Cholinergic Antagonists And Receptors

Question 1

What is cholinergic antagonist?

Answer 1

They produce the same effects as adrenergic agonist. Cholinergic antagonists prevent Ach binding to its receptors.

Question 2

What is the reason behind visual hallucination?

Answer 2

Drastic decline in Ach

Question 3

What is the mechanism of action of muscarinic antagonist?

Answer 3

No GPCR activation
-M1 ,M3 & M5: PLC not activated, IP3 not produced
-M2 & M4: adenylate cyclase not inhibited, K channel closes, cAMP production not affected

GPCR is metabotropic, ligand gated is ionotropic

Question 4

Example of cholinergic antagonist?

Answer 4

atropine (natural alkaloid)
-non specific antagonist
-reversible
-can cross BBB (lipophilic)
-prolonged half life

small dose:bradycardia
high dose: tachycardia due to blockade of muscarinic receptors [more pupillary dilation, less peristalsis, hot & dry skin, not sweating, vasodilation, not urinating]

eye: mydriasis (pupil dilation due to M3 in radial muscle), increase IOP, no tears, paralysis of accommodation/lens flat (can see far)

CNS effect: sedation, less tremor in Parkinson disease, correct vestibular disturbance

Question 5

The therapeutic uses of muscarinic antagonist

Answer 5

atropine:
Sinus bradycardia (post heart attack)
Heart block (AV conduction failure)
Cholinergic poisoning

tropicamide:premed before eye exam
scopolamine:motion sickness
benztropin:parkinson disease (can cross BBB)
ipratropium: COPD (bronchoconstriction), asthma
pirenzepine: peptic ulcer

Question 6

ADR of muscarinic antagonist?

Answer 6

Restlessness due to central effect
Increase IOP (blur vision)
Fever
Arrhythmias
Urinary retention in enlarged prostate patient
Constipation

Question 7

Contraindication of muscarinic antagonist

Answer 7

Glaucoma (scopolamine: increase IOP)
Prostatic hyperplasia

Question 8

Botulinum toxin can treat?

Answer 8

It blocks the release of Ach, causing progressive paralysis, blurred vision

Used to treat blephrospasm, skin wrinkles
It is secreted by clostridium botulinum

BOTOX

Question 9

Treatment for atropine poisoning (hot, dry, blind, red, mad)

Answer 9

Treatments:
1. Symptomatic
2. Limit absorption in intestine
3. Physostigmine (repeated dose): inhibits AchE, increase Ach in synaptic cleft which reverse the blocking effect
4. Benzodiazepine (sedation)

Question 10

Ach enhances effect of nitroglycerine by

Answer 10

Producing more NO to induce vasodilation