A 28-year-old woman is brought to the emergency department by her roommate due to severe confusion, profound weakness, and passing exceptionally large volumes of dilute urine for the past 48 hours. Her medical history is significant for a psychiatric condition managed with a medication that requires regular serum monitoring. She recently recovered from a mild diarrheal illness. Temperature is 37.1°C (98.8°F), blood pressure is 92/56 mm Hg, and pulse is 118/min. Mucous membranes are dry, and skin turgor is noticeably diminished. Laboratory results show:
| Laboratory Parameter | Result |
|---|---|
| Serum sodium | 156 mEq/L |
| Serum potassium | 4.1 mEq/L |
| Serum calcium | 9.2 mEq/L |
| Blood urea nitrogen | 32 mg/dL |
| Serum creatinine | 1.4 mg/dL |
| Serum osmolality | 332 mOsm/kg |
| Urine osmolality | 125 mOsm/kg |
Administration of 2 mcg of intravenous desmopressin (dDAVP) is performed. Two hours later, a repeat urine osmolality is 130 mOsm/kg. Which of the following best describes the fundamental cellular mechanism causing this patient's current laboratory abnormalities?
- AImpaired cleavage and axonal transport of preprovasopressin from the hypothalamus
- BPathological activation of the calcium-sensing receptor on the basolateral membrane of the thick ascending limb
- CSelective autoimmune destruction of the vasopressin V2 receptor
- Inhibition of adenylyl cyclase activity preventing apical translocation of aquaporin-2 channelsAnswer
- EAntagonism of the mineralocorticoid receptor leading to a diminished medullary osmotic gradient