Invited Commentary
Commentary on "Tiotropium in the Treatment of Patients with Asthma"
Abstract
Neural control of the airways occurs almost exclusively through the vagal nerve, and activation of this cholinergic system results in bronchoconstriction and mucus hypersecretion. The primary transmitter, acetylcholine, released from prejunctional parasympathetic synapses, acts upon muscarinic receptors, of which five distinct subtypes have been identified (M1-M5). Three of these subtypes (M1-M3) are present in airway smooth muscle1 and have distinct properties. M1 receptors enhance neurotransmission and potentiate the actions of M3 receptors, which cause bronchoconstriction. Activation of M2 receptors inhibits acetylcholine release; therefore, the inhibition of M2 and M3 receptors has opposing effects. M2 receptors are also present in cardiac muscle. Atropine blocks the muscarinic receptors, resulting in bronchodilation, reduction in airway mucus secretion, tachycardia, urinary retention, and pupillary dilation.This content is limited to qualifying members.
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