14C-labeled arachidonic acid bioconversion in guinea pig placenta during the last third of gestation

Prostaglandin H2 synthase-1 and -2 expression in guinea pig gestational tissues during late pregnancy and parturition

Increased intrauterine prostaglandin (PG) production is crucial for the initiation of parturition. To investigate the mechanisms controlling intrauterine PG synthesis, we examined the expression of the key PG biosynthetic isoenzymes, PG-H2 synthase (PTGS)-1 and -2, in the amnion, visceral yolk sac (VYS), placenta and myo-endometrium of pregnant guinea pigs. This animal model was chosen because the hormonal milieu of pregnancy and the role of PGs in the hormonal control of parturition are similar to those in the human. PTGS1 mRNA abundance, measured by real-time RT-PCR, increased in the amnion and the placenta during the last third of gestation. During labour, PTGS1 mRNA levels decreased precipitously in all four tissues. PTGS1 protein abundance, assessed by immunoblotting, increased to high levels in the amnion and the placenta by the end of pregnancy and remained high during labour. PTGS2 mRNA expression was higher in the placenta than in the other tissues, but did not change before and during labour. PTGS2 protein expression decreased in the placenta and remained low in the other tissues during labour. Immunohistochemistry showed pervasive PTGS1 protein expression in the amnion and strong expression in the parietal yolk sac membrane (PYS) covering the placenta. PTGS2 was expressed in the PYS and the endometrium. The PTGS inhibitor piroxicam, administered in doses that inhibited PTGS1 but not PTGS2, significantly prolonged gestation. These data suggest that PGs generated by intrauterine PTGS1 are involved in the timing of birth in guinea pigs. The induction of PTGS1 in the amnion and the PYS is a critical event leading to labour in guinea pigs and models analogous changes in the human gestational tissues before labour.

Development and review of radioimmunoassay of 12-S-hydroxyheptadecatrienoic acid

For more than 25 years 12-S-hydroxyheptadecatrienoic acid (HHT) has been known to be a product of thromboxanesynthase (TX-Syn) when synthesized with thromboxane A2 (TXA2). Although there are some hints that HHT has anti-aggregatory effects, to date, it has neither been shown to have any specific pathological relevance nor is there much information about its physiological role. This review presents a summary of the physicochemical properties of HHT, its chemical synthesis, the impact of various biological systems on its enzymatic and non-enzymatic production and its physiological function and metabolization, as well as a survey of the most important methods for analyzing this unsaturated hydroxy-fatty acid. Due to the low antibody-raising potency expected in HHT, no immunological system for HHT quantification has been developed so far. In our report we present the development and validation of a sensitive and reliable, competitive radioimmunoassay (RIA) suitable for the quantitative determination of HHT. HHT was produced by an enhanced enzymatic method using platelet-rich plasma (PRP). With an effective and modified liquid-liquid and solid-phase extraction method we were able to produce highly purified HHT (97% purity by GC/MS) in sub-milligram ranges. These fractions were used for the synthesis of BSA-antigen-conjugates and for immunization of rabbits. The tritiated tracer was synthesized using prostaglandin H synthase for the production of prostaglandin H2 (PGH2) followed by an aqueous reaction with Fe(2+)-solution to rear-range PGH2 to HHT. The dynamic range of the assay was from 30-400 pg/tube, with a sensitivity of approximately 40 pg/tube. The evaluation of the assay was performed by a HPLC-RIA method as well as by correlation with a quantitative HPLC method and correlation with TXB2 concentrations in a blood coagulation study. The assay may be useful for the quantification of HHT in several tissues and body fluids under various physiological conditions and may also help to understand the possible physiological role of HHT in biological processes.

Reversed-phase high-performance liquid chromatographic method for the determination of the 11-hydroxythromboxane B2 anomers equilibrium

An improved reversed-phase HPLC method for the separation and detection of both hemiacetalic 11-hydroxy anomers of thromboxane B2 (TXB2) is described. Water-acetonitrile mixtures have served as mobile phases. By diminishing stepwise the temperature of the chromatographic system from 40 to 0 degrees C, the UV-absorbance profile of TXB2 changed from one broad peak to two clearly separated narrow peaks corresponding to the two anomers existing in equilibrium. Modification of the mobile phase pH from 1.6 to 6.9 (0 degrees C) resulted in different concentration ratios of the anomers. The equilibrium constant and the Gibbs free energy were calculated. The intermediate open aldehyde form of TXB2 is unstable and, therefore, cannot be observed either by HPLC or by 1H NMR measurements.

Plasma type II phospholipase A2 levels are elevated in severe preeclampsia

OBJECTIVE

Our purpose was to compare plasma concentrations of type II phospholipase A2 in normal and preeclamptic pregnancies and to determine whether plasma from preeclamptic patients increases endothelial cell secretion of type II phospholipase A2.

STUDY DESIGN

We compared the plasma levels of type II phospholipase A2 in 23 patients with normal pregnancies and 25 patients with strictly defined preeclampsia. Plasma samples were collected throughout pregnancy and stored at -80 degrees C. Patients with preeclampsia were matched closely as possible with controls for maternal age, race, gestational age at blood sampling, and parity. Plasma levels of type II phospholipase A2 were measured by enzyme immunoassay. To investigate endothelial cell type II phospholipase A2 production, we measured levels of prostacyclin and type II phospholipase A2 in conditioned media from cultured human umbilical vein endothelial cells exposed to plasma from preeclamptic and normal pregnant patients.

RESULTS

The mean plasma type II phospholipase A2 level in the mild preeclampsia group (6.1 +/- 3.0 ng/ml, n = 6) was not different from that in control patients (6.0 +/- 3.2 ng/ml, n = 23). However, the mean type II phospholipase A2 level in patients with severe preeclampsia (19.9 +/- 12.3 ng/ml, n = 19) was significantly higher when compared with the other two groups (p < 0.001). Prostacyclin concentrations in conditioned media of endothelial cells exposed to plasma from patients with preeclampsia were elevated compared with cells incubated with control plasma (8.6 +/- 1.7 vs 4.0 +/- 5.0 ng/ml, p < 0.05). However, the concentration of type II phospholipase A2 in conditioned medium was not significantly different (1.6 +/- 0.3 vs. 1.8 +/- 1.0 ng/ml, p = 0.40).

CONCLUSIONS

Plasma concentrations of type II phospholipase A2 are elevated in preeclampsia and correlate well with the severity of disease. Plasma from preeclamptic women increased secretion of prostacyclin, but not type II phospholipase A2 by endothelial cells in culture.

Immunoreactive prostaglandin G/H synthase content increases in ovine cotyledons during late gestation

In this study, using gel electrophoresis and Western blotting, we have demonstrated that the content of irPGHS in ovine placenta increases during late gestation prior to the onset of labour. This increase in PGHS tissue content may contribute to the corresponding increased production of prostaglandins by the ovine placenta during this period of pregnancy. Although the mechanism by which PGHS tissue content is elevated at this time remains to be established, one possibility which is currently being investigated in our laboratory is that increased PGHS content reflects an increased level of PGHS gene expression.

Arachidonic acid metabolism by bovine placental tissue during the last month of pregnancy

Conversion of tritiated arachidonic acid (AA) into metabolites of the cyclo- and lipoxygenase pathways by bovine fetal placental tissue (200 mg) and fetal plus maternal placental tissue (400 mg) of Days 255, 265, 275 of gestation and at parturition (n = 5) during a 30 min incubation was measured using reverse-phase high pressure liquid chromatography. Fetal placental tissue produced 13,14-dihydro-15-keto-prostaglandin E2 (PGEM) as the major metabolite, the synthesis of which increased from Day 265 to Day 275 and parturition by 150% and 475%, respectively. In tissues collected at parturition, PGE2 synthesis was also detected. On Day 275 and at parturition fetal placental tissue synthesized the metabolite 12-hydroxyheptadecatrienoic acid (HHT), and throughout the experimental period the lipoxygenase product 15-HETE was detected with synthesis rates increasing over time of gestation. In addition, an unidentified metabolite was regularly found in the radiochromatograms which eluted at 1 h and 1 min (U101), between HHT and 15-HETE. The synthesis of this metabolite decreased as pregnancy progressed. Furthermore, various other polar and nonpolar metabolites pooled under the heading UNID were eluted, the production of which increased over time of gestation. The presence of maternal placental tissue did not influence the synthesis of PGEM, 15-HETE and U101, but the production of HHT was decreased when maternal tissue was present. Also, as pregnancy progressed, maternal placental tissue seemed to contribute to the pool of unidentified metabolites. In conclusion, fetal placental tissue seems to be the major source of the AA metabolites when compared with maternal placental tissue, and AA metabolism by bovine placental tissue is markedly increased throughout the last month of pregnancy, suggesting a role for AA metabolites in mechanisms controlling parturition.

Gas chromatographic/mass spectrometric quantitative analysis of eicosanoids in human oesophageal mucosa

In order to investigate the contribution of eicosanoids to human oesophageal functions and disorders (gastrooesophageal reflux, GOR and reflux oesophagitis, RO), we have used a selected ion monitoring gas chromatographic/mass spectrometric methodology to quantify the cyclooxygenase and lipoxygenase products biosynthesized in vitro by endoscopic mucosal biopsy specimens. Prostaglandins (PGs) were quantified as MEMOTMS derivatives and HETEs, as hydrogenated methyl ester of tert-butyldimethylsilyl) ether derivatives. PGE2, PGF2 alpha appeared as the major prostanoids, whereas 12HETE seemed to be the major lipoxygenase product. In the case of GOR or RO, biosynthesis of PGE2 was dramatically increased, while no change could be detected for 12HETE. PGE2 increase seems to be related to inflammatory reaction, in which its exact role remains unclear. Moreover, it cannot be excluded that PGE2 is a side product which might be protective to the oesophageal mucosa.