Age-related responses in rats to concentrated urban air particles (CAPs)

Epidemiological studies have reported that elderly individuals have a highe r risk of detrimental responses following exposure to elevated levels of am bient particulate matter. To investigate this finding in a toxicological mo del, aged Fisher rats were exposed for 3 days to concentrated urban air par ticles (CAPs) from Boston. The hypothesis tested was that older animals wou ld exhibit more severe pulmonary inflammation and hematological changes fol lowing the CAPs exposure when compared to young normal animals. Aged Fisher rats (> 77 mo) and juvenile Fisher rats (4-6 wk) were maintained in a viru s-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 fo r 5 h/day for 3 consecutive days (10 rats/group x 4 groups total = 40 rats) . Daily integrated CAPs concentrations were 80, 170, and 50 mu g/m(3) on da y 1, 2, and 3, respectively. None of the animals died throughout the durati on of exposure. Twenty-Tour hours following the last day of exposure, blood was collected by cardiac puncture, and bronchoalveolar lavage (BAL) was pe rformed. Young rats had significantly higher total BAL cell counts compared to old rats, as weil as a significant increase in BAL polymorphonuclear le ukocytes (PMN) following CAPs exposure compared to sham. Old rats also exhi bited a small, but significant increase in BAL PMN following exposure to CA Ps compared to sham. There were no CAPs-related significant changes in aged animals in total BAL cell counts, BAL lactate dehydrogenase, total white b lood cell (WBC) counts, or the percent of WBC PMN, lymphocytes, and monocyt es. When comparing aged versus young (CAPs- or filtered air-exposed) animal s, advanced age was associated with significant decrements in the total BAL cell counts, total WBC counts, percent or blood lymphocytes, and blood hem oglobin, a significant increase in the percent of blood PMN was also observ ed. The above results suggest: (1) Young fisher rats may represent a sensit ive model for the examination of pulmonary inflammatory responses following CAPs exposure, and (2) the lack of a pulmonary inflammatory response in th e aged rats, despite the presence of a higher percentage of circulating neu trophils, may reflect decreased sensitivity to inhaled particles.