Acute heat/exercise stress in rats: effects on fluid and electrolyte regulatory hormones.

Adult, male rats were exercised in the heat until hyperthermic exhaustion ensued. Plasma aldosterone levels were significantly (p less than 0.001) elevated after 8 min of exercise and remained increased throughout the exercise and recovery periods. Alternatively, plasma angiotensin I levels were unaffected during exercise, but increased significantly (p less than 0.001) during the recovery period. These rapid elevations in hormonal levels may be part of a sympathicoadrenal response to heat/exercise stress as well as an adaptational response to maintain plasma volume during and following exercise in the heat.