Early Changes in the Chemical Composition of the Rat Lung after Silica Administration

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Abstract
Male rats (200 g) were injected with 75 mg of quartz (< 5 .mu. particle size) and changes in lung DNA, noncollagenous protein, total lipids, and collagen were studied after 6, 24, 72, 96 and 144 h. 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 wt (24 h), DNA (24 h), noncollagenous proteins (72 h), total lipids (72 h), collagen (144 h). At the dose of 30 mg quartz/lung all the above parameters were significantly increased within 6 days after the lung injury. In early stages of experimental silicosis an excessive amount of collagen accumulates in the lung. Some of the deposited collagen is later resorbed. This indicates that in the course of the silicotic fibroproliferative inflammation, the balance between collagen deposition and degradation varies.