Vascular fluid shifts and endocrine responses to exercise in the heat

Effect of rehydration
  • G. Brandenberger
  • V. Candas
  • M. Follenius
  • J. P. Libert
  • J. M. Kahn
Article

DOI: 10.1007/BF00714993

Cite this article as:
Brandenberger, G., Candas, V., Follenius, M. et al. Europ. J. Appl. Physiol. (1986) 55: 123. doi:10.1007/BF00714993

Summary

This study examines the relationships between vascular changes and endocrine responses to prolonged exercise in the heat, associated with dehydration and rehydration by fluids of different osmolarity. Five subjects were exposed, in a 34‡ C environment for 4 h of intermittent exercise on a cycle ergometer at 85±12 Watts (SD). Fluid regulatory hormones and cortisol were analysed in 3 experimental sessions: one without any fluid supplement (NO FLUID), and two with progressive rehydration, either by spring water (WATER) or isotonic solution (ISO), given after 70 min of exercise. Results were expressed in terms of differences between the mean values observed at the end of the exercise and the first hour values taken as references.

Dehydration (NO FLUID) elicited a 4.0±0.8% (SE) decrease in plasma volume (PV) and an increase in osmolarity (8.4±3.1 mosmol · l−1). Concomitantly, plasma aldosterone (PA), renin activity (PRA), arginin vasopressin (AVP) and cortisol (PC) levels increased greatly in response to exercise in the heat (PA: 37.2+-10.8 ng. 100 ml−1; PRA: 13.4±2.5 ng · ml−1 · h−1; AVP: 3.8±1.3 pg · ml−1; PC: 12.2±2.7 Μ g · 100 ml−1). Rehydration with water led to decreased osmolarity (−8.2±2.1 mosmol · l−1) with no significant changes in PV. With ISO, PV increased by 6.0±1.3% and the decrease in osmolarity was −5.8±1.8 mosmol · l−1. With both modes of rehydration, the increases in PRA, AVP and cortisol were blunted; only ISO prevented the rise in PA.

These data indicate that prolonged exercise in moderate heat is extremely effective in increasing cortisol and fluid-electrolyte regulatory hormones in dehydrated subjects. Progressive rehydration with water or isotonic solution, in the absence of osmotic and volemic stimuli, prevents the hormonal increases.

Key words

Plasma volume Aldosterone Renin activity Arginine vasopressin Cortisol 

Copyright information

© Springer-Verlag 1986

Authors and Affiliations

  • G. Brandenberger
    • 1
  • V. Candas
    • 1
  • M. Follenius
    • 1
  • J. P. Libert
    • 1
  • J. M. Kahn
    • 1
  1. 1.Groupe de Physiologie EnvironnementaleCentre d'Etudes Bioclimatiques du CNRSStrasbourg CedexFrance
  2. 2.Zollikofen-BernSwiss

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