Anti-inflammatory agent, dexamethasone, does not affect exercise-induced arterial hypoxemia in Thoroughbreds.

This study investigated whether the anti-inflammatory drug, dexamethasone, influences exercise-induced low blood oxygen levels in racehorses. The researchers found that the drug had no significant effect, suggesting that inflammation might not be a major factor in such conditions.

Objective of the Study

• The research aimed to study whether an anti-inflammatory agent, dexamethasone, has any impact on exercise-induced low oxygen levels in the blood (EIAH) and decrease in oxygen-carrying capacity of the blood (hemoglobin desaturation) in Thoroughbred horses.
• The research was carried out in response to suggestions that EIAH in human athletes could be in part due to the release of histamine or other chemicals from inflammatory cells in the airway following injury to the lungs.

Methodology and Results

• Seven healthy, exercise-trained Thoroughbred horses underwent testing. The tests were performed twice, once without medication, then after a week with the administration of intravenous dexamethasone for three days consecutively.
• The exercise regimen involved incremental intensification leading to maximal exertion, resulting in significant EIAH, hemoglobin desaturation, hypercapnia, acidosis and hyperthermia under both conditions—with and without dexamethasone pretreatment.
• Interestingly, all horses experienced pulmonary hemorrhage during high intensity exercise, indicating that the stress had caused failure of the lung capillaries. This occurred despite dexamethasone treatment.
• However, no significant difference between the control (no dexamethasone) and dexamethasone treatments were observed in terms of EIAH, suggesting dexamethasone has no significant effect on EIAH in Thoroughbreds.

Conclusions and Implications

• The study concluded that the treatment with dexamethasone did not have a noticeable impact on EIAH, suggesting that the inflammation caused by injury to the lung airways might not play a major role in low oxygen levels in the blood experienced by racehorses during exercise.
• However, it was noted that EIAH developed quickly (evident within 30 seconds of exertion), and its severity was not affected by the duration of exercise. This suggests that EIAH likely has a functional basis—possibly associated with the brief transit time for blood in lung capillaries as the heart rate increases dramatically during exercise.
• The findings shed some light on origins of EIAH in racehorses. However, because the study results suggest a functional rather than inflammatory basis for EIAH, further research into managing and preventing EIAH in racehorses is required.