Myogenic and Endothelial Properties of Myometrial Resistance Arteries from Women with Preeclampsia

Abstract

Objecrive: To compare myometrial resistance arteries from women with preeclampsia and normal pregnant women with respect to myogenic behavior, acetylcholine-mediated dilatation, and distensibility.

Study Design: Arteries from women with preeclampsia (n = 14) and healthy term pregnant women (n = 17) were studied in a pressurized arteriograph system. Myogenic tone was evaluated during increments in intraluminal pressure from 20 to 120 mm Hg, as well as distensibility index at the same pressure steps in Ca2+-free solution substituted with papaverine. Endotheliumdependent relaxation was assessed by evaluating the response to acetylcholine (10⁻⁶ M) in the absence and presence of N^ω-nitro-L-arginine in arteries pressurized at a constant intraluminal pressure of 70 mm Hg.

Results: Overall myogenic tone did not differ between the arteries from the two patient groups studied, but the slope of the pressure-myogenic tone relationship in arteries from women with preeclampsia was significantly different (positive). Relaxation to acetylcholine was impaired in arteries from women with preeclampsia (6 ω 1% versus 18 t 4%, p < 0.05), whereas inhibition of nitric oxide synthase with N^ω-nitro-L-arginine abolished this response in both patients groups. The distensibility index (Ca^2+-free solution plus papaverine) of arteries from women with preeclampsia was increased as compared to arteries from normal pregnant women (p <0.05).

Conclusions: Pressure-induced myogenic tone and impaired acetylcholine-mediated vasodilatation in myometrial resistance arteries from women with preeclampsia might contribute to the increased vascular resistance in the uterine circulation seen in preeclampsia. The increased distensibility of the myornetrial arteries from women with preeclampsia might represent a compen-satory mechanism to preserve the blood flow in the uteroplacental vascular bed.

Key Words:

• Preeclampsia
• Myornetrial arteries
• Myogenic tone
• Acetylcholine
• Nitric oxide
• Distensibility