Evidence in hyponatremia related to inappropriate secretion of ADH that V1 receptor stimulation contributes to the increase in renal uric acid clearance.

In hyponatremia related to syndrome of inappropriate antidiuretic hormone (SIADH), hypouricemia is explained primarily by the high uric acid clearance rate that results from the decrease in tubular uric acid reabsorption. This modification of tubular handling of uric acid is considered to be induced by the increase in the "effective vascular volume". This study was designed to determine if V1-receptor stimulation participates in the development of a high uric acid clearance rate as in SIADH, in which the antidiuretic hormone acts on V1 and V2 receptors. Therefore, the urate clearance rate was measured in seven volunteers with 1-desamino-8-D-arginine vasopressin (dDAVP)-induced hyponatremia, with dDVAP stimulating exclusively the V2 receptors (Group I), and in six patients with SIADH (Group II) during both normo- and hyponatremia. As expected, in both groups, the serum uric acid concentration decreased during hyponatremia, but did so to a larger extent in the patients with SIADH (-53% versus -29%, P < 0.02). Despite similar levels of hyponatremia (126 +/- 5 mmol/L and 125 +/- 5.5 mmol/L), of hypoproteinemia (64 +/- 5 g/L and 63 +/- 5 g/L) and of salt excretion (FENa, 0.66 +/- 0.28% and 0.73 +/- 0.25%), the urate clearance (8.3 +/- 3.3 mL/min) and the fractional excretion of filtered uric acid (5.7 +/- 2%) in Group I were not significantly different during hyponatremia than during normonatremia (6.4 +/- 1.5 mL/min and 5.4 +/- 0.9%). On the other hand, in Group II, both parameters were increased (17.8 +/- 2.9 mL/min and 19.6 +/- 5.3%; P < 0.001) and both values were higher than in the dDAVP-induced hyponatremia (P < 0.01). Additionally, the administration of a potent V1-receptor agonist (triglycyl-lysine-vasopressin) in a patient with central diabetes insipidus with preexisting dDAVP-induced hyponatremia produced a rapid increase of urate clearance. Because dDAVP acts only on the V2 receptors, these data suggest that the higher urate clearance observed during hyponatremia related to SIADH is not only the consequence of an increased "effective vascular volume," but that V1-receptor stimulation also contributes to it, by a mechanism that remains to be determined.