Production of reactive oxygen species in neutrophils after repeated bouts of exercise in standardbred trotters.

The research paper investigates how repeated bouts of exercise affect the production of reactive oxygen species in neutrophils, a type of immune cell, in trained standardbred trotters (a breed of horse). The study suggests that the neutrophil to lymphocyte ratio (N:L ratio) is a sensitive stress indicator in these horses, with an attenuated N:L response indicating adaption to exercise stress.

Research Design and Execution

• The study involved six trained Standardbred trotters, which exercised on a racetrack on two separate days, separated by a three-day interval.
• On both exercise days, each horse performed three different bouts of exercise with increasing intensity, each bout separated by a 60-minute interval.

Observations and Results

• The researchers monitored for signs of exercise-induced stress, which included leucocytosis (an increase in white blood cells), an increase in the neutrophil to lymphocyte (N:L) ratio, and increased capacity to produce reactive oxygen species in the peripheral blood, an indicator was the increase in whole blood chemiluminescence.
• The leucocytosis was mainly due to neutrophilia (an increase in neutrophils), which lasted for 6 hours.
• The production of reactive oxygen species per single neutrophil did not change significantly during a day of exercise, but was lower on the second exercise day.

Indicators of Stress and Adaptation to Exercise Stress

• Two primary indicators were used by the researchers – cortisol concentrations and the N:L ratio.
• Despite expectations, cortisol levels did not see a significant change after exercise. This is interesting as cortisol is often associated with stress responses in the body.
• On the other hand, the N:L ratio increased, indicating a potential stress response in the horses. In the context of this study, an increase in the N:L ratio is attributed to the production of reactive oxygen species in neutrophils, indicating a stress response to exercise.
• The researchers suggest that in trained horses, the N:L ratio is a sensitive indicator of stress of short duration.
• Interestingly, they also observed that an attenuated (reduced) N:L response could be taken as an indicator of adaptation to exercise stress. This implies that exercising regularly may help the horses better manage and mitigate the stress associated with exercise.