Spare receptors MCQs With Answer

Spare receptors MCQs With Answer

Understanding spare receptors (receptor reserve) is essential for B.Pharm students studying pharmacodynamics. This concept explains how tissues can achieve maximal response with only a fraction of receptors occupied due to downstream signal amplification. Key topics include EC50 versus Kd relationships, effects of irreversible antagonists, impact on potency and efficacy, partial agonist behavior, receptor density, and clinical implications like tolerance and dosing. Mastery helps interpret dose–response curves, design experiments to estimate receptor reserve, and predict drug responses in different tissues. These MCQs focus on core mechanisms, experimental approaches, and therapeutic relevance to deepen your pharmacological insight. Now let’s test your knowledge with 30 MCQs on this topic.

Q1. What are spare receptors?

• Receptors in excess of those needed for a maximal response (receptor reserve)
• Receptors with permanently high affinity for agonists
• Receptors that cannot be antagonized by any drug
• Receptors only present during embryonic development

Correct Answer: Receptors in excess of those needed for a maximal response (receptor reserve)

Q2. Which experimental observation most directly indicates the presence of spare receptors?

• EC50 is significantly lower than Kd for the agonist
• EC50 equals Kd for the agonist
• Emax is lower than expected for full receptor occupancy
• Kd is lower than Bmax

Correct Answer: EC50 is significantly lower than Kd for the agonist

Q3. How do spare receptors typically affect apparent potency and maximal efficacy of a full agonist?

• Increase apparent potency (lower EC50) without changing maximal efficacy
• Increase both potency and maximal efficacy
• Decrease potency but increase maximal efficacy
• Eliminate all agonist effects

Correct Answer: Increase apparent potency (lower EC50) without changing maximal efficacy

Q4. What is the expected effect of an irreversible antagonist on a tissue with substantial receptor reserve?

• Rightward shift of the dose–response curve without Emax reduction until receptor reserve is depleted
• Immediate and proportional reduction of Emax with no change in potency
• No effect on potency or efficacy at any antagonist concentration
• Increase in receptor affinity (lower Kd)

Correct Answer: Rightward shift of the dose–response curve without Emax reduction until receptor reserve is depleted

Q5. Which statement about partial agonists in tissues with spare receptors is correct?

• Partial agonists produce submaximal responses even when all receptors are occupied
• Partial agonists become full agonists in the presence of spare receptors
• Partial agonists always act as irreversible antagonists
• Partial agonists increase receptor density

Correct Answer: Partial agonists produce submaximal responses even when all receptors are occupied

Q6. Which tissue is a classical example where spare receptors are often observed?

• Cardiac beta-adrenergic receptors
• Red blood cell membranes
• Hair follicle receptors
• Pancreatic amylase receptors

Correct Answer: Cardiac beta-adrenergic receptors

Q7. How does the presence of spare receptors change tissue sensitivity to reversible competitive antagonists?

• It decreases sensitivity, requiring more antagonist to reduce response
• It increases sensitivity, making antagonists more effective
• It converts competitive antagonists into agonists
• It abolishes antagonist binding completely

Correct Answer: It decreases sensitivity, requiring more antagonist to reduce response

Q8. If a tissue has spare receptors, what fraction of total receptors typically needs to be occupied for a maximal response?

• A small fraction of the total receptors
• All receptors must be occupied
• No receptors need to be occupied
• Exactly 50% of receptors

Correct Answer: A small fraction of the total receptors

Q9. What relationship between receptor density and receptor reserve is generally true?

• Higher receptor density relative to signaling components favors the existence of receptor reserve
• Lower receptor density always produces larger receptor reserves
• Receptor reserve is independent of receptor density
• Receptor reserve only depends on ligand structure

Correct Answer: Higher receptor density relative to signaling components favors the existence of receptor reserve

Q10. Which method is commonly used to estimate receptor reserve experimentally?

• Use of irreversible antagonists to inactivate a fraction of receptors and measuring changes in Emax
• Measuring urine excretion after agonist administration
• Sequencing the receptor gene
• Measuring blood pressure only

Correct Answer: Use of irreversible antagonists to inactivate a fraction of receptors and measuring changes in Emax

Q11. For a full agonist in a system with spare receptors, how does EC50 typically compare to Kd?

• EC50 is lower than Kd
• EC50 equals Kd
• EC50 is higher than Kd
• Kd is irrelevant

Correct Answer: EC50 is lower than Kd

Q12. If an agonist has Kd = 100 nM but produces half-maximal effect at 10 nM, what does this indicate?

• Presence of receptor reserve (spare receptors)
• Ligand has no efficacy
• Antagonist contamination in the assay
• Experimentally impossible result

Correct Answer: Presence of receptor reserve (spare receptors)

Q13. Which observation suggests absence of spare receptors in a tissue?

• EC50 approximately equals Kd for the agonist
• EC50 much lower than Kd
• Emax increases with low antagonist concentration
• Maximal response occurs without receptor occupancy

Correct Answer: EC50 approximately equals Kd for the agonist

Q14. What is a key clinical implication of receptor reserve?

• High receptor reserve may require larger antagonist doses to block physiological responses
• Receptor reserve reduces drug half-life
• Receptor reserve eliminates side effects
• Receptor reserve increases renal clearance of drugs

Correct Answer: High receptor reserve may require larger antagonist doses to block physiological responses

Q15. How does receptor downregulation affect tissues with spare receptors during chronic agonist exposure?

• Function may be maintained until receptor reserve is depleted, then declines
• Function increases continuously regardless of receptor number
• Downregulation has no effect if spare receptors exist
• Downregulation immediately increases Emax

Correct Answer: Function may be maintained until receptor reserve is depleted, then declines

Q16. Loss of receptor reserve is most closely associated with which pharmacological phenomenon?

• Tolerance or tachyphylaxis to a drug
• Enhanced drug absorption
• Increased renal clearance
• Immediate hypersensitivity reactions

Correct Answer: Tolerance or tachyphylaxis to a drug

Q17. When an irreversible antagonist reduces receptor number, what typically happens to the affinity (Kd) of remaining receptors?

• Kd of remaining receptors is usually unchanged
• Kd decreases dramatically for remaining receptors
• Kd increases for remaining receptors
• Kd becomes zero for all receptors

Correct Answer: Kd of remaining receptors is usually unchanged

Q18. During progressive receptor inactivation by an irreversible antagonist in a system with spare receptors, which parameter changes first?

• Potency (EC50) shifts before Emax falls
• Emax falls immediately with no change in potency
• Affinity (Kd) increases before any functional change
• Receptor mRNA expression doubles

Correct Answer: Potency (EC50) shifts before Emax falls

Q19. Why can a small number of occupied receptors produce a full response in systems with receptor reserve?

• Signaling amplification downstream of receptor activation multiplies the response
• Each receptor permanently activates all effectors
• Agonists convert into enzymes that synthesize more receptors
• Because drug concentrations are always extremely high

Correct Answer: Signaling amplification downstream of receptor activation multiplies the response

Q20. Which of the following physiological sites is a classic example where spare receptors allow rapid, large responses from few receptors?

• Neuromuscular junction
• Adipose tissue triglyceride stores
• Cerebrospinal fluid production
• Lens of the eye

Correct Answer: Neuromuscular junction

Q21. What comparison is typically made to demonstrate receptor reserve experimentally?

• Comparison of receptor occupancy (binding) curve and functional response curve
• Comparison of drug solubility and pKa
• Comparison of gene expression and urine output
• Comparison of liver size and receptor number

Correct Answer: Comparison of receptor occupancy (binding) curve and functional response curve

Q22. If 5% receptor occupancy yields 100% maximal effect, what concept does this illustrate?

• Presence of receptor reserve (spare receptors)
• Receptor antagonism
• Inverse agonism
• Allosteric modulation

Correct Answer: Presence of receptor reserve (spare receptors)

Q23. How does the presence of receptor reserve influence the dose selection of an agonist clinically?

• Lower doses may achieve therapeutic effects because few receptors need to be occupied
• Higher doses are always required to achieve effects
• Dose selection becomes irrelevant
• Only intravenous dosing is effective

Correct Answer: Lower doses may achieve therapeutic effects because few receptors need to be occupied

Q24. Which type of antagonist is most useful to reveal and quantify receptor reserve?

• Irreversible (non-competitive) antagonist
• Short-acting reversible antagonist
• Allosteric potentiator
• Enzyme inhibitor unrelated to the receptor

Correct Answer: Irreversible (non-competitive) antagonist

Q25. In the presence of a full agonist, how might a partial agonist behave in tissues with spare receptors?

• Act as a functional antagonist by occupying receptors and producing a smaller response
• Always increase the full agonist effect
• Convert into a full agonist physiologically
• Immediately degrade the full agonist

Correct Answer: Act as a functional antagonist by occupying receptors and producing a smaller response

Q26. If EC50 is one-tenth of Kd for a given agonist, what is the simplest interpretation?

• There is a significant receptor reserve in this system
• The agonist is an irreversible antagonist
• The drug has no efficacy
• The binding assay is invalid

Correct Answer: There is a significant receptor reserve in this system

Q27. Which pharmacodynamic concept explicitly incorporates the idea of receptor reserve?

• Occupancy–response model with receptor reserve
• Michaelis–Menten liver model
• Henderson–Hasselbalch acid–base model
• Fick’s diffusion model

Correct Answer: Occupancy–response model with receptor reserve

Q28. How can knowledge of spare receptors guide drug development?

• Allow design of partial agonists with sufficient effect but lower side effects due to reserve
• Eliminate the need for preclinical testing
• Guarantee no drug–drug interactions will occur
• Make pharmacokinetics irrelevant

Correct Answer: Allow design of partial agonists with sufficient effect but lower side effects due to reserve

Q29. If receptor number is halved in a system that still has spare receptors, what is the expected effect on potency and efficacy?

• Efficacy remains unchanged while potency decreases (EC50 increases)
• Efficacy decreases and potency increases
• Both efficacy and potency remain unchanged
• Efficacy increases and potency decreases

Correct Answer: Efficacy remains unchanged while potency decreases (EC50 increases)

Q30. Which experimental evidence supports the existence of spare receptors?

• Irreversible antagonist reduces Emax only after significant receptor inactivation, while early inactivation alters potency
• Reversible antagonist immediately eliminates Emax at low concentrations
• All ligands show identical EC50 and Kd values
• Agonist binding always equals physiological response

Correct Answer: Irreversible antagonist reduces Emax only after significant receptor inactivation, while early inactivation alters potency

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