[Assessment of bleomycin-induced pulmonary fibrosis by bronchoalveolar lavage]

To elucidate the pathogenesis of adult respiratory distress syndrome (ARDS), bleomycin is often used to induce lung injury because of is acute inflammatory and late fibrogenic effects on the lung. This study was undertaken to determine if fibroblast growth factors or suppressive factors might exist in bronchoalveolar lavage fluid (BALF) when acute lung injury is induced by bleomycin in rats. In the experimental group, 1.5 U of bleomycin was administered intratracheally, whereas in the control group, saline solution was given. In both groups, rats were sacrificed serially up to 4 wks. In each rat, bronchoalveolar lavage was done three times using an aliquot of 5 ml saline solution. BALF was centrifuged to obtain cells and supernatants which were further fractionated by gel-filtration. Fibroblast stimulatory and inhibitory activities were evaluated by [3H]-thymidine incorporation by fibroblasts. In the experimental group, the recovered cell count increased threefold compared with the control group and most of the increase was attributed to the increase of neutrophil. The fraction whose molecular weight is about 20,000 potentiated the [3H]-thymidine incorporation by fibroblast and its peak activity was found on the 5th day after BLM administration. On the other hand, the fraction of small molecular weight (less than 1,000) showed inhibitory activity which did not change throughout the study period. These results suggest that the imbalance between the fibroblast stimulatory and inhibitory activities after the acute lung injury may have a key role to develop pulmonary fibrosis.