Nephrogenic syndrome of inappropriate antidiuresis

Increased renal responsiveness to vasopressin and enhanced V2 receptor signaling in RGS2-/- mice

The antidiuretic effect of vasopressin is mediated by V2 receptors (V2R) that are located in kidney connecting tubules and collecting ducts. This study provides evidence that V2R signaling is negatively regulated by regulator of G protein signaling 2 (RGS2), a member of the family of RGS proteins. This study demonstrates that (1) RGS2 expression in the kidney is restricted to the vasopressin-sensitive part of the nephron (thick ascending limb, connecting tubule, and collecting duct); (2) expression of RGS2 is rapidly upregulated by vasopressin; (3) the vasopressin-dependent accumulation of cAMP, the principal messenger of V2R signaling, is significantly higher in collecting ducts that are microdissected from the RGS2(-/-) mice compared with their wild-type littermates; and (4) analysis of urine output of mice that were exposed to water restriction followed by acute water loading revealed that RGS2(-/-) mice exhibit an increased renal responsiveness to vasopressin. It is proposed that RGS2 is involved in negative feedback regulation of V2R signaling.

Syndrome of inappropriate antidiuresis

The syndrome of inappropriate antidiuresis is the most common cause of euvolemic hyponatremia and complicates a wide spectrum of diseases and neurosurgical conditions. The syndrome is characterized by clinical euvolemia, dilute plasma osmolality and inappropriately concentrated urine, with normal renal, adrenal and thyroid function. Hyponatremia in syndrome of inappropriate antidiuresis represents an excess of plasma water, rather than sodium deficiency. The severity of hyponatremia is limited by renal escape from antidiuresis. Treatment varies according to symptoms, severity and speed of onset of hyponatremia. Acute, severe, symptomatic hyponatremia may require rapid treatment with hypertonic saline, with care to avoid central pontine myelinosis. Chronic hyponatremia is managed with fluid restriction and demeclocycline for unresponsive cases. Vasopressin antagonists represent a new option for chronic hyponatremia of syndrome of inappropriate antidiuresis.