Plasma arginine vasopressin and motor activity in major depression

Background: Previously, we found that mean plasma concentrations of arginine vasopressin (AVP), but not of oxytocin (OT), were higher in depressed patients than in healthy controls. Plasma AVP concentrations were positively correlated to clinically rated psychomotor retardation. To further explore this previously reported relation we studied psychomotor retardation by means of an activity monitor, which is a more fine-focused and more objective instrument to analyze motor retardation than a clinical rating scale. Methods: Plasma AVP and OT concentrations, and day-and nighttime wrist activity were measured in 48 in- and outpatients with major depression and 30 healthy controls during a period of 5 consecutive days and nights. Results: Principal components analysis revealed three components of motor activity: motor activity during wakefulness, motor activity during sleep, and the awake/sleep time ratio. In patients and controls an inverse relationship between plasma AVP concentrations and motor activity during wakefulness was found. Patients with elevated AVP plasma levels showed increased motor activity during sleep. Conclusions: These results suggest that high plasma AVP levels are related to the clinical picture of daytime psychomotor retardation and nighttime motor activity in major depression. Mean plasma OT concentrations were not related to measures of motor activity.