Urocortin in human placenta and maternal plasma

Urocortin Protects Coronary Endothelial Function During Ischemia-Reperfusion: A Brief Communication

Urocortin is a vasodilator peptide related to corticotrophin-releasing factor, which may protect myocardium during coronary ischemia-reperfusion. To study whether urocortin also protects coronary endothelial function during ischemia-reperfusion, hearts from Sprague-Dawley rats were perfused at constant flow and then exposed to 15 mins ischemia followed by 15 mins reperfusion. In one series of experiments, we found that the coronary relaxation to urocortin (10–11 to 10–8 M) was reduced by ischemia-reperfusion (51 ± 4% vs. 79 ± 4% of the active tone, for the 10–10 Mdose). In other series of experiments, we observed that ischemia-reperfusion reduced the coronary relaxation to a test dose of acetylcholine (10–6 M) (25 ± 2% vs. 54 ± 9% of active tone), without modifying the relaxation to sodium nitroprusside (10–6 M). Treatment with a low threshold concentration of urocortin (10–11 M), administered before ischemia and during reperfusion, partly improved the coronary relaxation to acetylcholine (36 ± 3% of active tone). These results suggest that ischemia-reperfusion impairs the coronary vasodilation to urocortin and produces endothelial dysfunction and that this endothelial dysfunction may be improved by urocortin.

Distribution of urocortins and corticotropin-releasing factor receptors in the cardiovascular system

Urocortins are human homologues of urotensin I, a fish corticotropin-releasing-factor- (CRF-) like peptide secreted from the urophysis. There are three urocortins: urocortin 1, urocortin 2, and urocortin 3 in mammals. We have shown that urocortin 1 and urocortin 3 are endogenously synthesized in the myocardial cells of human heart and may act on CRF type 2 receptor (CRFR2) expressed in the heart. Expression levels of urocortin 1 in the heart and plasma urocortin 1 levels are elevated in patients with heart failure. Recent studies have shown that urocortins have various biological actions in the cardiovascular system, such as a vasodilator action, a positive inotropic action, a cardioprotective action against ischemia/reperfusion injury, and suppressive actions against the renin angiotensin system and the sympathetic nervous system. Urocortins and CRFR2 may therefore be a potential therapeutic target for cardiovascular diseases, such as congestive heart failure, hypertension, and myocardial infarction.

Urocortin and the brain

Urocortin is a member of the corticotropin-releasing hormone (CRH) family of peptides. In the brain, its potent suppression of food intake is mediated by CRH receptors (CRHR). Urocortin also participates in the regulation of anxiety, learning, memory, and body temperature, and it shows neuroprotection. This review will summarize the location of urocortin-producing neurons and their projections, the pharmacological evidence of its actions in the CNS, and information acquired from knockout mice. Urocortin interacts with leptin, neuropeptide Y, orexin, and corticotropin in the brain. Also produced by the GI tract, heart, and immune cells, urocortin has blood concentrations ranging from 13 to 152 pg/ml. Blood-borne urocortin stimulates the cerebral endothelial cells composing the blood-brain barrier and crosses the blood-brain barrier by a unique transport system. Overall, urocortin acts on a broad neuronal substrate as a neuromodulator important for basic survival.

Inhibitory effects of glucocorticoids on urocortin-mediated increases in interleukin-6 gene expression in rat aortic smooth muscle cells

Urocortin (Ucn) 1, Ucn2, and Ucn3 have potent effects on appetite and the cardiovascular system. Endogenous Ucns in combination with CRF receptor type 2beta may have a physiological role in the cardiovascular system. We previously demonstrated that both Ucn1 and Ucn2 increased IL-6 output levels in A7r5 aortic smooth muscle cells. In the present study, we extended observations on stress or hormone-induced changes in IL-6 gene expression in the cardiovascular system, and determined the effects of glucocorticoids on Ucn-mediated increases in IL-6 mRNA levels, protein levels, and gene transcription activity in A7r5 cells. Ucn1, Ucn2, and Ucn3 all increased IL-6 mRNA levels via CRF receptor type 2. Dexamethasone blocked the ability of Ucn1 to increase IL-6 mRNA and protein levels, while it failed to attenuate the Ucns-mediated changes in cyclic AMP (cAMP)-response element binding protein or extracellular signal-related kinases phosphorylation. Dexamethasone also suppressed Ucn1- or cAMP-stimulated IL-6 gene transcription via a glucocorticoid receptor. Together, these findings demonstrate that glucocorticoids suppress IL-6 gene transcription via Ucn-induced cAMP-dependent pathways in A7r5 cells.

Corticotropin-releasing hormone receptor (CRHR)1 and CRHR2 are both trafficking and signaling receptors for urocortin

Transport of urocortin, a potent satiety peptide, occurs at the blood-brain barrier of the mouse. Endocytosis of urocortin by the cerebral microvessel endothelial cells composing the blood-brain barrier is a rate-limiting step of this transport, but the cellular mechanisms involved have not been fully elucidated. The presence of both CRH receptors R1 and R2 in isolated cerebral microvessels shown in this study suggested that both subtypes might mediate urocortin transport. The roles of these two receptors in the endocytosis and signal transduction of urocortin were tested by overexpression studies in human embryonic kidney 293 cells. Both receptors led to a significant increase of binding and endocytosis of radiolabeled urocortin. CRHR1-mediated urocortin endocytosis was blocked by astressin (antagonist for both CRHRs), whereas CRHR2-mediated urocortin endocytosis was also blocked by antisauvagine 30 (selective CRHR2beta antagonist). Chlorpromazine, filipin, and nystatin had no effect on urocortin endocytosis, indicating the lack of significant involvement of clathrin or caveolae membrane microdomains. Both CRHR1 and CRHR2 were able to mediate the ligand-induced increase of cAMP production, suggesting that the overexpressed receptors were biologically active. Elevation of intracellular cAMP by forskolin or dibutyryl-cAMP, however, did not show acute modulation of the binding and endocytosis of urocortin. Despite the substantial intracellular degradation of endocytosed urocortin in cells overexpressing either CRHR1 or CRHR2, intact urocortin could be exocytosed during the 1-h study interval. We conclude that both CRHR1 and CRHR2 play a facilitatory role in the non-clathrin-, non-caveolae-mediated endocytosis and intracellular signal transduction of this potent peptide.

Plasma urocortin 1 in sheep: regional sampling and effects of experimental heart failure

Although urocortin 1 (Ucn-1) has been reported to circulate in human plasma and be raised in heart failure, little, if any, information is available regarding the source of circulating Ucn-1. Accordingly, we have performed trans-organ arteriovenous sampling for measurement of Ucn-1 concentration in anesthetized sheep before and after development of pacing-induced heart failure. Arterial plasma Ucn-1 levels measured 15.2 +/- 0.5 pmol/L in normal sheep and increased significantly following development of heart failure to 19.1 +/- 1.6 (p < 0.05). Small but significant positive arteriovenous gradients were observed across the hepatic and renal tissue beds in both states, with rises across the hind limb significant in normal animals and across the head in heart failure. This is the first report identifying sources of circulating Ucn-1.

Expression of urocortin in the extravillous human trophoblast at the implantation site

Urocortin (UCN) is a 40 amino acid peptide which is closely related to corticotropin-releasing hormone and binds with high affinity to both CRH type 1 and type 2 receptors. UCN is expressed in human reproductive tissues including endometrium, ovary, and placenta. This study was designed to investigate the cellular localization of UCN at the implantation site of the human blastocyst, as well as the regulation of the UCN promoter by two major intracellular signaling pathways, the cAMP/PKA and diacylglycerol/PKC pathways, in cells of placental origin. For this reason, immunohistochemistry was performed on tissue sections from paraffin-embedded human first trimester placentas and freshly isolated human invasive extravillous trophoblast cells (EVT) were analyzed for UCN expression using RT-PCR and immunofluorescence. Finally, UCN promoter activity was analyzed in the JEG3 human choriocarcinoma cell line. Immunohistochemistry revealed expression of UCN in the cytotrophoblast, the EVT and decidual cells. Both UCN mRNA and peptide were detectable in freshly isolated EVT. Finally, a human UCN promoter luciferase reporter construct transfected into JEG3 cells was significantly inducible by phorbol ester plus ionomycin, but not by phorbol ester alone or by forskolin. Collectively, the present study reports the expression of UCN in EVT and the activation of the UCN gene promoter by the diacylglycerol/PKC pathway. The functional significance of urocortin for the physiology of EVT requires further investigation.

Mechanisms of the protective effects of urocortin on coronary endothelial function during ischemia-reperfusion in rat isolated hearts

1 Urocortin is a vasodilator peptide related to corticotrophin-releasing factor, which may protect endothelial function during coronary ischemia-reperfusion (I-R). The aim of this study was to study the mechanisms of this protective effect. 2 Hearts from Sprague-Dawley rats were isolated and perfused at constant flow and then exposed to 15 min global zero-flow ischemia, followed by 15 min reperfusion. The relaxation to acetylcholine (10 nM-10 microM) was recorded after pre-constriction of the coronary vasculature with U46619 (100-300 nM) in ischemic-reperfused or time-control hearts. 3 After I-R, the coronary relaxation to acetylcholine was reduced and this reduction was attenuated by treatment with urocortin (10 pM), administered before ischemia and during reperfusion. 4 This urocortin-induced improvement of the relaxation to acetylcholine was not modified by tetraethylammonium (10 mM), blocker of Ca2+ dependent-potassium channels; glibenclamide (10 microM), blocker of K(ATP) channels; N(w)-nitro-L-arginine methyl ester (L-NAME, 100 microM), blocker of nitric oxide synthesis; or meclofenamate (10 microM), blocker of cyclooxygenase, but it was abolished by chelerythrine (3 microM), blocker of protein kinase C (PKC). 5 These results suggest that urocortin may protect coronary endothelial function during I-R by activation of PKC.

Reduced maternal plasma urocortin concentrations and impaired uterine artery blood flow at human mid pregnancy

OBJECTIVE

Urocortin is a placental neuropeptide belonging to the family of corticotropin-releasing factors (CRFs), playing a role in the uteroplacental blood flow regulation through the binding to specific CRF receptors. Since CRF receptors are expressed in the uterine vascular bed of pregnant rats, and because urocortin has a relaxant effect on uterine vasculature, we evaluated mid-gestation plasma urocortin levels in women with impaired blood flow through uterine arteries.

METHODS

Maternal plasma urocortin was assayed by specific radioimmunoassay and uterine artery resistance index (RI) by Doppler evaluation at 22-24 weeks' gestation in 57 healthy pregnant women, of which 29 showed a monolateral or bilateral uterine artery notch. Statistical analysis was performed by one-way analysis of variance (ANOVA), followed by post-hoc Tukey test for multiple comparison and Pearson correlation coefficient test.

RESULTS

The mean uterine artery RI was significantly (P <.001) higher in women with a notch than healthy controls. Mean +/- SEM maternal plasma urocortin levels were significantly (P <.001) lower in women with unilateral (52.03 +/- 3.25 pg/mL) or bilateral (47.01 +/- 4.16 pg/mL) uterine artery notch than in healthy control pregnant women (84.01 +/- 3.5 pg/mL). While no difference was found in urocortin levels between patients with unilateral or bilateral uterine artery notch, urocortin concentrations inversely correlated with the mean RI (Pearson r = -0.7318; 95% confidence interval -0.8334 to -0.5822; P <.0001).

CONCLUSIONS

The present findings suggest that reduced levels of circulating urocortin are associated with increased uterine artery resistances and support the hypothesis that urocortin may regulate uterine artery tone at mid gestation.

Urocortin stimulates tyrosine hydroxylase activity via the cAMP/protein kinase a pathway in rat Pheochromocytoma PC12 cells

Urocortin is a novel mammalian member of the corticotrophin releasing factor (CRF)-related peptides. We have investigated the expression, mechanism of action and second messenger for urocortin in rat pheochromocytoma PC12 cells. We initially confirmed the expression of urocortin and CRF-R2beta, which is thought to be an endogenous receptor for urocortin, in PC12 cells. We also demonstrate that urocortin (> or = 1 nM) significantly elevates the level of cAMP in these cells. Moreover, alpha-helical CRF-(9-41), a more specific antagonist of CRF-R2 than CRF-R1 and the adenylate cyclase inhibitor SQ22536, inhibited the urocortin-induced increase in the level of cAMP. Thus, urocortin may exert its physiological role in chromaffin cells via CRF-R2beta coupling to adenylate cyclase. Urocortin (> or = 1 nM) significantly increased the mRNA level and activity of tyrosine hydroxylase (TH), a rate-limiting enzyme in the biosynthesis of catecholamine. Furthermore, urocortin-induced changes in TH-mRNA and activity were inhibited by H89 (a PKA inhibitor) and SQ22536 as well as alpha-helical CRF-(9-41). However, urocortin did not affect DNA synthesis or catecholamine secretion in these cells. In conclusion, we have demonstrated that urocortin stimulates catecholamine biosynthesis via the cAMP/protein kinase A pathway in PC12 cells, where both urocortin and its receptor, CRF-R2, are expressed.

Effect of hypoxia on urocortin production in human gestational trophoblasts in vitro

PROBLEM

Urocortin is produced by the placenta throughout pregnancy but its regulation remains unknown. The effect of hypoxia on placental urocortin production is not known. The aim of this study was to determine the effect of in vitro hypoxia on human trophoblastic urocortin production.

METHOD OF STUDY

Placental explants and primary cultures were incubated in anaerobe hypoxic bags for 24 h in a humidified incubator. Urocortin peptide secretion and mRNA (messenger RNA) production was determined by enzyme-linked immunosorbent assay and reverse transcription-polymerase chain reaction, respectively. Morphological and functional integrity was verified by immunohistochemical analysis of urocortin expression. Vascular endothelial growth factor expression was used to verify the generation of cellular hypoxia in our in vitro system.

RESULTS

Hypoxia did not affect urocortin secretion or mRNA expression in explant and single-cell cultures. Production was greater from first trimester than term explants and from single-cell primary cultures more than from explant cultures.

CONCLUSIONS

Hypoxia does not influence human placental urocortin secretion or mRNA expression in vitro.

Localization and physiological roles of urocortin

Urocortin, a 40 amino acid peptide, is a corticotropin-releasing factor (CRF) related peptide, and can bind to all three types of CRF receptors (CRF type 1, type 2a and type 2b receptors) with higher affinities for these receptors than CRF. Immunoreactivity of urocortin is widely distributed in central nervous, digestive, cardiovascular, reproductive, immune and endocrine systems. Urocortin plays important roles in appetite-suppression, immunomodulation, steroidogenesis in the ovary, maintenance of the placental function, labor, and cardioprotection via CRF receptors. Although urocortin has potent adrenocorticotropin (ACTH) releasing activity in vitro, endogenous urocortin does not act on pituitary ACTH secretion in vivo.

Urocortins in human reproduction

Data on biological effects and localization of corticotropin-releasing factor (CRF), a neuropeptide structurally and biologically related to urocortins, have triggered the study on expression of urocortins and their function in human reproductive tissues. Ovary, endometrium, placenta and fetal membranes (amnion and chorion), myometrium, and prostate are sources of urocortin 1 and, they also express urocortin binding sites (receptors and CRF-binding protein), thus suggesting that these tissues are also targets of urocortin 1. The current concept thus is that urocortin 1 may affect the physiology of human reproduction through paracrine/autocrine actions. In particular, in vitro data have shown that urocortin 1 plays a major role in human placenta: it stimulates the secretion of ACTH, prostaglandins and activin A from cultured human placental cells, and regulates placental vessel resistance to blood flow. Furthermore, when incubated in myometrial strips, urocortins stimulate uterine contractility, by activating specific intracellular pathways. Taken together, these findings do suggest an important role of urocortins in the physiology of pregnancy and parturition.

CRF2 receptors are highly expressed in the human cardiovascular system and their cognate ligands urocortins 2 and 3 are potent vasodilators

1. Systemic infusions of urocortin 1 produce a decrease in mean arterial pressure. This effect may be mediated by a direct action on novel corticotropin-releasing factor type 2 (CRF(2)) receptors predicted to be expressed in blood vessels and the heart. Our objectives were to determine the presence of CRF(2) receptors in the human cardiovascular system using the selective radioligand [(125)I]antisauvagine 30. We also investigated the potential functional roles of novel CRF(2) ligands in the regulation of vascular tone in human arteries in vitro. 2. Radioligand binding techniques were used to characterise the CRF(2) receptor. [(125)I]antisauvagine 30 bound specifically, saturably, reversibly and with high affinity to CRF(2) receptors in human left ventricle (K(D) 0.21+/-0.03 nm, B(MAX) 0.80+/-0.18 fmol mg(-1) protein), and no change in receptor density or affinity was observed in the dilated cardiomyopathy group. 3. Autoradiographical studies revealed highly localised binding of [(125)I]antisauvagine 30 to intramyocardial blood vessels. Binding sites were also detected in the myocardium and in the medial layer of internal mammary arteries. 4. In endothelium-denuded human internal mammary artery in vitro, all peptides tested produced a potent and sustained vasodilator response reversing endothelin-1-induced constrictions (10 nm) (urocortin 1: pD(2) 8.39+/-0.32, E(MAX) 46+/-7.7%; urocortin 2: pD(2) 8.27+/-0.17, E(MAX) 60+/-8.5%; urocortin 3: pD(2) 8.61+/-0.25, E(MAX) 61+/-7.2%; CRF: pD(2) 8.28+/-0.27, E(MAX): 40+/-10%). 5. We have demonstrated the presence of CRF(2) receptors in the human cardiovascular system and a direct, endothelium-independent vasodilator action of urocortins 2 and 3, which may counter-balance the centrally mediated pressor effects of CRF and urocortin 1.

Cardiac expression of urocortin (Ucn) in diseased heart; preliminary results on possible involvement of Ucn in pathophysiology of cardiac diseases

Recently, several studies reported that urocortin (Ucn) had beneficial effects on cardiovascular system and was expressed both in the normal heart and in the heart of dilated cardiomyopathy (DCM), yet the relationship between high expression of Ucn and pathophysiology of Ucn in diseased heart has been discussed. Thus, the present study was designed to elucidate the expression of Ucn in the diseased heart by immunohistochemical approach using endomyocardial biopsy specimens. The involvement of immunoreactive Ucn in pathophysiology of cardiac disease was evaluated using endomyocardial biopsy specimens obtained from the patients with some heart diseases, including DCM and hypertrophic cardiomyopathy (HCM). Ucn was detected in all endomyocardial biopsy specimens of ventricular tissue obtained from the patients with such cardiac diseases, a specimens of atrial tissue, and normal heart specimens obtained from autopsy cases. In DCM patients, left ventricular end-diastolic pressure significantly elevated in severely stained group. On the contrary, in HCM patients, left ventricular ejection fraction was higher in the severely stained group. Ucn was expressed more abundantly in the diseased heart, especially in HCM and DCM, than in the normal heart. In conclusion, such close relationship between Ucn expression in the heart and cardiac function indicated that clinical features of Ucn resembled those of norepinephrine and Ucn could play a certain pathophysiological roles in the cardiac diseases.

Beneficial hemodynamic, endocrine, and renal effects of urocortin in experimental heart failure: comparison with normal sheep

OBJECTIVES

The goal of this study was to determine the bioactivity of urocortin (Ucn) in experimental heart failure (HF).

BACKGROUND

Urocortin may participate in cardiovascular function and pressure/volume homeostasis. Its effects in HF are unknown.

METHODS

Eight normal sheep and eight sheep with pacing-induced HF received ovine Ucn (10, 50, and 100 mg intravenous boluses at 2-h intervals) in vehicle-controlled studies.

RESULTS

Urocortin boluses dose-dependently increased plasma Ucn (p < 0.001). Pharmacokinetics were similar in normal and HF sheep with half-lives approximating 1.3 and 19.5 h for the first and second phases, respectively. In HF, cardiac output increased (twofold), while peripheral resistance, left atrial pressure (both 50% falls: p < 0.001), and mean arterial pressure (p < 0.05) fell. In normal sheep, changes in peripheral resistance and atrial pressure were blunted and in arterial pressure were directionally opposite. Urocortin induced persistent, dose-dependent falls (30% to 50%) in plasma vasopressin, renin activity, aldosterone, natriuretic peptides (all p < 0.001), and endothelin-1 (p < 0.05) in HF sheep, while adrenocorticotrophic hormone and cortisol levels rose acutely (both p < 0.001). In comparison, Ucn in normal sheep resulted in a similar rise in cortisol and fall in aldosterone, no significant effects on plasma renin activity and natriuretic peptides, and a rise in vasopressin. Urocortin produced dose-dependent, sustained increases in urine volume (twofold, p < 0.01), sodium excretion (>9-fold rise, p < 0.001), and creatinine clearance (p < 0.001) in HF sheep. No significant renal effects were observed in normal sheep.

CONCLUSIONS

Urocortin has profound and sustained hemodynamic, hormonal, and renal effects in experimental HF. Urocortin may have a role in pressure/volume homeostasis in HF and may provide a novel therapeutic approach to this disease.

Urocortin has cell-proliferative effects on cardiac non-myocytes

Urocortin (Ucn) is a member of the corticotropin-releasing hormone (CRH)-related peptides that has been reported to have cardiac inotropic and hypertrophic effects. In addition, Ucn mRNA was expressed in cardiac myocytes (MCs) and Ucn was suggested to have cardioprotective effects. Recently, it was reported that Ucn mRNA was expressed in cardiac non-myocytes (NMCs). Based on these facts, Ucn is assumed to affect not only MCs but also NMCs in an autocrine fashion. The present study was designed to elucidate a pathophysiological role of Ucn on NMCs. NMCs were prepared by the discontinuous Percoll gradient and adhesion method. Ucn increased [(3)H]-thymidine uptake into NMCs. Ucn also enhanced endothelin-1-induced increase of [(3)H]-thymidine uptake into NMCs. Effects of Ucn on [(3)H]-thymidine uptake into NMCs were significantly abolished by the protein kinase A inhibitor, H89 (10(-5) M), but not by a competitive antagonist of CRH receptors, astressin (10(-5) M). Ucn also increased intracellular cAMP accumulation more potently than CRH on a molar basis. Finally, both MCs and NMCs also secreted Ucn. Together with the recent findings, at least in NMCs, these data suggest that Ucn could exert its own actions via the cAMP signaling pathway, but not through known CRH type 2 receptors, in an autocrine fashion. In conclusion, the present study indicated that Ucn was secreted not only from MCs but also from NMCs and that the primary source of Ucn acting on heart was the heart itself. On the other hand, Ucn could proliferate NMCs as well as MCs, suggesting that Ucn could be involved in cardiac hypertrophy and fibrosis, i.e., cardiac remodeling, in spite of its putative cardioprotective actions.

Relaxation by urocortin of human saphenous veins

Urocortin, an endogenous peptide structurally related to corticotropin-releasing factor (CRF), has potent cardiovascular effects, suggesting that it may be of significance in cardiovascular regulation. The objective of this study was to analyse the effects of urocortin and its action mechanisms on human blood vessels. To this, 3 mm long segments from human saphenous veins were prepared for isometric tension recording in an organ bath. In the segments at basal resting tone, urocortin did not produce any effect, but in the segments precontracted with endothelin-1 (1 - 10 nM), urocortin (1 pM - 10 nM) produced concentration-dependent relaxation. This relaxation was not modified by the inhibitor of nitric oxide synthase NG-nitro-L-arginine methyl ester (L-NAME, 100 microM), but it was potentiated by the cyclo-oxygenase inhibitor meclofenamate (10 microM) and it was reduced by the inhibitors of high-conductance Ca2+-dependent potassium channels tetraethylammonium (TEA, 10 mM) and charybdotoxin (100 nM). These results indicate that human saphenous veins are very sensitive to urocortin, which produces vascular relaxation by a mechanism independent of nitric oxide and dependent of high-conductance Ca2+-dependent potassium channels, and that it may be opposed by the release of vasoconstrictor prostanoids. Therefore, urocortin may be of significance for regulation of the venous circulation in humans.

Human placental corticotropin-releasing factor (CRF) in the adaptive response to pregnancy

Several findings suggest a role of placental hormones in the regulation of maternal and fetal physiology during pregnancy. The placenta and its accessory membranes, amnion and chorion, although of fetal origin, actually undertake the role of intermediary barriers and active messengers in the maternal-fetal dialogue. They synthesize, metabolize and serve as targets for numerous hormones and cytokines which control all aspects of pregnancy and parturition. Among these, corticotropin-releasing factor (CRF) has been one of the most investigated in the last decade. The secretion of placental CRF is autonomous, but increasing evidence indicates that maternal or fetal physiological and pathological conditions may influence such secretion. In the event of acute or chronic metabolic, physical or infection stress, the placenta takes part in a stress syndrome by releasing CRF, which may contribute to restore local blood flow, and to influence the timing of delivery. Placental CRF and cytokines produced in case of intrauterine infection may activate labour, thereby helping the fetus to escape from a hostile environment.On the background of maternal and/or fetal stress elicited by a number of pathological conditions, CRF appears to play a role in coordinating adaptive changes in uterine perfusion,maternal metabolism, fluid balance and possibly uterine contractility.

Human placenta as a source of neuroendocrine factors

Progress in the understanding of the physiological and pathological functions of the placenta introduced the concept that the placenta is a neuroendocrine organ, since it shows local production and release of substances analog to neurohormones. These products act as endocrine, paracrine and autocrine factors to control the secretion of other regulatory molecules, including the pituitary hormones of both mother and fetus and their placental counterparts. Furthermore, they may play a role in the regulation of maternal and fetal physiology during pregnancy, ranging from the control of placental anchoring to fetal growth and maturation, fine regulation of uterine blood flow and/or initiation of labor. All this evidence underlines the decisive contribution of the placenta to all phases of gestation, through a range of substances largely exceeding the classically known sex steroids and chorionic gonadotropin, throughout normal pregnancy as well as in the presence of gestational diseases.

The peripheral CRH/urocortin system

The hypothalmus-pituitary-adrenal (HPA) axis and the immune system communicate at multiple levels: On the one hand, immune system-derived substances, such as interleukin-1, interleukin-6, tumor necrosis factor alpha, and leukemia inhibitory factor can stimulate the HPA axis. On the other hand, HPA axis-derived substances, most importantly glucocorticoids, can modulate the immune response. Furthermore, factors that were originally thought to be restricted to the HPA axis have been found to be expressed by immune cells. Proteins belonging to the CRH (corticotropin-releasing hormone) family represent important examples of such hormones. In the early 1990s, it was shown that immunoreactive CRH was present at sites of chemically induced inflammation. Administration of anti-CRH antibodies reduced the degree of inflammation, pointing to a pro-inflammatory role of "peripheral" CRH. We and others could show that lymphocytes are one source of immunoreactive CRH; however, the antiserum used in our study as well as in previous reports crossreacted with urocortin, a newly discovered member of the CRH family. Using RT-PCR, we could clearly demonstrate that human lymphocytes expressed urocortin but not CRH mRNA. These results were confirmed by immunocytochemistry, employing urocortin- and CRH-specific antibodies, respectively. The possible functional roles of urocortin expression in the immune system are discussed.

Localization and characterization of urocortin during human pregnancy

Urocortin, a recently identified peptide of the corticotropin releasing hormone (CRH) peptide family, has potent vasodilatory effects in the human fetal placental circulation in vitro, promoting us to hypothesize that urocortin is produced locally to regulate uteroplacental vascular tone during pregnancy. In the present study, we examined the distribution of urocortin in the human placenta, fetal membranes and uterine tissue at term in the presence and absence of labour, using a urocortin antibody produced in our laboratory and the immunoperoxidase staining method. Immunoreactive (IR)-urocortin was observed in the vascular smooth muscle of the myometrium (n=5), decidual stromal cells, syncytiotrophoblast and amnion epithelium (n=10). No differences in staining intensity for urocortin were detected between tissues obtained in the absence (n=5) or presence (n=5) of labour. Staining intensity for IR-urocortin was greatest in the decidua suggesting this may be a site of urocortin production during pregnancy. Subsequently, we tested urocortin secretion from chorio-decidual cells in vitro, using an immunoblot technique. Positive staining for urocortin was observed in 40 per cent of chorio-decidual cells with 34 per cent of these cells secreting urocortin under basal conditions. Since urocortin was secreted by decidual cells we questioned whether urocortin was present in maternal plasma throughout gestation, using radioimmunoassay. Urocortin was detectable in maternal plasma from 7 weeks of gestation and concentrations did not change as gestation progressed. IR-urocortin in the maternal plasma eluted from a Sephadex G-50 column at the same site as synthetic urocortin and had a calculated retention coefficient (Kd) of 0.44. In summary, this study indicates that urocortin is produced by the decidua during human pregnancy and is detectable in maternal plasma. These data are consistent with the hypothesis that urocortin is produced locally by the decidua and may act to regulate uteroplacental blood flow.