The effect of the rate of heat storage on serum heat shock protein 72 in humans.

Hsp72 concentration has been shown to be higher in the serum (eHsp72) of runners with symptoms of heat illness than in non-ill runners. Recently, it has been suggested that the rate of heat storage during exercise in the heat may be an important factor in the development of heat stroke. Therefore, we compared the effect of two rates of heat storage on eHsp72 concentration during exercise in which subjects reached the same final core temperature. We hypothesized that with a lower rate of heat storage the increase in eHsp72 would be attenuated compared to a higher rate of heat storage. Nine heat acclimated subjects performed two exercise trials in a counterbalanced order in the heat (42 degrees C, 30% relative humidity). The trials consisted of walking on a treadmill (approximately 50% VO (2) peak) dressed in military summer fatigues until rectal temperature reached 38.5 degrees C. A high rate of heat storage (HS, 1.04 +/- 0.10 W m(-2) min(-1), mean +/- SE) occurred when subjects walked without cooling. To produce a lower rate of heat storage (LS, 0.54 +/- 0.09 W m(-2) min(-1)) subjects walked while wearing a water-perfused cooling vest underneath clothing. eHsp72 increased pre- to post-exercise (P < 0.05) but there was no difference (P > 0.05) in eHSP between the two rates of heat storage (LS 1.25 +/- 0.73 to 2.23 +/- 0.70 ng ml(-1), HS 1.04 +/- 0.57 to 2.02 +/- 0.60 ng ml(-1)). This result suggests that eHsp72 is a function of the core temperature attained rather than the rate of heat storage.