Uteroplacental hemodynamic response to antihypertensive drugs in hypertensive pregnant sheep.

The production of renal hypertension by single renal artery constriction in pregnant sheep decreases uteroplacental blood flow. This decrease in uteroplacental perfusion persits for 7-10 days and then returns to normal control levels despite the persistence of hypertension. During hypertension the uteroplacental vascular bed is dependent upon the elevated arterial pressure for perfusion. Therefore, a pharmacologic lowering of this perfusion pressure may reduce uteroplacental blood flow. Antihypertensive agents whose major effect is the lower vascular resistance will tend to reduce uteroplacental blood flow, while those agents which increase cardiac output in addition to lowering the vascular resistance, will tend to maintain or increase uterine blood flow. Of the specific agents tested, hydralazine, which has a positive inotropic and chronotropic effect on the heart, was the only one that consistently increased uteroplacental blood flow. Blockade of these beta-mimetic effects resulted in a fall in uterine blood flow as the perfusion pressure was reduced.