Mechanical stretch and para- and/or autocrine factors, including endothelin-1, induce hypertrophy of cardiac myocytes and proliferation of fibroblasts. To investigate the effect of mechanical load on endothelin-1 production and on endothelin system gene expression in neonatal rat ventricular myocytes and fibroblasts, we exposed cells to cyclic mechanical stretch in vitro (0.5 Hz, 10% to 25% elongation, from 1 min to 24 hours). Endothelin-1 peptide levels were measured from culture media of myocytes and fibroblasts and human umbilical vein endothelial cells (positive control) by specific radioimmunoassay. Preproendothelin-1 promoter activity was measured by using transfection of reporter plasmids and mRNA levels with Northern blot or quantitative RT-PCR. Activity of extracellular signal regulated kinase was quantified with specific kinase assay. We found that stretching of myocytes activated preproendothelin-1 gene expression including promoter activation, transient increase in mRNA levels and augmented endothelin-1 secretion. In contrast, preproendothelin-1 gene expression was inhibited in stretched fibroblasts. Endothelin-converting enzyme-1 mRNA levels elevated in stretched fibroblasts, but decreased in stretched myocytes. Endothelin receptor type-A mRNA levels declined in stretched myocytes, while levels were below detection in fibroblasts. Stretch activated extracellular signal regulated kinase in myocytes, and when the kinase activity was pharmacologically inhibited, the preproendothelin-1 induction was suppressed. Transient overexpression of mitogenactivated ERK activating kinase -1 induced preproendothelin-1 promoter in myocytes. In summary, mechanical stretch distinctly regulates endothelin system gene expression in cardiac myocytes and fibroblasts. The inhibition of endothelin system may affect on cardiac mechanotransduction and therefore provides an approach in treatment of loadinduced cardiac pathology.