Liquiritin apioside attenuates laryngeal chemoreflex but not mechanoreflex in rat pups.

Abstract

Liquiritin apioside (LA), a main flavonoid component of licorice, reportedly suppresses cough responses to inhalation of aerosolized capsaicin [CAP; a stimulant to transient receptor potential vanilloid 1 (TRPV1)] in conscious guinea pigs via acting on peripheral nerves. However, the evidence of LA having a direct effect on airway sensory fibers is lacking. Considering the important role laryngeal chemoreceptors and mechanoreceptors play in triggering apnea and cough, we studied whether LA suppressed the apneic responses to stimulation of these receptors via directly acting on the superior laryngeal nerve (SLN). Intralaryngeal delivery of chemical [CAP, HCl, and distilled water (DW)] and mechanical [an air-pulse (AP)] stimulations was applied in anesthetized rat pups to evoke the apnea. These stimuli were repeated after intralaryngeal LA treatment or peri-SLN LA treatment to determine the direct effect of LA on the SLN. Our results showed that all stimuli triggered an immediate apnea. Intralaryngeal LA treatment significantly attenuated the apneic response to chemical but not mechanical stimulations. The same attenuation was observed after peri-SLN LA treatment. Owing that TRPV1 receptors of laryngeal C fibers are responsible for the CAP-triggered apneas, the LA impact on the activity of laryngeal C neurons retrogradely traced by DiI was subsequently studied using a patch-clamp approach. LA pretreatment significantly altered the electrophysiological kinetics of CAP-induced currents in laryngeal C neurons by reducing their amplitudes, increasing the rise times, and prolonging the decay times. In conclusion, our results, for the first time, reveal that LA suppresses the laryngeal chemoreceptor-mediated apnea by directly acting on the SLN (TRPV1 receptors of laryngeal C fibers).

• Authors: Wan Wei, Xiuping Gao, Lei Zhao, Jianguo Zhuang, Yang Jiao, Fadi Xu
• Journal: American journal of physiology. Lung cellular and molecular physiology (Am J Physiol Lung Cell Mol Physiol) Vol. 318 Issue 1 Pg. L89-L97 (01 01 2020) ISSN: 1522-1504 [Electronic] United States
• PMID: 31617735 (Publication Type: Journal Article, Research Support, N.I.H., Extramural, Research Support, Non-U.S. Gov't)

Chemical References

• Flavanones
• Glucosides
• TRPV Cation Channels
• TRPV1 receptor
• liquiritin

Topics

• Animals
• Apnea (drug therapy, metabolism)
• Cough (drug therapy, metabolism)
• Female
• Flavanones (pharmacology)
• Glucosides (pharmacology)
• Laryngeal Nerves (drug effects, metabolism)
• Larynx (drug effects, metabolism)
• Male
• Nerve Fibers, Unmyelinated (metabolism)
• Neurons (drug effects, metabolism)
• Pregnancy
• Rats
• Rats, Sprague-Dawley
• Reflex (drug effects)
• TRPV Cation Channels (metabolism)