Wiester M J, Tepper J S, Doerfler D L, Costa D L
Environmental Toxicology Division (MD-82), U.S. Environmental Protection Agency, Research Triangle Park, North Carolina 27711.
Fundam Appl Toxicol. 1995 Jan;24(1):42-51. doi: 10.1006/faat.1995.1006.
Studies in both humans and rats have indicated that certain pulmonary responses induced by exposure to an acute provocative concentration of ozone (O3) will eventually attenuate if the exposure is repeated on a daily basis. This phenomenon is commonly referred to as O3 adaptation. Whether or not a "state" of adaptation develops due to long-term low level O3 exposure is unknown. Two human studies have reported adaptation in subjects living in Los Angeles during periods when ambient O3 concentrations have been relatively high. At present, however, we are not aware of comparable information from rats. This study assessed O3 adaptation in rats following chronic (12 or 18 months) exposure and after a 4-month recovery period. A chronic exposure pattern, similar to that found in an urban area during the summer (0.06 ppm O3 for 13 hr/day, 7 days/week; Monday-Friday, peak to 0.25 ppm O3, over 9 hr), was used. To assess whether adaptation had occurred and/or persisted, awake rats were challenged with high provocative concentrations of O3 for up to 2 hr. During a challenge, rats were monitored for typical O3-induced alterations in spontaneous breathing parameters (e.g., increase in breathing frequency and decrease in tidal volume). Adaptation was defined as attenuation of breathing response during the challenge in rats chronically exposed to O3 as compared to that in "control" rats (chronically exposed to air). Adaptation was found in the rats within 8 hr following the chronic O3 exposure but not after the 4-month recovery period. Spontaneous breathing parameters that were significantly attenuated in the chronically exposed rats were breathing frequency, tidal volume, inspiratory and expiratory times, and maximum expiratory flow. We conclude that rats demonstrated adaptation to O3 after long-term exposure to an urban-type O3 profile and that the adaptation was not seen 4 months postexposure. These results suggest that exposure to environmental O3 in Los Angeles air may have been responsible for the adaptation found in residential subjects.
对人类和大鼠的研究均表明，如果每天重复暴露于急性激发浓度的臭氧（O₃），某些由此引发的肺部反应最终会减弱。这种现象通常被称为O₃适应。长期低水平O₃暴露是否会导致“适应状态”尚不清楚。两项人体研究报告称，在洛杉矶环境O₃浓度相对较高的时期，当地居民出现了适应现象。然而，目前我们尚未掌握来自大鼠的类似信息。本研究评估了大鼠在慢性（12或18个月）暴露及4个月恢复期后的O₃适应情况。采用了一种类似于夏季城市地区的慢性暴露模式（每天13小时暴露于0.06 ppm O₃，每周7天；周一至周五，峰值达到0.25 ppm O₃，持续9小时）。为了评估是否发生了适应和/或适应是否持续存在，对清醒的大鼠用高激发浓度的O₃进行长达2小时的激发试验。在激发试验期间，监测大鼠典型的O₃诱导的自发呼吸参数变化（例如呼吸频率增加和潮气量减少）。适应被定义为与“对照”大鼠（长期暴露于空气）相比，长期暴露于O₃的大鼠在激发试验期间呼吸反应减弱。在慢性O₃暴露后8小时内，大鼠出现了适应，但在4个月恢复期后未出现适应。长期暴露的大鼠中显著减弱的自发呼吸参数包括呼吸频率、潮气量、吸气和呼气时间以及最大呼气流量。我们得出结论，大鼠在长期暴露于城市型O₃环境后表现出对O₃的适应，且在暴露后4个月未观察到这种适应。这些结果表明，洛杉矶空气中的环境O₃暴露可能是导致居民出现适应现象的原因。
