Summary
Effects of triamcinolone acetonide (ta) on pulmonary function, bronchoalveolar lavage cytologic features and serum cortisol concentration, were studied in 5 control horses and 5 horses with chronic obstructive pulmonary disease (copd). In experiment 1, horses were brought in from pasture 3 weeks before administration of 1 injection of ta (0.09 mg/kg of body weight, im), and were stabled in dusty conditions throughout the experimental period. Measurements of respiratory rate (f), tidal volume, minute ventilation, expiratory-to-inspiratory time ratio, maximal change in transpulmonary pressure (ΔPL), pulmonary resistance (RL), and dynamic compliance (Cdyn) were obtained during quiet breathing, immediately before (baseline) and 1, 2, 3, 5, and 9 weeks after administration of ta. Pulmonary airway cells were collected by bronchoalveolar lavage while horses were at pasture, at baseline, and 2, 5, and 9 weeks after ta administration. Serum cortisol concentration was measured before and after adrenocortical stimulation with 100 IU of adrenocorticotropic hormone, 1 week prior to ta administration, and 4 and 8 weeks thereafter. In experiment 2, 4 months after ta injection, pulmonary function measurements were repeated in all horses immediately before and 30 minutes after administration of atropine (0.015 mg/kg, iv), to evaluate the reversibility of airway obstruction.
In experiment 1 at baseline, COPD-affected horses had significantly (P < 0.05) higher values than did controls for f, ΔPL, RL, and percentage of neutrophils, and had lower values for Cdyn and percentage of lymphocytes and macrophages. There were significant reductions in ΔPL and RL, and increase in macrophage percentage after ta administration in copd-affected horses only. The degree and duration of these changes varied among individual copd-affected horses, but ΔPL, and RL, values had returned to or were above baseline in all horses 5 weeks after treatment. Baseline cortisol concentration was decreased 4 weeks after ta administration, but the mean increase in cortisol values after adrenocorticotropic hormone stimulation was similar to that observed prior to treatment.
In experiment 2, values of ΔPL, RL, and Cdyn, after atropine administration were similar to those of controls in the 2 copd-affected horses that had improved most after ta, but were only partially improved in the 3 other horses, indicating possible irreversible lesions in the latter.
