Higher endothelin concentrations in the fetoplacental unit of pregnant women of African ancestry

Preeclampsia. Part 2: experimental and genetic considerations

Preeclampsia-eclampsia is still one of the leading causes of maternal and fetal morbidity and mortality. Despite active research for many years, the etiology of this disorder exclusive to human pregnancy is an enigma. Recent evidence suggests there may be several underlying causes or predispositions leading to the signs of hypertension, proteinuria, and edema, findings that allow us to make the diagnosis of the "syndrome" of preeclampsia. Despite improved prenatal care, severe preeclampsia and eclampsia still occur. Although understanding of the pathophysiology of these disorders has improved, treatment has not changed significantly in over 50 years. Although postponement of delivery in selected women with severe preeclampsia improves fetal outcome to a degree, this is not done without risk to the mother. In the United States, magnesium sulfate and hydralazine are the most commonly used medications for seizure prophylaxis and hypertension in the intrapartum period. The search for the underlying cause of this disorder and for a clinical marker to predict those women who will develop preeclampsia-eclampsia is ongoing, with its prevention the ultimate goal. This review began with the clinical and pathophysiologic aspects of preeclampsia-eclampsia (Part 1). Now, in Part 2, the experimental observations, the search for predictive factors, and the genetics of this disorder are reviewed.

[Regulation of fetal placental circulation]

The development and the reactivity of fetoplacental circulation appear to be extremely well coordinated phenomena which follow a precise chronology and are regulated by numerous angiogenic and vasoactive factors. The endothelium of the villous vessels, due to its capacity to release vasodilatating substances, would appear to play a crucial role in the gradual decrease in the vascular resistance of the placenta, thereby enabling it to meet the growing needs of the fetus right up until the end of pregnancy. In the endothelium, as in the smooth muscle of the placental vessels, control of production and mechanisms of action of the signal modulators of placental tone--endothelin 1, nitric oxide, prostanoids, etc.--as well as their dependence on oxygen, are far from being entirely elucidated. The study of their interactions could contribute to better evaluating the relative importance of each of them in the particular balances which are established at different stages of normal pregnancy, as well as during pathological situations (pre-eclampsia, intrauterine growth retardation, etc.) when placental blood flow and fetal development are at risk of being compromised.

Selective protein kinase C isoforms are involved in endothelin-1-induced human uterine contraction at the end of pregnancy

The role of protein kinase C (PKC) in contraction of the human myometrium induced by endothelin-1 (ET-1) was investigated at the end of pregnancy. The expression and subcellular distribution of PKC isoforms were examined by Western blot analysis using isoform-specific antibodies. At least three conventional PKC isoforms (cPKC; alpha, beta1, and beta2), two novel PKC isoforms (epsilon and delta), and an atypical PKC isoform (zeta) were detected in pregnant myometrium. Quantitative immunoblotting revealed that all these isoforms were mainly distributed in the particulate fraction. The lack of a calcium chelator to modify the particulate sequestration of cPKC suggests an interaction with an anchoring protein such as receptor-activated C kinase-1, which is evidenced in the particulate fraction of the pregnant myometrium. Of the six isoforms, only PKCbeta1, PKCbeta2, PKCdelta, and PKCzeta were translocated to the particulate fraction, and PKCepsilon to the cytoskeletal fraction, after stimulation with ET-1. Involvement of PKC in the ET-1-induced contractile response is supported by the inhibition caused by the PKC inhibitor calphostin C. However, we demonstrated that the selective cPKC isoform inhibitor, Gö 6976, as well as the substantial depletion of PKCbeta1 and PKCepsilon and the partial depletion of PKCalpha and PKCdelta by a long-term treatment with phorbol 12,13-dibutyrate did not prevent ET-1-induced contraction. Accordingly, our results suggest that PKCdelta and PKCzeta activation mediated ET-1-induced contraction, whereas cPKC isoforms were not implicated in the human pregnant myometrium.

Endothelin-1 and relaxation of the rat aorta during pregnancy in nitroarginine-induced hypertension

In pregnant rats during hypertension induced by NO synthase inhibition, endothelin (ET) plasma levels are increased as in some preeclamptic women. Previously, the enhanced vasodepressor effect of endothelin-1 (ET-1) has been observed in this model, thus we decided to study the relaxation induced by ET-1 on the aorta. Non-pregnant or pregnant Wistar rats (n = 7 by group) were fed for 7 days (day 13-day 20) on a nitroarginine-enriched diet (L-NNA, 0.063% i.e. 30 mg/kg/day) or a control diet. Systolic blood pressure, measured by the tail cuff method on conscious rats at day 20 of gestation, was raised by the chronic L-NNA treatment (mean +/- s.e.m., mmHg, p < 0.001: pregnant L-NNA treated, 145 +/- 1.84 vs. pregnant control, 101 +/- 2.00 and non-pregnant L-NNA treated, 148 +/- 3.11 vs. non-pregnant control, 119 +/- 1.80). On day 20 ex vivo aortic ring relaxation was produced by ET-1 in vessels previously precontracted with norepinephrine only when endothelium was present. In control rats, ET-1 (10(-8) to 5 x 10(-8) M) produced a short but significant relaxation (mean value between 4 to 19%) followed by a long-lasting contracting phase, and a higher ET-1 concentration (10(-7) M) only produced contraction. Chronic L-NNA treatment decreased the level of relaxation (at least p < 0.05, in non-pregnant and pregnant rats) and with a 30 min L-NAME (10(-4) M) preincubation, relaxation was completely inhibited in non-pregnant and pregnant rats. BQ-123, an ETA receptor antagonist, did not produce any effect on ET-1 induced relaxation. BQ-788, an ETB receptor antagonist, significantly decreased it. In conclusion, in female rats, as in male rats, ET-1 induces a transient relaxation in the preconstricted aorta which involves endothelial ETB receptors. Despite a decrease in the systemic vascular reactivity during late gestation, the vasodilating and vasoconstricting properties of ET-1 on the aorta are not changed.