DEPOSITION AND TRANSLOCATION OF INHALED SILICA IN RATS - QUANTIFICATION OF PARTICLE DISTRIBUTION, MACROPHAGE PARTICIPATION, AND FUNCTION

  • 1 January 1982
    • journal article
    • research article
    • Vol. 47  (6) , 533-542
Abstract
Chronic exposure to silica dust causes fibrotic lung disease. The initial patterns of dust deposition, anatomical compartments through which silica was translocated and the participation of pulmonary macrophages in clearing the inhaled dust was studied in rats exposed to aerosolized .alpha.-quartz. Animals were exposed to 109 mg/cm3 cystalline silica in inhalation chambers for 3 h and sacrificed at varying times after exposure. The lungs were fixed by vascular perfusion through the right ventricle and tissue blocks were prepared for tranmission and scanning electron microscopy. Lungs of additional animals were lavaged to recover populations of pulmonary macrophages for in vitro studies. Scanning electron microscopy in concert with back-scattered electron imaging showed that 24 h postexposure there was a significant decrease in the number of silica particles per unit area of alveolar duct surface when compared with lung tissue from animals sacrificed immediately after exposure. Transmission electron microscopy revealed that silica crystals had been translocated to alveolar type 1 cells, interstitium and macrophages. The percentage of silica-containing macrophages on alveolar surfaces increased from 36 .+-. 2% (mean .+-. SE) immediately after exposure to 66 .+-. 2% during the 24 h following exposure. This high percentage of macrophage participation was maintained through a 24 day postexposure period and then returned to 25 .+-. 2% 42 days after exposure. The percentages of silica-containing macrophages recovered by lavage were remarkably similar to those studied in situ: 24 .+-. 4% immediately postexposure, 62 .+-. 3% from 12 h through 24 days and 28 .+-. 4% 42 days postexposure. Although the percentage of macrophages with silica remained steady, the amount of silica per cell decreased during this 12-24 day period. Metabolic and viability studies of lavaged macrophages in vitro showed no differences between sham and silica-exposed animals. These events represented normal steady state clearance of a subpathogenic dose of potentially toxic particulates.