A New Positive Feedback Circuit in the Fibrosis–Cancer Axis for Male Livers

Serotonin (also known as 5-hydroxytryptamine [5-HT]) is a small-molecule neurotransmitter that was identified in a series of studies conducted between 1935 and 1953 because of its capacity to induce contractions in the intestine and blood vessels. A plethora of functions for the serotonin system have been described, including regulation of mood, blood clotting, gut motility, systemic energy homeostasis, and tissue repair. Serotonin is synthesized from the essential amino acid tryptophan via tryptophan hydroxylase (TPH) in the brain and enterochromaffin cells of the gastrointestinal tract.