Migraine Treatment – Allopathic – Part II

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Dear
Friends and Mentors

As we discussed
some basic overview on allopathic treatment last month....

Here it's time
to get into the mechanism behind the allopathic treatment....

Serotonin or 5- Hydroxy triptamine receptors:

Serotonin is a
vasoconstrictor. Chemically it is v-amnio ethyl -5-hydroxy indole, synthesized from
the amino acid tryptophan. It is degraded by the enzymes mono amino oxidase and
dehydrogenase.

On the basis of
pharmacological classification serotonin receptors includes musculotropic 'D'
type and neurotropic ' M' type.

Four families of 5-HT receptors have been
identified comprising of 14 subtypes. All these receptors are of G-protein
coupled receptors. They act either by increasing or decreasing the CAMP
production or by producing IP3/ DAG as second messengers.

5-HT RECEPTORS
TYPES AND SUB TYPES:

1)
5-HT1 RECEPTORS:

Five sub types of 5-HT1
receptors have been identified till now. They are 5-HT1A, B,D,E,F.

Mechanism: They act by inhibiting adenyl cyclase. 5-HT1A
can activate potassium channels and inhibit calcium channels. They inhibit the
release of 5-HT from neurons.

Location: Raphe nucleus of brainstem and hippocampus

Functions: 5-HT1D
receptor maintains the dopaminergic tone in substantia niagra-basal ganglia.
5-HT1B/1D causes the constriction of blood vessels. 5-HT1D
receptors also inhibit the release of noradrenaline from sympathetic nerve
endings and inflammatory neuro peptides from cranial blood vessel nerve
endings.

2)
5-HT2 RECEPTORS:

Three subtypes of 5-HT2 receptor s
have been identified. They are 5-HT2A, 2B, 2C.

Mechanism: They are coupled to phospholipase C and act
through IP3/DAG. 5-HT2A also inhibits potassium channels
and causes the depolarization the neurons.

Location:

5-HT2a located on the vascular and
visceral smooth muscles, platelets and prefrontal cortex.

5-HT2b
present in gastric fundus

5-HT2c
located on the vascular endothelium.

Functions: 5-HT2a
mediates vasoconstriction, uterine &bronchial constriction, platelet
aggregation and activation of cerebral neurons. 5-HT2b mediates
contraction of gastric fundus in rat. 5-HT2c elicits vasodilation
through EDRF release.

3)
5-HT3 receptors:

Mechanism: it
rapidly depolarizes nerve endings by opening cations channels.

Location:

Mainly at nerve endings,
NTS in brain

Functions: In
myentric plexus it causes augmentation of peristalisis and emetic reflex. acts
on NTS it causes nausea and vomiting.

4)
5-HT4-7 receptors:

The receptors
from 4-7 are considered as a single family.

Mechanism: They
act by decreasing potassium conductance and causing slow depolarization.

Location: They are located in the mucosa, plexus, and
smooth muscle of gut, brain mainly hippocampus.

Functions: They increase
intestinal secretions and peristalisis.

5-HT drugs for migraine:

Mainly 5-HT1B/1D
agonists named as triptans are used for migraine treatment.

EX: SUMATRIPTAN,
RIZATRIPTAN.

These drugs act
by constricting the dilated cranial extra cerebral blood vessels, mainly the
arterio-venous shunts in the carotid artery.

This blog does
not contain any plagiarized material

REF:

1. Essentials of
medical pharmacology, KD Tripathi

2. Goodman and Gillman's,
the pharmacological basis of therapeutics

About the Author

Vijay Chand's picture
Author: Vijay Chand

Comments

Santosh kumar. JH's picture

Dear Vijaya Chand, Thanks for the pharmacology of serotonin receptors, this made me to understand in a simpler way.
Vijay Chand's picture

Thanks for your encouraging comment......

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