The role of vasopressin in the impaired water excretion of myxedema.

The plasma vasopressin response to acute water ingestion was evaluated in 20 patients with myxedema prior to definitive treatment and in eight of these same patients following therapy of their hypothyroidism. Vasopressin levels were elevated and failed to completely suppress following water ingestion in 15 subjects (75 per cent). Two hypothyroid patients with elevated plasma vasopressin levels (10 per cent) had a normal renal response to the water challenge suggesting partial end organ hormonal unresponsiveness. In three (15 per cent) of the five patients with suppressible vasopressin, water excretion was impaired indicating a nonvasopressin-mediated renal defect. In eight patients restudied after achievement of a euthyroid state, vasopressin inhibition and urinary excretion were normal following the oral water load. Although intrinsic renal changes in the hypothyroid state may contribute to the observed defect in water diuresis, the present study suggests a role of endogenous vasopressin in this disorder.