Functional Characteristics of Small Placental Arteries

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OBJECTIVESThe aim of this study was to investigate characteristics of placental arteries capable of influencing vasomotor tone in the fetoplacental vascular bed. Contractile characteristics and endothelium-dependent and endothelium-independent relaxation were examined.STUDY DESIGNBy means of a small vessel myograph arteries of mean normalized internal diameter 353.22 +-\13.14 microns were studied under isometric conditions. Contractile function was assessed with a variety of agonists, including angiotensin II, endothelin-1, the thromboxane mimetic U46619, prostaglandin E2, and prostaglandin F2alpha. The effect of physiologic and supraphysiologic PO2 on vascular function was also examined. Relaxation was assessed in response to known endothelium-dependent vasodilators, including acetylcholine, bradykinin, histamine, and A23187 and to sodium nitroprusside (endothelium independent). The effect of indomethacin and the nitric oxide synthase inhibitor, NG -nitro-L-arginine methyl ester on contractile function was also evaluated.RESULTSSensitivity to sodium nitroprusside was reduced by a high PO (2). U46619 was the most potent constrictor agonist studied. The response of precontracted arteries to known endothelium-dependent vasodilators was minimal, other than for histamine, which led to modest relaxation. The constrictor response to U46619 was increased in the presence of NG -nitro-L-arginine methyl ester.CONCLUSIONSOxygen tension may be an important determinant of relaxation in small placental arteries. Receptor-mediated release of endothelium-derived relaxing factor is not a major mechanism in the fetoplacental circulation. (AM J OBSTET GYNECOL 1994;170:945-51.)

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