title: Anti-inflammatory agent, dexamethasone, does not affect exercise-induced arterial hypoxemia in Thoroughbreds.
abstract: In view of the suggestion that pulmonary injury-induced release of histamine and/or other chemical mediators from airway inflammatory and mast cells contribute to the exercise-induced arterial hypoxemia (EIAH) in human athletes, we examined the effects of pretreatment with a potent anti-inflammatory agent, dexamethasone, on EIAH and desaturation of hemoglobin in horses. Seven healthy, sound, exercise-trained Thoroughbreds were studied in the control (no medications) experiments, followed in 7 days by intravenous dexamethasone (0.11 mg.kg(-1).day(-1) for 3 consecutive days) studies. Blood-gas measurements were made at rest and during incremental exercise leading to maximal exertion at 14 m/s on a 3.5% uphill grade. Galloping at this workload induced pulmonary hemorrhage in all horses in both treatments, thereby indicating that stress failure of pulmonary capillaries had occurred. In both treatments, significant EIAH, desaturation of hemoglobin, hypercapnia, acidosis, and hyperthermia developed during maximal exercise, but significant differences between the control and dexamethasone treatments were not discerned. The failure of pretreatment with dexamethasone to significantly affect EIAH suggests that pulmonary injury-evoked airway inflammatory response may not play a major role in EIAH in racehorses. However, our observations in both treatments that EIAH developed quickly (being evident at 30 s of exertion) and that its severity remained unaffected by increasing exercise duration (to 120 s) suggest that EIAH has a functional basis, probably related to significant shortening of the transit time for blood in the pulmonary capillaries as cardiac output increases dramatically.
authors.affiliation: Department of Veterinary Biosciences, College of Veterinary Medicine, University of Illinois at Urbana-Champaign, 61801, USA. mmanohar@uiuc.edu
authors.forename: Murli
authors.initials: M
authors.lastname: Manohar
authors.forename: Thomas E
authors.initials: TE
authors.lastname: Goetz
authors.forename: Aslam S
authors.initials: AS
authors.lastname: Hassan
authors.forename: Tracy
authors.initials: T
authors.lastname: Depuy
authors.forename: Sarah
authors.initials: S
authors.lastname: Humphrey
mesh_terms: D000818:Animals; D000893:Anti-Inflammatory Agents / Q000494:pharmacology*; D001784:Blood Gas Analysis; D002245:Carbon Dioxide / Q000097:blood; D003907:Dexamethasone / Q000494:pharmacology*; D005260:Female; D006339:Heart Rate / Q000187:drug effects / Q000502:physiology; D006454:Hemoglobins / Q000378:metabolism; D006736:Horses / Q000502:physiology*; D006863:Hydrogen-Ion Concentration; D000860:Hypoxia / Q000097:blood*; D019344:Lactic Acid / Q000097:blood; D007828:Laryngoscopy; D008297:Male; D010100:Oxygen / Q000097:blood; D010101:Oxygen Consumption / Q000502:physiology; D010805:Physical Conditioning, Animal / Q000502:physiology; D005082:Physical Exertion / Q000502:physiology*; D014132:Trachea / Q000502:physiology
chemical_list: D000893:Anti-Inflammatory Agents; D006454:Hemoglobins; D002245:Carbon Dioxide; D019344:Lactic Acid; D003907:Dexamethasone; D010100:Oxygen