Excessive soluble fms-like tyrosine kinase-1 (sFlt-1) has been strongly implicated in preeclampsia. An increase in the serum sFlt-1 level occurs before the onset of preeclampsia, and the sFlt-1 level is already higher in women who are predisposed to preeclampsia than in normotensive pregnant women. This study aimed to investigate the relation between arginase and sFlt-1 in the plasma of preeclamptic women and normotensive pregnant women. We suggested that a regulatory mechanism exists that suppresses the level of sFlt-1. The relationship between arginase, one of the nitric oxide (NO) modulators, and sFlt-1 was examined. First, the pregnant women were divided into 4 groups: group 1, sFlt-1 <6000 pg/ml and arginase activity <110 U/L; group 2, sFlt-1 >= 6000 pg/ml and arginase activity <110 U/L.; group 3, sFlt-1 >= 6000 pg/ml and arginase activity >= 110 U/L; and group 4, sFlt-1 <6000 pg/ml and arginase activity >= 110 U/L. Groups 2 and 3 comprised preeclamptic women. The preeclampsia/normotensive ratio increased from groups 1 to 3. Under the higher sFlt-1 condition, lower arginase activity was associated with lower occurrence of preeclampsia. Next, in human umbilical endothelial vein cells (HUVECs), a slightly higher concentration of sFlt-1, as in group 2, reduced arginase expression and arginase activity, and S-(2-boronoethyl)-L-cysteine (BEC; arginase inhibitor) impaired sFlt-1 secretion. In contrast, a higher level of sFlt-1 increased arginase expression and activity in HUVECs, as in group 3. These results showed that arginase controlled sFlt-1 elevation to some extent. In conclusion, our results suggest the existence of a mechanism to maintain the level of sFlt-1. Soluble Flt-1 negatively regulated itself against increasing serum sFlt-1 in preeclampsia. Moreover, this study revealed that arginase inhibitors are a potential treatment option for preeclampsia. (C) 2018 Elsevier Inc. All rights reserved.