The Effect Of Mild Dehydration On Heat Shock Protein Induction During An Acute Cycling Bout

Abstract

Low to moderate doses of physiologic stressors, including heat, cold, and exercise have been shown experimentally to induce HSP72. However, the effect of dehydration on HSP72 expression has not been previously examined. PURPOSE: The present study evaluates the effect of mild dehydration on HSP72 expression during 90 minutes of continuous exercise. METHODS: Three male subjects (mean ± SD; ht, 177.7 ± 9.5 cm, wt 70.7 ± 8.6 kg, BF%, 7.8 ± 1.4%; cycle VO2 pk 53.0 ± 3.6 ml/kg/min-1) performed two cycling bouts at 70% VO2 pk (37.1 ± 2.5 ml/kg/min-1) in a temperate environment (21.8 ± 0.8°C, RH 42 ± 1 %) for 90 minutes. In one condition subjects were provided water for 48 hours prior to exercise testing to ensure euhydration, while in the other subjects were volitionally dehydrated. Nude bodyweight and urine osmolality were measured both pre and post exercise. During exercise core temperature, oxygen consumption, and power output were measured every 15 minutes. HSP72 was measured in peripheral blood mononuclear cells separated from blood samples taken pre and 1 hour post exercise. Western blot was used to quantify HSP72, with pretest levels being normalized to 1.0 for each condition to increase interpretation. RESULTS: There were no differences (p > 0.05) in peak core temperature (38.99 ± 0.15 vs. 38.74 ± 0.25°C), exercise induced change in bodyweight (1.8 ± 0.7 vs. 1.8 ± 0.8%), power output (185 ± 2 vs. 186 ± 5 W), or oxygen consumption (36.9 ± 3.2 vs. 36.4 ± 2.4 ml/kg/min-1) between the dehydrated and euhydrated conditions, respectively. Urine osmolality was greater in the dehydrated condition both pre (808 ± 159 vs. 163 ± 78 mosm/kg; p < 0.001) and post exercise (908 ± 189 vs. 302 ± 66 mosm/kg; p < 0.001). Following exercise HSP72 expression in the euhydrated condition was 47% lower then the dehydrated condition. Although this difference was large, variability in dehydrated subjects post exercise HSP72 values prevented us from showing a significant difference (p = 0.14). CONCLUSION: Preliminary findings (n = 3) indicate that mild dehydration may not be sufficient to induce HSP72 during an acute bout of exercise. Whether this trend will remain with greater n size remains to be determined.