Cytokine induction during exertional hyperthermia is abolished by core temperature clamping: neuroendocrine regulatory mechanisms.

The immunomodulatory effects of physiological temperature change remain poorly understood and inter-relationships between changes in core temperature, stress hormones and cytokines during exertional hyperthermia are not well established. This experimental study was designed to examine how cytokine (tumour necrosis factor (TNF)-α, interleukin (IL)-6, IL-12 and IL-1ra (receptor antagonist)) and hormone (epinephrine (Epi), norepinephrine (NE), growth hormone (GH) and cortisol (CORT)) responses are modified when the exercise-induced rise in core temperature is attenuated or exacerbated by immersion in a water bath. Ten men ((mean ± SD) age: 26.9 ± 5.7 years; height 1.75 ± 0.07 m; body mass 76.0 ± 10.9 kg; O2 peak: 48.0 ± 12.4 mL kg−1 min−1) completed two 40-min cycle ergometer exercise trials at 65% O2 peak while immersed to mid-chest. Rectal temperature (Tre) peaked at 39.1 ± 0.03 and 37.5 ± 0.13°C during the hot (39°C) and cold (18°C) conditions, respectively. Blood samples were collected before, during (20...