Autonomic Nervous System Drugs Practice Questions

Q: Which of the following drugs exhibits the phenomenon of vasomotor reversal of Dale after administration of an alpha-adrenergic blocker?

Adrenaline. **Explanation:** **Vasomotor Reversal of Dale** refers to the phenomenon where the typical pressor (blood pressure-increasing) effect of Adrenaline is converted into a depressor (blood pressure-lowering) effect following the administration of an alpha-blocker. **1. Why Adrenaline is correct:** Adrenaline is a potent agonist of **$\alpha_1, \alpha_2, \beta_1,$ and $\beta_2$** receptors. * **Normally:** Its $\alpha_1$-mediated vasoconstriction outweighs its $\beta_2$-mediated vasodilation, resulting in a net rise in blood pressure. * **After Alpha-blockade:** The $\alpha_1$ receptors are blocked. When Adrenaline is administered, only the **$\beta_2$ receptors** in the skeletal muscle blood vessels are available for activation. This leads to unopposed vasodilation, causing the blood pressure to fall instead of rise. **2. Why other options are incorrect:** * **Noradrenaline:** It acts primarily on $\alpha_1, \alpha_2,$ and $\beta_1$ receptors with **negligible effect on $\beta_2$**. Therefore, after alpha-blockade, there is no $\beta_2$ effect to cause vasodilation; the BP simply fails to rise (it stays near baseline). * **Isoprenaline:** It is a pure $\beta$-agonist ($\beta_1 + \beta_2$). It causes a fall in BP regardless of alpha-blockade because it has no alpha action to begin with. Thus, no "reversal" occurs. **High-Yield Clinical Pearls for NEET-PG:** * **Sir Henry Dale** first demonstrated this effect using ergot alkaloids (the first alpha-blockers). * **Key Concept:** For reversal to occur, the drug must have **both** alpha (constrictor) and beta-2 (dilator) properties. * **Clinical Relevance:** In patients with Pheochromocytoma, always give alpha-blockers *before* beta-blockers to avoid a hypertensive crisis caused by unopposed alpha-mediated vasoconstriction.

Q: Which of the following is NOT a contraindication to the use of beta-blockers?

Tachycardia. **Explanation:** Beta-blockers (β-adrenoceptor antagonists) work by blocking the effects of epinephrine and norepinephrine on beta receptors. Understanding their physiological effects is key to identifying their contraindications. **Why Tachycardia is the Correct Answer:** Beta-blockers are **indicated** (used for treatment), not contraindicated, in tachycardia. By blocking $\beta_1$ receptors in the sinoatrial (SA) node, they decrease the heart rate (negative chronotropic effect). They are first-line agents for rate control in conditions like sinus tachycardia, atrial fibrillation, and thyrotoxicosis. **Why the other options are Contraindications:** * **Bradycardia (Option A):** Since beta-blockers slow the heart rate, they can worsen pre-existing bradycardia or heart block, potentially leading to cardiac arrest. * **Bronchial Asthma (Option C):** Non-selective beta-blockers block $\beta_2$ receptors in the bronchial smooth muscle, leading to bronchoconstriction. This can precipitate a life-threatening asthma attack. (Note: Cardioselective $\beta_1$ blockers are preferred if a beta-blocker is absolutely necessary). * **Raynaud’s Disease (Option D):** Blocking $\beta_2$-mediated vasodilation leaves $\alpha$-mediated vasoconstriction unopposed. This worsens peripheral vasospasm and reduces cold tolerance in patients with peripheral vascular disease. **High-Yield Clinical Pearls for NEET-PG:** * **Diabetes Mellitus:** Beta-blockers are used with caution because they mask the warning symptoms of hypoglycemia (tachycardia/tremors), though sweating (mediated by cholinergic sympathetic nerves) remains. * **Prinzmetal Angina:** They are contraindicated as they may worsen coronary vasospasm due to unopposed $\alpha$-activity. * **Cardioselectivity:** Remember the mnemonic **"A to M"** (e.g., Atenolol, Metoprolol) for $\beta_1$ selective blockers, which are safer (but not absolute) in respiratory or peripheral vascular issues.

Q: Suxamethonium is:

A depolarizing muscle relaxant. **Explanation:** **Suxamethonium (Succinylcholine)** is the only clinically used **depolarizing neuromuscular blocking agent**. It consists of two acetylcholine (ACh) molecules joined together. **Why Option B is Correct:** Suxamethonium acts as an agonist at the nicotinic acetylcholine receptors ($N_m$) at the neuromuscular junction. Unlike ACh, it is not metabolized by acetylcholinesterase, leading to persistent depolarization of the motor endplate. This results in initial muscle twitching (**fasciculations**) followed by flaccid paralysis because the sodium channels remain in an inactivated state, preventing further action potentials. **Why Other Options are Incorrect:** * **Option A:** Non-depolarizing relaxants (e.g., **d-Tubocurarine, Vecuronium**) are competitive antagonists. They block ACh from binding to the receptor without causing initial depolarization or fasciculations. * **Option C:** Direct-acting muscle relaxants (e.g., **Dantrolene**) act directly on the muscle fiber by inhibiting calcium release from the sarcoplasmic reticulum, rather than acting at the neuromuscular junction. **High-Yield NEET-PG Pearls:** 1. **Metabolism:** It is rapidly hydrolyzed by **Pseudocholinesterase** (Butyrylcholinesterase). Patients with atypical pseudocholinesterase experience prolonged apnea (**Suxamethonium apnea**). 2. **Side Effects:** Hyperkalemia (dangerous in burn or trauma patients), muscle soreness, and increased intraocular/intragastric pressure. 3. **Malignant Hyperthermia:** Suxamethonium is a known trigger; the antidote is **Dantrolene**. 4. **Phase II Block:** With prolonged infusion, the block may transition from depolarizing to a pattern resembling non-depolarizing blockade.

Q: Which of the following drugs primarily increases uveo-scleral outflow?

Latanoprost. **Explanation:** The management of Glaucoma involves reducing intraocular pressure (IOP) by either decreasing aqueous humor production or increasing its drainage. Drainage occurs via two pathways: the **Trabecular meshwork** (conventional) and the **Uveoscleral pathway** (unconventional). **Why Latanoprost is correct:** **Latanoprost** is a PGF2α analogue. It is the drug of choice for Open Angle Glaucoma. It works primarily by increasing the **uveoscleral outflow** of aqueous humor by relaxing the ciliary muscle and remodeling the extracellular matrix. **Analysis of Incorrect Options:** * **Apraclonidine:** An alpha-2 agonist. It primarily works by **decreasing aqueous humor production** and, to a lesser extent, increasing trabecular outflow. * **Timolol:** A non-selective beta-blocker. It is a traditional first-line agent that works solely by **decreasing aqueous humor production** from the ciliary epithelium. * **Brinzolamide:** A topical Carbonic Anhydrase Inhibitor (CAI). It reduces IOP by **decreasing the secretion** of aqueous humor (bicarbonate ions) from the ciliary body. **NEET-PG High-Yield Pearls:** * **Prost** drugs (Latanoprost, Bimatoprost, Travoprost) are the most potent drugs for lowering IOP. * **Side effects of Prostaglandins:** Increased pigmentation of the iris (heterochromia iridis), thickening/darkening of eyelashes (trichomegaly), and cystoid macular edema. * **Miotics (Pilocarpine)** increase **trabecular** outflow by contracting the ciliary muscle. * **Drug of choice for Acute Angle Closure Glaucoma:** IV Acetazolamide/Mannitol (to rapidly lower pressure before surgery).

Q: Which beta agonist is used for stopping premature labor?

Terbutaline. **Explanation:** The correct answer is **Terbutaline**. **1. Why Terbutaline is correct:** Terbutaline is a **selective $\beta_2$-adrenergic agonist**. In the context of obstetrics, it acts as a **tocolytic** agent. Stimulation of $\beta_2$ receptors in the uterine smooth muscle (myometrium) increases intracellular cAMP, which leads to the relaxation of the uterus. This mechanism is used clinically to delay or stop premature labor (tocolysis), providing a window to administer corticosteroids for fetal lung maturity. **2. Why the other options are incorrect:** * **Carvedilol (A):** This is a non-selective $\beta$-blocker with additional $\alpha_1$-blocking activity. It is used in the management of heart failure and hypertension, not for uterine relaxation. * **Pindolol (C):** This is a non-selective $\beta$-blocker with **Intrinsic Sympathomimetic Activity (ISA)**. It is used for hypertension and would actually oppose uterine relaxation. * **Nadolol (D):** This is a long-acting non-selective $\beta$-blocker primarily used for hypertension, angina, and prophylaxis of migraine or variceal bleeding. **3. High-Yield Clinical Pearls for NEET-PG:** * **Other Tocolytics:** While Terbutaline is a classic $\beta_2$ agonist for this purpose, **Ritodrine** is another specific $\beta_2$ agonist developed for tocolysis. However, **Nifedipine** (Calcium Channel Blocker) and **Atosiban** (Oxytocin antagonist) are now often preferred due to fewer side effects. * **Side Effects:** A high-yield side effect of $\beta_2$ agonists used in labor is **maternal tachycardia**, palpitations, and potential **pulmonary edema**. * **Metabolic Effect:** $\beta_2$ agonists can cause **hypokalemia** and **hyperglycemia** (due to glycogenolysis).

Question 1

Which of the following is the binding site of organophosphorous compounds?

Accepted Answer

Esteric site of Acetylcholinesterase

Answer

Anionic site of Acetylcholinesterase

Answer

Neuromuscular receptors

Answer

Plasma cholinesterase

Question 2

Which of the following is the binding site of organophosphorous compounds?

Accepted Answer

Esteric site of Acetylcholinesterase

Answer

Anionic site of Acetylcholinesterase

Answer

Neuromuscular receptors

Answer

Plasma cholinesterase

Question 3

Which of the following drugs exhibits the phenomenon of vasomotor reversal of Dale after administration of an alpha-adrenergic blocker?

Accepted Answer

Adrenaline

Answer

Noradrenaline

Answer

Isoprenaline

Answer

All of the above

Question 4

Which of the following is NOT a contraindication to the use of beta-blockers?

Accepted Answer

Tachycardia

Answer

Bradycardia

Answer

Bronchial asthma

Answer

Raynaud's disease

Question 5

Suxamethonium is:

Accepted Answer

A depolarizing muscle relaxant

Answer

A non-depolarizing muscle relaxant

Answer

A direct-acting muscle relaxant

Answer

All of the above

Question 6

Which of the following drugs primarily increases uveo-scleral outflow?

Accepted Answer

Latanoprost

Answer

Apraclonidine

Answer

Timolol

Answer

Brinzolamide

Question 7

Methacholine has maximum agonist action at which of the following cholinergic receptors?

Accepted Answer

M2

Answer

M1

Answer

M3

Answer

M4

Question 8

Tolazine is used as:

Accepted Answer

A vasodilator in treating coronary artery stenosis during angioplasty procedures

Answer

A thrombin inhibitor in peripheral angiography

Answer

A vasoconstrictor in treatment of varices

Answer

An antispasmodic during biliary spasm

Question 9

Which of the following is an ionic channel?

Accepted Answer

Nicotinic cholinergic receptors

Answer

$\alpha$1 receptors

Answer

$\beta$1 receptors

Answer

Muscarinic cholinergic receptors

Question 10

Which beta agonist is used for stopping premature labor?

Accepted Answer

Terbutaline

Answer

Carvedilol

Answer

Pindolol

Answer

Nadolol

Autonomic Nervous System Drugs — MCQs

Autonomic Nervous System Drugs — MCQs

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