A patient goes to his family doctor complaining of persistent and severe headaches. His physician diagnoses migraine headaches and prescribes sumatriptan. What is the mechanism of action of this drug?
**Core Concept**
The mechanism of action of sumatriptan involves the inhibition of serotonin (5-HT) receptors, specifically the 5-HT1B and 5-HT1D subtypes, which are located on the blood vessels of the brain. This action leads to vasoconstriction of the intracranial blood vessels, which in turn alleviates the headache symptoms.
**Why the Correct Answer is Right**
Sumatriptan acts by binding to the 5-HT1B and 5-HT1D receptors on the blood vessels of the brain, which causes a reduction in the release of pro-inflammatory neuropeptides, such as calcitonin gene-related peptide (CGRP). This reduction in neuropeptide release leads to vasoconstriction of the blood vessels, which is thought to be the primary mechanism by which sumatriptan alleviates migraine headache symptoms. Additionally, sumatriptan also has a peripheral action, where it causes vasoconstriction of the extracranial blood vessels, which can help to reduce the sensation of pain.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because sumatriptan does not primarily act by inhibiting the action of acetylcholine at muscarinic receptors, which would be more relevant to the treatment of conditions such as glaucoma or gastrointestinal disorders.
* **Option B:** This option is incorrect because sumatriptan does not primarily act by inhibiting the action of dopamine at dopamine receptors, which would be more relevant to the treatment of conditions such as Parkinson's disease or schizophrenia.
* **Option C:** This option is incorrect because sumatriptan does not primarily act by inhibiting the action of histamine at histamine receptors, which would be more relevant to the treatment of conditions such as allergic reactions or asthma.
**Clinical Pearl / High-Yield Fact**
Sumatriptan is a selective 5-HT1B/1D receptor agonist, and its vasoconstrictive action on the blood vessels of the brain is thought to be the primary mechanism by which it alleviates migraine headache symptoms. However, it's worth noting that sumatriptan can also have a peripheral action, where it causes vasoconstriction of the extracranial blood vessels, which can help to reduce the sensation of pain.
**Correct Answer: C. Sumatriptan acts by binding to the 5-HT1B and 5-HT1D receptors on the blood vessels of the brain, which causes a reduction in the release of pro-inflammatory neuropeptides, such as calcitonin gene-related peptide (CGRP), leading to vasoconstriction of the blood vessels and alleviation of migraine headache symptoms.**