PERIBRONCHIOLAR FIBROSIS FOLLOWING ACUTE EXPERIMENTAL LUNG DAMAGE BY CADMIUM AEROSOL

Following exposure to an aerosol of 0.1% (0.005M) CaCl2 in physiologic saline, rat lungs were examined at 1 h, 1,2,3,4,5,7,10 and 21 days. Light microscopy showed that damage was most marked in respiratory bronchioles with a prominent increase in interstitial cells. Up to 3 days the interstitial cells were closely packed and monocytic in type, but on the 4th and 5th days, the cellular density had decreased and elongated cells resembling fibroblasts appeared. By 7 days the interstitial cells were predominantly fibroblastic. Ultrastructurally, the fibroblasts were active with prominent rough endoplasmic reticulum and numerous, single, haphazardly scattered collagen fibrils in lacunae at the cell margins. At 21 days after injury, interstitial collagen was seen as well organized, mature bundles. The fibrosis was seen in a peribronchiolar position with distortion of the bronchiole and adjacent alveoli. The peribronchiolar localization of fibrosis is the probable cause of centriacinar emphysema resulting from acute Cd fume poisoning in man.