Bioassay of oxytocin MCQs With Answer
The bioassay of oxytocin is an essential topic for B. Pharm students studying pharmacology and quality control of peptide hormones. This introduction covers principles of biological assays, common methods (uterine strip, mammary gland, in vivo tests), assay sensitivity, specificity, standardization to international units, dose–response analysis, and factors affecting potency such as pH, temperature, preservatives and estrogen priming. Understanding validation parameters, calculation of ED50, parallel line assays and cross‑reactivity with vasopressin prepares students for pharmaceutical QC and regulatory requirements. Clear knowledge of bioassay design and interpretation ensures accurate potency determination and safe clinical use. Now let’s test your knowledge with 30 MCQs on this topic.
Q1. What is the primary biological endpoint measured in the classical uterine bioassay for oxytocin?
- Increase in uterine blood flow
- Contraction amplitude and frequency of uterine smooth muscle
- Change in uterine temperature
- Estrogen receptor expression
Correct Answer: Contraction amplitude and frequency of uterine smooth muscle
Q2. Which animal tissue is most commonly used for in vitro oxytocin bioassays in classical pharmacology labs?
- Rabbit intestinal strip
- Rat uterine horn strip
- Guinea pig tracheal ring
- Dog cardiac papillary muscle
Correct Answer: Rat uterine horn strip
Q3. Before performing a uterine bioassay, why is estrogen priming of the animal often required?
- To reduce uterine sensitivity to oxytocin
- To increase uterine contractile responsiveness to oxytocin
- To induce immunosuppression
- To prevent bacterial contamination
Correct Answer: To increase uterine contractile responsiveness to oxytocin
Q4. In oxytocin bioassays, potency is frequently expressed relative to what standard?
- Milligrams per milliliter
- International Units (IU) of oxytocin standard
- Optical density at 280 nm
- pH units
Correct Answer: International Units (IU) of oxytocin standard
Q5. Which curve-fitting method is commonly used to determine ED50 in dose–response bioassays?
- Linear regression on raw response
- Log-dose probit or log‑dose response (sigmoidal) analysis
- Polynomial interpolation of ranks
- Fourier transform analysis
Correct Answer: Log-dose probit or log‑dose response (sigmoidal) analysis
Q6. Which factor does NOT significantly affect oxytocin bioassay results?
- Temperature of organ bath
- pH of the buffer
- Type of water used to prepare buffer
- Animal strain and hormonal status
Correct Answer: Type of water used to prepare buffer
Q7. Cross-reactivity in biological assays of oxytocin is a concern due to structural similarity with which peptide?
- Insulin
- Vasopressin (antidiuretic hormone)
- Atrial natriuretic peptide
- Glucagon
Correct Answer: Vasopressin (antidiuretic hormone)
Q8. Which validation parameter assesses the closeness of measured values to the true value in an oxytocin bioassay?
- Precision
- Specificity
- Accuracy
- Robustness
Correct Answer: Accuracy
Q9. When comparing bioassay and immunoassay for oxytocin, which statement is true?
- Bioassays measure biological activity, immunoassays measure antigen concentration
- Both techniques measure biological activity identically
- Immunoassays are always more specific than bioassays for activity
- Bioassays are faster and easier than immunoassays
Correct Answer: Bioassays measure biological activity, immunoassays measure antigen concentration
Q10. What is the common purpose of performing parallel line assays in oxytocin bioassay analysis?
- To compare slopes of unrelated drugs
- To demonstrate linearity over unrelated concentration ranges
- To determine relative potency between sample and standard assuming parallelism
- To measure absolute concentration using spectrophotometry
Correct Answer: To determine relative potency between sample and standard assuming parallelism
Q11. Which preservative is commonly used in oxytocin formulations but can affect bioassay outcomes if concentration changes?
- Sodium chloride
- Chlorobutanol or phenol-type preservatives
- Distilled water
- Sucrose
Correct Answer: Chlorobutanol or phenol-type preservatives
Q12. In a uterine strip assay, which parameter is most often measured quantitatively to build a dose–response curve?
- Time to first contraction only
- Maximal contractile force (tension) produced
- Rate of tissue necrosis
- Change in organ weight
Correct Answer: Maximal contractile force (tension) produced
Q13. Which storage condition best preserves oxytocin potency in aqueous solutions?
- Frozen at −20°C with no stabilizer
- Room temperature in light-exposed bottle
- Refrigerated at 2–8°C in absence of light with stabilizer
- Autoclaved and stored at 40°C
Correct Answer: Refrigerated at 2–8°C in absence of light with stabilizer
Q14. What is the main reason for diluting both sample and standard in the same buffer when performing a bioassay?
- To reduce assay sensitivity
- To ensure matrix matching and reduce matrix effects
- To change the pharmacology of oxytocin
- To sterilize the solutions
Correct Answer: To ensure matrix matching and reduce matrix effects
Q15. Which regulatory document or organization provides guidance on biological standardization and potency assays for hormones like oxytocin?
- WHO (World Health Organization) and pharmacopeial monographs
- IEEE standards
- ISO for food packaging only
- FDA cosmetic guidelines only
Correct Answer: WHO (World Health Organization) and pharmacopeial monographs
Q16. Which statistical concept assesses reproducibility of repeated bioassay measurements?
- Bias
- Precision (e.g., coefficient of variation)
- Specificity index
- Limit of quantification only
Correct Answer: Precision (e.g., coefficient of variation)
Q17. Which oxytocin analogue is designed to have longer duration of action and is relevant when discussing potency and bioassay cross-evaluation?
- Vasopressin
- Carbetocin
- Insulin lispro
- Atropine
Correct Answer: Carbetocin
Q18. What does ED50 represent in the context of an oxytocin bioassay?
- Dose producing 50% of the maximal effect
- Dose that kills 50% of animals
- Concentration at 50 mg/mL
- Time required for 50% degradation
Correct Answer: Dose producing 50% of the maximal effect
Q19. Which of the following is a robustness test parameter for an oxytocin bioassay?
- Changing the assay operator only
- Deliberate small variations in incubation temperature or pH to assess impact
- Changing the drug substance entirely
- Running assay without any standard
Correct Answer: Deliberate small variations in incubation temperature or pH to assess impact
Q20. In bioassay data plotting, why is the dose axis often transformed to a logarithmic scale?
- To compress the response range only
- Because biological responses typically follow a log‑dose relationship improving linearity
- To make calculations harder
- To hide outliers
Correct Answer: Because biological responses typically follow a log‑dose relationship improving linearity
Q21. Which sample preparation step is important to avoid tissue-damaging particulate matter when performing in vitro bioassays?
- Autoclaving sample
- Filtration or centrifugation to remove particulates
- Adding hydrochloric acid
- Lyophilization immediately before assay
Correct Answer: Filtration or centrifugation to remove particulates
Q22. Which control is essential to ensure responses in an oxytocin bioassay are drug-specific?
- Blank buffer control and vehicle control
- Only a positive control
- Only a negative control without buffer
- Temperature-only control
Correct Answer: Blank buffer control and vehicle control
Q23. What is a common cause of apparent loss of oxytocin potency during storage?
- Peptide hydrolysis or deamidation due to improper pH or temperature
- Increase in optical rotation
- Excessive refrigeration improving stability
- Binding to refrigerator shelves
Correct Answer: Peptide hydrolysis or deamidation due to improper pH or temperature
Q24. Which analytical approach complements bioassays by quantifying oxytocin mass rather than activity?
- Cellular contraction assay
- LC‑MS/MS or HPLC quantitation
- In vivo uterotonic test only
- Organ bath bioassay
Correct Answer: LC‑MS/MS or HPLC quantitation
Q25. In assay standardization, what does “parallelism” between standard and test dose–response curves indicate?
- Different mechanisms of action
- Comparable potency estimation is valid because slopes are similar
- Test is invalid regardless of slope
- That the assay is highly variable
Correct Answer: Comparable potency estimation is valid because slopes are similar
Q26. Which safety concern is most relevant when administering oxytocin clinically that is related to potency testing?
- Hyperglycemia
- Uterine hyperstimulation leading to fetal distress
- Permanent skin discoloration
- Renal failure
Correct Answer: Uterine hyperstimulation leading to fetal distress
Q27. Which parameter measures the smallest biologically meaningful change distinguishable by the bioassay?
- Specificity
- Limit of detection/limit of quantification
- pH tolerance
- Visual clarity
Correct Answer: Limit of detection/limit of quantification
Q28. Why is it important to include housekeeping or reference preparations when running multiple bioassays over time?
- To reduce workload
- To monitor assay drift and ensure long-term reproducibility
- To avoid using any standard
- To change assay sensitivity deliberately
Correct Answer: To monitor assay drift and ensure long-term reproducibility
Q29. Which matrix factor can cause suppression or enhancement in an oxytocin bioassay if samples are not adequately processed?
- Presence of salts, proteins, or excipients from formulation
- Air bubbles only
- Color of the vial cap
- Font used on label
Correct Answer: Presence of salts, proteins, or excipients from formulation
Q30. During method validation of an oxytocin bioassay, which attribute confirms the assay specifically measures oxytocin biological activity rather than unrelated responses?
- Linearity only
- Specificity/selectivity demonstrated by lack of response to unrelated peptides and known cross‑reactants
- Only high throughput capability
- Colorimetric endpoint presence
Correct Answer: Specificity/selectivity demonstrated by lack of response to unrelated peptides and known cross‑reactants
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.
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