Endurance exercise with and without a thermal clamp: effects on leukocytes and leukocyte subsets.

To test how leukocyte responses to endurance exercise were modified by clamping body temperature, nine men (27.3 +/- 6.0 yr) completed four 80-min immersions to midchest at water temperatures of 23 or 39 degrees C; two tests included 40-min of cycle ergometer exercise at 65% of aerobic power. When the subjects were exercising, rectal temperature peaked at 39.1 +/- 0.4 degrees C in the warm water and 37.8 +/- 0.3 degrees C in the cool water. When the subjects were sitting in warm water, rectal temperature closely matched the core temperature during exercise in cool water, whereas when they were sitting in cool water, rectal temperatures decreased to 36.4 +/- 0.6 degrees C. Total and differential white cell counts were determined by using a Coulter counter, and cortisol and growth hormone concentrations were determined by radioimmunoassay; all data were adjusted for changes of blood and plasma volumes. Heat clamping during exercise substantially reduced the rise in white cell, lymphocyte, and granulocyte counts but not the increase in monocyte count. Clamping also abolished previously observed associations between cell counts and cortisol and weakened associations with growth hormone concentrations (D. A. McCarthy and M. M. Dale. Sports Med. 6: 333-363, 1988). We conclude that both exercise and a rise of core temperature contribute to the changes in white cell and subset counts during and immediately after moderate exercise. Both cortisol and growth hormone concentrations appear to be mediators of these responses.