['Preeclampsia (PE) is associated with hypertension and elevated endothelin (ET-1), an indicator of endothelial cell activation and dysfunction. Reduction of uteroplacental perfusion (RUPP) in the pregnant rat model of PE is characterized by elevated mean arterial pressure, inflammatory cytokines, and activation of the ET-1 system. We aim to determine whether 17-alpha-hydroxyprogesterone caproate (17-OHPC) or progesterone suppresses these pathways.', 'Plasma progesterone was purified from normal pregnant (NP) and PE patients and measured via enzyme-linked immunosorbent assay. Human umbilical vein endothelial cells were exposed to the sera with or without progesterone added and ET-1 was\xa0measured. Pregnant rats underwent the RUPP procedure with or without intraperitoneal 17-OHPC. Mean arterial pressure was compared in RUPP vs NP rats. Human umbilical vein endothelial cells were exposed to NP or RUPP sera, with and without progesterone and ET-1 measured.', 'Progesterone was significantly decreased in PE women compared with NP women. In response to human sera, ET-1 was elevated in PE women compared to NP women, and decreased with addition of progesterone. Mean arterial pressure was significantly elevated in RUPP vs NP rats but was attenuated by 17-OHPC. ET-1 secretion was stimulated significantly by RUPP compared to NP rat sera, but attenuated by progesterone.'] Does progesterone blunt vascular endothelial cell secretion of endothelin-1 in response to placental ischemia?