Antidiuretic Response of Kidneys to Different Modes of Vasopressin Administration

The effect of vasopressin given simultaneously with a water load was studied in healthy human volunteers. During maximal water diuresis induced by oral water load of 20 ml water per kilogram body weight, the excreted water fraction was 12.4%, whereas the excretion of osmotically free water was 10.0 ± 1.8 ml/min per 1.73 m² of body surface area. These data suggest that the secretion of arginine vasopressin by the neurohypophysis was almost completely blocked. A water load simultaneously with 8 g sublingual or 0.2 mg oral desmopressin caused a strong and long-lasting antidiuretic response accompanied by a drastic increase in the reabsorption of osmotically free water in the kidneys. It was shown that the magnitude and the time course of the antidiuretic response to therapeutic doses of desmopressin depended on the mode of its administration.