PLACENTAL NITRIC-OXIDE SYNTHASE ACTIVITY AND ABNORMAL UMBILICAL ARTERY FLOW VELOCITY WAVE-FORMS

Objective: To assess the nitric oxide synthase activity in placentas f rom women with either normal or abnormal Doppler ultrasound umbilical artery flow velocity waveforms who delivered by elective cesarean. Met hods: 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 evide nce of fetal or maternal complications of pregnancy (with abnormal umb ilical artery Doppler studies, n = 8). Placental tissue was collected and frozen in liquid nitrogen immediately upon delivery. Following sto rage at -80C, nitric oxide synthase activity was analyzed by measuring the conversion of [H-3]L-arginine to [3H]L-citrulline. Results: Place ntas from women with abnormal umbilical artery now velocity waveforms showed significantly lower mean nitric oxide synthase activity than di d placentas from women with normal umbilical artery flow velocity wave forms (V-max = 11.3 pmol/minute/mg protein versus 22.6 pmol/minute/mg protein). Conclusion: There is a statistically significant reduction i n nitric oxide synthase activity in placentas from pregnancies with ab normal umbilical artery flow velocity waveforms. Copyright O 1997 by T he American College of Obstetricians and Gynecologists.