REGULATION OF ANTI-THROMBOGENETIC FACTORS IN ENDOTHELIUM

REGULATION OF ANTI-THROMBOGENETIC FACTORS IN ENDOTHELIUM prostacyclin, tissue plasminogen activator and plasminogen activator inhibitor type-1 Hans E Rydholm, Department of Surgery, Sahlgrenska University Hospital, Östra, Göteborg, Sweden. Endothelial cells, producing both pro and anti-thrombogenetic substances are central to the cardiovascular system. A basic knowledge of the pathway which regulates the synthesis of the anti-thrombogenetic substances, prostacyclin (PGI2), tissue plasminogen activator (t-PA) and the fast inhibitor, plasminogen activator inhibitor type-1 (PAI-1), is crucial in order to modulate a dysfunctional endothelium in cardiovascular diseases. The aim of the present investigation was to clarify important aspects of the regulation of anti-thrombogetic factors in endothelial cells of different origin, in particular the influence of adrenergic control in PGI2 production and the regulation t-PA and PAI-1 production. Endothelial cells from human umbilical and adult great saphenous veins were harvested and cultured. The production of PGI2, t-PA and PAI-1 antigens were analyzed from the conditioned medium. The regulation of the cellular synthesis was studied by adding defined agonists or antagonists to receptors or intracellular transduction pathways. Adrenergic stimulation with isoprenalin increased PGI2 production from endothelial cells. The ß-adrenoceptor blocker, propranolol or metoprolol, increased the effect of isoprenalin, but had no effect per se. Different isomers of metoprolol with a high or low receptor blocking effect produced equal results. In dose-response studies, the production of t-PA and PAI-1 from umbilical and adult endothelial cells was increased by phorbolester or thrombin. At high concentrations, endotoxin also increased the production from umbilical but not from adult cells. Isoprenalin, ephedrine or endothelin-1 had no influence. Forskolin decreased the production of PAI-1, and Nanitroprusside increased it slightly. Neither of these substances influenced t-PA production. In "cross-talking" studies, the production of t-PA and PAI-1 could be modulated by coincubating different substances. The protein kinase C inhibitor H7 decreased the t-PA and PAI1 production augmented by endotoxin, thrombin and phorbolester, indicating an on-going signal transduction. Combinations with forskolin generally decreased agonist-induced PAI-1 production. The effect on t-PA production diverged between umbilical and adult cells when endotoxin, thrombin or phorbolester were co-incubated with forskolin. In transduction studies, the thrombin-induced t-PA and PAI-1 production from adult endothelial cells was decreased by pertussis toxin or genistein, representing Gaj-protein and tyrosine kinase pathway inhibitors respectively. In conclusion: The production of prostacyclin from endothelial cells is under adrenergic control, modulating the effect of ß-adrenoceptor blockers. Signal transduction through adenylate cyclase, protein kinase C and tyrosine kinase pathways is critical in the regulation of t-PA and PAI-1 production from endothelial cells. Interference with these systems can be one way of modulating the balance between coagulation and fibrinolysis in the blood vessel. Endothelial cells of different origin regulate the production of t-PA and PAI-1 differently.