Endocrine responses during exercise-heat stress: Effects of prior isotonic and hypotonic intravenous rehydration

John W. Castellani, Carl M. Maresh, Lawrence E. Armstrong, Robert W. Kenefick, Deborah Riebe, Marcos Echegaray, Stavros Kavouras, V. Daniel Castracane

Research output: Contribution to journalArticle

17 Scopus citations

Abstract

Exercise following exercise-induced dehydration (EID) has been shown to elevate concentrations of plasma norepinephrine (NE) and hypothalamic-pituitary-adrenal axis hormones. However, it is not known how intravenous (i.v.) rehydration (Rh) with isotonic (ISO) or hypotonic (HYPO) saline affects these hormone concentrations. It was hypothesized that HYPO, versus ISO, would lead to lower plasma NE and cortisol concentrations ([CORT]) during subsequent exercise following EID due to a decrease in plasma sodium concentration [Na+]. Eight non-heat acclimated men completed three experimental treatments (counterbalanced design) immediately following EID (33°C) to -4% body mass loss. The Rh treatments were i.v. 0.9% NaCl (ISO, 25 ml.kg-1), i.v. 0.45% NaCl (HYPO, 25 ml.kg-1), and no fluid (NF). After Rh and rest (2 h total), the subjects walked at 53-54 percent of maximal O2 uptake for 45 min at 36°C. After Rh, the following observations were made before/during exercise: percentage change in plasma volume (PV) was lower in NF compared to ISO and HYPO but similar between ISO and HYPO; Δ [Na+] was similar between ISO and NF and higher in ISO compared to HYPO; Δ plasma NE was higher in NF compared to ISO and HYPO, but similar between ISO and HYPO; Δ plasma [CORT] was higher in NF compared to ISO and HYPO and higher in ISO compared to HYPO; rectal temperature was higher in NF compared to ISO and HYPO. These data would suggest that sympathetic nervous activity and [CORT] during exercise, subsequent to EID and Rh, was affected by lower PV (probably through cardiopulmonary baroreflexes) as well as core temperature. Furthermore, [CORT] was affected by Δ [Na+] after Rh through an unknown mechanism.

Original languageEnglish (US)
Pages (from-to)242-248
Number of pages7
JournalEuropean Journal of Applied Physiology and Occupational Physiology
Volume77
Issue number3
DOIs
StatePublished - Feb 1 1998
Externally publishedYes

Keywords

  • Plasma adrenocorticotropic hormone
  • Plasma cortisol
  • Plasma norepinephrine

ASJC Scopus subject areas

  • Physiology
  • Public Health, Environmental and Occupational Health

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