Randomized study of the effects of testosterone administration on severity of asthma in horses.

Low testosterone concentrations are associated with poor lung function in human asthmatics, and androgen administration improves airway obstruction in women with asthma. Testosterone improves clinical scores, lung function, airway neutrophilia, and airway remodeling in horses with severe asthma. Ten horses affected by severe asthma from a research herd. 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. 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. Testosterone is less effective than dexamethasone and only mildly improves pulmonary elastance in horses with severe asthma.