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Episodic ozone exposure in adult and Senescent Brown Norway rats: Acute and delayed cardiovascular and thermoregulatory responses
Citation:
Gordon, C., A. Johnstone, C. Aydin, P. Phillips, R. MacPhail, U. Kodavanti, A. Ledbetter, AND K. Jarema. Episodic ozone exposure in adult and Senescent Brown Norway rats: Acute and delayed cardiovascular and thermoregulatory responses. INHALATION TOXICOLOGY. Informa Healthcare USA, New York, NY, 26(7):380-90, (2014).
Impact/Purpose:
The senescent and aged are considered to be more susceptible to air pollutants; however, the animal models developed to study the sensitivity of the aged to environmental toxicants are sparse. We utilized radiotelemetry to assess the effects of ozone, a common air pollutant, on the cardiovascular and thermoregulatory function in mature adult and senescent rats. A unique model of episodic exposure to ozone was developed where rats were exposed for two consecutive days per week. Younger rats showed a protective hypothermic response to ozone and more profound inflammatory responses suggesting greater physiological sensitivity compared to senescent animals. Further development of senescent animal models of aging are needed to improve the translation from animal to human studies and better address how the aged may be more susceptible to air pollution
Description:
Setting exposure standards for environmental pollutants may consider the aged as a susceptible population but the few published studies assessing susceptibility of the aged to air pollutants are inconsistent. Episodic ozone (O(3)) is more reflective of potential exposures occurring in human populations and could be more harmful to the aged. This study used radiotelemetry to monitor heart rate (HR), core temperature (T(c)) and motor activity (MA) in adult (9-12 months) and senescent (20-24 months) male, Brown Norway rats exposed to episodic O(3) (6 h/day of 1 ppm O(3) for 2 consecutive days/week for 13 weeks). Acute O(3) initially led to marked drops in HR and T(c). As exposures progressed each week, there was diminution in the hypothermic and bradycardic effects of O(3). Senescent rats were less affected than adults. Acute responses were exacerbated on the second day of O(3) exposure with adults exhibiting greater sensitivity. During recovery following 2 d of O(3), adult and senescent rats exhibited an elevated T(c) and HR during the day but not at night, an effect that persisted for at least 48 h after O(3) exposure. MA was elevated in adults but not senescent rats during recovery from O(3). Overall, acute effects of O(3), including reductions in HR and T(c), were attenuated in senescent rats. Autonomic responses during recovery, included an elevation in T(c) with a pattern akin to that of a fever and rise in HR that were independent of age. An attenuated inflammatory response to O(3) in senescent rats may explain the relatively heightened physiological response to O(3) in younger rats.