Cortisol response to exercise and post-exercise suppression of blood lymphocyte subset counts

This study examined a temporal relationship between exercise-induced changes in blood cortisol levels and circulating leukocyte and lymphocyte subset counts during and after exercise. Twenty-one young male, sedentary subjects [mean age, 20.8 +/- 2.4 (SD) yr; mean VO2max, 48.0 +/- 7.9 (SD) ml/kg/min] underwent a cycle ergometer exercise for 60 min at 60% VO2max. Peripheral blood samples, collected every 30 min during exercise and at 30, 60 min, 2.5 and 6 h of recovery, were used for the determination of serum cortisol and plasma catecholamines; lymphocyte subsets were analyzed by flow-cytometry. Based on the analysis of serum cortisol levels in response to exercise, the subjects can be identified as two groups: cortisol-responder (n = 13) and non-responder (n = 8) groups. Other than the cortisol response, the two groups showed no significant differences in terms of age, physical build, aerobic fitness, maximal heart rate, and pre-exercise blood leukocyte and lymphocyte subset counts. The two groups also did not differ significantly in their relative work rate and catecholamine response to the exercise. Both cortisol responder and non-responder groups displayed a granulocytosis, lymphocytosis and monocytosis during exercise, and a further granulocytosis after exercise. Changes in lymphocyte count and distribution during recovery, however, differed significantly between the two groups. In the circulation of the cortisol non-responder group, total lymphocyte counts returned to the baseline level shortly after exercise, whereas a significant lymphopenia occurred at 2.5 h of recovery in the cortisol responder group: the CD4+ cells showed the greatest decrease in cell count, followed by the CD8+ cells. In both groups, the CD16+ cell-counts tended to decline below the pre-exercise values at 30 and 60 min of recovery and returned to the baseline values by 2.5 h of recovery. The CD19+ cell-count was not suppressed in both groups after exercise. These results suggest that exercise-induced secretion of blood cortisol may contribute to post-exercise suppression of the helper- and cytotoxic-T cell counts, but does not seem to be involved in post-exercise changes in the NK-cell and B-cell counts as well as in post-exercise granulocytosis.