[Sialic acid of glycoconjugates in amniotic fluid].
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Sialic acid is a negatively charged monosaccharide attached to non-reducing end of N- and O-linked carbohydrate chains of glycoconjugates. The claimed biological functions of sialic acid include its participation in cell to cell recognition and interaction as well as affecting the function of receptors by providing binding sites for ligand. Increased sialic acid concentration have been observed in several diseases e.g. malignancies, diabetes, inflammatory disorders, rheumatoid arthritis and alcoholism.The aim of the present work was to determine if the amount of sialic acid attached to glycoconjugates of amniotic fluid changes during pregnancy.The sialic acid content in 47 samples of amniotic fluid derived from pregnant women with gestational age between 13 and 42 was studied by sialic acid specific lectins immunosorbent assay. The patient samples were divided into seven groups.Time dependent changes in the degree of sialylation of glycoconjugates in amniotic fluid during pregnancy, particularly in advanced pregnancy were observed. Moreover, the highest sialic acid content on glycoconjugates in pregnancies complicated by premature rupture of membranes and is prolonged pregnancy were also detected.Sialic acid content determination in amniotic fluid could be a potentially useful marker of inflammation process of amniochorion during pregnancy.Keywords:
Glycoconjugate
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Glycoconjugate
Second trimester
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Sequential changes in maternal and fetal plasma and amniotic fluid concentrations of prolactin (PRL) and growth hormone (GH) were examined after the intravascular administration of thyrotropin releasing hormone (TRH) or L-dopa alone or combined directly to the near-term Rhesus fetus. The neonatal plasma responses to these same stimuli were also examined. Fetal and neonatal plasma PRL levels increased immediately after TRH injection and remained elevated from baseline levels (102–800%) throughout the 45 min sampling period. Maternal plasma PRL levels also increased markedly. Although amniotic fluid concentrations were more variable, the trend was an increase. After L-dopa injection, fetal and neonatal plasma PRL values declined 26-62% from baseline levels. Maternal plasma PRL concentrations also declined 30–50%, but amniotic fluid PRL concentrations progressively increased. When L-dopa and TRH were administered together, fetal plasma PRL levels declined 14–40% from initial levels, but maternal plasma PRL levels did not change in a consistent manner, and amniotic fluid PRL levels remained stable. There was no change from baseline fetal or neonatal plasma GH concentrations in these experiments. The plasma PRL responses of the primate conceptus to these stimuli are consistent with those found in the adult; the unresponsiveness of plasma GH is not. The direction and magnitude of changes in both maternal plasma and amniotic fluid PRL concentrations provide indirect evidence of placental transfer of TRH and L-dopa in some experiments, and require a biophysical explanation not apparent in others.
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Thyroxine (T4), 3,3',5'-tri-iodothyronine (reverse T3; rT3) and di-iodothyronines (3,3'-T2 and 3',5'-T2) were measured in pig amniotic fluid (AF) and allantoic fluid (Al) between 32 and 113 days of normal pregnancy. Low but measurable quantities of T4 in AF and Al (2.1 +/- 0.3 and 3.2 +/- 0.5 nmol/l respectively) were found before the onset of fetal thyroid gland function, which indicates the maternal source of T4. The presence of rT3 (55.8 +/- 4.1 pmol/l in AF and 49.8 +/- 5.3 pmol/l in Al), 3,3'-T2 (45.5 +/- 0.6 pmol/l in AF and 49.2 +/- 9.2 pmol/l in Al) and 3',5'-T2 (20.8 +/- 2.6 pmol/l in AF and 24.0 +/- 2.2 pmol/l in Al) may be attributed to the monodeiodinase system already active in fetal pig tissues in early pregnancy, as demonstrated previously. T3 concentration was undetectable in both AF and Al. An approximately twofold increase in the levels of T4, rT3 and T2s in AF and Al at mid-gestation was observed. T4 and rT3 in AF showed a positive correlation with protein concentrations. AF rT3 concentration (but not T4) correlated with rT3 in the cord and maternal serum. The 3,3'-T2 and 3',5'-T2 in AF and Al showed parallel changes to rT3, while the rT3/3,3'-T2 and rT3/3',5'-T2 molar ratios remained constant. T4 concentrations in AF and Al were markedly lower than in corresponding maternal and fetal serum; the rT3 concentration in Al was equal to that in AF and two to four times lower than in fetal serum. In spite of differences between serum hormone patterns in the pig and human near term, iodothyronine concentrations in AF showed some similarities, mainly the following: undetectable T3, a strong correlation between rT3, T4 and AF total protein and the presence of 3,3'-T2 and 3',5'-T2 in measurable levels. Comparative data for Al, except the ones in the present study in the pig, are not available.
Reverse triiodothyronine
Thyronine
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The concentrations of glycosylated (G-PRL) and nonglycosylated (non-G-PRL) forms of PRL and GH were measured during pregnancy in pigs of lean and obese (high backfat thickness) lines. Pregnant sows of the two genetic lines were killed, in groups of five to eight, at 60, 75, 90, and 105 days of gestation, and their pituitary glands and plasma were analyzed for the two hormones by immunoblotting, lectin-binding, and RIA techniques. In both lean and obese pigs, pituitary concentrations of G-PRL and non-G-PRL increased with advance in pregnancy, but there were no significant changes in either form of pituitary GH. Plasma concentrations of radioimmunoassayable PRL also increased with advance in pregnancy, with no consistent changes in serum GH concentrations. The dominant PRL constituent in plasma during the second half of pregnancy was G-PRL, and its concentration either increased or remained constant with advance in pregnancy. In contrast, plasma non- G-PRL concentrations decreased with advance in pregnancy in both lines of pigs, resulting in a steady rise in the plasma GPRL/ PRL ratio toward term. Compared to lean pigs, obese pigs had less radioimmunoassayable PRL and GH in their plasma and less GH (glycosylated as well as nonglycosylated) in their pituitary glands, but obese pigs had more G-PRL in their pituitary glands than lean pigs, and their plasma G-PRL levels tended to be higher and non-G-PRL levels lower than those of lean pigs. Pituitary concentrations of non-G-PRL in the two lines of pigs were similar. Overall, the results show a preponderance of G-PRL over non-G-PRL in the plasma of pregnant sows, with a preferential secretion of the glycosylated form during the latter half of pregnancy. Furthermore, they indicate a prevalence of higher G-PRL/PRL ratios in the pituitary glands of obese than lean pigs. These findings raise the possibility of a functional role for the glycosylated variant of PRL in the initiation and/or maintenance of events associated with pregnancy and obesity in the pig. (Endocrinology127: 410–418, 1990)
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Glycoconjugate
Sialidase
Asialoglycoprotein receptor
Oligosaccharide
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In order to ascertain whether the diminished pituitary growth hormone (HGH) response observed in late pregnancy may be quantitatively related to the duration of gestation, sequential studies in the HGH responses to insulin-induced hypoglycemia were made during each trimester of pregnancy and at 6–7 weeks post partum in 10 non-obese subjects. The HGH responsiveness to hypoglycemia was progressively diminished during the 3 trimesters and became blunted during the last trimester of pregnancy when compared with their own postpartum controls. Normal brisk HGH response to hypoglycemia was observed at 6–7 weeks post partum. Although the presence of a large quantity of circulating human placental lactogen may account for the inhibitory effect on the hypothalamic-pituitary HGH releasing mechanism in late pregnancy, other hormonal factors such as elevated progesterone and nonprotein-bound cortisol may play a role in the suppressive effect on HGH release during early pregnancy.
Human placental lactogen
Placental lactogen
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Sialic acid (Sia) is a highly important constituent of glycoconjugates, such as N- and O-glycans or glycolipids. Due to its position at the non-reducing termini of oligo- and polysaccharides, as well as its unique chemical characteristics, sialic acid is involved in a multitude of different receptor-ligand interactions. By modifying the expression of sialic acid on the cell surface, sialic acid-dependent interactions will consequently be influenced. This can be helpful to investigate sialic acid-dependent interactions and has the potential to influence certain diseases in a beneficial way. Via metabolic glycoengineering (MGE), the expression of sialic acid on the cell surface can be modulated. Herein, cells, tissues, or even entire animals are treated with C2-modified derivatives of N-acetylmannosamine (ManNAc). These amino sugars act as sialic acid precursor molecules and therefore are metabolized to the corresponding sialic acid species and expressed on glycoconjugates. Applying this method produces intriguing effects on various biological processes. For example, it can drastically reduce the expression of polysialic acid (polySia) in treated neuronal cells and thus affects neuronal growth and differentiation. Here, we show the chemical synthesis of two of the most common C2-modified N-acylmannosamine derivatives, N-propionylmannosamine (ManNProp) as well as N-butanoylmannosamine (ManNBut), and further show how these non-natural amino sugars can be applied in cell culture experiments. The expression of modified sialic acid species is quantified by high performance liquid chromatography (HPLC) and further analyzed via mass spectrometry. The effects on polysialic acid expression are elucidated via Western blot using a commercially available polysialic acid antibody.
Polysialic acid
Glycoconjugate
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Dynamic changes in the pituitary-thyroid axis were studied during pregnancy and lactation by measuring plasma concentrations of TSH, T4, and T3 and the free T4 fraction (FT4F) in the rat. In contrast to human pregnancy, plasma T4 progressively decreased during the second half of pregnancy to as low as 2.6 ±0.2 /μg/dl by term compared with 6.3 ± 0.3 /μg/dl on day 0 of pregnancy (P < 0.01). Plasma T3 concentration underwent a smaller proportional decrease than plasma T4 (66.5 ± 6.2 ng/dl at day 0 vs. 44.6 ± 4.9 at term; P < 0.05). Despite the dramatic drop in T4) plasma TSH remained at normal levels until the 16th day of pregnancy, after which a slight, but significant, increase was seen. FT4F was twice as high during late pregnancy as in nonpregnant rats, but the free T4 concentration index was significantly lower. After delivery, high plasma TSH and low thyroid hormone levels persisted throughout lactation and returned to normal only after weaning. In rats whose pups were removed shortly after delivery (nonlactating), these hormones returned to the normal ranges within a few days. FT4F became normal in both lactating and nonlactating rats after delivery, but the free T4 concentration index was significantly lower in the former. There was a significant reduction of plasma T4 in sucklings when their nursing mother was thyroidectomized. However, nearly normal levels of plasma T4 were maintained in sucklings whose thyroidectomized mother was supplemented with a physiological replacement dose of T4. Our findings suggest that the decrease in the concentration of plasma thyroid hormones during pregnancy, at least in part, results from a decreased binding capacity of plasma proteins, and, in contrast, that the decrease in plasma thyroid hormone concentration during lactation probably results from a loss of thyroid hormones into milk. In rats, the relative hypothyroid state in pregnancy thus appears to be due to a different mechanism than that in lactation.
Hypothalamic–pituitary–thyroid axis
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Sialic acid is a negatively charged monosaccharide attached to non-reducing end of N- and O-linked carbohydrate chains of glycoconjugates. The claimed biological functions of sialic acid include its participation in cell to cell recognition and interaction as well as affecting the function of receptors by providing binding sites for ligand. Increased sialic acid concentration have been observed in several diseases e.g. malignancies, diabetes, inflammatory disorders, rheumatoid arthritis and alcoholism.The aim of the present work was to determine if the amount of sialic acid attached to glycoconjugates of amniotic fluid changes during pregnancy.The sialic acid content in 47 samples of amniotic fluid derived from pregnant women with gestational age between 13 and 42 was studied by sialic acid specific lectins immunosorbent assay. The patient samples were divided into seven groups.Time dependent changes in the degree of sialylation of glycoconjugates in amniotic fluid during pregnancy, particularly in advanced pregnancy were observed. Moreover, the highest sialic acid content on glycoconjugates in pregnancies complicated by premature rupture of membranes and is prolonged pregnancy were also detected.Sialic acid content determination in amniotic fluid could be a potentially useful marker of inflammation process of amniochorion during pregnancy.
Glycoconjugate
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