| Abstract | Inflammatory responses are regulated by transcription factor NF-KB, predominately inactive in the cytoplasm. Upon activation, NF-KB translocation into the nucleus regulates gene transcription of pro inflammatory cytokines.
PURPOSE: The purpose of this study was to examine the effect of a single bout of exertional heat stress (EHS) on NF-?B DNA-binding in human peripheral blood mononuclear cells (PBMC) of trained (TR) and untrained (UT) individuals.
METHODS: Maximum oxygen consumption expressed per kg of lean body mass (LBM) and activity history was used to divide subjects into TR (n=12, VO2peak= 70 ± 2 mL-kgLBM-l-mm-1) and UT (n=10, VO2peak= 50 ± 1 mL-kgLBM-l-mm-1) groups. Subjects walked at 4.5 km-h-1 with 2% elevation in a climatic chamber (40°C; 30% R.H.) wearing military biological and chemical protective clothing until specific end-point criteria were attained. Venous blood samples were collected at baseline (B), rectal temperatures of 38.0°C, 38.5°C, 39.0°C and at exhaustion (Exh). Whole blood was analysed by flow cytometry for intranuclear inflammatory transcription factor NF-KB in PBMC. Similar analyses were performed following in vitro lipopolysacharide (LPS) stimulation (30 min,100ng/mL).
RESULTS: Rectal temperature (Tre) tolerated at Exh was higher in TR (39.7 ± 0.1 °C) compared to UT (39.1 ± 0.1°C), however, the rate of Tre increase was not significantly different between the groups (1.0 ± 0.05 °C/hr). Exertional heat stress induced a temperature dependent elevation in the absolute count (x109cell/L) of PBMC expressing NF-KB in TR and UT compared to B. Intranuclear NF-KB relative mean fluorescence intensity (MFI) was elevated compared to B in both TR and UT at 38.5°C and in TR at 39.5°C. At Exh, intranuclear NF-KB DNA-binding was not significantly different from B in vivo. Additional in vitro LPS stimulation induced a significantly greater increase in NF-KB DNA-binding from B compared to Exh.
CONCLUSIONS: These findings suggest that the observed upregulation of intranuclear NF-KB in circulating PBMC during EHS may be attributed to both leukocyte mobilization and/or NF-KB translocation. Although there were no significant differences observed between TR and UT up to 39.0°C, EHS was found to increase LPS tolerance upon stimulation in vitro. |
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