Altered Osmotic Threshold for Vasopressin Release and Impaired Thirst Sensation: Additional Abnormalities in Kallmann's Syndrome*

Seven subjects with Kallmann's syndrome were studied to determine whether they had disturbances of fluid homeostasis. Simultaneous measurements of urine and plasma osmolality (Uosm and Posm, respectively) were made during free access to fluids. The Uosm-Posm relationship was abnormal in five patients on at least one occasion. Patient 2 was frequently overhydrated (Posm ≤ 280 mosmol⁄kg) and patient 5 excreted a dilute urine when his Posm was 290 mosmol⁄kg. The three subjects (1, 5, and 7) tending to have an increased Posm (≥300 mosmol⁄kg) were able to concentrate their urine (Uosm < 800 mosmol⁄kg) and denied polyuria and polydipsia. Their elevated Posms could be explained by impairment of thirst, rather than increased excretion of water, because the patients concentrated their urines at normal Posms during fluid deprivation. The osmotic threshold for vasopressin release was decreased (Posm = 270.6 mosmol⁄kg) in one patient and increased (Posm 3s 294 mosmol⁄kg) in two others of the seven patients. The eleva...