Irritant-evoked reflex tachyarrhythmia in spontaneously hypertensive rats is reduced by inhalation of TRPM8 agonists l-menthol and WS-12

Abstract

Inhalation of noxious irritants activates nociceptive sensory afferent nerves innervating the airways, inducing reflex regulation of autonomic networks and the modulation of respiratory drive and cardiovascular (CV) parameters such as heart rate and blood pressure. In healthy mammals, irritant-evoked pulmonary-cardiac reflexes cause parasympathetic-mediated bradycardia. However, in spontaneously hypertensive (SH) rats, irritant inhalation also increases sympathetic drive to the heart. This remodeled pulmonary-cardiac reflex may contribute to cardiovascular risk caused by inhalation of air pollutants/irritants in susceptible individuals with cardiovascular disease (CVD). Previous studies have shown that the cooling mimic l-menthol, an agonist for the cold-sensitive transient receptor potential melastatin 8 (TRPM8), can alleviate nasal inflammatory symptoms and respiratory reflexes evoked by irritants. Here, we investigated the impact of inhalation of TRPM8 agonists l-menthol and WS-12 on pulmonary-cardiac reflexes evoked by inhalation of the irritant allyl isothiocyanate (AITC) using radiotelemetry. l-Menthol, but not its inactive analog d-menthol, significantly reduced the AITC-evoked reflex tachycardia and premature ventricular contractions (PVCs) in SH rats but had no effect on the AITC-evoked bradycardia in either SH or normotensive Wistar-Kyoto (WKY) rats. WS-12 reduced AITC-evoked tachycardia and PVCs in SH rats, but this more potent TRPM8 agonist also reduced AITC-evoked bradycardia. l-Menthol had no effect on heart rate when given alone, whereas WS-12 evoked a minor bradycardia in WKY rats. We conclude that stimulation of TRPM8-expressing afferents within the airways reduces irritant-evoked pulmonary-cardiac reflexes, especially the aberrant reflex tachyarrhythmia in SH rats. Airway menthol treatment may be an effective therapy for reducing pollution-associated CV exacerbations.NEW & NOTEWORTHY Irritant-evoked pulmonary-cardiac reflexes are remodeled in spontaneously hypertensive (SH) rats-causing de novo sympathetic reflexes that drive tachyarrhythmia. This remodeling may contribute to air pollution-associated risk in susceptible individuals with cardiovascular disease. We found that inhalation of TRPM8 agonists, l-menthol and WS-12, but not the inactive analog d-menthol, selectively reduces the reflex tachyarrhythmia evoked by allyl isothiocyanate (AITC) inhalation in SH rats. Use of menthol may protect susceptible individuals from pollution-associated CV exacerbations.

Keywords: TRPM8; arrhythmia; autonomic reflex; irritants; vagal sensory nerves.

Graphical abstract

Figure 1.

Representative ECG during allyl isothiocyanate (AITC), menthol, and WS-12 inhalation in conscious rats. A: Wistar–Kyoto (WKY) rats. B: spontaneously hypertensive (SH) rats. Red circle denotes a tachycardic beat. Blue square denotes a premature ventricular contraction (PVC). Scale bar denotes 1 s.

Figure 2.

Effect of menthol on allyl isothiocyanate (AITC)-evoked reflex modulation of heart rate parameters in conscious Wistar–Kyoto (WKY) and spontaneously hypertensive (SH) rats. A, C, and E: means ± SE of R-R interval (RRi) (A), percentage of tachycardic beats (C), and PVCs (E) during inhalation of vehicle (“Veh”, circles) and AITC (squares) without (“-”, gray symbols) or with l-menthol (“L”, blue symbols) or d-menthol (“D”, green symbols) in WKY rats (n = 7 or 8, left) and SH rats (n = 8–16, right). *Significant effect of AITC compared with vehicle (P < 0.05). B, D, and F: means ± SE of the difference (Δ) between vehicle- and AITC-evoked RRi (B), percentage of tachycardic beats (D), and PVCs (F) without (“-”, gray squares) or with l-menthol (“L”, blue squares) or d-menthol (“D”, green squares) inhalation in WKY rats (n = 7 or 8, left) and SH rats (n = 8–16, right). $Significant difference between WKY and SH rats (P < 0.05). #Significant difference between without and with menthol (P < 0.05). n refers to number of animals tested per group. Statistical analyses: ANOVA (A–D); Kruskal-Wallis test (E and F).

Figure 3.

Effect of WS-12 on allyl isothiocyanate (AITC)-evoked reflex modulation of heart rate parameters in conscious Wistar–Kyoto (WKY) and spontaneously hypertensive (SH) rats. A, C, and E: means ± SE of R-R interval (RRi) (A), percentage of tachycardic beats (C), and premature ventricular contractions (PVCs) (E) during inhalation of vehicle (“Veh,” circles) and AITC (squares) without (gray symbols) or with WS-12 (orange symbols) in WKY rats (n = 8 or 9, left) and SH rats (n = 8 or 9, right). *Significant effect of AITC compared with vehicle (P < 0.05). &Significant effect of WS-12 compared with vehicle (P < 0.05). B, D, and F: means ± SE of the difference (Δ) between vehicle- and AITC-evoked RRi (B), percentage of tachycardic beats (D), and PVCs (F) without (gray squares) or with WS-12 (orange symbols) inhalation in WKY rats (n = 8 or 9, left) and SH rats (n = 8 or 9, right). $Significant difference between WKY and SH rats (P < 0.05). #Significant difference between without and with WS-12 (P < 0.05). n refers to number of animals tested per group. Statistical analyses: ANOVA (A–D); Kruskal-Wallis test (E and F).