OVINE FETAL UMBILICAL ARTERY DOPPLER SYSTOLIC DIASTOLIC RATIOS AND NITRIC-OXIDE SYNTHASE

Objective: To evaluate the effect of nitric oxide synthase activity in hibition on the fetal lamb umbilical artery flow velocity waveform. Me thods: Five pregnant Corriedale cross ewes were operated on at 125-130 days' gestation. Fetal and maternal vascular catheters were inserted along with a Doppler flow meter cuff on the fetal common umbilical art ery. Each fetus received a 40-minute intravenous (IV) infusion of N-om ega-nitro-D-arginine as a control, and then after a recovery period of 1 hour, a 40-minute IV infusion of N-omega-nitro-L-arginine, an inhib itor of nitric oxide synthase activity. Maternal and fetal heart rate, blood pressure, blood gases, and fetal umbilical artery now velocity waveforms were recorded at basal time and after the 40-minute IV infus ions. Results: There were no differences in fetal or maternal heart ra te, blood pressure, or blood gases with the infusion of the nitric oxi de synthase inhibitor N-omega-nitro-L-arginine. However, N-omega-nitro -L-arginine caused a significant increase (41%) in the fetal umbilical artery flow velocity waveform systolic to diastolic ratio (S/D) above the baseline levels. Conclusions: Inhibition of nitric oxide synthase activity in the lamb fetoplacental circulation with N-omega-nitro-L-a rginine is associated with an increase in the umbilical artery S/D. Co pyright (C) 1997 by The American College of Obstetricians and Gynecolo gists.