Effects of vasodilators on isolated human uteroplacental arteries

The effects of the vasodilator drugs hydralazine, labetalol, prazosin, and nitrendipine were studied on responses to K+ (124 mmol/L), noradrenaline, vasopressin, and angiotensin II in small human maternal intramyometrial arteries and on responses to K+, prostaglandin (PG) F2 alpha, and angiotensin II in fetal stem villous arteries. The vessels were dissected from biopsy specimens obtained during term cesareans and mounted in organ baths. Hydralazine failed to inhibit responses to any of the agonists tested in the fetal and maternal arteries. Labetalol and prazosin decreased responses to noradrenaline but did not affect contractions induced by the other agonists in maternal arteries. In fetal arteries, which did not respond to noradrenaline, no effects of labetalol and prazosin were found. Nitrendipine inhibited responses to all the agonists tested in maternal arteries. In fetal preparations, the drug decreased responses to K+ and PGF2 alpha but did not affect contractions induced by angiotensin II. Vasodilator drugs applied for treatment of pregnancy-induced hypertension show differential effects on human maternal and fetal uteroplacental arteries, depending on their mode of action and the agonists responsible for the contractile activation in these vessels.