Abstract   

    The efficacy of atropine to attenuate Ascaris suum induced bronchospasm was studied in 6 conscious standing horses. Animals were challenged with saline and a 10-2 dilution of A. suum aerosolized for 3 minutes. Pulmonary function tests (PFT) were performed at 15, 30 and 60 minutes after antigen challenge. Pulmonary mechanics and ventilation values were measured using a differential pressure transducer and a Fleisch Pnemotachograph. One week later, animals were treated with atropine sulfate (6.0 mg administered IM) and rechallenged with saline followed by same dose of A. suum. Clinical signs noted after the inhalation of A suum alone included hyperpnea, dyspnea, sweating and salivation. The effect of antigen was rapid in onset starting during the inhalation and lasting for over 60 minutes. The PFT revealed significant (P<0.05) increases in W_b, max. r P_pl R_L, V₁, f, and V_T whereas the C_dyn decreased (P<0.05). The changes were more severe in lower airways. Atropine abolished the clinical signs. Comparison of post atropine saline and A. suum challenge values revealed significant increase in W_b, max. r P_pl at 15 minutes post antigen challenge. Changes in R_L, f and C_dyn were abolished. Comparison of responses to A. suum in the presence and absence of atropine revealed a significant (P<0.05) inhibition of changes in max. P_pl, W_b, inspiratory and expiratory R_L, V_I, f and flow. The study suggested that the A. suum induced bronchospasm in the horses is mediated, at least in part by vagal reflexes.    

Key words: Equine COPD; antigenic bronshospasm, atropine.