Intermittent exposures to mixed atmospheres of nitrogen dioxide and sulfuric acid: effect on particle clearance from the respiratory region of rabbit lungs

Inhaled particle retention in rats receiving low exposures of diesel exhaust

To study the effects of a low concentration exposure on the retention and clearance of submicron particles from the lungs, we exposed male Fisher 344 rats to diesel exhaust diluted to 50 micrograms diesel exhaust particles (DP)/m3, 20 h/d, 7 d/wk for 52 wk. Lung burdens (amount of DP in lungs) and the alveolar macrophage burdens were measured up to 52 wk postexposure. By 1 yr postexposure at least 80% of the DP was eliminated from the lungs and similarly cleared from the lavaged pool of macrophages. The DP remaining in the lungs was observed in alveolar, parabronchial and paravascular maculae. In contrast to previous high concentration exposure studies, only trace amounts of particles were observed in the mediastinal lymph nodes. To study the concentration dependence of particle retention, rats were exposed to equivalent exposures of 18 d x mg DP/m3 delivered at 5700 micrograms/m3 for 3 d, 1600 micrograms/m3 for 12 d, 250 micrograms/m3 for 72 d, or 50 micrograms/m3 for 365 d. Higher lung and macrophage burdens were initially achieved with the brief, high concentration exposures. During the postexposure period, animals exposed to the higher concentrations cleared more of the lung burden. Exposure to lower concentrations resulted in higher long-term lung burdens. These results are consistent with a model of lung clearance in which the macrophage burden and the duration of exposure are both important to the formation of the maculae. In a brief high concentration exposure, the macrophage burden rises rapidly, but then declines rapidly. However, in longer low concentration exposures, the macrophage burden will not reach the same peak, but stays at intermediate levels during the exposure and stimulates a steady development of the lung maculae from particle-laden macrophages leaving the active pool of pulmonary phagocytes.

Effects of intermittent inhalation exposures to mixed atmospheres of NO2 and H2SO4 on rabbit alveolar macrophages

Rabbits were exposed (2h/d) to atmospheres consisting of 0.5 mg/m3 (0.3 micron) H2SO4 plus NO2 at either 0.3 (low) or 1 ppm (high). Animals were sacrificed 24 h after 2, 6, or 13 exposures, and cells were recovered from the lungs by bronchopulmonary lavage. Exposure to high NO2 with acid resulted in an increase in neutrophils at all time points and an increase in phagocytic capacity of macrophages after two or six exposures. On the other hand, exposure to the low NO2 with acid resulted in depressed phagocytic capacity and mobility. The results were compared with those for NO2 or H2SO4 given alone.