Cloning and sequence analysis of cDNA encoding the precursor of a human endothelium-derived vasoconstrictor peptide, endothelin: identity of human and porcine endothelin

Conversion of big endothelin-1 and characterization of its contractile effects on isolated human placental arteries

OBJECTIVES

To study the conversion of human big endothelin-1 (bigET-1) to endothelin-1 (ET-1) and to characterize contractile ET-1 receptors in human placental arteries.

METHODS

BigET-1 was incubated with artery membranes and the formation of ET-1 was investigated. ET-1 and bigET-1-induced contractile responses were studied in the absence or presence of the metalloprotease inhibitor phosphoramidon, the ET(A)-receptor antagonist BQ 123, or the ETB-receptor antagonists IRL 1038 and RES 701-1.

RESULTS

The artery membranes hydrolysed bigET-1 to ET-1 through a partly phosphoramidon-sensitive pathway. The contractile responses to ET-1 and bigET-1 were similar, with pEC50% values of 8.1 +/- 0.2 and 7.8 +/- 0.1, respectively (NS; n = 17). Phosphoramidon decreased pEC50% for bigET-1-evoked contractions (p < 0.05; n = 8), without affecting the response to ET-1. A Schild plot of BQ 123 effects on ET-1 and bigET-1-induced contractions resulted in identical pA2 values and a slope of 0.56 +/- 0.2 and 0.47 +/- 0.01, respectively. IRL 1038 and RES 701-1 did not affect the contractile responses.

CONCLUSION

BigET-1-evoked contractions in isolated human placental arteries depend on a rapid and metalloprotease-dependent hydrolytic conversion to ET-1, which in turn causes a, mainly ETA-receptor-mediated, contraction.

Percutaneous in vivo gene transfer to the peripheral lungs using plasmid-liposome complexes

The purpose of this study was to investigate a new method of in vivo gene transfer to the lung parenchyma by the percutaneous approach. The plasmid that contains the gene for firefly luciferase driven by a cytomegalovirus (CMV) promoter (pCMVL) in combination with cationic lipids was percutaneously injected into the lung parenchyma. Luciferase activities were localized to the lobes of the lung where the plasmids with cationic lipids were injected. Percutaneous injection of the plasmid containing the human endothelin-1 (hET-1) gene driven by a CMV promoter (pRc/CMVhET-1) in combination with cationic lipids into the lungs caused pulmonary fibrosis localized to the injection site in the peripheral lungs. We concluded that percutaneous in vivo gene transfer to the lungs is a unique and important approach to introduce exogenous gene expression in the limited area of the lung parenchyma. This method of gene transfer will be applicable for human gene therapy for targeted areas of peripheral lung and will also be useful to assess the function of the proteins expressed by a gene in the local area of the lungs.

Functional parathyroid hormone receptors are present in an umbilical vein endothelial cell line

Acute parathyroid hormone exposure induces vascular smooth muscle relaxation. In contrast, continuous infusion of parathyroid hormone leads to vasoconstriction and an elevation of blood pressure. Despite the known effects of parathyroid hormone on vascular smooth muscle, possible direct effects on the vascular endothelium have not previously been investigated. Using a human umbilical vein endothelial cell line, we found that parathyroid hormone increased both intracellular calcium and cellular cAMP content in these endothelial cells. Furthermore, exposure of these cells to increasing concentrations of parathyroid hormone stimulated both [(3)H]thymidine incorporation and endothelin-1 secretion. Parathyroid hormone/parathyroid hormone-related peptide receptor mRNA could be detected at low levels in these cells. In summary, these data demonstrate that endothelium-derived cells contain functional parathyroid hormone receptors. The potential physiological role of these receptors remains to be determined.

The endothelin system in normal human colon

Endothelin (ET)-1 is a potent vasoconstrictor and mitogenic peptide that has a variety of biological effects in noncardiovascular tissues. The precise cellular distribution of the ET-1 system in the wall of the normal human colon was studied to identify the physiological role of ET in the gut. In situ hybridization revealed ET-converting enzyme-1 (ECE-1) mRNA in all vessels, the colon epithelium, and macrophages. Prepro-ET-1 (PPET-1) mRNA had a similar distribution except for a scattered signal in mucosal microvessels. ET(A) and ET(B) receptor mRNAs were mainly in the lamina propria, pericryptal myofibroblasts, microvessels, and mononuclear cells, with ET(A) mRNA more abundant than ET(B) mRNA. (125)I-ET-1 binding showed ET(B) along the crypts and in nerve fibers descending from the ganglionic plexus that contained PPET-1, ECE-1, and ET(B) transcripts, whereas glia contained ET(A) receptors. The finding of the entire ET system in the normal mucosa suggests its implication in some characteristic functions of the colon and its secretion as both a neuroactive and a vasoactive peptide.

Regulation of the endothelin system by shear stress in human endothelial cells

In this study, the effect of shear stress on the expression of genes of the human endothelin-1 system was examined. Primary cultures of human umbilical vein endothelial cells (HUVEC) were exposed to laminar shear stress of 1, 15 or 30 dyn cm-2 (i.e. 0.1, 1.5 or 3 N m-2) (venous and two different arterial levels of shear stress) in a cone-and-plate viscometer. Laminar shear stress transiently upregulates preproendothelin-1 (ppET-1) mRNA, reaching its maximum after 30 min (approx 1.7-fold increase). In contrast, long-term application of shear stress (24 h) causes downregulation of ppET-1 mRNA in a dose-dependent manner. Arterial levels of shear stress result in downregulation of endothelin-converting enzyme-1 isoform ECE-1a (predominating in HUVEC) to 36.2 +/- 8.5 %, and isoform ECE-1b mRNA to 72.3 +/- 1.9 % of static control level. The endothelin-1 (ET-1) release is downregulated by laminar shear stress in a dose-dependent manner. This downregulation of ppET-1 mRNA and ET-1 release is not affected by inhibition of protein kinase C (PKC), or tyrosine kinase. Inhibition of endothelial NO synthase (L-NAME, 500 microm) prevents downregulation of ppET-1 mRNA by shear stress. In contrast, increasing degrees of long-term shear stress upregulate endothelin receptor type B (ETB) mRNA by a NO- and PKC-, but not tyrosine kinase-dependent mechanism. In conclusion, our data suggest the downregulation of human endothelin synthesis, and an upregulation of the ETB receptor by long-term arterial laminar shear stress. These effects might contribute to the vasoprotective and anti-arteriosclerotic potential of arterial laminar shear stress.

The dissociation between upregulated endothelins and hemodynamic responses during polymicrobial sepsis

Polymicrobial sepsis is characterized by an early, hyperdynamic phase followed by a late, hypodynamic phase. Although studies have suggested that endothelins (ETs) contribute to the development of shock after a bolus injection of endotoxin, little is known about the role of ETs in the transition from the hyperdynamic phase to the hypodynamic phase of sepsis. To study this, male adult rats were subjected to sepsis by cecal ligation and puncture (CLP) followed by fluid resuscitation. Plasma levels of ET-1 and ET-2 were measured by radioimmunoassay at 2, 5, 10 h (i.e. the early stage of sepsis), and 20 h (late stage) following CLP or sham operation. Tissue levels of ET-1 and ET-2 were determined in the heart, lungs, small intestine, and spleen at 5 h after CLP or sham operation. In addition, preproendothelin-1 (precursor of ET-1) gene expression was analyzed by reverse transcription-polymerase chain reaction (RT-PCR) at 5 h in the heart, lungs, small intestine, spleen, and liver. The results indicate that plasma levels of ET-1 and ET-2 were not different from values of sham groups at 2 and 20 h, but were significantly higher than the sham values at 5 and 10 h after CLP. While there were no significant increases in tissue levels of ET-1 and ET-2 at 5 h post-CLP, RT-PCR analysis indicates a significant upregulation of preproendothelin-1 gene expression in the heart, spleen, and liver (but not in the lungs or small intestine) at 5 h after the onset of sepsis. These results indicate that the heart, spleen, and liver appear to be important ET-producing organs during the early stage of sepsis. The lack of significant increases in tissue ET levels could be due to the possibility that the newly converted peptide is quickly transferred to the bloodstream. Since the hyperdynamic phase of sepsis occurs at 2-10 h and the hypodynamic phase occurs at 20 h after CLP, the increased plasma levels of ET at 5 and 10 h suggest that mediators other than ETs (such as adrenomedullin) are responsible for producing the biphasic hemodynamic responses during the progression of polymicrobial sepsis.

Studies on the expression of endothelin, its receptor subtypes, and converting enzymes in lung cancer and in human bronchial epithelium

Lung cancer, particularly small cell lung cancer (SCLC), is characterized by production of numerous peptides and their resulting clinical syndromes. Such peptides can act as autocrine growth factors for these tumors. In this study, we investigated the role of endothelin (ET)-1 in lung cancer. Using reverse transcription/polymerase chain reaction (RT-PCR), enzyme-linked immunosorbent assay, and immunocytochemistry, we screened a panel of lung cancer cell lines for ET-1, its receptors, and endothelin converting enzyme-1 (ECE-1), which generates the active form of ET-1. ET-1 messenger RNA was expressed in five of seven SCLC, four of four non-small cell lung cancer (NSCLC), and human bronchial epithelial (HBE) cells. The intracellular isoform of ECE-1, important in processing ET-1 if an autocrine growth loop is to function, was downregulated in the lung cancer cell lines as compared with expression of the extracellular isoform. Endothelin A receptor (ETAR), which mediates the mitogenic effects of ET-1 in prostate and ovarian cancer, was upregulated in HBE cells compared with expression in three of seven SCLC and two of four NSCLC cell lines. Endothelin B receptor (ETBR) was more widespread, being expressed in seven of seven SCLC, four of four NSCLC, and the HBE cells. We used flow cytometry to measure mobilization of intracellular calcium as a functional assay for the ETAR. These data concurred with the RT-PCR results, indicating that the ETAR was downregulated or was involved in an alternative signal transduction pathway in lung cancer, and no evidence of functional receptor mediating an autocrine growth loop was found. From our study, the data do not support the putative functional autocrine growth role of ET-1 in lung cancer. We propose instead that ET-1 may act as a paracrine growth factor for surrounding epithelial and endothelial cells via alternative pathways, promoting angiogenesis and stromal growth.

The prepro vasoactive intestinal contractor (VIC)/endothelin-2 gene (EDN2): structure, evolution, production, and embryonic expression

Murine vasoactive intestinal contractor (VIC) and its human analog endothelin-2 (ET2) are potent vasoactive hormones composed of 21 amino acids. To study the structural characteristics of the VIC/ET2 gene (HGMW-approved symbol EDN2), we isolated the full length of the mouse VIC gene. Sequence analysis indicates that a biologically active mature VIC peptide is produced from a 175-residue precursor protein; preproVIC (PPVIC). Several remarkable similarities of the PPVIC gene to the human preproendothelin-1 gene strongly suggest that the two genes have arisen from a common progenitor by gene duplication. Transfection of ACHN adenocarcinoma cells with the cDNA resulted in the production of VIC peptide. VIC production was increased by the deletion of the 3'-untranslated region, which contains an AU-rich mRNA destabilizing sequence. Increased PPVIC gene expression during the late embryonic stage suggests an important function in development. This study provides the basis for disruption and regulation analysis of the gene, which may lead to a better understanding of VIC/ET2's physiological significance.

Dynamic Nature of Thrombin Generation, Fibrin Formation, and Platelet Activation in Unstable Angina and Non-Q-Wave Myocardial Infarction

Thrombin and platelets are directly involved in arterial thrombosis, typically occurring at sites of atherosclerotic plaque rupture among patients with acute coronary syndromes. Understanding the dynamic nature of pathologic thrombosis has important clinical implications. Methods: Fibrinopeptide A (FPA), thrombin-antithrombin complexes (TAT), and prothrombin activation fragment 1.2 (F1.2), plasma markers of fibrin formation (thrombin activity) and thrombin generation, and platelet activation, determined by the recognition of a surface-expressed platelet alpha-granule protein, P-selectin, using flow cytometry, were measured in 36 consecutive patients with unstable angina and non-Q-wave myocardial infarction participating in the Thrombolysis In Myocardial Ischemia (TIMI) III B trial. Results: Thrombin generation (TAT 12.1 +/- 17.8 ng/ml vs. 3.4 +/- 1.0 ng/ml; F1.2 0.19 +/- 0.14 nmol/l vs. 0.12 +/- 0.8 nmol/l), fibrin formation (FPA 15.8 +/- 23.5 ng/ml vs. 7.5 +/- 2.3 ng/ml), and platelet activation) 10.6 +/- 2.4% vs. 2.5 +/- 2.0%) were increased significantly in patients compared with healthy, age-matched controls (p < 0.01). Fibrin formation, represented by plasma FPA levels, did not correlate with the percentage of activated platelets (r = -.10, p = 0.69). Thrombin generation and platelet activation also did not correlate. A statistically insignificant trend between TAT and platelet activation was observed (r =.42, p = 0.07); however, even with TAT levels in excess of 20 ng/ml (nearly sixfold greater than normal healthy controls) platelet activation was increased by only 1.7-fold. Conclusions: Thrombin generation, fibrin formation, and platelet activation are increased modestly among patients with unstable angina and non-Q-wave myocardial infarction. Despite the involvement of platelets and coagulation proteins in arterial thrombotic processes, their relative contributions may vary, providing a pathophysiologic basis for the dynamic expression of di sease and response to treatment observed commonly in clinical practice.

Endothelin and the central and peripheral nervous systems: a decade of endothelin research

1. During the past decade, extensive investigation of the endothelin (ET) system, primarily characterized by its potent vasoactive peptide element ET-1, has suggested a prominent role for this humoral agent and its isopeptides in cardiovascular and neural regulation. 2. Major elements of this system, including its peptide isoforms, converting enzymes involved in their formation and metabolism, as well as multiple receptor subtypes, have been localized within various components of the cardiovascular system and the central and peripheral nervous systems. 3. An understanding of the possible roles for the ET system in neural regulation and development has progressed over the past several years; most notable is the influence of ET on the central control of cardiovascular function and sympathetic tone. 4. The present concentrated review of ET and the central and peripheral nervous systems is presented to introduce the other papers within this symposium by briefly describing the presence and influence of components of this unique peptide system within pertinent physiological structures involved in cardiovascular, adrenal, sympathetic and enteric developmental function.

Kell, Kx and the McLeod syndrome

The antigens of the Kell blood group system are carried on a 93 kDa type II glycoprotein encoded by a single gene on chromosome 7 at 7q33. XK is a 50.9 kDa protein that traverses the membrane ten times and derives from a single gene on the X chromosome at Xp21. A single disulphide bond, Kell Cys 72-XK Cys 347, links Kell to XK. The Kell component of the Kell/XK complex is important in transfusion medicine since it is a highly polymorphic protein, carrying over 23 different antigens, that can cause severe reactions if mismatched blood is transfused and in pregnant mothers antibodies to Kell may elicit serious fetal and neonatal anaemia. The different Kell phenotypes are all caused by base mutations leading to single amino acid substitutions. By contrast the XK component carries a single blood group antigen, termed Kx. The physiological functions of Kell and XK have not been fully elucidated but Kell is a zinc endopeptidase with endothelin-3-converting enzyme activity and XK has the structural characteristics of a membrane transporter. Lack of Kx, the McLeod phenotype, is associated with red cell acanthocytosis, elevated levels of serum creatine phosphokinase and late onset forms of muscular and neurological defects.

Peroxisome proliferator-activated receptor activators inhibit thrombin-induced endothelin-1 production in human vascular endothelial cells by inhibiting the activator protein-1 signaling pathway

Endothelin-1 (ET-1), a 21-amino acid vasoactive peptide mainly produced by vascular endothelial cells, is involved in the regulation of vascular tone and smooth muscle cell proliferation. Peroxisome proliferator-activated receptors (PPARs), key players in lipid and glucose metabolism, have been implicated in metabolic disorders that are predisposing to atherosclerosis. Because of the potential role of ET-1 in vascular disorders such as hypertension and atherosclerosis, we investigated the regulation of ET-1 expression by PPAR activators. Western blot and reverse transcription-polymerase chain reaction analyses demonstrated that both PPARalpha and PPARgamma are expressed in human coronary artery endothelial cells as well as in endothelial cell lines such as HMEC-1 and ECV304. In bovine aortic endothelial cells and HMEC-1 cells, both PPARalpha and PPARgamma ligands inhibited thrombin-induced ET-1 secretion, whereas basal ET-1 secretion was only slightly suppressed. Reverse transcription-polymerase chain reaction experiments showed that this inhibition of ET-1 production occurs at the gene expression level. Using transient transfection assays, we demonstrated that PPARs downregulate thrombin-activated transcription of the human ET-1 promoter. Transactivation studies with c-Jun and c-Fos expression plasmids indicated that PPARs negatively interfere with the activator protein-1 signaling pathway, which mediates thrombin activation of ET-1 gene transcription. Furthermore, electrophoretic mobility shift assays demonstrated that PPAR activators reduce the thrombin-stimulated binding activity of bovine aortic endothelial cell nuclear extracts as well as c-Jun binding to an activator protein-1 consensus site. Taken together, these data indicate that (1) both PPARalpha and PPARgamma are expressed in human vascular endothelial cells and (2) PPAR activators inhibit thrombin-induced ET-1 biosynthesis, indicating a novel role for PPARs in vascular endothelial function.

Paracrine regulation of ovarian cancer by endothelin

Previous studies have demonstrated that endothelin (ET) isoforms (ET-1, ET-2 and ET-3) can act in an autocrine manner in ovarian cancer while in breast cancer their role has been proposed to be that of a paracrine mitogen. To explore the possibility that endothelin isoforms might function not only as autocrine regulators but also as paracrine mitogens in ovarian cancers, we investigated their effects on the growth of ovarian fibroblasts derived from ovarian carcinomas, the interaction between ovarian carcinoma and fibroblast cells and the location of the isoform expression in primary ovarian tumours. ET-1, ET-2 and ET-3 stimulated the growth of three ovarian fibroblast cell lines at concentrations ranging from 10(-12) M to 10(-7) M. Inhibition of 125I-ET binding by the ETA receptor antagonist BQ123 and the ETB receptor antagonist BQ788 suggested the presence of both types of ET receptors in fibroblast cells. In the absence of ET-1, neither BQ 123 nor BQ 788 inhibited growth. However, both antagonists inhibited ET-1 stimulated growth suggesting the involvement of both receptor types in ET-1 growth regulation. In contrast to carcinoma cells which secrete measurable levels of ET-1, fibroblast cell lines did not secrete detectable protein. Co-culture experiments (using porous membrane insert wells) of fibroblasts with carcinoma cells demonstrated that growth of both populations of cells was increased compared with either grown in isolation. In this system, growth of the fibroblast cell line was partially inhibited by both BQ123 and BQ788, whilst growth of the PE014 carcinoma cell line was inhibited by only BQ123. RT-PCR measurements detected the presence of the ETA receptor subtype in 10/10 primary ovarian cancers but the presence of ETB receptor in only 6/10 cancers. Using specific antibodies, ET-1 was found in 11/15, ET-2 in 5 of 7 and ET-3 in 5/7 primary ovarian cancers predominantly in the epithelial cells but with some stromal expression. These data indicate that the ET isoforms may stimulate growth of the fibroblast population within an ovarian cancer in addition to stimulating the epithelial cells and since the ETs are expressed in the majority of ovarian cancers, this paracrine effect may contribute to the overall growth of the tumour.

Endothelins and asthma

In the decade since endothelin-1 (ET-1) and related endogenous peptides were first identified as vascular endothelium-derived spasmogens, with potential pathophysiological roles in vascular diseases, there has been a significant accumulation of evidence pointing to mediator roles in obstructive respiratory diseases such as asthma. Critical pieces of evidence for this concept include the fact that ET-1 is an extremely potent spasmogen in human and animal airway smooth muscle and that it is synthesised in and released from the bronchial epithelium. Importantly, symptomatic asthma involves a marked enhancement of these processes, whereas asthmatics treated with anti-inflammatory glucocorticoids exhibit reductions in these previously elevated indices. Despite this profile, a causal link between ET-1 and asthma has not been definitively established. This review attempts to bring together some of the evidence suggesting the potential mediator roles for ET-1 in this disease.

Solution structure of a novel ETB receptor selective agonist ET1-21 [Cys(Acm)1,15, Aib3,11, Leu7] by nuclear magnetic resonance spectroscopy and molecular modelling

The solution structure of a biologically active modified linear endothelin-1 analogue, ET1-21[Cys(Acm)1,15, Aib3,11, Leu7], has been determined for the first time by two-dimensional nuclear magnetic resonance spectroscopy in a methanol-d3/water solvent mixture. Out of approximately one hundred linear peptide analogues tested by biological assay, this peptide, together with a dozen others, showed significant ETB selective agonist activity. Here we report the solution structure of an ETB selective agonist of a full-length, synthetic linear endothelin analogue. The calculated structures indicate that the peptide adopts an alpha-helical conformation between residues Ser5-His16, whilst both N- and C-termini show no preferred conformation. These results suggest that the disulphide bridges normally associated with endothelin and sarafotoxin peptides may not necessarily be important for either ETB receptor binding activity or the formation of a helical conformation in solution.

Hypoxia increases thrombospondin-1 transcript and protein in cultured endothelial cells

The exposure of endothelial cells to hypoxic environments regulates the expression of a number of genes with products that are vasoactive or mitogenic for vascular tissue, including platelet-derived growth factor, endothelin-1, and endothelial nitric oxide synthase. Hypoxia is also known to alter the adhesive properties of endothelium toward a variety of blood cell types. Thrombospondin-1 (TSP-1) is a glycoprotein with major roles in cellular adhesion and vascular smooth muscle proliferation and migration. We report here that hypoxia induces TSP-1 gene and protein expression. Oxygen tensions of < or =30 torr resulted in TSP-1 transcript induction initially apparent at 1 to 6 hours, with maximal induction (6.5-fold+/-1.2-fold) within 24 to 48 hours in both human and bovine endothelial cells. TSP-1 protein levels remain elevated after 72 hours of continuous hypoxic exposure. The induction of TSP-1 steady-state transcript levels is caused in large part, if not entirely, by post-transcriptional stabilization of the TSP-1 mRNA. The TSP-1 induction by hypoxia is a graded and reversible physiologic response and can be mimicked by the use of cobalt chloride or the inhibition of nitric oxide production, suggesting both the involvement of a heme-containing oxygen sensor and a role for the endogenous production of nitric oxide in TSP-1 regulation. The effects of hypoxia both on the stabilization of the TSP-1 transcript and the stimulation of TSP-1 protein production are completely inhibited by arginine butyrate.

Development of ET(B) selective agonists: solution structure of a linear endothelin-1 analogue, ET-1 [Cys(Acm)(1,15), Ala3, Leu7, dAsp8, Aib11]

The solution structure of a synthetic ET(B) selective agonist, ET-1[Cys(Acm)(1,15), Ala3, Leu7, dAsp8, Aib11] has been solved by 1H NMR and molecular modelling studies. Such solution structures of linear modified peptides in aqueous methanol are being used in an ongoing program of research designed to assist in an understanding of the basic structural requirements for the biological activity of vasoconstrictors. The resulting structure of this peptide is characterised by an alpha-helical conformation between residues Leu6-His16 and by N- and C-termini which assume no defined conformation. A knowledge of the solution structures of this and related peptides, which are ET(B) selective agonists, are proving to be important in the understanding of how they interact with the ET(B) receptor.

Induction of endothelin-1 synthesis by IL-2 and its modulation of rat intestinal epithelial cell growth

Endothelin (ET), a vasoconstrictive peptide, is known to have a variety of biological actions. Although ET is released by vascular endothelial cells, other cell populations also have been reported to synthesize and release ET. In this study, we examined whether ET is synthesized by intestinal epithelial cells and whether it affects induction of epithelial cell proliferation by interleukin-2 (IL-2). Subconfluent monolayers of intestinal epithelial cells (IEC-6 and IEC-18) were maintained in serum-free medium before addition of rat IL-2. Both IEC-6 and IEC-18 cells released ET-1 into the medium under unstimulated conditions, as determined by a sandwich ELISA. IL-2 significantly enhanced ET-1 release in a time-dependent manner. ET-3 was not detectable in the culture media of either cell line. Expression of ET-1 and ET-3 mRNA in epithelial cells was assessed by competitive PCR. Both cell lines were shown to express ET-1 mRNA, but no ET-3 mRNA was detected. IL-2 treatment enhanced ET-1 mRNA expression by both IEC-6 and IEC-18 cells. Both cell lines also expressed mRNA for ETA and ETB receptor subtypes. When cell proliferation was assessed, exogenous ET-1 induced a slight proliferative response in both types of cells that was consistent and significant at low ET-1 concentrations; cell growth was inhibited at a higher concentration (10(-7) M). IL-2 produced a significant proliferative response in both cell lines. However, the addition of ET-1 (10(-7) M) to culture media attenuated the IL-2-induced increase in cell proliferation. ETA-receptor antagonists significantly enhanced cellular proliferation, suggesting involvement of the ETA receptor in modulation of IL-2-induced intestinal epithelial cell growth.

Oncostatin M regulates endothelin-1 production in human endothelial cells

The effect of the macrophage- and T-lymphocyte-derived cytokine oncostatin M (OSM) on endothelin-1 (ET-1) production in cultured human umbilical cord vein endothelial cells (HUVEC) was studied. OSM (2.5-10 ng/ml) stimulated ET-1 production and the expression of preproendothelin-1 mRNA. The stimulatory effect of OSM was reversed by anti-interleukin (IL)-6 IgG (33 microg/ml). IL-6 (10 ng/ml) was shown to stimulate ET-1 production. The tyrosine kinase inhibitors herbimycin (250-500 ng/ml) and genistein (1-4 microg/ml) suppressed basal ET-1 production and reversed the stimulatory effect of OSM, whereas daidzein (1-8 microg/ml), a less active analog of genistein, had no effect on basal ET-1 production and only partly reversed the stimulatory effect of OSM. The phorbol ester phorbol 12-myristate 13-acetate (PMA) inhibited ET-1 production. Downregulation of protein kinase C (PKC) with PMA (1 microM) preincubation potentiated OSM-induced ET-1 production. In summary, OSM stimulated ET-1 production in cultured HUVEC. The stimulation was probably mediated by IL-6. Furthermore, the present data suggest that tyrosine kinase activation was involved in ET-1 stimulation and that PKC activation leads to suppression of basal and OSM-stimulated ET-1 production.

Structure-activity analysis of C-terminal endothelin analogues

Several synthetic endothelin (ET) analogues of the C-terminal ET hexapeptide (ET16-21) were analyzed by radio-receptor competition binding assays and biologic activity using both ETA and ETB receptor subtypes. In addition, we produced a hybridoma monoclonal antibody, anti-ET15-21, that appeared to crossreact with the entire ET molecule and was able to neutralize its biologic activity. Antibody binding was measured with competition enzyme-linked immunosorbent assays and a surface plasmon resonance-based biosensor (BIA technology). The ET16-21 moiety was modified with systematic replacement of each residue by alanine (Ala-scan). Whereas the C-terminal residues (Asp18, Ile20, and particularly Trp21) were very important for both receptor binding and immunologic activity, Ala substitution in positions 16, 17, and 19 hardly affected such activities. Analysis of another series of synthetic ET16-21 analogues with the His16 residue replaced by a non-amino-acidic block confirmed that the last two C-terminal residues are essential for receptor and antibody binding, whereas the central region of this hexapeptide is much more tolerant to modification. However, a critical steric conformation of the active hexapeptide is necessary.

Solution conformation of an ET(B) selective agonist, ET-1[Cys(Acm)1,15,Ala3,Leu7,Aib11], in CD3OH/H2O by 1H NMR and molecular modelling

To understand the basic structural requirements for the biological activity of endothelin peptides, the solution structure of an ETB selective agonist, ET-1[Cys-(Acm)1,15, Ala3,Leu7,Aib11, was investigated by 1H NMR spectroscopy and molecular modelling. The structure is characterised by an alpha-helical conformation between residues Ser5-His16 but is undefined at both the N and C termini. To date, neither the solution structures of linear modified peptides nor the effects of a methanol/water solvent system have been examined for endothelin or endothelin-like peptides. This structure plays an important role towards the design of endothelin receptor selective agonists and antagonists.

Ontogeny of endothelins-1 and -3, their receptors, and endothelin converting enzyme-1 in the early human embryo

The targeted gene inactivation of endothelins-1 and -3 (ET-1 and ET-3) and of one of their receptors, ETB, in the mouse causes severe defects in the embryonic development. These defects, cardiovascular and craniofacial malformations for ET-1, and colonic agangliogenesis associated with skin pigmentation anomalies for ET-3 and the ETB receptor, reproduce pathological phenotypes due to natural mutations of the same genes in the mouse and the human. The mutant phenotypes have been causatively linked to deficient migration/proliferation/differentiation of neural crest cells, i.e., neurocristopathies. To bring new insight about the exact roles of ETs in development and the involvement of neural crest cells in these processes, we have explored, by in situ hybridization, the ontogeny in the early human embryo of the ET system (ET-1 and ET-3, ETA and ETB receptors, ET converting enzyme-1). ET receptor mRNA expression in neural crest cells starts at 3 wk of gestation and continues during the entire period studied (up to 6 wk of gestation). During this period, ETA expression progressively spreads to undifferentiated mesodermal components of various structures and organs (head and axial skeleton, lateral and ventral subdermal mesoderm), whereas ETB expression remains more restricted to fewer differentiated cells (neural tube, sensory and sympathetic ganglia, endothelium). Some of these tissues and structures that express either one of the receptors do not appear to be of neural crest origin. In the digestive tract and the cardiovascular area, the present observations on the sources of ETs and their target cells in the young embryo provide the basis for a dynamic interpretation of the results of gene targeting of the mouse and the human phenotypes, and point to other possible roles of ETs in other ontogenetic processes. The results support the concept of local, rather than hormonal, interactions between the sources and targets of ETs during development.

Detection and epitope mapping of immunoreactive human endothelin-1 using ELISA and a surface plasmon resonance-based biosensor

A surface plasmon resonance-based biosensor (BIA technology) and enzyme-linked immunosorbent assays (ELISA) have been used for detecting and characterizing human endothelin (ET), a potent vasoactive 21 amino acid polypeptide. Antibodies produced against the isoform ET-1 and its C-terminal eptapeptide ET-1(15-21) have been characterized with respect to their binding capacity to the two isoforms ET-1 and ET-3, the non-secreted portion of the precursor molecule Big.ET-1(22-38), the C-terminal of ET-1, six analogues of ET-1(16-21) each containing a substitution with Ala of a single amino acid in positions 16-21, respectively, and three synthetic cyclic peptides mimicking the N-terminal portion of ET-1. Antibodies reacting with ET-1 also bound to ET-1(16-21) and, with less affinity, to ET-3 but did not cross-react with Big.ET-1(22-38). Ala substitution in positions 16, 17 and 19 of ET-1(16-21) hardly affected the antibody binding capacity of ET-1(16-21), whereas Ala substitution of Asp18, Ile20 and, in particular, Trp21, inhibited its immunoreactivity. The C-terminus thus represents an immunodominant epitope in ET-1 and is important for antibody binding. Epitope mapping using as antibody pairs polyclonal anti-ET-1 and monoclonal anti-ET-1(15-21) antibodies indicated the presence of another immunogenic domain in the N-terminal portion of the molecule. There was excellent agreement between the epitopes determined using ELISA and BIA analyses.

Hypoxia regulates endothelin-1 production by the inner medullary collecting duct

Renal endothelin-1 (ET-1 ) production is increased by hypoxia and has been implicated in ischemia-induced renal hypoperfusion. Because the inner medullary collecting duct (IMCD) is a major source of ET- 1 in the kidney, and because ET- 1--in the setting of ischemic renal failure-may alter medullary perfusion, we sought to determine whether hypoxia modulated ET-1 production by IMCD cells. Primary cultures of rat IMCD cells were exposed to 21%, 3%, or 0%O2. IMCD ET-1 secretion significantly increased after exposure of cultures to 3% O2 (114.1% +/- 4.7% increase over control value) and 0%O2 (171.7% +/- 7.9% increase). ET-1 mRNA levels, as determined by reverse transcription-polymerase chain reaction, also increased 2.5-fold after 24-hour exposure to 0% O2. We speculate that a hypoxia-induced increase in IMCD ET-1 production plays a role in modulating renal medullary perfusion during ischemic renal failure.

Solution structure determination of endothelin-1 in methanol/water by NMR and molecular modelling methods

To understand the structural requirements for the biological activity of endothelin peptides and to develop receptor selective endothelin analogues further, the solution structure of the bicyclic 21 amino acid residue vasoactive peptide, endothelin-1, has been determined in methanol-d3/water using high-resolution 1H-NMR spectroscopy. To our knowledge, this solvent system has not previously been used in NMR studies of endothelin and/or endothelin-like peptides. Two-dimensional DQFCOSY, TOCSY and NOESY spectra were acquired along with a series of one-dimensional spectra. A total of 219 distance constraints and 5 angle constraints were derived from the NMR data. These were incorporated into structure calculations using distance geometry (DIANA) followed by simulated annealing and molecular dynamics. The resulting structures are characterized by an alpha-helical conformation, Lys9-His16, and residues Ser5-Asp8 form a type I beta-turn. The N-terminal region, which was not extensively constrained by NMR data, showed no preferred conformation. The C-terminal tail showed less extensive conformational averaging but no descriptive conformation could be observed. The results obtained in this study are in good agreement with previous proposals.

A live-cell assay for studying extracellular and intracellular endothelin-converting enzyme activity

Endothelin-1 (ET-1) is formed from its precursor preproET-1 via the cleavage of the intermediate bigET-1 by endothelin-converting enzyme (ECE-1). However, the subcellular site at which this step occurs is not clear: It could occur intravesicularly along the secretory pathway or bigET-1 might be released and processed extracellularly. To address this point, we have developed an integrated autocrine system that uses a recombinant Chinese hamster ovary (CHO) luciferase reporter cell line that permanently expresses the human ET(A) receptor. Into these cells we transiently transfected human ECE-1a cDNA, either together with the human preproET-1 cDNA (as an endogenous source of bigET-1), or alone (in which case exogenous bigET-1 was added). Phosphoramidon inhibited the conversion of exogenous bigET-1 (IC50 = 5 to 30 micromol/L) much better than that of endogenous bigET-1 (IC50 > 1 mmol/L). Both conversions showed similar high yields (20% to 100%) that depended on the amount of ECE-1a expressed. Thus, ECE-1a has two equally relevant activities in this recombinant system for CHO cells: (1) an intracellular, probably intravesicular activity, corresponding to the ECE-1a-mediated step of ET-1 biosynthesis and (2) an extracellular activity at the plasma membrane. If this is also the case for endothelial cells, ECE-1a inhibitors would have to cross the plasma and vesicle membranes to be effective. The present system could be useful for screening such inhibitors.

Endothelium-derived relaxing and contracting factors during the early neonatal period

The interaction and relative potency of nitric oxide, an endothelium-derived relaxing factor, and endothelin-1, an endothelium-derived contracting factor, may be important in the transition from fetal to extrauterine life. The change in level of nitric oxide during the early neonatal period has not been measured. Accordingly, the serum levels of nitric oxide metabolites (the sum of nitrite and nitrate) and plasma endothelin-1 were determined in 20 healthy neonates at birth, at 12 and 24 h postnatally, and at the age of 5 d. The lowest serum concentration of nitric oxide metabolites was observed at birth (26.2 +/- 9.1 micromol l(-1), mean +/- SD) and increased with age, whereas the highest plasma concentration of endothelin-1 was observed at birth (14.0 +/- 6.7 pg ml(-1)) and decreased with age. These changes suggest that nitric oxide and endothelin-1 play roles in the circulatory adaptation of the neonate to extrauterine life.

Distribution of endothelin 3-like immunoreactivity in gonadotrophs of the bullfrog (Rana catesbeiana) pituitary

Immunohistochemical and immunocytochemical techniques were employed to investigate the distribution of endothelin 3 (ET3)-like immunoreactivity in the pituitary of the bullfrog, Rana catesbeiana. ET3-immunoreactive (ET3-IR) cells were scattered all over the pars distalis of the female pituitary; however, only a few ET3-IR cells were observed in the male pituitary. ET3-IR cells were found to correspond to cells immunostained with monoclonal antibodies against the beta-subunit of bullfrog LH (fLH beta) or monoclonal antibodies against the beta-subunit of bullfrog FSH (fFSH beta) at the light microscopic level. However, we could not find ET3-IR cells which were immunoreactive for other pituitary hormones. So far, all ET3-IR cells showed both fLH beta and fFSH beta immunoreactivity. About 24% of the fLH beta-IR cells and about 33% of the fFSH beta-IR cells showed ET3-like immunoreactivity. Immunoelectron microscopic analysis using colloidal gold revealed the coexistence of ET3-like substance(s) and gonadotropins within the same granules. This study demonstrated the presence of ET3-like peptide(s) in bullfrog gonadotrophs, suggesting the possible participation of ET3 in regulating pituitary function as an autocrine and/or paracrine hormone.

Shear stress augments expression of C-type natriuretic peptide and adrenomedullin

Shear stress is known to dilate blood vessels and exert antiproliferative effects on vascular walls: these effects have been ascribed to shear stress-induced upregulation of endothelium-derived vasoactive substances, mainly nitric oxide and prostacyclin. We have demonstrated the significance of C-type natriuretic peptide (CNP) as a novel endothelium-derived relaxing peptide (EDRP) that shares a cGMP pathway with nitric oxide. Adrenomedullin is a recently isolated EDRP that elevates intracellular cAMP as prostacyclin does. To elucidate the possible role of these EDRPs under shear stress, we examined the effect of physiological shear stress on CNP mRNA expression in endothelial cells derived from the human umbilical vein (HUVECs), bovine aorta (BAECs), and murine lymph nodes (MLECs) as well as adrenomedullin mRNA expression in HUVECs. CNP mRNA was stimulated prominently in HUVECs under shear stress of 15 dyne/cm2 in a time-dependent manner (4 hours, sixfold increase compared with that in the static condition; 24 hours, 30-fold increase). Similar results were obtained in BAECs (4 hours, twofold increase; 24 hours, threefold increase) and MLECs (4 hours, threefold increase; 24 hours, 10-fold increase). Augmentation of CNP mRNA expression that was dependent on shear stress intensity was also observed (5 dyne/cm2, 2.5-fold increase of static; 15 dyne/cm2, 4.5-fold increase). Increased CNP secretion was also confirmed by the specific radioimmunoassay for CNP. Adrenomedullin mRNA expression in HUVECs increased under shear stress of 15 dyne/cm2 in a time-dependent manner (4 hours, 1.2-fold increase of static: 24 hours, threefold increase) and shear stress intensity-dependent manner (15 dyne/cm2, threefold increase compared with that at 5 dyne/cm2). These results suggest that the coordinated augmentation of mRNA expression of these novel EDRPs may constitute shear stress-dependent vasodilator and antiproliferative effects.

The characterization, localization and regulation of endothelin in ovine pars intermedia

The pituitary intermediate lobe (IL) contains a single population of cells and has recently been shown to express endothelin (ET)-like peptides. The IL thus provides an excellent in vivo model to study regulation, function and processing of ET in an endocrine cell. The primary aims of the present study were to locate and characterize the precise molecular forms of ET in the ovine IL and determine if levels and/or processing of ET is under dopaminergic or other influences. We have developed a radioimmunoassay (RIA) that detects each form of ET and, when combined with reverse phase-HPLC (RP-HPLC), shows the ovine IL to contain predominantly the ET-1 isoform. In addition, using a specific anti-endothelin antiserum for immunohistochemistry (IHC), we localized ET-1 with alpha-melanocyte stimulating hormone (alpha-MSH) within the melanotroph. The effects of dopamine agonists, antagonists and hypothalamo-pituitary disconnection (HPD) on both tissue levels and processing of ET in the ovine IL were also examined. Normal sheep were treated chronically with haloperidol or bromocriptine to investigate the possibility of dopaminergic regulation of ET in the IL. In the haloperidol-treated group, plasma prolactin levels did not vary significantly from day 0 to day 8, but the bromocriptine treatment reduced prolactin levels (t = 9.4 P < 0.01). Neither bromocriptine nor haloperidol, however, affected tissue ET peptide levels or forms. After HPD, the HPLC profile of pooled IL showed that ET-1 levels in the IL are slightly increased with no change in molecular forms.

Deletion of a single amino acid changes the folding of an apamin hybrid sequence peptide to that of endothelin

The solution conformations of a hybrid sequence peptide related to the bee venom peptide apamin have been determined using two-dimensional 1H-nmr. Apamin is an 18 amino acid peptide containing a C-terminal helix that is stabilized by two disulfide bonds. The deletion of one residue (K4) of the N-terminal "scaffold" region of the apamin sequence results in a helical peptide, but with a change in the pairing of cysteines to form the disulfide cross links. The new disulfide arrangement is analogous to that of the vasoconstrictor peptide endothelin. Two sets of nmr resonances were observed for the apamin-deletion (AD) peptide, due to cistrans isomerism at the A4-P5 peptide bond. The cis isomer of the AD peptide contains a tight turn in residues 3-6, which is required for formation of the alpha-helix in residues 7-15. Nuclear Overhauser effects observed for the trans AD peptide are not consistent with any single unique fold, indicating the presence of conformational averaging when the peptide adopts the trans form. Distance geometry calculations on the cis AD peptide reveal an alpha-helical structure that appears to be more like that of apamin than the crystal structure of human endothelin, despite the reversal of the disulfide pattern in the AD peptide from that of apamin to that of endothelin.

Processing of proendothelin-1 at the C-terminus of big endothelin-1 is essential for proteolysis by endothelin-converting enzyme-1 in vivo

Production of endothelin-1 is thought to be a three-step process consisting of an initial proteolytic cleavage of the proendothelin-1 precursor to big endothelin-1-Lys-Arg, C-terminal trimming by a carboxypeptidase and further processing of the big endothelin-1 peptide to endothelin-1 by endothelin-converting enzyme (ECE). To further clarify the mechanism of processing in the biosynthesis of endothelin-1, we introduced a point mutation into endothelin-1 cDNA to replace the Arg in the -4 position of the recognition motifs of furin-like convertase in human preproendothelin-1 (Arg49 or Arg89) by Gly. When mutant cDNAs were expressed in Chinese hamster ovary (CHO)-K1 cells, they failed to be processed at the mutated processing signal, suggesting that the Arg-Ser-Lys-Arg motifs of preproendothelin-1 are recognized by CHO-K1 furin-like convertase. Co-transfection with ECE-1 cDNA revealed that cleavage at Arg52 is not essential for cleavage by ECE-1, but that cleavage at Arg92 is critical. Although a high-molecular-mass form of endothelin-1 is produced by processing by ECE-1 without cleavage at Arg52, it did not evoke Ca2+ transient in endothelinA-receptor-expressing cells. In conclusion, prior cleavage at Arg92 by furin-like convertase is absolutely necessary for cleavage by ECE-1 at Trp73 to produce mature endothelin-1.

Endothelin expression in human megakaryoblastic leukemia cell lines and normal platelet precursors

The aim of the present investigation was to determine whether endothelin (ET) could be expressed in and released from the human leukemia megakaryoblastic cell lines HEL, MEG-01, DAMI and the normal human platelet progenitors. Using the reverse transcriptase-polymerase chain reaction (RT-PCR) on total RNA isolated from the cells, we amplified a cDNA of the expected size (453 bp). Southern-blotting hybridization revealed that RT-PCR products from the cell lines were specific of ET-1 mRNA. Immunocytochemical analyses highlighted immunoreactive ET-1 in the cytoplasm of these cells which also released the mature peptide. ET-1 release from the three cell lines was increased by thrombin exposure. Although MEG-01 cells express ET receptors, ET-1, the selective ETB agonist sarafotoxin 6C and the non-selective ET-receptor antagonist PD 142893 showed no proliferative or antiproliferative action in basal or stimulating medium. This indicated a lack of autocrine ET-mediated effect on growth. These results demonstrate for the first time that human megakaryoblastic leukemia cell lines and normal bone marrow platelet precursors express ET-1 mRNA and release the mature peptide.

Inhibitors of endothelin

With the advent of the first generation of both selective and nonselective endothelin antagonists being a relatively recent event, the manifold therapeutic potentials of these compounds are only now being explored clinically. Undoubtedly, numerous clinical utilities for these compounds will soon be realized.

Endothelins and cardiac hypertrophy

Cardiac hypertrophy is a commonly observed complication of a variety of cardiovascular diseases. As well as mechanical stresses such as pressure overload, several humoral factors may contribute to the development of cardiac hypertrophy. In the early 1990s, endothelin-1 (ET-1) was found to induce cardiomyocyte hypertrophy in cultured neonatal rat cardiomyocytes. Furthermore, evidence is accumulating to date to support the postulate that ET-1 may function as an autocrine/paracrine factor in the development of cardiac hypertrophy in vivo as well as in vitro In this review article, I discuss physiological and pathophysiological roles of ET-1 and its related peptides in cardiac hypertrophy associated with various cardiovascular diseases.

Efonidipine, a long-acting dihydropyridine derivative, attenuates coronary vasoconstriction induced by endothelin-1 in dogs

Effect of efonidipine, a long-acting dihydropyridine derivative, on the endothelin-1 (ET-1)-induced coronary vasoconstriction was studied in open-chest anesthetized dogs. Efonidipine (0.03 or 0.1 mg/kg) was administered i.v. 10 min before an intracoronary injection of ET-1 (30 pmol/kg). An intracoronary injection of ET-1 decreased coronary blood flow (CBF) that was measured by a flow probe. The ET-1-induced decrease in CBF was sustained for more than 30 min without significant changes in blood pressure and heart rate. Pretreatment with efonidipine attenuated the decrease in CBF induced by ET-1 significantly and dose-dependently. ET-1 also reduced coronary diameter for more than 30 min as evaluated by the coronary angiography technique. Pretreatment with efonidipine also attenuated the reduction in coronary diameter induced by ET-1 significantly and dose-dependently. These effects of efonidipine were sustained for at least 30 min after the ET-1 administration. It is concluded that efonidipine attenuates the ET-1-induced vasoconstriction, and therefore the drug would be useful for some patients with variant angina, in which ET-1 is involved in the genesis of coronary vasoconstriction.

Systemic hypertension induced by hepatic overexpression of human preproendothelin-1 in rats

Endothelin-1 (ET-1) has been implicated in the regulation of vascular tone in various pathological conditions. To examine the effect of in vivo overexpression of the peptide in rats, we prepared recombinant adenovirus stocks encoding the human preproET-1 cDNA (Ad.ET-1) or Escherichia coli lacZ (Ad.betaGal), each driven by cytomegalovirus early promoter. Ad.ET-1 or Ad.betaGal was injected into the caudal vein of rats and the animals were studied under anesthesia 96 h later. Hepatic overexpression of the virus-derived human ET-1 mRNA was accompanied by a 13-fold elevation of liver ET-1 content in the Ad.ET-1 group. Circulating plasma ET-1 levels in the Ad.ET-1 group were sixfold higher than those in the Ad.betaGal group. Mean arterial blood pressure was increased by 28 mmHg in the Ad.ET-1 group as compared with the Ad.betaGal group. In the Ad.ET-1 group, intravenous infusion of the ET(A) receptor antagonist FR 139317 reduced the blood pressure to levels seen in the Ad.betaGal group, whereas the same antagonist did not significantly alter the blood pressure in the Ad.betaGal group. Intravenous infusion of the ET(B) receptor antagonist BQ-788 caused a small but significant increase in blood pressure in both groups. These findings demonstrate that endogenous overexpression of preproET-1, accompanied by an elevation of plasma ET-1 concentrations to the levels seen in pathophysiological states, can cause systemic hypertension through the activation of the ETA receptor.

Increased concentrations of endothelin-1 messenger RNA in tissues and endothelin-1 peptide in plasma in septic pigs: modulation by betamethasone

OBJECTIVES

To study the expression of preproendothelin-1 messenger RNA (mRNA) in tissue after Escherichia coli lipopolysaccharide challenge and to evaluate the possible effects of betamethasone both regarding endothelin-1 production as well as hemodynamic and vascular effects during E. coli lipopolysaccharide infusion in pigs in vivo.

DESIGN

Prospective trial.

SETTING

Laboratory at a university medical center.

SUBJECTS

Ten domestic pigs, weighing 18 to 25 kg.

INTERVENTIONS

Anesthetized pigs were given continuous infusions of E. coli lipopolysaccharide (15 micrograms/kg/hr for 3 hrs), with or without prior treatment with betamethasone (0.5 mg/kg im 12 hrs before the start of the surgical preparation and 0.5/kg iv at the start of the preparation).

MEASUREMENTS AND MAIN RESULTS

The E. coli lipopolysaccharide infusion evoked the characteristic cardiovascular changes observed in septic shock: decreased mean arterial pressure and cardiac output; increased heart rate and increased pulmonary vascular resistance. Large increases in both arterial plasma concentrations of endothelin-1-like immunoreactivity, as well as preproendothelin-1 mRNA concentrations in tissues, were also observed during the E. coli lipopolysaccharide infusion. Treatment with betamethasone significantly attenuated the E. coli lipopolysaccharide-induced increase in endothelin-1 plasma concentrations, whereas the increased mRNA concentrations were only slightly affected. Furthermore, betamethasone treatment also affected cardiovascular parameters, with significant attenuation of the E. coli lipopolysaccharide-induced increase in heart rate and a higher cardiac output after 60 mins of the E. coli lipopolysaccharide infusion. The urine production, which was markedly decreased during the E. coli lipopolysaccharide infusion, was significantly higher in the betamethasone-treated group compared with the control group.

CONCLUSIONS

The present results indicate that the increased concentrations of endothelin-1-like immunoreactivity that are observed in septic shock may have negative effects on both cardiovascular parameters as well as renal function, which is in agreement with a possible role for endothelin-1 in the pathogenesis of septic shock.

Sequence and neuronal expression of mouse endothelin-1 cDNA

We have isolated and sequenced a cDNA that encodes mouse endothelin-1 (ET-1). The putative protein contains 202 amino acids corresponds to the prepro-form of ET-1. Twenty-one amino acids sequence of the putative mature ET-1 was identical with that of rat, porcine, bovine, and human. In situ hybridization histochemistry indicate that ET-1 mRNA was expressed in several hypothalamic nuclei including the suprachiasmatic nucleus (SCN) in rodent brain.

Bosentan-improved cardiopulmonary vascular performance and increased plasma levels of endothelin-1 in porcine endotoxin shock

1. To evaluate the possible contribution of endothelin-1 (ET-1) to the pathophysiology of porcine septic shock, the non-peptide, mixed ET-receptor antagonist, bosentan (RO 47-0203) was administered (5 mg kg-1, i.v.) 30 min before infusion of lipopolysaccharide (LPS) (E. coli., serotype 0111:B4) (15 micrograms kg-1 h-1) and at 3.5 h of endotoxaemia in six anaesthetized and mechanically ventilated pigs. Six other pigs served as controls and received only LPS infusion. Pulmonary and systemic haemodynamics as well as splenic, renal and intestinal blood flows were measured continuously. Release and synthesis of ET-1 and Big ET-1 were also measured. 2. Only three of the six pigs in the control group survived 3 h of LPS infusion while in the bosentantreated group all six pigs were alive at that time. A biphasic increase in mean pulmonary arterial pressure (MPAP) and pulmonary vascular resistance (PVR) was seen in control pigs. Pretreatment with bosentan did not influence the first peak but markedly attenuated the second, more prolonged increase in MPAP and PVR. The second dose of bosentan completely restored these parameters to pre-LPS levels. The LPS-induced changes in mean arterial blood pressure, heart rate and systemic vascular resistance were similar in both groups, while cardiac output (CO) was significantly higher in the bosentan-treated group. The second bosentan dose increased CO and splenic and intestinal blood flow without further lowering of blood pressure. 3. Bosentan caused an increase of the basal arterial plasma levels of ET-1-like immunoreactivity (LI), from 16.8 +/- 1.3 pM to 49.6 +/- 10.0 pM (n = 6, P < 0.01). However, the rate of the increase of ET-1 levels during the LPS infusion was not affected by bosentan. Repeated administration of bosentan during LPS infusion caused an additional increase of ET-1-LI levels. Neither the basal levels of Big ET-LI nor the LPS induced 8 fold increase in Big ET-LI were changed by bosentan. The level of preproET-1 mRNA in the lung was increased about 3 fold after 4.5 h of LPS treatment. This elevation was not influenced by bosentan. 4. From these studies using bosentan, a non-peptide, selective and mixed ET-receptor antagonist, we conclude that during LPS-induced shock bosentan can abolish the late phase pulmonary hypertension and improve cardiac output as well as increase blood flow to the splenic and intestinal vascular beds without causing a further decrease in mean arterial blood pressure. Further investigations in the clinical setting are needed to evaluate the use of ET-receptor antagonists, such as bosentan, in treatment of septic shock.

Hypoxia decreases constitutive nitric oxide synthase transcript and protein in cultured endothelial cells

Endothelial cell-generated nitric oxide (NO) accounts in large part for the labile vasodilator termed endothelium-derived relaxing factor. Two distinct types of NO synthase exist: a "constitutive' type (cNOS), found in endothelial cells, and an "inducible' enzyme. Endothelial cells sense pO2 levels in the range of 70-20 torr and respond to this hypoxia by inducing transcription of genes which encode the vasoactive proteins PDGF-B and endothelin-1. Exposure of human or bovine endothelial cells to low oxygen tensions results in a profound decrease in the transcript for cNOS and a corresponding fall in cNOS protein levels. The ability of endothelial cells exposed to hypoxia to produce NO in response to bradykinin, a stimulator of cNOS activity, was coordinately impaired. Cobalt inhibited the expression of cNOS transcripts, suggesting a mechanism comparable to that by which oxygen tension regulates expression of other vasoregulatory genes. In the presence of actinomycin-D, hypoxia had no effect on cNOS transcripts, suggesting that new gene transcription is required for cNOS suppression. The reducing agents PDTC and N-Ac did not mimic cNOS gene suppression by hypoxia, suggesting that this suppression is not related to the redox state of the intracellular environment. Thus, regulation of cNOS function in response to environmental factors can occur at the level of gene expression as well as at the level of enzyme activation.

Luteotropic and luteolytic mechanisms in the bovine corpus luteum

The function of the corpus luteum (CL) is a key element in many reproductive processes including ovulation, length of the estrous cycle, recognition of pregnancy and embryo survival in all mammalian species. The main function of the CL is to produce progesterone which acts on its tissues to prepare them for successful pregnancy. The CL is controlled by numerous biological compounds which provide luteotropic support during the estrous cycle and pregnancy and for inducing luteolysis at the end of the cycle The purpose of this paper is to review the mechansims responsible for controlling the endocrine function of this tissue in the bovine ovary.

Parathyroid hormone-related protein inhibits indothelin-1 production

The effect of human parathyroid hormone-related protein, a powerful vasodilator, on endothelin-1 production in cultured bovine pulmonary arterial endothelial cells was studied. Treatment with parathyroid hormone-related protein(1-34) at concentrations of 10(-9) to 10(-6) mol/L for 24 hours caused dose-dependent suppression of the secretion of endothelin-1, with maximal suppression at 10(-7) mol/L to 74% of the control value. This inhibitory effect was completely abolished by coincubation with 100 ng/mL pertussis toxin, an inhibitor of GTP binding protein. Furthermore, addition of Ng-monomethyl-L-arginine, an inhibitor of nitric oxide synthase, at 10(-3) mol/L significantly blocked the suppressive effect of parathyroid hormone-related protein (1-34) on endothelin-1 secretion, and further addition of 5x10(-3) mol/L L-arginine significantly attenuated the blocking effect of N(G)-monomethyl-L-arginine. Parathyroid hormone-related protein (1-34) at 10(-7) mol/L resulted in an approximately fivefold increase in intracellular cGMP level. Northern blot analysis revealed that parathyroid hormone-related protein (1-34) inhibited both basal and thrombin-induced endothelin-1 gene expression. These findings suggest that the vasodilating property of parathyroid hormone-related protein may be mediated in part through its inhibitory effect on endothelin-1 production, which is probably mediated through nitric oxide and cGMP in endothelial cells. Thus, a feedback regulatory mechanism may exist between parathyroid hormone-related protein and endothelin-1 in the vascular wall.

Effect of reactive oxygen species on endothelin-1 production by human mesangial cells

Reactive oxygen species (ROS) have been implicated in the pathophysiology of renal ischemia/reperfusion injury. Endothelin-1 (ET-1) is generated in abundance in renal ischemia/reperfusion with resultant decreases in renal blood flow and glomerular filtration rate. To determine if ROS regulate ET-1 production, the effect of ROS donors or scavengers on ET-1 protein and mRNA levels in cultured human mesangial cells was examined. Incubation with xanthine/xanthine oxidase, glucose oxidase, or H2O2 caused a dose-dependent rise in ET-1 release. Similarly, xanthine/xanthine oxidase or H2O2 augmented ET-1 mRNA levels. In contrast, the ROS scavengers dimethylthiourea (DMTU), dimethylpyrroline N-oxide, or pyrrolidine dithiocarbamate reduced basal ET-1 release, while DMTU lowered ET-1 mRNA levels. Deferoxamine, an iron chelator, also decreased basal ET-1 release. Superoxide dismutase potentiated the ET-1 stimulatory effect of xanthine/xanthine oxidase, while catalase abrogated the effect of xanthine/xanthine oxidase and H2O2. The effects of ROS were unrelated to changes in nitric oxide production or cytotoxicity. These data indicate that exogenously or endogenously-derived ROS can increase ET-1 production by human mesangial cells. While superoxide anion reduces ET-1 levels, H2O2 leads to enhanced production of the peptide. ROS stimulation of mesangial cell ET-1 production may contribute to impaired glomerular hemodynamics in the setting of renal ischemia/reperfusion injury.

Role of the neutral endopeptidase 24.11 in the conversion of big endothelins in guinea-pig lung parenchyma

1. We have studied the conversion of big endothelin-1 (big ET-1), big endothelin-2 (big ET-2) and big endothelin-3 (big ET-3) and characterized the enzyme involved in the conversion of the three peptides in guinea-pig lung parenchyma (GPLP). 2. Endothelin-1 (ET-1), endothelin-2 (ET-2) and endothelin-3 (ET-3) (10 nM to 100 nM) caused similar concentration-dependent contractions of strips of GPLP. 3. Big ET-1 and big ET-2 also elicited concentration-dependent contractions of GPLP strips. In contrast, big ET-3, up to a concentration of 100 nM, failed to induce a contraction of the GPLP. 4. Incubation of strips of GPLP with the dual endothelin converting enzyme (ECE) and neutral endopeptidase (NEP) inhibitor, phosphoramidon (10 microM), as well as two other NEP inhibitors thiorphan (10 microM) or SQ 28,603 (10 microM) decreased by 43% (P < 0.05), 42% (P < 0.05) and 40% (P < 0.05) the contractions induced by 30 nM of big ET-1 respectively. Captopril (10 microM), an angiotensin-converting enzyme inhibitor, had no effect on the contractions induced by big ET-1. 5. The incubation of strips of GPLP with phosphoramidon (10 microM), thiorphan (10 microM) or SQ 28,603 (10 microM) also decreased by 74% (P < 0.05), 34% and 50% (P < 0.05) the contractions induced by 30 nM big ET-2 respectively. As for the contractions induced by big ET-1, captopril (10 microM) had no effect on the concentration-dependent contractions induced by big ET-2. 6. Phosphoramidon (10 microM), thiorphan (10 microM) and SQ 28,603 (10 microM) significantly potentiated the contractions of strips of GPLP induced by both ET-1 (30 nM) and ET-3 (30 nM). However, the enzymatic inhibitors did not significantly affect the contractions induced by ET-2 (30 nM) in this tissue. 7. These results suggest that the effects of big ET-1 and big ET-2 result from the conversion to ET-1 and ET-2 by at least one enzyme sensitive to phosphoramidon, thiorphan and SQ 28,603. This enzyme corresponds possibly to EC 3.4.24.11 (NEP 24.11) and could also be responsible for the degradation of ETs in the GPLP.

The endothelin system and its potential as a therapeutic target in cardiovascular disease

Endothelin (ET)-1, an endothelium-derived peptide, is the most potent vasoconstrictor agent described to date. ET-1 also has positive inotropic and chronotropic effects in the heart and is a co-mitogen in both cardiac and vascular myocytes. The major elements of the system involved in formation of ET-1 and its isopeptides, as well as the receptors mediating their effects, have been cloned and characterised. Antagonists of the ET receptors are now available, and selective inhibitors of the ET-converting enzymes are being developed. Early studies using receptor antagonists support the involvement of ET-1 in the pathophysiology of several cardiovascular diseases. The relative merits of ET-converting enzyme inhibitors and receptor antagonists for the treatment of cardiovascular disease are discussed.