Screening models for ANS activity – parasympatholytics MCQs With Answer

Screening models for ANS activity – parasympatholytics MCQs With Answer
This concise introduction outlines screening models used to evaluate autonomic nervous system (ANS) activity, focusing on parasympatholytics and muscarinic antagonists. B.Pharm students will learn key concepts: isolated tissue preparations (guinea-pig ileum, rabbit jejunum, trachea), in vivo assays (salivation, gut motility, pupil dilation, heart rate), standard drugs (atropine, scopolamine, glycopyrrolate), and pharmacological analysis (dose–response curves, Schild plot, pA2, competitive vs noncompetitive antagonism). Emphasis is on selecting appropriate bioassays, interpreting shifts in potency and efficacy, and translating results to receptor subtype selectivity and safety profiling. Now let’s test your knowledge with 30 MCQs on this topic.

Q1. Which isolated tissue is most commonly used as a standard bioassay to screen parasympatholytic (muscarinic antagonist) activity?

• Guinea-pig ileum
• Rat vas deferens
• Rabbit aorta
• Mouse skeletal muscle

Correct Answer: Guinea-pig ileum

Q2. Which agonist is frequently used to elicit muscarinic responses in tissue baths when screening for parasympatholytics?

• Norepinephrine
• Acetylcholine
• Histamine
• Serotonin

Correct Answer: Acetylcholine

Q3. A rightward parallel shift in the agonist dose–response curve with no change in maximal response after antagonist addition indicates:

• Noncompetitive antagonism
• Inverse agonism
• Competitive antagonism
• Partial agonism

Correct Answer: Competitive antagonism

Q4. Which parameter estimates antagonist potency from Schild analysis and is commonly reported in screening studies?

• ED50
• pA2
• LD50
• Bioavailability

Correct Answer: pA2

Q5. In screening parasympatholytics, a reduction in Emax (maximal response) typically suggests which mechanism?

• Competitive blockade at the receptor
• Noncompetitive antagonism or irreversible blockade
• Increased agonist concentration
• Pure pharmacokinetic interaction

Correct Answer: Noncompetitive antagonism or irreversible blockade

Q6. Which in vivo assay is sensitive for detecting peripheral antimuscarinic effects such as secretion inhibition?

• Y-maze test
• Salivation assay (pilocarpine-induced)
• Tail-flick analgesia
• Forced swim test

Correct Answer: Salivation assay (pilocarpine-induced)

Q7. Which muscarinic receptor subtype is primarily responsible for bronchial smooth muscle contraction assessed in tracheal preparations?

• M1
• M2
• M3
• M4

Correct Answer: M3

Q8. When using isolated rabbit jejunum to screen parasympatholytics, which functional readout is most commonly measured?

• Vasoconstriction
• Contraction amplitude and frequency (gut motility)
• Platelet aggregation
• Neuronal firing rate

Correct Answer: Contraction amplitude and frequency (gut motility)

Q9. Which reference antagonist is classically used as a standard in parasympatholytic screening studies?

• Propranolol
• Atropine
• Phentolamine
• Haloperidol

Correct Answer: Atropine

Q10. Glycopyrrolate is preferred over atropine in some peripheral screens because it:

• Has stronger CNS penetration
• Does not cross the blood–brain barrier markedly
• Is a muscarinic agonist
• Has cholinesterase inhibitory activity

Correct Answer: Does not cross the blood–brain barrier markedly

Q11. A Schild slope significantly different from unity suggests:

• Simple competitive antagonism at a single site
• Multiple receptor populations, non-equilibrium conditions, or noncompetitive behavior
• Pure agonist action
• Complete absence of antagonist binding

Correct Answer: Multiple receptor populations, non-equilibrium conditions, or noncompetitive behavior

Q12. Which test helps distinguish between ganglionic and postganglionic muscarinic actions during screening?

• Using hexamethonium to block ganglionic transmission
• Measuring liver enzymes
• Applying naloxone
• Using a beta-adrenergic blocker

Correct Answer: Using hexamethonium to block ganglionic transmission

Q13. In a tissue bath bioassay, why might researchers pre-contract tissue with KCl before testing a parasympatholytic?

• To assess blockade of receptor-mediated contraction specifically
• To remove all receptors from the tissue
• To inactivate acetylcholinesterase
• To measure neurotransmitter synthesis

Correct Answer: To assess blockade of receptor-mediated contraction specifically

Q14. Which outcome in an in vivo screening indicates central antimuscarinic activity rather than purely peripheral effects?

• Reduced salivation only
• Mydriasis only
• Impaired learning, memory deficits, or sedation
• Decreased gut motility exclusively

Correct Answer: Impaired learning, memory deficits, or sedation

Q15. Which parameter describes the concentration of antagonist that produces half-maximal inhibition (often used in receptor binding or functional assays)?

• ED50
• IC50
• pKa
• Vmax

Correct Answer: IC50

Q16. Carbachol is sometimes preferred over acetylcholine in tissue assays because:

• It is rapidly broken down by acetylcholinesterase
• It is resistant to acetylcholinesterase and provides sustained stimulation
• It is a selective nicotinic agonist
• It blocks muscarinic receptors directly

Correct Answer: It is resistant to acetylcholinesterase and provides sustained stimulation

Q17. In bladder strip assays, effective parasympatholytics primarily reduce which response?

• Smooth muscle relaxation
• Spontaneous and acetylcholine-induced contraction
• Neurogenic vasodilation
• Skeletal muscle twitch

Correct Answer: Spontaneous and acetylcholine-induced contraction

Q18. Which adverse effect observed during in vivo screening suggests excessive systemic antimuscarinic action?

• Excessive salivation
• Bradycardia and increased secretions
• Hyperthermia, dry mouth, urinary retention, tachycardia
• Enhanced gastrointestinal motility

Correct Answer: Hyperthermia, dry mouth, urinary retention, tachycardia

Q19. For receptor subtype selectivity screening, which approach is most informative?

• Using only one generic tissue type
• Combining multiple tissues and recombinant cell lines expressing specific M1–M5 receptors
• Relying solely on behavioral assays
• Measuring blood glucose levels

Correct Answer: Combining multiple tissues and recombinant cell lines expressing specific M1–M5 receptors

Q20. When performing a Schild plot, what is plotted on the y-axis to determine antagonist potency?

• Log(concentration of agonist)
• Log(dose ratio − 1)
• Percent inhibition directly
• Absolute agonist Emax

Correct Answer: Log(dose ratio − 1)

Q21. Which muscarinic antagonist is known for causing central antiemetic and anti-motion sickness effects due to CNS penetration?

• Glycopyrrolate
• Tropicamide
• Scopolamine
• Tiotropium

Correct Answer: Scopolamine

Q22. In isolated tissue assays, using KCl-induced contraction vs acetylcholine-induced contraction helps differentiate:

• Receptor-mediated versus direct smooth muscle (membrane depolarization) effects
• Nicotine vs epinephrine responses
• Bacterial contamination
• Protein synthesis rates

Correct Answer: Receptor-mediated versus direct smooth muscle (membrane depolarization) effects

Q23. A test compound causes a parallel rightward shift in ACh dose–response in ileum with calculated pA2 similar to atropine. This suggests the compound is likely:

• A muscarinic agonist
• A nonselective beta-blocker
• A competitive muscarinic antagonist with potency comparable to atropine
• An acetylcholinesterase inhibitor

Correct Answer: A competitive muscarinic antagonist with potency comparable to atropine

Q24. Which experimental control is essential when interpreting bioassay results for parasympatholytics?

• Omitting temperature control
• Using vehicle and positive control (e.g., atropine) alongside test compound
• Randomizing tissue baths without baseline recordings
• Not measuring baseline responses

Correct Answer: Using vehicle and positive control (e.g., atropine) alongside test compound

Q25. In receptor-binding assays, Ki value represents:

• The intrinsic efficacy of an agonist
• The equilibrium dissociation constant of an inhibitor (affinity)
• The maximal response achievable
• Metabolic half-life

Correct Answer: The equilibrium dissociation constant of an inhibitor (affinity)

Q26. Which respiratory model is useful for screening antimuscarinic bronchodilators?

• Isolated tracheal chain or bronchial ring contraction assay
• Isolated urinary bladder strip
• Hepatocyte culture assay
• Isolated skeletal muscle twitch preparation

Correct Answer: Isolated tracheal chain or bronchial ring contraction assay

Q27. During screening, a compound that blocks muscarinic responses but spares M2-mediated cardiac effects would likely show which in vivo pattern?

• Marked tachycardia with no bronchial relaxation
• Bronchodilation and decreased secretions with minimal tachycardia
• Severe bradycardia and increased salivation
• Enhanced cognitive impairment

Correct Answer: Bronchodilation and decreased secretions with minimal tachycardia

Q28. Which laboratory consideration reduces variability when using isolated tissue preparations for parasympatholytic screening?

• Varying oxygenation between baths
• Standardizing animal species, tissue size, buffer composition, temperature, and agonist concentrations
• Changing agonist batches during the experiment
• Mixing tissues from different species in the same bath

Correct Answer: Standardizing animal species, tissue size, buffer composition, temperature, and agonist concentrations

Q29. In the context of parasympatholytic screening, what does an EC50 represent for an agonist like ACh?

• The potency of an antagonist
• The concentration producing 50% of the maximal agonist response
• The toxic dose that kills 50% of animals
• The affinity constant of antagonist binding

Correct Answer: The concentration producing 50% of the maximal agonist response

Q30. Which outcome from a screening assay would most strongly indicate irreversible muscarinic receptor antagonism?

• Complete recovery of response after washing out antagonist
• Persistent reduction in Emax after washout and high agonist challenge
• Immediate reversible rightward shift only
• No change in potency or efficacy

Correct Answer: Persistent reduction in Emax after washout and high agonist challenge

G S Sachin

I am a Registered Pharmacist under the Pharmacy Act, 1948, and the founder of PharmacyFreak.com. I hold a Bachelor of Pharmacy degree from Rungta College of Pharmaceutical Science and Research. With a strong academic foundation and practical knowledge, I am committed to providing accurate, easy-to-understand content to support pharmacy students and professionals. My aim is to make complex pharmaceutical concepts accessible and useful for real-world application.

Mail- Sachin@pharmacyfreak.com