Ozone enhances excitabilities of pulmonary C fibers to chemical and mechanical stimuli in anesthetized rats.
Acute exposure to ozone (O3) enhances pulmonary chemoreflex response to capsaicin, and an increased sensitivity of bronchopulmonary C-fiber afferent endings may be involved. The present study was aimed at determining the effect of O3 on the responses of pulmonary C fibers to chemical and mechanical stimuli. A total of 31 C fibers were studied in anesthetized, open-chest, and vagotomized rats. During control, right atrial injection of a low dose of capsaicin abruptly evoked a short and mild burst of discharge [0.77 +/- 0.28 impulses (imp)/s, 2-s average]. After acute exposure to O3 (3 parts/million for 30 min), there was no significant change in arterial blood pressure, tracheal pressure, or baseline activity of C fibers. However, the stimulatory effect of the same dose of capsaicin on these fibers was markedly enhanced (6.05 +/- 0.88 impulses/s; P < 0.01) and prolonged immediately after O3 exposure, and returned toward control in 54 +/- 6 min. Similarly, the pulmonary C-fiber response to injection of a low dose of lactic acid was also elevated after O3 exposure. Furthermore, O3 exposure significantly potentiated the C-fiber response to constant-pressure (tracheal pressure = 30 cmH2O) lung inflation (control: 0.19 +/- 0.07 imp/s; after O3: 1.12 +/- 0.26 imp/s; P < 0.01). In summary, these results show that the excitabilities of pulmonary C-fiber afferents to lung inflation and injections of chemical stimulants are markedly potentiated after acute exposure to O3, suggesting a possible involvement of these afferents in the O3-induced changes in breathing pattern and chest discomfort in humans.
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Department of Physiology, University of Kentucky, Lexington, Kentucky 40536, USA.
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D000344:Afferent Pathways / Q000187:drug effects / Q000502:physiology; D000704:Analysis of Variance; D000818:Animals; D002211:Capsaicin / Q000494:pharmacology*; D005071:Evoked Potentials / Q000187:drug effects; D019344:Lactic Acid / Q000494:pharmacology; D008168:Lung / Q000187:drug effects / Q000294:innervation / Q000502:physiology*; D008297:Male; D009412:Nerve Fibers / Q000187:drug effects / Q000502:physiology*; D009431:Neural Conduction / Q000187:drug effects / Q000502:physiology; D010126:Ozone / Q000494:pharmacology*; D010812:Physical Stimulation; D051381:Rats; D017207:Rats, Sprague-Dawley; D014132:Trachea / Q000502:physiology; D014628:Vagotomy; D014630:Vagus Nerve / Q000502:physiology*
D019344:Lactic Acid; D010126:Ozone; D002211:Capsaicin