In this study, the effect of shear stress on the expression of genes of the human endothelin-1 system was examined. Primary cultures of human umbilical vein endothelial cells (HUVEC) were exposed to laminar shear stress of 1, 15 or 30 dyn cm-2 (i.e. 0.1, 1.5 or 3 N m-2) (venous and two different arterial levels of shear stress) in a cone-and-plate viscometer. Laminar shear stress transiently upregulates preproendothelin-1 (ppET-1) mRNA, reaching its maximum after 30 min (approx 1.7-fold increase). In contrast, long-term application of shear stress (24 h) causes downregulation of ppET-1 mRNA in a dose-dependent manner. Arterial levels of shear stress result in downregulation of endothelin-converting enzyme-1 isoform ECE-1a (predominating in HUVEC) to 36.2 +/- 8.5 %, and isoform ECE-1b mRNA to 72.3 +/- 1.9 % of static control level. The endothelin-1 (ET-1) release is downregulated by laminar shear stress in a dose-dependent manner. This downregulation of ppET-1 mRNA and ET-1 release is not affected by inhibition of protein kinase C (PKC), or tyrosine kinase. Inhibition of endothelial NO synthase (L-NAME, 500 microm) prevents downregulation of ppET-1 mRNA by shear stress. In contrast, increasing degrees of long-term shear stress upregulate endothelin receptor type B (ETB) mRNA by a NO- and PKC-, but not tyrosine kinase-dependent mechanism. In conclusion, our data suggest the downregulation of human endothelin synthesis, and an upregulation of the ETB receptor by long-term arterial laminar shear stress. These effects might contribute to the vasoprotective and anti-arteriosclerotic potential of arterial laminar shear stress.