Isothermic and fixed-intensity heat acclimation methods elicit equal increases in Hsp72 mRNA

Abstract

Thermotolerance, to which Heat shock protein-72 (Hsp72) contributes, is an acquired state achieved following heat acclimation (HA), eliciting cellular adaption and protection against thermal stress. Optimal HA methods achieving the greatest heat shock response (HSR) are equivocal; therefore investigation of methods provoking the greatest sustained HSR is required to optimise cellular adaptation.

Twenty four males performed short term HA (STHA; five sessions) and long term HA (LTHA; STHA plus further five sessions) utilising fixed intensity (FIXED; workload = 50%V ̇O2peak), continuous isothermic HA (ISOCONT; target rectal temperature (T¬rec) = 38.5°C) or progressive isothermic HA (ISOPROG; target Trec = 38.5°C for STHA then target Trec = 39.0°C for LTHA). Leukocyte Hsp72 mRNA was measured pre and post day 1, day 5 and day 10 of HA via qRT-PCR to determine the HSR.

Hsp72 mRNA increased (p < 0.05) pre to post day 1, pre to post day 5, and pre to post day 10 in FIXED, ISO¬CONT and ISOPROG, but no differences were observed between methods (p > 0.05). The equal Hsp72 mRNA increases occurring from consistent, reduced or increased endogenous strain following STHA and LTHA suggest that transcription occurs following attainment of sufficient endogenous criteria. These data give confidence that all reported HA methods increase Hsp72 mRNA and are capable of eliciting adaptations towards thermotolerance.