BACKGROUND The major pathophysiologic changes observed in preeclampsia suggest that endothelial cell dysfunction plays an important role in this disorder. The pathway mediating to endothelial cell dysfunction is unknown, however, the pathogenesis of preeclampsia is thought to be related to increased oxidative stress and increased vasoconstriction. The concentration of tumor necrosis factor alpha (TNF-alpha), a cytokine produced by macrophages and many other cell types, has been observed to be significantly increased in preeclampsia. It has been hypothesized that TNF-alpha overproduction by the placenta may then may produce an increase in plasma levels and subsequent endothelial dysfunction in preeclampsia. This study investigated the effect of TNF-alpha on glutathione and lipid peroxide levels and on the secretion of vasoactive substances by human umbilical vein endothelial cells (HUVECs). METHODS Human umbilical vein endothelial cells were incubated for 24 h in the presence of different concentrations of TNF-alpha (0-1000 pg mL-1) that were shown in an earlier experiment to have no effects on the vitality and proliferation rate of HUVECs. The levels of reduced glutathione (GSH) and lipid peroxides (LPOs), assessed by malondialdehyde and 4-hydroxyalkenal, were measured in endothelial cell lysates. For the measurement of vasoactive substances, levels of prostacyclin (PGI2), determined by 6-keto-prostaglandin F1a, thromboxane A2 (TXA2), measured by thromboxane B2, endothelin-1 (ET-1), and nitric oxide (NO), measured by total nitrite, were assessed in endothelial cell supernatants. RESULTS At lower concentrations (10-100 pg mL-1), TNF-alpha increases the intracellular content of LPO and GSH, stimulates the secretion of ET-1 and TXA2, but inhibits the secretion of PGI2 in endothelial cells compared with control cells. At concentration of 1000 pg mL-1, TNF-alpha increases the secretion of PGI2 and TXA2, but it decreases the ET-1 concentration. TNF-alpha has no effect on NO secretion. CONCLUSIONS These findings demonstrate that at concentrations corresponding to values in plasma from preeclamptic women, TNF-alpha induces oxidative stress and results in altered secretion of vasoactive substances in favour of vasoconstrictors in human endothelial cells. We conclude that TNF-alpha may participate in the pathway leading to endothelial cell dysfunction seen in preeclampsia.