Clearance of inhaled insoluble particle from the alveolar regions via the extraalveolar perivascular sheath

Wistar rats were exposed to particle of fly ash from coal fired power plants (13-14 mg/cubicmeter) or titanium dioxide (8,6 mg/cubicmeter) for one year (7hours/day, 5 days/week). Animals were examined histopathologically by light-and electronmicroscopy. The deposition of particle in the alveolar regions showed differences between the two types of particle. Fly ash particle were located predominantly in alveolar macrophages. Ti02 particle were disaggregated in very small primary particle (0.03 mym) and located in the perivascular space. Alveolar macrophages laden with Ti02 were rarely seen in this region. The penetration mechanism to lung associated lymph nodes obviously differ accordingly to the particle size.