Randomized study of the effects of testosterone administration on severity of asthma in horses.
BACKGROUND: Low testosterone concentrations are associated with poor lung function in human asthmatics, and androgen administration improves airway obstruction in women with asthma. HYPOTHESIS/OBJECTIVES: Testosterone improves clinical scores, lung function, airway neutrophilia, and airway remodeling in horses with severe asthma. ANIMALS: Ten horses affected by severe asthma from a research herd. METHODS: In a randomized, blinded, crossover study, horses received dexamethasone (0.06 mg/kg PO q24h for 10 days) or a single intramuscular injection of testosterone cypionate (0.35 mg/kg), with a 2-week washout period. Clinical respiratory scores were assessed at days 0, 2, 5, and 10; lung function was evaluated at days 0, 5, and 10; and bronchoalveolar lavage fluid cytology and central airway remodeling at days 0 and 10. Mixed linear models were used for analysis. RESULTS: The respiratory clinical scores improved with dexamethasone administration (median [95% CI], from 12 (9-13) to 5 (3-6), P < .001), and remained unchanged with testosterone administration (from 10 [8-12] to 9 [8-11], P = .6). Pulmonary elastance improved with both treatments, but the effect was more pronounced with dexamethasone administration (from 5.1 cm H2O/L [2.4-5.8] to 0.5 [0.4-0.8], P < .001) than with testosterone administration (from 4.5 cm H2O/L [1.6-8.5] to 3.0 [1.0-4.1], P = .04). Pleural pressure and pulmonary resistance decreased only with dexamethasone. Neither treatment altered airway neutrophilia or bronchial remodeling. CONCLUSIONS AND CLINICAL IMPORTANCE: Testosterone is less effective than dexamethasone and only mildly improves pulmonary elastance in horses with severe asthma.