Canonical Question

GIT Pharm – Gastric fluid

V5 H2.vii Historical V4 O2.ii 1 appearance

Master answer

5HT Receptors

5-HT receptor subtypes comprise the largest known neurotransmitter-receptor family.

4 5-HT receptor families recognized
All members of GPCR superfamily except 5HT3
5HT3 is a ligand gated ion channel that conducts Na and K
Overall effects
- CNS
  - Vasoconstriction
  - Increased inotropy and chronotropy
- Resp
  - Bronchial smooth muscle constriction
- CNS
  - Sleep-wake cycle
  - Temperature regulation
  - Appetite
  - Mood
  - Impulsivity
  - Anxiety and Depression
  - Sexual behaviour

	Mechanism	Sites of Action	Effect	Drugs
5HT1	– GiPCR – Some subtypes also act as ligand gated ion channels	Inhibitory autoreceptor on serotonergic cells Endothelium	– Inhibition of serotonin secretion – Endothelial No release	Agonist – Sumitriptan (migraine) – Ergotamine – LSD
5HT2	Gq or G11PCR	CNS – Pre-frontal – Parietal – Somatosensory – Choroid plexus GI Tract Platelets	– Platelet aggregation and vasoconstriction	Agonist – LSD Antagonist – Clozapine – Risperidone
5HT3	Ligand gated Na and K channel	CNS – Area Postrema (CTZ) – NTS (Vomiting centre) GI Tract – Parasympathetic nerve terminals	Emesis	Antagonist Ondansetron
5HT4	GsPCR	CNS GI Tract – Myenteric plexus – Secretory cells	GI peristalsis and secretion

Additional receptors cloned
- 5HT5~7 (GsPCR) Unknown clinical relenvance
Other drugs with effects on serotonergic system
- Increase serotonin release
  - MDMA
- Decrease serotonin reuptake
  - Tramadol
    - 1R2R(+) Tramadol
  - SSRI
  - Tricyclic Antidepressants
- Decrease serotonin metabolism
  - MAO Inhibitors

Mooney 2016

Pharmacology of Ondansetron

Answer by Mooney

Exam appearances

Exam	Exact wording	Relationship	Success
2012B Q17	Classify the 5HT receptors and give examples of pharmacological agents that affect them (60% of marks). Outline the pharmacology of ondansetron (40% of marks).	historical_member	—