Serotonin (5-hydroxytryptamine or 5-HT) is a neurotransmitter associated with the Central Nervous System and the Enteric Nervous System. It is produced by a biochemical conversion process where the amino acid tryptophan, a component of proteins, combines with the enzyme tryptophan hydroxylase, to produce 5-hydroxytryptamine.
It is usually called the happy hormone because it contributes to well-being and happiness. A decrease in its level has been seen in various mental illnesses like depression and anxiety.
Apart from this, serotonin has another crucial role in gut motility. The microorganisms present in the gut are capable of synthesizing 5-HT, but this bacterial production is far exceeded by biosynthesis in Enterochromaffin (EC) Cells. Alternatively, these microbes help regulate the gut and plasma 5-HT levels by providing signals to the host mucosal cells in the form of Tryptophan hydroxylase 1 (TPH1) expression.
Luminal 5-HT is required for intestinal supplement and water assimilation, and impacts bicarbonate and electrolyte discharge into the lumen. Through stimulation of 5-HT3 receptors on intestinal vagal afferent nerve endings, EC-cell–derived 5-HT increases postprandial pancreatic protein release, synergistically with cholecystokinin. This, in turn, increases absorption and assimilation of additional luminal secretion. Gastrointestinal 5-HT increases bile activity by increasing the expression of the apical sodium-dependent bile salt transporter. As such, 5-HT may act as a referee of several impacts that are credited to both 5-HT and Glucagon-Like Peptide-2.
Serotonin and Irritable Bowel Syndrome
Numerous studies were done to legitimize the relation of Irritable Bowel Syndrome to the lack of serotonin synthesis and release.
Researchers examined that a decrease in the production of intestinal serotonin leads to the weakening of the intestinal lining, which inevitably results in clogging or constipation and an increment in serotonin levels within the gut
IBS and its symptoms largely impact daily activities and body image and are a cause of worry to patients. Fifty to 90% of IBS patients have a co-existing psychological condition, reminiscent of anxiety or depression.