Early Abnormal Placentation and Evidence of Vascular Endothelial Growth Factor System Dysregulation at the Feto-Maternal Interface After Periconceptional Alcohol Consumption

Adequate placentation, placental tissue remodeling and vascularization is essential for the success of gestation and optimal fetal growth. Recently, it was suggested that abnormal placenta induced by maternal alcohol consumption may participate in fetal growth restriction and relevant clinical manifestations of the Fetal Alcohol Spectrum Disorders (FASD). Particularly, periconceptional alcohol consumption up to early gestation can alter placentation and angiogenesis that persists in pregnancy beyond the exposure period. Experimental evidence suggests that abnormal placenta following maternal alcohol intake is associated with insufficient vascularization and defective trophoblast development, growth and function in early gestation. Accumulated data indicate that impaired vascular endothelial growth factor (VEGF) system, including their downstream effectors, the nitric oxide (NO) and metalloproteinases (MMPs), is a pivotal spatio-temporal altered mechanism underlying the early placental vascular alterations induced by maternal alcohol consumption. In this review we propose that the periconceptional alcohol intake up to early organogenesis (first trimester) alters the VEGF-NO-MMPs system in trophoblastic-decidual tissues, generating imbalances in the trophoblastic proliferation/apoptosis, insufficient trophoblastic development, differentiation and migration, deficient labyrinthine vascularization, and uncompleted remodelation and transformation of decidual spiral arterioles. Consequently, abnormal placenta with insufficiency blood perfusion, vasoconstriction and reduced labyrinthine blood exchange can be generated. Herein, we review emerging knowledge of abnormal placenta linked to pregnancy complications and FASD produced by gestational alcohol ingestion and provide evidence of the early abnormal placental angiogenesis-vascularization and growth associated to decidual-trophoblastic dysregulation of VEGF system after periconceptional alcohol consumption up to mid-gestation, in a mouse model.

Murine transcription factor Math6 is a regulator of placenta development

The murine basic helix-loop-helix transcription (bHLH) factor mouse atonal homolog 6 (Math6) is expressed in numerous organs and supposed to be involved in several developmental processes. However, so far neither all aspects nor the molecular mechanisms of Math6 function have been explored exhaustively. To analyze the in vivo function of Math6 in detail, we generated a constitutive knockout (KO) mouse (Math6^−/−) and performed an initial histological and molecular biological investigation of its main phenotype. Pregnant Math6^−/− females suffer from a disturbed early placental development leading to the death of the majority of embryos independent of the embryonic Math6 genotype. A few placentas and fetuses survive the severe uterine hemorrhagic events at late mid-gestation (E13.5) and subsequently develop regularly. However, these fetuses could not be born due to obstructions within the gravid uterus, which hinder the birth process. Characterization of the endogenous spatiotemporal Math6 expression during placenta development reveals that Math6 is essential for an ordered decidualization and an important regulator of the maternal-fetal endocrine crosstalk regulating endometrial trophoblast invasion and differentiation. The strongly disturbed vascularization observed in the maternal placenta appears as an additional consequence of the altered endocrine status and as the main cause for the general hemorrhagic crisis.

Does the dysregulation of matrix metalloproteinases contribute to recurrent implantation failure?

INTRODUCTION

The progress in in vitro fertilization (IVF) techniques for infertility management has led to the investigation of embryo implantation site proteins such as Matrix metalloproteinases (MMPs), which may have a key role in embryo-endometrium crosstalk and in the molecular mechanisms of the embryo implantation. Areas covered: Numerous studies have generated much information concerning the relation between the different proteins at the site of implantation such as cytokines, growth factors, adhesion molecules and MMPs. However, the exact role of the MMPs in embryo implantation and the impact of their dysregulation in recurrent implantation failure have yet to be characterized. Expert commentary: The proteomic investigation of the MMPs and their molecular pathways may enable scientists and clinicians to correct this dysregulation (via appropriate means of prevention and treatment), better manage embryo transfer during IVF cycles, and thus increase the ongoing pregnancy rate.

The role of NFκB in the three stages of pregnancy - implantation, maintenance, and labour: a review article

The transcription factor nuclear factor kappa B (NFκB) controls the expression of over 400 genes, some of which are associated with reproductive events. During implantation, immune cells accumulate in the maternal-fetal interface; they secrete inflammatory mediators under the control of NFĸB, the level of which also rises. NFĸB is then downregulated to maintain gestation, but its level rises again before birth to manage prostaglandin, cytokine, and chemokine synthesis, and to stimulate uterine contraction. This review summarises the current state of knowledge about NFκB and its role in the molecular regulation of processes related to pregnancy development.

TWEETABLE ABSTRACT

This review examines the current state of knowledge about role of NFκB in the development of pregnancy.

Restraint stress delays endometrial adaptive remodeling during mouse embryo implantation

In mice, previously, we showed that restraint stress reduces the number of embryo implantation sites in the endometrium. Here, we hypothesized that the uterine microenvironment is altered by restraint stress and consequently is suboptimal for embryo implantation. On embryonic day 1 (E1), 60 of 154 pregnant CD1 mice underwent restraint stress (4 h), repeated daily to E3, E5 or E7 (n = 10 mice per group). Restraint stress decreased food intake and suppressed body weight gain on E3, E5 and E7. Restraint stress decreased the actual and relative weight (percent body weight) of uterus and ovary on E5 (by 14.9%, p = 0.03; 16.1%, p = 0.004) and E7 (by 16.8%, p = 0.03; 20.0%, p = 0.01). Morphologically, restraint stress decreased relative endometrial area (by 8.94-18.8%, p = 0.003-0.021) and uterine gland area (by 30.6%, p < 0.01 on E3 and 44.5%, p < 0.01 on E5). Immunohistochemistry showed that restraint stress decreased microvessel density (by 12.9-70.5%, p < 0.01) and vascular endothelial growth factor expression (by 14.6-45.9%, p = 0.007-0.02). Restraint stress decreased by 32.4-39.8% (p = 0.002-0.01) the mean optical density ratio for proliferating cell nuclear antigen/terminal deoxynucleotidyl transferase dUTP nick end labeling. Methyl thiazolyl tetrazolium assay showed a dose-dependent decrease in proliferative activity of endometrial stromal cells (from 52 of 154 pregnant E5 control mice) incubated with H2O2 (100-1000 μM) in vitro. These findings supported the hypothesis that restraint stress negatively influences endometrial adaptive remodeling via an oxidative stress pathway, which resulted in fewer implantation sites.

Ion/Water Channels for Embryo Implantation Barrier

Successful implantation involves three distinct processes, namely the embryo apposition, attachment, and penetration through the luminal epithelium of the endometrium to establish a vascular link to the mother. After penetration, stromal cells underlying the epithelium differentiate and surround the embryo to form the embryo implantation barrier, which blocks the passage of harmful substances to the embryo. Many ion/water channel proteins were found to be involved in the process of embryo implantation. First, ion/water channel proteins play their classical role in establishing a resting membrane potential, shaping action potentials and other electrical signals by gating the flow of ions across the cell membrane. Second, most of ion/water channel proteins are regulated by steroid hormone (estrogen or progesterone), which may have important implications to the embryo implantation. Last but not least, these proteins do not limit themselves as pure channels but also function as an initiator of a series of consequences once activated by their ligand/stimulator. Herein, we discuss these new insights in recent years about the contribution of ion/water channels to the embryo implantation barrier construction during early pregnancy.

Matrix metalloproteinase expression and activity in trophoblast-decidual tissues at organogenesis in CF-1 mouse

During early placentation, matrix metalloproteinases (MMPs) play important roles in decidualization, trophoblast migration, invasion, angiogenesis, vascularization and extracellular matrix (ECM) remodeling of the endometrium. The aim of our study was to analyze the localization, distribution and differential expression of MMP-2 and -9 in the organogenic implantation site and to evaluate in vivo and in vitro decidual MMP-2 and -9 activities on day 10 of gestation in CF-1 mouse. Whole extracts for Western blotting of organogenic E10-decidua expressed MMP-2 and -9 isoforms. MMP-2 immunoreactivity was found in a granular and discrete pattern in ECM of mesometrial decidua (MD) near maternal blood vessels and slightly in non-decidualized endometrium (NDE). Immunoexpression of MMP-9 was also detected in NDE, in cytoplasm of decidual cells and ECM of vascular MD, in trophoblastic area and in growing antimesometrial deciduum. Gelatin zymography showed that MMP-9 activity was significantly lower in CM compared to the active form of direct (not cultured) and cultured decidua. The decidual active MMP-9 was significantly higher than the active MMP-2. These results show differential localization, protein expression and enzymatic activation of MMPs, suggesting specific roles for MMP-2 and MMP-9 in decidual and trophoblast tissues related to organogenic ECM remodeling and vascularization during early establishment of mouse placentation.

Hyperglycosylated hCG and pregnancy failures

Considerable evidence indicates that one third of early pregnancy failures, spontaneous abortions and biochemical pregnancies, are due to chromosomal abnormalities, and two thirds are due to inappropriate implantation. These findings led us to investigate the role of hyperglycosylated hCG, an important pregnancy implantation signal, in pregnancy failures. We used urinary hCG determinations to evaluate a total of 127 pregnancies on the day of implantation, as marked by a positive urinary hCG. These included 81 normal term pregnancies, 18 spontaneous abortion pregnancies, and 28 biochemical pregnancies. Of the normal term pregnancies, the mean±standard deviation concentration of hyperglycosylated hCG was 5.4±4.3 mIU/ml equivalents, and the percentage of hyperglycosylated hCG was 88±17%. All term pregnancies produced hyperglycosylated hCG>51%. Of the 18 cases that spontaneously aborted, both the mean hyperglycosylated hCG (1.9±2.0 mIU/ml equivalents) and the percentage of hyperglycosylated hCG (41±33%) were significantly lower than in the normal pregnancy group. Only 4/18 spontaneously aborting pregnancies produced more than 51% hyperglycosylated hCG on the day of implantation. Similarly, of the 28 biochemical pregnancies, both the mean hyperglycosylated hCG (0.63±1.3 mIU/ml equivalents) and the percentage of hyperglycosylated hCG (21±29%) were significantly lower than in the normal pregnancy group. Only 4/28 pregnancies produced more than 51% hyperglycosylated hCG. Low hyperglycosylated hCG concentrations are associated with pregnancy failure. Whether this association is a primary cause of pregnancy failure or is simply a marker for an abnormal conceptus requires further investigation.

Angiopoietin-like gene expression in the mouse uterus during implantation and in response to steroids

The purpose of this work was to determine if and where Angiopoietin-like genes are expressed in the mouse uterus during the implantation period of pregnancy and to determine if uterine expression of such genes is controlled by estrogen or progesterone. We found that all six known murine angiopoietin-like genes were expressed in the mouse uterus during implantation. The expression of four genes was controlled by either estrogen or progesterone. Only the levels of angiopoietin-like 4 (Angptl4) mRNA dramatically increased in implantation segments of the uterus during decidualization and was conceptus-independent. Due to this increased expression and the fact that angiopoietin-like 4 protein plays a role in lipid metabolism and angiogenesis in other tissues, only the expression of Angptl4 was further examined in the uterus and developing placenta. Angptl4 mRNA was localized to subpopulations of the endometrial stromal fibroblast and endothelial cell populations during decidualization. It was also localized to the ectoplacental cone, trophoblast giant cells and parietal endoderm of the conceptus at this time. By mid-pregnancy, Angptl4 mRNA was localized mainly to the mesometrial lymphoid aggregate region plus mesometrial endothelial cells of the uterus, as well as in various cell types of the conceptus. Additional work showed that Angptl4 expression increases in mouse endometrial stromal cells as they undergo decidualization in vitro. As in other cell types, the expression of Angptl4 in endometrial stromal cells was increased in response to an agonist of the peroxisome proliferator activated receptors. Taken together, the results of this work support the hypothesis that locally expressed Angptl4 might play a role in local uterine/placental lipid metabolism and vascular changes during implantation and thus provide a basis for future research.

Regulation of MMP-9 expression and activity in the mouse uterus by estrogen

Matrix metalloproteinases (MMPs) are spatiotemporally expressed in the uterus across normal estrous and menstrual cycles and are known to participate in the extensive endometrial tissue remodeling. MMP-9/gelatinase B is one of the major MMPs found in the uterus that modulates uterine biology during various reproductive processes. Although it seems that uterine MMP-9 is under ovarian steroid hormonal control, there are conflicting reports regarding steroidal hormonal regulation of MMP-9 expression, and there is little information on the effects of estrogen in vivo in this respect. We therefore examined the steroidal regulation of MMP-9 within the mouse uterus. Female mice (2-3 months old) were ovariectomized and treated with estradiol-l7beta (E(2)) or E(2) + progesterone (P(4)) and uterine gelatinase activity and expression were determined. Gelatin zymography revealed that E(2) alone or in combination with P(4) increased MMP-9 activation, whereas Northern analysis showed that E(2) decreased MMP-9 steady state mRNA expression and an estrogen receptor antagonist ICI-182, 780 blocked this effect. In contrast, uterine MMP-2 expression and activity were not affected by steroidal treatments. Pretreatment with a transcription inhibitor actinomycin D or translation inhibitor cycloheximide indicates that E(2) regulates uterine MMP-9 at multiple points, involving transcriptional and posttranscriptional control as well as modulation of inhibitor activities. Collectively, these data suggest that E(2) regulates uterine MMP-9 expression and activity in vivo via a complex mechanism. This estrogen regulation of MMP-9 activity may play an important role in uterine tissue remodeling.

Could the Defects in the Endometrial Extracellular Matrix During the Implantation Be a Cause for Impaired fertility?

PROBLEM

Assessment of concentration of the metalloproteinase 9 (MMP9), tissue inhibitor of metalloproteinases 1 (TIMP1), urokinase plasminogen activator (uPA) and its receptor (uPAR) and leukaemia inhibitory factor (LIF) in the uterine fluid in women with idiopathic infertility and unknown cause for recurrent miscarriage.

METHOD OF STUDY

Uterine fluid obtained from patients with idiopathic infertility (n = 13), patients with unknown cause of recurrent miscarriages (n = 16) and healthy fertile women (n = 14). The assessment of MMP9, TIMP1, uPA, uPAR and LIF were performed with enzyme-linked immunosorbent assay.

RESULTS

Statistically lower expression of MMP9 and TIMP1 in uterine fluid during implantation window in women with infertility and recurrent miscarriage of unknown cause.

CONCLUSION

Changed turnover of the extracellular matrix might be a cause of improper endometrial transition and in effect cause faulty implantation.

Implantation Serine Proteinases heterodimerize and are critical in hatching and implantation

Background

We have recently reported the expression of murine Implantation Serine Proteinase genes in pre-implantation embryos (ISP1) and uterus (ISP1 and ISP2). These proteinases belong to the S1 proteinase family and are similar to mast cell tryptases, which function as multimers.

Results

Here, we report the purification and initial characterization of ISP1 and 2 with respect to their physico-chemical properties and physiological function. In addition to being co-expressed in uterus, we show that ISP1 and ISP2 are also co-expressed in the pre-implantation embryo. Together, they form a heterodimer with an approximate molecular weight of 63 kD. This complex is the active form of the enzyme, which we have further characterized as being trypsin-like, based on substrate and inhibitor specificities. In addition to having a role in embryo hatching and outgrowth, we demonstrate that ISP enzyme is localized to the site of embryo invasion during implantation and that its activity is important for successful implantation in vivo.

Conclusion

On the basis of similarities in structural, chemical, and functional properties, we suggest that this ISP enzyme complex represents the classical hatching enzyme, strypsin. Our results demonstrate a critical role for ISP in embryo hatching and implantation.

Origin and characteristics of glycogen cells in the developing murine placenta

The junctional zone (Jz) of the mouse placenta consists of two main trophoblast populations, spongiotrophoblasts and glycogen cells (GCs), but the development and function of both cell types are unknown. We conducted a quantitative analysis of GC size, number, and invasion of cells into the decidua across gestation. Furthermore, we identified markers of GC function to investigate their possible roles in the placenta. While the spongiotrophoblast cell volume doubles, and cell number increases steadily from E12.5 to E16.5, there is a remarkable 80-fold increase in GC numbers. This finding is followed by a notable decrease by E18.5. Surprisingly, the accumulation of GCs in the decidua did not fully account for the decrease in GC number in the Jz, suggesting loss of GCs from the placenta. Glucagons were detected on GCs, suggesting a steady glucose release throughout gestation. Connexin31 staining was shown to be specific for GCs. GC migration and invasion may be facilitated by temporally regulated expression of matrix metalloproteinase 9 and the imprinted gene product, Decorin. Expression of the clearance receptor for type II insulin-like growth factor (IGF-II), IGF2R, in a short developmental window before E16.5 may be associated with regulating the growth effects of IGF-II from glycogen cells and/or labyrinthine trophoblast on the expansion of the Jz. Thus stereology and immunohistochemistry have provided useful insights into Jz development and function of the glycogen cells.

Complex regulation of decidualization: a role for cytokines and proteases--a review

Decidualization of the endometrial stroma is a precondition for successful establishment of pregnancy. While the local molecular mechanisms driving decidualization are still largely unknown, a number of autocrine/paracrine factors have been identified as differentiation factors in this process. These include the cytokines, interleukin 11, activin A and monoclonal non-specific suppressor factor beta (MNSFbeta). Furthermore, locally produced proteases, including proprotein convertase 6 and matrix metalloproteinases, enable expansion of the tissue and processing of regulatory molecules. This article reviews recent work from our laboratory on the roles of these factors in decidualization.

Uterine-ovarian biochemical and developmental interactions to the postimplantation treatment with a butadiene metabolite, diepoxybutane, in pregnant rats

An industrial chemical used in synthetic rubber production, 1,3-butadiene, is toxic to reproduction in rats and mice. Bioactivation of butadiene to reactive intermediates, i.e. diepoxybutane and other metabolites, is responsible for this toxicity. The present study examines the biochemical and developmental mechanisms of diepoxybutane at the feto-maternal placental axis during gestation. Female Sprague-Dawley rats were administered four daily intraperitoneal doses of diepoxybutane in groups (0.25, 0.30, 0.35, or 0.40 mmol in sesame oil per kg body weight, n = 6/group) during postimplantation (gestation days 5-8) and euthanized on gestation day 9 or 12 for retrieval of uterine and ovarian tissues, and serum for assays. The results demonstrate that this timely diepoxybutane treatment significantly decreased placental levels of pituitary adenylate cyclase-activating polypeptide mRNA expression that was measured by reverse transcription-polymerase chain reaction and of matrix metalloproteinase-9 activity that was determined by gelatin zymography, and serum progesterone levels on gestation days 9 and 12. From a developmental standpoint, fetal growth and viability were reduced in correlation with treatment-related effects of diepoxybutane on implantation losses and fetal resorptions on gestation day 9. Additionally, fetal mortality was maximally increased due to significantly pronounced, dose-independent effects on these parameters on gestation day 12. This trend towards more severe embryolethal treatment effects from gestation day 9 to 12 suggests that fetal metabolism in the gravid uteri of rats may be more sensitive to diepoxybutane exposure as pregnancy progresses. The inhibitory actions of diepoxybutane on placental pituitary adenylate cyclase-activating polypeptide expression and matrix metalloproteinase activity may contribute towards altering placental molecular support for fetal development and viability. Moreover, the reproductive toxicity of diepoxybutane in rats appears to be linked to progesterone action.

Embryos sired by males without accessory sex glands induce failure of uterine support: a study of VEGF, MMP and TGF expression in the golden hamster

To account for reproductive failure induced by surgical deletion of paternal accessory sex glands in the golden hamster in vivo, we studied expression of vegf, FLT-1 (VEGF-R1), FLK-1 (VEGF-R2), MMP and TGF-beta in endometrium of the dam and sired embryos during 5-7 days post coitum by immunohistochemistry, in situ hybridisation, semiquantitative RT-PCR and enzyme-linked immunosorbent assay. Spatiotemporal pattern of vegf expression in the control animals was similar to that reported for intact animals by our group. Removal of paternal ampullary glands did not disturb the normal expression pattern. Removal of ventral prostate glands alone or all accessory sex glands was associated with reduction of vegf transcripts and protein levels in both the embryo and endometrium. FLT-1, FLK-1 and MMP-2 were also reduced. MMP-1 was not changed whereas TGF-beta1 expression was enhanced. There was no expression in endometrium in between implantation sites. Thus the implanted embryos had a trophic effect on growth factor production by the endometrium, and the levels of expression were determined by viability and structural integrity of the conceptus. Based on these findings we concluded that incompetent embryos sired by males without the ventral prostate gland or all accessory sex glands reduced the potential of the uterus to support pregnancy. A negative cycle of events was thus set up and eventually led to premature termination of pregnancies.

Nitric oxide induces gelatinase A (matrix metalloproteinase 2) during rat embryo implantation

OBJECTIVE

To evaluate a reciprocal signaling interaction initiated by embryo-derived nitric oxide (NO) to facilitate implantation by increased production of gelatinase A (matrix metalloproteinase 2, MMP2) in uterine stroma.

DESIGN

Experimental animal studies.

SETTING

Reproductive-physiology research laboratory.

ANIMAL(S)

Female syngeneic Wistar rats aged 14 weeks.

INTERVENTION(S)

Vaginal smears to confirm pregnancy. Oviductal ligature to avoid the descent of blastocysts to the uterine lumen. Plasma exudation assays to locate uterine blastocyst implantation sites. Organ cultures treated with NO donors and nitric oxide synthase (NOS) inhibitors.

MAIN OUTCOME MEASURE(S)

Expression of MMP2 and NO was assessed by Western blot and zymography of tissue extracts and by immunofluorescence of tissue sections.

RESULT(S)

An increase in MMP2 activity was found in uterine extracts in early pregnant rats and was concentrated at implantation sites. Immunolocalization experiments showed that inducible NOS was expressed on the surface of the implanting blastocyst adjacent to the uterine epithelium at the sites of increased MMP2 expression. In organ culture experiments, NO donors were found to increase, whereas NOS inhibitors were found to decrease MMP2 activity in uterine tissue sections.

CONCLUSION(S)

Blastocyst-derived NO contributes to the production of uterine-derived MMP2, an essential component of implantation and initiation of placentation.

Tissue inhibitor of matrix metalloproteinase-3 expression in the mouse uterus during implantation and artificially induced decidualization

During implantation in mice, tissue inhibitor of matrix metalloproteinases-3 is believed to play a key role in inhibiting matrix metalloproteinase activity associated with embryo invasion and tissue remodeling. The first objective of this study was to quantitatively compare the steady-state mRNA levels of tissue inhibitors of matrix metalloproteinases between segments of the mouse uterus undergoing decidualization compared to those that are not during early pregnancy plus oil-induced decidualization. Steady-state tissue inhibitor of metalloproteinase-3 mRNA levels were significantly greater in implantation compared to interimplantation areas on days 6 and 7 of pregnancy and in stimulated compared to nonstimulated uterine horns at 48 and 72 hr after artificial induction of decidualization. Steady-state tissue inhibitor of metalloproteinase-1 mRNA levels were significantly greater in implantation compared to interimplantation areas on days 5-8 of pregnancy and in stimulated compared to nonstimulated uterine horns at 24, 48, and 72 hr after oil stimulation. Therefore, the steady-state mRNA levels of tissue inhibitors of metalloproteinase-1 and -3 increased in the uterus during decidualization. The second objective of this study was to determine if transforming growth factor-beta1 influences tissue inhibitors of metalloproteinase mRNA concentrations in mouse endometrial stromal cells. As determined by Northern blot analyses, transforming growth factor beta1 significantly increased tissue inhibitors of matrix metalloproteinases-1 and -3 mRNA levels in cultured mouse endometrial stromal cells isolated from uteri sensitized for decidualization. On the other hand, interleukin-1, epidermal growth factor, and leukemia inhibitory factor had no effect. The results of this study further characterize the tissue inhibitor of metalloproteinase expression in the uterus during implantation and artificially induced decidualization and the potential control of their expression in the stroma by transforming growth factor.

A mechanistic assessment of 1,3-butadiene diepoxide-induced inhibition of uterine deciduoma proliferation in pseudopregnant rats

Butadiene diepoxide (BDE), a reactive metabolite of 1,3-butadiene that is an important industrial chemical used in synthetic rubber production causes a dose-dependent inhibition of deciduoma development in pseudopregnant Sprague-Dawley rats. This study used 4 daily i.p. BDE doses of 0.20, 0.25, 0.30, 0.35, or 0.40 to characterize mechanisms that may be responsible for the antideciduoma effect. Pseudopregnant rats were treated either before (pseudopregnancy [PPG] days 1-4) or after (PPG days 5-9) deciduoma induction by endometrial trauma with a blunt needle. Animals were killed on PPG day 9 and evaluated for serum progesterone and endometrial protein and DNA. RT-PCR was used to measure message for estrogen receptor (ER) alpha and pituitary adenylate cyclase-activating polypeptide (PACAP). Substrate zymography and Western blotting were used respectively to measure matrix metalloproteinase (MMP)-9 and inducible nitric oxide synthase. The antideciduoma effects of BDE were associated with decreases in endometrial weight, protein, and DNA, with decreases in serum progesterone, and with decreases in PACAP message and MMP-9. A reduction in NOS was identified at the highest dose of BDE. Message for estrogen receptor (ER) alpha was not affected at any dose. We conclude that the reduction in decidual proliferation was direct and appeared to be associated with either 1) a decrease in the effectiveness of the deciduogenic stimulation and/or a weakened endometrial sensitivity to the stimulus; or 2) an effect on deciduoma development. Molecular mechanisms that apparently contributed to BDE inhibition of decidual metabolism included the synthesis of protein and DNA involved in decidual growth, the synthesis and activation of a matrix metalloproteinase for degradation of the extracellular matrix that is essential for tissue remodeling during deciduoma development, and the nitric oxide/nitric oxide synthase and pituitary adenylate cyclase-activating peptide systems that are involved in promoting vasodilation and increased vascular permeability to enhance the availability of substrates for maximal deciduoma growth. The ovotoxicity of BDE, which has previously been established, may indirectly affect decidual proliferation by reducing progesterone, the preeminent endocrine regulator of deciduoma development. The findings also suggest that BDE may possess no estrogenic action since it was associated with endometrial weight loss and unaltered levels of the estrogen receptor alpha mRNA expression.