Research Program Area: Health & Exposure
Particle-induced lung injury and heart responses were measured as a function of particle size in young adult and geriatric (senescent) rats exposed to laboratory generated particles composed of elemental carbon and ammonium nitrate. The particle compositions and concentrations used were consistent with ambient aerosols collected and characterized in California. Three particle size ranges were tested: 'Ultrafine' (dp « 200 nm), Fine (500 « dp « 1000 nm) and Coarse (2000« dp « 4000 nm). The biological responses studied included measures of cell replication, which are part of normal injury-repair processes, cellular immunological measures, which are related to defense mechanisms and hemodynamic factors (changes in blood pressure, variability in heart rate and abnormal heart rhythms).
Our primary hypothesis was that particle-induced lung injury at the tissue and cellular levels, and systemic effects would be a function of particle size when composition and concentration of particles were held constant. Also, given that epidemiological studies indicated that older individuals were at greater risk of adverse partile induced health effects, we hypothesized that senescent (geriatric) rats would be a more sensitive to the effects of PM than would be healthy young adult rats.
Acute (six hours) exposures to mixtures of particles and ozone at concentrations relevant to short-term peak ambient levels caused inflammatory responses in both old and young rats. The particle exposures also altered immunologic responses of lung macrophages, compared to responses measured in rats exposed to purified air. Particle exposures caused changes in blood pressure and heart rate, compared to measurements in rats exposed to purified air. These changes were observed in both young rats and in senescent rats, but the senescent rats responded with greater sensitivity than did the younger rats. Exposures to 'ultrafine' particles elicited greater blood pressure responses than either fine or coarse particles. However, ultrafine particles deposit more efficiently in the gas exchange (pulmonary) region of the lung than do either fine or coarse particles. Thus, the dose of 'ultrafine' particles could have been greater than the dose of particles in either of the other two size fractions, even though the exposure concentrations were the same.
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