Role of the Sympathetic Nervous System and Endogenous Catecholamines in the Regulation of Airways Smooth Muscle Tone

Expression of tyrosine hydroxylase and neuropeptide tyrosine in mouse sympathetic airway‐specific neurons under normal situation and allergic airway inflammation

“…This has previously been suggested for the guinea‐pigs [21, 25] Although there is a high density of NPY‐ and TH‐immunoreactive nerve fibres in small arteries and glands in the nasal mucosa and lower airways of most species, there is little functional evidence for a dense adrenergic innervation of human airway smooth muscles [26] In this respect, the neural bronchodilator mechanism in human and guinea‐pig airways is known to be mediated by inhibitory NANC (i‐NANC) nerves that can release NO to mediate bronchodilatation in central and peripheral airways [3–5] Catecholamines are known as potent vasoconstrictors and may therefore control pulmonary and bronchial blood flow [7, 27–29] It is difficult to study the effects of catecholamines on the airways because hormonal and neuronal effects of these classical neurotransmitters cannot be discriminated easily. This difficulty in discriminating hormonal from neuronal effects has therefore contributed to the poor understanding of the functional role of these airway nerves [30] The high expression of NPY in noradrenergic neurons and nerve fibre varicosities in many mammalian species including humans, cat, guinea‐pig and rat suggests that NPY and NA may have similar effects on airway functions [27, 31, 32] In this respect, NPY is known to be co‐localized with NA in sympathetic–adrenergic nerves and is also a potent vasoconstrictor. NPY acts on its receptors that have been cloned and identified as Y1, Y2 and Y5 receptor subtypes and that are present in human and mouse airways [33–37]…”

“…It is difficult to study the effects of catecholamines on the airways because hormonal and neuronal effects of these classical neurotransmitters cannot be discriminated easily. This difficulty in discriminating hormonal from neuronal effects has therefore contributed to the poor understanding of the functional role of these airway nerves [30]. The high expression of NPY in noradrenergic neurons and nerve fibre varicosities in many mammalian species including humans, cat, guinea-pig and rat suggests that NPY and NA may have similar effects on airway functions [27,31,32].…”

Physiology of Airway Smooth Muscle Contraction: An Overview

“…Opposite to cholinergic stimulation, adrenergic stimulation relaxes airways. Though adrenergic innervation of ASM in weak in humans, β2-adrenoceptors are largely expressed in ASM [17,18]. Additionally, adrenergic fibers may target parasympathetic ganglia, allowing an indirect adrenergic control of airway stimulation [13,19].…”