The use of aspirin to prevent pregnancy-induced hypertension and lower the ratio of thromboxane A2 to prostacyclin in relatively high risk pregnancies

Coagulation studies in the preeclamptic parturient: a survey

STUDY OBJECTIVE

To delineate current practice with regard to how coagulation status is evaluated before induction of regional anesthesia in the preeclamptic parturient, with the goal of defining appropriate testing.

DESIGN

A confidential survey was mailed to the chairmen of all 113 anesthesiology residency training programs in the United States listed in the American Medical Association's American Medical Graduation Education guide, to be passed on to the director of obstetric anesthesia.

SETTING

Academic institutions providing obstetric anesthesia services in the United States.

INTERVENTIONS

Following the original study, there was no additional follow-up or intervention.

MEASUREMENTS AND MAIN RESULTS

The 21-question survey explored institutional characteristics such as the number of deliveries, the use of regional anesthesia, and the laboratory tests required prior to placement of a regional anesthetic in the mildly or severely preeclamptic parturient under two degrees of operative urgency. In the 74 programs entered into the analysis, we found that regional anesthesia was used in the majority of cesarean sections and more than half of the vaginal deliveries. In an urgent situation, most of the programs required no test of coagulation status in the mild preeclamptic parturient and only a platelet count in the severe preeclamptic parturient.

CONCLUSIONS

In the majority of academic programs in the United States, we found that the evaluation of coagulation status in the preeclamptic parturient was based primarily on a platelet count. A review of the literature supports this pattern of testing.

Effects of fish oil supplementation in the third trimester of pregnancy on prostacyclin and thromboxane production

OBJECTIVE

Disturbance in thromboxane and prostacyclin biosynthesis has been observed in preeclampsia. We studied whether fish oil supplementation in late pregnancy interferes with maternal and fetal production of thromboxane A2 and prostacyclin I2.

STUDY DESIGN

Forty-seven women in the thirtieth week of pregnancy were randomly assigned in a ratio of 2:1:1 to receive fish oil (2.7 gm of n-3 fatty acid per day [Pikasol], or either olive oil or no oil supplementation as controls. Metabolites of thromboxane A2 and A3 and of prostacyclin I2 and I3 were quantified by mass spectrometry methods in serum and urine, respectively. Maternal serum and urine were sampled at baseline, in the thirty-third and thirty-seventh weeks of pregnancy. Fetal serum was sampled at delivery.

RESULTS

At the thirty-seventh week the mean concentrations of the eicosapentaenoic-derived metabolites, thromboxane B3 and prostacyclin I3, was twofold to threefold higher (p < 0.001) in the group receiving fish oil compared with combined control groups. There were no significant effects of fish oil on the prostacyclin I2 metabolite, although there was a trend toward a reduction in thromboxane B2 in this group. In umbilical cord blood the mean concentration of thromboxane B2 was lowest in the group receiving fish oil (p = 0.03).

CONCLUSIONS

Fish oil was metabolized to the eicosapentaenoic acid-derived eicosanoids thromboxane A3 and prostacyclin I3 in pregnant women. Correspondingly, analog products of arachidonic acid tended to be depressed. It remains to be established whether these biochemical effects will prove beneficial in the prevention or treatment of preeclampsia and intrauterine growth retardation.

Low-dose aspirin in the prevention of preeclampsia and fetal growth retardation: rationale, mechanisms, and clinical trials

Preeclampsia is characterized by a functional imbalance between vascular prostacyclin and thromboxane A2 production. On the basis of the hypothesis that preeclampsia is at least partially caused by an increase in thromboxane A2, some studies attempted to correct this pathologic condition by pharmacologic manipulation with low-dose aspirin. The current literature suggests that the use of low-dose aspirin during pregnancy is safe with regard to congenital anomalies and fetal, neonatal, and maternal cardiovascular physiologic state and hemostasis. Aspirin at least partially corrects the pathologic increase in angiotensin II sensitivity that precedes the clinical development of preeclampsia. In addition, some clinical trials have demonstrated that low-dose aspirin is effective in reducing the incidence of preeclampsia and/or fetal growth retardation in selected high-risk women. Currently, large clinical trials are in progress to evaluate the effectiveness and side effects of the use of low-dose aspirin in preventing preeclampsia and/or fetal growth retardation. Until these studies have been completed, it will remain unclear whether antiplatelet therapy, such as low-dose aspirin, should be adopted for the prevention of either preeclampsia or fetal growth retardation.

Reduction of thromboxane A2 synthesis in pregnancy by polyunsaturated fatty acid supplements

OBJECTIVE

High-dose supplements of fish oil reduce thromboxane synthesis in nonpregnant human subjects and were therefore proposed as a means of preventing various small-vessel disorders, including preeclampsia. The effect of fish oil on thromboxane metabolism in pregnancy was investigated in our study.

STUDY DESIGN

Sixteen normal pregnant women in the third trimester of pregnancy were treated with a daily ingestion of 6 gm fish oil capsules containing 1.6 gm of n-3 fatty acid. In five patients the treatment was stopped because of severe-flavored reflux and hiccups. Eleven patients completed 3 weeks of treatment. Twenty-four-hour urinary 11-dehydro-thromboxane B2 was measured by means of radioimmunoassay before and after completion of the study protocol in these 11 patients and in seven control pregnant women who did not receive the oil treatment.

RESULTS

A decrease ranging from 32% to 71%, in 24-hour urinary 11-dehydro-thromboxane B2 excretion (mean reduction from 1606 pg/mg creatinine to 779 pg/mg creatinine, p < 0.001) was found among the 11 fish oil-treated women. No change in excretion was found among the control women. No maternal, fetal, or neonatal bleeding disturbances occurred, and no laboratory changes in coagulation markers were observed.

CONCLUSIONS

High-dose n-3 fatty acid intake in pregnancy significantly reduces maternal thromboxane A2 synthesis. These results may provide a basis for a possible role of fish oil in managing patients at risk for preeclampsia.

Low dose aspirin in pregnancy: a clinical and biochemical study of effects on the newborn

Low dose Aspirin in pregnancy reduces the incidence of intra uterine growth retardation (IUGR) and pregnancy induced hypertension (PIH) in women at risk for these complications. To investigate if this drug, even in a low dose, could expose the newborn to hemorrhagic complications, we studied ten neonates whose mothers had been taking 50 mg/day of Aspirin from the 12th week of pregnancy until delivery and compared them with eight newborns whose mothers didn't take the drug. No hemorrhagic complications (emathemesis, ecchymoses or petechiae, subconjunctival hemorrhage, cephaloematomas etc.) were observed in the fetuses exposed to Aspirin or in the control group. No hemorrhagic lesions were found by ultrasound brain scan on the fourth day of life. Newborns exposed to Aspirin showed a significantly lower thromboxane concentration on the first day of life (median 73 ng/ml versus 217 ng/ml); however on the fourth day the level of serum thromboxane in the cases exposed reached the values of the unexposed ones (median 146 ng/ml versus 143 ng/ml). In conclusion low dose Aspirin in pregnancy can be considered a safe drug without and adverse effect on the newborn.

Thromboxane synthetase inhibition as a new therapy for preeclampsia: animal and human studies minireview

The role of the eicosanoids in the pathophysiology of preeclampsia is reviewed, and the results of animal model and human studies with thromboxane synthetase inhibitors in preeclampsia are described. Potential benefits and limitations of therapy are discussed.

What do we really know about autoantibody abnormalities and reproductive failure: a critical review

CONDENSATION

The diagnosis and treatment of autoantibody-associated forms of reproductive failure is critically reviewed.

OBJECTIVE

To critically evaluate the published literature in reference to autoantibody-associated forms of reproductive failure.

LOCATION

Medical School-affiliated private Infertility Center.

MATERIALS

A review of over 200 published papers reflecting on the topic.

RESULTS

Autoantibody associated reproductive failure, characterized by a decrease in fecundity and an increase in the risk of pregnancy loss, appears established. Autoantibody abnormalities, as routinely detected by standard laboratory assays, are, however, neither immunologically nor biologically specific since cross reactivities between autoantibodies are frequent and a specific autoantibody may cause a biological effect in one but not in another affected individual.

CONCLUSIONS

The evaluation of autoantibody abnormalities in all cases of suspected autoimmune-associated reproductive failure is valuable and will improve clinical care of affected patients. Clinicians need, however, to recognize the limitations of autoantibody testing and have to adjust their clinical management to the degree and quality of autoantibody evaluation available to them in their community.

Elevated second trimester maternal serum beta-HCG concentrations and subsequent adverse pregnancy outcome

Previous studies have found an association between elevated second trimester maternal serum alpha-fetoprotein (MS-AFP), in the absence of fetal anomalies, and adverse pregnancy outcome. We studied the association between elevated second trimester maternal serum beta-HCG, now also routinely measured by prenatal screening programs, and adverse pregnancy outcome by reviewing retrospectively the pregnancy outcomes among women with markedly elevated midtrimester beta-HCG in our prenatal screening program. Seven (0.23%) of 3,000 consecutively screened women had a serum beta-HCG above 5 MOM. Four (57%) of these 7 women had an adverse pregnancy outcome including severe preeclampsia (n = 2), abruptio placentae (n = 1), or preterm labor (n = 1). A concurrently elevated MS-AFP was found in only one of these 4 patients. Elevated mid-trimester maternal serum beta-HCG may be an independent risk factor for subsequent adverse pregnancy outcomes.

Fulminant subarachnoidal hemorrhage and coma subsequent to sudden-presenting hypertension

An unusual case of pre-eclampsia is presented, where a previously normotensive primigravida suddenly developed hypertension which evolved to subarachnoidal hemorrhage and coma within minutes. Delivery by cesarean section was followed by progressive and complete recovery in the next few days.

NSAIDs: maternal and fetal considerations

Nonsteroidal anti-inflammatory drugs (NSAIDs) gained popularity in the late 1970s. Inhibition of prostaglandin synthesis with indomethacin has been reported to be effective for prevention of labor and for treatment for symptomatic polyhydramnios. Concern about its possible constrictive effect on the fetal ductus arteriosus has limited its use in pregnancy. Maternal indomethacin therapy has also been associated with reduction in urine production in the fetus and with oligohydramnios. Obstetricians have discouraged pregnant women from taking analgesic doses of aspirin, mainly because of the availability of paracetamol (acetaminophen), which causes less gastric irritation, but also because of fear of maternal and fetal hemorrhage and of possible premature closure of the ductus. These fears largely derive from studies on patients taking large doses and from extrapolation from other NSAIDs. The likelihood that treatment with 60-75 mg/day of aspirin markedly reduces the incidence of preeclampsia and fetal intrauterine growth retardation makes it important to reexamine its use. This review describes the pharmacology and pharmacokinetics of aspirin with particular reference to pregnancy and considers teratogenesis, prolongation of pregnancy and labor, maternal bleeding, fetal and neonatal bleeding, possible effects on the ductus arteriosus and pulmonary circulation, and possible nonspecific effects on intelligence and breast feeding and acute toxicity in the neonate.

Study of thromboxane and prostacyclin metabolism in an in vitro model of first-trimester human trophoblast

OBJECTIVES

The purpose of our study was to establish an in vitro tissue culture system to study eicosanoid metabolism in first-trimester trophoblastic tissue. Thromboxane A2, a potent vasoconstrictor, and prostacyclin, a potent vasodilator, were analyzed to evaluate their production in early pregnancy.

STUDY DESIGN

Trophoblastic tissue was obtained via transabdominal chorionic villous sampling from 33 pregnancies at 9 to 12 weeks' gestation for cytogenetic diagnosis. Initially, tissue obtained from the cytogenetics lab was morphologically consistent with villous core cells. Through altering cell density and passage, the cells became morphologically consistent with cytotrophoblasts. The cell lines were exposed to arachidonic acid (50 mumol/L) and aspirin (1 to 100 mumol/L) for 24 hours. Thromboxane B2 and 6-keto prostaglandin F2 alpha were measured by radioimmunoassay.

RESULTS

Villous core cells and cytotrophoblasts increased production of thromboxane A2 and prostacyclin in the presence of arachidonic acid (p < 0.002). The villous core cells produced more thromboxane A2 and prostacyclin than cytotrophoblasts (p < 0.02). A significant inhibition of both thromboxane A2 and prostacyclin production was seen in the presence of 100 mumol/L aspirin in both cell types (p < 0.05).

CONCLUSIONS

This model may be useful for studying placental function in the first trimester because individual placental compartments can be evaluated in tissue culture. At the cellular level we were not able to detect a preferential decrease in thromboxane A2 production in the presence of aspirin (1 to 100 mumol/L).

The use of low dose aspirin in pregnancy

Pregnancy-induced hypertension (PIH) in general and preeclampsia in particular are major causes of maternal and perinatal morbidity. Data from our studies and from a number of prospective controlled trials have suggested that aspirin in doses of 60-150 md/day during the second and third trimester reduces the risk of PIH and improves maternal and neonatal outcomes. The number of patients enrolled in these studies is relatively small. However, meta-analysis of existing trials suggests that low dose aspirin reduces the risk of PIH and severe low birth weight. Although no maternal or neonatal adverse effects associated with aspirin were observed, the use of aspirin in the third trimester has been reported to cause hemostatic abnormalities in both mother and neonate. Other complications associated with prostaglandin synthetase inhibitors include premature closure of the ductus and neonatal primary pulmonary hypertension. The use of aspirin in the first trimester is not associated with increased risk of structural malformations. On the basis of these findings and pending the results of ongoing large-scale randomized multicenter trials, we suggest that daily low dose aspirin (1 to 2 mg/kg/day) be recommended only for select women at high risk for developing PIH and its associated complications.

Low-dose aspirin inhibits lipid peroxides and thromboxane but not prostacyclin in pregnant women

OBJECTIVE

Preeclampsia is associated with an imbalance of increased thromboxane and decreased prostacyclin and an abnormal increase of lipid peroxides. Lipid peroxides are toxic compounds that damage cells and inhibit prostacyclin synthesis. Low-dose aspirin therapy reduces the incidence of preeclampsia, presumably by selective inhibition of thromboxane to restore a balance between thromboxane and prostacyclin. However, the effectiveness of low-dose aspirin might also relate to inhibition of lipid peroxides.

STUDY DESIGN

To test this hypothesis, 10 women at risk of preeclampsia were placed on low-dose aspirin therapy (81 mg/day) between 9 and 34 weeks of gestation. Plasma samples were collected before and after 3 to 4 days and 3 to 4 weeks of aspirin therapy. Samples were analyzed for thromboxane and prostacyclin by radioimmunoassay of their stable metabolites, thromboxane B2 and 6-keto-prostaglandin F1 alpha, and for lipid peroxides by hydrogen peroxide equivalents.

RESULTS

Low-dose aspirin significantly decreased (p < 0.05) both lipid peroxides (130 +/- 18 vs 92 +/- 11 and 68 +/- 9 nmol/ml, mean +/- SE) and thromboxane (502 +/- 67 vs 138 +/- 67 and 8 +/- 5 pg/ml), but it did not affect prostacyclin (55 +/- 10 vs 41 +/- 8 and 40 +/- 11 pg/ml, p > 0.1).

CONCLUSION

Low-dose aspirin selectively inhibits both lipid peroxides and thromboxane without affecting prostacyclin. Inhibition of both lipid peroxides and thromboxane by low-dose aspirin reveals a new mechanism of action and may account for its effectiveness in the prevention of preeclampsia.

Thromboxane in the pathogenesis of glomerular injury in diabetes

The present study examined the role of thromboxane (TX) in the initiation and progression of glomerular injury in diabetic rats, as reflected by albuminuria and glomerular histology. Urinary thromboxane and albumin excretion (UTX and UAlb) were elevated by four months after induction of diabetes in the moderately hyperglycemic (200 to 400 mg/dl glucose) streptozotocin diabetic rat (SDR) compared to age-matched control rats. UTX and UAlb both increased progressively in SDR over the seven month period of study. Glomerular TX production, glomerular volume, fractional and absolute mesangial volume and glomerular basement membrane (GBM) width were also increased after seven months in SDR compared to control. Treatment of SDR with a thromboxane synthetase inhibitor (TXI) 4' (imidazol-l-yl) acetophenone (100 mg/kg/day) for seven months beginning at the time of induction of diabetes prevented the increases in UTX, UAlb, glomerular TX production, glomerular volume and mesangial volume and attenuated, but did not prevent, GBM thickening. When the same dose of the TXI was begun five months after induction of diabetes and continued for two months, UTX and ex vivo glomerular TX production were reduced by only 60% compared to untreated SDR and remained higher than corresponding values in control rats. Delayed treatment with the TXI alone did not alter UAlb compared to untreated SDR. By contrast, treatment of five month albuminuric SDR for only two months with the TXI plus the TX receptor antagonist (TXRA) Bay U3405 (5 mg/kg/day) prevented a further increase in UAlb, and reduced fractional albumin clearance and mesangial volume compared to values in untreated SDR. Combined treatment with the TXI and TXRA had no effect on GBM width or glomerular volume compared to values in untreated SDR. The results support roles for TX in the initiation of, and for TX and/or endoperoxides in the progression of glomerular injury in SDR.

Prevention of anticardiolipin antibody-related pregnancy losses with prednisone and aspirin

PURPOSE

Prevention and treatment of pregnancy loss associated with the antiphospholipid syndrome (APS) are controversial. Successful pregnancies have been reported with prednisone and low-dose aspirin in patients with lupus anticoagulant and anticardiolipin antibodies (aCL), but failure has also been reported. The purpose of this prospective study was to define the efficacy of such combination therapy in the prevention of pregnancy loss related to aCL.

PATIENTS AND METHODS

Consecutive pregnant patients with a minimum of one pregnancy loss and at least two positive aCL determinations more than 3 months apart, and in whom other causes of pregnancy loss were ruled out, were included in the study. aCL concentrations were determined by enzyme-linked immunosorbent assay before and during therapy. Patients received prednisone, at a dosage of 40 mg/d, for 4 weeks. The dose was then tapered down 10 mg every 4 weeks, and then to a maintenance dose of 5 mg/d. They also received aspirin, 81 mg/d, throughout the pregnancy. Babies were evaluated during the pregnancy by measurement of fetal heart rate and ultrasonography, and after the delivery by measurement of weight and Apgar scores, and, in some cases, by arterial gasometry.

RESULTS

Eleven patients with a mean (+/- SD) age of 33.2 +/- 5.01 years were included. Prior to therapy, the rate of live-born babies was 15.6% (32 previous fetal losses and 5 live-born babies), and, after therapy, it was 100% (12 pregnancies and 12 live-born babies). There were no significant adverse effects to either mothers or babies. All the patients had positive aCL determinations. Nine patients had positive IgG aCL. The levels of the antibodies decreased during treatment in these nine patients. IgM aCL determinations were positive in nine patients. The levels of this isotype decreased in eight patients (90%) during treatment.

CONCLUSIONS

Treatment with prednisone and aspirin appears to be efficacious, safe, and economic in the prevention of pregnancy loss and fetal growth retardation in patients with aCL.

An immunohistologic study of endothelialization of uteroplacental vessels in human pregnancy--evidence that endothelium is focally disrupted by trophoblast in preeclampsia

OBJECTIVE

Our objective was to study the endothelial status of the luminal lining of uteroplacental vessels in the human placental bed in normal and abnormal pregnancy in the third trimester.

STUDY DESIGN

Six placental basal plates from uncomplicated pregnancies and five from pregnancies complicated by preeclampsia (n = 3), preeclampsia and a small-for-gestational-age infant (n = 1), and diabetes mellitus (n = 1) were accessioned from the archives because of documentation of their containing uteroplacental vessels. Five placental bed biopsy specimens with intraluminal endovascular trophoblast in the third trimester were also studied. Sections were subjected to immunohistochemical analysis with monoclonal and polyclonal antibodies labeling endothelium and trophoblast.

RESULTS

In third-trimester normal uncomplicated pregnancies the uteroplacental arteries and veins were completely endothelialized with no disruption of the endothelium. In third-trimester abnormal pregnancies the uteroplacental veins were also completely endothelialized. However, intraluminal endovascular trophoblast was seen within the uteroplacental arteries in eight of the 10 complicated pregnancies; this finding was associated with disruption of the endothelium.

CONCLUSION

In preeclampsia there is an aberrant wave of endovascular trophoblast migration in the third trimester, resulting in focal disruption of the endothelium. This may be responsible for the endothelial cell dysfunction thought to be of pathogenetic importance in preeclampsia.

A randomized placebo-controlled study of the effect of low dose aspirin on platelet reactivity and serum thromboxane B2 production in non-pregnant women, in normal pregnancy, and in gestational hypertension

OBJECTIVE

To investigate the effect of 60 mg aspirin daily on platelet reactivity and prostaglandin production in various groups of patients. Similar regimens, which are thought to act through inhibition of platelet thromboxane production, are currently undergoing clinical assessment for the prevention of pre-eclampsia and intrauterine growth retardation.

DESIGN

A prospective randomized placebo controlled study.

SETTING

University Hospital, Nottingham.

SUBJECTS

12 non-pregnant female volunteers, 18 normal primigravidae before 16 weeks gestation and 16 pregnant women admitted with gestational hypertension (GH) at a mean gestation of 38 weeks.

INTERVENTIONS

In the non-pregnant women blood samples were taken before and after a 10-day course of 60 mg aspirin daily. The primigravidae had blood samples taken at 16 weeks and then they were randomized to receive either 60 mg aspirin daily or a matched placebo. Further blood samples were obtained at 28, 32 and 36 weeks.

MAIN OUTCOME MEASURES

Changes in platelet reactivity and release reaction, and serum thromboxane production, were estimated in whole blood.

RESULTS

60 mg aspirin daily significantly inhibited cyclo-oxygenase dependent platelet aggregation, release reaction and serum thromboxane production in non-pregnant and pregnant women, and in women with GH (P less than 0.01). When adrenaline was used as the aggregating agent, the cyclo-oxygenase pathway was recruited in the increased reactivity seen in the third trimester of normal pregnancy, and was sensitive to inhibition by low dose aspirin.

CONCLUSION

Low dose aspirin would appear to be an appropriate agent for the inhibition of platelet reactivity associated with hypertensive pregnancy.

The effect of pregnancy on renal function: physiology and pathophysiology

Marked changes in renal function occur with pregnancy. We present a summary of these changes in this review and give insight into possible mechanisms if they are known. Controversies exist regarding the therapy of pregnancy-induced hypertension and asymptomatic and recurrent bacteriuria. The current views on these topics are given. Specific renal diseases are summarized, including transplantation, and optimum management strategies and maternal and fetal prognosis during pregnancy are given.

Foetal vascular responses to thromboxane receptor blockade

We hypothesized that foetal administration of SQ-29,548, a putative thromboxane receptor blocker, would prevent foeto–placental vasoconstriction produced by the thromboxane mimic U46619. Arterial blood gases, continuous monitoring of maternal and foetal heart rates and blood pressures were performed in chronically catheterized pregnant ewes. Foetal blood flows and vascular resistance were determined with radioactive microspheres. SQ-29,548 effectively blocked the expected vasoconstrictive effects of thromboxane. However, prolonged infusion of SQ-29,548 resulted in significant decreases in umbilical–placental blood flow and foetal mean arterial pressure. This was accompanied by a respiratory acidemia. Potential therapy for the vasoconstrictive disorders of pregnancy with SQ-29,548 awaits further investigation of its intrinsic vasoactive properties in the umbilical–placental vasculature.

Maternal toxemia is associated with reduced incidence of germinal matrix hemorrhage in premature babies

To evaluate prenatal and perinatal risk factors for development of germinal matrix hemorrhage-intraventricular hemorrhage (GMH-IVH), we conducted a prospective epidemiologic study of 449 babies whose birth weight was less than 1501 grams. This study permitted us to test our previously generated hypothesis that babies born to mothers with preeclampsia were at substantially reduced risk of developing GMH-IVH. Seventy-two (16%) of the babies in this population developed GMH-IVH. One (2.5%) of the 40 mothers with a diagnosis of preeclampsia and 71 (17.4%) of 409 mothers without preeclampsia gave birth to babies who developed GMH-IVH. GMH-IVH was seen in 6/107 (5.6%) of babies born to women with hypertension including 4/69 (5.8%) of babies born to women with pregnancy-induced hypertension, compared to 66/352 (18.8%) of babies born to mothers who did not have hypertension. Only 7.3% (8/108) of babies born to women who had proteinuria had GMH-IVH, compared to 18.3% (64/350) of babies whose mothers did not have proteinuria. GMH-IVH was seen in 5/89 (5.6%) of babies whose mothers had both hypertension and proteinuria, whereas 63/332 (19%) of babies born to mothers who lacked both factors, developed GMH-IVH. In stepwise logistic regression analysis, these significant findings were not explained by the presence of labor, postnatal acidemia, need for intubation, antenatal administration of steroids, birth weight, or gestational age. In addition, we found that maternal receipt of magnesium sulfate was associated with diminished risk of GMH-IVH even in those babies born to mothers who apparently did not have preeclampsia.(ABSTRACT TRUNCATED AT 250 WORDS)

Contribution of platelet thromboxane production to enhanced urinary excretion and glomerular production of thromboxane and to the pathogenesis of albuminuria in the streptozotocin-diabetic rat

Previous studies have demonstrated that urinary thromboxane B2 (TXB2) excretion (UTXB2) and glomerular production of TXB2 are enhanced in experimental diabetes and that selective inhibitors of TX synthesis prevent or delay the development of albuminuria. The present study was conducted to examine the contribution of platelet TXB2 production to the enhancement of UTXB2 and glomerular TXB2 production and to the pathogenesis of albuminuria in the partially insulin-treated moderately hyperglycemic (blood glucose, 200 to 400 mg/dL) streptozotocin-diabetic rat (SDR). Treatment of control rats or of SDR with diabetes of 5 months' duration with antiplatelet serum for 4 consecutive days reduced circulating platelet counts and serum TXB2 generation, an index of platelet cyclooxygenase activity, by 80% or greater, but reduced UTXB2 excretion by only 30%. UTXB2 and glomerular production of TXB2 of thrombocytopenic SDR remained markedly elevated compared with corresponding values from age-matched thrombocytopenic or platelet-replete, nondiabetic controls. Similarly, treatment of rats for 180 days with a dose of aspirin (ASA), which selectively inhibited platelet versus renal cyclooxygenase activity, reduced UTXB2 of both SDR and controls by 25% to 35%. The absolute reductions in UTXB2 induced by either ASA or thrombocytopenia in SDR were significantly greater than the absolute decrements in corresponding controls, suggesting that increased platelet TXB2 production in SDR may contribute to the enhanced UTXB2. However, as in the thrombocytopenic SDR, UTXB2 and glomerular production of TXB2 of SDR treated with ASA remained clearly above corresponding control values. Moreover, chronic ASA treatment failed to prevent the development of albuminuria in SDR.(ABSTRACT TRUNCATED AT 250 WORDS)

Is pre-eclampsia preventable?

Pre-eclampsia is characterised by reduced utero-placental blood flow which in turn results from vascular damage occurring early in pregnancy. Endothelial damage and reduced prostacyclin and nitric oxide synthesis will initiate excessive platelet aggregation, fibrin deposition and vascular occlusion. Prevention of pre-eclampsia is dependent on affecting this process. Antiplatelet therapy is being assessed as a prophylaxis. Screening tests using increased platelet turnover as their basis are also being assessed.

Platelet reactivity and serum thromboxane B2 production in whole blood in gestational hypertension and pre-eclampsia

OBJECTIVE

To determine the nature and extent of changes in platelet reactivity in gestational hypertension and pre-eclampsia (using whole blood techniques which may be more physiological than those previously employed).

DESIGN

Cross-sectional observational study.

SUBJECTS

8 normal primigravidae, 16 women with gestational hypertension and 12 women with pre-eclampsia, studied at around 36 weeks gestation.

RESULTS

Platelet reactivity (aggregation and release reaction) induced by stimulation with adrenaline was decreased in the pre-eclamptic group. Serum thromboxane B2 production was unchanged in both hypertensive groups compared with the control group.

CONCLUSIONS

In the context of evidence of platelet activation in pre-eclampsia, our findings are interpreted as reflecting platelet exhaustion.

Is genetic susceptibility to pre-eclampsia conferred by homozygosity for the same single recessive gene in mother and fetus?

OBJECTIVE

To determine whether any simple, purely genetic mechanism can account for susceptibility to pre-eclampsia.

DESIGN

Six simple Mendelian models of inheritance were considered, and predictions concerning the incidence of pre-eclampsia in various family members of index cases were calculated for each genetic model. Data were then extracted from published family studies in which a suitable disease definition had been used, and compared to our theoretical expectations.

RESULTS

Only one of the genetic models considered, in which both mother and fetus must express the same recessive gene to confer susceptibility, was consistent with the observed incidence values for relatives of index cases. This model was also consistent with the putative association with HLA-DR4, but could not account for the comparative rarity of pre-eclampsia in parous women.

CONCLUSION

Homozygosity for a single recessive gene shared by mother and fetus, unlike five other genetic mechanisms tested, is consistent with published family studies in pre-eclampsia, and should be considered the best working hypothesis at present.

First antenatal visit haematocrit and pregnancy induced hypertension

First antenatal visit haematocrit values during the first and second trimesters were retrospectively collected from 546 nulliparas with singleton pregnancies. The results were analysed for correlation with development of pregnancy induced hypertension (PIH) later in pregnancy. It was found that women with higher haematocrit values, especially over 0.40, had an increased risk of developing PIH. However, there appeared to be no absolute level of haematocrit which had sufficient discriminative value to be useful in clinical practice.

High plasma cellular fibronectin levels correlate with biochemical and clinical features of preeclampsia but cannot be attributed to hypertension alone

Current concepts of the pathogenesis of preeclampsia involve the generalized dysfunction of maternal vascular endothelial cells. We measured the endothelial isoform of fibronectin as a marker of endothelial cell injury throughout pregnancy in a prospective, case-control study. Nineteen women met strict criteria for the diagnosis of preeclampsia. Nineteen normal pregnant women, and 19 women with gestational hypertension but without other stigmata of preeclampsia (transient hypertension) were selected from the same cohort and matched according to race, age, nulliparity, and gestational age at delivery. Plasma levels of cellular fibronectin were significantly elevated in women meeting strict clinical and biochemical criteria for preeclampsia but not in women with normal pregnancies or transient hypertension. Moderate but significant elevations in mean levels were found in the second trimester in women destined to have preeclampsia, as compared with matched normal and transient hypertension groups (p less than 0.05). The results indicate that elevated plasma levels of cellular fibronectin are not simply the result of increased blood pressure but reflect a maternal insult specific to the syndrome of preeclampsia. Elevation of the mean concentration during the midtrimester is consistent with the hypothesis that endothelial cell injury is a specific lesion that occurs early in the course of preeclampsia, before clinical signs and symptoms.

Prevention and treatment of pregnancy-associated hypertension: what have we learned in the last 10 years?

High blood pressure (BP) complicates approximately 10% of all pregnancies. Hypertension in pregnancy falls into four categories: (1) preeclampsia-eclampsia, (2) chronic hypertension of whatever cause, (3) preeclampsia-eclampsia superimposed to chronic hypertension or renal disease, and (4) transient or late hypertension (gestational hypertension). Preeclampsia, the association of hypertension, proteinuria, and edema, accounts for more than 50% of all the hypertensive disorders of pregnancy and is a major cause of fetal and maternal morbidity and mortality. Unfortunately, distinguishing between preeclampsia and other causes of hypertension on clinical grounds can be difficult because of the lack of specific tests for differential diagnosis. Increased vascular resistance has been claimed as the primary cause of preeclampsia; however, a variable hemodynamic profile with relatively high cardiac outputs, normal filling pressures, and inappropriately high systemic vascular resistances is now reported by most investigators. Imbalance between vasodilator and vasoconstrictor eicosanoids may account for platelet activation and increased responsiveness to pressor peptides. Altered prostacyclin (PGI2) to thromboxane A2 (TxA2) ratio in maternal uteroplacental vascular bed may favor local platelet activation and vasoconstriction contributing to placental insufficiency and fetal distress. Alternatively, recent evidence seems to suggest that fetal umbilical placental circulation may be the site of the primary vascular injury. Whether low-dose aspirin prevents preeclampsia because it inhibits the excessive maternal TxA2 or whether the partial inhibition of fetal TxA2 is also of therapeutic value remains to be established. Treatment of severe hypertension in pregnancy is probably important to prevent cardiac failure or cerebrovascular accidents in the mother. The need for pharmacological therapy of mild to moderate hypertension is still debated, since no formal studies are available to clarify whether pharmacological treatment in such instances effectively reduces maternal or fetal risk. For the treatment of preeclampsia, hydralazine and nifedipine may be used when delivery is not applicable. Labetalol and diazoxide are effective for hypertensive emergencies. Life-threatening hypertension that does not respond to more conventional therapy is an indication for the use of sodium nitroprusside. For chronic hypertension, alpha-methyldopa remains the treatment of choice; if ineffective, hydralazine or beta-blockers are suitable. Effectiveness and safety of other molecules remain elusive.

Prevention of perinatal consequences of pre-eclampsia with low-dose aspirin: results of the epreda trial. The Epreda Trial Study Group

A multicentric randomized double-blind trial was realized in order to determine whether a treatment with a low-dose aspirin (150 mg/day) with or without dipyridamole (225 mg/day) was able to prevent the perinatal consequences of pre-eclampsia. This study demonstrated a significant difference in birthweight and incidence of fetal growth retardation between treatment and placebo groups. No difference was demonstrated between aspirin and aspirin + dipyridamole patients.

Prevention of fetal growth retardation with low-dose aspirin: findings of the EPREDA trial

The efficacy of low-dose aspirin in preventing fetal growth retardation was tested in a randomised, placebo-controlled, double-blind trial. A secondary aim was to find out whether dipyridamole improves the efficacy of aspirin. 323 women at 15-18 weeks' amenorrhoea were selected at twenty-five participating centres on the basis of fetal growth retardation and/or fetal death or abruptio placentae in at least one previous pregnancy. They were randomly allocated to groups receiving placebo, 150 mg/day aspirin, or 150 mg/day aspirin plus 225 mg/day dipyridamole, for the remainder of the pregnancy. In the first phase of the trial all actively treated patients (n = 156) were compared with the placebo group (n = 73). Mean birthweight was significantly higher in the treated than in the placebo group (2751 [SD 670] vs 2526 [848] g; difference 225 g [95% CI 129-321 g], p = 0.029) and the frequency of fetal growth retardation in the placebo group was twice that in the treated group (19 [26%] vs 20 [13%]; p less than 0.02). The frequencies of stillbirth (4 [5%] vs 2 [1%]) and abruptio placentae (6 [8%] vs 7 [5%]) were also higher in the placebo than in the treated group. The benefits of aspirin treatment were greater in patients with two or more previous poor outcomes than in those with only one. In the second analysis, of aspirin only (n = 127) vs aspirin plus dipyridamole (n = 119), no significant differences were found. There was no excess of maternal or neonatal side-effects in the aspirin-treated patients.

Heparin lowers blood pressure and vascular calcium uptake in hypertensive rats

Increased calcium uptake by vascular tissue, leading to elevated cytosolic calcium, has been implicated in the pathophysiology of hypertension. Heparin treatment of hypertensive rats has been known to lower blood pressure but its mechanism is not known. This study examined the effect of chronic heparin treatment on systolic blood pressure, aortic calcium and 87Rubidium (86Rb) uptake of spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto (WKY) rats. Starting at 12 weeks of age SHR and WKY rats were given either sodium heparin 300 units s.c. or equal amounts of saline once a day for a period of 6 weeks. At 18 weeks, systolic blood pressure, uptakes of calcium and 86Rb by aortae were significantly higher (p less than 0.01) in saline-treated SHR compared with heparin-treated SHR and WKY. Heparin treatment lowered the elevated calcium and 86Rb Uptake and blood pressure in SHR but had no effect on WKY. The parallel increase in systolic blood pressure and vascular calcium uptake suggests that increased calcium uptake mechanisms are associated with hypertension in SHR. Heparin appears to lower elevated blood pressure in SHR by lowering elevated vascular calcium uptake.

The role of endogenous thromboxane in contractions to U46619, oxygen, 5-HT and 5-CT in the human isolated umbilical artery

1. The effects of selective thromboxane antagonists and a thromboxane synthase inhibitor on the contraction to 9,11-dideoxy-11 alpha,9 alpha-epoxymethano-prostaglandin F2 alpha (U46619) and oxygen in the human umbilical artery (HUA) were examined. The effect of the antagonists on contractions to both 5-hydroxytryptamine (5-HT) and 5-carboxamidotryptamine (5-CT) were also examined. 2. U46619 (0.3 nM-10 microM) contracted the HUA. This contraction was antagonized by two selective thromboxane receptor antagonists EP092 (10 nM-1 microM) and GR32191B (10 nM-1 microM). The contraction was not affected by the selective thromboxane synthase inhibitor, dazoxiben (10 nM-1 microM). 3. When the oxygen tension was increased from 16 mmHg to 120 mmHg, the HUA transiently contracted. Both thromboxane antagonists inhibited this contraction in a concentration-dependent manner with 1 microM almost completely abolishing the response (the oxygen-induced contraction of the control preparation normally increases with a second exposure to 120 mmHg oxygen). 4. In low (16 mmHg) oxygen, responses to both 5-HT and 5-CT were unaffected by both thromboxane receptor antagonists at concentrations up to 1 microM. In high oxygen (120 mmHg) responses to both 5-HT and 5-CT were biphasic in nature, with an additional initial high sensitivity phase, which was abolished by a cyclo-oxygenase inhibitor. In high oxygen, EP092 and GR32191B blocked this initial phase in a concentration-dependent manner, returning sensitivity to 5-HT and 5-CT to that seen in low oxygen. 5. The thromboxane synthase inhibitor, dazoxiben, at concentrations greater than 10 nm inhibited the contraction to 120 mmHg oxygen and at 1 microM, dazoxiben almost abolished the response. In low oxygen, the response to 5-HT was unaffected by dazoxiben at concentrations up to 10 microM. In high oxygen, the initial phase of the contraction to 5-HT was inhibited by concentrations greater than 10 nm, with no effect on the maximum response. 6. The results show that thromboxane receptor antagonism or blockade of thromboxane synthesis selectively attenuates oxygen-induced contractions and those responses to 5-HT and 5-CT which are dependent on high oxygen for their expression. This suggests that the contractions caused by high oxygen tension, and the enhancement of the contractile effects of low concentrations of 5-HT and 5-CT in the presence of high oxygen tension are mediated by endogenously released thromboxane A2.

Effect of low-dose aspirin on vascular refractoriness in angiotensin-sensitive primigravid women

The hypothesis that an enhanced vasopressor response to angiotensin II in pregnancy may be corrected by suppressing production of platelet thromboxane A2 with low-dose aspirin was tested in a randomized, placebo-controlled, double-blind trial. We studied 36 normotensive primigravid women with an elevated blood pressure response to intravenously infused angiotensin II at 28 weeks' gestation; 18 women received 60 mg of aspirin daily and the same number received matched placebo until 34 weeks' gestation, when angiotensin-sensitivity was again determined. In women taking aspirin, values of thrombin-induced platelet malondialdehyde production were approximately 10% of those determined in the placebo group, indicating marked suppression of thromboxane A2 synthesis. In the aspirin group vascular refractoriness to angiotensin II was restored in 14 of 17 treated women, by comparison with 5 of 15 women in the placebo group who had remained normotensive. These results support the hypothesis that prostacyclin/thromboxane imbalance is an important pathophysiologic factor in the development of the enhanced angiotensin-sensitivity associated with pregnancy-induced hypertensive disorders.

A longitudinal study of platelet behaviour and thromboxane production in whole blood in normal pregnancy and the puerperium

A longitudinal study of platelet behaviour (platelet aggregation and release reaction) in whole blood and of serum thromboxane B2 production was performed before, during and after normal pregnancy. The response of platelets to arachidonic acid and to adrenaline was significantly increased in the third trimester. Six weeks after delivery, values were still modestly increased but return to non-pregnant values was complete by 12 weeks. Serum thromboxane B2 production was unchanged throughout pregnancy and the puerperium.

Low-dose aspirin. II. Relationship of angiotensin II pressor responses, circulating eicosanoids, and pregnancy outcome

Forty pregnant women (28 to 32 weeks' gestation) were given low-dose aspirin therapy (81 mg/day) from the time of enrollment until delivery; circulating eicosanoid levels and angiotensin II pressor responses were measured before and after 1 week of aspirin therapy. Subsequent clinical outcome was correlated with these results. All women had significant reductions in serum and plasma thromboxane B2 levels with aspirin treatment (p less than 0.01). Eleven women who remained sensitive to the pressor effects of angiotensin II (effective pressor dose less than 10 ng/kg/min) after 1 week of low-dose aspirin treatment exhibited significant decreases (p less than 0.05) in plasma 6-keto-prostaglandin F1 alpha (264 +/- 119 vs 161 +/- 31 pg/ml, mean +/- SD) and prostaglandin E2 (476 +/- 174 vs 351 +/- 112 pg/ml) levels. In contrast, patients who were either nonsensitive (refractory) to angiotensin II (n = 18; greater than or equal to 10 ng/kg/min) before aspirin or became nonsensitive after aspirin administration (n = 11) had no change in either plasma 6-keto-prostaglandin F1 alpha or prostaglandin E2 concentrations. The occurrence of pregnancy-induced hypertension was 100% in the women who remained angiotensin II sensitive during aspirin therapy as compared with 36% and 39% in the other two groups (x2 = 16.14; p less than 0.001). Thus during low-dose aspirin therapy a failure to develop refractoriness to infused angiotensin II is associated with a nonselective inhibition of eicosanoids and the almost certain development of pregnancy-induced hypertension. These observations may reflect a basic defect in vascular adaptation to pregnancy.

A possible preventive effect of low-dose fish oil on early delivery and pre-eclampsia: indications from a 50-year-old controlled trial

A preventive effect of dietary marine n-3 fatty acids on early delivery and toxaemia has recently been hypothesized. In only one published controlled trial fish oil has been given to pregnant women, namely in that conducted during 1938-9 in London by the People's League of Health with a dietary supplement containing vitamins, minerals, and halibut liver oil. Although it was of high quality and its findings are hitherto unexplained, neglect and misinterpretation of the trial seem to occur commonly in reviews. Of the 5644 women who were enrolled the 622 withdrawals were independent of treatment. Alternate allocation to treatment was used, producing two groups that were well balanced as to age and parity. The supplement was given from about week 20. The control group did not receive any supplement. Reductions of 20.4% (95% confidence interval 9-30%, P = 0.00083) and 31.5% (95% confidence interval 11-47%, P = 0.0047) were seen in odds of delivering before 40 weeks of gestation and pre-eclampsia respectively. No significant effects were seen on perinatal mortality, average birth weight, deliveries after 40 weeks, hypertension in the absence of oedema and proteinuria, duration of labour, sepsis or breast-feeding occurrence. Later controlled trials with vitamins or minerals given in the same amounts as in this trial have largely failed to show convincing effects as seen here. A controlled trial assessing the isolated effects of fish oil in pregnancy is warranted.

National High Blood Pressure Education Program Working Group Report on High Blood Pressure in Pregnancy

This consensus report focuses the presentation, pathophysiology, and management of the hypertensive disorders of pregnancy expanding on recommendations first presented in 1988 by the Joint National Committee on Detection, Evaluation, and Treatment of High Blood Pressure. Practicing physicians should determine whether a patient's hypertension during pregnancy falls into the classification of (1) chronic hypertension, (2) preeclampsia, (3) preeclampsia superimposed on chronic hypertension, or (4) transient hypertension. The distinction, for management considerations, is made between hypertension that is present before pregnancy (chronic and preexisting) and that occurring as part of the pregnancy-specific condition preeclampsia. When maternal blood pressure reaches diastolic levels of 100 mm Hg or greater, treatment should be instituted to avoid hypertensive vascular damage. The report includes a discussion of antihypertensive therapy specific to the chronic or acute hypertension occurring concomitantly with pregnancy. The roles of calcium supplementation and low-dose aspirin to prevent preeclampsia and chronic and transient hypertension are under investigation.