Cholinergic and noncholinergic parasympathetic control of airway smooth muscle

In mammals, including humans, drugs that block cholinergic muscarinic receptors cause significant and, in some cases, near maximal bronchodilation [1-3]. Moreover, in animal studies, the bronchodilating effect of the anticholinergic drugs can be mimicked by sectioning the right and left vagus nerves [4,5]. Considered together, these observations support the hypothesis that the parasympathetic branch of the autonomic nervous system is the major regulator of mammalian airway smooth muscle tone.