Experimental silicosis. I. Acute effects of intratracheally instilled quartz on collagen metabolism and morphologic characteristics of rat lungs.

Rats were intratracheally instilled with 50 mg of silica as quartz (0.5-mu particles) at day 0. One and 2 weeks later, lungs were evaluated histologically and by a variety of biochemical measurements. Protein, proline, and hydroxyproline content (as an index of total lung collagen) were quantitated, as were the lung collagen synthesis rate and the total lung protein biosynthesis rate (evaluated with lung minces in vitro). The ratio of newly synthesized Type I/Type III collagen was determined, as was the same ratio for total lung collagen. These experiments were performed in parallel on chronic respiratory disease-free rats and in a strain of conventional animals. The authors conclude that 1) changes in lung structure and composition can be appreciated as early as 1 week, the earliest time point studied, after intratracheal instillation of 50 mg of quartz; 2) observed morphologic changes during the first 2 weeks are consistent with biochemical changes; 3) there are essentially no differences in the response of chronic respiratory disease-free Sprague-Dawley and conventional Wistar rats to intratracheally instilled silica. Both strains of rats developed silica-containing granulomas, which ultimately developed into silicotic nodules, as well as areas of alveolar lipoproteinosis associated with interstitial pneumonitis.