Endothelin-1 (Et-1) is a peptide synthesized by endothelial cells (ECs) both in culture and in vivo. Cyclic strain induces gene expression of Et-1, however, the molecular mechanisms remain unclear. Since cyclic strain induces a sustained increase in intracellular reactive oxygen species (ROS), we hypothesized that the ROS could be a modulator in strain-induced Et-1 gene expression. Human umbilical vein ECs (HUVECs) subjected to cyclic strain had increased Et-1 secretion. Pretreatment of HUVECs with antioxidants, catalase (300 U/ml) or 1,3-dimethyl-2-thiourea (DMTU, 0.1 mm), abolished the strain-induced Et-1 release. ECs strained for 6 h had elevated Et-1 mRNA levels. In contrast, ECs treated with catalase or DMTU did not have increase Et-1 mRNA levels stimulated by cyclic strain. Bovine aortic ECs (BAECs) transfected with fusion plasmid containing Et-1 5'-flanking sequence (4.4 kb) and chloramphenicol acetyltransferase reporter gene produced a maximal Et-1 promoter activity after undergoing strain for 6 h, whereas pretreatment with catalase decreased this activity. BAECs cotransfected with a dominant negative mutant of Ras (RasN17), Raf-1 (Raf301), or catalytically inactive mutant of extracellular signal-regulated kinase (mERK2) had inhibited strain-induced Et-1 promoter activity, indicating the Ras/Raf/ERK pathway was involved; moreover, ERK phosphorylation was induced in ECs which were strained. This strain-activated ERK phosphorylation was attenuated in the presence of catalase. Functional analysis of the Et-1 promoter with site-directed mutagenesis indicates that the activator protein-1 (AP-1) binding site had to be within 143 base-pairs upstream of transcription initiation site for strain-induced promoter activity. Pretreatment of ECs with catalase also decreased the strain-induced promoter activity in the minimal construct (-143 bp). Our data demonstrate that strain-induced Et-1 gene expression is modulated by ROS via Ras/Raf/ERK signaling pathway, and indicate the responsiveness of the AP-1 binding site for strain-induced Et-1 expression.