Placental neurohormones: secretion and physiological implications

Correlation between second trimester maternal serum inhibin-A and human chorionic gonadotrophin for the prediction of pre-eclampsia

We aimed to investigate the relationship between inhibin-A and human chorionic gonadotrophin (hCG) concentrations in the second trimester in the same cohort of women and compare their screening efficiency for the subsequent development of pre-eclampsia. The main outcome measures were pre-eclampsia and pre-eclampsia requiring delivery before 37 weeks.We carried out a retrospective examination of inhibin-A and free beta-hCG levels taken between 15 and 19 weeks of gestation, from 685 women. The values were corrected for weight and gestation and presented as multiples of the median (MoM). Receiver operator characteristic (ROC) curves for the prediction of pre-eclampsia and pre-eclampsia requiring delivery before 37 weeks were created for both analytes alone and in combination. Based on this data the sensitivities for the prediction of pre-eclampsia using inhibin-A and hCG, alone and in combination were examined for a specificity of 90 per cent.Thirty-five (5.5 per cent) women developed pre-eclampsia, of whom 15 (2.7 per cent) required delivery before term as a result of pre-eclampsia. There was no correlation between inhibin-A and hCG for the whole population (r=0.08) but there was a significant correlation for women who subsequently developed pre-eclampsia (r=0.648) or preterm pre-eclampsia (r=0.84). For a specificity of 90 per cent the sensitivity using inhibin-A was significantly better than for hCG (48.6 per cent versus 31.4 per cent, P< 0.05). The results were similar for preterm pre-eclampsia (P< 0.05). The addition of hCG data to inhibin-A data did not improve the sensitivity for pre-eclampsia compared to inhibin-A alone (42.9 per cent versus 48.6 per cent, P< 0.20).Inhibin-A is a more sensitive marker for the subsequent development of pre-eclampsia than hCG. Addition of hCG data to inhibin-A did not improve the screening efficacy for pre-eclampsia suggesting that inhibin-A and hCG are markers of the same underlying pathological process.

Paracrine regulation of human placenta: control of hormonogenesis

There is much evidence indicating that the human placenta plays a very important role in modulating the endocrinology of pregnancy. Placental tissue produces cytokines, hormones and growth factors that are essential in the regulation of the feto-maternal unit. The production of these substances is regulated by a network of interactions within and between intra-uterine through paracrine and/or autocrine mechanisms. Communication between the gestational intra-uterine tissues is critical for successful pregnancy, from the earliest stage of implantation until the expulsive phase of delivery. This is confirmed by the demonstration that the human placenta directly controls the release of substances such as hCG, hPL, steroid hormones and prostaglandins. Furthermore, there is evidence that intra-uterine tissues also can regulate ACTH release and have effects on the hypothalamus-pituitary-gonadal axis and the hypothalamus-pituitary-adrenal axis. The set of data reported in this article confirms that the placenta must be considered an organ that is essential for the initiation, maintenance and successful conclusion of pregnancy and that an imbalance between the complex network of placental regulating systems may cause serious gestational disorders.

The human placental renin-angiotensin system

The human placenta and related tissues are considered to be examples of the recently accepted local renin-angiotensin systems (RAS). The brain is another example of a system that is thought to be regulated independently of the kidney and the role of angiotensin within the CNS as a neural mediator has drawn considerable attention. It has been known for a long time that many of the neuroendocrine mediators and receptors are expressed in the placenta and it has been suggested that there are many parallels between the classical neuroendocrine system and the placental one. The present review summarizes information that components of the RAS are expressed in uteroplacental tissues, are regulated by endogenous substances, and have important biological functions within this reproductive system. A comparison of similarities and differences between the classical and the placental RAS may provide clues to functions in other endocrine and neuroendocrine systems. The major components of the placental RAS that are considered are renin, prorenin, angiotensin I, angiotensin II, angiotensin converting enzyme (ACE), angiotensin receptors, and angiotensinogen (renin substrate). The factors that regulate these components at the cellular and the nuclear level are described. It is concluded that prorenin via angiotensin-dependent and angiotensin-independent mechanisms influences functions within uteroplacental tissues. Some of these actions are direct and others are mediated by the release of different signalling molecules. These features are similar to many neuroendocrine systems and utilize some of the same messengers.

The effect of hypoxia on human trophoblast in culture: morphology, glucose transport and metabolism

The response to hypoxia of trophoblast isolated from term placenta and maintained in culture was studied. Trophoblast exposed to normoxic (PO2 120-130 mmHg) or hypoxic (PO2 12-14 mmHg) conditions were examined by electron microscopy. After 48 h, the cytoplasm of the hypoxic cells was more electron-dense with increased numbers of mitochondria, lysosomes and vacuoles. Compared to normoxic cells, the surface microvilli of the hypoxic cells were sparse, short and unevenly distributed. [3H]thymidine incorporation by both hypoxic and normoxic trophoblast fell rapidly and equivalently after 2 days in culture. The percentage of cells with the proliferation-associated nuclear antigen, Ki 67, also decreased, but remained higher in hypoxic cells suggesting that hypoxia retarded completion of the cell cycle (normoxia, 10.80 +/- 2.51 s.e.; hypoxia, 19.87 +/- 2.73, P < 0.01). Glucose consumption was elevated in hypoxia (3.73 +/- 1.07 s.e. mumol/10(6) cells/24 h) as compared to normoxia (1.46 +/- 0.83, P = 0.01). Although lactate production was consistently higher in hypoxia, the difference was not statistically significant (hypoxia 5.38 +/- 1.54 mumol/10(6) cells/24 h versus normoxia, 1.52 +/- 0.29, P = 0.07). After 48 h, uptake of [3H]2-deoxglucose ([3H]2DG) by hypoxic cells was reduced to 12 per cent +/- 4.3 s.e. of that in normoxic cells; return to normoxia resulted in recovery within 10 min. Lineweaver-Burk plots of [3H]2DG uptake indicated high affinity (KM 2.2 +/- 0.4 x 10(-4) M) and low affinity transporters (KM 4.5 +/- 1.6 x 10(-3) M). Northern blot analysis identified mRNA for GLUT1 and GLUT3. In hypoxia, steady-state GLUT1 and GLUT3 mRNA were approximately three- and 10-fold higher than in normoxia respectively. Inhibitors of oxidative metabolism of glucose increased the uptake of [3H]2DG within 2 h, whereas hypoxia reduced uptake. Hence, trophoblast in culture survives in extreme hypoxia, but manifests striking changes in morphology and in glucose metabolism and transport. Completion of cell cycle appears to be retarded.

Interaction of D2-dopamine receptor with two pertussis toxin sensitive G proteins in human placenta

We have demonstrated the presence in human placenta of D2 dopamine receptors (D2R) which inhibit human placental lactogen (hPL) release. This inhibitory effect of dopamine (DA) was sensitive to pertussis toxin (PTX) indicating that it may be mediated by the Gi/Go family of G proteins. However, nothing is known on this G proteins/D2R interaction in human placenta. In this study, we demonstrate that DA (10(-4) M) inhibits by 39% the ADP-ribosylation by PTX of two G proteins of 40 and 41 kDa. This inhibition is receptor specific since it is reversed by spiperone, a D2R antagonist. Moreover we show that bromocriptine, a D2 agonist, inhibited the labeling of these two proteins in a dose-dependent manner with a maximal inhibition of 37% at a concentration of 10(-6) M. In order to understand the role of D2R in placental endocrinology, we have analyzed the interactions of these two PTX-sensitive G proteins with D2R in normal and abnormal pregnancies. The autoradiographs of both PTX ADP-ribosylated placental proteins of 40 and 41 kDa showed differential labeling during normal pregnancy. Thus, the relative levels of ADP-ribosylation by PTX of both proteins were 2.5 and 3.0 fold lower at term than those observed during first and second trimester whereas no difference was observed between the first and second trimester. Also, no significant change in the level of inhibition by DA was observed between 7-9 weeks and 18-40 weeks of pregnancies (35-45% inhibition). However, we observed a maximal inhibition between 10 to 17 weeks of pregnancy (64% inhibition). In placentas from preeclamptic pregnancies, the levels of ADP-ribosylation were similar to those observed in normal pregnancy, while the DA inhibition was increased by 24%. The levels of ADP-ribosylation in molar placentas reached 20% of normal values, while no difference in DA inhibition was observed. This study demonstrates that two distinct PTX-sensitive G proteins are coupled to human placental D2R. The physiological significance of the variations in these ADP-ribosylated-G proteins/D2R interaction during normal and preeclamptic pregnancies remains to be investigated.

Localization and distribution of vasoactive neuropeptides in the human placenta

Neuropeptides play an important role in the regional regulation of blood flow and hormone secretion. Few studies report the presence of peptides in the human placenta. Our experiment evaluates neuropeptides in the human placenta using immunocytochemical techniques. Representative tissue sections from full-term placentae were fixed immediately after delivery and processed into paraffin sections or frozen. They were treated with multiple immunofluorescence, streptavidin-biotin-peroxidase complex and immunogold-silver staining techniques in combination with well-established monoclonal and polyclonal antibodies, using appropriate absorption controls to ensure the validity of the staining. Vasoactive intestinal polypeptide (VIP), calcitonin gene-related peptide (CGRP), neuropeptide tyrosine (NPY), galanin, somatostatin, met-enkephaline, helodermin and substance P-like immunoreactivities were demonstrated within decidual cells. Endothelin-1 was found in both trophoblasts and endothelial cells. Peptide immunoreactivities in the human placenta especially at the decidual interface between mother and fetus supports a role for the diffuse neuroendocrine system (DNES) in the regulation of placental blood flow critical for fetal growth and development.

The discomforts of pregnancy

During pregnancy, women may experience one or more of a wide variety of discomforts. Every pregnancy is different; discomforts felt during one pregnancy may not appear in another. Most discomforts experienced during pregnancy are thought to be the result of abundant hormonal changes. As pregnancy progresses, other discomforts are attributed to physical changes associated with the enlarging uterus. Selected discomforts of pregnancy are presented with suggestions for clinical management. Nurses can do something to decrease discomforts associated with pregnancy.

D2-dopamine agonists inhibit adenosine 3':5'-cyclic monophosphate (cAMP) production in human term trophoblastic cells

We previously reported that dopamine (DA) acted via D2-dopamine receptors on human trophoblastic cells to inhibit basal and hormone-stimulated secretion of human placental lactogen (hPL). We also described that these DA effects were coupled with inhibition of calcium influx. The present study examines the interaction of placental D2-dopamine receptor with adenylate cyclase (AC). Incubations of isolated human term trophoblastic cells with R(-)-propylapomorphine (NPA), (+/-)-PPHT, and bromocriptine (3 different D2 agonists) led to time- and dose-dependent inhibitions of cAMP production as determined by measuring the conversion of [2-3H]-ATP into [2-3H]-cAMP. The maximal inhibition was reached after 15 min of incubation and was 33 +/- 1 (SE) %, 29 +/- 3% and 31 +/- 1% for bromocriptine (10(-5) M), NPA (10(-7) M) and (+/-)-PPHT (10(-8) M) respectively. However, the time- and dose-dependent curves were biphasic with NPA and (+/-)-PPHT and the inhibition of cAMP production was abolished at higher agonist concentrations or after time incubations longer than 15 min. These inhibitions were receptor specific since they were reversed by spiperone and haloperidol, two specific--dopamine antagonist, and by butaclamol (mix D2/D1-dopamine antagonists) but not by alpha- and beta-adrenergic, D1- and D4-dopaminergic, and 5-HT2-serotonergic antagonists. The results reported here suggest that human placental D2 receptors interact with AC to inhibit its activity. Also, bromocriptine seems a better agonist for the characterization of dopaminergic effects on human placenta.

Corticotropin-releasing hormone modulates cytokines release in cultured human peripheral blood mononuclear cells

Immune and neuroendocrine systems interact at various levels. In particular, either cytokines activate the hypothalamus-pituitary-adrenal axis (HPA) or corticotropin-releasing hormone (CRH) induces the release of beta-endorphin from peripheral human mononuclear cells. The aim of the present study was to investigate whether CRH may affect cytokine production and activity in human peripheral blood mononuclear cells (PBMC). Primary cultures of human PBMC and monocytes were used. They were incubated in presence of different doses of synthetic human CRH. Media were collected and interleukin-1 beta (IL-1 beta) and interleukin-6 (IL-6) levels were measured by ELISA, while interferon-gamma (IFN-gamma) levels were measured by bioassay. In addition, phytohemoagglutinin-induced lymphocyte proliferation was evaluated by testing [3H]thymidine incorporation in the presence of various doses of CRH. CRH significantly increased IL-6 release from PBMC (p < 0.01). The addition of CRH to PBMC significantly decreased IFN-gamma levels, in a dose dependent manner (p < 0.01). No significant effect of CRH was observed on lymphocyte proliferation or IL-1 beta production. The present results suggest a role for CRH as a paracrine mediator for human immune cells, increasing the evidence of a clear correlation between immune and neuroendocrine system.