Pharmacological modulation of the endotoxin-induced increase in plasminogen activator inhibitor activity in rats.

Pharmacological modulation of the in vivo induction of plasminogen activator inhibitor type-1 (PAI-1) synthesis was studied in rats using the induction of PAI-1 by endotoxin as a model system. Both the cyclooxygenase inhibitors acetylsalicylic acid and indomethacin enhanced PAI-1 induction. The combined cyclooxygenase-lipoxygenase inhibitor, BW755C, dose-dependently inhibited induction. Since five other lipoxygenase inhibitors, a phospholipase inhibitor, an inhibitor of leukotriene formation and dexamethasone had no effect on the endotoxin-induced increase in PAI-1 synthesis, the effect of BW755C could not be ascribed to its known pharmacological properties. In addition, induction of PAI was enhanced by isobutyl-methylxanthine, a phosphodiesterase inhibitor, but not, however, by other phosphodiesterase inhibitors, or by forskolin or NG-nitro-L-arginine, suggesting an effect of isobutyl-methylxanthine other than through cyclic nucleotides. Heparin and hirudin had no effect either. Overall, the data showed that the induction of PAI-1 synthesis by endotoxin in vivo can be up- and down-regulated pharmacologically, but the mechanisms involved remain elusive.