Effects of neuraminidase on equine isolated bronchi.

It has been demonstrated in mammals that the airway hyper-responsiveness, which accompanies viral infections, is the result of increased reflex bronchoconstriction due to inhibition of muscarinic prejunctional receptors, which belong to M2 subtypes. Multiple mechanisms account for virus-induced M2 receptor dysfunction. Viral neuraminidase may deglycosylate the M2 receptor, decreasing acetylcholine affinity. Equine influenza remains a common viral respiratory disease of horses worldwide, which results in loss to the equine industry, by decreasing performance, convalescence time and loss of peak performance due to chronic sequelae, such as airway hyper-responsiveness. The purpose of this study was to evaluate the effect of neuraminidase on equine isolated bronchi, assessed in equine bronchial smooth muscle rings, derived from five healthy equine male lungs. A pretreatment with vehicle did not modify contraction induced by electrical field stimulation (EFS) studies at each frequency tested. A pretreatment with pilocarpine (1-100 microM) significantly reduced, while methoctramine (1-100 microM) significantly increased contraction induced by EFS. Finally, neuraminidase (0.5 UI) significantly increased contraction induced by EFS. These results suggest that airway hyper-responsiveness that follows a viral influenza infection might be related to a dysfunction of muscarinic prejunctional receptors.