The Effect of Substance P on Nasal Mucosal Hypersensitivity through Sensory Nerve Axonal Reflex

ABSTRACT

The mucus secretion of airway glands is known to be controlled by the various autonomic neurotransmitters such as noradrenalin and acetylcholine. However, a recent study suggests that non-adrenergic, non-cholinergic (NANC) nerves may contribute to the secretory activity of glands. Substance P (SP) has been proposed as a neurotransmitter of the NANC nervous system. SP is present within nerve fibers innervating the airway mucosa and is known to be released from sensory nerves via an axonal reflex. SP activity is controlled by neutral endopeptidase (NEP) which degrades SP. In this study, we evaluated the effects of NEP inhibitor (thiorphan) and substance P on nasal mucosa and histamine on the nasal mucosa in healthy males. In the thiorphan-substance P experimental group, the nasal volume decreased after nebulization of substance P in proportion to the concentration of histamine. In the thiorphan-substance P experimental group, the frequency of sneezing increased in proportion to the concentration of histamine, but there was no increased frequency of sneezing from thiorphan, SP and normal saline. The results of this study suggest that axonal reflexes can play a role in the pathogenesis of nasal mucosal hypersensitivity and neurogenic inflammation.