- Binds to, and activates 5-HT receptors.
- Tissue and organ effects as follows:
- Potent vasoconstrictor, except in the heart and skeletal muscles, where it causes vasodilation.
- Small positive inotropic and chronotropic action.
- May elicit the chemoreceptor reflex/Bezold Jarish reflex, where serotonin activates 5HT3 receptors on the heart, leading to profound hypotension and bradycardia.
- Immunological function
- Found in platelets – assists with platelet aggregation
- Nervous system
- CNS: functions as a neurotransmitter
- 5HT3 receptors participate in the vomiting reflex.
- Implicated in depression/migraine. Also implicated in mood/pain perception/sleep
- Causes bronchoconstriction and hyperventilation
- Prokinetic and secretory effect, resulting in diarrhea.
- Excessive serotonin leads to a potentially fatal syndrome called serotonin syndrome. It is a predictable (rather than idiosyncratic) reaction. It is similar in presentation to MH and NMS, but the pathophysiology and treatment are different.
||SSRIs, MAOIs, triptans, ondansetron, St. John’s Wort, morphine, pethidine, linezolid, tramadol.
||HTN, hyper-reflexia, tremor, hyperthermia, diarrhea, mydriasis, agitation and coma (onset occurs within hours).Also clonus, increased bowel sounds.
||Sedation (BZDs), paralysis, intubation and sedation. Possibly cyproheptadine or chlorpromazine (5HT blockade)
||Anti-psychotic drugs that block D2.
||Acute, severe parkinsonism. Hypertension, hyperthermia, normal/reduced bowel sounds. Onset 1-3 days.
||Diphenhydramine, sedation and cooling.
||Volatile anaesthetics, suxemethonium
||Hyperthermia, muscle rigidity, HTN, tachycardia. Onset within minutes.