Secretion of prolactin and insulin-like growth factor I by decidual explant cultures from pregnancies complicated by intrauterine growth retardation

Complex, coordinated and highly regulated changes in placental signaling and nutrient transport capacity in IUGR

The most common cause of intrauterine growth restriction (IUGR) in the developed world is placental insufficiency, a concept often used synonymously with reduced utero-placental and umbilical blood flows. However, placental insufficiency and IUGR are associated with complex, coordinated and highly regulated changes in placental signaling and nutrient transport including inhibition of insulin and mTOR signaling and down-regulation of specific amino acid transporters, Na⁺/K⁺-ATPase, the Na^+/H⁺-exchanger, folate and lactate transporters. In contrast, placental glucose transport capacity is unaltered and Ca²⁺-ATPase activity and the expression of proteins involved in placental lipid transport are increased in IUGR. These findings are not entirely consistent with the traditional view that the placenta is dysfunctional in IUGR, but rather suggest that the placenta adapts to reduce fetal growth in response to an inability of the mother to allocate resources to the fetus. This new model has implications for the understanding of the mechanisms underpinning IUGR and for the development of intervention strategies.

Endocrine regulation of human fetal growth: the role of the mother, placenta, and fetus

The environment in which the fetus develops is critical for its survival and long-term health. The regulation of normal human fetal growth involves many multidirectional interactions between the mother, placenta, and fetus. The mother supplies nutrients and oxygen to the fetus via the placenta. The fetus influences the provision of maternal nutrients via the placental production of hormones that regulate maternal metabolism. The placenta is the site of exchange between mother and fetus and regulates fetal growth via the production and metabolism of growth-regulating hormones such as IGFs and glucocorticoids. Adequate trophoblast invasion in early pregnancy and increased uteroplacental blood flow ensure sufficient growth of the uterus, placenta, and fetus. The placenta may respond to fetal endocrine signals to increase transport of maternal nutrients by growth of the placenta, by activation of transport systems, and by production of placental hormones to influence maternal physiology and even behavior. There are consequences of poor fetal growth both in the short term and long term, in the form of increased mortality and morbidity. Endocrine regulation of fetal growth involves interactions between the mother, placenta, and fetus, and these effects may program long-term physiology.

Stimulation of hCG protein and mRNA in first trimester villous cytotrophoblast cells in vitro by glycodelin A

AIM

Human chorionic gonadotropin (hCG) is produced by fetal trophoblast cells and secreted into maternal circulation mainly in the first trimester of pregnancy. Another glycoprotein, glycodelin A, is one of the main products of the maternal decidua during this period. The purpose of this study was to investigate the effect of glycodelin A on hCG release by isolated cytotrophoblast cells in vitro.

METHODS

Cytotrophoblast cells were prepared from human first trimester placenta and incubated with varying concentrations of glycodelin A. Supernatants were assayed for hCG protein concentrations, and quantification of beta hCG mRNA was carried out by RT-PCR. Expression of hCG was analysed in stimulated trophoblast cells and in unstimulated controls by immunocytochemistry.

RESULTS

Glycodelin A induces a dose-dependent increase of hCG production. An increase of hCG expression was measured at 100 and 200 microg/mL glycodelin-A treatment in trophoblast cell culture by TaqMan assay on mRNA level. We found a moderate staining of hCG in control trophoblast cells, whereas a strong hCG staining was seen in glycodelin A-treated trophoblast cells.

CONCLUSIONS

HCG is a marker for the differentiation process of trophoblast cells. Our results suggest that glycodelin A secreted by the decidualized endometrium is involved in the regulation of hormones produced by the trophoblast.

Insulin-like growth factor I, epidermal growth factor and transforming growth factor beta expression and their association with intrauterine fetal growth retardation, such as development during human pregnancy

AIM

Fetal intrauterine growth retardation (IUGR) is one of the most common obstetric problems, with a frequency of 12% in Mexico. In the past, investigations have focused on extrinsic causes of IUGR. More recent studies have examined the intrinsic factors that cause fetal intrauterine growth. Maintenance of fetal growth has been attributed to insulin-like growth factor (IGF), epidermal growth factor (EGF) and transforming growth factor beta (TGF-beta). The objective of this study was to assess the levels of these growth factors during pregnancy and to determine whether or not low concentrations are associated with IUGR.

METHODS

Nine women whose pregnancies were complicated by IUGR and a group of nine women whose pregnancies exhibited normal fetal intrauterine growth were studied. IUGR was determined by sonography and confirmed by weight at birth. Venous blood samples were taken from both groups of pregnant women at the end of each trimester. Enzyme-linked immunosorbent assays, immunoradiometric assays and radioimmunoassays were used to process samples, and the results were analysed by anova.

RESULTS

IGF-I levels increased in both groups during pregnancy, but the increase was lower (p < 0.001) in the IUGR group throughout pregnancy and at delivery. EGF did not show any significant changes during pregnancy. Blood TGF-beta levels varied only during the first trimester of pregnancy. The differences were not statistically significant. However, TGF-beta concentrations were higher in the pregnancies with IUGR. Women in the IUGR group were smaller than in the control group (p < 0.05), and, using the covariance test (p < 0.05), this was found to be correlated with IGF-I levels but not with EGF or TGF-beta levels.

CONCLUSIONS

Changes in fetal weight might be explained by the different concentrations of IGF. The structural homology between IGF-1 and insulin could mean that the presence of higher levels of IGF would result in a increased energetic metabolism that could contribute to fetal growth. EGF levels were not related to IUGR, and TGF-beta levels increased only during the first 3 months in the IUGR group. This observation correlates with the in vitro action of TGF-beta as a negative factor of growth, but as a positive support for sustaining early pregnancy. Our data illustrates that low height represents an increased risk factor for IUGR. These data also correlate with the studies involving extrinsic factors.

The effects of L-arginine on the release of prolactin from decidual explants in vitro

OBJECTIVE

Our aim was to elucidate a role for the L -arginine-nitric oxide-cyclic guanosine monophosphate pathway in the control of decidual prolactin release in vitro.

STUDY DESIGN

In decidua obtained from normal vaginal deliveries, we examined the effects of L -arginine; a stable analog of cyclic guanosine monophosphate, 8-bromo-cyclic guanosine monophosphate; and two nitric oxide synthase inhibitors, L -nitro arginine methyl ester (L -NAME) and L -nitro monomethyl arginine (L -NMMA) on the release of prolactin from decidual tissue in vitro.

RESULTS

L -arginine, at 100 micromol/L, produced an increase in medium prolactin concentration after a 2-hour exposure; however, its inactive isomer, D -arginine, at the same concentration, did not. The increase in prolactin release initiated by L -arginine was sustained after a 24-hour incubation. In addition, 8-bromo-cyclic guanosine monophosphate (10 micromol/L) stimulated prolactin release. At 2 hours, the effects of L -arginine were reversed by L -NAME (100 micromol/L), which by itself was without effect. Incubation of tissue with L -NAME for 24 hours inhibited prolactin secretion (24 hours; P <.05, vs control); however, L -NMMA was without effect.

CONCLUSIONS

These results suggest that the L -arginine-nitric oxide-cyclic guanosine monophosphate pathway is involved in the regulation of prolactin secretion by decidual tissue.

Effect of anticardiolipin antibodies on prolactin and insulin-like growth factor binding protein-1 production by human decidual cells

PROBLEM

The effect of anticardiolipin antibodies (ACAs) on basal- and growth factor-stimulated prolactin and insulin-like growth factor (IGF) binding protein (BP)-1 production by cultured human decidual cells was investigated.

METHOD OF THE STUDY

Decidual cells were cultured for 24, 48, or 96 hr in medium supplemented with 5% ACA-containing or 5% control serum and increasing concentrations of insulin (1-10 micrograms/mL) or IGF-1 (10-100 ng/mL).

RESULTS

No significant increase in prolactin production was observed after addition of increasing doses of insulin and IGF-I in the presence of ACA-containing serum, while a dose-dependent stimulation was seen with control serum. Time-dependent prolactin accumulation was also reduced when cells were cultured in the former conditions. IGF BP-1 release was not affected by insulin and IGF-I in the presence of both sera. However, lower IGF BP-1 levels and a less pronounced time-dependent accumulation were observed in the presence of ACA-positive serum.

CONCLUSIONS

Our data suggest that ACAs affect cellular transduction mechanisms regulating critical events, such as decidual cell differentiation. These cellular dysfunctions might be relevant in the induction of some obstetric disorders typical of this syndrome.

The secretion of insulin-like growth factor I, prolactin and insulin-like growth factor binding protein 1 by the decidua as predictors of human fetal growth

To determine if in vitro secretion of the decidual peptides insulin-like growth factor I (IGF-I), prolactin or insulin-like growth factor binding protein 1 (IGFBP-1) correlates with infant birthweight in uncomplicated, term human pregnancies, decidua from 45 pregnancies with normally distributed birthweights was cultured in defined medium for 24 h. IGF-I, prolactin and IGFBP-1 concentrations in the culture medium were measured by radioimmunoassay. Neither infant birthweight nor a normalized measure of infant birthweight (birthweight z-score) correlated with the quantity of IGF-I, prolactin or IGFBP-1 secreted by the decidua from that pregnancy. There were no differences in any of the peptide hormones assayed when the pregnancies were grouped by infant sex. IGF-I and prolactin secretion by individual decidual samples correlated positively. IGF-I and IGFBP-1 secretion also correlated positively in individual samples. A previously identified correlation between decidual IGF-I secretion and infant birthweight among a group of normal and growth restricted (IUGR) pregnancies was not confirmed in the current study. These data indicate that the decrease in decidual IGF-I and prolactin secretion seen in IUGR pregnancies is not the hormone profile of the low birthweight end of a normal population, but a distinct endocrine profile.

Dose-related effect of IGF-I on placental prostanoid release

Prostanoids play an important role throughout all of pregnancy and during the initiation and progress of labor. The human placenta at term produces large quantities of prostanoids, yet little is known of the factors regulating their biosynthesis. In a previous study we observed that insulin-like growth factor I (IGF-I) specifically inhibits thromboxane B2 (TxB2) and prostaglandin F2 alpha (PGF2 alpha) from human term placental explants. In these studies we have defined the dose-related action of IGF-I on the release of placental prostanoids. With use of a perifusion system, the basal release of prostaglandin E2 (PGE2), PGF2 alpha, TxB2 and 6-keto-prostaglandin F1 alpha (6-keto-PGF1 alpha) from human term placental explants increased from the fifth hour in culture, while the release of 13,14-dihydro-15-keto-PGF2 alpha (PGFM) remained constant. The addition of IGF-I (5.2-83.3 ng/mL) to the perifusing medium effected an inhibition of TxB2 and PGF2 alpha. The release of TxB2 was inhibited in a dose-related fashion from the initiation of IGF-I treatment and throughout the five hours of treatment, whereas the inhibition of PGF2 alpha was significant only at a dose of 83.3 ng/mL of IGF-I. Yet, the release of 6-keto-PGF1 alpha, PGE2, or PGFM was not altered by any dose of IGF-I studied. Because both TxB2 and PGF2 alpha are vasoconstrictors, we have proposed that IGF-I may enhance vasodilation in the placenta. Therefore, IGF-I may allow for increased blood flow, thus affecting the maintenance of pregnancy and the supply of nutrients available for the growth of the fetus.