Which agent is a relatively selective vasopressin V2 receptor agonist used in pituitary diabetes insipidus and pediatric primary nocturnal enuresis?

• A. Tolvaptan
• B. Vasopressin
• C. Conivaptan
• D. Desmopressin

Answer: (D)

Desmopressin is a synthetic analogue of vasopressin that preferentially activates the kidney’s V2 receptors. When V2 receptors on the collecting ducts are stimulated, aquaporin-2 channels insert into the lining, increasing water reabsorption and producing more concentrated urine. This makes it an effective treatment for central (pituitary) diabetes insipidus, where there is a deficiency of endogenous ADH, and for pediatric primary nocturnal enuresis by reducing nighttime urine production. Its relative selectivity for V2 receptors means fewer vasoconstrictive (V1) effects, making it safer for routine antidiuretic use. In contrast, options like vasopressin act on both V1 and V2 with added vasoconstriction, while tolvaptan and conivaptan are antagonists of vasopressin receptors and used for hyponatremia, not as antidiuretic therapy.