Partial reversal of established bleomycin-induced pulmonary fibrosis by rh-urokinase in a rat model.

Pulmonary fibrosis was induced in male Sprague-Dawley rats by intratracheal instillation of bleomycin. By 30 d post-bleomycin, the lungs exhibited elevated interstitial collagen levels. Thirty d after exposure to bleomycin, animals were further treated by intratracheal administration of phosphate-buffered saline (PBS) or 12,500 units of recombinant human urokinase (rh-UK). Three days later, the animals were sacrificed and the lungs fixed, sectioned, and assessed for fibrosis. The presence of interstitial collagen was quantitated using a BioQuant Image Analysis System (R and M Biometrics, Inc., Nashville, TN). Urokinase treatment of animals with established pulmonary fibrosis induced by exposure to 0.5 units of bleomycin was found to diminish the collagen content of lungs to near control levels by 3 d post-UK treatment. By 36 d post-UK treatment (66 d post-bleomycin), values for interstitial collagen were again partially elevated, indicating that UK treatment interfered with established fibrosis but did not stop the bleomycin-mediated process. However, the extent of fibrosis was less than that observed in lungs from non-UK treated animals 66 d post-bleomycin. UK treatment initiated 63 d post-bleomycin exposure again revealed a decline in the extent of fibrosis, but the values did not return to baseline levels. A repeat of the short-term experiment with a higher dose of bleomycin (0.85 units) again revealed that UK treatment was effective in diminishing the extent of fibrosis from 22% to 12% collagen. These results indicate that exogenous UK may be an effective therapeutic modality in the treatment of pulmonary fibrosis induced by some stimuli or developing in association with diseases such as scleroderma.