Objective: Cardiovascular autonomic dysfunction is a common non-motor phenotype of Parkinson's disease (PD), that frequently presents as the coexistence of orthostatic hypotension (OH) and supine hypertension (SH). The regulation of blood pressure (BP) and water balance in this context is complex and not fully understood. In recent years, the apelin/Elabela system has emerged as a key modulator of fluid homeostasis, interacting closely with antidiuretic hormone (ADH) signalling. Objective: To study the interplay between apelin, Elabela and ADH with respect to BP profiles in a cohort of patients with PD and cardiovascular autonomic dysfunction. Design and method: Seventeen PD patients were enrolled and stratified into two groups according to 24-hour ABPM: patients experiencing OH (n=6) and patients with combined OH and SH (SHOH, n=11). The control group consisted of 22 healthy, age-matched subjects. All participants underwent 24-hour urine collection and a morning blood test. Plasma concentrations of copeptin (a marker of ADH secretion), apelin, and Elabela were measured using ELISA. Results: As expected, SH-OH patients had higher night-time BP levels than the OH and control groups. Conversely, daytime BP was significantly higher in controls than in PD patients, reflecting the presence of diurnal episodes of hypotension. Similar results were found when analysing 24-hour diuresis profiles. Interestingly, PD patients had reduced apelin and Elabela levels, as well as increased copeptin, compared to controls. Additionally, apelin showed a significant positive correlation with daytime systolic BP and daytime diuresis, and a negative correlation with nigh-time values, while copeptin exhibited the opposite trend. No significant difference was found with regard to natriuresis. Conclusions: According to our results, albeit from a very limited sample, water homeostasis appears to be more closely related to BP variability characteristic of PD patients than sodium balance. Reduced apelin and increased copeptin levels were specifically associated with a reversal of the diuresis pattern and the loss of the physiological dipping profile in PD patients, proposing the apelin system as a key regulator of water balance and a novel potential therapeutic target for managing blood pressure and fluid imbalance.
Bongrani et al. (Fri,) studied this question.