The sodium pump (SP or Na+,K+-ATPase) is a membrane embedded protein complex that pumps 3 sodium ions out and 2 potassium ions into the cell per cycle and in so doing creates a cell membrane electrochemical potential. The membrane potential is critical for any functional cell. In the vasculature, reduction in the voltage potential causes vascular smooth muscle contraction and a narrowing of blood vessels (vasoconstriction) which can lead to increased blood pressure (hypertension). Substantial research over the past several decades has provided a vast amount of research on SP inhibitors, sometimes called endogenous digitalis-like factors (EDLF). Increased levels of these factors have been implicated in many hypertensive disorders including preeclampsia (PE), a life-threatening complication of pregnancy. It has been demonstrated that EDLF might be a causative factor in the pathophysiology of hypertension in PE. In order to elucidate EDLF production and regulation in PE, We developed a radioimmunoassay (RIA) measuring EDLF that could be applied to serum from pregnant women, placental homogenate and placental tissue culture. This assay employs Digibind, a commercially available Fab fragment derived from polyclonal antidigoxin antibodies that cross reacts with EDLF, as the primary antibody. Using Digibind RIA, we demonstrated that placenta is a source of EDLF production and regulation. Moreover, the identification of an inhibitor, ketoconazole and a substrate, 17-hydroxyprogesterone of the synthetic pathway of EDLF in placenta proved that this pathway shares steps with the steroid synthetic pathway. Some potential regulatory agents which have elevated levels in PE or be associated in PE and thus are thought to mediate PE, such as hydrogen peroxide, tumor necrosis factor-α (TNF-α) and hypoxia have also been demonstrated to be stimuli of EDLF production in placenta. These findings are helpful to the further study on EDLF synthesis and regulation in placenta. Once we elucidate the mechanisms, it could be easier to provide deeper insights into the pathogenesis of PE and subsequently develop earlier diagnosis and effective prevention of or therapeutic approaches to PE.