Age-Related Responses in Rats to Concentrated Urban Air Particles (CAPs)

Abstract

Epidemiological studies have reported that elderly individuals have a higher risk of detrimental responses following exposure to elevated levels of ambient particulate matter. To investigate this finding in a toxicological model, aged Fisher rats were exposed for 3 days to concentrated urban air particles (CAPs) from Boston. The hypothesis tested was that older animals would exhibit more severe pulmonary inflammation and hematological changes following the CAPs exposure when compared to young, normal animals. Aged Fisher rats (> 17 mo) and juvenile Fisher rats (4–6 wk) were maintained in a virus-antigen free facility for 3 mo prior to exposure. Following this period, aged and young rats were exposed to CAPs or sham-exposed to filtered air for 5 h/day (or 3 consecutive days (10 rats/group X 4 groups total = 40 rats). Daily integrated CAPs concentrations were 80, 170, and 50 μ/m₃ on day 1, 2, and 3, respectively. None of the animals died throughout the duration of exposure. Twenty-four hours following the last day of exposure, blood was collected by cardiac puncture, and bronchoalveolar lavage (BAL) was performed. Young rats had significantly higher total BAL cell counts compared to old rats, as well as a significant increase in BAL polymorphonuclear leukocytes (PMN) following CAPs exposure compared to sham. Old rats also exhibited a small, but significant, increase in BAL PMN following exposure to CAPs compared to sham. There were no CAPs-related significant changes in aged animals in total BAL cell counts, BAL lactate dehydrogenase, total white blood cell (WBC) counts, or the percent of WBC PMN, lymphocytes, and monocytes. When comparing aged versus young (CAPs-or filtered air-exposed) animals, advanced age was associated with significant decrements in the total BAL cell counts, total WBC counts, percent of blood lymphocytes, and blood hemoglobin; a significant increase in the percent of blood PMN was also observed. The above results suggest: 1I) Young Fisher rats may represent a sensitive model for the examination of pulmonary inflammatory responses following CAPs exposure, and (2) the lack of a pulmonary inflammatory response in the aged rats, despite the presence of a higher percentage of circulating neutrophils, may reflect decreased sensitivity to inhaled particles.