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At least 919 records · Page 51Linked to original sources
PubMed1996

Evidence for estrogen receptor-mediated regulation of human gonadotropin-releasing hormone promoter activity in human placental cells.

Two fragments of the human gonadotropin-releasing hormone (GnRH) promoter, one containing 0.6 kb of the downstream promoter sequence (H-1) and another 1.8 kb fragment (H-2) containing the upstream promoter region with a deletion of the downstream promoter sequence, were fused to a promoterless luciferase (Luc) reporter construct and transfected into the human placental (JEG) cells. JEG cells transfected with both constructs showed insignificant changes in luciferase activity in response to estradiol. However, cotransfection of H-2-Luc construct with a vector expressing a human estrogen receptor (ER) cDNA results in dose-dependent decreases in luciferase activity in response to estradiol. This ER mediated down-regulation of promoter activity was retained in constructs with the GnRH promoter deleted to position 548 bp 5' to the upstream transcription start site. Further deletion of upstream promoter sequence to 169 bp reversed the estrogen responsiveness from inhibitory to stimulatory. Thus, this study demonstrated that the upstream GnRH promoter region can be regulated by estrogen in transfected JEG cells.

Dose-Response Relationship, Drug↗
PubMed1994

Characterization of ovine growth hormone (oGH) and ovine placental lactogen (oPL) binding to fetal and adult hepatic tissue in sheep: evidence that oGH and oPL interact with a common receptor.

The GH receptor (GHR) plays a key role in postnatal growth regulation. Although plasma concentrations of GH are high during fetal life, its role during fetal development is not well understood. Recent data suggest that GHR are present in fetal hepatic tissue as early as 51 days gestation. However, the levels of GHR expression are markedly lower in fetal hepatic tissue compared to postnatal values, and there are conflicting data suggesting that ovine placental lactogen (oPL) and oGH share a common receptor. Given the uncertainty about whether oPL acts via the oGHR or a distinct receptor, we performed ligand binding and affinity cross-linking studies on hepatic microsomal membranes from adult castrated male, pregnant female, and fetal sheep. Ligand binding assays at a constant concentration of membranes showed that [125I]oPL yielded consistently higher (P < 0.001) specific binding (59.5 +/- 6.4%, 30.5 +/- 5.7%, and 7.6 +/- 2.4% for castrated male, pregnant female, and fetal sheep, respectively) compared to [125I]oGH (17.8 +/- 4.7%, 5.0 +/- 1.6%, and 1.2 +/- 0.4% for castrated male, pregnant female, and fetal sheep, respectively). Cross-reactivity studies showed that unlabeled oPL was consistently more potent than unlabeled oGH in displacing either of the labeled ligands. The dissociation constant (Kd) for oPL binding ranged from 0.16-0.40 nM and was not changed by solubilization with Triton X-100. Equilibrium binding analysis for oGH showed lower affinity for hepatic microsomal membranes (Kd, 1.7-3.2 nM) in each of the three groups of animals. Affinity cross-linking of microsomal membranes from castrated male and pregnant female sheep liver showed four major cross-linked complexes with both [125I]oPL and [125I]oGH, with mol wt of 150, 97, 75, and 60 kilodaltons. All four bands were identified with both ligands. Unlabeled oPL showed markedly higher potency than unlabeled oGH in reducing the signal of the [125I]oPL cross-linked complexes, whereas unlabeled oGH and oPL showed comparable potencies in reducing the signal of the [125I]oGH complexes. Immunoprecipitation of detergent-solubilized hepatic microsomal membranes from pregnant and fetal sheep using a panel of monoclonal antibodies raised against the extracellular region of the rabbit GHR showed potent immunological recognition of the [125I]oPL-receptor complexes. We suggest that oGH and oPL bind to a common or a related receptor protein(s). It is possible that differences in receptor dimerization or association with other membrane proteins are the basis of the differences in affinity and biological actions of the two hormones.

Aging↗
PubMed2000

Limited effects of placental and pituitary growth hormone on cytokine expression in vitro.

The hypothesis that growth hormone (GH) can affect immune responses in man has been evaluated by monitoring cytokine expression in cultures from peripheral blood mononuclear cells, by enzyme-linked immunosorbent assay (ELISA) and ribonuclease protection assay, and in tonsillar cells by ELISA. In addition to pituitary GH (GH-N), the placental form (GH-V), differing from pituitary GH by 13 amino acids has also been tested. Only few effects reached statistical significance and were in no case greater than 15%. Pituitary GH slightly reduced IL-5 production and stimulated IFN-gamma production. The latter effect was also observed with prolactin and could thus be induced through the prolactin receptor. It is proposed that GH has no strong effects on the parameters investigated, possibly as a result of redundancy in the cytokine network. Alternatively, effects on leukocytes are mediated by other tissues such as the liver or are clear only in response to stronger challenges.

Cells, Cultured↗
PubMed1983

Ovine placental lactogen, but not growth hormone, stimulates amino acid transport in fetal rat diaphragm.

Previous studies from this laboratory indicate that ovine placental lactogen (oPL) and ovine growth hormone (oGH) stimulate amino acid transport in diaphragms of postnatal rats with equal potencies. However, in studies reported here using diaphragms from fetal rats on day 20 of gestation, oPL (2,5 and 20 micrograms/ml) stimulated a dose-dependent increase in amino acid uptake, while oGH (5,20 and 100 micrograms/ml) and rat growth hormone (rGH, 2 and 40 micrograms/ml) were without effect. The effect of oPL on fetal AIB transport was neither enhanced nor antagonized by oGH (100 microgram/ml). The magnitude of stimulation of AIB transport by oPL was comparable to that observed with insulin (100 and 1000 microU/ml). Human placental lactogen (hPL) and ovine prolactin (oPRL) had no effect on fetal AIB transport. Since oPL is present in high concentrations in fetal blood, these studies suggest that oPL may have a direct role in the regulation of fetal amino acid and protein metabolism, that oPL and oGH may bind to different receptors in fetal rat tissues, and that oPL may function as a "fetal growth hormone".

Amino Acids↗
PubMed1987

[Discovery of a placental variant of human growth hormone: biochemistry, physiology and implication in the secretion of hypophyseal forms].

Using two monoclonal antibodies (Mabs), each specific of two distinct hGH epitopes, we evidenced a decrease in serum 22K hGH in pregnant women and increasing levels of a GH-related factor, different from hPL. This factor was extracted from the placenta and partially characterized. Because of its binding to GH hepatic receptors with at least the potency of 22K hGH, it was named human placental growth hormone (hPGH). This hormone alone or together with hPL could therefore take over the role of the lacking pituitary GH in the mother during the last half of pregnancy.

Female↗
PubMed2003

Placentation in the alpaca Lama pacos.

Reproduction in South American camelids is poorly studied. To extend our knowledge of the development and cellular physiology of the placenta in the alpaca Lama pacos, we have examined specimens from day 150 of pregnancy to term. Morphological investigations using light, transmission and scanning electron microscopy, the histochemical localization of iron, alkaline and acid phosphatase activity, and the immunodetection of placental lactogen hormone were performed. Throughout pregnancy there was a progressive increase in the depths of folds on the uterine mucosa surface together with a thickening of the endometrium. Glandular cells exhibited PAS and acid phosphatase (AcP) positive secretion granules. In the chorion, giant trophoblast polyploid cells gradually became more numerous and larger. Non-giant cells exhibited positive granules for PAS, alkaline phosphatase (AkP) reaction and immunostaining for bovine placental lactogen hormone (PLH). SDS -PAGE electrophoresis and Western blotting procedures also confirmed the presence of a bovine PLH-like glycoprotein in the fetal alpaca placenta. Over the glandular openings, the chorion formed typical areolae, where the trophoblast exhibited AcP and PAS positive reactions. At these sites, the fetal endothelial cells contained iron-storage granules in their cytoplasm. The trophoblast-epithelial interface exhibited a complex microvillous interdigitation, in which an AkP reaction was very prominent. The chorionic capillaries progressively indented adjacent trophoblast cells. These data suggest that although the epitheliochorial alpaca placenta is diffuse, various trophoblast cell types and specialized areas of the maternofetal interface give the placenta micro-regional functions where histiotrophic nutrition, hormone production and molecular exchange are prevalent.

Acid Phosphatase↗
PubMed1976

Hormonal regulation of fetal brain cell proliferation: presence in serum of a trophin responsive to pituitary growth hormone stimulation.

Previous studies led us to hypothesize that brain growth was regulated by a growth hormone-dependent brain trophin. An in vitro bioassay system to assess this proposal was developed. Serum was shown to stimulate the uptake of tritiated thymidine into fetal brain cell DNA. This action could not be attributed to any nutrient contribution but was due to a non-dialyzable, heat-stable serum growth factor. The levels of the growth factor in serum were reduced after pituitary removal. When added in physiological concentration, growth hormone, prolactin, placental lactogen, insulin, nerve growth factor, thyroid and steroid hormones failed to stimulate the action of serum or to act synergistically with a serum component to stimulate DNA synthesis. Thyroxine, estradiol-17beta, and corticosterone inhibited serum activity. Administration of growth hormone to hypophysectomized rats restored serum levels to normal demonstrating that the serum growth factors was a mediating trophin responsive to pituitary growth hormone stimulation. The relationship of the brain trophin to other serum growth factors and its specificity of action remain to be defined. The present findings were in accordance with in vivo studies of hormonal influence on brain growth and support the proposal that fetal brain cell proliferation is stimulated by a serum trophin responsive to pituitary growth hormone.

Animals↗
PubMed1995

The effect of pre-eclampsia on human placental corticotrophin-releasing hormone content and processing.

Prior studies have shown that levels of corticotrophin-releasing hormone (CRH) in the umbilical cord blood of infants born after pregnancies complicated by pre-eclampsia are significantly higher than fetal plasma CRH concentrations in uncomplicated pregnancies. In the present study we have measured CRH by radioimmunoassay in the placenta and fetal membranes from 13 pregnancies complicated by pre-eclampsia and compared them to 24 uncomplicated pregnancies. In addition we have investigated the effect of chronic intrauterine fetal stress on the processing of CRH in the placenta and fetal membranes. Placental CRH peptide content was significantly higher in the pregnancies complicated by pre-eclampsia, 12,900 +/- 4230 pg/g tissue, than in the uncomplicated pregnancies, 3130 +/- 430 pg/g of tissue (P < 0.01). Gel filtration of the homogenates of normal placenta revealed a major peak of CRH immunoactivity eluting in the same position as synthetic human CRH. A second smaller molecular weight peak of CRH-immunoactivity was also present and in both the amnion and the chorion, the CRH eluted in the position of the smaller molecular weight peak. In contrast, the bulk of the CRH immunoactivity in the placenta and fetal membranes obtained after pregnancies complicated by pre-eclampsia eluted in the position of intact synthetic human CRH. Thus, in pregnancy complicated by pre-eclampsia, both placental CRH release into fetal plasma and CRH peptide content is higher than in uncomplicated pregnancy.

Amnion↗
PubMed1988

Parathyroid hormone receptor in human placental syncytiotrophoblast brush border and basal plasma membranes.

The syncytiotrophoblast of the placenta is the site of exchange of nutrients and minerals between the mother and fetus. We have recently demonstrated that PTH influences, in vitro, phosphate transport through the placenta brush border membranes (BBM) and increases cAMP accumulation in placental tissue. To demonstrate the site of binding of PTH in the cytoplasmic membrane, we have purified two polar membranes: the first located on the apical side, the BBM, and the second, on the fetal side, the basal plasma membrane (BPM). BBM were enriched 24-fold in alkaline phosphatase (marker for BBM), and the BPM was enriched 37-fold in binding of [3H] dihydroalprenolol (marker for BPM) compared to homogenate. Both placental membranes contain binding sites (maximum binding = 0.550 +/- 0.032 and 0.298 +/- 0.065 pmol/mg protein for BBM and BPM, respectively) with similar affinities (Kd = 2.05 +/- 0.23 and 1.78 +/- 0.19 nM, respectively) for 125I-[Nle8,Nle18,Tyr34] bovine (b) PTH-(1-34) amide. The three bovine preparations [bPTH-(1-34), its analog [Nle8,Nle18,Try34]bPTH-(1-34) amide, and the antagonist bPTH-(3-34)] were equipotent in binding to both placental membranes. In contrast, human PTH-(1-84) was more effective in displacing the bovine radioligand in BBM. Thyrocalcitonin and insulin, two non-PTH peptides, did not significantly displace the radioligand in BBM and BPM. Adenylate cyclase activity, located exclusively in BPM, was stimulated by PTH. Since the enzyme is absent from BBM, it is probable that the binding of the hormone to this membrane activates another system of messengers.

Adenylyl Cyclases↗
PubMed1997

Prolactin-mediated inhibition of 20alpha-hydroxysteroid dehydrogenase gene expression and the tyrosine kinase system.

The rat luteal 20alpha-hydroxysteroid dehydrogenase plays a key role at catabolizing progesterone and at decreasing the level of this steroid secreted by the ovaries. Throughout pregnancy and before parturition neither the mRNA nor the protein for this enzyme could be detected. In this investigation we set to examine whether PRL and PRL-like hormone from placental origin silence the expression of this gene and whether PRL action involves tyrosine kinase activity and/or de novo protein synthesis. The results revealed that PRL and PRL-like hormone from rat placental origin (rPL-1 and rPL-2), but not rat growth hormone, caused a rapid and profound inhibition of 20alpha-HSD mRNA expression in highly luteinized granulosa cells. Immunoprecipition and western blot analysis indicate that PRL-R associates with JAK2 and Stat5, and this association is increased within 30 seconds with PRL treatment. Although both JAK2 and Stat5 were phosphorylated on tyrosine upon PRL treatment, the PRL mediated inhibition of 20alpha-HSD was not reversed by either tyrosine kinase inhibitors, AG18 and genistein, but was largely reversed by the protein synthesis inhibitor cycloheximide. In summary, results of this investigation indicate that although PRL can activate the JAK2/Stat5 system in the corpus luteum, the down regulation of 20alpha-HSD mRNA by PRL does not appear to involve tyrosine kinase activity but depends on de novo synthesis of protein(s).

20-Hydroxysteroid Dehydrogenases↗
PubMed1998

The effects of ovine placental lactogen and bovine growth hormone on hepatic and mammary gene expression in lactating sheep.

The ability of ovine placental lactogen (oPL) to bind to the growth hormone receptor (GHR) raises the possibility that oPL may exert a growth hormone (GH)-like action on galactopoiesis. We have compared the effects of treating lactating ewes for 5 days with an equimolar dose (0.1 mg/kg/day, administered as two equal doses 12 hourly) of either bovine growth hormone (bGH) (n = 10), oPL (n = 10) or saline (n = 9) on hepatic and mammary GHR, insulin-like growth factor-I (IGF-I) and IGF-binding protein-3 (IGFBP-3) gene expression and hepatic GHR number. Hepatic GHR and IGFBP-3 mRNA were unaltered by bGH or oPL treatment. Hepatic IGF-I mRNAs increased following bGH (P < 0.05) but not oPL treatment. GHR gene expression was greater in liver compared to mammary gland extracts. There was no effect of either bGH or oPL treatment on mammary GHR, IGF-I or IGFBP-3 mRNA or hepatic GHR number. These studies confirm the galactopoietic effects of bGH in lactating ruminants and suggest that the mechanism of this action is not via increased hepatic GHR number or gene expression. In addition, the increase in hepatic but not mammary IGF-I mRNA with bGH treatment suggests an endocrine action of IGF-I on milk synthesis. These studies also demonstrate that an equimolar dose of oPL is not galactopoietic or somatogenic in the lactating ewe.

Animals↗
PubMed1996

Measurement of luteal and placental gonadotrophin-releasing hormone (GnRH) binding sites: role of inactivation of GnRH tracer.

The ability of radiolabelled gonadotrophin-releasing hormone (GnRH) and GnRH analogues to bind to homogenates and membranes of rat, rabbit and sheep pituitary and to luteal homogenates and membranes from a number of species was measured. In addition, inactivation of tracer during binding incubation was estimated by measurement of the ability of the unbound tracer fraction to bind to fresh GnRH-receptor or anti-GnRH antibody. Following incubation of rat, sheep and rabbit pituitary gland with a radiolabelled GnRH agonist tracer, appreciable amounts of specific binding of GnRH agonist to fresh rat pituitary or human placental GnRH receptors could still be demonstrated. In contrast, no specific binding of [125I]-labelled GnRH analogues were measured following incubation of the tracer with homogenates or membranes of bovine, sheep and porcine luteal tissue, nor with rabbit and rat placental homogenates. However, during incubation of GnRH tracers with these tissues, almost complete inactivation of GnRH tracers occurred. There was an inverse relationship between binding and inactivation of [125I]-labelled GnRH for a number of human corpora lutea. We conclude that degradation of GnRH tracers may prevent the measurement of specific GnRH binding sites in some tissues.

Animals↗