R. Lovell, L. Madden, L. R. McNaughton, and S. Carroll
Applied Physiology Laboratory, University of Hull, Hull, U.K. Received July 27, 2006 Accepted February 13, 2007 Published online October 12, 2007; Springer-Verlag 2007.
The purpose of this study was to delineate the effects of hyperthermia and physical exercise on the heat shock protein 70 (HSP70) response in circulating peripheral blood mononuclear cells (PBMCs). Six healthy, young (age: 24 3 yrs), moderately trained males (VO2max: 48.9 2.7 ml kg min1) undertook two experimental trials in a randomised fashion in which the core temperature (Tc) was increased and then maintained at 39 C during a 90 min bout by either active (AH) or passive (PH) means. AH involved subjects cycling at 90% of their lactate threshold in attire designed to impede heat loss mechanisms. In the PH trial, subjects were immersed up to the neck in a hot bath (40.2 0.4 C), once the critical Tc was achieved, intermittent cycling and water immersions were prescribed for the AH and PH conditions, respectively, to maintain the Tc at 39 C. HSP70 was measured intracellularly pre, post and 4 h after trials, from circulating PBMCs using an ELISA technique. Tc reached 39 C quicker in PH than during AH trials (PH: 21 4 min vs. AH: 39 6 min+- P<0.01), thereafter Tc was maintained around 39 C (PH: 39.1 0.2 C; AH: 38.8 0.3 C+- P>0.05). AH induced a marked leukocytosis in all sub-sets (P<0.05). PH generated significant monocytosis and granulocytosis (P<0.05), without changes in lymphocyte counts (P>0.05). There were no significant increases in intracellular HSP70 at 0 h (AH: 21.1 44.8; PH: þ12.5 32.4 ng=mg TP=103=ml PBMCs; P>0.05) and 4 h (AH: 30.0 40.1+- PH: þ36.3 70.4 ng= mg TP=103=ml PBMCs+- P>0.05) post active and passive heating. Peak HSP70 expressed as a fold-change from rest was also not increased by AH (1.1 0.9+- P>0.05) or PH (3.2 4.8+- P>0.05). There were no significant differences between the AH and PH trials at any time-point, and the HSP70 response appeared to be individual specific. These results did not allow us to delineate the effects of hyperthermia and other exercise associated stressors on the heat shock response and therefore further work is warranted.
Heat shock proteins are synthesised by cells upon exposure to stress. They are known as molecular chaperones since their functions are to re-assert cellular stasis through translocation, re-folding or dis-assembly of nascent polypeptides (Morimoto et al., 1994). A number of changes in the intracellular milieu have been shown to produce an accumulation of HSPs, a process known as the HSR. The term ‘heat’ shock proteins was applied as a heat shock of 42 C was shown to produce an accumulation of these proteins in drosophilia (Ritossa, 1962). Since then, alterations in pH (Gapen and Moseley, 1995), increased calcium accumulation (Kiang et al., 1994), glucose depletion (Febbraio et al., 2004), and oxidative stress (Benjamin et al., 1990), have been shown to produce a HSR. Each of these conditions are associated with the physiological response to exercise, which has been shown to induce a marked acute HSR in organ (Walters et al., 1998; Kim et al., 2004) and muscle tissues (Skidmore et al., 1995; Khassaf et al., 2001) and also circulating leukocytes (Ryan et al., 1991; Fehrenbach et al., 2000a, b). The role of temperature in the HSR has been determined passively in in vivo and in vitro models. Rats exposed to high (0.166 C min1) and low (0.045 C min1) whole-body heating rates produced a greater accumulation of HSP70 in the small intestine, liver and kidney following the high body heating rate condition (Flanagan et al., 1995). In addition, whole blood exposed to high temperatures (42–43 C) produced a HSR in leukocytes (Oehler et al., 2001; Schneider et al., 2002). However, it is not clear whether temperature is the major contributor to the HSR during physical exercise, or whether the cumulative effects of metabolic changes such as alterations in pH and calcium, oxidative stress or a reduced energy availability are the primary signals. There are few studies that have attempted to delineate the effects of hyperthermia and exercise on the HSR. Those that have tried have produced contradictory findings using various tissue extracts from animal models (Skidmore et al., 1995; Walters et al., 1998; Harris and Starnes, 2001; Kim et al., 2004). To our knowledge, no study has yet investigated the role of temperature during exercise on the HSR in humans. If temperature is the primary stimulus for HSP70 up-regulation, these can be used as molecular markers of thermal history in populations that work=perform in high ambient temperatures. Therefore it was the aim of the current study to delineate the effects of hyperthermia and physical exercise on the HSP70 response in circulating leukocytes. Since circulating leukocytes visit all organs and tissues their HSR may give an overall marker of stress (Sonna et al., 2002).