Serotonin and purines Flashcards
Where can serotonin be found?
In the periphery
In the CNS
What is the main source of serotonin in the periphery?
Enterochromaffin cells in the mucosa of the stomach and intestine
What is the main source of serotonin in the CNS?
Midbrain Raphe nucleus
What peripheral organs do serotonin affect?
Blood
GI tract
Platelets
What is the effect of serotonin on the GI tract?
Increases secretion and motility
What is the effect of serotonin in the blood?
Controls microvasculature
What is the effect of serotonin in platelets?
Mediates aggregation and inflammation
What functions of the CNS is serotonin implicated in?
Appetite
Sleep
Vomiting
Mood
Descending control of pain inputs
In which conditions is serotonin dysfunctional?
Affective disorders
Anxiety
Enterochromaffin tumours
Where is serotonin synthesised from?
Dietary tryptophan
What is another name for serotonin?
5-HT
How does 5-HT go to the neurons?
Through reuptake transporters
Important targets of SSRIs
What is the main way of terminating 5-HT action in the CNS?
Through reuptake
How does 5-HT go to platelets?
Platelets lack enzyme required for 5-HT synthesis
So they actively take up the neurotransmitter
How is 5-HT degraded in the GI?
Most of it will be deaminated in the liver by MAO
The 5-HT that survives first-pass liver metabolism is taken up by endothelial cells lung blood vessels with MAO
How many families of 5-HT receptors exist?
7 families
14 receptors in total
What type of receptors are 5-HT receptors?
G-protein coupled
Where are most 5-HT receptors found?
In the brain
Neuronal characteristics of migraines
Abnormal neuronal discharge
Changes in cerebral blood flow
Why is it thought that serotonin is involved with migraines?
There is increased urinary excretion of 5-HIAA (degradation product) during a migraine attack
Useful clinical benefits obtained by modification of 5-HT mechanisms
How is serotonin involved in migraine?
Causes visual effects through vasoconstriction
Causes inflammatory dilation
Therapies for migraine
5-HT2 antagonists - inhibits early vasoconstriction
5HT-1 agonists have been useful through constricting cranial blood vessels
Example of purines
ATP
Adenosine
How are purines synthesised?
Through breakdown of ATP in the extracellular space using ATPases
What type of receptors bind to ATP/Adenosine?
G-protein coupled recepors
Except one ATP receptor - ligand-gated
Drugs used to treat migraines
Beta-blockers
NSAIDs
Calcium channel blockers
Antiepileptics
Antidepressants
Receptors of Adenosine
A1 - Gi
A2A - Gs
A2B
A3 - Gi
Receptors of ATP
Ligand-gated ion channel
G-protein channel
