Hypersensitivity of vagal pulmonary C-fibers induced by increasing airway temperature in ovalbumin-sensitized rats.
Our recent study has shown that hyperventilation of humidified warm air (HWA) triggered cough and reflex bronchoconstriction in patients with mild asthma. We suggested that a sensitizing effect on bronchopulmonary C-fibers by increasing airway temperature was involved, but direct evidence was lacking. This study was carried out to test the hypothesis that HWA enhances the pulmonary C-fiber sensitivity in Brown-Norway rats sensitized with ovalbumin (Ova). In anesthetized rats, isocapnic hyperventilation of HWA for 3 min rapidly elevated airway temperature to a steady state of 41.7°C. Immediately after the HWA challenge, the baseline fiber activity (FA) of pulmonary C-fibers was markedly elevated in sensitized rats, but not in control rats. Furthermore, the response of pulmonary C-fibers to right atrial injection of capsaicin in sensitized rats was significantly higher than control rats before the HWA challenge, and the response to capsaicin was further amplified after HWA in sensitized rats (ΔFA = 4.51 ± 1.02 imp/s before, and 9.26 ± 1.74 imp/s after the HWA challenge). A similar pattern of the HWA-induced potentiation of the FA response to phenylbiguanide, another chemical stimulant of C-fibers, was also found in sensitized rats. These results clearly demonstrated that increasing airway temperature significantly elevated both the baseline activity and responses to chemical stimuli of pulmonary C-fibers in Ova-sensitized rats. In conclusion, this study supports the hypothesis that the increased excitability of these afferents may have contributed to the cough and reflex bronchoconstriction evoked by hyperventilation of HWA in patients with asthma.
Departments of Physiology and.
Yu-Jung
YJ
Lin
Departments of Physiology and.
Ruei-Lung
RL
Lin
Internal Medicine, University of Kentucky Medical Center, Lexington, Kentucky.
Mehdi
M
Khosravi
Departments of Physiology and lylee@uky.edu.
Lu-Yuan
LY
Lee
D000818:Animals; D006358:Hot Temperature; D006813:Humidity; D008168:Lung / Q000294:innervation*; D008297:Male; D010047:Ovalbumin / Q000276:immunology*; D011897:Random Allocation; D051381:Rats; D012130:Respiratory Hypersensitivity / Q000139:chemically induced*; D014630:Vagus Nerve / Q000187:drug effects*
D010047:Ovalbumin
TRPV1; airway inflammation; asthma; bronchoconstriction; cough