ABSTRACT
5-Hydroxytryptamine (5-HT) or serotonin is a vital cellular signaling molecule mostly present in the central and peripheral nervous systems (serotoninergic neurons), gastrointestinal tract (intestinal myenteric plexus and enterochromaffin cells), bronchopulmonary system (enterochromaffin cells) and cardiovascular system (blood platelets) [1]. While serotoninergic neurons and enterochromaffin cells can synthesize serotonin, platelets only rely on uptake mechanisms to proceed with serotonin storage [2]. The synthesis of serotonin is a complex biochemical pathway that initially involves the conversion of the essential amino acid L-tryptophan to 5-hydroxytryptophan (5-HTP) by the enzyme L-tryptophan hydroxylase (TPH) [3]. It is important to highlight that this reaction is a rate-limiting step for serotonin production in non-neuronal tissues. Subsequently, the aromatic L-amino acid decarboxylase (AADC) catalyzes the final production of 5-HT, and this is internalized by the vesicular monoamine transporter (VMAT) and released to induce both autocrine and paracrine actions [4] (Figure 46.1a).
