LAUSR

OBJECTIVE Primary polydipsia is characterized by excessive fluid intake which may suppress vasopressin levels. It is speculated that suppressed vasopressin levels lead to a dysregulated hypothalamic-pituitary-adrenal (HPA) axis as vasopressin co-modulates the HPA axis. However, data is contradictory. The aim of this study was to investigate markers of the HPA axis in patients with primary polydipsia compared to healthy controls. DESIGN Exploratory analysis combining data from two different prospective observational studies. PATIENTS We included 34 patients with primary polydipsia (68% females, median aged 29.5 years (IQR 26.0, 38.8)) and 20 healthy volunteers (55% females, median age 24.0 years (IQR 22.0, 27.2)). MEASUREMENTS The main outcome was difference in HPA axis activity assessed using circadian serum and salivary cortisol, 24-hour urinary free cortisol, and cortisol levels before and after adrenocorticotropic hormone (ACTH) stimulation between patients with primary polydipsia and healthy volunteers using Wilcoxon Rank Sum Test. RESULTS No difference was seen in circadian serum cortisol levels (p=0.9), urinary free cortisol levels (p=0.17), and serum cortisol in response to ACTH stimulation (p=0.77) between patients with primary polydipsia and healthy volunteers. Circadian salivary cortisol levels were significantly lower in patients with primary polydipsia compared to healthy volunteers with an estimated difference of -3.7 nmol/l (95%-CI -5.5, -1.8 nmol/l, p<0.001). CONCLUSION Our results suggest no difference in HPA axis activity between patients with primary polydipsia and healthy volunteers. The observed difference in salivary cortisol levels may be linked to a dilution effect in saliva rather than an altered stress axis considering the other findings. This article is protected by copyright. All rights reserved.