Acute effect of an antihypertensive drug, labetalol, on uteroplacental blood flow.

The effect of a new antihypertensive drug, labetalol, on uteroplacental blood flow was determined in eight pre-eclamptic women. After injection of 0.5 mCi of 113mIn the radioactivity in the placenta was recorded by a gamma camera linked to a computer and the placental blood-flow index was calculated from the ratio between the maximum radioactivity of the isotope-accumulation curve and the rise time of the curve. Labetalol, a combined alpha- and beta-adrenoceptor antagonist was given intravenously and after 30 min a second uteroplacental blood-flow index was calculated. There was a significant mean decrease of blood pressure from 147/98 to 128/83 mmHg, but no change in uteroplacental blood-flow index, so that uteroplacental vascular resistance tended to decrease.