Autonomic Nervous System Drugs Practice Questions

Q: Which of the following statement is correct regarding the mechanism of action of labetalol?

Blocks both alpha and beta-adrenergic receptors.. ***Blocks both alpha and beta-adrenergic receptors*** - Labetalol is a unique **non-selective beta-blocker** (blocking $\beta_1$ and $\beta_2$) that also possesses **selective $\alpha_1$-adrenergic blocking activity**. - This combined mechanism makes it effective for conditions like **hypertensive emergencies**, providing both reduced heart rate (via beta block) and peripheral vasodilation (via alpha block). *Directly acts as arterial vasodilator resulting in indirect effect tachycardia* - While labetalol causes **vasodilation** (due to $\alpha_1$ blockade), it also **blocks $\beta$-receptors**, preventing the typical **reflex tachycardia** that occurs with direct vasodilators like hydralazine. - Its primary mechanism is receptor blockade, not direct smooth muscle relaxation. *Primarily acts as a vasodilator with little effect on arterioles* - Labetalol acts as a potent **arteriolar vasodilator** (via $\alpha_1$ blockade), which is crucial for lowering systemic vascular resistance and blood pressure. - Its vasodilatory effect is significant and targeted at arterioles. *Decreases peripheral vascular resistance by directly acting as a relaxant for vascular smooth muscles* - Labetalol decreases **peripheral vascular resistance (PVR)** through **antagonism of $\alpha_1$ receptors** in vascular smooth muscles, preventing vasoconstriction. - It does not act as a direct smooth muscle relaxant like nitroprusside or hydralazine.

Q: Which of the following is the site of action of botulinum toxin? (Recent NEET Pattern 2016-17)

Synaptobrevin and SNAP-25. ***Synaptobrevin and SNAP-25*** - Botulinum toxin (BoNT) is a neurotoxin that cleaves **SNARE proteins** involved in neurotransmitter release. - Specifically, BoNT A, C, and E target **SNAP-25**, while BoNT B, D, F, and G target **synaptobrevin (VAMP)**. *Syntaxin and Synaptotagmin* - **Syntaxin** is part of the SNARE complex, however, synaptotagmin is primarily involved in **calcium sensing** and triggering vesicle fusion, not a direct cleavage target of common botulinum toxins. - While syntaxin is part of the overall fusion machinery, other SNARE proteins are the primary targets for cleavage. *Synaptic cleft* - The **synaptic cleft** is the space between the presynaptic and postsynaptic neurons where neurotransmitters are released, but it is not a direct site of action for botulinum toxin which works intracellularly. - Botulinum toxin acts *inside* the presynaptic neuron, preventing the release of neurotransmitters into the cleft. *Synaptic vesicle* - The **synaptic vesicle** contains neurotransmitters, and its fusion with the presynaptic membrane is inhibited by botulinum toxin. - However, the toxin's action is on the **proteins** associated with the vesicle and the presynaptic membrane, specifically those involved in docking and fusion, rather than on the vesicle itself.

Q: Which of the following statement is correct regarding the graph shown? (AllMS Nov 2016)

Drug acting on graph B is isoproterenol. ***Drug acting on graph B is isoproterenol*** - Graph B shows a definite **increase in pulse rate** and a **decrease in peripheral resistance**, while blood pressure remains largely unchanged due to the combined effects. - **Isoproterenol** is a non-selective β-adrenergic agonist that causes increased heart rate (β1 effect) and vasodilation leading to decreased peripheral resistance (β2 effect). - This unique hemodynamic profile is characteristic of isoproterenol and distinguishes it from other catecholamines. *Drug in graph A is epinephrine* - Graph A shows a **decrease in pulse rate**, which is **not characteristic** of epinephrine at the dose shown (10 μg/min). - Epinephrine typically causes **tachycardia** due to β1-adrenergic stimulation, not bradycardia. - The cardiovascular profile in graph A does not match epinephrine's expected effects. *Effect on heart in graph A can be overcome by antimuscarinic* - The decreased pulse rate in graph A suggests **reflex bradycardia** or parasympathetic stimulation. - However, without knowing the actual drug, we cannot definitively state whether antimuscarinic agents would reverse this effect. - This option makes assumptions that cannot be verified from the graph alone. *Drug acting on graph C is nor-epinephrine* - Graph C shows **increased pulse rate** and **decreased peripheral resistance** with slight drop in blood pressure. - **Norepinephrine** primarily acts on α1-receptors, causing **vasoconstriction and increased peripheral resistance**, not decreased. - Norepinephrine would also increase blood pressure significantly, which contradicts the graph. - This cardiovascular profile does not match norepinephrine.

Q: Which of the following conditions can the shown injection be used for emergency management?

Brittle asthma. ***Brittle asthma*** - The image shows an **EpiPen auto-injector**, which contains **epinephrine** (adrenaline). - Epinephrine is a potent **beta-2 agonist** with strong bronchodilatory effects, making it useful in severe acute asthma exacerbations, including **brittle asthma**, when immediate bronchodilation is needed. - While the **primary indication** for EpiPen is anaphylaxis, epinephrine's mechanism (beta-2 receptor stimulation causing bronchodilation, alpha-1 receptor stimulation reducing mucosal edema) provides life-saving relief in severe bronchoconstriction. - In emergency settings with severe asthma unresponsive to standard therapy, subcutaneous or intramuscular epinephrine may be administered. *Hay fever* - Hay fever (allergic rhinitis) involves mild symptoms like sneezing, rhinorrhea, and conjunctival irritation. - Management includes **antihistamines** (e.g., cetirizine, loratadine) and **intranasal corticosteroids** (e.g., fluticasone). - Epinephrine is vastly excessive for routine allergic rhinitis and is reserved only for severe systemic allergic reactions (anaphylaxis). *Snake bite* - Snake bite management centers on **species-specific antivenom** administration plus supportive care (fluid resuscitation, monitoring for coagulopathy, compartment syndrome). - Epinephrine is **not** a primary treatment for envenomation itself. - It may be used only if the patient develops an **anaphylactic reaction to antivenom**, which is a separate indication. *Flushing episodes in carcinoid* - Carcinoid syndrome involves episodic flushing, diarrhea, and bronchoconstriction due to **serotonin, histamine, and vasoactive peptides** released by neuroendocrine tumors. - Treatment involves **somatostatin analogs** (octreotide, lanreotide) which inhibit hormone release from tumor cells. - Epinephrine would not address the underlying mediator release and could potentially worsen hemodynamic instability.

Q: Match the following: Column A: a. Beta 1 b. Beta 2 c. Beta 3 Column B: 1. Mirabegron 2. Betaxolol 3. Salbutamol

a-2, b-3 ,c-1. ***a-2, b-3, c-1*** - This pairing correctly matches **Betaxolol** with **Beta 1 selective** antagonism, **Salbutamol** with **Beta 2 selective** agonism, and **Mirabegron** with **Beta 3 selective** agonism. - **Betaxolol** is a beta-1 selective adrenergic receptor antagonist, primarily used in ophthalmology to reduce intraocular pressure and as an antihypertensive. **Salbutamol** is a selective beta-2 adrenergic agonist used as a bronchodilator in asthma and COPD, causing relaxation of bronchial smooth muscle. **Mirabegron** is a selective beta-3 adrenergic agonist used to treat overactive bladder by relaxing the detrusor muscle. *a-2, b-1, c-3* - This option incorrectly assigns **Mirabegron** to Beta 2. Mirabegron is a **Beta 3 selective agonist**. - It also incorrectly assigns **Salbutamol** to Beta 3. Salbutamol is a **Beta 2 selective agonist**. *a-3, b-2, c-1* - This option incorrectly assigns **Salbutamol** to Beta 1. Salbutamol is a **Beta 2 selective agonist**. - It also incorrectly assigns **Betaxolol** to Beta 2. Betaxolol is a **Beta 1 selective antagonist**. *a-3, b-1, c-2* - This option incorrectly assigns **Salbutamol** to Beta 1 and **Betaxolol** to Beta 3. - **Salbutamol** is a Beta 2 selective agonist, and **Betaxolol** is a Beta 1 selective antagonist.

Q: An investigator is developing a new intravenous medication that acts as a selective agonist at β-2 receptors. In addition to causing bronchodilation, this drug is most likely to have which of the following effects?

Bladder detrusor relaxation. ***Bladder detrusor relaxation*** - **β2-adrenergic receptors** are located in the detrusor muscle of the bladder, and their activation leads to **relaxation** of this smooth muscle. - This effect is mediated by the **sympathetic nervous system**, which generally promotes storage of urine. *Peripheral vasoconstriction* - **Vasoconstriction** in peripheral arteries is primarily mediated by **α1-adrenergic receptors**, not β2-receptors, which generally cause vasodilation in skeletal muscle. - Activation of β2-receptors typically leads to **vasodilation** in certain vascular beds to increase blood flow during fight-or-flight responses. *Increased uterine tone* - **β2-adrenergic receptor activation** in the uterus causes **relaxation** of the uterine smooth muscle, not increased tone. - This property is exploited therapeutically with **tocolytic agents** (e.g., terbutaline) to prevent premature labor. *Increased gastrointestinal peristalsis* - **Peristalsis** in the gastrointestinal tract is primarily regulated by the **parasympathetic nervous system** and local enteric reflexes. - **β2-receptor activation** [3] generally leads to **decreased gastrointestinal motility** and relaxation of smooth muscles in the GI tract. *General β2-Selective Agonist Properties* - β2-selective agonists are designed to minimize cardiac side effects mediated by β1-receptors [1], although this selectivity is relative [1]. They are primarily used as bronchodilators [3], acting to relax airway smooth muscle [2].

Q: Ritodrine is a:-

β2 agonist. ***β2 agonist*** - Ritodrine is a **selective beta-2 adrenergic receptor agonist** primarily used as a **tocolytic agent** to relax the uterus and stop premature labor. - Its action involves stimulating **beta-2 receptors** in the myometrium, leading to decreased intracellular calcium and uterine smooth muscle relaxation. *α1 antagonist* - Alpha-1 antagonists block **alpha-1 adrenergic receptors**, causing vasodilation and are used to treat conditions like **hypertension** or **benign prostatic hyperplasia**. - Ritodrine's mechanism is distinct, as it targets beta-2 receptors, not alpha-1. *β antagonist* - Beta antagonists (beta-blockers) block **beta adrenergic receptors** (beta-1, beta-2, or both) and are used for conditions like **hypertension**, **angina**, or **arrhythmias**. - Ritodrine is an agonist, meaning it activates receptors, rather than blocking them. *α agonist* - Alpha agonists stimulate **alpha adrenergic receptors**, causing vasoconstriction and increased blood pressure, as seen with agents like **phenylephrine**. - Ritodrine specifically targets beta-2 receptors, leading to opposite effects like smooth muscle relaxation in the uterus and bronchi.

Q: Shortest-acting muscle relaxant is:

Succinylcholine. ***Correct: Succinylcholine*** - **Succinylcholine** is a depolarizing neuromuscular blocker with a rapid onset and a very short duration of action, typically **5-10 minutes**, due to its rapid hydrolysis by **plasma pseudocholinesterase**. - Its ultrashort action makes it ideal for **rapid sequence intubation** and other procedures requiring brief muscle relaxation. *Incorrect: Atracurium* - **Atracurium** is an intermediate-acting nondepolarizing muscle relaxant with a duration of action of approximately **20-35 minutes**. - Its metabolism occurs via Hoffman elimination and ester hydrolysis, making it suitable for patients with **renal or hepatic dysfunction**. *Incorrect: Tubocurarine* - **Tubocurarine** is a long-acting nondepolarizing muscle relaxant that is now rarely used due to its significant adverse effects, including **histamine release** and ganglion blockade. - Its duration of action can be **60-120 minutes**. *Incorrect: Pancuronium* - **Pancuronium** is a long-acting nondepolarizing muscle relaxant with a duration of action of **60-90 minutes**. - It is eliminated primarily by the **kidneys**, making its duration prolonged in patients with **renal impairment**.

Q: Mechanism of action of atropine in treatment of organophosphate poisoning is?

It has antimuscarinic activity. ***It has antimuscarinic activity*** - **Organophosphate poisoning** leads to **excessive acetylcholine** at muscarinic receptors, causing symptoms like miosis, bradycardia, and increased secretions. - **Atropine** is a **competitive antagonist** at these muscarinic receptors, thereby blocking the effects of excess acetylcholine. *It inhibits secretion of acetylcholine* - Atropine does not directly inhibit the secretion of **acetylcholine** from nerve terminals. - Its action is postsynaptic, specifically at the **receptor level**. *It is reactivator of acetylcholine esterase enzyme* - **Pralidoxime (2-PAM)** and other **oximes** are the drugs that reactivate **acetylcholinesterase**. - Atropine does not reactivate the enzyme; it only blocks the effects of acetylcholine. *It is agonist of acetylcholine receptors* - An **agonist** would mimic the effects of acetylcholine, which would worsen the symptoms of organophosphate poisoning. - Atropine is an **antagonist**, meaning it blocks the receptors.

Question 1

Which of the following statement is correct regarding the mechanism of action of labetalol?

Accepted Answer

Blocks both alpha and beta-adrenergic receptors.

Answer

Primarily acts as a vasodilator with little effect on arterioles

Answer

Decreases peripheral vascular resistance by directly acting as a relaxant for vascular smooth muscles.

Answer

Directly acts as arterial vasodilator resulting in indirect effect tachycardia.

Question 2

Which of the following is the site of action of botulinum toxin? (Recent NEET Pattern 2016-17)

Accepted Answer

Synaptobrevin and SNAP-25

Answer

Syntaxin and Synaptotagmin

Answer

Synaptic cleft

Answer

Synaptic vesicle

Question 3

Which of the following statement is correct regarding the graph shown? (AllMS Nov 2016)

Accepted Answer

Drug acting on graph B is isoproterenol

Answer

Drug in graph A is epinephrine

Answer

Effect on heart in graph A can be overcome by antimuscarinic

Answer

Drug acting on graph C is nor-epinephrine

Question 4

A 25-year-old woman going on a luxury holiday cruise has motion sickness. She is prescribed this transdermal scopolamine delivery patch. All are true about its usage except:

Accepted Answer

Remove patch immediately if there is pupil constriction and sialorrhea

Answer

Postauricular hairless skin has best delivery

Answer

Contact with the exposed adhesive layer should be avoided to prevent contamination of fingers with scopolamine

Answer

Slow absorption with lack of first pass metabolism

Question 5

Which of the following conditions can the shown injection be used for emergency management?

Accepted Answer

Brittle asthma

Answer

Hay fever

Answer

Snake bite

Answer

Flushing episodes in carcinoid

Question 6

Match the following:

Column A:
a. Beta 1
b. Beta 2
c. Beta 3

Column B:
1. Mirabegron
2. Betaxolol
3. Salbutamol

Accepted Answer

a-2, b-3 ,c-1

Answer

a-2, b-1, c-3

Answer

a-3, b-2, c-1

Answer

a-3, b-1, c-2

Question 7

An investigator is developing a new intravenous medication that acts as a selective agonist at β-2 receptors. In addition to causing bronchodilation, this drug is most likely to have which of the following effects?

Accepted Answer

Bladder detrusor relaxation

Answer

Peripheral vasoconstriction

Answer

Increased uterine tone

Answer

Increased gastrointestinal peristalsis

Question 8

Ritodrine is a:-

Accepted Answer

β2 agonist

Answer

β antagonist

Answer

α agonist

Answer

α1 antagonist

Question 9

Shortest-acting muscle relaxant is:

Accepted Answer

Succinylcholine

Answer

Atracurium

Answer

Tubocurarine

Answer

Pancuronium

Question 10

Mechanism of action of atropine in treatment of organophosphate poisoning is?

Accepted Answer

It has antimuscarinic activity

Answer

It inhibits secretion of acetylcholine

Answer

It is reactivator of acetylcholine esterase enzyme

Answer

It is agonist of acetylcholine receptors

Autonomic Nervous System Drugs — MCQs

Autonomic Nervous System Drugs — MCQs

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