A patient with central diabetes insipidus receives intranasal desmopressin and promptly develops concentrated urine. At the cellular level, the antidiuretic effect results from which event?
- A Insertion of aquaporin-2 channels into the apical membrane of collecting duct principal cells ✓
- B V1 receptor activation causing contraction of mesangial cells
- C Opening of urea transporters in the descending thin limb of Henle
- D Increased activity of the Na-K-2Cl cotransporter in the thick ascending limb
Correct answer: A. Insertion of aquaporin-2 channels into the apical membrane of collecting duct principal cells
Explanation
Desmopressin acts on V2 receptors on the basolateral membrane of collecting duct principal cells. Via Gs, adenylyl cyclase and PKA, preformed aquaporin-2 vesicles fuse with the apical membrane, allowing water reabsorption down the medullary gradient. V1 receptor activation mediates vascular smooth muscle constriction, not antidiuresis, and the thick ascending limb cotransporter is unaffected by vasopressin.
Reference: Ganong Review of Medical Physiology, 26th ed.
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