Decreased prostaglandin E2 synthesis by lung fibroblasts isolated from rats with bleomycin-induced lung fibrosis

In order to clarify the mechanism of pulmonary fibrosis, we examined the functional changes of lung fibroblasts in bleomycin (BLM)-induced pulmonary fibrosis. Lung fibroblastic cells were obtained from rat lungs after an intratracheal treatment of BLM or saline. The spontaneous proliferation of BLM-treated rat fibroblasts (BRF), which was estimated by H-3-TdR incorporation and direct cell counting, was significantly more rapid than that of normal saline-treated rat fibroblasts (NRF). Next, we investigated prostaglandin (PG) E-2 synthesis by BRF and NRF, with or without stimulation by interleukin (IL)-1 alpha, and found that PGE(2) production by BRF was significantly less than that by NRF. There was no significant difference in cyclooxygenase (COX) activity and COX-2 mRNA level between BRF and NRF, indicating that the change in PGE(2) production was independent of COX, a rate-limiting enzyme for the production of PGE(2). These results suggest that the proliferation of fibroblasts is down-regulated by PGE(2) released from themselves in normal lungs in an autocrine fashion, thus the decreased PGE, production observed in lung fibroblasts from rats with BLM-induced pulmonary fibrosis may result in the excessive fibroblast proliferation in this disorder. Overall, these findings throw some light on the mechanism of development of BLM-induced pulmonary fibrosis.