Ozone enhances excitabilities of pulmonary C fibers to chemical and mechanical stimuli in anesthetized rats |
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Authors: | Ho, Ching-Yin Lee, Lu-Yuan |
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Abstract: | Acute exposureto ozone (O3) enhances pulmonarychemoreflex response to capsaicin, and an increased sensitivity ofbronchopulmonary C-fiber afferent endings may be involved. The presentstudy was aimed at determining the effect ofO3 on the responses of pulmonary Cfibers to chemical and mechanical stimuli. A total of 31 C fibers werestudied in anesthetized, open-chest, and vagotomized rats. Duringcontrol, right atrial injection of a low dose of capsaicin abruptlyevoked a short and mild burst of discharge [0.77 ± 0.28 impulses (imp)/s, 2-s average]. After acute exposure toO3 (3 parts/million for 30 min),there was no significant change in arterial blood pressure, trachealpressure, or baseline activity of C fibers. However, the stimulatoryeffect of the same dose of capsaicin on these fibers was markedlyenhanced (6.05 ± 0.88 impulses/s;P < 0.01) and prolonged immediatelyafter O3 exposure, and returnedtoward control in 54 ± 6 min. Similarly, the pulmonary C-fiberresponse to injection of a low dose of lactic acid was also elevatedafter O3 exposure. Furthermore,O3 exposure significantly potentiated the C-fiber response to constant-pressure (tracheal pressure = 30 cmH2O) lunginflation (control: 0.19 ± 0.07 imp/s; afterO3: 1.12 ± 0.26 imp/s;P < 0.01). In summary, these results show that the excitabilities of pulmonary C-fiber afferents to lunginflation and injections of chemical stimulants are markedly potentiated after acute exposure toO3, suggesting a possible involvement of these afferents in theO3-induced changes in breathing pattern and chest discomfort in humans. |
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