Early changes in the chemical composition of the rat lung after silica administration.

A group of 200 g male Sprague-Dawley rats was injected with 75 mg of quartz (less than 5 mu particle size) and changes in lung DNA, noncollagenous protein, total lipids, and collagen were studied after 6, 24, 72, 96, and 144 hr. Another group of rats received 10, 30, 59, and 75 mg quartz and the above lung analysis was performed 6 days later. Control rats received saline only. Both sets of experiments indicate that striking changes in the above parameters occur very early. The sequence of statistically significant changes was: lung weight (24 hr), DNA (24 hr), noncollagenous proteins (72 hr), total lipids (72 hr), collagen (144 hr). At the dose of 30 mg quartz/lung all the above parameters were significantly increased within 6 days after the lung injury. It is proposed that in early stages of experimental silicosis an excessive amount of collagen accumulates in the lung. Later, some of the deposited collagen is resorbed. This indicates that in the course of the silicotic fibroproliferative inflammation, the balance between collagen deposition and degradation varies.