Abstract

The most studied roles of serotonin (5-hydroxytryptamine, 5HT) have been related to its action in the Central Nervous System (CNS). However, most of 5HT is produced outside the CNS, mainly in the enterochromaffin cells of the gut. Additionally, other tissues such as the endocrine pancreas, particularly beta-cells, have its own serotonin system able to synthesize, secrete and respond to extracellular 5HT through cell surface receptors subtypes that have been grouped in 7 families (HTR1-7). Interestingly, 5HT is stored in granules and released together with insulin from beta-cells and its biological significance is likely a combination of intra and extracellular actions. The expression of enzymes involved in 5HT synthesis and their receptors varied markedly in beta-pancreatic cells during pregnancy, in parallel with an increase in their insulin secretion potential (probably through the action of Htr3a) and an increase in I3-cell mass (through the action of Htr2b and Htrld). In addition, it has been suggested that gut-derived 5HT may promote hepatic gluconeogenesis during prolonged fasting through Htr2b receptor. Taken together, these findings suggest that peripheral 5HT plays an important role in the regulation of glucose homeostasis through the differential expression and activation of 5-HT membrane receptors on the surface of hepatocytes, adipocytes and pancreatic beta-cells.