A 29-year-old patient presents to her primary care physician with persistent amenorrhea and inability to breastfeed over the last 5 months. She says that she has also been very tired since her baby was born and this fatigue was accompanied by an inability to deal with cold weather despite having no problem with cold prior to becoming pregnant. She has gained an additional 5 pounds since delivery. Review of her hospital records reveals that she had a vaginal delivery that was complicated by severe hemorrhage and episodes of hypotension. Which of the following hormone levels is most likely to be normal in this patient?

Follicle-stimulating hormone (FSH)

A 42-year-old woman comes to the physician because of urinary leakage over the last year. She reports involuntarily losing small amounts of urine after experiencing a sudden need to void. She has difficulty making it to the bathroom in time, and only feels comfortable going out into public if she has documented the location of all nearby restrooms. She also has begun to wake up at night to urinate. These symptoms have persisted despite 6 months of bladder training and weight loss and reducing soda and coffee intake. Physical examination shows no abnormalities. The most appropriate pharmacotherapy for this patient is a drug that has which of the following mechanisms of action?

Antagonism of muscarinic M3 receptors

Agonism of muscarinic M2 receptors

Antagonism of beta-3 adrenergic receptors

Antagonism of alpha-1 adrenergic receptors

Agonism of beta-2 adrenergic receptors

A 65-year-old woman is brought to the emergency department by her husband who found her lying unconscious at home. He says that the patient has been complaining of progressively worsening weakness and confusion for the past week. Her past medical history is significant for hypertension, systemic lupus erythematosus, and trigeminal neuralgia. Her medications include metoprolol, valsartan, prednisone, and carbamazepine. On admission, blood pressure is 130/70 mm Hg, pulse rate is 100 /min, respiratory rate is 17/min, and temperature is 36.5°C (97.7ºF). She regained consciousness while on the way to the hospital but is still drowsy and disoriented. Physical examination is normal. Finger-stick glucose level is 110 mg/dl. Other laboratory studies show: Na+ 120 mEq/L (136—145 mEq/L) K+ 3.5 mEq/L (3.5—5.0 mEq/L) CI- 107 mEq/L (95—105 mEq/L) Creatinine 0.8 mg/dL (0.6—1.2 mg/dL) Serum osmolality 250 mOsm/kg (275—295 mOsm/kg) Urine Na+ 70 mEq/L Urine osmolality 350 mOsm/kg She is admitted to the hospital for further management. Which of the following is the next best step in the management of this patient's condition?

Rapid resuscitation with hypertonic saline

A 42-year-old man who is employed as a construction worker presents to his primary care physician with complaints of moderate headaches and profuse sweating. He reports the need to carry up to 3 additional shirt changes to work because they drench quickly even with tasks of low physical exertion. His coworkers have commented about his changing glove and boot sizes, which have increased at least 4 times since he joined the company 10 years ago. Physical examination is unremarkable except for blood pressure of 160/95 mm Hg, hyperhidrosis, noticeably large pores, hypertrichosis, widely spaced teeth, and prognathism. Which of the following best explains the patient’s clinical manifestations?

Increased serum insulin-like growth factor 1 (IGF-1)

Increased thyroid-stimulating hormone

Posterior pituitary hormones for USMLE Step 2 CK: High-Yield Pharmacology Lessons

Posterior Pituitary: Oxytocin - The Love & Labor Hormone

Hypothalamus-Pituitary Axis and Hormone Target Organs

Source: Synthesized in the paraventricular nuclei of the hypothalamus; stored and released from the posterior pituitary.
Physiologic Functions:
- Stimulates uterine smooth muscle contraction during labor.
- Triggers myoepithelial cell contraction in the breast for milk letdown (ejection).
- Associated with social bonding and maternal behaviors.
Clinical Use (as Pitocin):
- Induction and augmentation of labor.
- Control of postpartum hemorrhage by contracting the uterus.
Adverse Effects:
- Uterine hyperstimulation, potentially causing fetal distress.
- Hypotension and reflex tachycardia.

⭐ High-Yield: At high doses, oxytocin has an antidiuretic effect due to its structural similarity to ADH. This can lead to water retention, hyponatremia, and seizures.

Posterior Pituitary: ADH Agonists - The Water & Pressure Pressers

Mechanism: Synthetic analogs of ADH that act on vasopressin (V) receptors. V1 receptors mediate vasoconstriction; V2 receptors mediate antidiuresis via aquaporin-2 insertion in renal collecting ducts.

Drug	Mechanism	Primary Uses	Key Side Effects
Desmopressin	Selective V2 agonist	Central Diabetes Insipidus (DI), nocturnal enuresis, von Willebrand disease, Hemophilia A	Hyponatremia, headache, flushing
Vasopressin	Non-selective V1 & V2 agonist	Septic shock (vasopressor), esophageal variceal hemorrhage	Ischemia (coronary, mesenteric), hyponatremia, hypertension

-   **Conivaptan** (IV): V1a/V2 antagonist
-   **Tolvaptan** (oral): Selective V2 antagonist

⭐ High-Yield: Desmopressin-induced hyponatremia can cause seizures. Monitor sodium levels closely, especially in children (enuresis) and the elderly. Fluid restriction is often necessary.

📌 Mnemonic: "Vaps" & "tans" are for Vasopressin. Conivaptan/Tolvaptan block ADH, while Vasopressin/Desmopressin mimic it.

Posterior Pituitary: ADH Antagonists - The Vaptan Clan

Mechanism: Block ADH (vasopressin) action at the V2 receptor in the collecting duct, promoting free water excretion (aquaresis) without affecting sodium excretion.
Indications: Euvolemic and hypervolemic hyponatremia (e.g., SIADH, heart failure, cirrhosis).

Drug	Route	Receptor	Clinical Pearl
Conivaptan	IV	V1a/V2	For inpatient/emergent use.
Tolvaptan	Oral	V2 selective	For outpatient use; limited to <30 days due to hepatotoxicity.

-   Hypernatremia, dehydration
-   Central Pontine Myelinolysis (CPM) if hyponatremia is corrected too rapidly.
-   Tolvaptan: Hepatotoxicity (Black Box Warning).

⭐ High-Yield: Avoid rapid correction of hyponatremia. The goal is a slow increase in serum sodium, typically <8-10 mEq/L in the first 24 hours to prevent osmotic demyelination syndrome.

High‑Yield Points - ⚡ Biggest Takeaways

Oxytocin is crucial for inducing labor and controlling postpartum hemorrhage.

ADH (vasopressin) acts on V2 receptors in collecting ducts, promoting water reabsorption to regulate plasma osmolality.

Desmopressin (DDAVP) is the primary treatment for central diabetes insipidus and von Willebrand disease.

ADH antagonists (e.g., tolvaptan) are key for treating SIADH by blocking ADH effects.

Central DI is an insufficient ADH problem, whereas nephrogenic DI is an ADH receptor problem.

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