Two years of combined high-intensity physical training and heat acclimatization affect lymphocyte and serum HSP70 in purebred military working dogs

Abstract

Military working dogs in hot countries undergo exercise training at high ambient temperatures for at least 9 mo annually. Physiological adaptations to these harsh conditions have been extensively studied; however, studies focusing on the underlying molecular adaptations are limited. In the current study, military working dogs were chosen as a model to examine the effects of superimposing endurance exercise on seasonal acclimatization to environmental heat stress. The lymphocyte HSP70 profile and extracellular HSP70 were studied in tandem with physiological performance in the dogs from their recruitment for the following 2 yr. Aerobic power and heat shock proteins were measured at the end of each summer, with physical performance tests (PPTs) in an acclimatized room (22°C). The study shows that together with a profound enhancement of aerobic power and physical performance, hsp72 mRNA induction immediately post-PPT and 45 min later, progressively increased throughout the study period (relative change in median lymphocyte hsp72 mRNA first PPT, 4.22 and 12.82; second PPT, 17.19 and 109.05, respectively), whereas induction of HSP72 protein was stable. These responses suggest that cellular/molecular adaptive tools for maintaining HSP72 homeostasis exist. There was also a significant rise in basal and peak median optical density extracellular HSP at the end of each exercise test (first PPT, 0.13 and 0.15; second PPT, 1.04 and 1.52, respectively). The relationship between these enhancements and improved aerobic power capacity is not yet fully understood.

Hospitalized dogs recovery from naturally occurring heatstroke; does serum heat shock protein 72 can provide prognostic biomarker?

“…In the current setup, median eHSP72 levels were significantly higher than the normal reference range observed in dogs at all-time points (Bruchim et al 2014). The reference range used in this study was based on our previous study using military working dogs, before initiation of physical training and exposure to high environmental temperatures.…”

“…We have shown that lymphocyte HSP72 protein levels and lymphocyte HSP72 mRNA are detectable and accurately measurable in working military dogs. In addition, in acclimated trained dogs, basal eHSP72 levels were higher than in naïve dogs, with significantly higher post-exercise levels in the acclimated dogs (Bruchim et al 2014). To the best of our knowledge, eHSPs levels have never been assessed in naturally occurring heatstroke patients.…”

“…The average optical density (OD) of each triplicate was calculated and used for statistical analysis. The normal range was determined to be 0.09-0.15 OD based on control dogs (Bruchim et al 2014) and studies of eHSP72 in humans (Xiao et al 2003) and monkeys (Dehbi et al 2010).…”

“…Serum heat shock protein (eHSP) was recently evaluated as biomarkers for heat tolerance and acclimation and during experimental heatstroke (Bruchim et al 2014;Dehbi et al 2010;Periard et al 2012;Sandstrom et al 2008). One study of induced heatstroke in six monkeys demonstrated that eHSP 72 serum levels correlated with the liver, myocardium, and skeletal muscle necrosis, and were lower in the survivors (Dehbi et al 2010), therefore, eHSP72 levels may serve as a prognostic indicator of heatstroke (Dehbi et al 2010).…”

Adaptations and mechanisms of human heat acclimation: Applications for competitive athletes and sports

“…Other studies have also observed that team-sport athletes participating in preseason (Racinais et al, 2014), in-season (Buchheit et al, 2011), and off-season (heat and altitude; Buchheit et al, 2013) training camps in the heat (∼34°C) improve performance by 7% and 44% (Yo-Yo Intermittent Recovery test level 1 and 2, respectively) in temperate conditions (∼22°C). The mechanisms modulating the transfer between hot and cool conditions could be linked to a variety of ergogenic responses, with cardiovascular/ thermoregulatory and cellular (Bruchim et al, 2014) adaptations. As recently highlighted by Corbett et al (2014), heat acclimation may provide a stimulus for improving performance in nonthermally challenging environments via improvements in VO 2max , lactate threshold, and economy.…”