Pulmonary Response to Intratracheally Instilled Silicon Nitride in Rats

Abstract

The pulmonary effects and fibrogenic potential of intratracheally instilled silicon compounds were evaluated at 3, 7, 74, and 28 days post instillation. Evaluations consisted of examination of lavaged cell populations, as well as biochemical and histologic techniques. Alpha-quartz (SiO₂), a known fibrogenic material, caused significant pulmonary toxicity, manifested by pulmonary edema, acute and chronic inflammation, granuloma formation, and fibrosis. An examination of the cell populations recovered from the lavaged lungs of rats exposed to quartz revealed an increase in polymorpho-nuclear leukocytes and macrophages, and a decrease in macrophage viability, when compared to saline-instilled controls. In addition, these lungs had increased hydroxy-proline content. Two commercially prepared, nonfibrous silicon nitride (Si₃N₄) materials produced minimal pulmonary responses similar to that of glass beads, which were instilled in one group of rats as an inert or nuisance particle control. Although intrac-tracheal instillation of a fibrous Si₃N₄ powder was only minimally successful in dose delivery, biological activity including granuloma and inflammation was greater then the two nonfibrous Si₃N₄ powders.