Placental Nitric Oxide Synthase Activity and Abnormal Umbilical Artery Flow Velocity Waveforms

OBJECTIVE: To assess the nitric oxide synthase activity in placentas from women with either normal or abnormal Doppler ultrasound umbilical artery flow velocity wave-forms who delivered by elective cesarean. METHODS: This prospective observational study involved 16 women admitted either for elective cesarean for standard obstetric indications (with normal umbilical artery Doppler waveform studies, n = 8) or with evidence of fetal or maternal complications of pregnancy (with abnormal umbilical artery Doppler studies, n = 8). Placental tissue was collected and frozen in liquid nitrogen immediately upon delivery. Following storage at -80C, nitric oxide synthase activity was analyzed by measuring the conversion of [3H]L-arginine to [3H]L-citrulline. RESULTS: Placentas from women with abnormal umbilical artery flow velocity waveforms showed significantly lower mean nitric oxide synthase activity than did placentas from women with normal umbilical artery flow velocity wave-forms (Vmax = 11.3 pmol/minute/mg protein versus 22.6 pmol/minute/mg protein). CONCLUSION: There is a statistically significant reduction in nitric oxide synthase activity in placentas from pregnancies with abnormal umbilical artery flow velocity waveforms.