Preeclampsia: Evidence for impaired shear stress–mediated nitric oxide release in uterine circulation

Abstract

Objective: We sought to compare flow-mediated dilatation and myogenic and norepinephrine-induced tone in myometrial resistance arteries from women with preeclampsia and healthy pregnant women and to evaluate the role that nitric oxide may play in these responses. Study Design: Arteries (approximately 200μm, at 50 mm Hg) were dissected from myometrial biopsy specimens from women undergoing emergency cesarean delivery because of preeclampsia (n = 6) and from healthy control subjects undergoing planned cesarean delivery (n = 9). Responses to intraluminal flow, pressure, and a constrictor agonist (norepinephrine, 10–6 mol/L) were studied in the absence and presence of the nitric oxide synthase inhibitor N ωnitro-L -arginine (10–4 mol/L). Myogenic and norepinephrine-induced tone were calculated after the determination of artery diameter in the absence of extracellular calcium and in the presence of papaverine (10–4 mol/L). Results: An increase in intraluminal flow led to dilatation of isolated myometrial arteries from healthy gravid women, whereas flow-mediated dilatation was absent in arteries from gravid patients with preeclampsia (increase in diameter at maximum flow rate of 204 μL/min, 28% ± 5% in healthy gravid patients vs –15% ± 6% in gravid women with preeclampsia; analysis of variance, P <.05). Addition of N ω-nitro-L -arginine had no significant effect on flow-mediated responses in arteries from women with preeclampsia, whereas flow-mediated dilatation was abolished after addition of N ω-nitro-L -arginine in arteries from healthy gravid women (increase in diameter at a maximum flow rate of 204 μL/min, 28% ± 5% control vs –9% ± 5% N ω-nitro-L -arginine; analysis of variance, P <.05). Arteries from women with preeclampsia developed pressure-induced myogenic and norepinephrine-induced tone, similar to that obtained in arteries from healthy gravid women. In arteries from gravid women with preeclampsia, inhibition of nitric oxide synthase enhanced myogenic-induced tone (25% ± 4% control vs 35% ± 5% N ω-nitro-L -arginine; P <.05) and norepinephrine-induced tone (36% ± 4% control vs 46% ± 6% N ω-nitro-L -arginine; P <.05), as in arteries from healthy gravid women. Conclusions: Nitric oxide may participate in modulation of pressure- and norepinephrine-induced tone even in preeclampsia, but the shear stress–mediated release of nitric oxide is absent. Failure of shear stress–mediated dilation in myometrial arteries from gravid women with preeclampsia might contribute to the impaired uteroplacental blood flow in this disease. (Am J Obstet Gynecol 2000;183:160-6.)