Age-related changes in cardiac and respiratory adaptation to acute ozone and carbon black exposures: Interstrain variation in mice

Abstract

Context: Epidemiological studies show positive associations between increased ambient air pollutant levels and adverse cardiopulmonary effects. These studies suggest that the elderly and those with certain genetic polymorphisms are susceptible to adverse air pollution-associated health events.

Hypothesis/objective: We hypothesize that physiological responses to air pollutants vary with age and are genetically influenced.

Materials and methods: To test this hypothesis, we exposed mice from three inbred strains (C57BL/6J, B6; C3H/HeJ, HeJ; C3H/HeOuJ, OuJ) to ozone (O₃) and carbon black (CB) at two ages, (5 months, 12 months), for 3 consecutive days, to either filtered air (FA), CB particles, or O₃ and CB sequentially (O₃CB) (CB, 550 µg/m³; O₃, 600 ppb). Heart rate (HR), HR variability (HRV), breathing, and core temperature (Tco) responses were analyzed.

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

Discussion/conclusion: Our results suggest that age considerably attenuates physiological responses to O₃ and O₃CB exposures. Age-related physiological changes such as increased oxidative stress in mouse tissue may be involved in this attenuation.