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 degree s C; two tests included 40-min of cycle ergometer exercise at 65% of a erobic power. When the subjects were exercising, rectal temperature pe aked at 39.1 +/- 0.4 degrees C in the warm water and 37.8 +/- 0.3 degr ees C in the cool water. When the subjects were sitting in warm water, rectal temperature closely matched the core temperature during exerci se in cool water, whereas when they were sitting in cool water, rectal temperatures decreased to 36.4 +/- 0.6 degrees C. Total and different ial white cell counts were determined by using a Coulter counter, and cortisol and growth hormone concentrations were determined by radioimm unoassay; all data were adjusted for changes of blood and plasma volum es. Heat clamping during exercise substantially reduced the rise in wh ite cell, lymphocyte, and granulocyte counts but not the increase in m onocyte count. Clamping also abolished previously observed association s between cell counts and cortisol and weakened associations with grow th 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 t emperature contribute to the changes in white cell and subset counts d uring and immediately after moderate exercise. Both cortisol and growt h hormone concentrations appear to be mediators of these responses.