The effects of inhaled silica and chrysotile on the elastic properties of rat lungs; physiological, physical and biochemical studies of lung surfactant.

When rats breathed air containing approximately 70 mg m-3 of respirable crystalline silica 7 h daily for 10 days (2000 mg m-3 h) the surface tension forces of the alveolar lining film were reduced. This was shown both by surface tension measurements on lung extracts and by pressure-volume studies with air and saline filling of excised lungs. Larger quantities of inhaled silica produced similar effects. Chrysotile inhalation caused an even more marked decrease in the surface tension forces. In the chrysotile studies these findings were supported by biochemical estimations of the quantity of surfactant in the lungs, which was increased 10-fold by an inhalation of 6500 mg m-3 h. Electron microscopy showed an increased number of the type II alveolar cells which produce surfactant and of free phospholipid lattices in the air spaces of the lungs of rats exposed to chrysotile and silica. Both the surface tension and biochemical estimations on a control group of rats suggest that there is an increase in the amount of surfactant in the lungs up to about 12 months of age.