Basic fibroblast growth factor (bFGF), a potent inducer of angio-genesis in vivo, stimulates the production of both the cell-associated and the secreted forms of urokinase-and tissue-type plasminogen activators (PA) in cultured bovine capillary endothelial cells. This stimulation was counteracted by picogram amounts of transforming growth factor beta The stimulatory effect of bFGF was not completely abolished by increasing the amount of TGFb However, the inhibition by TGFb was greatly enhanced if the cells were pretreated for 1-3 hours with TGFb before addition of bFGF, and the inhibition was almost total, if the' preincubationtime with TGFb was 6 hours.Sequential chanqes of serum-containing medium prior to addition ofbFGF also blocked the PA stimulatory effect of bFGF. This inhibitory activity of serum was reduced by incubation of the serum with anti-TGFb-IgG. After pro-longed incubation of cultures treated simultaneously with bFGF' and TGFb, the inhibitory effect of the added bFGF dominated as assayed by PAlevels. TGFbdid not alter the receptor binding of labeled bFGF, nor did a 6 hour pretreatment with TGFb reducethe amount of bound bFGF. The major difference between effects by bFGF and TGFb was thatwhile bFGF effectively enhanced PA-activi-ty expressed by the cells, TGF decreased the amounts of both cell-associated and secreted PA activity by decreasing enzyme production and proenzyme activation. Both bFGF and TGFb increased the secretion of the endothelial type 1 plasminogen activatorinhibitor (PAI 1). The highest concentration of TGFb is found in platelets, and it is known to be released during clot formation. The suppression of PA production by theendothelium by the release of TGFb shouldresult in a decrease in the fibrinolytic activity and promote clot maintenance. In addition, the rapid stimulation of high levels of PAI 1 secretion from the surrounding capillarycells by platelet released TGFb may further suppress fibrinolysis'. The reversabil it.y of theTGFb effect and domination of bFGF stimulation may be important in relation to the subsequentonset of clot lysis or angiogenesis leadino to thrombus reorganization and wound healing.
