title: H1-receptor antagonist, tripelennamine, does not affect arterial hypoxemia in exercising Thoroughbreds.
abstract: It has been suggested that pulmonary injury and inflammation-induced histamine release from airway mast cells may contribute to exercise-induced arterial hypoxemia (EIAH). Because stress failure of pulmonary capillaries and EIAH are routinely observed in exercising horses, we examined whether preexercise administration of an H1-receptor antagonist may mitigate EIAH. Two sets of experiments, placebo (saline) and antihistaminic (tripelennamine HCl at 1.10 mg/kg iv, 15 min preexercise) studies, were carried out on seven healthy, exercise-trained Thoroughbred horses in random order 7 days apart. Arterial and mixed venous blood-gas and pH measurements were made at rest before and after saline or drug administration and during incremental exercise leading to maximal exertion at 14 m/s on 3.5% uphill grade for 120 s. Galloping at this workload elicited maximal heart rate and induced exercise-induced pulmonary hemorrhage in all horses in both treatments, thereby indicating that capillary stress failure-related pulmonary injury had occurred. In both treatments, EIAH, desaturation of hemoglobin, hypercapnia, and acidosis of a similar magnitude developed during maximal exertion, and statistically significant differences between the placebo and antihistaminic studies could not be demonstrated. The failure of the H1-receptor antagonist to modify EIAH significantly suggests that pulmonary injury-induced histamine release may not play a major role in bringing about EIAH in Thoroughbred horses.
authors.affiliation: Department of Veterinary Biosciences, College of Veterinary Medicine, University of Illinois at Urbana-Champaign, Urbana, Illinois 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: Sarah
authors.initials: S
authors.lastname: Humphrey
authors.forename: Tracy
authors.initials: T
authors.lastname: Depuy
mesh_terms: D000818:Animals; D001158:Arteries; D001831:Body Temperature; D002245:Carbon Dioxide / Q000097:blood; D004724:Endoscopy; D005260:Female; D006634:Histamine H1 Antagonists / Q000494:pharmacology*; D006736:Horses; D000860:Hypoxia / Q000175:diagnosis / Q000188:drug therapy* / Q000517:prevention & control; D007275:Injections, Intravenous; D008297:Male; D008407:Mast Cells / Q000187:drug effects / Q000502:physiology; D010100:Oxygen / Q000097:blood; D010108:Oxyhemoglobins / Q000378:metabolism; D010313:Partial Pressure; D005082:Physical Exertion / Q000502:physiology*; D014309:Tripelennamine / Q000494:pharmacology*; D014680:Veins
chemical_list: D006634:Histamine H1 Antagonists; D010108:Oxyhemoglobins; D002245:Carbon Dioxide; D014309:Tripelennamine; D010100:Oxygen