THE EFFECTS OF PROLONGED EXERCISE IN A HOT ENVIRONMENT ON NEUTROPHIL DEGRANULATION IN TRAINED CYCLISTS

Abstract

PURPOSE To examine the influence of a prolonged bout of exercise in hot and humid conditions on neutrophil degranulation, activation status and band cell count. METHODS On two occasions, in random order and separated by one week, six well trained male cyclists reported to the laboratory at 1230 h following a 4 h fast. Subjects cycled for 2 h on a stationary ergometer at 55% peak power output (186 ± 5 W, mean ± SEM) in an environmental chamber on one occasion (HOT: 29.8°C, 79% RH) and on another occasion (CONTROL: 19.4°C, 68% RH). Venous blood samples were collected at pre, post and 2 h post-exercise. Neutrophil expression of CD11b (a marker of neutrophil activation status) was determined using flow cytometry. Band (immature) neutrophil count was determined microscopically on blood smears. Elastase released from lipopolysaccharide (LPS)-stimulated neutrophils (degranulation) and the plasma cortisol concentration were determined using ELISA. RESULTS The increase in exercising heart rate, rating of perceived exertion and rectal temperature was greater during HOT (P < .05). Plasma cortisol increased post-exercise (P < .01) with no difference between trials. A marked neutrophilia was evident at post-exercise and 2 h post-exercise (P < .01) with no difference between trials. Neutrophil CD11b expression increased post-exercise but this did not reach significance (P < .06). There was no effect of exercise or trial on the percentage of band neutrophils. LPS-stimulated elastase release per neutrophil decreased post-exercise (P < .01) similarly on both trials. CONCLUSION These data suggest that prolonged exercise results in a decrease in neutrophil degranulation that is unaffected by performing the exercise in hot and humid conditions. Also, the decrease in neutrophil degranulation after prolonged exercise is not associated with changes in the percentage of band neutrophils.