THE EFFECT OF A NITRIC-OXIDE DONOR ON DOPPLER FLOW VELOCITY WAVE-FORMS IN THE UTERINE ARTERY DURING THE FIRST-TRIMESTER OF PREGNANCY

Our objectives were to study the effect of a nitric oxide donor on ute rine blood flow velocity waveforms and maternal heart rate and blood p ressure during the first trimester of pregnancy. Eleven women were exa mined at 8-12 weeks' gestation, prior to elective termination of pregn ancy. Each woman was randomly given a sublingual tablet containing 5 m g of isosorbide dinitrate or placebo, on two consecutive days. Measure ments of maternal blood pressure, heart rate and Doppler flow velocity waveforms of the ascending branch of the main uterine artery were obt ained before, and every 2 min (for 20 min) after taking the drug or pl acebo. Following administration of isosorbide dinitrate, the mean arte rial blood pressure fell from a control value of 82.5 +/- 5.6 mmHg to a nadir of 73 +/- 4.1 mmHg at 16 min (p < 0.0001). The mean maternal h eart rate increased from a control value of 80.9 +/- 2.8 beats/min to a peak of 90.4 +/- 4.6 beats/min at 10 min (p < 0.001). The mean resis tance inner in the uterine artery fell from a control value of 0.80 +/ - 0.02 to a nadir of 0.73 +/- 0.03 at 10 min (p < 0.0001). Analysis of covariance was employed to compensate for the effect of heart rate on the resistance index. The drug had a significant effect on the resist ance index in the uterine artery independent of maternal heart rate. T hese results suggest that drugs such as isosorbide dinitrate may have a potential benefit under such conditions where the production of nitr ic oxide (i.e. endothelium-derived relaxing factor) is decreased.