Ritodrine infusion during late pregnancy: effects on fetal and placental blood flow, prostacyclin, and thromboxane.
To study the effects of ritodrine on fetal and placental blood flow and maternal prostacyclin and thromboxane A2, 14 women with premature uterine contractions between the thirty-first and thirty-sixth weeks of pregnancy were treated with intravenous infusions of ritodrine, with incremental doses up to 200 micrograms per minute. The intervillous and the umbilical vein blood flows were measured before and after 1 hour of infusion of ritodrine, with the xenon 133 method and with a combination of real-time and Doppler ultrasonic equipment, respectively. Ritodrine decreased maternal diastolic and mean arterial pressures, as well as placental vascular resistance, but caused no significant changes in intervillous and umbilical vein blood flows. Ritodrine stimulated the synthesis of vasodilatory prostacyclin, as seen from a rise in maternal plasma 6-keto-prostaglandin F1 alpha, but inhibited the platelets' capacity to generate the vasoconstrictor thromboxane A2. Thus, apart from maternal hemodynamic changes, the intervillous and umbilical circulations are maintained during short-term administration of ritodrine in normotensive pregnancies.
D015121:6-Ketoprostaglandin F1 alpha / Q000097:blood; D001794:Blood Pressure / Q000187:drug effects; D011464:Epoprostenol / Q000378:metabolism*; D005260:Female; D005318:Fetal Heart / Q000187:drug effects; D005333:Fetus / Q000098:blood supply* / Q000187:drug effects; D006339:Heart Rate / Q000187:drug effects; D006801:Humans; D007752:Obstetric Labor, Premature / Q000503:physiopathology / Q000517:prevention & control*; D010920:Placenta / Q000098:blood supply* / Q000187:drug effects; D011247:Pregnancy; D011412:Propanolamines / Q000627:therapeutic use*; D012039:Regional Blood Flow / Q000187:drug effects; D012312:Ritodrine / Q000627:therapeutic use*; D013928:Thromboxane A2 / Q000378:metabolism*; D013929:Thromboxane B2 / Q000097:blood; D013931:Thromboxanes / Q000378:metabolism*; D014471:Umbilical Veins / Q000187:drug effects; D014655:Vascular Resistance / Q000187:drug effects
D011412:Propanolamines; D013931:Thromboxanes; D013929:Thromboxane B2; D013928:Thromboxane A2; D015121:6-Ketoprostaglandin F1 alpha; D011464:Epoprostenol; D012312:Ritodrine