Understanding the Bioassay of vasopressin MCQs With Answer is essential for B.Pharm students studying endocrinology and pharmacology. This concise guide reviews vasopressin pharmacodynamics, V1/V2 receptor actions, pressor and antidiuretic bioassays, assay design, standardization, potency (ED50), sensitivity, specificity, sample preparation, and common interferences. Emphasis is placed on classic bioassays (pressor assay, antidiuretic assay, isolated tissue preparations), assay validation parameters, and interpretation of dose–response curves. Practical knowledge of bioassay methodology, controls, and data analysis helps students evaluate vasopressin activity and compare analogs like desmopressin. You will learn assay selection, control preparation, calculation of relative potency, and troubleshooting common assay errors for robust experimental results. Now let’s test your knowledge with 30 MCQs on this topic.
Q1. Which receptor subtype primarily mediates vasopressin-induced vasoconstriction?
- V2 receptor
- V1 receptor
- V3 receptor
- β2-adrenergic receptor
Correct Answer: V1 receptor
Q2. The antidiuretic effect of vasopressin in the kidney is mainly mediated through which second messenger?
- cGMP
- cAMP
- IP3/DAG
- Calcium-calmodulin
Correct Answer: cAMP
Q3. A classic pressor bioassay of vasopressin measures which physiological endpoint?
- Urine osmolality
- Blood pressure increase
- Heart rate decrease
- Serum sodium concentration
Correct Answer: Blood pressure increase
Q4. In an antidiuretic bioassay, which animal preparation is commonly used to assess water retention?
- Water-loaded rat
- Isolated guinea pig ileum
- Rabbit cornea
- Isolated frog heart
Correct Answer: Water-loaded rat
Q5. Which parameter describes the concentration of hormone producing 50% of the maximal response in a bioassay?
- ED50
- ECmax
- IC50
- Kd
Correct Answer: ED50
Q6. What is the main advantage of a bioassay over an immunoassay for vasopressin?
- Higher throughput
- Measures biological activity rather than just antigenicity
- Less ethical concern
- No need for standard curves
Correct Answer: Measures biological activity rather than just antigenicity
Q7. Which analytical step improves accuracy when measuring vasopressin in plasma for bioassay?
- Direct injection without processing
- Acidification and peptide extraction
- Heating plasma at 95°C for 10 min
- Adding EDTA only
Correct Answer: Acidification and peptide extraction
Q8. Parallel line assay analysis in bioassays assumes:
- Different maximal responses for test and standard
- Different slope but same potency
- Linear and parallel dose–response curves for test and standard
- No need for replication
Correct Answer: Linear and parallel dose–response curves for test and standard
Q9. Which vasopressin analog is commonly used for antidiuretic replacement with prolonged action and minimal vasopressor activity?
- Oxytocin
- Desmopressin (DDAVP)
- Terlipressin
- Phenylephrine
Correct Answer: Desmopressin (DDAVP)
Q10. A major limitation of in vivo vasopressin bioassays is:
- Complete specificity to vasopressin
- Inter-animal variability affecting reproducibility
- No requirement for standards
- Unlimited assay sensitivity
Correct Answer: Inter-animal variability affecting reproducibility
Q11. Which factor is critical to control during a pressor bioassay to reduce variability?
- Ambient light only
- Animal baseline blood pressure and anesthesia level
- Color of the injection syringe
- Time of day is irrelevant
Correct Answer: Animal baseline blood pressure and anesthesia level
Q12. In vasopressin bioassays, specificity can be increased by:
- Using crude plasma without purification
- Using selective receptor antagonists to confirm receptor-mediated effects
- Omitting negative controls
- Pooling unrelated samples
Correct Answer: Using selective receptor antagonists to confirm receptor-mediated effects
Q13. Which validation parameter assesses how close measured values are to true values in a bioassay?
- Precision
- Accuracy
- Robustness
- Slope
Correct Answer: Accuracy
Q14. Proteolytic degradation of vasopressin in biological samples is best minimized by:
- Leaving samples at room temperature overnight
- Adding protease inhibitors and rapid cooling
- Boiling samples for 1 hour
- Diluting samples with saline only
Correct Answer: Adding protease inhibitors and rapid cooling
Q15. Which tissue preparation could be used as an isolated tissue bioassay to study vasopressin vasoconstrictor action?
- Isolated rat aorta or tail artery
- Isolated hepatocytes
- Isolated pancreatic islets
- Isolated skeletal muscle strips
Correct Answer: Isolated rat aorta or tail artery
Q16. In a dose–response curve, increasing potency of a test sample compared to a standard shifts the curve:
- To the right (higher concentration required)
- Downward (lower maximum response)
- Upward without shift
- To the left (lower concentration required)
Correct Answer: To the left (lower concentration required)
Q17. Which statistical parameter describes the repeatability of responses in a bioassay?
- Bias
- Precision (e.g., coefficient of variation)
- Specific activity
- Slope heterogeneity
Correct Answer: Precision (e.g., coefficient of variation)
Q18. When comparing bioassay and immunoassay for vasopressin, which statement is true?
- Immunoassays always measure functional activity
- Bioassays measure biological activity; immunoassays detect antigenic presence
- Bioassays are unaffected by matrix components
- Immunoassays require live animals
Correct Answer: Bioassays measure biological activity; immunoassays detect antigenic presence
Q19. Which of the following is a common control used in vasopressin bioassays?
- Blank without vehicle
- Standard vasopressin preparation of known potency
- Unrelated enzyme as positive control
- Only negative control is used
Correct Answer: Standard vasopressin preparation of known potency
Q20. A bioassay displays non-parallelism between test and standard dose–response curves. This suggests:
- Equal potency and specificity
- Possible different modes of action or assay interference
- Perfect assay validation
- That dilution series were unnecessary
Correct Answer: Possible different modes of action or assay interference
Q21. Which pre-analytical variable can falsely lower measured vasopressin activity in a sample?
- Immediate freezing at −80°C
- Delays in processing leading to proteolysis
- Adding protease inhibitors
- Acidifying and extracting promptly
Correct Answer: Delays in processing leading to proteolysis
Q22. Terlipressin is a vasopressin analog with enhanced selectivity for which effect?
- Antidiuretic with no vasoconstriction
- Prolonged vasopressor action
- Pure V2 receptor agonism
- Beta-adrenergic blockade
Correct Answer: Prolonged vasopressor action
Q23. When calculating relative potency in a bioassay, which comparison is required?
- Comparison of ED50 values between test and standard
- Comparison of molecular weights only
- Comparison of pH values
- No comparison needed
Correct Answer: Comparison of ED50 values between test and standard
Q24. Which reagent or condition can interfere with vasopressin bioassays causing false positive responses?
- Use of saline as vehicle
- Contaminating vasoactive substances in sample matrix
- Appropriate negative control
- Standardized assay buffers
Correct Answer: Contaminating vasoactive substances in sample matrix
Q25. The term “specific activity” in peptide bioassays refers to:
- Activity per unit mass of peptide
- Total protein concentration
- Volume of sample
- pH of assay buffer
Correct Answer: Activity per unit mass of peptide
Q26. Why are serial dilutions important when performing a vasopressin bioassay?
- To ensure the dose–response covers the dynamic range and allows ED50 estimation
- To reduce assay time
- To avoid preparing standards
- They are not important
Correct Answer: To ensure the dose–response covers the dynamic range and allows ED50 estimation
Q27. Which environmental condition must be controlled to maintain assay reproducibility?
- Ambient music
- Temperature of organ bath or animal room
- Color of lab coats
- Brand of pipette tips only
Correct Answer: Temperature of organ bath or animal room
Q28. Which analytical approach can be used to confirm that vasopressin bioassay responses are receptor-mediated?
- Use of non-selective electrolytes
- Pre-treatment with selective V1 or V2 receptor antagonists
- Ignoring dose–response shape
- Measuring unrelated hormones
Correct Answer: Pre-treatment with selective V1 or V2 receptor antagonists
Q29. During validation of a vasopressin bioassay, linearity assesses:
- Whether response is proportional to concentration over a range
- If the assay uses live animals
- Only the rank order of potency
- Whether the assay is cheap
Correct Answer: Whether response is proportional to concentration over a range
Q30. Which sample matrix typically poses the greatest challenge for vasopressin bioassays due to proteases and binding proteins?
- Purified synthetic standard
- Plasma/serum
- Deionized water
- Buffer-only controls
Correct Answer: Plasma/serum
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