Vasoactive mediators in pregnancy-induced hypertensive disorders: a longitudinal study

Placental growth factor blunts uterine artery responses to angiotensin II

OBJECTIVE

Changes in maternal serum concentration of placental growth factor (PlGF) and vascular response to intravascular infusion of Angiotensin II (Ang II) follow a bell-shaped curve pattern during gestation. This study evaluates the effects of PlGF and soluble vascular endothelial growth factor receptor-1 (sFlt-1) on responses of human uterine arteries (UA) to Ang II.

DESIGN

Experimental.

SETTING

Baylor College of Medicine and Texas Children's Hospital-Pavilion for Women.

SAMPLE

Uterine arteries samples (n = 14) were obtained from normotensive women undergoing caesarean hysterectomy at ≥32 weeks.

METHODS

Uterine arteries rings were incubated with (1) Krebs solution; (2) PlGF at 1.45, 14.5, and 500 pg/ml; (3) sFlt-1 at 2 ng/ml; and (4) a combination of sFlt-1, and PlGF. Dose-contraction responses to Ang II were determined in UA rings incubated in the above-mentioned conditions. Responses were also measured in presence of L-NAME or inhibitors of endothelium-derived hyperpolarising factor: apamine and charybdotoxin. The t-test was used for comparisons.

MAIN OUTCOME MEASURE

Changes in vascular reactivity of UA rings.

RESULTS

PlGF blunted (P = 0.03) and sFlt-1 increased (P <0.01) the UA maximum responses to Ang II. A combination of sFlt-1 and PlGF blunted UA responses to Ang II (P < 0.05). l-NAME, apamine, and charybdotoxin reversed the relaxation effects of PlGF on UA responses to Ang II (P < 0.05).

CONCLUSIONS

PlGF contributes to the blunted vascular response to Angiotensin II during normotensive pregnancies and sFlt-1 appears to attenuate this effect. PlGF and sFlt-1 may contribute to the regulation of vascular tone during pregnancy by altering the vascular response to Angiotensin II.

FUNDING

Baylor College of Medicine.

TWEETABLE ABSTRACT

Placental growth factor and soluble vascular endothelial growth factor receptor-1 modulate the uterine artery response to Angiotensin II in normotensive pregnant women.

Plasmatic levels of N-terminal pro-atrial natriuretic peptide in preeclamptic patients and healthy normotensive pregnant women

BACKGROUND AND OBJECTIVE

To compare plasma N-terminal pro-atrial natriuretic peptide concentrations in preeclamptic patients and healthy normotensive pregnant women.

METHODS

A cases-controls study was done with 180 patients at Hospital Central Dr. Urquinaona, Maracaibo, Venezuela, that included 90 preeclamptic patients (group A; cases) and 90 healthy normotensive pregnant women selected with the same age and body mass index similar to group A (group B; controls). Blood samples were collected one hour after admission and prior to administration of any medication in group A to determine plasma N-terminal pro-atrial natriuretic peptide and other laboratory parameters.

RESULTS

Plasma N-terminal pro-atrial natriuretic peptide concentrations in group A (mean 1.01 [0.26] pg/mL) showed a significant difference when compared with patients in group B (mean 0.55 [0.07] pg/mL; P<.001]. There was no significant correlation with systolic and diastolic blood pressure values in preeclamptic patients (P=ns). A cut-off value of 0.66ng/mL had an area under the curve of 0.93, sensitivity of 87.8%, specificity of 83.3%, a positive predictive value of 84.0% and a negative predictive value of 87.2%, with a diagnostic accuracy of 85.6%.

CONCLUSION

Preeclamptic patients have significantly higher concentrations of plasma N-terminal pro-atrial natriuretic peptide compared with healthy normotensive pregnant women, with high predictive values for diagnosis.

Cytokines, angiogenic, and antiangiogenic factors and bioactive lipids in preeclampsia

Preeclampsia is a low-grade systemic inflammatory condition in which oxidative stress and endothelial dysfunction occurs. Plasma levels of soluble receptor for vascular endothelial growth factor (VEGFR)-1, also known as sFlt1 (soluble fms-like tyrosine kinase 1), an antiangiogenic factor have been reported to be elevated in preeclampsia. It was reported that pregnant mice deficient in catechol-O-methyltransferase (COMT) activity show a preeclampsia-like phenotype due to a deficiency or absence of 2-methoxyoestradiol (2-ME), a natural metabolite of estradiol that is elevated during the third trimester of normal human pregnancy. Additionally, autoantibodies (AT1-AAs) that bind and activate the angiotensin II receptor type 1 a (AT1 receptor) also have a role in preeclampsia. None of these abnormalities are consistently seen in all the patients with preeclampsia and some of them are not specific to pregnancy. Preeclampsia could occur due to an imbalance between pro- and antiangiogenic factors. VEGF, an angiogenic factor, is necessary for the transport of polyunsaturated fatty acids (PUFAs) to endothelial cells. Hence reduced VEGF levels decrease the availability of PUFAs to endothelial cells. This leads to a decrease in the formation of anti-inflammatory and angiogenic factors: lipoxins, resolvins, protectins, and maresins from PUFAs. Lipoxins, resolvins, protectins, maresins, and PUFAs suppress insulin resistance; activation of leukocytes, platelets, and macrophages; production of interleukin-6 and tumor necrosis factor-α; and oxidative stress and endothelial dysfunction; and enhance production of prostacyclin and nitric oxide (NO). Estrogen enhances the formation of lipoxin A4 and NO. PUFAs also augment the production of NO and inhibit the activity of angiotensin-converting enzyme and antagonize the actions of angiotensin II. Thus, PUFAs can prevent activation of angiotensin II receptor type 1 a (AT1 receptor). Patients with preeclampsia have decreased plasma phospholipid concentrations of arachidonic acid (AA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA), the precursors of lipoxins (from AA), resolvins (from EPA and DHA), and protectins (from DHA) and prostaglandin E1 (PGE1 from DGLA: dihomo-γ-linolenic acid) and prostacyclin (PGI2 derived from AA). Based on these evidences, it is proposed that preeclampsia may occur due to deficiency of PUFAs and their anti-inflammatory products: lipoxins, resolvins, protectins, and maresins.

Preeclampsia: an obstetrician's perspective

Preeclampsia is a pregnancy-specific syndrome that usually develops after 20 weeks gestation. The exact pathogenic mechanisms remain uncertain and are likely multifactorial. Preeclampsia is a heterogeneous condition with potentially maternal and fetal consequences. As part of the spectrum of hypertensive disorders of pregnancy, preeclampsia may progress rapidly and is a leading cause of maternal and perinatal morbidity and mortality worldwide. In the United States, the incidence of preeclampsia has increased. Clinical manifestations are highly variable and may occur antepartum, intrapartum, or postpartum. Hypertension and proteinuria are the traditional hallmarks for the diagnosis of preeclampsia. These signs may occur with or without multisystem dysfunction and fetal involvement. Risk factors have been identified for the development of preeclampsia; however, ideal methods for prevention, screening, and treatment remain elusive. Preeclampsia resolves after delivery of the fetus, but patients may still have hypertension postpartum. Women and fetuses affected by preeclampsia are at higher risk of developing long-term health issues. There appear to be risk factors common to hypertensive disorders of pregnancy and cardiovascular disease seen later in adulthood. Physicians providing healthcare to women are urged to recognize potential risk factors that arise from patient obstetric histories so that optimal long-term health surveillance is provided.

Endothelin Converting Enzyme (ECE) Activity in Normal Pregnancy and Preeclampsia

OBJECTIVE

Enhanced production of endothelin-1, due to endothelial cell dysfunction has been considered to be the cause of increased plasma levels of endothelin-1 in preeclampsia. The present study was aimed at analyzing endothelin-converting-enzyme activity, (which reflect the production rate of endothelin-1 (ET-1) from big endothelin-1 (big ET-1)), big endothelin-1, and endothelin-1 concentrations from women with preeclampsia compared to normal pregnant women. Moreover, we analyzed plasma levels of these substances longitudinally throughout normal pregnancy.

STUDY DESIGN

Twenty-nine pregnant healthy women were recruited to the study. Blood samples were obtained at 18, 28, and 38 weeks gestation and six weeks postpartum. Twenty-seven women with preeclampsia were included. Blood samples were taken at diagnosis (average 35 weeks gestation; range 27-39 weeks) and six weeks postpartum. Endothelin-1 was analyzed by enzyme linked immunoassay (ELISA) and big-ET-1 by radioimmunoassay (RIA). Endothelin-converting-enzyme activity was measured using big endothelin-1 as a substrate and thiorphan as an inhibitor of serum neutral endopeptidase. The amount of endothelin-1 generated during one hour was measured by RIA. Mean +/- SEM is given.

RESULTS

In normal pregnancy endothelin-1 concentrations at 38 weeks and postpartum were increased by 30% (p < 0.01) and 50% (p < 0.001), respectively compared with the second trimester values. Endothelin-converting-enzyme activity did not change. At diagnosis endothelin-1 was higher in women with preeclampsia than in the controls at 38 weeks (0.96 +/- 0.07 vs. 0.64 +/- 0.06 pmol/L; p < 0.001). Likewise, endothelin-converting-enzyme activity was higher in the preeclampsia group (222 +/- 15 vs. 172 +/- 8 pmol ET/ml/h; p < 0.01). This difference remained at six weeks postpartum.

CONCLUSION

Our findings imply enhanced ET-1 production in preeclampsia. The elevated endothelin-converting-enzyme activity postpartum may indicate an inherent endothelial dysfunction predisposing to preeclampsia or that preeclampsia may cause irreversible changes in endothelial function.

Natriuretic peptides and hemodynamics in preeclampsia

OBJECTIVE

The purpose of this study was to evaluate the relationship between natriuretic peptides (NT-proANP and NT-proBNP) and hemodynamic parameters in preeclampsia.

STUDY DESIGN

This was a cross-sectional study of 19 preeclamptic, 15 chronic hypertensive, and 26 normotensive women in the third trimester of pregnancy. Stroke index (SI), heart rate (HR), cardiac index (CI), systemic vascular resistance index (SVRI), and left cardiac work index (LCWI) were derived by whole-body impedance cardiography. Systolic blood pressure (SAP), diastolic blood pressure (DAP), and mean arterial pressure (MAP) were measured. The plasma levels of NT-proANP and NT-proBNP were determined with radioimmunoassays.

RESULTS

NT-proANP and NT-proBNP concentrations were significantly higher in preeclamptic women compared to chronic hypertensive and normotensive pregnancies. Preeclamptic women had lower CI and HR and higher SAP, MAP, and SVRI than the control groups. In preeclampsia NT-proANP correlated significantly with SAP and SVRI; meanwhile, NT-proBNP correlated significantly with SVRI and CI. These correlations persisted in the subgroup of nonmedicated preeclamptic women, except in the case of NT-proBNP and CI.

CONCLUSION

High NT-proANP and NT-proBNP concentrations in preeclampsia reflect the strain on the heart caused by high afterload, rather than the function of the heart expressed as SI or CI.

Preeclampsia: a renal perspective

Preeclampsia is a syndrome that affects 5% of all pregnancies, producing substantial maternal and perinatal morbidity and mortality. The aim of this review is to summarize our current understanding of the pathogenesis of preeclampsia with special emphasis on the recent discovery that circulating anti-angiogenic proteins of placental origin may play an important role in the pathogenesis of proteinuria and hypertension of preeclampsia.

Cyclooxygenase involvement in thromboxane-dependent contraction in rat mesenteric resistance arteries

The influence of cyclooxygenase pathway activation following thromboxane-endoperoxide (TP) receptor stimulation was studied in rat mesenteric resistance arteries (n=6 to 10 per group). We studied isolated, perfused, and pressurized mesenteric resistance arteries (mean internal diameter 214 microm) using an arteriograph, enabling us to study arteries in physiological conditions of flow and pressure. Changes in diameter were continuously recorded, and contractions measured as internal diameter reduction. Release of cyclooxygenase pathway metabolites was also assessed by enzyme immunoassay (EIA) analysis of mesenteric bed perfusions. The thromboxane A2 (TxA2) analog U-46619 (1 micromol/L) induced a significant contraction (108 microm maximal diameter reduction). Inhibition by 3 chemically different cyclooxygenase inhibitors (ie, flurbiprofen, indomethacin, and aspirin) potently reduced the contraction to 27%, 25%, and 6% of control, respectively. The selective cyclooxygenase-1 inhibitor SC-58560 inhibited U-46619 contraction, whereas selective cyclooxygenase-2 inhibition (SC-58236) had no effect. Thromboxane synthase inhibition (furegrelate) did not affect U-46619-induced contraction, but it was reduced by cytosolic phospholipase A2 inhibition. Measurement of cyclooxygenase derivatives produced by the isolated mesenteric bed showed that PGE2 was produced after TxA2-receptor stimulation with U-46619. Exogenous prostaglandin E2 (in the presence of the TxA2 receptor antagonist SQ 29 548) and U-46619 contracted mesenteric arteries with a similar potency (EC50: 0.30 and 0.48 micromol/L, respectively). This study provides the first evidence that TxA2-receptor-dependent contraction in a resistant artery involved cyclooxygenase stimulation and, at least in part, a PGE2 formation. This mechanism of TxA2-dependent contraction in resistant arteries might be of importance in the understanding of diseases affecting resistant arteries and involving TxA2, such as hypertension.

Maternal and fetal plasma endothelin levels in intrauterine growth restriction: relation to umbilical artery Doppler flow velocimetry

The objective of this study was to examine maternal and fetal endothelin-1 (ET-1) in pregnancies complicated with intrauterine growth restriction (IUGR) and to correlate these data with umbilical artery Doppler flow velocity waveforms (FVW). Higher mean maternal (13.8 +/- 6.4 vs 9.2 +/- 3.4 pmol/L, p < 0.05) and fetal (18.5 +/- 9.6 vs 11.7 +/- 6.9 pmol/L, p < 0.05) ET-1 levels were found in pregnancies complicated with IUGR than in controls. Fetal ET-1 level was related to birth weight percentile for gestational week. Maternal and fetal ET-1 concentrations were not related to umbilical artery Doppler flow S/D ratio, PI and RI. Maternal or fetal ET-1 concentrations were also not related to umbilical artery pH, PO2 and PCO2. Pregnancy-induced hypertension was significantly associated with an elevated fetal and maternal ET-1 concentration. In conclusion, increased production and secretion of ET-1 may play a role in the pathophysiology of idiopathic IUGR. Over-production of ET-1 in IUGR is not associated with increased placental resistance as reflected in abnormal umbilical artery Doppler FVW.

Prostacyclin/thromboxane early changes in pregnancies that are complicated by preeclampsia

OBJECTIVE

The purpose of this study was to examine 6-keto-prostaglandin F(1)(alpha) and thromboxane B(2) plasma levels throughout normotensive and preeclamptic pregnancies and to analyze the predictive values of these quantifications for the detection of preeclampsia during the second trimester of pregnancy.

STUDY DESIGN

Blood samples were collected from 30 healthy, nonpregnant women and at 4-week intervals from a cohort of nulliparous women who were recruited before 16 weeks of gestation. Preeclampsia developed in 26 patients; 52 normotensive control subjects were matched from the same cohort. The 6-keto-prostaglandin F(1)(alpha) and thromboxane B(2) were assayed by radioimmunoassay. Trends were compared between pregnancy groups and with the nonpregnant women. Predictive values were determined with the second-trimester assessments.

RESULTS

The 6-keto-prostaglandin F(1)(alpha)/thromboxane B(2) ratio decreased throughout pregnancy in women with preeclampsia; there were no significant changes in normotensive women. We found higher thromboxane B(2) levels within the group with preeclampsia during the first gestational trimester (preeclampsia, 188 +/- 17 pg/mL; control, 119 +/- 4.8 pg/mL [mean +/- SEM]; P =.001). During the third trimester, patients with preeclampsia had lower 6-keto-prostaglandin F(1)(alpha) levels than did control subjects (preeclampsia, 191 +/- 9.8 pg/mL; control, 288 +/- 10 pg/mL; P =.001). The 6-keto-prostaglandin F(1)(alpha)/thromboxane B(2) ratio was suitable to calculate predictive values; the best cutoff point and time interval were 3.0 and 22 to 26 weeks of gestation, respectively. Sensitivity, specificity, and positive and negative predictive values were 88%, 97%, 69%, and 99%, respectively; the odds ratio was 14.6 (95% CI, 6.9-30.4).

CONCLUSION

The prostacyclin/thromboxane ratio favored vasoconstriction early in gestation in women in whom preeclampsia developed. A 6-keto-prostaglandin F(1)(alpha)/thromboxane B(2) ratio of <or=3.0 at 22 to 26 weeks of gestation had a high predictive value for the development of preeclampsia.

Increased NO-mediated and reduced TxA2-dependent responses in skeletal muscle arterioles in pregnancy

The contribution of skeletal muscle microvessels to pregnancy-induced decrease in peripheral vascular resistance and its underlying mechanisms are not fully understood. We aimed to test the hypothesis that pregnancy enhances arteriolar dilation and reduces constriction by increasing NO-mediation and decreasing reactivity to TxA2. Thus, changes in diameter of isolated, pressurized gracilis muscle arterioles (d: approximately 180 microm) of non-pregnant (NP) and pregnant (P) rabbits to vasoactive agents were measured by videomicroscopy. Acetylcholine (ACh) elicited significantly greater dilations in P than in NP arterioles that could be inhibited by L-NAME, a NO synthase blocker. Dilations to the NO donor SNP did not differ between P and NP arterioles. Constrictions to norepinephrine and the TxA2 receptor agonist U46619 were significantly attenuated in P as compared to NP arterioles. L-NAME increased norepinephrine-induced arteriolar constrictions eliminating the difference between responses of NP and P arterioles. L-NAME enhanced constrictions to U46619 in P and NP arterioles, but the constrictions were still greater in NP vessels. The number of vascular TxA2 receptors-characterized by the TxA2 analog [125I]-BOP in aortic membrane preparations-was significantly less in P as compared to NP rabbits (NP: 284 +/- 83, P: 62 +/- 14 fmol/mg protein, p<0.01). Thus, pregnancy up-regulates endothelial NO- and down regulates TxA2-mediation of responses of skeletal muscle arterioles. These changes in the local regulation of microvascular tone are likely to favor a dilated state of skeletal muscle arterioles, which may contribute to the decreased peripheral vascular resistance during normal pregnancy.

Normalization of vasoactive changes in preeclampsia precedes clinical recovery

OBJECTIVE

The objective of this study is to compare the serum levels of fibronectin, nitric oxide (NO), cyclic guanosine-monophosphate, endothelin-1, and 6-keto-prostaglandin-F 1alpha in women with and without preeclampsia before and after delivery.

METHODS

We studied 20 singleton pregnancies complicated by preeclampsia, and 20 women undergoing elective cesarean delivery were selected as controls. The normalization of circulating concentrations of maternal plasma NO, cyclic guanosine-monophosphate, fibronectin, endothelin-1, thromboxane-B 2 and renin, and urinary 6-keto-prostaglandin-F 1alpha after delivery was evaluated.

RESULTS

Mean systolic and diastolic blood pressure (BP) in the puerperium of preeclamptic women remained high after discharge from hospital, and only circulating fibronectin levels were found to be elevated in affected women at the end of hospital stay 5 days after delivery. Normalization of the imbalance in vasoactive substances and renal impairment in preeclampsia occur more rapidly than the patient's clinical recovery, within 2-3 days postpartum.

CONCLUSIONS

Slow normalization of circulating fibronectin concentrations reflects slow recovery of endothelial damage in preeclampsia, which may play a major role in maintaining high BP in the puerperium. Plasma levels of endothelin-1 declined to normal levels by the third postpartum day and the finding is consistent with the hypothesis that endothelin-1 is not the major vasoconstrictor in the pathophysiology of preeclampsia.

Predictive value of hormone measurements in maternal and fetal complications of pregnancy

Intrauterine tissues (placenta, amnion, chorion, decidua) express hormones and cytokines that play a decisive role in maternal-fetal physiological interactions. The excessive or deficient release of some placental hormones in association with gestational diseases may reflect an abnormal differentiation of the placenta, an impaired fetal metabolism, or an adaptive response of the feto-placental unit to adverse conditions. This review is focused on the applicability of hormone measurements in the risk assessment, early diagnosis, and management of pregnancies complicated by Down's syndrome, fetal growth restriction, preeclampsia, preterm delivery, and diabetes mellitus. Combined hormonal tests or the combination of hormones and ultrasound may achieve reasonable sensitivity, but research continues to simplify the screening programs without sacrificing their accuracy. Only in a few instances is there sufficient evidence to firmly recommend the routine use of hormone tests to predict maternal and fetal complications, but the judicious use of selected tests may enhance the sensitivity of the risk assessment based solely on clinical and ultrasound examination.

Pathophysiology of preeclampsia and the role of serotonin

Hypertensive disorders constitute the most common medical complications of pregnancy. In normal pregnancy, impressive physiological changes take place in the maternal cardiovascular system. Morphological changes are the result of invasion of migratory trophoblast cells into the walls of the spiral arteries. After destruction of elastic, muscular and neural tissue in the media, the trophoblast cells get incorporated into the vessel wall and the endothelial lining of the spiral arteries is restored. The physiological changes create a low-resistance, low-pressure, high-flow system with the absence of maternal vasomotor control. Biochemical adaptations in maternal vasculature include changes in the prostaglandin system, the renin-angiotensin-aldosteron system and the kallikrein-kinin system. In preeclampsia, physiological changes in the spiral arteries are confined to the decidual portion of the arteries. Myometrial segments remain anatomically intact and fail to dilate. In addition, the adrenergic nerve supply is left intact. The cause of this impaired endovascular trophoblast invasion is not yet elucidated. But in combination with the imbalance between vasodilator and vasoconstrictor eicosanoids, it gives rise to reduced perfusion of the intervillous space. In the absence of an adequate production of antiaggregatory prostacyclin (PGI(2)), nitric oxide, or both, surface-mediated platelet activation is supposed to occur on the surface of the spiral arteries. Because platelets are the principal source of circulating serotonin, the increased platelet aggregation in preeclampsia causes an increase in serotonin levels. Interaction of serotonin with serotonin(1)- or serotonin(2)-receptors depends on the state of the endovascular trophoblast or endothelium in the spiral arteries and has opposite effects with regard to vasodilating and vasoconstrictive influences.

Endothelin type a receptor blockade attenuates the hypertension in response to chronic reductions in uterine perfusion pressure

A chronic reduction in uterine perfusion pressure in pregnant rats is associated with a significant elevation in mean arterial pressure (MAP) and reduction in kidney function. The purpose of this study was to examine the role of endothelin in mediating the hypertension in response to chronic reductions in uterine perfusion pressure in conscious, chronically instrumented, pregnant rats. MAP in pregnant rats with chronic reductions in uterine perfusion pressure (123.0+/-1.8 mm Hg) was significantly higher than that in control pregnant rats (101.3+/-4.0 mm Hg). Renal expression of preproendothelin mRNA as determined by ribonuclease protection assay was also significantly elevated in the medulla (>45%, P<0.05) and in the cortex (>22%, P:<0.05) of the pregnant rats with chronic reductions in uterine perfusion pressure compared with control pregnant rats. Chronic administration of the selective endothelin type A receptor antagonist (ABT-627, 5 mg/kg per day for 10 days) markedly attenuated the increase in MAP observed in the pregnant rats with chronic reductions in uterine perfusion pressure (103.3+/-5.6 mm Hg, plus endothelin antagonist; P<0.05). However, endothelin type A receptor blockade had no significant effect on blood pressure in the normal pregnant animals (96.0+/-2.7 mm Hg, plus endothelin antagonist). These findings suggest that endothelin plays a major role in mediating the hypertension produced by chronic reductions in uterine perfusion pressure in pregnant rats.

Primary, secondary, and tertiary prevention of pre-eclampsia

Pre-eclampsia remains one of the major obstetrical problems in less-developed countries. The causes of this condition are still unknown, thus effective primary prevention is not possible at this stage. Research in the past decade has identified some major risk factors for pre-eclampsia, and manipulation of these factors might result in a decrease in its frequency. In the early 1990s aspirin was thought to be the wonder drug in secondary prevention of pre-eclampsia. Results of large trials have shown that this is not the case: if there is an indication for using aspirin it is in the patient at a very high risk of developing severe early-onset disease. The calcium story followed a more or less similar pattern, with the difference that existing evidence shows that women with a low dietary calcium intake are likely to benefit from calcium supplementation. Proper antenatal care and timed delivery are of utmost importance in tertiary prevention of pre-eclampsia. There is evidence to suggest that the intrinsic direct effect of moderate degrees of maternal hypertension is beneficial to the fetus. Severe hypertension needs treatment. If antihypertensive is indicated, there is no clear choice of a drug. Hydralazine should no longer be thought of as the primary drug, most studies show a preference for calcium channel blockers.

Maternal thromboxane and prostacyclin levels in relation to fetal birth weight

OBJECTIVE

To analyse whether pregnancies resulting in a small for gestational age neonate are preceded by a prostacyclin deficiency or an imbalance between thromboxane and prostacyclin.

STUDY DESIGN

At five fixed time points during pregnancy, 24-h urine samples were collected for the measurement of thromboxane and prostacyclin metabolites thromboxane-B(2) (TXB(2)) and 6-keto-prostaglandin F(1alpha) (6-keto-PGF(1alpha)). In order to study trend differences between pregnancies with appropriate (AGA; n=26) and small for gestational age neonates (SGA; n=17), trend analysis with simple contrasts were accomplished for TXB(2), 6-keto-PGF(1alpha) and the TXB(2)/6-keto-PGF(1alpha) ratio.

RESULTS

Trend analysis showed higher TXB(2) levels and higher TXB(2)/6-keto-PGF(1alpha) ratios in patients with SGA versus AGA newborns. No statistically significant difference in 6-keto-PGF(1alpha) excretion between patients with SGA and AGA newborns was detected.

CONCLUSION

The birth of an SGA neonate is not preceded by prostacyclin deficiency. With ongoing pregnancy an imbalance between thromboxane and prostacyclin becomes more obvious in pregnancies with SGA newborns.

Urinary prostaglandin excretion in pregnancy: the effect of dietary sodium restriction

INTRODUCTION

Dietary sodium restriction results in activation of the renin-angiotensin-aldosterone-system. In the non-pregnant situation renin release in response to a low sodium diet is mediated by prostaglandins. We studied the effect of dietary sodium restriction on urinary prostaglandin metabolism in pregnancy.

PATIENTS AND METHODS

In a randomized, longitudinal study the excretion of urinary metabolites of prostacyclin (6-keto-PGF(1 alpha)and 2,3-dinor-6-keto-PGF(1 alpha)) and thromboxane A(2)(TxB(2)and 2,3-dinor-TxB(2)) was determined throughout pregnancy and post partum in 12 women on a low sodium diet and in 12 controls.

RESULTS

In pregnancy the excretion of all urinary prostaglandins is increased. The 6-keto-PGF(1 alpha)/ TxB(2)-ratio as well as the 2, 3-dinor-6-keto-PGF(1 alpha)/ 2,3-dinor-TxB(2)-ratio did not significantly change in pregnancy. CONCLUISION Prostacyclin and thromboxane do not seem to play an important role in sodium balance during pregnancy.

Endothelin-mediated preeclampsia at high altitude

Preeclampsia is pregnancy-induced hypertension. The hypoxia at high altitude increases the incidence of preeclampsia. Endothelin is released in response to hypoxia and is associated with other hypertensive states at high altitude. Endothelin may play a major role in preeclampsia for individuals residing at high altitude. Endothelin antagonists may prove useful in the treatment of preeclampsia.

Perfusion of the hypothalamic paraventricular nucleus with N-methyl-D-aspartate produces thromboxane A2 and centrally activates adrenomedullary outflow in rats

We applied a microdialysis technique for the measurement of hypothalamic thromboxane B2, a stable metabolite of thromboxane A2, in urethane-anesthetized rats. Perfusion with N-methyl-D-aspartate (1.5 and 2.5mM) of the paraventricular nucleus by microdialysis probe concentration-dependently elevated the levels of thromboxane B2 in this region and plasma levels of catecholamines. The elevation of adrenaline was much more marked than that of noradrenaline. Pretreatment with dizocilpine maleate (0.1 mM), a non-competitive antagonist of N-methyl-D-aspartate receptors, of the paraventricular nucleus by microdialysis probe attenuated the N-methyl-D-aspartate (1.5 mM)-induced elevations of both thromboxane B2 and plasma catecholamines. Intracerebroventricular administration of furegrelate (250 microg/animal), a thromboxane A2 synthase inhibitor, also abolished the responses evoked by N-methyl-D-aspartate. These results indicate that N-methyl-D-aspartate applied into the paraventricular nucleus produces thromboxane A2 in this region and elevates plasma levels of catecholamines, especially adrenaline. Thromboxane A2 produced in this hypothalamic nucleus is probably involved in the N-methyl-D-aspartate-induced central adrenomedullary outflow.