IFPA meeting 2015 workshop report I: placental mitochondrial function, transport systems and epigenetics

Workshops are an important part of the IFPA annual meeting as they allow for discussion of specialized topics. At IFPA meeting 2015 there were twelve themed workshops, three of which are summarized in this report. These workshops covered areas of placental regulation and nutrient handling: 1) placental epigenetics; 2) placental mitochondrial function; 3) placental transport systems.

Chronic hypoxia in vivo reduces placental oxidative stress

Decreased placental oxygenation and increased oxidative stress are implicated in the development of preeclampsia. Oxidative stress arises from imbalance between pro-versus anti-oxidants and can lead to biological oxidation and apoptosis. Because pregnant women living at high altitude (3100 m, HA) have lowered arterial PO2 and an increased incidence of preeclampsia, we hypothesized that HA placentas would have decreased anti-oxidant enzyme activity, increased oxidative stress (lipid peroxidation, protein oxidation and nitration) and greater trophoblast apoptosis than low-altitude (LA) placentas. We measured enzymatic activities, lipid and protein oxidation and co-factor concentrations by spectrophotometric techniques and ELISA in 12 LA and 18 HA placentas. Immunohistochemistry (IHC) was used to evaluate nitrated proteins and specific markers of apoptosis (activated caspase 3 and M30). Superoxide dismutase activity was marginally lower (p=0.05), while glutathione peroxidase activity (p<0.05), thioredoxin concentrations (p<0.005) and thioredoxin reductase activity p<0.01 were all reduced in HA placentas. Decreased anti-oxidant activity was not associated with increased oxidative stress: lipid peroxide content and protein carbonyl formation were lower at HA (p<0.01). We found greater nitrotyrosine residues in the syncytiotrophoblast at 3100 m (p<0.05), but apoptosis did not differ between altitudes. Our data suggest that hypoxia does not increase placental oxidative stress in vivo. Nitrative stress may be a consequence of hypoxia but does not appear to contribute to increased apoptosis. Lowered placental concentrations of anti-oxidants may contribute to the susceptibility of women living at HA to the development of preeclampsia, but are unlikely to be etiological.

Increased biological oxidation and reduced anti-oxidant enzyme activity in pre-eclamptic placentae

Oxidative stress occurs when cellular levels of reactive oxygen species exceed anti-oxidant capabilities and has been implicated in the pathogenesis of pre-eclampsia. In this study we have examined the tissue levels of endogenous anti-oxidant proteins (superoxide dismutase, glutathione peroxidase, thioredoxin reductase and thioredoxin) and the level of lipid and protein oxidation in placental samples from normal and pre-eclamptic pregnancies. Pre-eclamptic tissue homogenates demonstrated significantly increased levels of lipid peroxidation (20.68 +/- 7.811 microM protein versus 5.33 +/- 4.03 microM/mg protein, P < 0.001) and a trended increase in protein carbonyl concentration (248.1 +/- 97.71 units/mg protein versus 209.7 +/- 82.6 U/mg protein) when compared to controls. The levels and activities of the anti-oxidant proteins superoxide dismutase (2.48 +/- 0.6 U/mg protein versus 2.02 +/- 0.51 U/mg protein, P <0.02), thioredoxin reductase (19.25 +/- 9.81 U/mg protein versus 13.02 +/- 5.66 U/mg protein,P = 0.02), thioredoxin (107.00 +/- 18.11 ng/mg protein versus 91.12 +/- 21.18 ng/mg protein, P = 0.02) and glutathione peroxidase (17.33 +/- 6.63 mmol/min/mg protein versus 11.50 +/- 3.11 mmol/min/mg, P < 0.02) were all found to be significantly reduced when comparing pre-eclamptic placental tissue homogenates to gestational age-matched control placentae from non-pre-eclamptic pregnancies. The results of this study demonstrate a decreased enzymatic anti-oxidant capacity and increased oxidation in placental tissue from pre-eclamptic women, which may contribute to the pathogenesis of this complex disorder.

Increased anti-oxidant enzyme activity and biological oxidation in placentae of pregnancies complicated by maternal asthma

Our previous work has demonstrated that alterations in placental function are associated with changes in fetal development in pregnancies complicated by asthma. The pathophysiology of asthma in adults and children and intrauterine growth restriction during pregnancy are associated with oxidative stress. Based on this information, we examined whether placental anti-oxidant pathways and markers of biological oxidation were altered in pregnancies complicated by asthma. Anti-oxidant enzyme activities of superoxide dismutase, glutathione peroxidase and thioredoxin reductase, thioredoxin concentrations, lipid and protein oxidation levels were measured in placentae of pregnancies complicated by asthma and compared to uncomplicated, non-asthmatic pregnancies. Placental tissue homogenates of pregnancies complicated by asthma demonstrated significantly increased levels of lipid peroxidation (25.7+/-1.8 micromol/mg protein versus 12.1+/-1.6 micromol/mg protein, P=0.008) and protein carbonyl concentrations (414.6+/-51.4 units/mg protein versus 222.3+/-32.6 units/mg protein, P=0.0032) when compared to non-asthmatic controls. The activities of the anti-oxidant proteins superoxide dismutase (2.17+/-0.09 units/mg protein versus 1.67+/-0.09 units/mg protein, P=0.014) and thioredoxin reductase (54.0+/-6.9 units/mg protein versus 28.7+/-6.0 units/mg protein, P=0.009) were significantly increased in the presence of maternal asthma. Placental thioredoxin levels (102.9+/-5.3 ng/mg protein versus 92.9+/-8.6 ng/mg protein, P=0.37) and glutathione peroxidase activity (27.3+/-2.2 mmol/min/mg protein versus 28.3+/-2.2 mmol/min/mg, P=0.83) were not significantly different in pregnancies complicated by asthma and non-asthmatic pregnancies. There was no effect of fetal sex, asthma severity or treatment for asthma on these pathways. Maternal asthma during pregnancy is associated with increased placental enzymatic anti-oxidant capacity and also increased protein oxidation suggesting there is a compensatory increase in anti-oxidant activity in response to increased oxidative stress.

Selenium deficiency as a model of experimental pre-eclampsia in rats

Epidemiological studies andin vitroanalysis demonstrate correlations between selenium status and human pre-eclampsia (PET). Selenium is an essential component in the anti-oxidant proteins glutathione peroxidase and thioredoxin reductase, which are produced in lower amounts in pre-eclamptic placenta. This study examined the effect of modulating dietary selenium content in pregnant rats. Rats were fed diets containing no selenium, 239 μg/kg selenium or 1000 μg/kg selenium, four weeks prior to and following conception. Significant pregnancy-specific increases in systolic blood pressure (116.4 ± 5.2 mmHg vs 108 ± 6.8 mmHg vs 111.4 ± 4.7 mmHg) and proteinuria (9.68 ± 2.12 μg/ml vs 5.93 ± 1.59 μg/ml vs 4.43 ± 0.96 μg/ml) were demonstrated in animals fed a selenium free-diet when compared with normal or high selenium diets. Placental weight and pup number were not affected by selenium deprivation, however a significant decrease in the pup weight was evident. Selenium deprivation caused dose-dependent decreases in liver glutathione peroxidase (28.55 ± 3.82 mmoles/min/mg vs 34.68 ± 8.64 mmoles/min/mg) and thioredoxin reductase (2.37 ± 1.25 U/mg vs 6.68 ± 1.82 U/mg) activity, whereas superoxide dismutase activity remained constant. Placental activity of these enzymes also decreased leading to oxidative stress as measured by increased lipid peroxides (17.92 ± 1.78 μmoles/mg vs 8.30 ± 5.52 μmoles/mg) and protein carbonyls in tissue extracts from selenium-free animals. These results suggest that selenium deficiency in pregnant rats leads to symptoms similar to those seen in human PET and may provide an experimental model for studying this complex disease.

The serum concentration of estradiol after embryo transfer and the decline from preovulatory levels may influence the success of IVF treatment

AIM

To establish the influence that serum estradiol concentrations prior to oocyte retrieval and 3 days after embryo transfer have on the establishment of in vitro fertilization (IVF) pregnancy.

METHOD

Preovulatory (day-0) and luteal-phase (day-6) estradiol concentrations were retrospectively analyzed in 310 infertile patients, undertaking 1st-cycle conventional IVF or intracytoplasmic sperm injection.

RESULTS

The IVF treatment success is significantly reduced in patients with an estradiol level <600 pg/ml and also when a rapid decline in luteal-phase estradiol concentrations from preovulatory concentrations (day 0:day 6 ratio) was exhibited.

CONCLUSION

A day 0:day 6 estradiol ratio >5 and a serum estradiol concentration <600 pg/ml may adversely impact on the establishment of pregnancy in IVF.

Expression and localization of thioredoxin during early implantation in the marmoset monkey

Thioredoxin is a powerful redox protein expressed in invasive cytotrophoblasts and essential for blastocyst implantation in mice. Isolated marmoset thioredoxin cDNA showed that the deduced amino acid sequence differed from the human sequence by four amino acids. The close homology of thioredoxin in the two species enabled us to use monoclonal antibodies against human thioredoxin to detect marmoset thioredoxin in implantation sites, blastocysts and culture medium. Immunocytochemistry on marmoset implantation sites, on pregnancy days 12 and 15, showed that thioredoxin is highly expressed in uterine luminal epithelium, glands and in some endometrial stromal cells. In attached blastocysts, thioredoxin staining was detected in mural and polar trophoblast cells and both visceral and parietal endoderm, whereas no staining was present in the inner cell mass. A similar pattern of thioredoxin expression was detected in hatched blastocysts attached to Matrigel in tissue culture. Trophoblastic vesicles derived from blastocysts expressed thioredoxin in inner endoderm-like cells and outer trophoblast-like cells and secreted thioredoxin into the culture medium. These experiments have demonstrated thioredoxin expression during early stages of embryo-maternal interaction. We propose that thioredoxin protects the early placenta from oxidative damage and that the marmoset is a valuable model for studying thioredoxin regulation and function during implantation and blastocyst differentiation.

Processing of procorticotropin-releasing hormone (pro-CRH): molecular forms of CRH in normal and preeclamptic pregnancy

This study examined the different molecular forms of CRH in normal and preeclampsia maternal plasma and protease-blocked placental extracts using antibodies to different regions of the CRH precursor, pro-CRH. In the absence of protease inhibitors, chromatographed normal placental extracts contained four peaks of immunoreactivity corresponding to unprocessed approximately 19-kDa pro-CRH, its approximately 8-kDa intermediate metabolite, pro-CRH125-194, its approximately 2.8-kDa midportion fragment, pro-CRH125-151, and 4.75-kDa CRH1-41. However, if protease inhibitors were included in the extraction medium, only pro-CRH and pro-CRH125-194 were found. Pro-CRH processing was more extensive in protease-blocked preeclampsia placentas than in those from normal pregnancy, with three peaks corresponding to pro-CRH, proCRH125-194, and mature CRH1-41 peptide found. Using quantitative competitive PCR, the messenger ribonucleic acid levels of CRH precursor in preeclampsia placentas were 1.7-fold higher than those in normal placentas (37.83 +/- 3.48 vs. 21.83 +/- 2.59 attomoles/microg total ribonucleic acid, respectively; P < 0.005). Preeclampsia placentas contained significantly more CRH1-41 cross-reactivity (4.72 +/- 1.22 pmol/g) than normal term placentas (1.52 +/- 0.39 pmol/g; P < 0.048) extracted in medium containing protease inhibitors. The content of pro-CRH(125+/-151)-reactive species in these extracts followed the same pattern, with more immunoreactivity detected in preeclampsia placentas (4.23 +/- 1.39 pmol/g) than in those from normal term pregnancies (1.44 +/- 0.32 pmol/g; P < 0.01). Sequential plasma samples from 10 women with normal pregnancy and 5 women with preeclampsia were assayed for pro-CRH(125-151)- and CRH(1-41)-immunoreactive species In normal pregnancy, maternal plasma CRH(1-41) immunoreactivity rose with increasing gestational age, reaching 460 +/- 48 pmol/L at term. In women with preeclampsia, CRH(1-41) levels at each gestational age point were higher than those at the equivalent stage of normal pregnancy. In contrast, the levels of pro-CRH(125-151)-immunoreactive species remained barely detectable throughout normal and preeclamptic pregnancy. Both pro-CRH and CRH(1-41), but not pro-CRH(125-151), were shown to bind to the plasma CRH-binding protein. Our findings highlight the importance of protection of placental tissue from degrading enzymes during extraction and show that most of the CRH in the human placenta exists as unprocessed pro-CRH, with very little in the form of CRH(1-41) except in preeclampsia. Our studies using maternal plasma indicate that CRH(1-41) is the only one of the pro-CRH fragments studied to be maintained in significant amounts in the maternal circulation and also the only fragment studied for which a specific plasma binding protein exists.

Procorticotrophin-releasing hormone: endoproteolytic processing and differential release of its derived peptides within AtT20 cells

Procorticotrophin-releasing hormone (proCRH) is expressed mainly in the hypothalamus and in the placenta, where it undergoes tissue-specific endoproteolysis. Our results show that within stably transfected AtT20/D16V cells proCRH is cleaved to generate two fragments of approximately 8 and 3 kDa which could account for proCRH(125-194) and proCRH(125-151), respectively, and a 4.5 kDa product which could account for mature IR-CRH(1-41). The immunofluorescence staining patterns for IR-CRH and IR-ACTH and their response of secretagogues indicate targeting of proCRH and POMC to the secretory pathway in transfected AtT20 cells. In this work, we have used a unique set of specific RIAs and IRMAs to the full length POMC and proCRH molecules and several products of endoproteolytic processing to assess if they could be released differentially in response to stimulation. Although the release of both IR-ACTH and IR-CRH peptides from transfected AtT20 cells is stimulated in response to exposure to high potassium stimulation (51 mM KCl/SmM CaCl2), the sorting index (SI) suggests that mature ACTH is sorted to the regulated secretory pathway 2.1-fold more efficiently than mature CRH(1-41). Mature ACTH is also sorted to the regulated secretory pathway 9-fold more efficiently than IR-proCRH(125-151). Also, mature CRH(1-41) is sorted to the regulated secretory pathway 3-fold more efficiently than IR-proCRH(125-151). These results therefore indicate that the intracellular mechanisms for the storage and release of POMC, proCRH and their endoproteolytic products differ and would sustain the hypothesis that within mammalian peptidergic cells, different biologically active peptides originating from the same or different precursor molecules, could be differentially released in response to specific stimuli. This would give these cells the capacity to finely regulate neurotransmitter release in response to environmental and physiological demands.

Corticotrophin-releasing hormone receptor type 1: generation and characterization of polyclonal antipeptide antibodies and their localization in pituitary cells and cortical neurones in vitro

Corticotrophin-releasing hormone (CRH) is a 41 amino acid neuropeptide which plays a major role in regulating the endocrine response to stress. CRH acts by first binding to specific receptors on the plasma membrane of target cells. A CRH receptor from a human corticotroph adenoma and rat brain has recently been cloned (CRH-R1). In this paper, we have chosen three different peptide sequences within the CRH-R1 molecule which bear no similarity to other members of this receptor subfamily (or indeed any known protein) and which are likely to be exposed on the surface of the native protein, for antibody production. Some of these fragments produced antipeptide antibodies of good titre which cross-reacted with the CRH-R1 receptor expressed in transiently transfected COS-7 cells and in tissue extracts from rat cerebellum, cortex, pituitary gland and human myometrium, both in Western blots and in liquid-phase radioimmunoassay. We used immunofluorescence techniques to localize the CRH receptor in transiently transfected COS-7 cells, primary cultures of rat anterior pituitary (AP) cells, the corticotroph-tumour cells AtT20 D16-16 and cortical neurons in primary culture. Our results indicate IR-CRH-R1 receptors have a punctate distribution on the plasma membrane of AP cells and AtT20 D16-16 cells. Whilst in AP cells their appearance is a fine punctate pattern, in AtT20 cells, they appear as large patches which could account for receptor clusters. Within primary cortical neurons, their distribution does not appear to be polarized. Our results suggest that distribution of CRH-R1 receptors within the different cell-types investigated depends not only on the amino acid sequence but also on cellular factors.

Immunocytochemical localization of thioredoxin in human trophoblast and decidua

An immunocytochemical investigation into the expression of thioredoxin in human reproductive tissues was performed using monoclonal antibodies produced against recombinant human thioredoxin. First trimester and term human placental villi, decidua and term fetal membranes were examined for thioredoxin content and cellular localization. In first trimester tissue strong thioredoxin staining was observed in the underlying cytotrophoblast cells and in the stromal cells present in the decidua, but not in the syncytiotrophoblast surrounding the chorionic villi. In term placental villi very little thioredoxin was observed. Term fetal membranes proved to be a rich source of thioredoxin, the most intense staining was seen in the cytotrophoblast cells in the chorionic membrane, with the amnion and decidua also showing positive immunoreactivity. The potential role/s that thioredoxin may play within the placental bed is considered.

Corticotrophin-releasing hormone-binding protein in human fetal plasma

During pregnancy maternal plasma corticotrophin-releasing hormone (CRH) levels rise 1000-fold whilst fetal plasma levels are often 100-fold higher than the concentrations seen in normal non-pregnant human plasma. Despite these high CRH levels neither the maternal nor fetal pituitary releases excessive amounts of ACTH. A specific CRH-binding protein (CRHBP) exists in the maternal circulation which is able to bind and inactivate the ACTH releasing activity of CRH. In this study we have used a specific CRHBP radioimmunoassay to determine the level of CRHBP in fetal and maternal plasma samples. Fetal samples were collected by cordocentesis between 20 and 33 weeks gestation and matched maternal samples were taken by venepuncture at the same time. In a second study, plasma samples were collected from 8 women at fortnightly intervals from week 20 to term, at labour and post-partum. A fetal sample, taken from the umbilical vein, was collected immediately post-delivery. The mean maternal CRHBP concentration for the samples collected between 20 and 33 weeks (n = 23) was 8.12 nmol/l and the fetal level was 8.62 nmol/l. Data from the second study showed that at term the maternal CRHBP concentration decreased significantly (P < 0.025) to 6.32 nmol/l. The fetal CRHBP level also decreased significantly (P < 0.001) at term to a level of 5.84 nmol/l. The CRHBP in both fetal and maternal plasma was shown to be functional by 125I-CRH binding and gel permeation chromatography. The capacity of maternal and fetal plasma to bind 125I-CRH decreased at term in agreement with the quantitation of plasma CRHBP by radioimmunoassay.

Corticotrophin-releasing hormone (CRH)-binding protein interference with CRH antibody binding: implications for direct CRH immunoassay

Direct immunoassay of plasma corticotrophin-releasing hormone (CRH) is potentially subject to interference from high levels of CRH-binding protein (CRH-BP) that exist in the human circulation. In this study, we tested the effect of CRH-free, native CRH-BP (6.4 nmol/l) purified from human plasma, CRH-BP diluent alone, normal human plasma (containing 5.8 nmol endogenous CRH-BP/l) and normal sheep plasma (containing no CRH-BP) on the binding of 125I-labelled CRH tracer to five N-terminal and four C-terminal CRH antibodies. All anti-(1-20)CRH N-terminal antibody dilution curves displayed marked inhibition of binding in the presence of purified CRH-BP and human plasma in comparison with the curves with the control diluent or sheep plasma. Almost no inhibition of binding was obtained with any of the C-terminal antibodies (all directed against epitopes within the last six amino acids of CRH) and the four dilution curves were nearly superimposable. Liquid-phase CRH IRMAs were then developed with different combinations of two of each of the N- and C-terminal antibodies, using radiolabelled IgG prepared from purified C-terminal antisera as tracer and raw N-terminal antisera as the link antibodies to the separating system. The addition of dilutions of purified CRH-BP over the range 1.25-20 nmol/l to the IRMA standard curve in assay buffer resulted in a dose-dependent reduction in the signal; with 5 nmol CRH-BP/l, a level commonly found in human plasma, the reduction in binding was 67% and 81% in two different IRMAs at a CRH concentration of 631 pmol/l.(ABSTRACT TRUNCATED AT 250 WORDS)

Identification and isolation of corticotrophin-releasing hormone-positive cells from the human placenta

During human pregnancy, plasma corticotrophin-releasing hormone (CRH) levels rise from undetectable amounts prior to 20 weeks gestation to reach a peak near term, with an exponential rise during the final 5 weeks of gestation. Within hours of parturition plasma levels fall and rapidly return to undetectable baseline measurements. The appearance of CRH in maternal plasma has been attributed to the placental production and subsequent release into the maternal circulation of this hormone. Previous studies have shown that human placental extracts contain a CRH-like peptide and this has been reinforced by the observation of CRH mRNA in placental tissue. Initial attempts to identify the site of production using immunocytochemistry have led to conflicting results. This study attempts to clarify this situation by using a variety of highly specific anti-CRH antibodies to show the cellular expression of placental CRH. Intense CRH staining was observed in the syncytial trophoblast layer in first trimester and term chorionic villi, whilst the underlying cytotrophoblast appeared to be negative. The fetal membranes also contained CRH immunoreactivity with the cytotrophoblast cells in the chorionic membrane displaying the most intense staining. CRH immunoactivity was also observed in the amnion and in some cells in the decidua. As a model of cellular CRH expression, cytotrophoblast cells from term chorionic membrane were isolated and shown to be positive for CRH.

Corticotrophin-releasing hormone and corticotrophin-releasing hormone binding protein in normal and pre-eclamptic human pregnancies

OBJECTIVE

To measure the plasma levels of corticotrophin-releasing hormone and corticotrophin-releasing hormone binding protein in normal pregnancy and in pregnancies complicated by pre-eclampsia.

SETTING

John Radcliffe Hospital, Oxford and St Thomas's Hospital, London.

SUBJECTS

One hundred and twenty pregnant women sampled prospectively throughout gestation, of whom 91 experienced a normal pregnancy and eight developed pre-eclampsia; in a second study, 10 women with severe pre-eclampsia, presenting at a range of gestational ages, were sampled once and compared with appropriately matched normal pregnant women.

MAIN OUTCOME MEASURE

Plasma levels of corticotrophin-releasing hormone determined by immunoradiometric assay. Plasma levels of corticotrophin-releasing hormone binding protein measured by direct radioimmunoassay.

RESULTS

In the prospective study, plasma samples from women with pre-eclampsia exhibited higher (390.2 versus 292.7 pmol/l at 36 weeks) levels of corticotrophin-releasing hormone and significantly lower (5.24 versus 8.14 nmol/l at 36 weeks, P < 0.002) levels of corticotrophin-releasing hormone binding protein than normal controls. In the second, single time point study a significant elevation in CRH (P < 0.002) and reduction in CRH-BP (P < 0.001) was found in pre-eclamptic pregnancies compared with controls.

CONCLUSIONS

In human pregnancies complicated by pre-eclampsia there is an elevated level of corticotrophin releasing hormone whilst there is less corticotrophin-releasing hormone binding protein; therefore there is a net increase in free potentially bioactive hormone which may play a role in the pathology of the disease.

Plasma measurements of corticotrophin-releasing hormone-binding protein in normal and abnormal human pregnancy

Using corticotrophin-releasing hormone-binding protein (CRHBP) purified from human plasma and a 25 amino acid peptide corresponding to the C-terminus of CRHBP we have been able to produce rabbit polyclonal antisera specific for CRHBP. This has allowed the development of a radioimmunoassay which is able to detect CRHBP specifically in human plasma regardless of the presence of endogenous CRH. We have used this assay to estimate the level of CRHBP in non-pregnant human plasma to be approximately 20 nmol/l with a range of 9.1-40.6 nmol/l. We have also examined sequential plasma samples taken from 84 normal pregnant women at fortnightly intervals from 16 weeks gestation through to term. Four women were also sampled during labour and the first week postpartum. The median plasma level of CRHBP at week 16 of normal pregnancy was 21.59 nmol/l, levels rose slightly during the early part of the third trimester (26.76 nmol/l at week 30, (P < 0.01) and fell markedly towards term (19.72 nmol/l, P < 0.01) with only 8.70 nmol/l at labour. CRHBP levels returned to normal non-pregnant levels within 48 h of parturition suggesting a role for the fetoplacental unit in CRHBP production. In eight pregnancies complicated by diabetes, CRHBP levels at each gestational age were similar to those recorded for normal pregnancy. However, in pregnancies complicated by pre-term labour (n = 9) and pre-eclampsia (n = 7), plasma CRHBP levels were significantly reduced (P < 0.01).

Alterations in hypothalamic NPY and CRF in anorexic tumor-bearing rats

Regional hypothalamic concentrations of neuropeptide Y (NPY) and corticotropin-releasing factor (CRF), respectively a stimulant and an inhibitor of feeding behavior, were investigated in hypothalamic nuclei in rats carrying the Yoshida sarcoma. Tumor-bearing rats (n = 10), non-tumor-bearing controls (n = 10), and food-restricted rats (n = 10), which did not carry tumors but were pair-fed to match the reduced food intake of the tumor-bearing group, were studied after 10 days. NPY concentrations in the arcuate nucleus (ARC, the main site of NPY synthesis) were significantly increased above controls (P < 0.01) in both tumor-bearing and food-restricted groups. However, NPY concentrations in the paraventricular nucleus (PVN, an NPY-sensitive site of NPY release) showed opposing changes, with a 25% decrease (P = 0.052) in the tumor-bearing but a 48% increase (P < 0.01) in the food-restricted group. CRF concentrations in both the PVN and the ARC were significantly reduced (P < 0.01) in the food-restricted group, but remained close to control values in the tumor-bearing group (P not significant). Changes in hypothalamic appetite-regulating neuropeptides in cancer anorexia, which may result from the action of cytokines produced by a host defense response or the tumor itself, may account for reduced feeding. Such changes may include impaired activity of NPY or failure of CRF activity to be suppressed after underfeeding and weight loss.

Corticotropin releasing hormone-binding protein (CRH-BP): plasma levels decrease during the third trimester of normal human pregnancy

In pregnancy, maternal plasma corticotropin releasing hormone (CRH) concentrations rise substantially in the third trimester and fall rapidly post-partum. A binding protein (BP) specific for CRH exists in the human circulation which inactivates CRH, thus possibly explaining why maternal ACTH does not rise outside normal limits throughout gestation. We here describe the measurement of CRH-BP directly in plasma during human pregnancy using a radioimmunoassay that is not affected by the presence of the high plasma levels of CRH that occur at this time. In 119 healthy non-pregnant individuals, mean CRH-BP levels were 4.46 nmol/L +/- 1.0 (SD), with a wide range of 1.81-7.24 nmol/L. Plasma CRH-BP in 34 pregnant women randomly sampled during the first and second trimesters also averaged 4.46 nmol/L +/- 1.54, with individual values ranging from 1.59-7.51 nmol/L and there was no correlation of CRH-BP levels with gestational age. In a group of 14 women sampled sequentially throughout the third trimester, plasma CRH-BP averaged 4.56 nmol/L +/- 1.70 at 30-35 weeks gestation and fell dramatically to 1.84 nmol/L +/- 0.43 at weeks 38-40 (P < 0.001). The post partum recovery in CRH-BP levels occurred within 48 hours of delivery. These results indicate that there is an increase in the availability of free, potentially bioactive CRH at term to stimulate the release of ACTH from the maternal pituitary and/or to act at a peripheral, non-pituitary CRH receptor(s).

Identification of molecules involved in the 'early pregnancy factor' phenomenon

An isolated preparation from ovine placental extracts which was active in the rosette inhibition assay mimicking the activity of the so-called 'early pregnancy factor' (EPF) has been shown to contain a 12 kDa polypeptide which could be partially resolved from low-molecular-weight active moieties. N-terminal amino acid sequence analysis of the polypeptide indicated that it was ovine thioredoxin, an identification confirmed by isolation and complete sequence analysis of the corresponding cDNA. The cDNA for human thioredoxin was expressed in Escherichia coli and the recombinant protein isolated and purified. Pure recombinant thioredoxin alone did not induce the expression of increased rosette inhibition titres (RITs) when tested in the rosette inhibition assay; but, when tested in combination with cell stimuli such as platelet-activating factor (PAF) or serum, it allowed the expression of increased RITs where none was achieved in its absence. Thioredoxin acted in the assay to reverse a refractory state normally induced by these stimuli, allowing lipoxygenase-dependent moieties also induced by the stimuli to exert their effects, resulting in the expression of increased RITs. Antibodies to recombinant thioredoxin removed from pregnancy sera the capacity to induce increased RITs, i.e. to express EPF activity, thus establishing a role for thioredoxin or thioredoxin-like proteins and associated molecules in the mechanisms which allow pregnancy sera to induce increased RITs. Based on a consideration of these and other results, a new model for the study of the EPF phenomenon is presented and discussed.

Partial characterization of the PAF-induced soluble factors which mimic the activity of 'early pregnancy factor'

Platelet-activating factor (PAF) stimulated mouse spleen cells to release soluble factors (termed S2 factors) which were capable of inducing increased rosette inhibition titres when applied to fresh mouse spleen cells in the rosette inhibition assay. In this ability the S2 factors mimic that of pregnancy serum, an action previously ascribed to 'early pregnancy factor'. The PAF-stimulated production of these S2 factors was not influenced by inhibitors of cyclooxygenase metabolism, but was completely inhibited by the lipoxygenase inhibitors, diethyl carbamazine and nordihydroguaiaretic acid. The S2 factors had a lipid-like character in that they were extractable in organic solvents. The calcium ionophore A23187 also stimulated the production of these factors which may well be products of the lipoxygenase pathway of arachidonic acid metabolism.

Platelet-activating factor and serum components from oestrous mice co-operate to mimic the activity of 'early pregnancy factor' in the rosette inhibition assay

When male mouse spleen cells were incubated with a combination of platelet activating factor (PAF, 1-0-alkyl-2-acetyl-sn-glycero-3-phosphocholine) and sera from female mice in oestrus, the cells displayed a markedly increased rosette inhibition titre (RIT) when subsequently tested in the rosette inhibition assay. Neither PAF nor oestrous mouse sera alone could induce this effect, the combined action was required. Lyso-PAF could not substitute for the PAF, nor could male mouse sera nor the sera from females in dioestrus or metoestrus substitute for the oestrous mouse serum requirement. Pro-oestrous mouse sera could replace oestrous mouse sera but were less effective in their dose-responses. Studies on the mechanism of action of the PAF and oestrous mouse serum components suggested that the PAF stimulated the production and release of soluble factors (termed S2 factors) which by themselves could induce increased RIT values when applied to fresh spleen cells. The PAF-stimulated cell populations were rendered refractory to the action of these S2 factors and did not display increased RIT values, unless oestrous mouse serum was added. This serum acted to reverse the refractory state, allowing the S2 factors to exert their effect, and so cells treated with PAF and oestrous mouse serum displayed increased RIT values.