Marathon running leads to partial exhaustion of ROS-generating capacity in leukocytes.

Purpose: The aim of the present study was to investigate the changes occurring in leukocyte levels of reactive oxygen species (ROS) and total blood plasma antioxidant capacity (TAS) as a result of a marathon/half-marathon race.

Methods: Fourteen men participating in the Oslo Marathon 2000 and 8 women and 8 men participating in the Oslo Half-Marathon 2001 were recruited to the study. Flow cytometry and the ROS-sensitive probe dihydroethidium (DHE) were used to study the intracellular levels of ROS in circulating leukocytes. Both basal ROS levels as well as the capacity of leukocytes to respond with ROS synthesis upon a defined in vitro stimulus, i.e., phorbol myristate acetate (PMA) was assessed before and immediately after the races. TAS was measured using the ABTS+ reduction assay kit.

Results: The basal levels of ROS in leukocytes were either not significantly changed (men, 3-25% reduced) or reduced 33% (women, P < 0.01) as a result of the marathon/half-marathon race. After the marathon race, the capacity of leukocytes to produce ROS upon PMA stimulation was reduced, i.e., 6% (granulocytes) (P < 0.001) and 23% (monocytes) (P < 0.01) residual capacity compared with the prerace situation. A 22-30% reduction (P < 0.05) in monocyte ROS response was seen also as a result of the half-marathon race, whereas the granulocyte ROS response was maintained at the prerace level (19% (women) and 15% (men) reduction, NS)). TAS increased significantly (11-19%, P < 0.05) after both races.

Conclusions: The present results indicate an exhaustion of leukocyte ROS-generating mechanisms after prolonged strenuous exercise. This may partly explain the observation that athletes are more sensitive to attract infectious diseases if exposed to pathogenic micro-organisms during the immediate period after intensive physical activity.