Abstract
Serotonin (5-hydroxytryptamine, 5-HT) plays two important roles in humans—one central and the other peripheral—depending on the location of the 5-HT pools of on either side of the blood-brain barrier. In the central nervous system it acts as a neurotransmitter, controlling such brain functions as autonomic neural activity, stress response, body temperature, sleep, mood and appetite. This role is very important in intensive care, as in critically ill patients multiple serotoninergic agents like opioids, antiemetics and antidepressants are frequently used. High serotonin levels lead to altered mental status, deliria, rigidity and myoclonus, together recognized as serotonin syndrome. In its role as a peripheral hormone, serotonin is unique in controlling the functions of several organs. In the gastrointestinal tract it is important for regulating motor and secretory functions. Apart from intestinal motility, energy metabolism is regulated by both central and peripheral serotonin signaling. It also has fundamental effects on hemostasis, vascular tone, heart rate, respiratory drive, cell growth and immunity. Serotonin regulates almost all immune cells in response to inflammation, following the activation of platelets.
Highlights
Peripheral serotonin is important for a proper immune response, especially in the fight against infection and sepsis in critically ill patients. 5-HT impacts various inflammatory diseases, e.g., inflammatory conditions of the gut, rheumatoid arthritis or allergic airway dispositions
The innate immune system forms the first line of defense against invading pathogens and is nonspecific in its action; meaning that the same response is elicited by different stimuli, such as microorganisms, anaphylatoxins and other soluble factors
It is released from peripheral nerve fibers in locally inflamed tissue, and nociceptive information is carried by nerve fibers to the central nervous system (CNS)
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Serotonin carries out a number of immune functions as a neurotransmitter and as a peripheral hormone It is critical for the inflammatory response, possibly influencing the development of the systemic inflammatory response syndrome (SIRS). The aim of this review is to take the perspective of the intensive care specialist and highlight these roles of serotonin, from influencing immune functions, progression of sepsis and its influence on hemostasis. Another objective was to explore its effects on enteral nutrition, the risk of polypharmacy and the likelihood of developing the life-threatening serotonin syndrome.
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