V2 Receptor Effects on Fluid Regulation and Performance
Condition: Electrolyte Imbalance; Hyponatremia; Hypernatremia
MeSH terms: Hyponatremia; Hypernatremia
Study type: Interventional

Summary: 
      This primary aim of this study was to critically assess whether or not sweat water content
      and sodium concentration were acutely regulated by dynamic changes in antidiuretic hormone
      (arginine vasopressin or AVP) acting on the Vasopressin 2 receptor (V2R) during exercise.
      Secondary aims were to evaluate running performance and core temperature to further
      characterize the role of AVP in the coordinated balance of fluid and temperature homeostasis
      during exercise. The primary hypothesis was that activation of the V2R in sweat glands would
      result in water reabsorption and fluid conservation during endurance exercise.
    

Detailed description: 
      Ten healthy habitual runners (> 50km running per week) between 18-60 years of age
      participated in this double blind randomized control trial. Each subject presented to the
      exercise lab on four separate occasions. Trial 1 was a familiarization trial to determine
      each subject's maximal aerobic capacity and peak treadmill running speak (VO2 Peak test).
      Trials 2, 3 and 4 utilized the same exact protocol, differing only in pharmacological
      intervention. In a randomized, double-blind order (both participant and investigator blinded
      to the intervention), either a placebo pill, the V2 receptor antagonist tolvaptan (Samsca™,
      30mg tablet), or the V2 receptor agonist desmopressin (DDAVP™, 0.2mg tablet) was ingested
      along with the CorTemp™ Core Temperature Sensor two hours before commencement of the Exercise
      Trial with 240mL of bottled water. The exercise protocol consisted of 60 minutes of treadmill
      running at 60% of peak speed (steady-state) followed by a performance test (the VO2 Peak
      test). Blood, saliva and urine, were collected before the exercise trial (baseline) and again
      after both the steady-state run and performance runs. Sweat was obtained from sweat patches
      after both the steady-state and performance runs. Core temperature, fluid intake, performance
      time, body weight, thirst and sodium palatability ratings were also assessed. Free access to
      water was allowed during the trial and all urine produced during the trial was measured and
      collected. The main outcome measure was sweat sodium concentration.
    

Intervention name(s): V2R (Vasopressin 2 receptor)
Intervention type(s): Drug
Intervention description(s): All ten subjects were used as their own controls in this double-blind, randomized controlled trial assessing the effect of the V2R on sweat sodium concentration via use of a V2R blocker (antagonist), stimulator (agonist), against a placebo (drug naive state).
Other intervention name(s): V2R antagonist: tolvaptan (30mg tablet); V2R agonist: desmopressin (0.2mg tablet)
Intervention MeSH terms: Vasopressins; Arginine Vasopressin; Tolvaptan
Allocation: Randomized
Intervention model: Crossover Assignment
Masking: Double (Participant, Investigator)
Keywords: arginine vasopressin; sweat sodium; V2 antagonist; running