NITRIC-OXIDE IS INVOLVED IN FLOW-INDUCED DILATION OF ISOLATED HUMAN SMALL FETOPLACENTAL ARTERIES

OBJECTIVES: The aim of this study was to determine the dilation that o ccurs in response to increments of intraluminal flow in isolated human small fetoplacental arteries and to investigate the role played by ni tric oxide. STUDY DESIGN: Small fetoplacental arteries (mean luminal d iameter 482 +/- 31 mu m, n = 17, at zero flow and pressure) were disse cted from samples of placental tissue obtained from normal term vagina l deliveries and elective term cesarean sections for breech presentati on. The arteries were mounted on a pressure myograph, and the response to increasing intraluminal flow was investigated in the presence and absence of a nitric oxide synthase inhibitor (N-omega-nitro-L-arginine methyl ester, 10(-4) mol/L). Basal tone was assessed in a separate gr oup of arteries (n = 7) by the removal of extracellular calcium. RESUL TS: The presence of significant basal tone was demonstrated in these a rteries. The arteries dilated in response to increasing luminal flow, and the dilation was significantly reduced by inhibition of nitric oxi de synthase (control, 5.5% +/- 1.0% increase in artery diameter, n = 1 0, vs 0.95 +/- 0.84, n = 10, in the presence of N-omega-nitro-L-argini ne methyl ester, 10(-4) mol/L, p < 0.01). CONCLUSIONS: The data substa ntiate previous indirect studies suggesting that nitric oxide plays a role in the fetoplacental circulation. Flow-induced nitric oxide relea se in the stem villous arteries may make an important contribution to maintenance of this low-resistance circulation.