Secretion of corticotropin-releasing hormone by superfused human placental fragments

The physiological roles of placental corticotropin releasing hormone in pregnancy and childbirth

In response to stress, the hypothalamus releases cortiticotropin releasing hormone (CRH) that travels to the anterior pituitary, where it stimulates the release of adrenocorticotropic hormone (ACTH). ACTH travels to the adrenal cortex, where it stimulates the release of cortisol and other steroids that liberate energy stores to cope with the stress. During pregnancy, the placenta synthesises CRH and releases it into the bloodstream at increasing levels to reach concentrations 1,000 to 10, 000 times of that found in the non-pregnant individual. Urocortins, which are CRH analogues are also secreted by the placenta. Desensitisation of the maternal pituitary to CRH and resetting after birth may be a factor in post-partum depression. Recently, CRH has been found to modulate glucose transporter (GLUT) proteins in placental tissue, and therefore there may be a link between CRH levels and foetal growth. Evidence suggests CRH is involved in the timing of birth by modulating signalling systems that control the contractile properties of the myometrium. In the placenta, cortisol stimulates CRH synthesis via activation of nuclear factor kappa B (NF-κB), a component in a cellular messenger system that may also be triggered by stressors such as hypoxia and infection, indicating that intrauterine stress could bring forward childbirth and cause low birth weight infants. Such infants could suffer health issues into their adult life as a result of foetal programming. Future treatment of these problems with CRH antagonists is an exciting possibility.

Placental corticotrophin-releasing hormone, local effects and fetomaternal endocrinology

The human placenta produces corticotrophin-releasing hormone (CRH) in exponentially increasing amounts during pregnancy with peak levels during labour. CRH in human pregnancy appears to be involved in many aspects of pregnancy including placental bloodflow, placental prostaglandin production, myornetrial function, fetal pituitary and adrenal function and the maternal stress axis. Since fetal cortisol levels are associated with pulmonary development and maturity, placental CRH may have an indirect role in fetal development.Although the precise role of placental CRH in the regulation of gestational length and timing of parturition is unclear it appears to be involved in a placental clock. While glucocorticoids inhibit hypothalamic CRH production they stimulate CRH gene expression in the placenta.This difference may allow the fetal and maternal stress axes to influence this placental clock.Maternal CRH levels are elevated in many pathological conditions of pregnancy where fetal well-being is compromised, and in these situations it may act to maintain a stable intrauterine environment. Therefore, CRH appears to link placental function, maternal well-being, fetal well-being and fetal development to the duration of gestation and the timing of parturition.

Activation of L-type calcium channels induces corticotropin-releasing factor secretion from human placental trophoblasts

The ultimate outcome of pregnancy, parturition, is a well orchestrated process in which placental corticotropin-releasing factor (CRF) seems to play an important role. The objective of the present study was to investigate the involvement of L-type calcium channels and calcium-dependent signaling in the depolarization-induced CRF release from human syncytiotrophoblast. The basal secretion of CRF by trophoblastic cells, isolated from human term placenta, was maximal after their functional differentiation, which was monitored by hCG measurements. On the fourth day of culture, the basal CRF secretion of the cells in serum-free medium was linear between 2 and 8 h. Incubation of the trophoblasts with KCl, a depolarizing stimulus, or with Bay K8644, an L-type calcium channel agonist, for 3 or 8 h led to an increase in CRF secretion, but was without effect on its synthesis. This stimulated CRF release was calcium dependent, as it could be prevented by loading cells with 1,2-bis(0-Aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (acetoxymethyl) ester. Furthermore, the KCl-induced CRF secretion involved L-type calcium channels activation, as 2 micromol/L nitrendipine, an L-type specific blocker, abolished the stimulation. In trophoblasts, where we have previously shown calcium-dependent protein kinase C (cPKCs) activity, incubation with Bay K8644 also stimulated calcium calmodulin kinase II (CaMKII) and extracellular regulated kinase activities. In the present study we observed that CaMKII and cPKCs were linked to the Bay K8644-induced secretion of CRF, as only the autocamtide-2 related inhibitory peptide, a CaMKII inhibitor, and Gö6976, an inhibitor of mu and cPKCs partially prevented (30-78%) the activation of CRF release by Bay K8644. The use of PD 098056, an inhibitor of the ERKs kinases, showed no effect on CRF release. Taken together, these results support a depolarization-induced and calcium-dependent exocytotic-like secretion of CRF from human placental trophoblasts. In addition, CaMKII and cPKCs seem to be potential modulators or mediators of these calcium effects on CRF secretion.

Characterization of neuropeptide Y-mediated corticotropin-releasing factor synthesis and release from human placental trophoblasts

Neuropeptide Y (NPY) is a CRF secretagogue for human placental cells in culture. We have studied the involvement of intracellular calcium and calcium-dependent signaling in the NPY-induced CRF release in trophoblastic cells. The incubation of trophoblasts with NPY for 3 and 8 h led to a dose-dependent increase in CRF secretion. Also, NPY stimulated synthesis of this peptide hormone upon an 8-h incubation period. BIBP3226, a selective Y1 receptor antagonist, and pertussis toxin (PTX) eliminated these effects. NPY-stimulated CRF secretion was mostly prevented by loading cells with BAPTA-AM, suggesting that elevation of intracellular calcium is responsible for the increase of CRF secretion. However, this calcium chelator had no effect on CRF synthesis. Furthermore, U-73122, a phospholipase C-betas (PLC) inhibitor or xestospongin C, an inositol triphosphate receptor (InsP3-R) blocker, have partially prevented the effect of NPY on CRF synthesis and secretion. Therefore, the increase in CRF synthesis and secretion rely in part on the release of calcium from intracellular store. Interestingly, SKF 96365, an inhibitor of store operated calcium (SOC) influx, also partially blocked the NPY stimulatory effect on CRF release but not its synthesis, suggesting that calcium influx is also involved in this stimulation. In the syncytiotrophoblast, known to possess a NPY-activated protein kinase C (PKCs) activity, NPY also stimulated calcium calmodulin kinase II (CaMKII) and extracellular regulated kinase (ERK1/2) activities. In the present study, we observed that bisindolylmaleimide (BIM), a nonspecific PKCs inhibitor partially prevented the NPY-induced CRF release. On the other hand, autocamtide-2 related inhibitory peptide (AIP), a CaMKII inhibitor, prevented most of the stimulatory effect of NPY on both CRF synthesis and release. Go6976, an inhibitor of the conventional and mu PKCs and PD 098059, an inhibitor of the ERK cascade, had no effect on neither CRF synthesis nor release. Altogether, these results support a Y1 receptor-mediated PTX-sensitive induction on CRF synthesis and release by NPY from human placental trophoblasts. The stimulation of CRF synthesis by NPY seems to depend mainly on a PLC-beta to InsP3-R axis and on CaMKII activity. Also, the release of CRF depends on the PLC-beta to InsP3-R axis and CaMKII activity but also entails the participation of a calcium-independent PKCs.

Corticotropin releasing hormone: therapeutic implications and medicinal chemistry developments

Corticotropin releasing hormone (CRH, sometimes known as CRF) is an endogenous 41 amino acid peptide that has been implicated in the onset of pregnancy, the 'fight or flight' response, in addition to a large number of physiological disorders. Recently, medicinal chemists have developed a number of potent and selective compounds that show promise in a vast array of therapeutic uses. Herein we review the current status of research.

Urocortin in human placenta and maternal plasma

Plasma immunoreactive (IR-) urocortin (Ucn) and corticotropin-releasing factor (CRF) levels in pregnant women were measured by their specific radioimmunoassays after extraction. Although plasma IR-CRF levels were increased in pregnant women as compared to men and non-pregnant women, there was no difference of plasma IR-Ucn levels among groups. Ucn mRNA was detected in cytotrophoblasts and syncytiotrophoblasts by in situ hybridization. A reverse-phase high-performance liquid chromatography (HPLC) showed the major peak of IR-Ucn in placenta and plasma that had similar chromatographic mobility to synthetic Ucn1-40. These data suggest that Ucn is produced and processed into the same form of synthetic Ucn in placenta, but not secreted into maternal blood.

Steroid-protein interaction in human placenta

Human placenta produces a large variety of bioactive substances with endocrine and neural competence: pituitary and gonadal hormones, hypothalamic-like releasing or inhibiting hormones, growth factors, cytokines and neuropeptides. The most recent findings indicate that locally produced hormones regulate the secretion of other placental hormones supporting a paracrine/autocrine regulation. In placental endocrinology, a particular relevance is played by steroid hormones. In fact, a specific gonadotropin-releasing hormone (GnRH)-human chorionic gonadotropin (hCG) regulation of placental steroidogenesis has been proposed as a placental internal regulatory system acting on steroids production from human placenta. In addition, activin and inhibin have been proposed as further regulatory substances of the synthesis and secretion of steroids; the addition of activin A to placental culture augments GnRH, hCG and progesterone, and this effect can be significantly reduced by the addition of inhibins. Finally, a steroid-steroid interaction is suggested by the evidence that placental estrogen has a positive role in the regulation of progesterone biosynthesis. Other steroid-protein interactions have been observed in human placenta. In fact, recent data indicate that progesterone inhibits placental corticotropin-releasing factor (CRF) and estrogens act on placental conversion of cortisol to cortisone, activating cortisol secretion by the fetal adrenal and enhancing fetal adrenal function with advancing gestation.

The effect of pre-eclampsia on human placental corticotrophin-releasing hormone content and processing

Prior studies have shown that levels of corticotrophin-releasing hormone (CRH) in the umbilical cord blood of infants born after pregnancies complicated by pre-eclampsia are significantly higher than fetal plasma CRH concentrations in uncomplicated pregnancies. In the present study we have measured CRH by radioimmunoassay in the placenta and fetal membranes from 13 pregnancies complicated by pre-eclampsia and compared them to 24 uncomplicated pregnancies. In addition we have investigated the effect of chronic intrauterine fetal stress on the processing of CRH in the placenta and fetal membranes. Placental CRH peptide content was significantly higher in the pregnancies complicated by pre-eclampsia, 12,900 +/- 4230 pg/g tissue, than in the uncomplicated pregnancies, 3130 +/- 430 pg/g of tissue (P < 0.01). Gel filtration of the homogenates of normal placenta revealed a major peak of CRH immunoactivity eluting in the same position as synthetic human CRH. A second smaller molecular weight peak of CRH-immunoactivity was also present and in both the amnion and the chorion, the CRH eluted in the position of the smaller molecular weight peak. In contrast, the bulk of the CRH immunoactivity in the placenta and fetal membranes obtained after pregnancies complicated by pre-eclampsia eluted in the position of intact synthetic human CRH. Thus, in pregnancy complicated by pre-eclampsia, both placental CRH release into fetal plasma and CRH peptide content is higher than in uncomplicated pregnancy.

Neuroendocrinology of the hypothalamo-pituitary-adrenal axis in pregnancy and the puerperium

Plasma cortisol, adrenocorticotrophic hormone (ACTH), beta-endorphin and corticotrophin releasing hormone or factor (CRF) all rise progressively as pregnancy advances, and fall postnatally. The placenta produces large amounts of CRF in the third trimester and this is released into the maternal circulation. Present evidence suggests that it stimulates the maternal pituitary to produce ACTH while desensitizing the maternal pituitary to further stimulation with CRF. Maternal control of ACTH production is retained, allowing a persistent response to stress and a diurnal rhythm, perhaps through the secretion of vasopressin. The placenta also produces pro-opiomelanocortin peptides; however, the nature of the fragments produced from the precursor differs from that formed in the anterior pituitary of the mother and the role of these fragments in the control of maternal adrenal function is unclear. These changes in the hypothalamo-pituitary-adrenal axis during pregnancy are associated with loss of the normal suppression of cortisol by dexamethasone and elevated basal levels of cortisol with preservation of a diurnal rhythm, features also found in some patients with endogenous depression. Several studies have suggested a relationship between alterations in maternal concentrations of cortisol and beta-endorphin and the development of postnatal mood disturbances.

The corticotrophin releasing hormone test in late pregnancy: lack of adrenocorticotrophin and cortisol response

Biologically active corticotrophin-releasing-hormone (CRH) is produced by the placenta in large amounts and can be measured in the maternal circulation during third trimester of pregnancy. Its physiological significance is unknown. To further investigate the action of CRH in pregnancy, we performed a standard CRH-test (1 micrograms/kg synthetic human CRH) in seven pregnant women 1 week prior to their calculated delivery data and 4-5 weeks post-partum. No response of plasma ACTH to CRH administration could be measured in any of the third trimester pregnant women. Post-partum, basal ACTH levels were significantly lower (1.6 +/- 0.3 vs 5.3 +/- 0.2 pmol/l) and reacted promptly to CRH administration (1.6 +/- 0.3-4.2 +/- 0.5 pmol/l; P less than 0.05). Concentration of cortisol in plasma and salivary cortisol paralleled the ACTH response to administration of CRH. However, one pregnant woman experienced physical and emotional stress during the CRH-test and reacted with a sharp rise in cortisol secretion. The lack of the ACTH and cortisol response in this study to exogenously administered CRH in third trimester pregnancy may be due to high circulating glucocorticoid concentrations, desensitization of the pituitary corticotroph and/or in part due to circulating specific CRH-carrier protein.

Intracellular mechanisms governing the acute phase of beta-endorphin secretion from the corticotrope in vitro

It is not certain which protein kinase (A, C or both) is involved in the acute phase of beta-endorphin (beta-EP) release stimulated in the corticotrope by vasopressin (VP) and corticotropin-releasing factor (CRF). We have employed an isolated ovine anterior pituitary cell superfusion system to determine the dynamic effects of forskolin, a protein kinase A (PKA) stimulator, and phorbol 12-myristate 13-acetate (PMA), a protein kinase C (PKC) activator. Both secretagogues stimulated beta-EP release within 5 min and therefore both PKA and PKC are potential mediators of the acute phase of hormonal stimulation of the corticotrope. Pretreatment with PMA specifically desensitized the pituitary cell columns to subsequent PMA exposure while not significantly altering sensitivity to forskolin or 50 mM KCl.

Large Molecular Weight Immunoreactive Corticotrophin-Releasing Hormone has Bioactivity on Superfused Ovine Pituitary Cells

Abstract Human placental extracts fractionated with Sephadex G-50 produced three peaks of corticotrophin-releasing hormone immunoreactivity, a large molecular weight peak (M(r)30,000), an intermediate peak (4,758 < M(r) < 10,000) and a low molecular weight peak coeluting with the 41-residue hormone. All three peaks of immunoreactivity stimulated the release of beta-endorphin-like immunoreactivity from ovine pituitary cells superfused in vitro. No response was observed from unstimulated cells superfused in parallel. Gel chromatography indicated that intermediate and small molecular weight forms of human corticotrophin-releasing hormone immunoreactivity remained intact after contact with the ovine pituitary cells, whereas the large molecular weight material dissociated to produce 41-residue hormone immunoreactivity. The secreted beta-endorphin immunoreactivity was shown by gel chromatography to comprise both beta-lipotrophin-like and the 31-residue beta-endorphin-like immunoreactivity. The data show that the intermediate and low molecular weight forms of placental corticotrophin-releasing hormone immunoreactivity are bioactive and suggest that the intermediate form is a hormone precursor, possibly procorticotrophin-releasing hormone(125-196), and the small form is identical to the hypothalamic hormone. The results with the larger molecular weight material indicate that it is likely to be a complex of the mature 41-residue hormone and a binding protein.