Plasma concentrations of natriuretic peptides increase in some pathological conditions, but very little is known about the effect of these vasodilator peptides on the regulation of the blood coagulation system. The fundamental role in the regulation of fibrinolysis is played by plasminogen activator inhibitor type 1 (PAI-1). Recent studies demonstrate that natriuretic peptides can modulate PAI-1 expression in bovine aortic smooth muscle cells and rat aortic endothelial cells. In this report, we tested the effect of natriuretic peptides on PAI-1 expression in the human endothelial cell line (EA.hy 926). For this purpose, we treated the cell cultures with ANP, BNP and CNP, and modulation of PAI-1 synthesis was evaluated. We compared the effect of natriuretic peptides on synthesis and release of PAI-1 in unstimulated cells, and after activation with tumour necrosis factor α (TNFα). Natriuretic peptides abolished TNFα-induced upregulation of PAI-1 expression at both the PAI-1 mRNA and the antigen levels. The inhibitory efficiency was higher in the case of CNP when compared to that produced by ANP and BNP, particularly when TNFα-stimulated cells were used. We observed an inhibition of stimulatory effect of TNFα on PAI-1 expression also at the level of the PAI-1 promoter in cells transfected with a PAI-1 promoter fragment (+71 to -800) [1], The PAI-1 promoter activity was markedly inhibited by C-type natriuretic peptide, already at a very low (0.001 µM) concentration of the peptide.
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