title: Changes in plasma arginine vasopressin concentrations in cyclists participating in a 109-km cycle race.
abstract: OBJECTIVE
  To evaluate the osmotic and non-osmotic regulation of arginine vasopressin (AVP) during endurance cycling.
  
  
  METHODS
  Observational study. Setting 109 km cycle race.
  
  
  METHODS
  33 Cyclists.
  
  
  METHODS
  None.
  
  
  METHODS
  Plasma sodium concentration ([Na(+)]), plasma volume (PV) and plasma arginine vasopressin (AVP) concentration ([AVP](p)).
  
  
  RESULTS
  A fourfold increase in [AVP](p) occurred despite a 2-mmol l(-1) decrease in plasma [Na(+)] combined with only modest (5%) PV contraction. A significant inverse correlation was noted between [AVP](p) Delta and urine osmolality Delta (r = -0.41, p<0.05), whereas non-significant inverse correlations were noted between [AVP](p) and both plasma [Na(+)] Delta and % PV Delta. Four cyclists finished the race with asymptomatic hyponatraemia. The only significant difference between the entire cohort with this subset of athletes was postrace plasma [Na(+)] (137.7 vs 133.5 mmol l(-1), p<0.001) and plasma [Na(+)] Delta (-1.9 vs -5.1 mmol l(-1), p<0.05). The mean prerace [AVP](p) of these four cyclists was just below the minimum detectable limit (0.3 pg ml(-1)) and increased marginally (0.4 pg ml(-1)) despite the decline in plasma [Na(+)].
  
  
  CONCLUSIONS
  The osmotic regulation of [AVP](p) during competitive cycling was overshadowed by non-osmotic AVP secretion. The modest decrease in PV was not the primary non-osmotic stimulus to AVP. Partial suppression of AVP occurred in four (12%) cyclists who developed hyponatraemia during 5 h of riding. Therefore, these results confirm that non-osmotic AVP secretion and exercise-associated hyponatraemia does, in fact, occur in cyclists participating in a 109 km cycle race. However, the stimuli to AVP is likely different between cycling and running.
authors.affiliation: University of Cape Town, Cape Town, South Africa. tamara.hew@overhydration.org
authors.forename: T
authors.initials: T
authors.lastname: Hew-Butler
authors.forename: J P
authors.initials: JP
authors.lastname: Dugas
authors.forename: T D
authors.initials: TD
authors.lastname: Noakes
authors.forename: J G
authors.initials: JG
authors.lastname: Verbalis
mesh_terms: D000328:Adult; D001127:Arginine Vasopressin / Q000097:blood*; D001642:Bicycling / Q000502:physiology*; D015444:Exercise / Q000502:physiology*; D005260:Female; D006801:Humans; D007010:Hyponatremia / Q000209:etiology; D008297:Male; D009994:Osmolar Concentration
chemical_list: D001127:Arginine Vasopressin