Cholinergic bronchospasm with

Bronchial asthma - Atropine and related agents are effective in some patients with cholinergic-mediated bronchospasm. 

The parasympathetic division is the dominant portion of the pulmonary autonomic nervous system in all mammals. Airway smooth muscle is richly supplied with muscarinic receptors and stimulation of M3 receptors results in smooth muscle contraction and bronchoconstriction. Cholinergic stimulation is the primary mechanism of bronchospasm in horses with recurrent airway obstruction (Robinson et al 1996). Parasympathetic innervation can be demonstrated throughout the tracheobronchial tree of the horse but smooth muscle contraction evoked by stimulation of cholinergic nerves is more pronounced in the trachea than in the smaller bronchi. It is expected that parasympathetic blockade with a muscarinic antagonist will have the greatest effect in large, central airways. 

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