Abstract
Ozone (O3) is toxic to respiratory epithelium and causes airway inflammation and hyperreactivity. To evaluate the role of the epithelium in the development of hyperreactivity, we examined in guinea pigs the effects of inhaled O3 (3 ppm for 1 h; 0–24 h after exposure) on 1) reactivity to inhaled methacholine (MCh), 2) reactivity of the isolated, perfused trachea (IPT) to MCh, 3) epithelium-derived relaxing factor (EpDRF)-mediated relaxations of IPT induced by mucosal hyperosmolar solutions, 4) neurogenic contraction and relaxation responses, 5) transepithelial potential difference, and 6) microscopic analysis of nitrotyrosine immunofluorescence, substance P fiber density, and tracheal morphology. At 0 h, O3caused hyperreactivity to inhaled MCh and mucosally but not serosally applied MCh in IPT (only in the presence of the epithelium) and a decrease in transepithelial potential difference. Inhibition of EpDRF-induced relaxation responses occurred at 2 h. All of these changes returned to control by 12 to 18 h. O3 had no effect on neurogenic responses. Nitrotyrosine immunofluorescence appeared in the trachea at 0 h in detached epithelial cell ghosts and in intrapulmonary airways by 6 h. Substance P fiber density was elevated in smooth muscle at 0 and 18 h but not in epithelium or lamina propria of intrapulmonary and extrapulmonary bronchi. Loss of cilia and mucosubstances in the mucosa occurred at 0 h; the epithelium became markedly attenuated over 12 to 24 h. A reversible increase in epithelial permeability and a decrease in EpDRF production may contribute to O3-induced hyperreactivity to MCh.
Footnotes
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Send reprint requests to: Dr. Jeffrey S. Fedan, Health Effects Laboratory Division, National Institute for Occupational Safety and Health, 1095 Willowdale Rd., Morgantown, WV 26505. E-mail:jsf2{at}cdc.gov
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↵1 Mention of a brand name does not constitute product endorsement.
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↵2 The IL/EL maximum response ratio is an index of the modulatory effect of the epithelium on the maximum contractile responses (Fedan and Frazer, 1992). The ratio is unity in the absence of epithelium and less than unity in the presence of the epithelium. The greater the inhibitory effect of the epithelium, the smaller is the value of the ratio.
- Abbreviations:
- MCh
- methacholine
- EpDRF
- epithelium-derived relaxing factor
- MKH
- modified Krebs-Henseleit
- PMN
- polymorphonuclear leukocyte
- IL
- intraluminal
- EL
- extraluminal
- VT
- transepithelial potential difference
- EFS
- electric field stimulation
- Received September 27, 1999.
- Accepted February 18, 2000.
- U.S. Government
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