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At least 685 records · Page 38Linked to original sources
PubMed1987

Regulation of DNA synthesis in human fetal hepatocytes by placental lactogen, growth hormone, and insulin-like growth factor I/somatomedin-C.

Hepatocytes were isolated by gentle collagenase digestion of liver fragments from human fetuses of 8-16 weeks gestation obtained following prostaglandin-induced pregnancy terminations. They were maintained on collagen-coated tissue culture dishes in selective arginine-free medium for up to 72 hr, and the action of hormones and growth factors on DNA synthesis was studied by autoradiography following incubation with 3H-thymidine. The labeling index of hepatocytes was consistently enhanced by 25-250 ng/ml human placental lactogen (HPL), 25-250 ng/ml human growth hormone (HGH), 10-50 ng/ml insulin-like growth factor I/somatomedin-C (IGF I/Sm-C), and 10% dialyzed fetal calf serum, reaching a maximum of three- to four-fold greater than in basal medium alone. Under basal conditions, 30% of hepatocytes stained positively for the presence of IGF peptides using a monoclonal antibody raised against purified human IGF I/Sm-C. Although this proportion did not change following treatment with HGH and HPL, IGF I/Sm-C released by cells into culture medium was considerably increased in the presence of both hormones. Incubation with the SmC 1.2 monoclonal antibody abolished the increase in labeling index in response to IGF I/Sm-C and partially blocked the response to both HPL and HGH. These results indicate that both HPL and HGH stimulate DNA synthesis in human fetal hepatocytes and suggest that this effect is at least partly indirect through the release and paracrine action of IGF I/Sm-C.

DNA Replication↗
PubMed1971

Sequences of pituitary and placental lactogenic and growth hormones: evolution from a primordial peptide by gene reduplication.

Human placental lactogen has been found to resemble human pituitary growth hormone very closely in amino acid sequence, about 80% of the residues examined being identical in the two molecules when a revised sequence for growth hormone is used as the basis for comparison. The structural features responsible for the differing biological potency of the two hormones may therefore reside in rather limited regions of primary structure. The observation of internal sequence homologies within the pituitary growth hormone and prolactin and the placental lactogen molecules suggests that these polypeptide hormones may have evolved by genetic reduplication from a smaller common ancestral peptide. This finding directs further attention to subfragments of these molecules as possible possessors of intrinsic somatotrophic and lactogenic activity.

Amino Acid Sequence↗
PubMed2000

Human placental gonadotrophin-releasing hormone-like factors: an artefact of human placental peptidases?

Non-denatured human placental cytosol fractions displaced tracer binding in parallel with gonadotrophin-releasing hormone (GnRH) isoform and agonist peptides in GnRH-specific radioimmunoassays and radioreceptor assays. However, placental immuno- and receptor binding-GnRH-like activity was highly correlated with inactivation of GnRH tracers, suggesting that placental GnRH-like factors may be an artefact of ligand degradation during assay. The properties and inhibitor sensitivities of the major (125)I-labelled GnRH-degrading enzymes of term placental cytosol were studied using a dextran-coated charcoal (DCC) adsorption assay as a rapid screen for GnRH tracer inactivation. Three different activities were demonstrable: (i) a cathepsin D-like enzyme (M(r) 55 kDa), active against all radiolabelled GnRH isoforms and agonists tested, optimal at acid pH, and inhibited specifically by pepstatin; (ii) a metallo-thiol endopeptidase activity (M(r) 70 kDa) optimal at alkaline pH (7-9) which degraded GnRH isoforms to a greater extent than GnRH analogues, inhibited dose-dependently by low concentrations of thiol reagents (N-ethylmaleimide, thimerosal), chelating agents (o-phenanthroline, EDTA), and by tosyl-phenylalanyl-chloromethyl ketone but not by other serine protease inhibitors; and (iii) a bacitracin-sensitive enzyme optimal at physiological pH. These observations permitted the development of a robust radioreceptor assay which minimized GnRH tracer degradation. Under these assay conditions, the GnRH-like radioreceptor assay activity of human placental cytosol fractions was markedly reduced.

Adsorption↗
PubMed1988

The physiology of growth hormones (GHs) in pregnant women and partial characterization of the placental GH variant.

This work was undertaken to study the heterogeneity of GH in serum and placental and pituitary extracts and to study GH physiology in pregnant women. Two distinct monoclonal antihuman GH (anti-hGH) antibodies (MAb) coded 5B4 and K24 were selected for their high binding affinity and specificity. The 5B4 MAb recognized the epitope comprising the NH2-terminal end of hGH, and the K24 MAb recognized an internal epitope. Both MAbs were used in RIAs to measure serum GH concentrations in various circumstances, including pregnancy. The two RIAs yielded slightly different serum GH results in normal men and nonpregnant women, but the overall correlation between the data was excellent. Since the RIAs were not affected by human placental lactogen, the evolution of serum GH in pregnant women could be studied. In such women, serum GH levels progressively declined to undetectable levels during the second half of pregnancy, while a pregnancy-associated serum GH-like antigen [tentatively called human placental growth hormone (PGH)] appeared in the circulation at midpregnancy and increased thereafter up to term. PGH contained the NH2-terminal epitope of pituitary GH, but lacked the internal one. Consequently, it reacted selectively with the 5B4 MAb only. After delivery, PGH disappeared from maternal serum within 1 h. Amniotic fluid contained low GH concentrations; cord serum contained high GH levels, but no PGH. Thus, PGH appears to be secreted selectively into the maternal compartment. PGH was purified from term placenta extracts. According to its chromatographic behavior, it appears more basic than pituitary 22K and 20K GHs. Size dimorphism was demonstrated; PGH was composed of two entities of 22K and 25K, respectively. Pure PGH, obtained in small quantities by preparative electrophoresis, was found to bind to hepatic GH receptor with an apparent high potency compared to that of pituitary GH, PGH, thus, should act in vivo as a GH agonist sharing most of its biological properties. These results lead to the conclusion that PGH is likely to replace the pituitary hormone in governing maternal metabolism during the second half of pregnancy.

Amniotic Fluid↗
PubMed2001

Involvement of central, but not placental corticotropin releasing hormone (CRH) in heat stress induced immunosuppression during pregnancy.

To clarify whether corticotropin releasing hormone (CRH) and beta-endorphin (betaEP) system mediate maternal immunosuppression in pregnant rats exposed to heat through central or placental pathway, we examined the effects of intravenous (iv) (100 or 500 microg) or intracerebroventricular (icv) (5 microg) administration of CRH receptor antagonist alpha-helical CRH (9-41) on splenic natural killer cell activity (NKCA) as well as betaEP in blood, pituitary lobes, and placenta in pregnant rats at 15 to 16 days gestation. Two-way ANOVA revealed that heat reduced NKCA and elevated blood and pituitary betaEP but did not change placental betaEP. Iv administered 500 microg and icv administered alpha-helical CRH reversed the reduced NKCA and the elevated pituitary betaEP, while iv administration of 100 microg alpha-helical CRH did not. The increased blood betaEP was reversed by iv 100 and 500 microg alpha-helical CRH and icv administration. Both iv and icv administrations reduced placental betaEP independent of heat exposure. Thus, the response of placental betaEP to iv administration of alpha-helical CRH seemed to be stronger than that of pituitary betaEP. These results indicate that alpha-helical CRH which acts on pituitary betaEP antagonizes heat-induced immunosuppression during pregnancy, suggesting that immunosuppression produced by heat stress during pregnancy is mediated by the central CRH system. The placental CRH-betaEP system seems unlikely to be involved in the immunosuppression. Physiologic roles of placental CRH and opioid system should be clarified by future in vitro experiments using placenta specimen including placental immunocyte.

Animals↗
PubMed1980

Placental proteins and steroid hormones in the soluble fraction of human syncytiotrophoblast plasma membrane.

Placental protein 5 (PP5), pregnancy-specific glycoprotein (SP1), pregnancy-associated alpha 2-glycoprotein (SP3) and chorionic gonadotrophin could not be demonstrated in appreciable molar quantities in the soluble fraction from microvillous plasma membrane preparations isolated from the syncytiotrophoblast of full-term human placentae. However, progesterone, total oestriol and placental lactogen may have some association with this membrane.

Cell Membrane↗
PubMed1986

The glycogenic effects of placental lactogen and growth hormone in ovine fetal liver are mediated through binding to specific fetal ovine placental lactogen receptors.

To examine the relative roles of placental lactogen (PL) and GH in fetal metabolism, we have examined the effects of ovine PL (oPL), ovine GH (oGH), and ovine PRL (oPRL) on glycogen metabolism in cultured ovine fetal hepatocytes and have examined the binding of these hormones to hepatic membranes from fetal and neonatal lambs. In ovine fetal hepatocytes, oPL (150 ng/ml-20 micrograms/ml) stimulated dose-dependent increases in [14C]glucose incorporation into glycogen (18-167%) and total cellular glycogen content (10-69%). oGH and oPRL also stimulated glycogen synthesis in fetal hepatocytes, but the potencies of these hormones were only 12% and 4% that of oPL. The dose-response curves of the three hormones were parallel, and their maximal effects were identical, suggesting a common mechanism of action. In hepatic membranes from fetal lambs, the maximal specific binding of [125I]oPL was 26.3% while the maximal specific binding of [125I]oGH was only 0.9-1.5%. The binding of [125I]oPL was saturable and reversible and varied with incubation time and temperature. Unlabeled oPL (1 ng/ml-5 micrograms/ml) caused a dose-dependent inhibition of the binding of [125I]oPL to fetal hepatic membranes, with half-maximal displacement of [125I]oPL by 5-7 ng unlabeled oPL/ml. oGH and oPRL caused parallel displacement of [125I]oPL, but with potencies only 2% and 0.1% that of oPL. Scatchard analysis of oPL dose-response curves indicated that the hormone bound to a single class of receptors with a dissociation constant of 1.1 X 10(-10) M. The maximal specific binding of [125I]oGH to hepatic membranes of neonatal lambs (20.1%) greatly exceeded the binding of oGH to fetal hepatic membranes. In addition, the potency of oGH in competing for [125I]oPL binding sites in neonatal liver greatly exceeded the potency of oGH in competing for [125I]oPL binding sites in fetal liver. Although the biological effects of both oPL and oGH in postnatal subprimate tissues may be mediated through binding to nonprimate GH receptors, the results of these studies suggest that the glycogenic effects of oPL in ovine fetal liver are mediated through binding to specific fetal oPL receptors. The relatively weak biological effects of oGH and oPRL in ovine fetal liver appear to be mediated through the binding of the hormones to fetal oPL receptors. The presence of specific, high affinity PL receptors in ovine fetal tissues provides a mechanism whereby oPL may function as a GH in the ovine fetus.

Animals↗
PubMed1989

Binding sites for growth hormone in rabbit placental cytosol.

A soluble GH-binding protein, which cross-reacted with a monoclonal antibody (Mab) to the rabbit liver membrane GH receptor, has been identified in cytosol preparations from both fetal and maternal portions of rabbit placenta. Structural studies using gel filtration chromatography and chemical covalent cross-linking techniques have shown that the GH-binding protein in fetal/maternal placental cytosol has a native mol wt of 104,000 and a denatured subunit of about 57,000 mol wt (with or without dithiothreitol). Very low levels of GH-specific [125I]human (h) GH binding were observed in membrane preparations from the corresponding placentae, even after desaturation of any endogenously bound hormone by 5 M MgCl2. No PRL-specific binding was observed in placental membranes or cytosols. Scatchard analysis of [125I]hGH binding to fetal and maternal placental cytosol revealed linear plots with Ka values of 6.1 +/- 1.1 nM-1 (fetal) and 5.31 +/- 0.63 nM-1 (maternal; mean +/- SEM; n = 5). The binding capacity of maternal placental cytosol, when expressed as femtomoles per mg protein (170 +/- 10.10) or femtomoles per g tissue (3245 +/- 123), was about 3-fold higher than that for fetal placental cytosol. Northern blot analysis of fetal and maternal placental mRNA probed with a GH receptor oligonucleotide probe revealed hybridization to a 4.4 to 4.7-kilobase and a 2.2-kilobase species in fetal placenta only. The level of GH-specific binding observed in fetal and maternal placental cytosol did not correlate directly with the level of mRNA expression. A GH-binding protein has also been shown to be present in fetal rabbit serum and is known to be structurally and immunologically related to the rabbit placental and liver cytosolic GH-binding proteins. Scatchard analysis of [125I]hGH binding to fetal serum GH-binding protein revealed a single class of high affinity sites with a Ka of 4.64 +/- 1.29 nM-1 and a capacity of 338 +/- 167 fmol/ml serum (mean +/- SEM; n = 4). Given the relative binding capacities and the demonstration of GH receptor mRNA in fetal placental cytosol, it is highly unlikely that contamination of fetal placental cytosol by fetal serum accounts for all of the placental binding capacity observed. However, no such definitive conclusion regarding contamination by maternal rabbit serum of maternal placental cytosol can be made. The presence of GH-binding proteins in placental cytosol has not been described previously, and these observations suggest that GH may have a role in placental metabolism.

Animals↗