Intracellular pancreatic B cell serotonin and the dynamics of insulin release

The role of intracellular pancreatic B cell serotonin in the dynamics of insulin release was investigated in an in situ perfused rat pancreas preparation. Animals were pretreated with 5-hydroxytryptophan (5-HTP) to increase the intracellular levels of serotonin (5-HT) as shown by fluorescence histochemistry. Despite a clear induction of intracellular 5-HT fluorescence in pancreatic islets neither the pattern nor the total amount of insulin released were significantly modified after perfusion with either glucose or tolbutamide. However, the L-amino acid decarboxylase inhibitor, RO 4--4602, significantly decreased both phases of glucose-mediated insulin release in normal animals as well as in those receiving 5-HTP.