Objective: To determine the effects of nitroglycerin on placental circulation in severe preeclampsia.
Methods: Twelve women with severe preeclampsia were examined. Uterine and umbilical artery pulsatility indices (PI) were assessed by pulsed Doppler ultrasound before and after infusion of nitroglycerin, starting at 0.25 micrograms/kg per minute with stepwise dosage increases until a diastolic blood pressure (BP) of 100 mmHg was achieved. Blood pressure and heart rate were recorded every 5 minutes. Blood was sampled for analysis of the second messenger of nitric oxide, cyclic guanosine monophosphate (cGMP), before and at the end of the infusion.
Results: During the infusion, the mean systolic BP decreased from 161 (95% confidence interval [CI] 154-169) to 138 mmHg (95% CI 131-146), and the diastolic pressure decreased from 116 (95% CI 111-122) to 103 (95% CI 96-110) mmHg (P < .01). The PI of the uterine artery did not change significantly (1.23 [95% CI 1.01-1.61]) versus 1.30 [95% CI 1.01-1.88]), whereas umbilical artery PI decreased significantly (P < .01), from 1.35 (95% CI 1.09-1.73) to 1.20 (95% CI 1.05-1.40), with a more pronounced decrease in patients with high basal values. Cyclic GMP remained essentially unchanged (6.4 [95% CI 5.4-7.7] versus 5.5 [4.7-6.6] nmol/L).
Conclusion: The reduction in the PI of the umbilical artery during nitroglycerin-induced BP reduction implies vasodilation in the umbilical circulation. The absence of an increase in cGMP does not support the view that the nitroglycerin effect is reflected by the plasma concentration of cGMP.