Regulation of anti-thrombogenetic factors in endothelium : prostacyclin, tissue plasminogen activator and plasminogen activator inhibitor type-1

Abstract

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 b-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 Na-nitroprusside 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 co-incubating different substances. The protein kinase C inhibitor H7 decreased the t-PA and PAI-1 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 Gai-protein and tyrosine kinase pathway inhibitors respectively.