Hirudin stimulates prostacyclin but not endothelin-1 production in cultured human vascular endothelial cells

To study the effect of hirudin on endothelial cell prostacyclin (PGI(2)) and endothelin-1 (ET-1) production, we cultured human umbilical vein endothelial cells (HUVECs), stimulated them with 0.00001-10 kU/l of hirudin for 12-24 hours, and measured by radioimmunoassays the concentrations of 6-ketoprostaglandinF(1alfa) (6-keto, a metabolite of PGI(2)) and ET-1 in the incubation medium. In incubation medium containing 10% serum hirudin stimulated PGI(2)-production dose-dependently. The lowest stimulatory hirudin concentration was 0.001 kU/l, which increased the concentration of 6-keto by 10.8+/-4.4% (mean+/- S.E) (p<0.01). The greatest stimulation rate (28.6+/-6.2%, p<0.001) was obtained with the highest hirudin concentration (10 kU/l), when the culture medium contained 10% human serum. The PGI(2)-stimulating activity was exaggerated in the absence of serum, when 1 kU/l of hirudin increased PGI(2)-production by 59.7+/-6.2% (p<0.001, n=14). Stimulation of PGI(2) appeared after 12 hour incubation. Hirudin had no effect on the conversion of exogenous arachidonic acid to 6-keto or on the production of ET-1. We thus conclude that hirudin stimulates PGI(2)-production through de novo protein synthesis. Stimulation of PGI(2)-production by hirudin may contribute to its antithrombotic activity, since PGI(2) favours vasodilatation and attenuates platelet aggregation.