Effect of intra-tracheal instillation and inhalation of silicon dioxide onsome biochemical variables in broncho-alveolar lavage fluid and lung histopathology in rats

In the present study, the bronchial alveolar lavage fluid (BALF) biochemica l and lung histopathological changes occurring in response to single large intra-tracheal exposure to silica have been compared to the changes seen af ter continued chronic exposure via inhalation. Male albino rats (200-250gms ) were exposed to silicon dioxide via intratracheal instillation (8mg/0.05m l saline) and whole body inhalation (200mg/m(3), 6 hours/day for 2 and 4 we eks) in separate groups. The respective control animals were instilled with normal saline (0.05 ml) or exposed to fresh air in simulation chamber for the same duration. BALE was analyzed for total protein, elastase, malondial dehyde (MDA) levels and catalase activity and histopathology of right lung was carried out after 4 weeks post-exposure in intra-tracheal model and aft er 2 and 4 weeks of exposure in the inhalation model. The levels of total p rotein, elastase and malondialdehyde (MDA) were significantly elevated, whi le catalase activity was significantly decreased in the BALF of exposed ani mals as compared to controls. The histopathological studies of lungs, showe d exudates of inflammatory cells, chiefly of macrophages in the alveolar sp aces and interstitial septa with multifocal nodular granulomatous lesions. The biochemical findings in BALF of both the models indicate inflammatory c hanges, lipid peroxidation and fibrosis. However, comparatively lower catal ase activity and higher elastase levels in the 4 week inhalationally expose d group than the 4 week post intratracheally exposed group, suggests that t hese parameters may be affected by acute and chronic exposure and require f urther confirmation.