We examined the hypothesis that the short, intensive exercise-induced increase in circulating neutrophil counts is affected by the interaction between the endocrine and immune systems. Twelve male winter-sports athletes underwent a maximal exercise test on a treadmill. Blood samples were collected before, immediately after (Post), and 1 h (Post 1 h) and 2 h (Post 2 h) after the exercise. The neutrophil counts increased significantly at Post 1 h (P < 0.05) and remained significantly high even at Post 2 h (P < 0.05), showing a leftward shift. Plasma granulocyte colony-stimulating factor (G-CSF) increased at Post (P < 0.05), and interleukin-6 (IL-6) increased at Post 1 h (P < 0.05). Plasma G-CSF at Post significantly correlated with the numbers of both neutrophils and stab cells at Post 1 h (P < 0.05). Plasma IL-6 at Post 1 h levels also correlated significantly with the number of neutrophils at Post 2 h (P < 0.05). The increase in the levels of plasma G-CSF and IL-6 after intensive exercise may play a role in the mobilization of neutrophils into the circulatory system.
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