The role of placental lactogen in the regulation of fetal metabolism and growth.
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Embryonic and Fetal Development↗
Biomedical subjects
S Handwerger
Publications and source records attributed to S Handwerger.
Insulin stimulates the synthesis and release of prolactin from human decidual cells.
Insulin-like growth factor I (IGF-I) and insulin have been implicated in the regulation of differentiated functions in many cells. We have reported that IGF-I stimulates the release of decidual PRL, acting through the type I IGF receptor (1). To determine whether insulin regulates the synthesis and secretion of decidual PRL, monolayer cultures of human decidual cells were exposed to insulin at concentrations ranging from 10 ng to 10 micrograms/ml for up to 5 days. Insulin stimulated a dose-dependent increase in PRL release (half-maximal concentration, 50 ng/ml), beginning 48 h after initial exposure. Insulin-exposed cells released 62 +/- 2% (mean +/- SEM), 97 +/- 3% and 82 +/- 6% more PRL than control cultures on days 3, 4, and 5, respectively. Insulin also stimulated de novo PRL synthesis. During the final 24-h culture period, insulin-exposed cells released 73 +/- 7% more immunoprecipitable [35S]-methionyl PRL than control cells, comparable to the 60 +/- 7% increase in PRL (by RIA) during the same period. Insulin effects were relatively specific to PRL, since insulin had a much smaller effect on the synthesis of total trichloroacetic acid-precipitable proteins. Additionally, insulin had no significant effect on cell number, total DNA, or total cellular protein. Specific and saturable insulin-binding sites were observed in decidual cells, and polyclonal antibodies to the insulin receptor acted as insulin agonists, stimulating an increase in PRL release comparable to that produced by insulin alone. These observations suggest that the responses to insulin are mediated through the insulin receptor. Furthermore, our studies suggest that insulin may have a role in the regulation of PRL synthesis and release from human decidua.
Binding, Competitive↗
High density lipoprotein3 binding and biological action: high affinity binding is not necessary for stimulation of placental lactogen release from trophoblast cells.
High density lipoprotein (HDL3) binds with high affinity to many types of cells, but controversy exists concerning the nature and biological significance of the binding. We have recently demonstrated that HDL and apoproteins (apo)-AI, -AII, and -CI stimulate a specific and dose-dependent increase in placental lactogen (hPL) release from human trophoblast cells. To examine the possible relationship between HDL3 binding and stimulation of hPL release, we have characterized the binding of [125I]HDL3 to an enriched fraction of hPL-producing trophoblast cells. Binding studies were performed on trophoblast cells isolated by isopycnic centrifugation of collagenase/hyaluronidase-dispersed placental tissue and apo-E free-HDL3 (density, 1.125-1.215 g/ml). Scatchard analysis of binding studies performed at 37 C for 2 h revealed two classes of binding sites: 1) high affinity binding sites with a Kd of 9.7 +/- 2.2 micrograms/ml (1.3 x 10(-7) M) and 9.8 +/- 3.2 x 10(5) binding sites/trophoblast cell, and 2) low affinity binding sites with a Kd of 172.8 +/- 64.8 micrograms/ml (2.3 x 10(-6) M) and an estimated 3.2 x 10(6) sites/cell. As has been found in hepatocytes and other cells, the number of HDL3-binding sites per trophoblast cell (but not the binding affinity) decreased at lower incubation temperatures. In addition, HDL3 binding to trophoblasts cells did not require calcium and was not affected by prior treatment of the cells with pronase or trypsin. HDL3-binding sites on trophoblast cells, however, were not specific for HDL3. Low density lipoprotein (density, 1.063-1.055 g/ml), which does not stimulate hPL release, was nearly as potent on a molar basis as HDL3 in binding to the high and low affinity binding sites on trophoblast cells. Furthermore, nitrated HDL3, which does not compete for high affinity binding to trophoblast cells, stimulated hPL release. Although the characteristics of HDL3 binding to trophoblast cells are similar to those of other cells, these results strongly suggest that the binding of HDL3 to high affinity binding sites is not essential for HDL-mediated hPL release.
Binding Sites↗
High-density lipoproteins (HDL) stimulate placental lactogen secretion in pregnant ewes: further evidence for a role of HDL in placental lactogen secretion during pregnancy.
Previous studies from our laboratory showed that high-density lipoproteins (HDL) stimulate the release of human placental lactogen (PL) from cultured trophoblast cells from normal pregnant women. To determine whether HDL stimulates PL secretion in vivo, ovine HDL was infused over 2-5 min into 11 pregnant ewes (22 separate experiments) at 86-130 days of gestation via an indwelling catheter into the maternal jugular vein. The HDL, freshly prepared from the plasma of pregnant ewes by differential flotation ultracentrifugation, was greater than 99% purified as judged by SDS-PAGE. Plasma samples were obtained from the ewes before and at 0.5-h intervals for 6 h following the infusions and were assayed for PL by a specific homologous radioimmunoassay. The maternal infusion of HDL at doses of 302-784 mg (5.3-13.8 mg/kg body weight) stimulated significant increases in maternal plasma PL concentrations in six out of eight experiments (six ewes), and the infusion of 108-264 mg (1.9-4.6 mg/kg) stimulated plasma PL concentrations in two out of six experiments. In contrast, HDL at doses less than 100 mg were without effect in eight experiments. The response to the HDL infusions was characterized by a sustained increase in plasma PL concentrations beginning 1.5-2.5 h after the infusions, reaching a maximum 274.2 +/- 21.9% of the baseline value (P less than 0.001). In contrast, the maternal infusion of lipoprotein-free plasma proteins or saline had no effect on maternal plasma PL concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)
Animals↗
Treatment of cytomegalovirus retinitis with ganciclovir (9-[2-hydroxy-1-(hydroxymethyl) ethoxymethyl] guanine (BW B759U).
Six patients (11 eyes) with virologically confirmed cytomegalovirus (CMV) retinitis involving the posterior pole of the eye were treated with a new drug, ganciclovir. Treatment with intravenous ganciclovir consistently halted progression of retinitis and produced improvement in measures of visual function. However, within three weeks after cessation of therapy renewed CMV activity and worsening of visual function were observed in most cases. Maintenance therapy with ganciclovir extended the period of remission from CMV retinitis.
Acquired Immunodeficiency Syndrome↗
Decidual prolactin (PRL)-releasing factor stimulates the synthesis of PRL from human decidual cells.
Previous studies from our laboratory demonstrated that the acute release of PRL from human decidual tissue is stimulated by a 23.5 kilodalton placental protein which we designated decidual PRL-releasing factor (PRL-RF). To determine whether PRL-RF may also affect the synthesis of PRL and/or cause a secondary increase in PRL release, we have examined the effects of purified PRL-RF on the synthesis and release of PRL over a 96-h period. Exposure of dispersed decidual cells to PRL-RF (0.5 microgram/ml) stimulated a biphasic increase in PRL release with acute transient stimulation during the first 0.5 h and a delayed and sustained stimulation beginning about 8 h after exposure which persisted for the duration of the 96 h. The amounts of PRL released from PRL-RF-exposed cells after 0.5, 8, 12, 24, and 96 h were 321.2 +/- 36.2 (mean +/- SEM, n = 3), 110.2 +/- 5.3, 138.2 +/- 7.2, 194.5 +/- 11.2, and 201.5 +/- 14.2% that of control cells. Studies of the de novo synthesis of [35S]methionyl PRL indicated that the increase in PRL release after the first few hours of exposure to PRL-RF was secondary to an increase in PRL synthesis. Somatostatin (100 nM) inhibited the acute stimulatory effect of PRL-RF, but had no effect on the delayed stimulation of PRL release. On the other hand, cycloheximide (20 microM) completely inhibited the secondary increase in PRL release in response to PRL-RF but had no effect on the acute release. These results demonstrate that PRL-RF stimulates both the synthesis and release of decidual PRL.
Cells, Cultured↗
High density lipoproteins stimulate placental lactogen release and adenosine 3',5'-monophosphate (cAMP) production in human trophoblast cells: evidence for cAMP as a second messenger in human placental lactogen release.
Recent studies from our laboratory indicate that high density lipoproteins (HDL) and apolipoproteins-AI, -AII, and -CI stimulate the release of human placental lactogen (hPL) from human placental explants and trophoblast cells. However, the intracellular mechanisms by which HDL stimulate hPL release are unknown. Since earlier investigations from our laboratory indicated that pharmacological agents that increase intracellular cAMP levels [such as (Bu)2cAMP, isobutylmethylxanthine, and cholera toxin] also stimulate hPL release, we have performed studies to determine whether the stimulation of hPL release by HDL may be mediated by cAMP. Exposure of an enriched fraction of enzymatically dispersed hPL-producing cells to HDL (10-1500 micrograms/ml) for 0.5 h resulted in a significant dose-dependent stimulation of both cAMP production and hPL release. The half-maximal effective HDL dose for cAMP production and hPL release was 60-100 micrograms/ml. When perifused trophoblast cells were exposed to HDL (150 micrograms/ml) for 25 min, the increase in cAMP production preceded the increase in hPL release. The increase in cAMP production occurred during the first 5 min of exposure to HDL and reached a maximum (12.1 +/- 1.6-fold greater than base-line levels) 10 min after exposure. The increase in hPL release occurred about 10 min after the initial increase in cAMP production, reaching a maximum (9.7 +/- 1.4-fold greater than base-line levels) 15 min after exposure to HDL. HDL (300 micrograms/ml) also stimulated a 2.7-fold (P less than 0.001) increase in adenylate cyclase activity in placental plasma membranes, a magnitude of stimulation comparable to that caused by epinephrine (1 mM). Apolipoprotein-AII stimulated cAMP formation and hPL release in trophoblast cells with a pattern identical to that of HDL. These results, the first to demonstrate an effect of HDL on adenylate cyclase activity and cAMP production, strongly suggest a role for cAMP as a second messenger in HDL-stimulated hPL release.
Apolipoproteins↗
Insulin-like growth factor I stimulates the synthesis and release of prolactin from human decidual cells.
Recent studies suggest a role for insulin-like growth factor I (IGF-I) in the regulation of hormone release from placental, gonadal, and pituitary tissues. To examine whether IGF-I may also regulate the release of PRL from human decidual tissue, we have investigated the effect of recombinant human IGF-I on PRL release from monolayer cultures of human decidual cells exposed to IGF-I for up to 4 days. IGF-I (10-1000 ng/ml) stimulated a sustained dose-dependent increase in PRL release (half-maximal concentration, 25 ng/ml) beginning 48 h after initial exposure, but had no effect on the intracellular PRL content. The amounts of PRL released from maximally stimulated cultures on days 3 and 4 were 168 +/- 3% (mean +/- SEM) and 258 +/- 8% of control values, respectively. IGF-I-mediated effects were inhibited by cycloheximide (3.6 microM), suggesting that the increase in PRL was the result of newly synthesized hormone. The increase in PRL release was not due to a generalized effect on protein release, since IGF-I had no effect on the release of trichloroacetic acid-precipitable [35S]methionyl proteins. Radioligand competition studies indicate that the biological actions of IGF-I are mediated through interaction with the IGF-I receptor. Binding of radiolabeled IGF-I to decidual cells in suspension was specific, saturable, and displacable by unlabeled IGF-I, with a potency nearly 10 times greater than that of insulin. Furthermore, exposure of decidual cells to a monoclonal antibody to the IGF-I receptor (alpha-IR3) completely inhibited both IGF-I-mediated PRL release and specific binding of [125I]IGF-I to decidual cells. Since the actions of IGF-I occurred at physiological concentrations, these findings strongly support a role for IGF-I in the regulation of PRL secretion by human decidua.
Antibodies, Monoclonal↗
Placental lactogen and growth hormone receptors in human fetal tissues: relationship to fetal plasma human placental lactogen concentrations and fetal growth.
The specific binding of human placental lactogen (hPL) and human GH (hGH) to particulate cell membranes from human fetal liver and skeletal muscle at 12-19 weeks gestation was examined. Fetal liver and muscle specifically bound [125I]hPL. This binding was inhibited by increasing concentrations of unlabeled hPL (half-maximal concentrations, 2.2 and 3.4 nmol/L, respectively). Scatchard analysis of the hepatic membrane binding revealed curvilinear plots with higher (Kd, 2.2 nmol/L) and lower (Kd, 24 nmol/L) affinity sites, while binding to muscle involved a single receptor class of Kd 5.6 nmol/L. The binding capacities for the two hepatic sites correlated positively with fetal body weight. [125I]hGH specifically bound to liver, but not muscle, with higher (Kd, 1.6 nmol/L) and lower (Kd, 8.6 nmol/L) affinity sites. [125I]PRL bound to hepatic membranes, but was preferentially displaced by hPL or hGH. Between 4 and 500 micrograms/L (mean, 82 micrograms/L, 3.8 nmol/L) hPL were present in fetal plasma. The findings identify distinct hPL receptors in human fetal liver and skeletal muscle and a hepatic hGH receptor in midgestation.
Embryonic and Fetal Development↗
Leuconostoc, an emerging vancomycin-resistant pathogen.
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Aged↗
Purification of decidual prolactin-releasing factor, a placental protein that stimulates prolactin release from human decidual tissue.
Decidual prolactin-releasing factor (PRL-RF), a placental protein that stimulates the release of prolactin from human decidual tissue, has been purified from conditioned medium of human placental explants. The purification scheme consisted of ethanol extraction, anion exchange chromatography on DEAE-cellulose, size exclusion chromatography on Spherogel TSK-3000, and either a) immunoaffinity chromatography using an antiserum to a partially purified PRL-RF preparation or b) acetic acid-urea/SDS 2-dimensional PAGE. The apparent molecular weight of the purified releasing factor, estimated by SDS-PAGE, was 23,500 Da; and the half-maximal dose for the acute stimulation of prolactin release from human decidual cells was 0.05-0.1 ug/ml (2.2-4.4 nM).
Biological Assay↗
Role of placental lactogen and prolactin in human pregnancy.
In summary, studies from our and other laboratories strongly suggest that placental lactogen has direct effects on fetal growth and metabolism as well as on maternal metabolism. Prolactin may be important in the regulation of water and ion transport across the amnion, the production of surfactant by the fetal lung, and the immune response during pregnancy. A summary of the postulated effects of placental lactogen on maternal and fetal physiology is depicted in Figure 9 and a summary of the postulated effects of prolactin during pregnancy is shown in Table 6. Undoubtedly, future studies of the physiology of placental lactogen and prolactin will uncover new functions for these hormones during gestation.
Female↗
Serum gastrin, calcitonin, and prolactin as markers of multiple endocrine neoplasia syndromes in patients with primary hyperparathyroidism.
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Calcitonin↗
Cyclic AMP inhibits the synthesis and release of prolactin from human decidual cells.
Exposure of human decidual cells for 0.5 h to dibutyryl cAMP, isobutyl-methylxanthine (IBMX), cholera toxin or forskolin caused a dose-dependent inhibition of prolactin release with maximal inhibition by each agent of 50-60%. Dibutyryl cAMP (5 mM), IBMX (0.5 mM), and cholera toxin (10 micrograms/ml) also inhibited prolactin synthesis to the same extent as prolactin release. Dibutyryl cAMP, IBMX, and cholera toxin, however, had no effect on the release of 35S-methionyl-prolactin from decidual cells preincubated for 24 h in medium with 35S-methionine. These agents, however, had no effects on the synthesis or release of TCA-precipitable 35S-decidual proteins and did not cause the degradation of intracellular or released prolactin. The demonstration that agents which increase intracellular cAMP levels inhibit the synthesis and release of decidual prolactin strongly implicates cAMP as a second messenger in the regulation of the synthesis and release of the hormone. The inhibitory effect of cAMP on prolactin release appears to be on the release from a rapidly releasable, newly synthesized intracellular prolactin pool.
1-Methyl-3-isobutylxanthine↗
Biochemical evidence that human placental lactogen and human chorionic gonadotropin are not stored in cytoplasmic secretion granules.
The intracellular storage sites for the human placental hormones placental lactogen (hPL) and chorionic gonadotropin (hCG) are unknown. To determine whether hPL and hCG are stored in cytoplasmic secretion granules, we have compared the localization of hPL and hCG in placental homogenates following differential and density-gradient centrifugations to those of prolactin (PRL) and luteinizing hormone (LH) in human and rat pituitary homogenates. In the differential centrifugation studies, 93.1 +/- 4.1% (mean +/- SE) of the hPL and 79.4 +/- 6.0% of the hCG were detected in the postmicrosomal supernatant of placental homogenates. In contrast, 95-98% of the hPRL and hLH in the pituitary homogenates were detected in particulate fractions. Following centrifugation on sucrose-density gradients, particulate hPL and hCG were distributed diffusely throughout the gradients, while greater than 90% of the pituitary hormones sedimented as single peaks with densities of 1.22 g/cm3. When human placental and rat pituitary tissues were homogenized together prior to differential and density-gradient centrifugations, similar marked differences were observed between the distribution of the placental and pituitary hormones. These results strongly suggest that the placental hormones hPL and hCG, unlike pituitary PRL and LH, are not stored in large secretory granules. Differences in the intracellular storage sites of the hormones may explain, in part, differences in the regulation of peptide hormone secretion by placental and pituitary tissues.
Animals↗
Apolipoproteins AI, AII, and CI stimulate placental lactogen release from human placental tissue. A novel action of high density lipoprotein apolipoproteins.
High density lipoproteins (HDL) stimulated a dose-dependent increase in the release of placental lactogen (hPL) from human placental explants. The stimulation was not prevented by delipidation of HDL but was completely blocked by tryptic digestion. Delipidated apolipoproteins (Apo) AI, AII, and CI also stimulated hPL release but other apolipoproteins were without effect. HDL and Apo CI had no effects on the release of luteinizing hormone and follicle-stimulating hormone from rat pituitary cells or the release of prolactin from human decidual cells. Because placental cells have specific HDL receptors and plasma HDL concentrations increase during pregnancy, these results strongly suggest a role for HDL in the regulation of hPL release during pregnancy possibly independent of their usual role in plasma lipid transport.
Apolipoprotein A-I↗
A unique placental lactogen receptor: implications for fetal growth.
To determine whether there are structural differences between the binding sites for placental lactogen (PL) and GH, we have compared the molecular weights of complexes formed by the covalent cross-linking of [125I]ovine (o) PL and [125I]oGH to hepatic membranes from fetal and pregnant sheep in mid- and late gestation and from postnatal nonpregnant sheep at 3 days to 7 months of age. Specific [125I]oPL binding sites in fetal liver were detected as early as midgestation, and cross-linking of [125I]oPL to fetal hepatic membranes yielded a major radiographic band with a mol wt of 60 +/- 5 K (mean +/- SD). Unlabeled oPL at low concentrations (0.9-9 nM) specifically competed with [125I]oPL for binding to the 60 K complex. In contrast, oGH and oPRL competed for binding to the 60 K complex only at much higher concentrations (greater than or equal to 90 nM). In addition, no specific cross-linking of [125I]oGH or [125I]oPRL to fetal hepatic membranes was observed. These findings suggest the presence of a distinct and unique PL binding site in ovine fetal liver. Since the mol wt of oPL is 22 K, the estimated mol wt of the oPL receptor protein is 38 +/- 5 K. During the first week after birth, there was a striking increase in the number of [125I]oGH binding sites. Cross-linking of [125I]oGH to postnatal liver yielded radiographic bands with apparent mol wts of 75 K and 140 K. The relative potencies of oPL, oGH, and oPRL in competing for binding to the 75 K and 140 K complexes were similar to the relative potencies of these hormones in competing for [125I]oGH binding sites in postnatal liver, suggesting that the 75 K and 140 K bands represent subunits of the oGH receptor bound covalently to [125I]oGH. Cross-linking of [125I]oPL to pregnant and postnatal nonpregnant liver yielded three radiographic bands with mol wts of 60 K, 75 K, and 140 K. The intensities of all three bands were reduced by low concentrations (0.9-9 nM) of oPL. Higher concentrations of oGH abolished the 75 K and 140 K bands but reduced the intensity of the 60 K band by only 20-30%. oPRL had minimal effect on band intensities. These observations suggest the presence of two functionally and structurally distinct receptors in pregnant liver: the oPL receptor, which has high affinity for oPL and low affinity for oGH and oPRL.(ABSTRACT TRUNCATED AT 400 WORDS)
Animals↗
Cyclic adenosine-3',5'-monophosphate stimulates the acute release of placental lactogen from human trophoblast cells.
cAMP has been shown to be a second messenger in the release of many hormones and other secretory products. To determine whether cAMP also plays a role in the mechanism of release of human placental lactogen (hPL), we examined the effects of (Bu)2cAMP, isobutyl methylxanthine, forskolin, and cholera toxin on the acute release of hPL from an enriched fraction of hPL-producing trophoblast cells. Static cultures of trophoblast cells exposed to (Bu)2cAMP (5 mM) for 2 h released 2.6 times as much hPL as control cells (P less than 0.01) during the first 0.5 h of exposure. The increase in hPL release was followed by a decrease rate of release during the subsequent 1.5 h. Perifused trophoblast cells (1.5 X 10(6) exposed to 5 mM cAMP for 20 min released 3.2 times as much hPL as control cells. The rate of hPL increased markedly during the first 10 min of exposure, rapidly decreased toward control values during the remainder of the exposure period, and then declined to a subnormal rate for the next 30 min before returning to normal to control values. (Bu)2cAMP, however, had no acute effects on the release of human CG or the release of the cytosolic enzymes alkaline phosphatase and lactic dehydrogenase. The phosphodiesterase inhibitors theophylline (5 mM) and isobutyl methylxanthine (0.5 mM) and the adenylate cyclase activators forskolin (5 micrograms/ml) and cholera toxin (25 micrograms/ml) stimulated hPL release by 75-95%. These results strongly suggest that cAMP is a second messenger in the acute release of hPL.
1-Methyl-3-isobutylxanthine↗