Chapter 21 Quiz — Oxytocin and Vasopressin

22 items. Multiple choice, true/false, and short answer. The answer key is collapsed at the bottom; work through the whole set before opening it. Several items are designed so that the tempting answer is the popular one.

1. Oxytocin and vasopressin are each how many amino acids long?

A. 7 B. 9 C. 15 D. 30

2. At how many positions do oxytocin and vasopressin differ?

A. 1 B. 2 C. 4 D. 6

3. Which substitution introduces a full positive charge and is the more consequential of the two differences?

A. Position 3, isoleucine → phenylalanine B. Position 8, leucine → arginine C. Position 1, cysteine → serine D. Position 9, glycine → alanine

4. Vincent du Vigneaud received the Nobel Prize in Chemistry in 1955 for work including:

A. The discovery of the oxytocin receptor B. Determining oxytocin's structure and synthesizing it — the first synthesis of a peptide hormone C. The first recombinant production of a peptide hormone D. Establishing the pulsatile nature of posterior pituitary secretion

5. True or false. Because oxytocin and vasopressin have different receptors, oxytocin cannot produce vasopressin-like effects at any concentration.

6. High-concentration oxytocin infusion during labor can produce water retention. This occurs because:

A. Oxytocin is metabolized into vasopressin B. Oxytocin binds vasopressin V2 receptors at high concentration C. The infusion fluid itself causes retention D. Uterine contraction reduces renal blood flow

7. Oxytocin's role in lactation is to cause:

A. Milk production in the alveolar cells B. Milk ejection by contracting myoepithelial cells C. Both production and ejection D. Neither — that is prolactin's exclusive domain

8. Which of these is not an approved or established clinical use of oxytocin?

A. Labor induction B. Labor augmentation C. Treatment of postpartum hemorrhage D. Enhancement of social bonding in adults

9. Atosiban is:

A. A longer-acting oxytocin analog B. An oxytocin receptor antagonist used to suppress preterm labor C. A vasopressin V2 agonist D. A vasopressin V1a antagonist

10. The key neuroanatomical difference between socially monogamous prairie voles and their non-monogamous relatives is best described as a difference in:

A. The sequence of oxytocin and vasopressin B. The total amount of oxytocin produced C. The distribution and density of oxytocin and vasopressin receptors in the brain D. The number of hypothalamic neurons

11. Short answer. State in one sentence the general principle the prairie vole work established about how a conserved signaling molecule can produce species-specific behavior.

12. Applying rating rule 3, the vole literature can:

A. Upgrade a human affiliation claim from ❌ to ⚠️ B. Upgrade a human affiliation claim from ⚠️ to ✅ C. Establish that a mechanism can work, without moving any human claim D. Substitute for a human trial where trials are impractical

13. True or false. The failure of the human trust-game literature to replicate is best explained by researcher fraud.

14. The "winner's curse" in this context refers to:

A. Journals preferring surprising results B. Published effect sizes from small studies being systematically inflated because noise was required to clear significance C. The first lab to publish receiving disproportionate credit D. Replication attempts being harder to publish than original findings

15. Short answer. Name three moderating variables the literature has reported for oxytocin's social effects — variables that can change the direction, not merely the size, of the effect.

16. The social salience hypothesis holds that oxytocin:

A. Reliably increases affiliation across contexts B. Reliably increases aggression across contexts C. Amplifies the salience of social cues, so the situation determines the direction of the effect D. Has no measurable central effect at all

17. Which statement best characterizes the intranasal delivery question as of this writing?

A. It has been definitively shown that intranasal oxytocin does not reach the brain B. It has been definitively shown that it does C. It is a live methodological controversy that a large behavioral literature has not resolved D. It is irrelevant, because effects can be produced peripherally

18. Which of the following is a genuine complication for interpreting intranasal oxytocin studies?

A. Plasma oxytocin measurably rises after dosing, so peripheral mechanisms are not excluded B. Cerebrospinal fluid findings after intranasal dosing have been mixed C. Plasma oxytocin assays with and without an extraction step give values differing by more than an order of magnitude D. All of the above

19. A large multisite randomized trial of intranasal oxytocin in children and adolescents with autism, published in 2021:

A. Demonstrated benefit on its primary outcome B. Did not demonstrate benefit on its primary outcome C. Was terminated for safety reasons D. Has not yet reported

20. Short answer. The chapter says the ❌ for intranasal oxytocin in autism is a different kind of ❌ from most in the book. Explain the difference in two sentences, and state why it is a stronger scientific position and a weaker commercial one.

21. Desmopressin is approved for all of the following except:

A. Central diabetes insipidus (arginine vasopressin deficiency) B. Nocturnal enuresis C. Certain bleeding disorders D. Vasodilatory shock in critical care

22. Short answer. Oxytocin holds a ✅ rating and three ❌ ratings in this chapter. Explain to a skeptical reader in three sentences why this is not a contradiction, naming the rating rule involved.

Answer key **1. B — 9.** Both are nonapeptides, roughly 1,000 Da, at the small end of the peptide range. **2. B — 2.** Positions 3 and 8. **3. B — Position 8, leucine → arginine.** Leucine is nonpolar; arginine carries a positive charge at body pH. Position 3 (isoleucine → phenylalanine) swaps one nonpolar residue for another of different bulk — real, but less dramatic than introducing a charge onto a residue doing receptor-contact work. **4. B.** Structure determination plus synthesis, the first chemical synthesis of a peptide hormone. The significance beyond the molecules: it established that a hormone is a molecule and nothing more, and it is the direct ancestor of modern peptide synthesis chemistry. **5. False.** Selectivity is concentration-dependent (§21.1, Ch 2 §2.2). At high concentrations oxytocin binds vasopressin receptors and vice versa. Two substitutions establish a preference, not a wall. **6. B — oxytocin binds vasopressin V2 receptors at high concentration.** This is why hyponatremia is a recognized complication of high-dose oxytocin infusion, particularly when combined with large fluid volumes. It follows directly from chemistry, not from an impurity or an allergy. **7. B — milk ejection.** Production is prolactin's role. Oxytocin moves milk that already exists, by contracting the myoepithelial cells wrapped around the alveoli. This confusion is extremely common. **8. D.** A, B, and C are established, approved obstetric uses; oxytocin appears on the WHO Model List of Essential Medicines. D is the ❌ claim of §21.4 and §21.5. **9. B — an oxytocin receptor antagonist used as a tocolytic in some countries.** Note the shared "-tocin" stem: a stem identifies the family, not the direction of action. Compare "-relin" versus "-relix" in Chapter 1 §1.8. **10. C — receptor distribution and density.** The peptides themselves are essentially the same across these species. What differs is where the receptors sit — notably in reward-related regions such as the nucleus accumbens and ventral pallidum. **11.** Acceptable answers convey: *a conserved signaling molecule can produce species-specific behavior through species-specific receptor placement — the peptide alone is not the instruction; the peptide plus the map of where its receptors sit is.* **12. C.** Rating rule 3: never upgrade with mechanism. Animal work establishes that a mechanism can operate. It does not move a human claim by one tier, and it never substitutes for a human trial (Ch 5 §5.3). **13. False.** The pattern is fully explained by small samples, noisy behavioral measures, flexible analysis, and publication incentives that reward positive results. No dishonesty is required. Treating it as a fraud story is its own error. **14. B.** With a small true effect and a small study, the study is mostly measuring noise; the runs that clear significance are the ones where noise happened to help, so the published magnitude is the true effect plus the noise it took to get published. **15.** Any three of: in-group versus out-group framing of the social target; individual attachment style (for example, attachment anxiety); personality profile or clinical features (for example, borderline personality features); competitive versus cooperative task structure. **16. C.** The molecule supplies the gain; the situation supplies the sign. Note the chapter's two cautions: this is a hypothesis with live competitors, and much of its supporting work used the same contested administration route. **17. C.** Not debunked, not established. The honest statement is that central penetration at behaviorally meaningful concentrations has not been established, and a large literature assumes it. **18. D — all of the above.** Each is a distinct interpretive problem, and they compound. **19. B — did not demonstrate benefit on its primary outcome.** This is the trajectory of Chapter 5: encouraging small trials, then a large well-conducted one, then a much quieter field. **20.** Acceptable answers convey: most ❌ ratings in this book mean *evidence is absent* — no completed human trials to evaluate. This one means *evidence is present and negative* — the experiment was run and the answer was no. That is stronger scientifically because we actually know something, and weaker commercially because a compound that has failed a trial is harder to sell than one that has never entered one. Credit for also noting that the unresolved delivery question makes the null ambiguous between "does not work" and "did not arrive." **21. D.** Vasopressin itself is used as a vasopressor in vasodilatory shock; desmopressin is V2-selective precisely so that it produces water retention *without* much vasoconstriction, which makes it the wrong tool for that job. Chapter 29 covers desmopressin fully. **22.** Acceptable answers invoke **rating rule 6: one molecule, many ratings** — and rule 1, that a rating attaches to a claim with a population and an endpoint, never to a molecule. Intravenous oxytocin for postpartum hemorrhage in an obstetric setting and intranasal oxytocin for social functioning in healthy adults are different interventions, different populations, and different endpoints. A source that gives one overall verdict on "oxytocin" has thrown away the information the reader needs.