5-HT metabolism in the intestinal wall of the rat-II. The nerves plexuses-interactions between 5-HT containing cells.

The presence of serotonin (5-HT) in dissected intestinal muscular wall of the caecum was demonstrated by the determination of endogenous level of the amine by both spectrofluorimetric and radioenzymatic assays. Biosynthesis of [(3)H]5-HT from [(3)H]tryptophan in in vitro conditions revealed the presence of tryptophan hydroxylase in these muscular layers and therefore strongly suggest the presence of serotoninergic neurons. Following dissection of the mucosa from the muscular layers containing the nerve plexuses, endogenous 5-HT and 5-hydroxyindol acetic acid levels as well as amounts of [(3)H]5-HT synthesized from [(3)H]tryptophan were always higher than those found in intact fragments of the caecum. These results are discussed in terms of metabolic processes involved in the regulation between the two 5-HT containing compartments.