Cholinergic Transmission and Parasympathomimetics

Questions and Answers

What is the reason Acetylcholine is not therapeutically useful?

It has a multiplicity of actions and is rapidly inactivated by cholinesterase enzyme

What type of receptors does Pilocarpine bind to?

Muscarinic acetylcholine receptors (mAChR)

What is the effect of Acetylcholine on the heart rate?

Decreases heart rate

Which of the following is an indirectly acting cholinergic agonist?

Neostigmine Signup and view all the answers

What is the effect of Acetylcholine on the salivary secretion?

Increases salivary secretion Signup and view all the answers

How do directly acting cholinergic agonists work?

By binding directly to cholinoreceptors Signup and view all the answers

What is the effect of Acetylcholine on the tone of urinary bladder muscles?

Increases the tone of urinary bladder muscles Signup and view all the answers

What type of receptors does Nicotine bind to?

Nicotinic acetylcholine receptors (nAChR) Signup and view all the answers

What is the effect of atropine on the pupil?

Mydriasis Signup and view all the answers

What is the therapeutic application of atropine in ophthalmology?

To measure refractive errors of the eye Signup and view all the answers

What is the effect of atropine on heart rate at low doses?

Bradycardia Signup and view all the answers

What is the use of atropine as an antidote?

For overdose of cholinergic agonists Signup and view all the answers

What is the effect of atropine on intraocular pressure (IOP) in patients with glaucoma?

Increases IOP Signup and view all the answers

What is the source of atropine?

Atropa belladonna Signup and view all the answers

What is the historical use of atropine?

To dilate pupils for cosmetic reasons Signup and view all the answers

What is the meaning of 'belladonna'?

Beautiful lady Signup and view all the answers

What is the primary mechanism of action of anticholinesterases?

Increasing the levels of acetylcholine at the neuromuscular junction Signup and view all the answers

What is the primary use of pilocarpine in ophthalmology?

To lower intraocular pressure in emergency situations Signup and view all the answers

What is the primary cause of myasthenia gravis?

Autoimmune disorder Signup and view all the answers

What is the purpose of the edrophonium test in diagnosing myasthenia gravis?

To temporarily increase the levels of acetylcholine at the neuromuscular junction Signup and view all the answers

What is a common adverse effect of pilocarpine?

Stimulation of profuse sweating and salivation Signup and view all the answers

What is the name of the disease characterized by fluctuating weakness and fatigability?

Myasthenia gravis Signup and view all the answers

What is a treatment option for myasthenia gravis?

Cholinesterase inhibitors Signup and view all the answers

What is the duration of action of pilocarpine when applied topically to the cornea?

About one day Signup and view all the answers

Study Notes

Cholinergic Transmission

Parasympathomimetics

Parasympathomimetics can be classified into directly and indirectly acting cholinergic agonists.
Directly acting cholinergic agonists mimic the effect of acetylcholine (ACh) by binding directly to cholinoreceptors.
Examples of directly acting cholinergic agonists include:
- Acetylcholine (ACh)
- Pilocarpine
ACh has both nicotinic and muscarinic activity, but it is therapeutically of no importance due to its multiplicity of actions and rapid inactivation by cholinesterase enzyme.
Actions of ACh:
- Heart rate: decreased
- Blood pressure: decreased
- Salivary secretion: increased
- GIT secretion and motility: increased
- Bronchial secretion: increased
- Tone of urinary bladder muscles: increased
- Pupil sphincter muscle: contracted
- Ciliary muscle: contracted

Adverse Effects of Cholinergic Drugs

Cholinergic drugs can cause adverse effects such as:
- Increased salivation
- Increased sweating
- Nausea and vomiting
- Abdominal cramps
- Diarrhea

Cholinergic Antagonists

Anti-Muscarinic Agents

Examples of anti-muscarinic agents include:
- Atropine
- Scopolamine
- Ipratropium
Atropine:
- Isolated from Atropa belladonna
- Has muscarinic activity
- Actions:
  - Eye: mydriasis, unresponsiveness to light, cycloplegia, increased IOP in patients with glaucoma
  - CVS: bradycardia at low doses, modest tachycardia at high doses
- Therapeutic applications:
  - Ophthalmic: mydriatic and cycloplegic effect
  - Antisecretory: blocks respiratory secretions prior to surgery
  - Antidote: for overdose of cholinergic agonists

Indirectly Acting Cholinergic Agonists (Anticholinesterases)

Examples of anticholinesterases include:
- Neostigmine (Prostigmine)
- Edrophonium
Uses:
- To stimulate bladder and GIT contraction
- To treat myasthenia gravis

Myasthenia Gravis

Myasthenia gravis is a neuromuscular disease characterized by fluctuating weakness and fatigability.
It is an autoimmune disorder caused by circulating antibodies that block acetylcholine receptors at the post-synaptic neuromuscular junction, inhibiting ACh.
Diagnosis: Edrophonium test
Treatment:
- Cholinesterase inhibitors to directly improve muscle function
- Immunosuppressant drugs to reduce the autoimmune process

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Description

Learn about cholinergic transmission, parasympathomimetics, and their classification into directly and indirectly acting cholinergic agonists. Understand the actions and therapeutic uses of Acetylcholine and Pilocarpine.