Effects of aerosolized albuterol on physiologic responses to exercise in Standardbreds

Objective-To examine the effects of an aerosolized beta (2)-adrenoreceptor agonist, albuterol, on performance during a standardized incremental exerci se test in clinically normal horses. Animals-8 Standardbred pacing mares. Procedure-Clinically normal horses, as judged by use of physical examinatio n, hematologic findings, serum biochemical analysis, and airway endoscopy, were randomly assigned to 2 groups and were given 900 mug of albuterol via a metered-dose inhaler 30 minutes before beginning a standardized increment al exercise test in a crossover design with a 7-day minimum washout. Furthe r examination included measurement of baseline lung mechanics, response to histamine bronchoprovocation, and bronchoalveolar lavage. Results-No significant differences (albuterol vs placebo) were seen for any incremental exercise test variables (i.e, maximum oxygen consumption, maxi mum carbon dioxide consumption, respiratory quotient, treadmill speed at he art rate of 200 beats/min, or number of steps completed during an increment al exercise protocol). Mast cell percentage was significantly (r = -0.84) a ssociated with the concentration of aerosolized histamine that evoked a 100 % increase in total respiratory system resistance. No other direct correlat ions between bronchoalveolar lavage fluid cell types and any indices of exe rcise capacity or airway reactivity were found. Conclusions and Clinical Relevance-Although no horse had exercise intoleran ce, 4 horses had airway hyperreactivity with bronchoalveolar lavage fluid m astocytosis; these horses may have been subclinically affected with inflamm atory airway disease. In our study, albuterol did not enhance performance i n 8 clinically normal racing-fit Standardbreds.