Serotonin is an important neurotransmitter of the central nervous system (CNS) with several roles in human health. In this post I will be giving some insight into serotonin’s role within the gastrointestinal tract (GIT) and it’s effects on diseases and dysfunction of the GIT. The main role of serotonin in the GIT is to act as a regulator of the physiology of the gut.
Serotonin (5-HT) is primarily produced in GIT by enterochromaffin (EC) cells, with a link to diseases and disorders including:
- Irritable Bowel Disease (IBD) which includes Crohn’s Disease and Ulcerative Colitis
- Irritable Bowel Syndrome (IBS) with symptoms ranging from diarrhea (IBS-D), constipation (IBS-C) and alternating (IBS-A). IBS-A signifies a change in symptoms between diarrhea and constipation. There is usually cramping, pain and flatulence with IBS
- Celiac Disease results in a heightened immune response to gliadin (wheat protein or gluten) and leads to diarrhea and fatigue (among other symptoms) with the consumption of wheat and wheat containing foods and products.
- Diverticulitis is where pouches form on the outside of the GIT mucosa
Serotonin (5-HT) affects gut motility and and modulates the immune system, as 5-HT receptors are found on immune cells which can synthesize serotonin from tryptophan. The close proximity of EC cells to immune, neural and vascular cells within the GIT influence immune responses and endocrine system function.
In order for serotonin synthesis to occur by the EC cells, tryptophan (an amino acid) needs to be converted to 5-hydroxy-L-tryptophan (5-HTP) and catalyzed by tryptophan hydroxylase (TpH). The EC cells convert 5-HTP to 5-HT.
EC cells release serotonin (5-HT) via stimulation of the vagal nerve. This stimulation occurs with the ingestion of food, amino acids, various solutions in the GIT, or the presence of acid in the GIT. Short Chain Fatty Acids (SCFA’s) produced by bacteria in the gut, also help to stimulate the release of serotonin. Serotonin then moves into the lumen of the GIT which affects the enteric nervous system (ENS) cells.
Signalling alterations in 5-HT are associated with celiac disease, colorectal cancer and diverticular diseases.
In Crohn’s Disease, there is an increase in EC cells, serotonin and tryptophan.
Ulcerative Colitis sees reduced EC cells, tryptophan and serotonin.
Irritable Bowel Syndrome (IBS) has a higher amount of EC cells with decreased serotonin, while IBS-C has increased serotonin.
In terms of gastrointestinal health, serotonin plays a huge role, and balancing this, along with several other factors, is crucial in the healing and repair of the gut so as to bring about balance, encourage and support gastrointestinal health, reduce symptoms of disease and dysfunction, and promote general overall health and well-being.
Photo: Vaga Nutrition