Differential effects of intravenous hydralazine on myoendometrial and placental blood flow in hypertensive pregnant ewes

OBJECTIVE: The differential vasoactive effects of hydralazine on the uteroplacental vascular bed were studied. STUDY DESIGN: After control measurements were taken, near-term chronically prepared pregnant sheep were continuously infused with angiotensin II. Maternal arterial pressure was increased by 32 mm Hg. Hydralazine was then administered; the effects on regional resistance and blood flow were evaluated with a radionuclide-labeled microsphere technique. Analysis of variance for repeated measures was used to compare observations. RESULTS: When compared with the hypertensive state, hydralazine caused the following changes by 40 minutes (mean ± SEM): Although maternal blood pressure fell 31% ± 5% (p = 0.0005), placental blood flow was unchanged, total uteroplacental blood flow increased 24% ± 8% (p = 0.03), total uteroplacental resistance decreased 43% ± 4% (p = 0.0002), placental resistance decreased 19% ± 9% (p = 0.01 ), myoendometrial blood flow increased 390% ± 82% (p = 0.0005), and myoendometrial resistance decreased 82% ± 4% (p = 0.0005). CONCLUSIONS: In angiotensin II-induced hypertensive ewes, hydralazine is an effective dilator of the uteroplacental vascular bed and can maintain placental blood flow while reducing blood pressure. (AM J OBSTET GYNECOL 1992;167:1672-8.)