Anticholinergics bronchoconstriction inhibition

Being an anticholinergic, ipratropium interrupts the parasympathetic activities including the blocking of muscarinic receptors in the lung, resulting in an inhibition of bronchoconstriction and of mucus secretion. 

When given by inhalation, anticholinergics snch as ipratropinm or atropine produce bronchodilation by competitively inhibiting cholinergic receptors in bronchial smooth muscle. This activity blocks acetylcholine, with the net effect being a reduction in cyclic gnanosine monophosphate (cGMP), which normally acts to constrict bronchial smooth muscle. Muscarinic receptors on airway smooth muscle include Ml, M2, and M3 subtypes. Activation of Mi and M3 receptors by acetylcholine results in bronchoconstriction however, activation of M2 receptors inhibits further acetylcholine release. 

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