Journal of Applied Physiology, Vol 41, Issue 5 708-713, Copyright © 1976 by American Physiological Society
Effect of heat acclimatization on intravascular responses to acute heat stress in man
R. M. Bonner, M. H. Harrison, C. J. Hall and R. J. Edwards
The effects of a 185-min exposure to 48 degrees C db/33 degrees C wb, on
intravascular volume and osmolarity and on intravascular electrolyte,
aldosterone, and cortisol concentrations have been studied in five male
subjects before and after acclimatization to heat. Changes in the
hematocrit and plasma protein concentration indicated that a hemodilution
occurred during the first 35 min of the heat exposures, and that this was
followed by a hemoconcentration. Although these changes in intravascular
volume were not affected by acclimatization, the plasma volume after heat
acclimatization was 6.7% greater than before. This increase in plasma
volume was associated with an elevation in the ratio [Na]/[K]. However,
since plasma osmolarity decreased the intravascular expansion could not be
explained in terms of elevated electrolyte levels. Plasma aldosterone and
cortisol levels were not affected by heat acclimatization, although both
were elevated following exercise in the heat. It is concluded that the
adrenal cortex is not an important factor in maintaining a state of heat
acclimatization once a salt balance has been achieved.
