5-HT metabolism in the intestinal wall of the rat-I. The mucosa. 
Serotonin (5-HT) metabolism was studied on isolated mucosa of the rat caecum in order to determine its characteristics in enterochromaffin cells.  High levels of 5-HT were found in these cells and weak catabolic processes were demonstrated.  Enterochromaffin cells of the mucosa are able to synthesize ((3)H)5-HT from ((3)H)tryptophan in vitro indicating that these cells might contain tryptophan hydroxylase.  In addition, a high affinity uptake of exogenous ((3)H)5-HT is demonstrated.  These results show that enterochromaffin cells of the mucosa present similar biochemical properties compared to those described for serotoninergic neurons of the central nervous system.