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

The aim of this investigation was focused on mechanisms involved in toxicok inetics of particles and fibers within the rat lung. Biologically inert pol ystyrene particles or an asbestos - particle comixture were followed in the ir pathways of depositin and retention in the lung, particularly in the alv eolar space and their accumulation in the lymph node tissue of exposed rats . One group of Wistar rats was intratracheally instilled with 0.4 ml phosph ate buffered saline containing 2.4 x 10(8) inert polystyrene microspheres, a second group of animals was instilled with comixture containing 1.25 mg/m l of crocidolit asbestos fibers and previously prepared microspheres. Bronc hoalveolar lavage of each lung was performed on postinstillation 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 di ssolved and tissue aliquots passed through Nucleopor membrane filters. The number of particles in the tissue aliquot samples was determined using fluo rescence microscopy. The results show that the fate of particulates in the respiratory system is highly dependent on the physical properties of the in stilled material. Clearance patterns for particles and fibers are markedly different. Long-term consequences are the translocation and retention of fi brous material in the interstitum, involving the major route of clearance t hrough the lymphatics.