Not prostacyclin synthase but prostaglandin endoperoxide synthase increases with human placental development

Examination of the expression of cyclooxygenase-2 in placenta villi from sufferers of pregnancy induced hypertension

OBJECTIVES

The purpose of this paper is to elucidate the roles of phospholipase A(2) (PLA(2)), cyclooxygenase-2 (COX-2), and prostaglandin I(2) (PGI(2)) synthase in pregnancy induced hypertension (PIH).

METHODS

In placentas from normal pregnant women and pregnant women with severe PIH, the enzyme expression of PLA(2), COX-2, and PGI(2) synthase was measured using real time reverse transcription-polymerase chain reaction (RT-PCR).

RESULTS

The expression of each enzyme was compared between normal (n=12) and PIH (n=12) groups. The expression levels of COX-2 and PGI(2) synthase during PIH pregnancy were significantly decreased to about 51% and 68%, respectively, of their values in normal pregnancy. However, the expression of PLA(2) was hardly changed by PIH.

CONCLUSIONS

The decreases in COX-2 and PGI(2) synthase expression in severe PIH placentas may be causal factors in the disruption of the PGI(2)-thromboxane A(2) (TXA(2)) balance in favor of TXA(2). The decrease in COX-2 was more marked than that of PGI(2) synthase.

Effects of indomethacin, NS-398 (a selective prostaglandin H synthase-2 inhibitor) and protein synthesis inhibitors on prostaglandin production by the guinea-pig placenta

The outputs of PGF(2 alpha), PGE2 and 6-keto-PGF(1 alpha)were similar from the day 22 guinea-pig placenta and sub-placenta in culture, except for PGE2 output from the sub-placenta which was lower. Between days 22 and 29 of pregnancy, the outputs of PGF(2 alpha), PGE2 and 6-keto-PGF(1 alpha)during the initial 2 h culture period increased 6.9-, 1.1- and 3.2-fold, respectively, from the placenta, and 2.1-, 1.4- and 2.2-fold, respectively, from the sub-placenta. Therefore, there was a relatively specific increase in PGF(2 alpha)production by the guinea-pig placenta between days 22 and 29 of pregnancy. The output of PGFM from the cultured placenta also increased between days 22 and 29, indicating that the increase in PGF(2 alpha)output was due to increased synthesis rather than to decreased metabolism. By comparing the amounts of prostaglandins produced by tissue homogenates during a 1 h incubation period, it appears that there is approximately a 2-fold increase in the amount of prostaglandin H synthase (PGHS) present in the guinea-pig placenta between days 22 and 29. NS-398 (a specific inhibitor of PGHS-2) and indomethacin (an inhibitor of both PGHS-1 and PGHS-2) both inhibited prostaglandin production by homogenates of day 22 and day 29 placenta. Indomethacin was more effective than NS-398, except for their actions on PGF(2 alpha)production by the day 29 placenta where indomethacin and NS-398 were equiactive. Indomethacin and NS-398 were both very effective at inhibiting the outputs of PGF(2 alpha), PGE2 and 6-keto-PGF(1 alpha)from the day 22 and day 29 placenta and sub-placenta in culture, indicating that prostaglandin production by the guinea-pig placenta and sub-placenta in culture is largely dependent upon the activity of PGHS-2. The high production of PGF(2 alpha)by the day 29 placenta is not dependent on the continual synthesis of fresh protein(s), as inhibitors of protein synthesis did not reduce PGF(2 alpha)output from the day 29 guinea-pig placenta in culture.

DNA adducts of 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) in fetal tissues of patas monkeys after transplacental exposure

Transplacental genotoxicity of the heterocyclic amine food-derived mutagen/carcinogen 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) has been investigated by (32)P-postlabeling assay for IQ-DNA adducts in maternal liver, placenta, and several fetal tissues of patas monkeys, after exposure to 15, 35, or 50 mg/kg IQ near the end of gestation or to the highest dose in the first or second trimester. Dose-dependent adduct formation occurred in all tissues, with the highest levels occurring in maternal liver. Adduct amounts were similar among fetal tissues and placenta, except for lower levels in fetal brain and slightly more adducts in fetal liver. Adducts in placenta, fetal liver, lung, kidney, skin, and adrenal gland, but not in maternal liver or fetal brain, increased significantly as gestation progressed. Pretreatment with phenobarbital, which induces CYP enzymes that detoxify IQ, decreased adducts in maternal liver and possibly placenta, but not in fetal tissues. The CYP inducer beta-naphthoflavone caused a significant increase in IQ-DNA adducts in fetal lungs. Regression analysis suggested that IQ activation in maternal and fetal liver and possibly placenta contributed to adduct formation in fetal tissues; adducts in placenta and/or fetal liver were strong predictors for those in most fetal tissues. The results indicate that exposure of pregnant primates to IQ results in DNA adduct formation in most fetal tissues, especially late in gestation; that upregulation of maternal detoxification does not provide fetal protection; and that adducts in placenta indicate adduct levels in fetal tissues.

Endothelial vasodilator production by uterine and systemic arteries. V. Effects of ovariectomy, the ovarian cycle, and pregnancy on prostacyclin synthase expression

Prostacyclin (PGI(2)) is a potent vasodilator, the level of which is increased during pregnancy, and is the main eicosanoid of which production is elevated in the endothelium and vascular smooth muscle (VSM) of both uterine and omental (systemic) arteries. We tested the hypothesis that during physiologic states that have high uterine blood flow, such as pregnancy and the follicular phase of the ovarian cycle (versus luteal phase and ovariectomized ewes), there is an increased level of prostacyclin synthase (PGIS) expression in ovine uterine and omental artery endothelium and VSM. To investigate this, the cellular localization and PGIS protein expression level in uterine and systemic arteries was examined by immunohistochemistry as well as by Western immunoblot analysis of endothelial-isolated protein and denuded vessels (VSM). Whole uterine, but not omental (systemic), arteries from the pregnant ewes showed an increase (P < 0.001) in PGIS expression. Further localization of PGIS protein by immunohistochemistry and quantification by Western analysis showed PGIS to be somewhat higher in the uterine artery VSM (69 +/- 7%) than endothelium (31 +/- 7%). PGIS protein levels in uterine and omental artery endothelial isolated protein were not altered by ovariectomy or the ovarian cycle, although they were both significantly elevated by pregnancy. Uterine and omental artery VSM PGIS expression levels also were not altered by ovariectomy or the ovarian cycle, whereas PGIS expression, in uterine but not omental artery VSM showed a significant elevation during pregnancy. Thus, the rise in PGI(2) production by uterine arteries observed in ovine pregnancy is paralleled by an elevation in PGIS expression in both endothelium and VSM, whereas those seen in omental arteries is associated with increases in endothelial PGIS.

Pregnancy and lipid peroxide-induced alterations of eicosanoid-metabolizing enzymes in the aorta of the rat

OBJECTIVES

We examined whether pregnancy modulates the expression of prostaglandin endoperoxide synthase, prostacyclin synthase, and thromboxane A2 synthase in the systemic vasculature. Further, we examined whether elevated lipid peroxidation during pregnancy (induced by vitamin E deprivation) affects the normal adaptive process to pregnancy.

STUDY DESIGN

Western immunoblotting was performed on aortas from normal and vitamin E-deprived late pregnant (18 to 19 days) and age-matched virgin control rats.

RESULTS

Normal pregnancy resulted in an increased expression of prostaglandin endoperoxide synthase (2.91 vs 1.06 fmol/ng deoxyribonucleic acid, p < 0.05). Surprisingly, the expression for both prostacyclin and thromboxane A2 synthases were significantly decreased by pregnancy: prostacyclin synthase 2.60 versus 13.82 units/ng deoxyribonucleic acid and thromboxane A2 synthase 1.32 versus 9.85 units/ng of deoxyribonucleic acid. Elevation of endogenous lipid peroxidation partially reversed this normal pregnancy trend in enzyme expression: prostaglandin endoperoxide synthase 1.85 fmol/ng deoxyribonucleic acid, prostacyclin synthase 9.38 units/ng deoxyribonucleic acid, thromboxane A2 synthase 4.36 units/ng deoxyribonucleic acid.

CONCLUSION

Changes in prostanoid activity in the systemic vasculature during pregnancy may be mediated by concerted induction and down-regulation of specific enzymes. Increased lipid peroxidation interferes with this normal pregnant pattern. Further studies on the cell-specific expression of these genes will help to define the cardiovascular role of prostaglandins in pregnancy and in preeclampsia.

Changes in urinary 6-keto-prostaglandin F1 alpha excretion during pregnancy and labor

Urinary excretion of 6-keto-PGF1 alpha was measured by high pressure liquid chromatography and radioimmunoassay at various stages of pregnancy and labor. In the first trimester of pregnancy, urinary 6-keto-PGF1 alpha concentrations were not different from those measured before pregnancy, but they showed a significant increase in the second trimester of pregnancy (p less than 0.001). The levels rose further in the third trimester, although this increase was not statistically significant when compared to levels obtained in the second trimester. There was no evidence for a significant change in 6-keto-PGF1 alpha excretion with the onset of labor. During well-established, progressive labor mean values of 6-keto-PGF1 alpha excretion were about twice as high as before the onset of labor, but the range of values during labor was so wide that there was no statistical difference with values obtained in the second half of pregnancy. It is concluded that the increase in the urinary excretion of 6-keto-PGF1 alpha occurs later in pregnancy than the increase in TXB2 excretion and that labor at term is not associated with marked changes in 6-keto-PGF1 alpha excretion.