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PubMed2006

Gestational and hormonal regulation of human placental lipoprotein lipase.

The fetal demand for FFA increases as gestation proceeds, and LPL represents one potential mechanism for increasing placental lipid transport. We examined LPL activity and protein expression in first trimester and term human placenta. The LPL activity was 3-fold higher in term (n = 7; P < 0.05) compared with first trimester (n = 6) placentas. The LPL expression appeared lower in microvillous membrane from first trimester (n = 2) compared with term (n = 2) placentas. We incubated isolated placental villous fragments with a variety of effectors [GW 1929, estradiol, insulin, cortisol, epinephrine, insulin-like growth factor-1 (IGF-1), and tumor necrosis factor-alpha] for 1, 3, and 24 h to investigate potential regulatory mechanisms. Decreased LPL activity was observed after 24 h of incubation with estradiol (1 micro g/ml), insulin, cortisol, and IGF-1 (n = 12; P < 0.05). We observed an increase in LPL activity after 3 h of incubation with estradiol (20 ng/ml) or hyperglycemic medium plus insulin (n = 7; P < 0.05). To conclude, we suggest that the gestational increase in placental LPL activity represents an important mechanism to enhance placental FFA transport in late pregnancy. Hormonal regulation of placental LPL activity by insulin, cortisol, IGF-1, and estradiol may be involved in gestational changes and in alterations in LPL activity in pregnancies complicated by altered fetal growth.

Adenosine Triphosphate↗
PubMed2002

[Placental proteins and protein hormones in high risk pregnancies].

Experimental part of this study contains a description of an in vitro pattern of protein and protein hormones synthesis in the placental slices of various gestational ages. Incorporation of leucine -14C into placental proteins in vitro was followed-up for the purpose of measuring intensity of protein biosynthesis during pregnancy. It has been detected that the most intensive biosynthesis occurs in placentas from 6 to 8 weeks of gestation, decreases already in the 12th week, slightly increases from 22 to 24 weeks, and significantly falls at term. The same procedure was applied for the human placental lactogen (HPL) synthesis. HPL synthesis was found to be very intensive in young placentas, low in placentas from 22 to 24 weeks, and again intensive in placentas at term. The author indicates to the presence of certain yet unknown regulatory mechanisms influencing the synthesis. Concentrations of total human chorionic gonadotropins (HCG), HCG beta, HPL and beta1-glycoproteins (SP1) were determined paralelly in placentas of various gestational ages. Clinical and laboratory part of this study is dealing with the significance of dosing HPL, HCG, SP1 and alpha-fetoproteins (AFP) in various high risk pregnancies. The course of pregnancy and the obtained laboratory findings were compared with acid-base states of the newborn infants and with perinatal mortality.

Chorionic Gonadotropin↗
PubMed1988

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↗
PubMed1981

Characterization of placental luteinizing hormone-releasing factor-like material.

High pressure liquid chromatography (HPLC) and radioimmunoassay were employed to characterize luteinizing hormone-releasing factor (LRF)-like material in the human placenta. Methanol extracts of the placenta were washed with acetic acid and chloroform, further purified on coarse octadecylsilane columns, fractionated on HPLC, and tested by radioimmunoassay. In HPLC, placental LRF had the same retention time as synthetic LRF, and such fractions gave an inhibition curve which was parallel to that of synthetic LRF in radioimmunoassay. It is concluded that human placental LRF is similar or identical to LRF in the central nervous system.

Chromatography, High Pressure Liquid↗
PubMed1994

[Effect of growth hormone on fetal and placental growth of spontaneous dwarf rat].

The effect of growth hormone on fetal and placental growth was studied in the spontaneous dwarf rat (SDR). The SDR is a newly established experimental model for pituitary growth hormone (GH) deficient dwarfism with an autosomal recessive mode of inheritance. The growth of heterogenic fetuses which were made by crossing female SDRs with normal male rats was similar to that of homogenic SDR fetuses on day 16 of gestation (Day 16), but on Day 20 heterogenic fetuses which had GH in their serum were significantly heavier than homogenic fetuses. There was no significant difference between the two groups in placental weight. The daily infusion of ovine-GH into pregnant SDR caused a significant increase in placental weight on Day 20, but had no effect on fetal growth. These results suggest that fetal GH plays a role in the fetal growth without affecting placental growth, and that maternal GH affects placental growth without affecting fetal growth.

Animals↗
PubMed1994

Placental corticotropin-releasing hormone and the hypercortisolism of pregnancy.

OBJECTIVE: Our purpose was to clarify whether placental corticotropin-releasing hormone regulates pituitary-adrenal function in human pregnancy. STUDY DESIGN: We examined the relationship between maternal plasma corticotropin-releasing hormone concentrations and levels of pituitary-adrenal hormones at 5-week intervals in 21 uncomplicated term pregnancies. RESULTS: Maternal plasma corticotropin-releasing hormone concentrations rose significantly from 115 +/- 45 pg/ml at 11 to 15 weeks to 4346 +/- 754 pg/ml at 36 to 40 weeks (p < 0.001). Afternoon plasma corticotropin concentrations also rose significantly from 8.8 +/- 2.8 pg/ml to 18 +/- 2.6 pg/ml (p < 0.005). Urinary free cortisol concentrations rose from 54.8 +/- 7.3 micrograms per 24 hours to 111 +/- 8.7 micrograms per 24 hours (p < 0.005). Maternal dehydroepiandrosterone sulfate levels fell from 102 +/- 14 micrograms/dl to 63.8 +/- 7.1 micrograms/dl (p < 0.005). Maternal plasma corticotropin-releasing hormone was significantly correlated with afternoon plasma corticotropin concentrations (r = 0.6, p < 0.0001) and with urinary free cortisol concentrations (r = 0.04, p < 0.01). CONCLUSIONS: Similar modest elevations of corticotropin and cortisol, as occur in pregnancy, have been reported in vitro and in vivo studies of long-term administration of corticotropin-releasing hormone. Our findings support the concept that placental corticotropin-releasing hormone modulates pituitary-adrenal function in pregnancy.

Adrenal Cortex Hormones↗
PubMed1982

Effects of growth hormone, prolactin, and placental lactogen on insulin content and release, and deoxyribonucleic acid synthesis in cultured pancreatic islets.

The direct effects of human GH (hGH), ovine pituitary PRL (oPRL), and human chorionic somatomammotropin [placental lactogen (hPL)] on the endocrine pancreas were studied in isolated pancreatic islets maintained in tissue culture. Islets of Langerhans were isolated by collagenase treatment of pancreatic tissue obtained from adult NMRI mice and adult or newborn Wistar rats. The islets were maintained for up to 3 weeks in petri dishes containing tissue culture medium RPMI 1640 supplemented with newborn calf serum or normal human serum. The release of insulin during culture and the islet content of insulin, glucagon, and DNA after culture were determined. The DNA synthesis in the newborn rat islets was evaluated by the incorporation of [methyl-3H]thymidine into islet cell DNA. In mouse islets, 1 micrograms/ml hGH, oPRL, or hPL markedly stimulated insulin release during a 2-week culture period and caused a significant increase in the insulin content in the islets after culture. While hGH did not affect the DNA content in adult mouse islets, an increase was observed in adult rat islets after 2-3 weeks of culture. In islets isolated from 3- to 5-day-old rats cultured for 2 weeks with hGH, there was a 30-40% higher DNA content than that found without hGH. Correspondingly, a significant stimulation of the incorporation of [methyl-3H]thymidine could be demonstrated 24 h after the addition of hGH, oPRL, or hPL. hCG and porcine ACTH had no effect. In conclusion, these results indicate that GH and related hormones have a direct stimulatory effect on both the insulin production and DNA synthesis in isolated islets of Langerhans. Whether the effect is directly on the beta-cell or mediated via locally produced growth factors remains to be determined.

Adrenocorticotropic Hormone↗
PubMed1980

Placental protein and peptide hormone synthesis: impact of maternal nutrition.

The human placenta is an organ with a long period of growth in cell number later succeeded by cessation of cell division but some continued growth in cell size. The RNA concentration and content per cell (RNA/DNA ratio) are reduced between the end of the first trimester and the end of pregnancy, and there is a change in availability of placental chromatin for transcription when incubated in vitro with RNA polymerase II. Synthesis and secretion of placental peptide hormones on membrane-bound polyribosomes also undergo changes during pregnancy. During early pregnancy, levels of human chorionic gonadotropin are maximal, declining in later pregnancy, levels of human chorionic gonadotropin are maximal, declining in later pregnancy. The messenger RNA for this hormone undergoes similar changes in relative amount in the placenta. In contrast, the plasma level of placenta lactogen increases progressively during pregnancy, and in parallel with this, the placenta content of mRNA for this hormone increases throughout later pregnancy. It is concluded that placental programing regulates the relative amounts of mRNA for each hormone, and this in turn determines the amounts secreted at any stage of pregnancy. Nutritional status of the mother can affect placental RNA content, most clearly established in studies on rats in which a diet low in protein or with added alcohol results in a reduced capacity to form and secrete placental lactogen. The extent of this depression parallels the reduction in placental RNA content. It is suggested that underproduction of placental lactogen may be a factor in reducing flow of nutrients from the maternal tissues to the fetus in later pregnancy, under conditions of malnutrition.

Animals↗
PubMed2002

Roles of prolactin and related members of the prolactin/growth hormone/placental lactogen family in angiogenesis.

Prolactin, growth hormone and placental lactogen are members of a family of polypeptide hormones which share structural similarities and biological activities. Numerous functions have been attributed to these hormones, among which stand out their recently discovered effects on angiogenesis, the process by which new blood vessels are formed from the pre-existing microvasculature. Prolactin, growth hormone and placental lactogen, along with two non-classical members of the family, proliferin and proliferin-related protein, can act both as circulating hormones and as paracrine/autocrine factors to either stimulate or inhibit various stages of the formation and remodeling of new blood vessels, including endothelial cell proliferation, migration, protease production and apoptosis. Such opposing actions can reside in similar but independent molecules, as is the case of proliferin and proliferin-related protein, which stimulate and inhibit angiogenesis respectively. The potential to exert opposing effects on angiogenesis can also reside within the same molecule as the parent protein can promote angiogenesis (i.e. prolactin, growth hormone and placental lactogen), but after proteolytic processing the resulting peptide fragment acquires anti-angiogenic properties (i.e. 16 kDa prolactin, 16 kDa growth hormone and 16 kDa placental lactogen). The unique properties of the peptide fragments versus the full-length molecules, the regulation of the protease responsible for specific protein cleavage, the selective expression of specific receptors and their associated signal transduction pathways are issues that are being investigated to further establish the precise contribution of these hormones to angiogenesis under both physiological and pathological situations. In this review article, we summarize the known and speculative issues underlying the effects of the prolactin, growth hormone and placental lactogen family of proteins on angiogenesis, and address important remaining enigmas in this field of research.

Animals↗
PubMed1991

The stimulatory effect of growth hormone, prolactin, and placental lactogen on beta-cell proliferation is not mediated by insulin-like growth factor-I.

The effects of GH, PRL, and placental lactogen (PL) on the proliferation of pancreatic beta-cells in vitro were studied as well as the possible effect of insulin-like growth factor-I (IGF-I) in mediating this effect. Proliferating beta-cells were identified by staining with a monoclonal antibody to bromodeoxyuridine (BrdU) after cells were incubated for 1 h in the presence of 10 microM BrdU. By double staining with insulin antibodies it was found that 6.3% of the beta-cells had incorporated BrdU when cultured for 7 days in the presence of 1 microgram/ml human GH (hGH) compared to 0.6% when cultured in the absence of hGH. Similar results were obtained using rat GH. The half-maximal effect of hGH on beta-cell proliferation was observed at 10 ng/ml, and the maximal effect at 100 ng/ml. Islet cells cultured in the presence of PRL or PL caused a dose-dependent increase in beta-cell proliferation similar to that caused by hGH. GH, PRL, and PL had no effect on the proliferation of glucagon- or somatostatin-producing cells. The addition of 100 ng/ml IGF-I to either control or GH-stimulated islet cells did not affect the labeling index. When GH-stimulated proliferation of beta-cells was measured in the presence of neutralizing concentrations of a rabbit IGF-I antiserum, the percentage of beta-cells incorporating BrdU was unaffected. Using Northern blot analysis, no IGF-I transcripts could be detected in RNA from GH-stimulated islets, whereas IGF-I transcripts were readily detected in RNA isolated from rat liver tissue. These data suggest that the stimulatory effect of GH, PRL, and PL on beta-cell proliferation is not mediated by IGF-I, but, rather, is a direct mitogenic effect on the beta-cell.

Animals↗