Document Detail

Heat acclimation improves regulation of plasma volume and plasma Na(+) content during exercise in horses.
MedLine Citation:
PMID:  10710397     Owner:  NLM     Status:  MEDLINE    
This study determined the plasma volume (PV) and ion responses to heat acclimation and exercise in six trained Thoroughbred horses during 21 days of exposure to heat and humidity (33 degrees C, 83% relative humidity) for 4 h/day. During the 2nd h on days 0, 3, 7, 14, and 21, horses performed a standardized treadmill test, running at 50% of peak O(2) uptake until pulmonary artery temperature reached 41.5 degrees C. Heat acclimation resulted in an increase in PV from 21.3 +/- 1.1 liters on day 0 to 24.3 +/- 1.0 liters on day 14, returning to 22.6 +/- 0.9 liters on day 21. The corresponding total plasma protein contents were 1,273 +/- 53, 1,455 +/- 81, and 1,377 +/- 57 g, respectively, and increases in total plasma Na(+) plus Cl(-) content were 5,145 +/- 126, 5,749 +/- 146, and 5,394 +/- 114 mmol, respectively. Thus changes in PV were accompanied by direct changes in plasma protein and osmolyte contents. With exercise on day 0, PV decreased by 7.1 +/- 0.7% at 5 min of exercise and remained decreased (-6.7 +/- 1.3%) at 5 min of recovery. By day 21, PV decreased significantly less than on day 0 (by 5.2 +/- 0.9% at 5 min of exercise), was decreased by only 2.0 +/- 1.6% at 5 min of recovery, and was fully restored at 15 min of recovery. Plasma Na(+) concentration increased 3 meq/l during the first 5 min of exercise and was normalized by 5 min of recovery on day 0 and by end exercise on day 21. It is concluded that improved ability to regulate PV during exercise in response to heat acclimatization is associated with an increased PV and an improved conservation of Na(+).
M I Lindinger; L J McCutcheon; G L Ecker; R J Geor
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Publication Detail:
Type:  Comparative Study; Journal Article; Research Support, Non-U.S. Gov't    
Journal Detail:
Title:  Journal of applied physiology (Bethesda, Md. : 1985)     Volume:  88     ISSN:  8750-7587     ISO Abbreviation:  J. Appl. Physiol.     Publication Date:  2000 Mar 
Date Detail:
Created Date:  2000-04-24     Completed Date:  2000-04-24     Revised Date:  2013-09-26    
Medline Journal Info:
Nlm Unique ID:  8502536     Medline TA:  J Appl Physiol (1985)     Country:  UNITED STATES    
Other Details:
Languages:  eng     Pagination:  1006-13     Citation Subset:  IM    
Department of Human Biology and Nutritional Sciences, University of Guelph, Guelph, Ontario, Canada N1G 2W1.
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MeSH Terms
Acclimatization / physiology*
Carotid Arteries / physiology
Horses / blood*,  physiology*
Hot Temperature
Physical Exertion / physiology*
Plasma Volume / physiology*
Pulmonary Artery / physiology
Sodium / blood*
Species Specificity
Time Factors
Water-Electrolyte Balance / physiology
Reg. No./Substance:

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