Question 17

Classify the 5HT receptors and give examples of pharmacological agents that affect  them (60% of marks). Outline the pharmacology of ondansetron (40% of marks).

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College Answer

The 5HT (5 Hydroxytryptamine or serotonin) receptor is a monoamine neurotransmitter 
synthesized from tryptophan, and is an important receptorin the body.. It is found in the 
CNS, gastrointestinal tract, platelets and mast cells. There are 7 main receptor subtypes (GProtein coupled are 5HT1, 5HT2, 5HT4 and 5HT7 and ligand-gated ion channel 5HT3). Drugs 
may affect them by acting on serotonergic transmission (degradation inhibitors- MAOI e.g.
selegiline, storage inhibitors- amphetamine, reuptake inhibitors- SSRI’s or tricyclic 
antidepressants), serotonin agonists(selective-5HT1B, 5HT1D e.g.triptans for migraine, 
non-selective, e.g. ergotamine), serotonin antagonists(ketanserin, clozapine, ondansetron). 
Ondansetron is a commonly used anti-emetic. Candidates were expected to mention,that it 
is a selective antagonist at the 5HT3 receptor centrally and peripherally. To outline 
“pharmacology” it was also expected that answers would mention that it comes in a variety 
of formulations and to outline itsfundamental pharmacokinetic properties.