Measurements of enzymes of collagen synthesis in rats with experimental silicosis.

The levels of two enzymes of collagen biosynthesis namely lysyl oxidase and prolyl hydroxylase were measured in the lungs of rats 3 and 6 weeks after receiving a single intratracheal instillation of silica or sterile saline. Circulating levels of lysyl oxidase were also estimated. Significant increased lung-enzyme activities were observed in the silica-exposed rats at both time intervals. Plasma levels of lysyl oxidase were also found to be raised in the silica-exposed rats. These changes were not, however, accompanied by profound pathological alterations. These results demonstrate that after exposure to silica histologically detectable fibrosis is preceded by significant changes in the activities of enzymes associated with collagen synthesis.