Prostacyclin in pregnancy

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.

The role of prostaglandins in obstetrical disorders

All pregnancy-associated tissues are capable of producing prostaglandins including PGI2 and TXA2. In normal pregnancy there is a dominance of PGI2 over TXA2 which may contribute to the maternal circulatory adaptation to pregnancy. Furthermore, both fetoplacental PGI2 and TXA2 production are important regulators of the fetal blood supply. It has been clearly established that in pre-eclampsia PGI2 production decreases in the fetoplacental tissues and quite probably also in the maternal tissues. The effect of this change may be further exaggerated by the simultaneous stimulation in pre-eclampsia of TXA2 production. The reason for PGI2 deficiency is not known. Other vasoactive agents, such as endothelin, may act in concert with prostaglandins. Relative PGI2 deficiency is likely to exist also in IUGR and lupus anticoagulant syndrome of pregnancy. In the latter, lupus anticoagulant may directly inhibit the synthesis of PGI2. One study suggests PGI2 deficiency also in early pregnancies of women with a history of repeated abortions. Prostaglandin production increases during full-term labour, and similar but smaller changes also occur in preterm labour. A silent bacterial infection may trigger the onset of preterm labour through cytokine-stimulated increase of prostaglandin production. No data were found on prostaglandin production in post-term pregnancies. That oligo-polyhydramnios is possibly prostaglandin mediated is suggested by the control of polyhydramnios by indomethacin treatment. Smoking decreases the production of PGI2 and possibly increases that of TXA2, which may lead to decreased blood flow and IUGR. Which constituent of cigarette smoke exerts this effect is not known. Ethanol consumption causes aberrations in prostaglandin metabolism which cannot be directly connected with fetal alcohol effects.

Low-dose aspirin and vascular response in pregnant patients sensitive to angiotensin II

The angiotensin sensitivity test was performed in 25 high risk pregnant women before and after administration of low-dose aspirin (100 mg/day for 7 days). After aspirin administration there was a significant decrease in AII sensitivity in sensitive patients with no change in nonsensitive patients. Low-dose aspirin favorably affects sensitivity to AII in sensitive patients, thus indicating a reduced vascular reactivity as a consequence of this regimen.

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.

Prediction of pregnancy-induced hypertensive disorders by angiotensin II sensitivity and supine pressor test

An angiotensin II sensitivity test and a supine pressor test were done consecutively at 28 weeks gestation in 90 healthy, normotensive nulliparous women. None of the supine pressor tests was positive, applying the predefined threshold of a rise of 20 mmHg in diastolic blood pressure after rolling over; nine tests were positive using a corrected 9 mmHg cut-off level. Ten women had a positive angiotensin sensitivity test using a threshold of the effective pressor dose of 8 ng/kg/min; 22 women were positive using an effective pressor dose of less than or equal to 10 ng/kg/min. Later in pregnancy 12 women (13%) developed pregnancy-induced hypertensive disease (PIH). The specificity of both tests of predicting the development of PIH was about 90%. The sensitivity of the angiotensin sensitivity test at the 10 ng/kg/min level was 92%. Because of its low sensitivity of 25% the supine pressor test appears to have no value for the prediction of PIH. There was a significant positive association between angiotensin II refractoriness and birthweight.

Severe systemic hypertension during pregnancy

Severe hypertension during pregnancy remains an important cause of maternal mortality. Cerebral complications are frequently responsible for these deaths. Early detection of preeclampsia and preventive treatment are certainly goals for the future. In the management of severe pregnancy-induced hypertension, central issues are delivery and antihypertensive and anticonvulsive treatment. Cerebral disease consists mainly of bleeding and edema. Antihypertensive therapy can be dangerous and it is essential that hemodynamic control is provided.

Volume homeostasis in normal and hypertensive human pregnancy

In this chapter are outlined the many factors involved in the regulation of sodium and volume homeostasis in normal human pregnancy and their interrelationships. New developments concerning the role of sodium/potassium ATPase, atrial natriuretic peptide, arginine vasopressin and angiotensin II as regulatory forces are outlined, together with a review of earlier work. Abnormalities found in women with, or destined for, PAH are described and their significance is discussed.

Low-dose aspirin prevents pregnancy-induced hypertension and pre-eclampsia in angiotensin-sensitive primigravidae

The possibility of preventing pregnancy-induced hypertension (PIH) and pre-eclampsia in primigravidae by suppressing production of thromboxane A2 with low-dose aspirin was investigated in a randomised, placebo-controlled, double-blind trial. 46 normotensive women at 28 weeks' gestation, judged to be at risk of PIH or pre-eclampsia because of an increased blood-pressure response to intravenously infused angiotensin II, were studied. 23 women received 60 mg aspirin daily, and the same number received matching placebo until delivery. In the placebo group PIH, pre-eclampsia, and eclampsia developed in 4, 7, and 1 cases, respectively, whereas only 2 women in the aspirin group had mild PIH. There were no adverse effects of treatment in mothers or infants. Low-dose aspirin may restore prostacyclin/thromboxane imbalance, previously suggested as an important aetiological factor in PIH and pre-eclampsia.