Flávio de Castro Magalhães & Fabiano Trigueiro Amorim & Renata L. Freitas Passos & Michele Atalla Fonseca & Kenya Paula Moreira Oliveira & Milene Rodrigues Malheiros Lima & Juliana Bohen Guimarães & João Batista Ferreira-Júnior & Angelo R. P. Martini & Nilo R. V. Lima & Danusa Dias Soares & Edilamar Menezes Oliveira & Luiz Oswaldo Carneiro Rodrigues.
Received: 9 May 2008 /Revised: 26 March 2010 /Accepted: 31 March 2010 / Published online: 23 April 2010 Cell Stress Society International 2010
In order to verify the effects of heat and exercise acclimation (HA) on resting and exercise-induced expression of plasma and leukocyte heat shock protein 72 (Hsp72) in humans, nine healthy young male volunteers (25.0±0.7 years; 80.5±2.0 kg; 180±2 cm, mean ± SE) exercised for 60 min in a hot, dry environment (40±0°C and 45±0% relative humidity) for 11 days. The protocol consisted of running on a treadmill using a controlled hyperthermia technique in which the work rate was adjusted to elevate the rectal temperature by 1°C in 30 min and maintain it elevated for another 30 min. Before and after the HA, the volunteers performed a heat stress test (HST) at 50% of their individual maximal power output for 90 min in the same environment. Blood was drawn before (REST), immediately after (POST) and 1 h after (1 h POST) HST, and plasma and leukocytes were separated and stored. Subjects showed expected adaptations to HA: reduced exercise rectal and mean skin temperatures and heart rate, and augmented sweat rate and exercise tolerance. In HST1, plasma Hsp72 increased from REST to POST and then returned to resting values 1 h POST (REST: 1.11±0.07, POST: 1.48±0.10, 1 h POST: 1.22±0.11 ng mL−1; p<0.05). In HST2, there was no change in plasma Hsp72 (REST: 0.94±0.08, POST: 1.20±0.15, 1 h POST: 1.17±0.16 ng mL−1; p>0.05). HA increased resting levels of intracellular Hsp72 (HST1: 1±0.02 and HST2: 4.2±1.2 density units, p<0.05). Exercise-induced increased intracellular Hsp72 expression was observed on HST1 (HST1: REST, 1±0.02 vs. POST, 2.9±0.9 density units, mean ± SE, p<0.05) but was inhibited on HST2 (HST2: REST, 4.2±1.2 vs. POST, 4.4±1.1 density units, p>0.05). Regression analysis showed that the lower the pre-exercise expression of intracellular Hsp72, the higher the exercise-induced increase (R=−0.85, p<0.05). In conclusion, HA increased resting leukocyte Hsp72 levels and inhibited exercise-induced expression. This intracellular adaptation probably induces thermotolerance. In addition, the non-increase in plasma Hsp72 after HA may be related to lower stress at the cellular level in the acclimated individuals.
Heat and exercise acclimation (HA) refers to an organism’s ability to perform exercise or work in high environmental temperatures (Robinson et al. 1943). HA is attained by a series of sessions of sustained increased core temperature, usually generated by performing work or exercise during repeated days in a hot environment (Moseley 1997). The most common reported adaptations to HA are lower rest and exercise core temperature, lower exercise heart rate and augmented sweat rate (Nadel et al. 1974). HA, however, is a complex process involving adaptations not only at whole-body but also at the cellular level (Horowitz 2002; Yamada et al. 2007; McClung et al. 2008). Heat shock proteins (Hsps) are a highly conserved group of proteins that serve as molecular chaperones and accelerate cellular repair from heat stress, ischemia and endotoxic shock (Kregel 2002; Lau et al. 2000). The most thermosensitive and highly inducible Hsp belongs to the 70-kDa family (Mizzen and Welch 1988) and is commonly known as Hsp72. Although the function of intracellular Hsp72 (iHsp72) has been extensively investigated, it has also been suggested that Hsp72 has a functional role when released by a variety of cells (Febbraio et al. 2002a; Broquet et al. 2003; Hunter-Lavin et al. 2004; Lancaster et al. 2004) into the circulation (Pockley et al. 1998). Extracellular Hsp72 (eHsp72) is thought to stimulate innate immunity (Matzinger 1994), act as a danger signal resulting in increased immune responses and facilitate host defense to pathogenic challenges (Fleshner and Johnson 2005). For example, eHsp72 has been suggested to have an immuno-logical function (Moseley 1998; Asea et al. 2000; Campisi and Fleshner 2003; Fleshner et al. 2003) with the attachment of eHsp72 to the surface of monocytes being found to stimulate the production of several cytokines in vitro (Asea et al. 2000).