Male golden hamsters were exposed to coal fly ash (FA) at the concentration of 2 or 5mg/m3 for 10 days (20 hr/day, Experiment 1) or 5 mg/m3 for 4 weeks (10 hr/day, 7 days/week) and maintained in clean air condition for subsequent 4 weeks (Experiment 2) to investigate the effect on the induced changes of lung free cells. Free cells were collected by lung lavage in Exp. 1 and histologically examined in lung sections in Exp.2. In Exp.1 the number of alveolar macrophages (AMs) increased in a dose-dependent manner. In Exp. 2 AMs increased till at 2 weeks of exposure, while the subsequent increase did not occur. The ratio of particle-laden AMs increased in a dose- and time-dependent manner in each exposed group. Particle number ingested in AMs tended to increase with exposure time. In the recovery period in Exp. 2 the ratio of particle-laden AMs reduced from about 80 to 20% at the 1st week after the cessation of exposure and remained at the similar level to the termination of the experiment. On the other hand decrease in the number of total AMs was slight in the recovery period. These results suggest that the pool size of AMs is mainly dependent on the inhaled dust concentrations and some of particle-laden AMs remain in alveoli for a long time. The unmber of polymorphonuclear leukocytes (PMNs) also increased after inhalation of FA particles. In Exp. l an abrupt and transient increase of PMNs occurred in 5 mg/m3-exposed group on the 1st day after the initiation of exposure, whereas such a change did not occur in 2 mg/m3-exposed group. In Exp. 2 the number of PMNs increased exponentially with the duration of exposure and some of PMNs ingested inhaled particles. The number of PMNs in recovery period decreased quickly. These results indicate that influx of PMNs into alveoli depends on the exposure conditions and PMNs also phagocytize the deposited particles.
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Negishi et al. (1993) studied this question.