Osmoregulation in Alzheimer's Disease

Abstract

In order to investigate the integrity of osmoregulatory systems in dementia of the Alzheimer type (DAT), we studied DAT and healthy control subjects during a 16-hour overnight fast which was followed by a 4-hour rehydration period. Both DAT patients and controls demonstrated increases in urine osmolality and plasma vasopressin over the course of the fast. However, plasma vasopressin levels peaked earlier in the controls than in the DAT patients. Serum electrolytes and osmolality were not significantly changed from baseline in either group. The DAT patients drank less fluid than the controls during the rehydration period (p < 0.05), despite encouragement to drink. This study suggests that the hypothalamic vasopressin system may be less rapidly responsive in DAT patients than in healthy controls and that the perception and awareness of thirst may be diminished in DAT, beyond that observed with normal aging.