Increased Renal Sensitivity to Vasopressin in Two Patients with Essential Hypernatremia*

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Abstract
Patients with essential hypernatremia maintain urinary concentrating ability despite plasma hyperosmolality and low plasma vasopressin concentrations. We investigated renal sensitivity to ultralow dose vasopressin infusions in two patients with a syndrome of hypodipsia, hypernatremia with selective osmoreceptor dysfunction, early puberty, and aggressive behavior. The patients were water loaded until a hypotonic diuresis was established. Vasopressin was infused in stepwise increments from 0.4–12 fmol/kg·min. Both patients had increased renal sensitivity to vasopressin, achieving negative free water clearance at infusion rates of 0.4 and 4 fmol/kg·min (normal ≥6). Treatment for 3 months with l-desamino-8-D-arginine vasopressin (DDAVP) led to an improvement in behavior and the reporting, for the first time, of a sensation of thirst. After DDAVP therapy both patients had a reduction of their renal sensitivity to infused vasopressin. We conclude that untreated patients with essential hypernatremia have increased renal sensitivity to vasopressin which is reduced by DDAVP administration.