Enzyme changes during experimental silicotic fibrosis: I. PZ peptidase and collagen deposition in the lungs

In various time intervals from 2 to 22 weeks after intratracheal quartz dust instillation (25 mg DQ 12) the content of collagen proteins, deoxyribonucleic acid, soluble proteins, and collagen peptidase activity (PZ substrate) in rat lungs were estimated. In the period from 2 to 8 weeks the total amount of collagen as well as enzyme activity increased in parallel by about 200% in comparison to controls. In later periods (16 and 22 weeks after dust instillation) disproportions occurred. Collagen content in silicotic lungs continued to increase; the total activity of collagen peptidase in lungs started to decrease as did the specific enzyme activity. There was also observed a decrease in the content of lung proteins soluble in isotonic KCl. From 6 weeks onward, disc electrophoresis showed changes in the proportions of these proteins in dusted rats. The changes were particularly manifest in postalbumins, α 2- and γ-globulins, indicating more severe disorders in lung metabolism. There were found no differences in the amount and in the electrophoretic characteristics of serum proteins as well as in specific activity of PZ peptidase in serum of control and quartz-dusted rats. Neither control nor silicotic rat sera disclosed inhibitory effects on the activity of lung PZ peptidase. It appears that the increase of collagen proteins in lungs of animals dusted with quartz is also accelerated by the impairment of collagen breakdown.