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Questions and Answers
How does the activation of muscarinic receptors in bronchiolar smooth muscle typically manifest?
How does the activation of muscarinic receptors in bronchiolar smooth muscle typically manifest?
- Activation of adenylyl cyclase, leading to bronchodilation.
- Inhibition of protein kinase C, causing a reduction in bronchial secretions.
- Decrease in cAMP formation mediated by G-proteins, promoting smooth muscle relaxation.
- Increase in IP3 and DAG, which leads to bronchoconstriction. (correct)
Which systemic effect is most likely to be observed following the administration of a muscarinic agonist?
Which systemic effect is most likely to be observed following the administration of a muscarinic agonist?
- Reduced urinary frequency due to increased sphincter tone.
- Reduced heart rate (bradycardia) as a result of enhanced vagal tone. (correct)
- Increased blood pressure due to peripheral vasoconstriction.
- Mydriasis (dilation of the pupil) caused by contraction of the radial muscle of the iris.
What characterizes the mechanism of action of Acetylcholine (ACh) at cholinergic receptors?
What characterizes the mechanism of action of Acetylcholine (ACh) at cholinergic receptors?
- ACh inhibits both muscarinic (M) and nicotinic (N) receptors, leading to a decrease in parasympathetic activity.
- ACh directly stimulates both M and N receptors, initiating a cascade of intracellular events. (correct)
- ACh indirectly enhances the release of norepinephrine, which then stimulates adrenergic receptors.
- ACh selectively stimulates M receptors while blocking N receptors, causing a mixed response.
Why is Acetylcholine (ACh) typically administered via injection rather than orally?
Why is Acetylcholine (ACh) typically administered via injection rather than orally?
Which physiological responses are associated with activation of M3 muscarinic receptors?
Which physiological responses are associated with activation of M3 muscarinic receptors?
How does the activation of M2 muscarinic receptors in the heart affect cardiac function?
How does the activation of M2 muscarinic receptors in the heart affect cardiac function?
What are the primary effects of stimulating nicotinic (Nn) receptors located in autonomic ganglia?
What are the primary effects of stimulating nicotinic (Nn) receptors located in autonomic ganglia?
How does Carbachol differ mechanistically from Bethanechol in its interaction with cholinergic receptors?
How does Carbachol differ mechanistically from Bethanechol in its interaction with cholinergic receptors?
What is the rationale for using Carbachol eye drops in the treatment of open-angle glaucoma?
What is the rationale for using Carbachol eye drops in the treatment of open-angle glaucoma?
Why is Bethanechol specifically used to treat post-operative urinary retention and paralytic ileus?
Why is Bethanechol specifically used to treat post-operative urinary retention and paralytic ileus?
What distinguishes Pilocarpine from Cevimeline in terms of their origin and receptor selectivity?
What distinguishes Pilocarpine from Cevimeline in terms of their origin and receptor selectivity?
In what specific clinical scenario is Cevimeline primarily indicated, and what is its mechanism of action in this context?
In what specific clinical scenario is Cevimeline primarily indicated, and what is its mechanism of action in this context?
What mechanisms underlie the contraindication of muscarinic agonists in patients with bronchial asthma?
What mechanisms underlie the contraindication of muscarinic agonists in patients with bronchial asthma?
Which of the following describes the mechanism by which muscarinic agonists are contraindicated in patients with peptic ulcers?
Which of the following describes the mechanism by which muscarinic agonists are contraindicated in patients with peptic ulcers?
What is the effect of muscarinic agonists on the detrusor muscle and internal urethral sphincter, and how does this relate to their therapeutic use?
What is the effect of muscarinic agonists on the detrusor muscle and internal urethral sphincter, and how does this relate to their therapeutic use?
How do irreversible cholinesterase inhibitors differ from reversible inhibitors in their mechanism of action and duration of effect?
How do irreversible cholinesterase inhibitors differ from reversible inhibitors in their mechanism of action and duration of effect?
What is the primary mechanism by which activation of nicotinic receptors at the neuromuscular junction leads to skeletal muscle contraction?
What is the primary mechanism by which activation of nicotinic receptors at the neuromuscular junction leads to skeletal muscle contraction?
What is a key clinical difference between the effects of muscarinic agonists and nicotinic agonists on blood vessels?
What is a key clinical difference between the effects of muscarinic agonists and nicotinic agonists on blood vessels?
Which of the following best describes the role of cholinesterase enzyme (AChE) in the context of cholinergic neurotransmission?
Which of the following best describes the role of cholinesterase enzyme (AChE) in the context of cholinergic neurotransmission?
What is the significance of the Gq protein in the context of muscarinic receptor activation, specifically concerning M1 and M3 receptors?
What is the significance of the Gq protein in the context of muscarinic receptor activation, specifically concerning M1 and M3 receptors?
Flashcards
Autonomic Nervous System
Autonomic Nervous System
Controls involuntary body activities
Parasympathetic Nervous System
Parasympathetic Nervous System
The 'rest and digest' system, promotes relaxation and digestion.
Neurotransmitter
Neurotransmitter
A biological substance that transmits nerve impulses across a synapse.
Acetylcholine (ACh)
Acetylcholine (ACh)
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Cholinesterase (AChE)
Cholinesterase (AChE)
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Cholinergic Receptors
Cholinergic Receptors
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Muscarinic Receptor
Muscarinic Receptor
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Muscarinic Receptor (M1)
Muscarinic Receptor (M1)
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Muscarinic Receptor (M2)
Muscarinic Receptor (M2)
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Muscarinic Receptor (M3)
Muscarinic Receptor (M3)
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Nicotinic Receptors
Nicotinic Receptors
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Nicotinic Receptor (Nn)
Nicotinic Receptor (Nn)
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Nicotinic Receptor (Nm)
Nicotinic Receptor (Nm)
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Parasympathomimetics
Parasympathomimetics
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Direct-Acting Cholinergic Agonists
Direct-Acting Cholinergic Agonists
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Indirect-Acting Cholinergic Agonists
Indirect-Acting Cholinergic Agonists
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Carbachol
Carbachol
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Bethanechol
Bethanechol
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Pilocarpine
Pilocarpine
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Cevimeline
Cevimeline
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Study Notes
- Cholinergic drugs are discussed in this lecture
- This lecture covers cholinergic receptors, classification of parasympathomimetics, the mechanism of action of parasympathomimetics, uses of different cholinergic agonists, and side effects and contraindications of parasympathomimetics
Autonomic Nervous System
- The autonomic nervous system controls involuntary body activities
- The sympathetic branch triggers stress responses
- The parasympathetic branch promotes peace, rest, and digestion
Parasympathetic System
- The parasympathetic system's preganglionic and postganglionic neurons release acetylcholine
- This system causes miosis (pupil constriction), salivation, bronchoconstriction, bradycardia (slowed heart rate), digestion, and urination
Parasympathetic (Cholinergic) System
- Acetylcholine (ACh) serves as the neurotransmitter
- Cholinesterase enzyme (AChE) metabolizes acetylcholine
- Receptors include muscarinic (M) and nicotinic (N) cholinoceptors
Muscarinic Receptors
-
Muscarinic receptors are G-protein coupled receptors
-
M1 receptors are located in the CNS
- They affect motor activity, attention, and memory
- M1 receptors are also in the stomach, stimulating HCL secretion
- M1 receptors increase IP3 and DAG, which in turn increase Ca2+
-
M2 receptors decrease cAMP
-
M3 receptors control miosis (constrict pupil), Bronchioles constriction (BC), blood vessel dilation (VD)
Nicotinic Receptors
- Nicotinic receptors are ion channel receptors, increasing Na+ and causing depolarization
- Nn receptors are located in the adrenal medulla and autonomic ganglia.
- Nm receptors are located in the somatic nerves and skeletal muscles.
- Nicotinic receptors stimulate the release of catecholamine
Para-sympathomimetics Classification
- Direct acting parasympathomimetics :
- Choline esters: Acetylcholine, Bethanechol, Carbachol, Methacholine
- Alkaloids: Pilocarpine, Cevimeline
- Indirect acting parasympathomimetics (ChE inhibitors):
- Reversible: Physostigmine, Neostigmine, Pyridostigmine, Donepezil
- Irreversible: Organo-phosphate compounds
Acetylcholine
- Acetylcholine is administered by injection, not effective orally due to poor absorption
- Rapidly hydrolyzed by cholinesterase enzyme
Muscarinic Effects
- Cardiovascular System (CVS):
- Decreases heart rate (M2)
- Vasodilation of blood vessels (M3)
- Decreases blood pressure
- Respiratory System (M3):
- Bronchoconstriction
- Increases bronchial secretion
- Eyes (M3):
- Miosis (constriction of the pupil)
- Accommodation for near objects
- Gastrointestinal Tract (GIT) (M3): Increases motility and relaxes the sphincters
- Urinary Tract (M3): Stimulates the detrusor muscle and relaxes the internal urethral sphincter, resulting in bladder evacuation
- Exocrine Glands (M3): Stimulates salivary, gastric, bronchial, lacrimal, and sweat gland secretions
Nicotinic Effects
- All types of autonomic ganglia (Nn) are impacted
- Increases motor end plate (neuromuscular junction), leading to skeletal muscle contractions (Nm)
Carbachol
- Resists hydrolysis by AChE, effective orally, and has a long duration
- Stimulates both muscarinic and nicotinic receptors
- Treats open-angle glaucoma by causing miosis and increasing aqueous humor drainage
Bethanechol
- Stimulates muscarinic receptors only
- Used for post-operative urine retention
- Used also for paralytic ileus
Pilocarpine
- Natural plant alkaloid
- Exhibits muscarinic effects but no nicotinic effects
- Local eye drops are used to decrease IOP in chronic open-angle glaucoma
Cevimeline
- Synthetic alkaloid
- Muscarinic effects only
- Given orally to increase salivary secretion and treat xerostomia (dry mouth)
Muscarinic Agonists Side Effects and Contraindications
- Side effects include:
- Hypotension
- Diarrhea, nausea, vomiting
- Bradycardia
- Bronchoconstriction
- Sweating, salivation
- Contraindications
- Bronchial asthma
- Heart block
- Peptic ulcer
Review Questions
- Activation of muscarinic receptors in bronchiolar smooth muscle is associated with an increase in IP3 and DAG
- Reduced heart rate (bradycardia) is a systemic effect of a muscarinic agonist
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