Age-Related Changes in Cardiac and Respiratory Adaptation to Acute Ozone and Carbon Black Exposures. Interstrain Variation in Mice

ALI HAMADE (1), Richard Rabold (2), Clarke Tankersley (2)

(1) Gradient, Cambridge, MA, (2) Johns Hopkins University, Baltimore, MD

     Abstract Number: 72
     Last modified: October 15, 2009

Abstract
Epidemiological studies show positive associations between increases in ambient air pollutant levels and adverse cardiac and pulmonary health effects. These studies suggest that the elderly and those with certain genetic polymorphisms are susceptible to adverse air pollution-associated health events. We hypothesize that the responses to air pollutants vary with age and are genetically influenced. We exposed mice from three inbred strains [C57BL/6J, B6; C3H/HeJ, HeJ; C3H/HeOuJ, OuJ] to ozone and CB at two different ages, [5, 12 months], for 3 consecutive days to either filtered air (FA), carbon black particles (CB), or ozone (O3) and CB sequentially (O3CB) [target concentrations: CB, 550 µg/m3; O3, 600 ppb]. Heart rate (HR), heart rate variability (HRV), breathing parameters, and core temperature (Tco) responses were acquired and analyzed.

We observed time-dependent physiological changes in response to O3CB exposure in each strain relative to FA exposure at both age groups. Each mouse strain showed distinct adaptation profiles to repeated acute exposures to O3. In the younger mice, several time-dependent effects (decreased HR and increased HRV) were prominent in HeJ and OuJ mice but not the B6 mice. We also observed variation in adaptation with the older mice. However, the responses with older age were generally attenuated or lacked statistical significance when compared to the younger age. In addition, cardiac-respiratory interactions were affected with CB and O3CB exposures albeit with differing patterns by age and by exposure.

Our results suggest that age considerably attenuates the physiological responses to ozone and the O3CB exposure. However, this attenuation does not necessarily mean lower risk since physiological responses to air pollutants may be beneficial health defenses. Age-related physiological changes such as increased oxidative stress in mouse tissue may be involved in this attenuation.