Hsp72 and Hsp90α mRNA transcription is characterised by large, sustained changes in core temperature during heat acclimation

Increased intracellular heat shock protein-72 (Hsp72) and heat shock protein-90 alpha (Hsp90 alpha) have been implicated as important components of acquired thermotolerance, providing cytoprotection during stress. This experiment determined the physiological responses characterising increases in Hsp72 and Hsp90 alpha mRNA on the first and tenth day of 90-min heat acclimation (in 40.2 A degrees C, 41.0 % relative humidity (RH)) or equivalent normothermic training (in 20 A degrees C, 29 % RH). Pearson's product-moment correlation and stepwise multiple regression were performed to determine relationships between physiological [e.g. (T-rec, sweat rate (SR) and heart rate (HR)] and training variables (exercise duration, exercise intensity, work done), and the leukocyte Hsp72 and Hsp90 alpha mRNA responses via reverse transcription quantitative polymerase chain reaction (RT-QPCR) (n = 15). Significant (p < 0.05) correlations existed between increased Hsp72 and Hsp90 alpha mRNA (r = 0.879). Increased core temperature was the most important criteria for gene transcription with Delta T-rec (r = 0.714), SR (r = 0.709), T-recfinal45 (r = 0.682), area under the curve where T-rec aeyen 38.5 A degrees C (AUC38.5 A degrees C; r = 0.678), peak T-rec (r = 0.661), duration T-rec aeyen 38.5 A degrees C (r = 0.650) and Delta HR (r = 0.511) each demonstrating a significant (p < 0.05) correlation with the increase in Hsp72 mRNA. The T-rec AUC38.5 A degrees C (r = 0.729), Delta T-rec (r = 0.691), peak T-rec (r = 0.680), T-recfinal45 (r = 0.678), SR (r = 0.660), duration T-rec aeyen 38.5 A degrees C (r = 0.629), the rate of change in T-rec (r = 0.600) and Delta HR (r = 0.531) were the strongest correlate with the increase in Hsp90 alpha mRNA. Multiple regression improved the model for Hsp90 alpha mRNA only, when T-rec AUC38.5 A degrees C and SR were combined. Training variables showed insignificant (p > 0.05) weak (r < 0.300) relationships with Hsp72 and Hsp90 alpha mRNA. Hsp72 and Hsp90 alpha mRNA correlates were comparable on the first and tenth day. When transcription of the related Hsp72 and Hsp90 alpha mRNA is important, protocols should rapidly induce large, prolonged changes in core temperature.