EFFECTS OF LABETALOL ON UTERINE BLOOD-FLOW AND CARDIOVASCULAR HEMODYNAMICS IN THE HYPERTENSIVE GRAVID BABOON

OBJECTIVE: The purpose of this study was to investigate the effects of labetalol on uterine blood flow and cardiovascular parameters in acut ely instrumented, hypertensive gravid baboons. STUDY DESIGN: During th e latter half of pregnancy six gravid baboons were acutely instrumente d, with ultrasonic flow probes placed on ipsilateral, external iliac, and uterine arteries and a flow-directed pulmonary artery catheter in the pulmonary artery. After a stable arterial pressure baseline was ob tained, norepinephrine was infused to increase mean arterial pressure by at least 20%. A 20-minute hypertensive steady state was obtained. L abetalol at 0.5 and 1.0 mg/kg was randomly infused, followed by a 2.0 mg/kg dose, each over 1 minute. A 20-minute recovery period followed e very labetalol infusion, allowing the hypertensive steady state to ree stablish. External iliac and uterine blood flow measurements were cont inuously recorded during the baseline and experimental trials. Mean ar terial blood pressure, heart rate, pulmonary artery and capillary wedg e pressure, central venous pressure, and cardiac output were obtained at 5, 10, and 15 minutes during each steady state and after each labet alol infusion. RESULTS: Labetalol at all dosages significantly reduced the mean arterial pressure and the systemic vascular resistance at 1. 0 and 2.0 mg/kg. External iliac blood flow was not consistently signif icantly reduced; however, uterine blood flow was significantly reduced after the 1.0 and 2.0 mg/kg labetalol dosages (p < 0.05). Although ut erine vascular resistance tended to increase after the 1.0 and 2.0 mg/ kg doses, statistical significance was not achieved. CONCLUSION: Low-d ose labetalol (0.5 mg/kg) significantly reduces the pharmacologic hype rtensive gravid baboon's mean arterial blood pressure without adversel y affecting uterine blood flow.