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Changes in plasma arginine vasopressin concentrations in cyclists participating in a 109-km cycle race
  1. T Hew-Butler1,
  2. J P Dugas1,2,
  3. T D Noakes1,
  4. J G Verbalis3
  1. 1University of Cape Town, Cape Town, South Africa
  2. 2University of Illinois, Chicago, Illinois, USA
  3. 3Georgetown University Medical Center, Washington, DC, USA
  1. Correspondence to Dr Tamara Hew-Butler, Arizona State University, PEBE Rm 110, Orange St, Tempe, AZ 85287, USA; tamara.hew{at}overhydration.org

Abstract

Objective To evaluate the osmotic and non-osmotic regulation of arginine vasopressin (AVP) during endurance cycling.

Design Observational study.

Setting 109 km cycle race.

Participants 33 Cyclists.

Interventions None.

Main outcome measurements 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 Δ and urine osmolality Δ (r = −0.41, p<0.05), whereas non-significant inverse correlations were noted between [AVP]p and both plasma [Na+] Δ and % PV Δ. 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+] Δ (−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.

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Footnotes

  • Competing interests None.

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