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

Article Abstract:

Angiotensin II is one of several hormones which regulate blood pressure. Most pregnant women are less responsive to angiotensin II, but those who develop hypertension are sensitive to this protein that constricts blood vessels. Prostaglandins and thromboxanes, or eicosanoid factors, are locally secreted and locally acting hormones whose levels are altered by aspirin and which may modulate blood vessel responsiveness to angiotensin II. Indeed, low-dose treatment with aspirin, which inhibits prostaglandin synthesis, is effective in some but not all women with preeclampsia, a hypertensive disorder of pregnancy. The relationship between low-dose aspirin therapy, blood pressure, and angiotensin II sensitivity was further evaluated in 18 pregnant women insensitive to angiotensin II, and 22 pregnant women who were sensitive to the hormone. The sensitive women were given low doses of aspirin for one week, and 11 of the 22 women then became nonsensitive. The remaining women remained sensitive to angiotensin II throughout the study. These women weighed an average of 30 pounds more than the other women, while those who were never sensitive had lower blood pressure and higher heart rates. Levels of three eicosanoids were initially similar among all patients. Levels of 6-keto prostaglandin F1-alpha and prostaglandin E2 decreased significantly in the group which remained sensitive throughout, and were unchanged in others. The ratio of 6-keto prostaglandin F1-alpha to thromboxane B2 increased in all groups after treatment and became greatest among patients who became nonsensitive; it was second greatest among patients who were sensitive throughout. Pregnancy-induced hypertension developed in 7 of 18 nonsensitive women, 4 of 11 patients who became nonsensitive, and 11 of 11 women who were angiotensin II-sensitive throughout the study. Birth weights were lower in infants born to women who remained sensitive. The results indicate that the general outcome of women who remained sensitive was not improved by aspirin therapy. Outcome of women who became sensitive was improved by aspirin, as they had a lower rate of complications than angiotensin II-sensitive women. Changes in eicosanoids accompanied changes in angiotensin II sensitivity but did not predict hypertensive complications. The study suggests that pregnancy-induced hypertension appears to result from some defect other than alterations in eicosanoid handling. (Consumer Summary produced by Reliance Medical Information, Inc.)

Prostaglandins, Preeclampsia, Aspirin, Angiotensins

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Platelet-activating factor-acetylhydrolase activity in normotensive and hypertensive pregnancies

Article Abstract:

Activity of the enzyme platelet-activating factor-acetylhydrolase appears to decrease in healthy pregnant women but not in pregnant women with high blood pressure. Platelet-activating factor (PAF) is a protein in the body that lowers blood pressure, and its concentration is regulated by PAF-acetylhydrolase. It is thought that a drop in PAF-acetylhydrolase activity increases the level of PAF, lowering blood pressure. Levels of PAF-acetylhydrolase were compared in 24 healthy pregnant women, 7 pregnant women with high blood pressure, 10 healthy women who were not pregnant and 10 healthy men. Among the pregnant women, PAF-acetylhydrolase activity was significantly higher in those with high blood pressure than in those with normal blood pressure. Levels of PAF-acetylhydrolase in the pregnant women with high blood pressure were similar to those seen in the healthy women who were not pregnant. PAF-acetylhydrolase activity was higher in the men than in all the women.

Measurement, Enzyme activation, Platelet activating factor

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Ontogeny of angiotensin II vascular smooth muscle receptors in ovine fetal aorta and placental and uterine arteries

Article Abstract:

Angiotensin II vascular smooth muscle receptors may not be responsible for the differences in fetal and maternal response to angiotensin II. Angiotensin II is a substance that stimulates contraction of capillaries and arteries. Fetal blood vessels may be less responsive to angiotensin II than maternal blood vessels. A study examined the characteristics of angiotensin II vascular smooth muscle receptors in fetal and maternal blood vessels from pregnant sheep. One type of receptor with a high affinity for angiotensin was found in both fetal and maternal arteries. No significant difference was found between maternal and fetal blood vessels in affinity for or binding of angiotensin II.

Placenta, Uterine circulation, Angiotensin receptors

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