric method before and after various periods of peripheral vagal nerve stimulation. The fluorescence intensities in randomized cell samples were measured photometrically after a standard illumination time before and after nerve stimulation. A significant decrease in 5-HT concentration in the enterochromaffin cells all through the small intestine could be demonstrated, which is in support of the hypothesis of a neurogenic release of 5-HT from enterochromaffin cells, possibly caused by vagal adrenergic fibres.