Effect of platelet-activating factor on the release of PGF-2 alpha and PGE-2 by separated cells of human endometrium

Prostaglandin E2 promotes nitric oxide synthase 2, platelet-activating factor receptor, and matrix metalloproteinase-2 expression in Escherichia coli-challenged ex vivo endometrial explants via the prostaglandin E2 receptor 4/protein kinase a signaling pathway

Prostaglandin E₂ (PGE₂) is an inflammatory mediator involved in the pathogenesis of several chronic inflammatory conditions, including endometritis. Previous studies have shown that PGE₂ accumulates in Escherichia coli-challenged ex vivo endometrial explants, increasing the expression of pro-inflammatory factors and aggravating tissue damage; these alterations are linked to key enzymes involved in the synthesis of PGE₂, including cyclooxygenases-2 (COX-2) and microsomal PGES-1 (mPGES-1). In this study, we aimed to investigate whether administration of PGE₂ modulated the activities of nitric oxide synthase 2 (NOS2), platelet-activating factor receptor (PAFR), and matrix metalloproteinase (MMP)-2 in E. coli-challenged ex vivo bovine endometrial explants. Our findings showed that COX-2 and mPGES-1 inhibitors significantly reduced NOS2, PAFR, and MMP-2 expression in the E. coli-challenged ex vivo endometrial explants. In addition, NOS2, PAFR, and MMP-2 expression levels were strongly increased in response to treatment with 15-prostaglandin dehydrogenase inhibitors in the E. coli-challenged ex vivo endometrial explants. However, these stimulatory effects could be blocked by PGE₂ receptor 4 (EP4) and protein kinase A (PKA) inhibitors. Overall, these findings show that pathogenic PGE₂ upregulated NOS2, PAFR, and MMP-2 expression, which may enhance inflammatory damage via the EP4/PKA signaling pathway in E. coli-challenged ex vivo endometrial explants.

Vascular Endothelial Growth Factor Activation of Intramembranous Absorption: A Critical Pathway for Amniotic Fluid Volume Regulation

OBJECTIVE

The purpose of this review is to propose a critical role for vascular endothelial growth factor (VEGF) in mediating the transfer of amniotic fluid from the amniotic compartment through the fetal membranes and fetal surface of the placenta into fetal blood.

METHODS

Experimental findings in humans and animal models on the action of VEGF in mediating fluid transfer are reviewed and interpreted in order to postulate a proposed mechanism for VEGF regulation of amniotic fluid absorption through the fetal membranes and placenta.

RESULTS

Recent scientific advances suggest that up-regulation of VEGF gene expression in the amnion and chorion is associated with increased transfer of amniotic fluid into fetal blood. The possible mechanisms of action for VEGF appear to involve regulation of intramembranous blood vessel proliferation and membrane transport via passive permeation as well as nonpassive transcytotic vesicular movement of fluid.

CONCLUSION

Currently evolving concepts suggest that amniotic fluid volume is regulated through modulation of the rate of intramembranous absorption of amniotic fluid by both passive and nonpassive mechanisms. The permeability factor VEGF appears to be a critical regulator of amniotic fluid transport in the fetal membranes.

The role of platelet-activating factor in the mammalian female reproductive tract

Platelet-activating factor (PAF) is a potent lipid mediator produced by various cell types of mammals and is involved in an inflammatory-like process with increased vascular permeability. Platelet-activating factor exerts its actions through the activation of specific PAF receptors (PAF-R) found in cells and tissues of the female reproductive tract. The aim of this article was summarized briefly in the current research on the role of PAF in female reproductive functions. Platelet-activating factor has been implicated in processes of ovulation, implantation and parturition because of its angiogenic and growth factor properties. This factor is influenced by ovarian steroid hormones in bringing about changes in the uterus and is a candidate molecule for initial embryo-maternal dialogue. Tissue concentrations of PAF are regulated by the equilibrium between biosynthesis and degradation by PAF-acetylhydrolase (PAF-AH). Antagonists of PAF interfere with ovulation and implantation. Platelet-activating factor, its receptor, and PAF-AH activity play an important role in the maintenance of pregnancy.

The role of paf in embryo physiology

Embryo-derived paf (1-o-alkyl-2-acetyl-sn-glycero-3-phosphocholine) is produced by de novo synthesis. This synthesis commences soon after fertilization and persists throughout the preimplantation phase. Paf is produced and released by the embryos of all mammalian species studied to date. Its release from the embryo involves binding to extracellular albumin in a manner that protects paf from enzymatic degradation. Released paf causes a range of alterations in maternal physiology, including platelet activation, changes in oviductal, endometrial and maternal immune function. Paf also acts in an autocrine fashion as a trophic/survival factor for the early embryo. In vitro, supplementation of culture media with paf improves embryo development. Embryo-derived paf's autocrine actions are transduced by 1-o-phosphatidylinositol-3-kinase, which induces characteristic calcium transients within the early embryo. The calcium transients require both the influx of external calcium and release of inositol trisphosphate-dependent internal calcium stores. Buffering these transients compromised embryo development in a manner that was reversed by exogenous paf. Assisted reproductive technologies compromise the production of paf by some embryos and retard the expression of the paf receptor. This deprivation of paf's action is one of the factors limiting the survivability of embryos produced by assisted reproductive technologies. Paf is one of several autocrine and paracrine trophic/survival factors that act on the early embryo. These factors probably act cooperatively and may, to some degree, be mutually redundant. As the earliest-released and the best-described embryotrophin, paf provides an important exemplar for understanding the role of ligand-mediated trophic support of the early embryo.

Components of a platelet-activating factor-signaling loop are assembled in the ovine endometrium late in the estrous cycle

Pulsatile release of uterine prostaglandin F(2alpha) (PGF(2alpha)) induces luteolysis in ruminants. Exogenous PAF is well known to cause PGF(2alpha) release from the ovine uterus. This study examines whether the components of a PAF-signaling loop exist in sheep at the time luteolysis is normally initiated. Day 14 of the cycle was the first day the uterus responded to an infusion of PAF, inducing a significant short-term increase in circulating levels of the PGF(2alpha) metabolite. There was a significant increase of PAF concentration (P < 0.001) in the endometrium and PAF release by tissue explants (P < 0.001) from day 10 to day 16 of the cycle. Endometrial tissue PAF receptor mRNA expression was induced (P < 0.01) by estradiol and progesterone treatment of animals, and transcripts were present between days 10 and 16 of the estrous cycle. Western analysis of endometrial tissue showed marked upregulation of PAF receptor protein expression from day 14 of the cycle, and immunolocalization studies showed that the receptor expression was predominantly around the endometrial glands. PAF:acetylhydrolase was primarily located within the lumen of the endometrial glands. The study shows that a PAF-signaling loop was assembled within the ovine endometrium at the time that PGF(2alpha) pulsatility was first observed.

Morphometric analysis of the uterine endometrium of swine on days 12 and 16 postestrus

The uterine endometrium of swine is comprised of luminal epithelial, glandular epithelial, and stromal cells that secrete the luteolysin, prostaglandin F(2alpha) (PGF(2alpha)), during late diestrus. However, which of these cells contribute the most to luteolytic PGF(2alpha) secretion is unknown because the cellular composition of the endometrium has not been quantified. Therefore, this study quantified the cellular composition of the endometrium on days 12 and 16 postestrus by histologic and morphometric analyses. On day 12, the endometrium consisted predominantly of stromal cells (47% of total cell quantity) and glandular epithelial cells (37%), whereas luminal epithelial cells represented only 16% of the total of the three cell types. The number of glandular epithelial cells tended to increase (P < 0.10) between days 12 and 16, such that they comprised 45% of the endometrium by day 16, while the number of stromal and luminal cells did not change and accounted for 45% and 10% of the cells, respectively. Luminal epithelial cells had a 58% greater cross-sectional area (P < 0.001) than glandular epithelial cells, whereas glandular epithelial cells had a 22% greater area (P < 0.001) than stromal cells. Glandular epithelial cells decreased (P < 0.001) in cross-sectional area between days 12 and 16, whereas the area of luminal epithelial and stromal cells remained unchanged. These results indicate that the porcine endometrium is comprised predominantly of stromal and glandular epithelial cells that are likely to contribute substantially to endometrial PGF(2alpha) secretion during luteolysis. The contribution of glandular epithelium to luteolytic PGF(2alpha) secretion probably increases during diestrus as the number of these cells increases.

Platelet-activating factor (PAF)-like activity, localization of PAF receptor (PAF-R) and PAF-acetylhydrolase (PAF-AH) activity in bovine endometrium at different stages of the estrous cycle and early pregnancy

PAF-like activity in the endometrium increased from days 2-4 to day 12 and day 20 in both cyclic and pregnant cows. There was an increase in platelet aggregation induced by PAF-like activity in the endometrium of pregnant animals on day 20 as compared to cyclic animals at the same point in time. Two major bands of PAF-R protein at 67 kDa and 97 kDa were detected by Western blot analysis. PAF-R was localized mainly in luminal and glandular epithelium of the endometrium, but the staining was markedly increased in the endometrium of pregnant cows on day 20 compared to cyclic animals on the same day. The purified PAF-AH from the endometrium is similar to in plasma. In cyclic cattle, no changes in PAF-AH activity of endometrium were observed, whereas a decrease in enzyme activity occurred in pregnant cows on day 20 as compared to cyclic animals on the same day. We suggest that the bovine endometrium produces PAF-like activity, expresses the PAF-R and possesses a PAF-AH activity which varies during pregnancy.

Fluorometric detection of platelet activating factor receptor in cultured oviductal epithelial and stromal cells and endometrial stromal cells from bovine at different stages of the oestrous cycle and early pregnancy

During the oestrous cycle and early pregnancy, the oviduct and uterus undergo a variety of morphological and physiological modifications in which the platelet activating factor receptor (PAF-R) plays an important role. PAF-R levels were quantified in bovine oviductal epithelial and stromal cells and endometrial stromal cells at days 2 to 4, 12, and 20 of the estrous cycle and during early pregnancy. Cells were grown in vitro and their intracellular PAF-R concentration was measured by flow cytometry using a polyclonal anti-PAF-R antibody system. A significant increase (P < 0.05) in the portion of PAF-R-positive oviductal epithelial and stromal cells was detected in both non-pregnant and pregnant cattle on days 2 to 4 in comparison to day 12 and 20. In endometrial stromal cells derived from day 20 pregnant bovine, a significant increase (P < 0.05) in PAF-R staining was observed in comparison to the day 20 non-pregnant and days 2 to 4 or 12 pregnant and non-pregnant animals. The PAF-R was detected in oviductal cells by using immunoblotting and immuno-gold postembedding method. Positive binding of the anti-PAF-R antibody was found on the cell membrane and in the cytoplasm. We concluded that the increased PAF-R concentration measured in cultured oviductal epithelial and stromal cells of cyclic and pregnant heifers on days 2 to 4 was hormonally regulated. The increased PAF-R in endometrial stromal cells on day 20 of pregnant heifers was a pregnancy-specific effect and may mediate a local increase in endometrial vascular permeability known to precede the implantation.

Localization, quantification, and activation of platelet-activating factor receptor in human endometrium during the menstrual cycle: PAF stimulates NO, VEGF, and FAKpp125

Implantation is characterized by an inflammatory-like response with expansion of extracellular fluid volume, increased vascular permeability, and vasodilatation. These effects are believed to be mediated at the paracrine level by prostaglandin E2 and platelet-activating factor (PAF), but the cellular mechanism (or mechanisms) remains largely unknown. We demonstrate that PAF receptor (PAF-R) immunoreactivity and mRNA are detected in proliferative and secretory endometrial glands, however, the responsiveness of endometrium to physiological concentrations of PAF is confined predominantly to the secretory endometrium. Semiquantitative reverse transcription-polymerase chain reaction revealed that PAF-R transcript levels were highest in the mid-late proliferative and late secretory phases of the cycle. Interaction of PAF with its receptor resulted in the rapid release of nitric oxide (NO), increased expression of vascular endothelial growth factor (VEGF), and activation of FAKpp125, a focal adhesion kinase, demonstrating that the PAF-R is functionally active. Inhibition of NO synthesis by NG-monomethyl-L-arginine produced dose-dependent attenuation of PAF-evoked NO release, indicating NOS activation; the dependency of PAF-evoked NO release on PKC and extracellular Ca2+ was confirmed by PKC inhibitor Ro 31-8220 and by the removal of extracellular Ca2+. PAF up-regulated VEGF gene expression in a concentration- and time-dependent fashion in human endometrial epithelial cell lysates. Transcription of VEGF was rapidly followed by secretion of the protein. These data support our premise that this autocoid acts as an angiogenic mediator in the regeneration of the endometrium after menses and as a vasodilator to promote blastocyst attachment during the implantation process.

Interaction between uterine PGE and PGF2 alpha production and the nitridergic system during embryonic implantation in the rat

Embryonic implantation is a complex process in which both maternal and embryonic signals are involved. In the present study, we evaluated changes in uterine prostaglandins production and nitric oxide synthase (NOS) activity during the course of early pregnancy and their interaction during implantation in rats. Uterine phospholipase A2 (PLA2) activity is increased on days 5 (day of ovoimplantation) and 6, compared to preimplantation days (3 and 4). This enhanced activity might be responsible for the observed increase in uterine PGE and PGF2 alpha production observed on day 5 of pregnancy, which induces endometrial vascular permeability and decidualization. When embryo access to the uterus is impaired, the increase of PG production is suppressed. During postimplantation, PGE levels return to preimplantation values, while PGF2 alpha decreased with respect to preimplantation values. Uterine NOS activity is also increased on day 4 and reaches a maximum on day 5, with a profile similar to PGE and PGF2 alpha. Dexamethasone administered in vivo decreased uterine NOS activity on day 4 of pregnancy but not on day 5, suggesting the presence of at least two types of NOS enzymes in the early days of pregnancy. A competitive inhibitor of NOS, L-NAME (600 and 1000 microM) induced a decrease in PGE and PGF2 alpha production in uterine tissue on day 5 of pregnancy. These results suggest the existence of a physiologically relevant nitridergic system which modulates prostaglandin production in the rat uterus during embryonic implantation.

Platelet activating factor and conception

PURPOSE

This review provides evidence for the involvement of platelet activating factor (PAF) in the several facets of pregnancy establishment.

METHODS

A comprehensive literature review and new data.

RESULTS

PAF has a role in spermatozoal function, fertilization, embryo development, and implantation.

CONCLUSIONS

PAF is intimately involved in conception.

The control of prostaglandin production by the endometrium in relation to luteolysis and menstruation

Oestradiol acting on a progesterone-primed uterus stimulates prostaglandin (PG) F2 alpha synthesis by the endometrium. In some species (notably the sheep, cow and goat) oxytocin released from the ovary also forms part of the physiological stimulus for increased endometrial PGF2 alpha production. The corpus luteum contains high concentrations (> 1 microgram/g tissue) of this peptide in these species. The intracellular mechanisms by which these three hormones control endometrial PGF2 alpha synthesis and release are far from clear. Oxytocin stimulates the synthesis of inositol phosphates and diacylglycerol in the endometrium of some species, but whether this pathway is involved in endometrial PGF2 alpha synthesis is still open to question. There is evidence that increased endometrial PGF2 alpha synthesis is dependent upon increased endometrial protein synthesis but, apart from the recorded effects of steroid hormones on the concentrations of phospholipase A2, prostaglandin H synthase and oxytocin receptors, it is not known what other endometrial proteins are involved. Some disorders of menstruation are associated with abnormal PG production by the endometrium, but the reasons for this abnormality are not clear. During early pregnancy an increase in PGF2 alpha synthesis by the endometrium is prevented, except in the pig where the PGF2 alpha produced is directed from the venous drainage to the uterine lumen. In those species in which endometrial PGF2 alpha synthesis is dependent upon oxytocin secreted by the ovary, the conceptus secretes an interferon-tau (previously named trophoblast protein-1) which prevents oestradiol and oxytocin acting on a progesterone-primed uterus from stimulating endometrial PGF2 alpha synthesis. The identities of the factors produced by the conceptus which prevent endometrial PGF2 alpha synthesis during early pregnancy in other species are not known, although it is clear that they are not interferons.

Activation of human endometrial phospholipase D by bradykinin

Bradykinin may act as a promoter of endometrial regeneration. In [3H]myristate-labelled endometrial stromal cells, bradykinin and tetradecanoylphorbol acetate (TPA) mediated activation of phospholipase D (PLD) as measured by the accumulation of [3H]phosphatidylbutanol ([3H]PtdBut). Kinetics of bradykinin-evoked PLD activation was rapid and transient, whereas the TPA response was relatively slow in onset. Bradykinin induced a dose-dependent (EC50 0.11 nM) [3H]PtdBut accumulation at concentrations at which it stimulated DNA synthesis. In [3H]inositol-labelled cells, bradykinin evoked a rapid increase in inositol phosphates which preceded the increase in [3H]PtdBut formation. Chronic pretreatment with 400 nM TPA abolished PLD activation to subsequent treatment with either TPA and bradykinin. Staurosporine, an inhibitor of protein kinase C, strongly inhibited (IC50 96 nM) TPA-induced [3H]PtdBut formation, but bradykinin-stimulated [3H]PtdBut accumulation was only partially inhibited (IC50 65 microM). The effect of bradykinin and TPA on PLD activity was synergistic, suggesting that the two agents may act via different mechanisms. These results suggest PKC-dependent and independent pathways are involved in bradykinin-induced PLD activation and that the mitogenic activity of this vasoactive peptide on endometrial stromal cells may in part be mediated via the PLD pathway. This may have significance both to implantation and endometrial cancer.

Anti-platelet activating factor (PAF) antibody inhibits CFW mouse preimplantation embryo development

OBJECTIVE

Our purpose was to investigate the effect of anti-PAF antibodies on CFW mouse embryo development in vitro.

DESIGN

We studied the in vitro development of CFW mouse one-cell-stage embryos cultured in MEM supplemented with anti-PAF, anti-IgG, or MEM alone to the hatched blastocyst stage.

RESULTS

Mouse embryos cultured with anti-PAF (1:5 dilution; 61%) significantly decreased embryo development compared to controls (MEM alone; 93%), whereas embryos cultured in anti-mouse IgG-supplemented MEM (1:10 dilution; 93%) had no effect.

CONCLUSIONS

The results provide additional evidence that PAF is produced and secreted by cleavage-stage embryos and is required during the preimplantation period.

Effect of alcohol on platelet-activating factor acetylhydrolase activity in pregnant and nonpregnant mice

Platelet-activating factor (PAF) induces platelet aggregation and hypotension. It has been implicated in embryonic implantation, fetal lung maturation, and parturition. Alcohol abuse is associated with platelet dysfunction, chronic hypertension, and alcohol-related birth defects. We hypothesized that alcohol may cause, in part, these effects by increasing the activity of PAF-acetylhydrolase (PAF-AH), thereby decreasing PAF concentration. Pregnant mice were given 3.5 g/kg of alcohol orally twice daily from gestation days 7-17. PAF-AH was measured on gestation days 5, 14, and 19 in pregnant females. Nonpregnant females were treated and sampled at parallel time intervals. Pair-fed and untreated control groups were also used. The maternal plasma PAF-AH decreased with gestational age in the untreated controls. Alcohol significantly increased PAF-AH levels in both the pregnant and nonpregnant animals. PAF deficiency might contribute to the tocolytic action of alcohol, as well as some alcohol-related pregnancy complications.

Platelet-activating factor in human endometrium

Platelet-activating factor (PAF) is a phospholipid actively produced by human endometrium and deeply involved in the processes of ovoimplantation and labor. We recently found that PAF represents a new autocrine growth factor for a human adenocarcinoma cell line, HEC-1A. Indeed, biologically active PAF is synthesized by HEC-1A cells, under progesterone control. In HEC-1A cells, PAF regulates intracellular calcium concentration ([Ca2+]), DNA synthesis and expression of early oncogenes. All these effects are blocked by the receptor antagonist L659,989. However, while nanomolar concentrations of PAF mobilize [Ca2+], only micromolar concentrations affect cell growth, suggesting heterogeneity of PAF receptors or signaling. Two distinct populations of PAF receptors are present in HEC-1A cells, which bind PAF in nanomolar and micromolar concentrations, respectively. Since HEC-1A cells are producing elevated concentrations of PAF and micromolar concentrations of the PAF antagonist L659,989 inhibit cell proliferation, an autocrine role for PAF is suggested in HEC-1A cells.

Platelet activating factor-acetylhydrolase activity following chorionic villus sampling and amniocentesis

OBJECTIVE

Platelet activating factor (PAF) is essential for embryonic development and is a potent vasodilator. It increases vascular permeability and stimulates prostaglandin E2 (PGE2) production. Platelet activating factor-acetylhydrolase (PAF-AH), the enzyme that degrades PAF, is synthesized by decidual macrophages. The aim of this study was to test the hypothesis that chorionic villus sampling (CVS) and/or amniocentesis might cause an increase in maternal PAF-AH activity.

METHODS

Maternal plasma PAF-AH activity was evaluated before and after genetic amniocentesis (N = 13) and transcervical CVS (N = 29). A control group (N = 9) was evaluated to study the effects of venipuncture.

RESULTS

Chorionic villus sampling caused a significant elevation in PAF-AH activity (P < .0005). No changes were noted in PAF-AH activity in the amniocentesis or the control group.

CONCLUSIONS

Chorionic villus sampling causes subclinical release of PAF-AH, possibly from the decidual macrophages. Increased PAF-AH activity might result in decreased PAF levels, which might lead to vasoconstriction in the placental circulation due to lack of the vasodilator effects of PAF and possibly PGE2. This mechanism might explain the increased risk for fetal limb reduction noted with CVS performed at very early gestational ages.

Platelet-activating factor production from in vitro and in vivo fertilized murine embryos is similar

PROBLEM

This study measured platelet-activating factor (PAF) production of in vitro and in vivo fertilized murine embryos to ascertain whether site of fertilization impacted subsequent embryonic PAF production.

METHOD

Oocytes and embryo were collected from stimulated B6D2F1 mice. PAF production throughout the preimplantation phase from the two-celled stage through expanded blastocysts was measured and compared among normally developing embryos with the only difference being site of fertilization.

RESULTS

A striking increase in PAF production was noted for both in vivo and in vitro fertilized embryos over the four days of culture. Significantly higher (P < .001) levels of PAF production were noted with development from the two-celled stage (47.22 +/- 4.13; 44.30 +/- 2.43) to expanded blastocysts (254.31 +/- 24.01; 255.11 +/- 5.35 ng/embryo/24 h) for both in vitro and in vivo fertilized embryos, respectively. There was no significant difference (P > .05) in PAF production between the two groups of embryos.

CONCLUSIONS

Embryonic PAF production in the mouse increases in a stage-specific manner, and specifically the site of fertilization in vitro versus in vivo does not affect PAF production in normally developing embryos.

Embryonic platelet activating factor production in the rabbit increases during the preimplantation phase

OBJECTIVE

This study measured platelet activating factor (PAF) production by rabbit embryos in vitro and ascertained if there is increased PAF production associated with advancing embryonic development.

STUDY DESIGN

Two-cell rabbit embryos were recovered from superovulated New Zealand White does and cultured in vitro for 96 hr. Every 24 hr embryos were scored for developmental stage and PAF activity from the corresponding culture medium was measured by platelet aggregation and organic phosphate analyses.

RESULTS

PAF was detected in culture medium at all stages from two cells to blastocysts and rose significantly (P < 0.001) at each 24-hr interval, reaching maximal levels at the expanded blastocyst stage.

CONCLUSION

Maximal PAF production by expanded blastocysts may be an embryonic paracrine signal that facilitates implantation.

Arachidonic acid release and inositol lipid metabolism in response to bradykinin and related peptides in human endometrial cells in vitro

Prostaglandins of the 2 series are known to play a role in the regulation of menstruation and implantation but, more recently, other vasoactive peptides have been considered as potential regulators of these endometrial processes. The aim of the present study was to investigate the action of the potent vasoactive peptide bradykinin and the structurally related peptide, kallidin, on endometrial function by examining their effect on phosphoinositide hydrolysis and arachidonic acid release from endometrial cells in vitro. Primary cultures of endometrial glands and stromal cells were prelabelled with [14C]-arachidonic acid (AA) or [3H]-inositol to monitor arachidonic acid release and inositol phosphate accumulation respectively. Bradykinin and kallidin stimulated a dose and time-dependent release of arachidonic acid from stromal cells which, with 100 nmol/L bradykinin, was 30-150% above basal release and maximal at 5 min. Glands were less responsive; 100 nmol/L bradykinin (at 5 min) caused a release of AA of 30-69% above basal level. Bradykinin also stimulated a dose dependent increase in inositol monophosphate production. The maximum response with stromal cells was 8- to 10-fold and with glands, 2-fold (1 and 100 nmol/L bradykinin, respectively). Kallidin was equipotent to bradykinin with respect to both AA and inositol phosphate accumulation. The bradykinin analogue des Arg bradykinin (which acts through the B1 receptor) released AA from stromal cells but did not alter phosphoinositide hydrolysis, suggesting that these two cellular responses are mediated by different receptors (B1 and B2 respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

The effects of platelet-activating factor on the output of prostaglandins from the guinea-pig uterus

Platelet-activating factor (PAF) significantly increased the output of prostaglandin (PG) F2 alpha from the guinea-pig uterus during the mid-cycle phase (Days 6-10), but only had a small, non-significant stimulatory effect on the outputs of PGE2 and 6-keto-PGF1 alpha. PAF significantly increased the outputs of PGF2 alpha, PGE2 and 6-keto-PGF1 alpha from the guinea-pig uterus during the later phase of the cycle (Days 15-17). Lack of extracellular calcium did not affect the stimulatory effect of PAF on uterine PG output. However, TMB-8 (an intracellular calcium antagonist) prevented the increases in uterine PG output produced by PAF at both phases of the cycle. These results suggest that the stimulatory effect of PAF on uterine PG output in the guinea-pig is dependent upon the mobilization of intracellular calcium but is not dependent upon the uptake of extracellular calcium. Also, the weak stimulatory effect of PAF on PGE2 output from the uterus during the mid-cycle phase indicates that, if PAF is involved in implantation in guinea-pigs, it probably does not act via PGE2. Also, the lack of an inhibitory effect of PAF on uterine PGF2 alpha synthesis and release suggests that PAF is not the anti-luteolytic factor produced by the guinea-pig conceptus during early pregnancy.

Platelet-activating factor levels in human follicular and amniotic fluids

Platelet-activating factor (PAF) was estimated in extracts of human follicular and amniotic fluids using a commercially available 125I-radioimmunoassay. Levels obtained before and after purification of the extracts by thin-layer chromatography were similar and PAF could be estimated with high accuracy and reproducibility over a wide dilution range. PAF levels in fluid aspirated from mature (17 mm average diameter) follicles from in vitro fertilization patients were 1005 +/- 129 fmol/ml in successful (clinical pregnancy) cycles and 949 +/- 75 fmol/ml in unsuccessful (failure of implantation) cycles. PAF levels were also similar in follicles containing eggs and those where no egg was found, and in fluid from follicular cysts characterised by low oestradiol and progesterone levels. PAF was detected in midtrimester amniotic fluid (60 +/- 20 fmol/ml). At term, PAF was low or undetectable in amniotic fluid obtained at elective caesarean section before the onset of labour, but increased to 102 +/- 28 fmol/ml in samples obtained following spontaneous labour and vaginal delivery. The data suggest that PAF may be involved in ovulation and parturition but further studies into the mechanism of action of PAF are necessary. The good performance of the radioimmunoassay and the convenience of gamma-counting are strong advantages of this method over the available bioassays, but its expense remains a drawback.

Platelet-activating factor stimulates phospholipase C activity in human endometrium

Human preimplantation embryos secrete platelet-activating factor (PAF), which stimulates prostaglandin E2 synthesis from secretory endometrium. This study investigated the action of PAF on phosphatidylinositol 4,5-bisphosphate (PtdIns(4,5)P2)-specific phospholipase C activity in human endometrium. Slices of normal endometrium were incubated with 5 microCi/ml myo-[2-3H] inositol for 3 h at 37 degrees C in 95% O2 and 5% CO2 to label tissue phosphoinositides. Inositol phosphates were extracted using trichloroacetic acid precipitation and diethylether neutralization and production was measured using Dowex 1-X8 anion-exchange column chromatography. PAF induced rapid and concentration-dependent accumulation of inositol phosphates (IP) from secretory endometrium, but had no effect on endometrium removed in the proliferative phase of the menstrual cycle. The IP3 fraction was significantly elevated from a median value of 14.0 c.p.m. mg-1 dry wt [range: 8-41 c.p.m. mg-1 dry wt] to 28.0 c.p.m. mg-1 dry wt [range: 11-87 c.p.m. mg-1 dry wt, P less than 0.002] following 1 min exposure of secretory endometrium to PAF-acether, in the presence of 10 mM LiCl. PAF-induced hydrolysis of PtdIns(4,5)P2 was inhibited by the specific PAF receptor antagonist WEB 2086, in a dose-dependent manner (P less than 0.02), indicating that in human endometrium PtdIns(4,5)P2 hydrolysis is mediated via a PAF receptor. These results indicate that PAF receptor coupling activates endometrial PtdIns(4,5)P2-specific phospholipase C only in the secretory phase of the menstrual cycle, suggesting that the PAF response may be under ovarian steroid regulation. It is proposed that the ability of the endometrium to respond to PAF appears to be a feature of the preparation of this tissue for implantation and that the second messengers generated may play a role in cellular processes involved in the maternal recognition of very early human pregnancy.

Effect of 17 beta-estradiol on PAF and prostaglandin levels in oophorectomized rat uterus

The effects of 17 beta-estradiol on the levels of platelet-activating factor (PAF) and prostaglandins and their precursor phospholipid in the uterus of oophorectomized rats were studied. Oophorectomy results in the decrease in the uterine PAF level to one-third of that in natural estrus. This level was recovered by subcutaneous administration of 17 beta-estradiol. The level of uterine phospholipids, which are rich in arachidonic acid, was significantly decreased by estradiol treatment. More arachidonate-PC was depleted than arachidonate-PE. The molecular structure was confirmed by gas chromatography-mass spectrometry. The amount of PGF2 alpha in the oophorectomized uterine tissue was 10-times that of PAF, but like the latter, increased 3-4 times on estradiol treatment. The chemical structures of PAF and PGF2 alpha formed on estradiol treatment were confirmed by mass spectrometry. The present data strongly suggest a correlation between the formations of PAF and PGF2 alpha, and indicate that estradiol may regulate the physiological formations of PAF and PGs in non-pregnant rat uterus.

Effect of platelet activating factor on prostaglandin release from ovine endometrial cells in culture

Platelet activating factor (PAF) added in vitro to ovine endometrial cells in primary culture caused a dose-dependent increase in the release of prostaglandin (PG) E into the medium compared with release from untreated cells. At a concentration of 1000 ng/ml of PAF, PGE levels in treatment dishes were significantly higher (P less than 0.05) than those in control dishes [130 +/- 8% vs 100% (mean +/- SEM, N = 5 ewes)]. PAF did not alter the release of PGF2 alpha by the same cells. By contrast, the ovine trophoblast interferon, ovine trophoblast protein-1 (oTP-1, 1 ng/ml) attenuated the release of both PGE and PGF2 alpha and this was not overcome by the presence of PAF (100 ng/ml). Thus does not appear that PAF contributes to the antiluteolytic signal in sheep by a direct action on release of PGF2 alpha although it could influence implantation via stimulation of PGE.

Prostaglandin E and E2 alpha secretion by glandular and stromal cells of the pig endometrium in vitro: effects of estradiol-17 beta, progesterone, and day of pregnancy

Prostaglandins (PGs) are believed to play important roles in the establishment of pregnancy. Glandular and stromal cells were isolated from pig endometrium on days 11 through 19 of pregnancy and cultured in the presence of estradiol-17 beta (E2) and progesterone (P4) to determine the effect of day of pregnancy and steroids on the secretion of PGE and PGF2 alpha. Estradiol at concentrations between .01 and 1 microM did not affect PGE and PGF2 alpha secretion into the medium by glandular and stromal cells. Progesterone (.1 microM) suppressed (P less than .001) PGE and PGF2 alpha production from both cell types. Glandular cells secreted more (P less than .01) PGF2 alpha than PGE, whereas stromal cells collected on days 11, 12, 13, and 19 secreted more (P less than .05) PGE than PGF2 alpha. Stromal cells isolated from tissues collected on day 13 of pregnancy produced PGs with higher (P less than .01) PGE:PGF2 alpha ratio than those from tissues harvested on other days of pregnancy. Glandular cells isolated from tissues collected on days 13 and 19 and stromal cells isolated from tissue collected on day 13 of pregnancy secreted more (P less than .05) PGE and PGF2 alpha than cells isolated on other days of pregnancy. We conclude that: 1) P4 has a suppressing effect on PG secretion; 2) endometrial glandular and stromal cells each produce a unique profile of PGs; and 3) endometrial cells harvested on different days of pregnancy secrete different amounts of PGE and PGF2 alpha.

Autoradiographic localization of platelet-activating factor (PAF) binding sites in the rabbit endometrium during the peri-implantation period

This communication describes the use of in-vivo and in-vitro autoradiography to map specific platelet-activating factor (PAF) receptors in the rabbit uterus. Specific [3H]PAF uptake was predominantly localized on epithelial, but not on stromal or myometrial cells. Very few silver grains were associated with the luminal epithelial cells in the uterus of the estrous rabbit, primarily because of the non-differentiated state of the epithelium. In the differentiated pregnant uterus, significantly more [3H]PAF was bound to the glandular epithelial cells, with the stromal cells binding consistently significantly less. The highest density of silver grains was observed at the implantation sites on day 7 of pregnancy. There was no apparent difference in [3H]PAF C18:0 uptake between the epithelial cells at the inter-implantation zone on day 7 and on day 6. Bound [3H]PAF was displaceable by lyso-PAF, U66985, CV3988, but not U66982, L652,731, SRI 63,441 or the inactive PAF isomer, oleoyl PAF. Bovine serum albumin (BSA) significantly inhibited tissue uptake of [3H]PAF C18:0. Intraluminally administered [3H]PAF C18:0 and intravenously injected [3H]methylcarbamyl-PAF, a non-metabolizable PAF analog, penetrated the implanted blastocyst and bound to the embryoblast. This event was reproducible in vitro with pre-implantation blastocysts from day-6 pregnant rabbits, which suggests that uterine-derived PAF may translocate into the blastocyst after attachment.

Macrophages and migratory cells in endometrium relevant to implantation

The implantation of an appropriately developed embryo into a suitably conditioned uterine lining depends on the synchronous maturation of the preimplantation embryo and uterine lining. The pre- and postimplantation embryo also requires protection from immunocompetent maternal immune effectors. Preimplantation embryo development is affected by genotype, intercellular communication and autocrine growth factors (polyamines, TGF-alpha, TGF-beta 1, PAF). Factors of maternal origin may also enhance embryo development (EGF, TGF-alpha, TGF-beta 1, IGF, polyamines). The preimplantation embryo signals its presence to the mother by release of factor(s) such as IFN-alpha-II and a PAF-like factor. PAF may induce EPF in the mother and enhances vascular permeability at the implantation site. Uterine or peritoneal leukocytosis may inhibit development via toxic effects of lymphokines/monokines (IL-2, IL-1?, IFN-gamma, TNF-alpha). Immunoprotection of the preimplantation embryo is conferred by embryo derived maternal factors (EPF, T-cell suppressor factors). The uterus is receptive during a limited period of time (implantation window) and the substrate adhesion molecules produced by uterine and embryonic trophectoderm cells are crucial for the initial stages of implantation. At implantation, trophoblast expression of MHC and non-MHC antigens is shut off and both immunocompetent maternal cells (macrophages, dendritic cells, granulocytes, IELs, immunocytes) and lymphatics become sparse at implantation sites. Peri-implantation cytokines of maternal origin, such as CSF-1, GM-CSF and IGF-1 binding protein, are probably important for trophoblast growth and development. Immuno-protection of the embryo at this stage may be mediated by embryo derived factors that inactivate macrophages and by a population of large, hormone dependent Lyt 2+ (CD8+) suppressor cells. It is possible that these CD8+ cells respond to progesterone and secrete molecules that inactivate natural effector (NK-type) cells against trophoblast. Prostaglandins (PGE2) may play a brief role in immunosuppression at the time of implantation but its role is probably more important with respect to the decidual response. Defects in the pre- and peri-implantation stages of pregnancy may lead to delayed failure in the form of clinical miscarriage.

Pregnancy suppression by a structurally related antagonist for platelet activating factor, CV-6209, in mice

The effects of CV-6209, a structurally related antagonist for platelet activating factor (PAF), on pregnancy were investigated in mice, so that the physiologic significance of PAF production by and secretion from preimplantation embryos could be elucidated. When it was repeatedly administered to pregnant mice during days 1-6 of pregnancy, CV-6209 prevented preimplantation thrombocytopenia and reduced the number of implantation sites dose-dependently, CV-6209 suppression of pregnancy was eliminated by concomitant administrations of PAF. When it was administered on various fractional days of pregnancy, CV-6209 suppressed pregnancy most effectively in mice treated during days 4-5 of pregnancy, the days of implantation. CV-6209 treatment exhibited no apparent effect on embryonic development. Implantation was suppressed when day 4 embryos from saline-treated donor mice were transferred in utero to CV-6209-treated recipient mice. Once implanted, however, their in utero growth was normal. The results indicate that PAF is prerequisite to pregnancy by promoting embryonic implantation.

Platelet-activating factor alters the dynamics of prostaglandin and protein synthesis by endometrial explants from pregnant and cyclic cows at Day 17 following estrus

Factors produced by bovine conceptuses alter prostaglandin (PG) and protein secretion by endometrial explants from cyclic cows and induce an intracellular inhibitor of PG synthesis. Endometrial explants from cyclic (n = 4) and pregnant (n = 3) cows at Day 17 following estrus were incubated for 24 h with 0, 0.1, 0.5, 1 and 5 microg platelet-activating factor (PAF)/ml. Cotyledonary microsomes from parturient cows were utilized to determine levels of an intracellular/cytosolic inhibitor of PG synthesis. Endometrial explants from additional cyclic cows (n = 4) were incubated for 24 h with 0 or 5 microg PAF/ml with and without 50 microCi [(3)H]leucine. Endometrial explants (cyclic cows, n = 3) were also incubated for 12 h with each of the following treatments: 1) Control; 2) PAF (1 microg/ml); 3) lyso-PAF (2 to 10 microg/ml); 4) PAF-receptor antagonist (2 to 10 microg/ml); 5) PAF (1 microg/ml) + antagonist (2 to 10 microg/ml); 6) bovine conceptus secretory proteins (bCSP; 25 microg/ml); and 7) bCSP (25 microg/ml) + antagonist (5 microg/ml). Platelet-activating factor had distinct negative and positive dose effects on PGF and PGE-2 secretion, respectively, by explants from cyclic cows, whereas PG secretion was not altered by PAF in the endometrium of pregnant cows. Platelet-activating factor did not alter the level of an intracellular inhibitor of prostaglandin synthesis, whereas, bCSP increased the level of this inhibitor. Platelet-activating factor decreased the incorporation of [(3)H]leucine into tissue and secreted proteins for explants from cyclic cows. Lyso-PAF did not alter endometrial prostaglandin secretion. The effects of PAF but not of bCSP were blocked by the PAF-receptor antagonist. Platelet-activating factor altered PG and protein secretion by the endometrium from cyclic cows, and it may be a potential regulatory factor during early pregnancy if secreted by the bovine conceptus.

Pregnancy suppression by a platelet activating factor antagonist, ONO-6240, in mice

Mouse embryos produce an embryo-derived platelet activating factor (EDPAF) during their early developmental stages. The present study was aimed at investigating the physiological significance of EDPAF by using a specific PAF antagonist, ONO-6240. EDPAF-induced platelet decrease was antagonized by ONO-6240 in a dose-dependent manner, although this alone did not affect circulating platelet concentrations. ONO-6240, when administered to maternal mice, increased the proportion of mice conceiving small litter sizes, whereas it did not affect in vivo or in vitro development of embryos. EDPAF was suggested to play an important role in establishing pregnancy in mice by promoting implantation.