Nitric Oxide Synthase Activity and Doppler Parameters in the Fetoplacental and Uteroplacental Circulation in Preeclampsia

Objective: We investigated the hypothesis that changes in blood flow in the uteroplacental and fetoplacental circulation in preeclampsia are associated with an abnormality of placental or uterine placental bed nitric oxide (NO) synthesis. Methods: We measured pulsatility indices on Doppler waveform analysis from uterine and umbilical arteries in 20 patients with preeclampsia and 14 healthy pregnant controls before elective cesarean section. During cesarean section, biopsies from the uterine placental bed and the placenta were taken and the nitric oxide synthase (NOS) activity was measured by the [3H] L-arginine-[3H] L-citrulline conversion assay in these samples. Results: The NOS activity was significantly lower in the uterine placental bed in comparison to the placental tissue (p < 0.01). Placental NOS activity was similar between patients with preeclampsia and healthy controls and in the groups with either a pathological or a normal Doppler flow in the umbilical artery. In the uterine placental bed however, NOS activity from patients with preeclampsia was significantly lower (p 0.01), whereas the blood flow resistance in the uterine arteries was elevated (p < 0.01) in comparison to healthy controls. Conclusions: Our data show that pathological Doppler waveforms in the uterine arteries of patients with preeclampsia are paralleled by diminished NOS activity in the uterine placental bed. Therefore, the compromised NO production in the uterine placental bed may play an important role in the impaired uteroplacental blood flow and potentially in some pathological features of preeclampsia such as intervillous thrombosis formation and fetal growth retardation.