The mechanism of peritoneal fibrosis in patients on continuous ambulatory peritoneal dialysis is poorly understood. The production of basic fibroblast growth factor (bFGF) by human peritoneal mesothelial cells cultured in high glucose medium was investigated, and the behavior of peritoneal fibroblasts, as well as the inhibitory effect of prednisolone, was assessed. Reverse transcriptase-PCR and immunocytochemistry showed the expression of glucocorticoid receptors in mesothelial cells. The semiquantitative reverse transcriptase-PCR showed that high glucose medium (4.0%) increased bFGF mRNA by 2.5-fold relative to control medium (0.1% glucose), with 83% suppression of the increase by 1 microM prednisolone. The bFGF protein level in culture supernatant was also increased by 1.5-fold in high glucose medium, with this change showing 45% suppression by 1 microM prednisolone. These effects of prednisolone were prevented by a glucocorticoid receptor antagonist (RU486) in a concentration-dependent manner. The proliferation of peritoneal fibroblasts was increased 1.9-fold by the supernatant of mesothelial cells cultured in high glucose medium, with 85% suppression by 1 microM prednisolone and suppression to 16% below basal proliferation by an anti-bFGF neutralizing antibody (10 microg/ml), whereas proliferation showed a concentration-dependent increase on addition of an anti-transforming growth factor beta-neutralizing antibody. Recombinant bFGF (50 to 1000 pg/ml) likewise caused a concentration-dependent increase of peritoneal fibroblast proliferation and fibronectin release by these cells was also increased (at 50 to 5000 pg/ml). These results suggest the potential importance of bFGF for initiation of peritoneal fibrosis and the possible efficacy of glucocorticoids for preventing such fibrosis in patients receiving peritoneal dialysis.