Prostacyclin and thromboxane changes predating clinical onset of preeclampsia: a multicenter prospective study

Pregnancy, vascular tone, and maternal hemodynamics: a crucial adaptation

The adaptation of vascular tone in early pregnancy precedes and probably triggers blood volume and cardiac output increase. Because the endothelium is known to regulate vascular smooth muscle action, the role of nitric oxide (NO) in the setting up of adequate uteroplacental and renal blood flow during normal pregnancy was investigated. The persistence of abnormally high uteroplacental resistance is a strong predisposing factor for intrauterine growth retardation and preeclampsia and can be screened by second trimester Doppler assessment of the uterine arteries. Current hypotheses suggested by experimental and clinical data concerning preeclampsia confirm the crucial role played by the endothelium and vascular tone adaptation. The analysis of these data leads to consider apart early-onset preeclampsia affecting pregnancies with growth retarded fetuses and associated with high vascular resistance. Lastly, NO donors seem to significantly decrease the impedance in the uteroplacental circulation and to improve fetoplacental hemodynamics assessed by Doppler measurements, and their therapeutic use in some forms of preeclampsia might be promising.

TARGET AUDIENCE

Obstetricians & Gynecologists, Family Physicians

LEARNING OBJECTIVES

After completion of this article, the reader will be able to summarize the events that regulate vascular tone in pregnancy, specifically the role of nitric oxide and other vasoactive prostaglandins in the regulation of vascular tone and to describe the various hypotheses concerning the mechanism and the mediators responsible for initiating endothelial damage in the various disorders of vascular tone in pregnancy.

Nitric oxide dysfunction in the pathophysiology of preeclampsia

Researchers disagree as to the importance of nitric oxide (NO) in preeclampsia. Many researchers have alluded to NO's possible primary or secondary role in the development of preeclampsia, but few have correlated the dysfunction of nitric oxide production with the other metabolic derangements seen in this condition. This paper will review the evidence that the primary dysfunction in preeclampsia is a relative deficiency of available NO (secondary to oxidative degradation) and an excess of peroxynitrite (ONOO(-)). The combination of a deficiency of NO and an increase in ONOO(-) can directly or indirectly initiate the vast majority of physiological and serological changes associated with preeclampsia, such as blood pressure, increased glomerular filtration rate, proteinuria, platelet dysfunction, increased thromboxane and endothelin, and a decrease in prostacyclin. Understanding the complex role of nitric oxide in this condition may explain why previous interventions have been unsuccessful and suggest possible strategies for prevention and treatment in the future.

Differential effects of sera from normotensive and hypertensive pregnant women on Ca(2+) metabolism in normal vasular smooth muscle cells

The clinical features of preeclampsia have been traditionally ascribed to a generalized vascular endothelial cell dysfunction. The present study investigates the effect of sera from preeclamptic women and normal pregnancy on the metabolism of intracellular Ca(2+) concentration ([Ca(2+)](i)) in normal cultured vascular smooth muscle cells (VSMC). Sera were obtained from normotensive pregnant women (NTP) (n = 17), preeclamptic women (PE) (n = 15), pregnant women with chronic (essential) hypertension (pregnant EHT) (n = 8), non-pregnant women with essential hypertension (non-pregnant EHT) (n = 12), and age-matched non-pregnant normotensive women (NNP) (n = 18). Serum (10%) was applied to both primary cultures of rat aortic smooth muscle cells and to the A-10 vascular muscle cell line. Levels of [Ca(2+)](i) were determined fluorometrically. After a 4-h incubation with serum, basal [Ca(2+)](i) was not significantly altered. However, compared with normal pregnant sera, PE sera markedly reduced hormonally induced Ca(2+) transients. Thus, following acute stimulation of rat VSMC (primary cultures) with 10(-8)M angiotensin II, peak [Ca(2+)](i) responses (% increment over baseline) were 443 +/- 22, 184 +/- 18, 259 +/- 12, 274 +/- 23, and 255 +/- 15% in NTP, PE, pregnant EHT, non-pregnant EHT, and NNP, respectively (P <0.01 PE versus NTP, P <0.05 PE versus NNP and pregnant and non-pregnant EHT). These effects of sera on [Ca(2+)](i) were qualitatively reproduced in platelets obtained from healthy volunteers. Also, depolarization-activated Ca(2+) influx in VSMC was affected by the different sera groups in a manner similar to that seen with hormonally induced [Ca(2+)](i) responses. The altered [Ca(2+)](i) changes by PE sera disappeared 5 wk after delivery. The effect of the different sera groups on hormonally triggered Ca(2+) transients in normal VSMC, as well as the normalization of [Ca(2+)](i) responses after delivery, suggest the presence of a circulating serum factor in PE. Inasmuch as [Ca(2+)](i) is the major determinant of VSMC tone, it is possible that consequent to the attenuation of [Ca(2+)](i) responses, this putative circulating factor counterbalances the intense vasoconstriction in PE.

AT(1) receptor agonistic antibodies from preeclamptic patients cause vascular cells to express tissue factor

BACKGROUND

We recently described autoantibodies (angiotensin-1 receptor autoantibodies, AT(1)-AA) directed at the AT(1) receptor in the serum of preeclamptic patients, whose placentas are commonly infarcted and express tissue factor (TF). Mechanisms of how AT(1)-AA might contribute to preeclampsia are unknown. We tested the hypothesis that AT(1)-AA cause vascular smooth muscle cells (VSMC) to express TF.

METHODS AND RESULTS

IgG from preeclamptic patients containing AT(1)-AA was purified with anti-human IgG columns. AT(1)-AA were separated from the IgG by ammonium sulfate precipitation. We transfected Chinese hamster ovary cells overexpressing the AT(1) receptor with TF promoter constructs coupled to a luciferase reporter gene. VSMC were obtained from human coronary arteries. Extracellular signal-related kinase activation was detected by an in-gel kinase assay. AP-1 activation was determined by electromobility shift assay. TF was measured by ELISA and detected by immunohistochemistry. Placentas from preeclamptic women stained strongly for TF, whereas control placentas showed far less staining. We proved AT(1)-AA specificity by coimmunoprecipitating the AT(1) receptor with AT(1)-AA but not with nonspecific IgG. Angiotensin (Ang) II and AT(1)-AA both activated extracellular signal-related kinase, AP-1, and the TF promoter transfected VSMC and Chinese hamster ovary cells, but only when the AP-1 binding site was present. We then demonstrated TF expression in VSMC exposed to either Ang II or AT(1)-AA. All these effects were blocked by losartan. Nonspecific IgG or IgG from nonpreeclamptic pregnant women had a negligible effect.

CONCLUSIONS

We conclude that AT(1)-AA and Ang II both stimulate the AT(1) receptor and initiate a signaling cascade resulting in TF expression. These results show an action of AT(1)-AA on human cells that could contribute to the pathogenesis of preeclampsia.