Human blood neutrophil responses to prolonged exercise with and without a thermal clamp

The purpose of this study was to investigate the effects of prolonged exercise with and without a thermal clamp on neutrophil trafficking, bacterial-stimulated neutrophil degranulation, stress hormones, and cytokine responses. Thirteen healthy male volunteers (means +/- SE: age 21 +/- 1 yr; mass 74.9 +/- 2.1 kg; maximal oxygen uptake 58 +/- 1 ml x kg(-1) x min(-1)) completed four randomly assigned, 2-h water-immersion trials separated by 7 days. Trials were exercise-induced heating (EX-H: water temperature 36 degrees C), exercise with a thermal clamp (EX-C: 24 degrees C), passive heating (PA-H: 38.5 degrees C), and control (CON: 35 degrees C). EX-H and EX-C was comprised of 2 h of deep water running at 58% maximal oxygen uptake. Blood samples were collected at pre-, post-, and 1 h postimmersion. Core body temperature was unaltered on CON, clamped on EX-C (-0.02 degrees C), and rose by 2.23 degrees C and 2.31 degrees C on EX-H and PA-H, respectively. Exercising with a thermal clamp did not blunt the neutrophilia postexercise (EX-C postexercise: 9.6 +/- 1.1 and EX-H postexercise: 9.8 +/- 1.0 x 10(9)/liter). Neutrophil degranulation decreased (P < 0.01) similarly immediately after PA-H (-21%), EX-C, and EX-H (-28%). EX-C blunted the circulating norepinephrine, cortisol, granulocyte-colony stimulating factor, and IL-6 response (P < 0.01) but not the plasma epinephrine and serum growth hormone response. These results show a similar neutrophilia and decrease in neutrophil degranulation after prolonged exercise with and without a thermal clamp. As such, the rise in core body temperature does not appear to mediate neutrophil trafficking and degranulation responses to prolonged exercise. In addition, these results suggest a limited role for cortisol, granulocyte-colony stimulating factor, and IL-6 in the observed neutrophil responses to prolonged exercise.