Effect of silica and volcanic ash on the content of lung alveolar and tissue phospholipids

Silica or volcanic ash (VA) was administered to rats via intratracheal instillation and the changes in extracellular (i.e., lavage fluid) and tissue phospholipids, as well as various biochemical parameters, were monitored over a 6-month period. VA produced relatively minor (up to 2.8-fold) increases in lung tissue or lavage fluid phospholipids that were maximal at 1 month postinstillation. These increases were quantitatively similar to the increases in protein and DNA content of lung tissue and lavage fluid induced by VA and, thus, may be attributable to hypercellularity and accumulation of cellular breakdown products in the alveolar lumen. Instillation of silica produced a much greater (up to 11-fold) increase than VA in total phospholipid over time, primarily due to a 14-fold increase in phosphatidylcholine (PC). The accumulation of PC was more pronounced in the lavage fluid during the first month following silica instillation, but thereafter progressed more rapidly in the lung tissue. The relatively small increases (1.3- to 3.5-fold) in other phospholipids induced by silica appeared to be nonspecific, since they did not differ greatly from the increases in lung weight, DNA, and protein. Collectively, these results indicate that intratracheal instillation of silica induces selective accumulation of lung PC, implying enhanced synthesis and secretion of pulmonary surfactant from alveolar epithelial Type II cells into the lumen.