Pathways and quantification of insoluble particles in the lung compartments of the rat

The aim of this investigation was focused on mechanisms involved in toxicokinetics of particles and fibers within the rat lung. Biologically inert polystyrene particles or an asbestos--particle comixture were followed in their pathways of deposition and retention in the lung, particularly in the alveolar space and their accumulation in the lymph node tissue of exposed rats. One group of Wistar rats was intratracheally instilled with 0.4 ml phosphate buffered saline containing 2.4 x 10(8) inert polystyrene microspheres, a second group of animals was instilled with comixture containing 1.25 mg/ml of crocidolit asbestos fibers and previously prepared microspheres. Bronchoalveolar lavage of each lung was performed on post-instillation days 1, 7, 30, 80 and 150. Particles associated with alveolar phagocytes were counted using light microscopy. The lung and lymph node tissues were chemically dissolved and tissue aliquots passed through Nucleopor membrane filters. The number of particles in the tissue aliquot samples was determined using fluorescence microscopy. The results show that the fate of particulates in the respiratory system is highly dependent on the physical properties of the instilled material. Clearance patterns for particles and fibers are markedly different. Long-term consequences are the translocation and retention of fibrous material in the interstitum, involving the major route of clearance through the lymphatics.