Effect of Acute Exercise-Heat Exposure on extracellular HSP70 (eHSP70): International Convention on Science, Medicine in Sport, Glasgow

BACKGROUND Expression of heat shock protein, HSP70, increases in tissue and extracellular fluid following exposure to conditions eliciting physiological stress. Variation in methods and experimental design, including environmental and exercise stimuli have elicited varied mediation of the biochemical response to stress. AIM The present study aimed to quantify the extent of increased expression in extracellular HSP70 (eHSP70) with increased heat stress, and determine any relationship between systemic heat strain, represented by peak and change in core temperature (Tc), and local heat strain, represented by end and change in exercising muscle temperature (Tm) in a heat-exercise model. METHODS Six male distance runners (Age 23.2 ± 1.5 years; height 178.8 ± 5.1cm; mass 72.9 ± 4.0kg; VO<startsub>2peak<endsub> 3.96 ± 0.70 l.min-1) completed 90 min of cycling at 50% VO<startsub>2peak<endsub> in ambient (AMB, 20.3 ± 0.3<degree>C/63 ± 2.4%R.H.), hot (HOT, 30.2 ± 0.1<degree>C/51 ± 3.3%R.H.) and very hot (VHOT, 40.0 ± 0.2<degree>C/37 ± 4.8%R.H.) conditions. Pre, post and 24-h post plasma was analysed for eHSP70 using an ELISA. RESULTS Differences were observed between conditions for peak (AMB =38.0 ± 0.3<degree>C, HOT=38.6 ± 0.5<degree>C, VHOT=39.4 ± 0.2<degree>C) (P<less>0.001) and change (AMB =1.2 ± 0.3<degree>C, HOT=1.7 ± 0.7<degree>C, VHOT=2.5 ± 0.3<degree>C) (P<less>0.001) in Tc, and post (AMB =37.3 ± 0.6<degree>C, HOT=38.0 ± 0.8<degree>C, VHOT=39.5 ± 0.4<degree>C) (P<less>0.001) and change (AMB =2.0 ± 1.0<degree>C, HOT=3.1 ± 0.5<degree>C, VHOT=4.6 ± 0.9<degree>C) (P<less>0.001) in exercising Tm. Increased eHSP70 concentration was observed post VHOT trial (+38%) (P<less>0.05) but not AMB (+11%) and HOT (+8%). eHSP70 returned to baseline values within 24-h in all conditions (AMB +6%, HOT +3%, VHOT% +3%). No relationship (P<less>0.05) was observed between eHSP70 and peak or change Tc or Tm. CONCLUSION Data suggests a critical internal temperature may be required to increase significantly eHSP70 post acute heat-exercise stimuli. Within 24-h eHSP70 elevation had returned to pre test levels suggesting increases are transient, repeated exposures may preserve elevation.