Autoradiographical localization of binding sites for porcine [125I]endothelin-1 in humans, pigs, and rats: functional relevance in humans

Sovateltide (ILR-1620) Improves Motor Function and Reduces Hyperalgesia in a Rat Model of Spinal Cord Injury

BACKGROUND

Spinal cord injury (SCI) presents a major global health challenge, with rising incidence rates and substantial disability. Although progress has been made in understanding SCI's pathophysiology and early management, there is still a lack of effective treatments to mitigate long-term consequences. This study investigates the potential of sovateltide, a selective endothelin B receptor agonist, in improving clinical outcomes in an acute SCI rat model.

METHODS

Thirty male Sprague-Dawley rats underwent sham surgery (group A) or SCI and treated with vehicle (group B) or sovateltide (group C). Clinical tests, including Basso, Beattie, and Bresnahan scoring, inclined plane, and allodynia testing with von Frey hair, were performed at various time points. Statistical analyses assessed treatment effects.

RESULTS

Sovateltide administration significantly improved motor function, reducing neurological deficits and enhancing locomotor recovery compared with vehicle-treated rats, starting from day 7 post injury. Additionally, the allodynic threshold improved, suggesting antinociceptive properties. Notably, the sovateltide group demonstrated sustained recovery, and even reached preinjury performance levels, whereas the vehicle group plateaued.

CONCLUSIONS

This study suggests that sovateltide may offer neuroprotective effects, enhancing neurogenesis and angiogenesis. Furthermore, it may possess anti-inflammatory and antinociceptive properties. Future clinical trials are needed to validate these findings, but sovateltide shows promise as a potential therapeutic strategy to improve functional outcomes in SCI. Sovateltide, an endothelin B receptor agonist, exhibits neuroprotective properties, enhancing motor recovery and ameliorating hyperalgesia in a rat SCI model. These findings could pave the way for innovative pharmacological interventions for SCI in clinical settings.

Comprehensive analysis of the endothelin system in the kidneys of mice, rats, and humans

The intrarenal endothelin (ET) system is an established moderator of kidney physiology and mechanistic contributor to the pathophysiology and progression of chronic kidney disease in humans and rodents. The aim of the present study was to characterize ET system by combining single cell RNA sequencing (scRNA-seq) data with immunolocalization in human and rodent kidneys of both sexes. Using publicly available scRNA-seq data, we assessed sex and kidney disease status (human), age and sex (rats), and diurnal expression (mice) on the kidney ET system expression. In normal human biopsies of both sexes and in rodent kidney samples, the endothelin-converting enzyme-1 (ECE1) and ET-1 were prominent in the glomeruli and endothelium. These data agreed with the scRNA-seq data from these three species, with ECE1/Ece1 mRNA enriched in the endothelium. However, the EDN1/Edn1 gene (encodes ET-1) was rarely detected, even though it was immunolocalized within the kidneys, and plasma and urinary ET-1 excretion are easily measured. Within each species, there were some sex-specific differences. For example, in kidney biopsies from living donors, men had a greater glomerular endothelial cell endothelin receptor B (Ednrb) compared with women. In mice, females had greater kidney endothelial cell Ednrb than male mice. As commercially available antibodies did not work in all species, and RNA expression did not always correlate with protein levels, multiple approaches should be considered to maintain required rigor and reproducibility of the pre- and clinical studies evaluating the intrarenal ET system.

Outer Membrane Vesicle-Host Cell Interactions

Outer membrane vesicles (OMVs) are nanosized proteoliposomes derived from the outer membrane of Gram-negative bacteria. They are ubiquitously produced both in culture and during infection and are now recognized to play crucial roles during host-microbe interactions. OMVs can transport a broad range of chemically diverse cargoes, including lipids and lipopolysaccharides, membrane-embedded and associated proteins and small molecules, peptidoglycan, and nucleic acids. Particularly, virulence factors such as adhesins and toxins are often enriched in OMVs. Here we discuss a variety of ways in which OMVs facilitate host-microbe interactions, including their contributions to biofilm formation, nutrient scavenging, and modulation of host cell function. We particularly examine recent findings regarding OMV-host cell interactions in the oral cavity and the gastrointestinal tract.

Endothelin

The endothelins comprise three structurally similar 21-amino acid peptides. Endothelin-1 and -2 activate two G-protein coupled receptors, ETA and ETB, with equal affinity, whereas endothelin-3 has a lower affinity for the ETA subtype. Genes encoding the peptides are present only among vertebrates. The ligand-receptor signaling pathway is a vertebrate innovation and may reflect the evolution of endothelin-1 as the most potent vasoconstrictor in the human cardiovascular system with remarkably long lasting action. Highly selective peptide ETA and ETB antagonists and ETB agonists together with radiolabeled analogs have accurately delineated endothelin pharmacology in humans and animal models, although surprisingly no ETA agonist has been discovered. ET antagonists (bosentan, ambrisentan) have revolutionized the treatment of pulmonary arterial hypertension, with the next generation of antagonists exhibiting improved efficacy (macitentan). Clinical trials continue to explore new applications, particularly in renal failure and for reducing proteinuria in diabetic nephropathy. Translational studies suggest a potential benefit of ETB agonists in chemotherapy and neuroprotection. However, demonstrating clinical efficacy of combined inhibitors of the endothelin converting enzyme and neutral endopeptidase has proved elusive. Over 28 genetic modifications have been made to the ET system in mice through global or cell-specific knockouts, knock ins, or alterations in gene expression of endothelin ligands or their target receptors. These studies have identified key roles for the endothelin isoforms and new therapeutic targets in development, fluid-electrolyte homeostasis, and cardiovascular and neuronal function. For the future, novel pharmacological strategies are emerging via small molecule epigenetic modulators, biologicals such as ETB monoclonal antibodies and the potential of signaling pathway biased agonists and antagonists.

Regulation of aldosterone synthesis and secretion

Aldosterone is a steroid hormone synthesized in and secreted from the outer layer of the adrenal cortex, the zona glomerulosa. Aldosterone is responsible for regulating sodium homeostasis, thereby helping to control blood volume and blood pressure. Insufficient aldosterone secretion can lead to hypotension and circulatory shock, particularly in infancy. On the other hand, excessive aldosterone levels, or those too high for sodium status, can cause hypertension and exacerbate the effects of high blood pressure on multiple organs, contributing to renal disease, stroke, visual loss, and congestive heart failure. Aldosterone is also thought to directly induce end-organ damage, including in the kidneys and heart. Because of the significance of aldosterone to the physiology and pathophysiology of the cardiovascular system, it is important to understand the regulation of its biosynthesis and secretion from the adrenal cortex. Herein, the mechanisms regulating aldosterone production in zona glomerulosa cells are discussed, with a particular emphasis on signaling pathways involved in the secretory response to the main controllers of aldosterone production, the renin-angiotensin II system, serum potassium levels and adrenocorticotrophic hormone. The signaling pathways involved include phospholipase C-mediated phosphoinositide hydrolysis, inositol 1,4,5-trisphosphate, cytosolic calcium levels, calcium influx pathways, calcium/calmodulin-dependent protein kinases, diacylglycerol, protein kinases C and D, 12-hydroxyeicostetraenoic acid, phospholipase D, mitogen-activated protein kinase pathways, tyrosine kinases, adenylate cyclase, and cAMP-dependent protein kinase. A complete understanding of the signaling events regulating aldosterone biosynthesis may allow the identification of novel targets for therapeutic interventions in hypertension, primary aldosteronism, congestive heart failure, renal disease, and other cardiovascular disorders.

Inotropic action of the puberty hormone kisspeptin in rat, mouse and human: cardiovascular distribution and characteristics of the kisspeptin receptor

Kisspeptins, the ligands of the kisspeptin receptor known for its roles in reproduction and cancer, are also vasoconstrictor peptides in atherosclerosis-prone human aorta and coronary artery. The aim of this study was to further investigate the cardiovascular localisation and function of the kisspeptins and their receptor in human compared to rat and mouse heart. Immunohistochemistry and radioligand binding techniques were employed to investigate kisspeptin receptor localisation, density and pharmacological characteristics in cardiac tissues from all three species. Radioimmunoassay was used to detect kisspeptin peptide levels in human normal heart and to identify any pathological changes in myocardium from patients transplanted for cardiomyopathy or ischaemic heart disease. The cardiac function of kisspeptin receptor was studied in isolated human, rat and mouse paced atria, with a role for the receptor confirmed using mice with targeted disruption of Kiss1r. The data demonstrated that kisspeptin receptor-like immunoreactivity localised to endothelial and smooth muscle cells of intramyocardial blood vessels and to myocytes in human and rodent tissue. [¹²⁵I]KP-14 bound saturably, with subnanomolar affinity to human and rodent myocardium (K_D = 0.12 nM, human; K_D = 0.44 nM, rat). Positive inotropic effects of kisspeptin were observed in rat, human and mouse. No response was observed in mice with targeted disruption of Kiss1r. In human heart a decrease in cardiac kisspeptin level was detected in ischaemic heart disease. Kisspeptin and its receptor are expressed in the human, rat and mouse heart and kisspeptins possess potent positive inotropic activity. The cardiovascular actions of the kisspeptins may contribute to the role of these peptides in pregnancy but the consequences of receptor activation must be considered if kisspeptin receptor agonists are developed for use in the treatment of reproductive disorders or cancer.

Contractile Response of Human Omental Arteries to Endothelin

The effects of endothelin have been studied in isolated arterial segments (0·8–1 mm in external diam.) of human omental arteries obtained during the course of abdominal operations (15 patients, 7 men and 8 women). Paired segments, one normal and the other de-endothelized, were mounted for isometric recording of tension in organ baths. Endothelin produced concentration-dependent contractions with an EC50 value of 5·4 × 10−9  m. Removal of endothelium did not affect significantly endothelin-induced contractions (EC50, 6·7 × 10−9  m). Removal of extracellular calcium or addition of the calcium channel blocker nicardipine (10−6  m) diminished but did not abolish responses to endothelin. These results indicate that endothelin exerts powerful contractile effects on human isolated omental arteries which are independent of the presence of an intact endothelial cell layer; this contraction cannot be explained solely by voltage-dependent calcium channels.

The interaction between endothelin-1 and nitric oxide in the vasculature: new perspectives

Nitric oxide (NO) and endothelin-1 (ET-1) are natural counterparts in vascular function, and it is becoming increasingly clear that an imbalance between these two mediators is a characteristic of endothelial dysfunction and is important in the progression of vascular disease. Here, we review classical and more recent data that suggest that ET-1 should be regarded as an essential component of NO signaling. In particular, we review evidence of the role of ET-1 in models of acute and chronic NO synthase blockade. Furthermore, we discuss the possible mechanisms by which NO modulates ET-1 activity. On the basis of these studies, we suggest that NO tonically inhibits ET-1 function, and in conditions of diminished NO bioavailability, the deleterious effects of unmitigated ET-1 actions result in vasoconstriction and eventually lead to vascular remodeling and dysfunction.

Regulation of blood pressure and salt homeostasis by endothelin

Endothelin (ET) peptides and their receptors are intimately involved in the physiological control of systemic blood pressure and body Na homeostasis, exerting these effects through alterations in a host of circulating and local factors. Hormonal systems affected by ET include natriuretic peptides, aldosterone, catecholamines, and angiotensin. ET also directly regulates cardiac output, central and peripheral nervous system activity, renal Na and water excretion, systemic vascular resistance, and venous capacitance. ET regulation of these systems is often complex, sometimes involving opposing actions depending on which receptor isoform is activated, which cells are affected, and what other prevailing factors exist. A detailed understanding of this system is important; disordered regulation of the ET system is strongly associated with hypertension and dysregulated extracellular fluid volume homeostasis. In addition, ET receptor antagonists are being increasingly used for the treatment of a variety of diseases; while demonstrating benefit, these agents also have adverse effects on fluid retention that may substantially limit their clinical utility. This review provides a detailed analysis of how the ET system is involved in the control of blood pressure and Na homeostasis, focusing primarily on physiological regulation with some discussion of the role of the ET system in hypertension.

Endothelins in reproduction

Endothelin-1 (ET-1) is a 21 amino acid peptide, first isolated in 1988 from porcine aortic endothelial cells in tissue culture (Figure 1). The peptide was shown to be the most potent known vasoconstrictor of porcine coronary arteries. A powerful endothelium-derived vasoconstrictor had been predicted for some time, but it was when Yanagisawa and his colleagues elucidated the structure, and provided information about the molecular biology and mode of action of the peptide that an unprecedented interest was stimulated in the endothelins.

Vaso-active factors in pregnancy

Pregnancy results in profound physiological changes in the cardiovascular system, yet these changes are completely reversible. It is apparent that vaso-active factors, some as yet probably unidentified, which act as humoral or local autocrine or paracrine regulators of vasular resistance, play a major role in these cardio-vascular changes. This role may be heightened in pregnancy when there has to be a large increase in blood flow to the uterus and placenta while maintaining adequate flow to other vascular beds. Our knowledge of the mechanisms of action of these vaso-active factors and their interactions with each other still remains incomplete. Alterations in synthesis and action of these vaso-active factors may occur in pregnancies associated with pregnancy-induced hypertension, pre-eclampsia or intra-uterine growth retardation. Investigation of such alterations may help to elucidate the roles of vaso-active factors in both normal and pathological situations. The gestational hormones oestrogen and progesterone, are obviously prime candidates as overall regulators of the cardiovascular changes of pregnancy and as agents which alter the synthesis or action of other vaso-active factors. Currently, much attention is being focused on the role of local autocrine or paracrine vaso-active factors which may be produced by the endothelium or by the underlying vascular smooth muscle cells and alterations in their production or action in the hyptertensive disorders of pregnancy. The endothelium forms the largest endocrine organ within the body and so its importance in the mediation of vascular events should not be under-estimated. The principal objective of this review is to examine the roles of these many autocrine and paracrine vaso-active factors during pregnancy and their relation with the overall regulation of the vascular system. Changes which may occur and be involved in the aetiology of pre-eclampsia and growth retardation will also be examined.

Reversal of the expression pattern of Aldolase C mRNA in Purkinje cells and Ube 1x mRNA in Golgi cells by a dopamine D1 receptor agonist injections in the methamphetamine sensitized-rat cerebellum

The cerebellum has a parasagittal modular structure, in which Zebrin (Aldolase) positive and negative bands expressed in Purkinje cell layers alternate, and is involved in amphetamine psychosis. Administration of SKF38393, a D1 receptor agonist, reversed the behavioral sensitization of methamphetamine. In the vermis, there were the binding sites of SKF38393. In methamphetamine-sensitized rats the expression of the Aldolase mRNA positive bands move laterally in the rat vermis. We provide here the evidence that the D1 agonist injections also reversed the expression pattern of both the Aldolase mRNA in Purkinje cells and Ube (ubiquitin activating enzyme) 1x mRNA in Golgi interneurons of the sensitized rats. Thus the reverse changes in gene expression pattern in the vermis may be involved in the mechanisms of the behavioral plasticity and suggests the new treatment of drug abuse.

Endothelin

In humans, the endothelins (ETs) comprise a family of three 21-amino-acid peptides, ET-1, ET-2 and ET-3. ET-1 is synthesised from a biologically inactive precursor, Big ET-1, by an unusual hydrolysis of the Trp21 -Val22 bond by the endothelin converting enzyme (ECE-1). In humans, there are four isoforms (ECE-1a-d) derived from a single gene by the action of alternative promoters. Structurally, they differ only in the amino acid sequence of the extreme N-terminus. A second enzyme, ECE-2, also exists as four isoforms and differs from ECE-1 in requiring an acidic pH for optimal activity. Human chymase can also cleave Big ET-1 to ET-1, which is cleaved, in turn, to the mature peptide as an alternative pathway. ET-1 is the principal isoform in the human cardiovascular system and remains one of the most potent constrictors of human vessels discovered. ET-1 is unusual in being released from a dual secretory pathway. The peptide is continuously released from vascular endothelial cells by the constitutive pathway, producing intense constriction of the underlying smooth muscle and contributing to the maintenance of endogenous vascular tone. ET-1 is also released from endothelial cell-specific storage granules (Weibel-Palade bodies) in response to external stimuli. ETs mediate their action by activating two G protein-coupled receptor sub-types, ETA and ET(B). Two therapeutic strategies have emerged to oppose the actions of ET-1, namely inhibition of the synthetic enzyme by combined ECE/neutral endopeptidase inhibitors such as SLV306, and receptor antagonists such as bosentan. The ET system is up-regulated in atherosclerosis, and ET antagonists may be of benefit in reducing blood pressure in essential hypertension. Bosentan, the first ET antagonist approved for clinical use, represents a significant new therapeutic strategy in the treatment of pulmonary arterial hypertension (PAH).

Effect of endothelins on the cardiovascular system

Endothelins (ETs) exert a persistent constrictor effect on the vessels via an increase in intracellular Ca2+ concentration due to the activation of Na+/H+ and Na+/Ca2+ exchangers of the vascular smooth muscle fibres. They also produce a transient dilator effect via the activation of endothelial nitric oxide synthase mediated by protein kinase B/Akt. ETA and ETB2 receptors are involved in vasoconstriction, whereas transient vasodilatation depends on the activation of ETB1 receptors. Depending on animal species and experimental conditions, ETs can also play a role in cardiac muscle contraction and induce either an increase or a decrease in contractility. It is likely that only ETA, and not ETB, receptors are involved in the ET-induced increase in myocardial contractility. As in the case of vasoconstriction, this inotropic effect depends on an increase in intracellular Ca2+ concentration induced by Na+/H+ and Na+/Ca2+ exchangers. Activation of the Na+/H+ exchanger is stimulated by protein kinase C, which is activated by diacylglycerol released in response to ET activity. It has also been proposed that the positive inotropic effect can occur without the contribution of the Na+/Ca2+ exchanger, if the cell alkalinisation produced by the Na/H exchanger improves myofibrillar Ca2+ sensitivity. A reduction in contractility has been attributed to the involvement of the Gi protein/protein kinase G pathway or to the activation of protein kinase C without an increase in intracellular Ca2+ concentration or in myofibrillar Ca2+ sensitivity. The chronic effect of ETs on the myocardium results in hypertrophy and prevention of apoptosis, two processes that are together responsible for the contradictory effect of ETs in heart failure.

Synergistic activation of salmon cardiac function by endothelin and beta-adrenergic stimulation

The aim was to find out the effects of endothelin-1 (ET-1) in salmon (Salmo salar) cardiac contractile and endocrine function and its possible interaction with beta-adrenergic regulation. We found that ET-1 has a positive inotropic effect in salmon heart. ET-1 (30 nM) increased the contraction amplitude 17+/-4.7% compared with the basal level. beta-Adrenergic activation (isoprenaline, 100 nM) increased contraction amplitude 30+/-13.1%, but it did not affect the contractile response to ET-1. ET-1 (10 nM) stimulated the secretion of salmon cardiac natriuretic peptide (sCP) from isolated salmon ventricle (3.3+/-0.14-fold compared with control) but did not have any effect on ventricular sCP mRNA. Isoprenaline alone (0.1-1,000 nM) did not stimulate sCP release, but ET-1 (10 nM) together with isoprenaline (0.1 nM) caused a significantly greater increase of sCP release than ET-1 alone (5.4+/-0.07 vs. 3.3+/-0.14 times increase compared with control). The effects on the contractile and secretory function could be inhibited by a selective ETA-receptor antagonist BQ-610 (1 microM), whereas ETB-receptor blockage (by 100 nM BQ-788) enhanced the secretory response. Thus ET-1 is a phylogenetically conserved regulator of cardiac function, which has synergistic action with beta-adrenergic stimulation. The modulatory effects of ET-1 may therefore be especially important in situations with high beta-adrenergic tone.

Intraspinal application of endothelin results in focal ischemic injury of spinal gray matter and restricts the differentiation of engrafted neural stem cells

Previous data have shown that pluripotent stem cells engrafted into the contused spinal cord differentiate only along an astrocytic lineage. The unknown restrictive cues appear to be quite rigid as even neuronal-restricted precursors fail to differentiate to the mature potential they exhibit in vitro after similar grafting into the contused spinal cord. It has been hypothesized that this potent lineage restriction is, in part, the result of the significant loss of both gray and white matter observed following spinal contusion, which elicits a massive acute inflammatory response and is manifested chronically by dramatic cystic cavitation. To evaluate the gray matter component, we developed a clinically relevant model of focal gray matter ischemic injury using the potent vasoconstrictor endothelin (ET-1) and characterized the differentiation of pluripotent stem cells transplanted into this atraumatic vascular SCI. Results demonstrate that low dose ET-1 microinjection into cervical spinal gray matter results in an inflammatory response that is temporally comparable to that observed following traumatic SCI, as well as chronic gray matter loss, but without significant cystic cavitation or white matter degeneration. However, despite the preservation of host spinal parenchyma, no elaboration of neuronal phenotypes was observed from engrafted stem or precursor cells. These results suggest that a common pathologic component responsible for this lineage restriction exists between contusive SCI and ET-1 mediated focal ischemic SCI.

Emerging roles of apelin in biology and medicine

The family of apelin peptides is derived from a single gene and activates the 7-transmembrane G-protein-coupled receptor (GPCR) APJ. Apelins have been shown to be involved in the regulation of cardiovascular function and fluid homeostasis and interestingly represent substrates for ACE2, a carboxypeptidase recently described as a novel key enzyme in the renin-angiotensin-aldosterone system (RAS). APJ has further been reported to be a coreceptor for the infection of CD4-positive cells with HIV in the central nervous system (CNS). Apelin-36 and shorter C-terminal sequences have different potencies and efficacies in regulating these functions. Shorter sequences, especially (Pyr(1))apelin-13, are potent regulators of cardiovascular function, while longer peptides such as apelin-36 are more effective in inhibiting human immunodeficiency virus (HIV) infection by blocking the HIV coreceptor APJ. The pyroglutamate modification characteristic of the short apelin peptide (Pyr(1))apelin-13 indicates paramount biological importance of this peptide. The aim of this review is to compile conclusive evidence for the involvement of apelin/APJ in the regulation of cardiovascular function and HIV pathology, emphasizing the properties of this receptor system that may make it a successful future drug target.

Selective changes in the shapes of parasagittal bands of Aldoc (Zebrin) mRNA in the rat vermis of the cerebellum after repeated methamphetamine injections

In the cerebellum the mossy and climbing projections, which excite Purkinje cells, display a parasagittal and striped organization. These projections also excite Zebrin (aldolase C: Aldoc) parasagittally. To evaluate the possibility that external stimuli can change the organization of the bands of Aldoc mRNA, we compared the effects of repeated methamphetamine administration on the Aldoc mRNA stripes in the four transverse (anterior, central, posterior and nodular) regions of the vermis with the effects on the glutamate transporter EAAT4 (SCL1A 6) mRNA stripes. In the posterior region the injections four times daily increased the fragmentation of the Aldoc mRNA stripes. The presence of a large amount of fragmentation (forty/cerebellum slice), was accompanied with large lateral dislocations of the Aldoc mRNA stripes. In the central and nodular regions, where the size of the stripe areas decreased significantly the stripes were dislocated laterally. The dislocations of the Aldoc mRNA bands did not occur after a single methamphetamine injection and thus repeated injections were necessary to change the distributions of the lateral bands. In contrast, the distributions of the SCL1A 6 mRNA stripes did not change, even though there was mild fragmentation (six/slice) of the SLC1A 6 mRNA stripes in the anterior region and decreases in the numbers (twelve/slice) in the nodular region. We concluded that excess dopamine selectively changes the location of the Aldoc mRNA compartments in the vermis while the SLC1A 6 mRNA stripes could be changed by other inputs and thus the specific transmitter system might change the specific compartment of the cerebellum.

Endothelin receptor expression in the normal and injured spinal cord: potential involvement in injury-induced ischemia and gliosis

The endothelins (ETs) are a family of peptides that exert their biological effects via two distinct receptors, the endothelin A receptor (ET(A)R) and the endothelin B receptor (ET(B)R). To more clearly define the potential actions of ETs following spinal cord injury, we used immunohistochemistry and confocal microscopy to examine the protein expression of ET(A)R and ET(B)R in the normal and injured rat spinal cord. In the normal spinal cord, ET(A)R immunoreactivity (IR) is expressed by vascular smooth muscle cells and a subpopulation of primary afferent nerve fibers. ET(B)R-IR is expressed primarily by radial glia, a small population of gray and white matter astrocytes, ependymal cells, vascular endothelial cells, and to a lesser extent in smooth muscle cells. Fourteen days following compression injury to the spinal cord, there was a significant upregulation in both the immunoexpression and number of astrocytes expressing the ET(B)R in both gray and white matter and a near disappearance of ET(B)R-IR in ependymal cells and ET(A)R-IR in primary afferent fibers. Conversely, the vascular expression of ET(A)R and ET(B)R did not appear to change. As spinal cord injury has been shown to induce an immediate increase in plasma ET levels and a sustained increase in tissue ET levels, ETs would be expected to induce an initial marked vasoconstriction via activation of vascular ET(A)R/ET(B)R and then days later a glial hypertrophy via activation of the ET(B)R expressed by astrocytes. Strategies aimed at blocking vascular ET(A)R/ET(B)R and astrocyte ET(B)Rs following spinal cord injury may reduce the resulting ischemia and astrogliosis and in doing so increase neuronal survival, regeneration, and function.

Cardiac endothelial-myocardial signaling: its role in cardiac growth, contractile performance, and rhythmicity

Experimental work during the past 15 years has demonstrated that endothelial cells in the heart play an obligatory role in regulating and maintaining cardiac function, in particular, at the endocardium and in the myocardial capillaries where endothelial cells directly interact with adjacent cardiomyocytes. The emerging field of targeted gene manipulation has led to the contention that cardiac endothelial-cardiomyocytal interaction is a prerequisite for normal cardiac development and growth. Some of the molecular mechanisms and cellular signals governing this interaction, such as neuregulin, vascular endothelial growth factor, and angiopoietin, continue to maintain phenotype and survival of cardiomyocytes in the adult heart. Cardiac endothelial cells, like vascular endothelial cells, also express and release a variety of auto- and paracrine agents, such as nitric oxide, endothelin, prostaglandin I(2), and angiotensin II, which directly influence cardiac metabolism, growth, contractile performance, and rhythmicity of the adult heart. The synthesis, secretion, and, most importantly, the activities of these endothelium-derived substances in the heart are closely linked, interrelated, and interactive. It may therefore be simplistic to try and define their properties independently from one another. Moreover, in relation specifically to the endocardial endothelium, an active transendothelial physicochemical gradient for various ions, or blood-heart barrier, has been demonstrated. Linkage of this blood-heart barrier to the various other endothelium-mediated signaling pathways or to the putative vascular endothelium-derived hyperpolarizing factors remains to be determined. At the early stages of cardiac failure, all major cardiovascular risk factors may cause cardiac endothelial activation as an adaptive response often followed by cardiac endothelial dysfunction. Because of the interdependency of all endothelial signaling pathways, activation or disturbance of any will necessarily affect the others leading to a disturbance of their normal balance, leading to further progression of cardiac failure.

Comparison of vasodilators in human internal mammary artery: ghrelin is a potent physiological antagonist of endothelin-1

1 The potential vasodilator function of the peptide ghrelin, recently identified as the endogenous ligand of the growth hormone secretagogue orphan receptor (GHS-R), was investigated in human endothelium-denuded internal mammary artery. The peptide endothelin-1 (ET-1) is a potent and long-lasting vasoconstrictor. Comparisons were made with established and putative endogenous vasodilators to determine if any could reverse ET-1-induced vasoconstriction in this vessel. 2 Ghrelin (0.1-300 nM) potently dilated 10 nM ET-1-induced constrictions (pD(2) 8.39+/-0.29; E(MAX) 63+/-5.6%; n=9/14, responders/total). 3 ANP (pD(2) 7.75+/-0.14; E(MAX) 106+/-2.0; n=5/5) and CGRP (pD(2) 8.08+/-0.17; E(MAX) 76+/-15% n=5/6) both produced complete reversal of the constrictor response to ET-1 (E(MAX) not significantly different from 100%, P>0.05 one-sample t-test). 4 The following caused partial reversal of the ET-1 response: Adrenomedullin (n=9/9) and two peptides derived from proadrenomedullin, PAMP-12 (n=6/7) and PAMP-20 (n=9/9) (pD(2) values 7.63+/-0.28, 7.97+/-0.23 and 8.51+/-0.29; E(MAX) 58+/-7.3, 54+/-10 and 51+/-7.8% respectively). Unexpectedly, amylin was only 2 fold less potent than CGRP, although there was less than 50% reversal of the ET-1 constriction (pD(2) 7.86+/-0.30; E(MAX) 41+/-5.4%; n=7/9). CNP (n=6/6) also partially reversed constrictions to ET-1 (E(MAX) 53+/-6.3; pD(2) 8.07+/-0.38). 5 BNP (n=4/5) and PGI(2) (n=6/8) were weak vasodilators, since concentration-response curves failed to reach a maximum within the range tested. PGE(2) caused a small dilatation in some vessels (E(MAX) 17+/-2.1%; pD(2) 8.63+/-0.36; n=4/8). 6 We have demonstrated ghrelin to be an effective, endothelium-independent vasodilator of the long-lasting constrictor ET-1 in human arteries producing responses similar to those of adrenomedullin (P>0.05, ANOVA). British Journal of Pharmacology (2002) 136, 1146-1152

SRC family kinases mediate epithelial Na+ channel inhibition by endothelin

The epithelial Na(+) channel (ENaC) is implicated in the pathogenesis of salt-sensitive hypertension. Recent evidence from animal models suggests that the vasoactive peptide, endothelin (ET-1), may be an important negative regulator of ENaC in vivo. We investigated the signaling pathway involved in endothelin-mediated ENaC inhibition. Experiments were performed in NIH 3T3 cells stably expressing genes for the three (alpha, beta, and gamma) ENaC subunits. In whole cell patch clamp experiments, we found that ET-1 treatment induced a dose-dependent decrease in amiloride-sensitive currents. Using receptor-specific antagonists, we determined that the effects of ET-1 were attributed to activation of the ET(B) receptor. Moreover, the inhibitory effect of ET-1 on ENaC could be completely blocked when cells were pretreated with the selective Src family kinase inhibitor, PP2. Further studies revealed that basal Src family kinase activity strongly regulates ENaC whole cell currents and single channel gating. These results suggest that Src family kinases lie in a signaling pathway activated by ET-1 and are components of a novel negative regulatory cascade resulting in ENaC inhibition.

Role of endogenous endothelin on coronary flow in health and disease

The role of the endothelium in the control of coronary flow has been demonstrated. Results of recent studies, both on animals and on humans, suggest that endogenous endothelin also plays an important role in basal coronary tone. Disease processes such as ischaemia-reperfusion injury, congestive heart failure, hypertension and atherosclerosis may be contributed to by an imbalance in, or excess of, release of endothelin. With the discovery of newer endothelin antagonists and endothelin converting enzyme inhibitors, especially with fewer hepatic side effects, there is the potential for much future research into novel therapeutic management of these common cardiovascular disorders.

Endocardial expression and functional characterization of endothelin-1

Endothelin-1 (ET-1), a 21 amino acid peptide exerts a wide range of biological activities including vasoconstriction, mitogenesis and inotropic effects on the heart. In this study, we examined whether endocardial endothelial cells express ET-1 and evaluated its functional properties. Using immunofluorescence localization method, we demonstrated cytoplasmic staining of ET-1 in the human endocardial endothelial cells from the right atrium and left ventricle. Employing reverse transcriptase polymerase chain reaction (RT-PCR) expression of ET-1 mRNA and its receptors ET(A) and ET(B) mRNAs were found in human myocardial as well as in endocardial endothelial cells. Biological activity of endocardial endothelial cells derived ET-1 was established as the conditioned media obtained from cultured porcine endocardial endothelial cells induced a slowly developing, strong and long-lasting contraction of circular rat aortic segments, with similar characteristics to that obtained with exogenous ET-1. Furthermore, the selective endothelin-A receptor antagonist, FR 139317, blocked the conditioned media induced contractions. Our results suggest that endocardial endothelial cells express and release biologically active ET-1 which could play a pivotal role in the regulation of myocardial contractility as well as a circulatory peptide may further act in other peripheral target organs.

Plasma endothelin-1 and big endothelin-1 levels in superior and inferior vena cava during protracted antiorthostatic hypokinetic/hypodynamia in rats

The plasma levels of endothelin-1 and big endothelin-1 were evaluated in blood of rats in the superior and inferior vena cava, in normal posture (synchronous controls), and after 12 days head-down suspension and 1 day recovery in normal posture. In synchronous controls, the mean plasma concentration of endothelin-1 in inferior vena cava or superior vena cava was almost the same (5.89+/-0.63 pmol/l and 5.67+/-0.64 pmol/l, respectively), whereas the mean plasma concentration of big endothelin-1 was higher (p<0.05) in superior vena cava compared to inferior vena cava (5.49+/-0.75 pmol/l and 1.39+/-0.15 pmol/l, respectively). In samples from superior vena cava of head-down suspended rats big endothelin-1 levels were significantly lower (p<0.05) up to day 9 of suspension, compared to non-suspended synchronous controls, whereas endothelin-1 values were higher (p<0.05). Big endothelin-1 concentration was higher (p<0.05) in inferior vena cava compared to non-suspended synchronous controls. The behaviour of endothelin-1 was more complex, endothelin-1 levels were lower (p<0.05) on day 1 of head-down suspension and higher (p<0.05) in samples taken on days 9 and 12. After 1 day recovery endothelin-1 and big endothelin-1 concentrations returned to normal in both superior vena cava and inferior vena cava. These data indicate that the endothelial system involvement for the two venous beds is different and suggest that local rather than systemic evaluation could better explain endothelial involvement and the contribution of different anatomic sites to the biosynthesis, conversion and clearance of the various involved molecules.

Physiological antagonism of endothelin-1 in human conductance and resistance coronary artery

The ability of four endogenous vasodilators, nitric oxide (NO; 0.01 - 30 microM), atrial (ANP), brain (BNP) and C-type (CNP) natriuretic peptide (0.1 - 300 nM), to reverse endothelin-1 (ET-1; 10 nM) constrictions in human resistance and conductance coronary arteries (CA) in vitro was investigated. ET-1 (0.1 - 300 nM) constricted resistance CA more potently than conductance CA (P<0.05; EC(50) values 2.98 nM (95% CI: 1.49 - 5.95 nM and 8.58 (4.72 - 15.6 nM) respectively)). The NO-donor diethylamine NONOate fully reversed the ET-1 constriction in conductance CA (E(MAX) 127+/-9.16%), however only partial reversal was observed in resistance CA (E(MAX) 78.8+/-8.13; P<0.05). The soluble guanylate cyclase inhibitor 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (100 microM) reduced the maximum response to diethylamine NONOate to 76.9+/-14.4% in conductance CA (P<0.05), but had no effect on resistance CA (E(MAX) 77.2+/-18.4%). There was no difference between responses to ANP in conductance and resistance CA (EC(50) values 4.25 nM (0.84 - 21.4 nM) and 18.4 nM (2.92 - 116 nM), E(MAX) 53.1+/-14.7% and 48.6+/-11.8% respectively). BNP was a more potent vasodilator of conductance than resistance CA. In conductance CA the mean EC(50) value was 2.4 nM (0.74 - 7.75 nM), E(MAX) 54.5+/-14.9%. Concentration-response curves to BNP were incomplete in resistance CA. Concentration-response curves to CNP were incomplete in both conductance and resistance CA. The greater potency of ET-1 in resistance vessels may exacerbate the effects of increased circulating levels of the peptide in disease. Only NO could fully reverse ET-1 mediated constrictions in conductance CA, and none of the dilators tested could completely counteract constrictions in resistance CA.

Nitric oxide-mediated modulation of the endothelin-1 signalling pathway in the human cardiovascular system

1. We studied the ability of nitric oxide (NO) to physiologically antagonize endothelin-1 (ET-1) induced constrictions in human internal mammary artery (IMA). We also investigated the hypothesis that NO interacts directly with ET-receptor binding in human heart and aorta. 2. ET-1 potently contracted IMA (EC(50) 6.86 nM, 95% CI: 3.5 - 13.4 nM; n=12). The constrictor response to 10 nM ET-1 was fully reversed by the NO-donor diethylamine NONOate (DEA/NO; EC(50) 2.0 microM, 95% CI: 0.8 - 4.8 microM; n=5). The guanylate cyclase inhibitor ODQ (100 microM) reduced the response to DEA/NO but did not abolish it (E(MAX) 50.9+/-8.5% in the presence of ODQ; 113.0+/-8.4%, control). 3. The increase in cyclic GMP by 30 microM DEA/NO was abolished in the presence of 100 microM ODQ (n=6). 4. In saturation binding experiments the NO-donor Diethyltriamine NONOate (DETA/NO; 1 mM) caused a 90% reduction in maximum binding of [(125)I]-ET-1 in human heart, without affecting the affinity. This reduction in binding was abolished by haemoglobin. Pre-incubating either the radiolabel or the tissue with NO-donors did not reduce binding. A similar effect was observed in aortic smooth muscle. 5. We have shown that DEA/NO is able to reverse ET-1-induced contractions in the human vasculature. The binding studies suggest a direct interaction between NO and the ET receptor or receptor-ligand complex in human ventricular and aortic tissue. NO is released continuously in vivo, thus this apparent modification of ET-receptor binding may provide an additional mechanism by which NO counter-balances the effects of ET.

Physiologic significance of nitric oxide and endothelin-1 in circulatory adaptation

BACKGROUND

The purpose of the present paper was to evaluate the physiologic significance of nitric oxide (NO) and endothelin (ET)-1 in circulatory adaptation in the neonate.

METHODS

The serum levels of NO metabolites (NOx; the sum of nitrites and nitrates) and the plasma level of ET-1 were determined in 14 healthy full-term infants at 0-6 h, 24 h and 5 days after birth. We measured the heart rate, the mean systemic blood pressure and the mean pulmonary arterial pressure, estimated by pulsed Doppler echocardiography, at each time point.

RESULTS

The serum concentration of NOx was lowest at birth and increased with age. The plasma concentration of ET-1 was highest at birth and decreased with age. The ratio of NOx to ET-1 was inversely related to the estimated mean pulmonary arterial pressure in the early neonatal period. The ratio of NOx to ET-1 was not correlated with the systemic blood pressure.

CONCLUSION

Increased NO synthesis and decreased production of ET-1 during the early neonatal period may contribute to the decrease in pulmonary arterial pressure.

Endothelin enhances and inhibits adrenal catecholamine release in deoxycorticosterone acetate-salt hypertensive rats

Endothelin (ET) and the sympathoadrenal system contribute to the development and maintenance of deoxycorticosterone acetate (DOCA)-salt hypertension. ET can act directly on the adrenal medulla to enhance the release of catecholamines. In addition, the level of ET peptide is increased in the adrenal glands of DOCA-salt hypertensive rats. Therefore, we tested the hypothesis that ET enhances adrenal medullary catecholamine release during DOCA-salt hypertension. The infusion of exogenous ET-1 into an isolated, perfused adrenal gland preparation resulted in an increase in the basal release of norepinephrine (NE) and epinephrine (EPI) in control and DOCA-salt hypertensive rats. Nerve-stimulated (0.3 Hz) release of NE was significantly inhibited during ET-1 infusion in the DOCA-salt hypertensive rats but not in the control rats. The role of endogenous ET on basal and nerve-stimulated NE and EPI release was also examined. An infusion of either BQ-123 (10(-7) mol/L), an ET(A) receptor antagonist, or BQ-788 (10(-7) mol/L), an ET(B) receptor antagonist, did not alter basal NE or EPI release in either control or DOCA-salt hypertensive rats. BQ-788 did not alter nerve-stimulated release of NE and EPI. In contrast, the nerve-stimulated release of EPI, but not NE, was enhanced during BQ-123 infusion in DOCA-salt hypertensive rats. Nerve-stimulated NE and EPI release was unaffected by BQ-123 in the control rats. These data suggest that ET can stimulate adrenal medullary catecholamine release in normotensive and DOCA-salt hypertensive rats. However, ET also inhibits adrenal medullary catecholamine release in DOCA-salt hypertensive rats.

Endothelin regulation of adrenal function

1. The goal of the present review is to recount the evidence that endothelin (ET) has a significant influence on the peripheral sympathetic nervous system by regulating the function of the adrenal medulla. 2. The presence of an active ET system in the adrenal medulla has been clearly demonstrated. Endothelin protein, mRNA, binding sites and ET-converting enzyme have been identified in adrenal tissue and medullary chromaffin cells, suggesting that this peptide may contribute to the regulation of adrenal medullary function. 3. Studies investigating the function of ET in the adrenal gland have demonstrated that ET has a stimulatory effect on the adrenal medulla. Endothelin elicits an increase in catecholamine release from perfused intact adrenal glands as well as from cultured chromaffin cells. This effect has been shown to be mediated by ETA and ETB receptors. 4. The mechanism by which ET causes an increase in catecholamine release from the adrenal medulla appears to be independent of cholinergic activation of chromaffin cells. Endothelin has been shown to act directly at chromaffin cells to increase intracellular calcium, which results in catecholamine release. 5. Endothelin can indirectly affect catecholamine release by its effect on adrenal blood flow. Studies indicate that ET has both vasoconstrictor and vasodilator effects in the adrenal gland, which suggests a role for ET in the regulation of adrenal blood flow. Endothelin has also been proposed to participate in the selective contraction of the adrenomedullary veins, which enhances the discharge of catecholamines from the adrenal gland during activation.

Endothelin-1 levels in infants with pulmonary hypertension receiving extracorporeal membrane oxygenation

We studied the possibility of an etiological role for endothelin-1 (ET-1) in the development of persistent pulmonary hypertension of the newborn (PPHN). Ten infants with severe PPHN requiring extracorporeal membrane oxygenation (ECMO) were studied. Pre and post pulmonary blood samples were obtained on commencing ECMO and on recovery. The samples were analyzed by radio-immunoassay. The infants with PPHN requiring ECMO had a significantly higher mean ET-1 concentration (21.1 pmol/l, S. D. 3.59) than a group of healthy controls (16.6 pmol/l, S. D. 4.44); however 8 of our 10 infants had individual ET-1 levels within our reference range for healthy newborns. Pre and post pulmonary ET-1 levels did not differ significantly and there was no evidence of a decline in ET-1 levels with resolution of PPHN. Pulmonary overproduction of ET-1 does not appear to be the cause of PPHN, although the endothelin system may still play a role in the pathophysiology of PPHN, probably mediated through changes in receptor expression.

The many aspects of endothelins in ischemia-reperfusion injury: emergence of a key mediator

The endothelins (ETs) are regulatory peptides, distributed in many organ systems and producing potent physiological effects. They are the most powerful vasoconstrictive substances known today. They also act as promitogens. Many data supporting pathophysiological roles for ETs are reported, especially regarding diseases related to the vascular system, such as hypertension, pulmonary hypertension, preeclampsia, ischemic heart diseases, renal failure, subarachnoidal hemorrhage, and cerebral ischemia. The development of drugs blocking ET binding to its receptors (antagonists) and the biosynthesis of ETs (ECE inhibitors) presently attracts great interest in terms of establishing new treatments for diseases in which ETs are believed to be involved. Here we review the evidence supporting a role for ETs in the various etiologies related to ischemia-reperfusion injury, such as is found in heart disease, cerebral ischemia, and organ transplantation.

Endothelin receptor subtypes and their functional relevance in human small coronary arteries

1. The potent constrictor peptide endothelin (ET) has been implicated in various cardiovascular disorders including myocardial infarction and atherosclerosis. We have investigated the nature of ET receptor subtypes present on human small coronary arteries. 2. Small coronary arteries were mounted in a wire-myograph for in vitro pharmacology. To investigate the ET receptor subtypes present in different segments of the coronary vascular tree, arteries were grouped according to internal diameter. Responses in arteries with small internal diameters (mean 316.7+/-7.9 microm; Group B) were compared to those in larger arteries (mean 586.2+/-23.1 microm; Group A). 3. ET-1 consistently and potently contracted arteries from Group A and B, with EC50 values of 1.7 (0.9-3.2) nM (n=15) and 2.3 (1.4-4.2) nM (n=14), respectively. No correlation was observed between ET-1 potency and internal diameter. The response to ET-1 was potently antagonized by the selective ET(A) receptor antagonist PD156707 in both Group A and Group B, yielding pA2 values of 8.60+/-0.12 (n=4-6) and 8.38+/-0.17 (n=4-6), respectively. Slopes from Schild regression were not significantly different from unity. 4. In contrast to ET-1, individual responses to ET-3 were variable. While all arteries from Group A responded to ET-3 (EC50 approximately 69 (23-210) nM) (n=12), no response was obtained in 5 of the 14 tested in Group B. Of those responding, many failed to reach a maximum at concentrations up to 1 microM. ET-1 was more potent than ET-3 in all arteries tested. A biphasic ET-3 response was observed in 8 arteries suggesting that a small ET(B) population was also present in some patients. The selective ET(B) receptor agonist sarafotoxin S6c had little or no effect up to 10 nM (n=4-6). 5. Responses to ET-1 and ET-3 were unaffected by removal of the endothelium in arteries from both groups suggesting a lack of functional, relaxant ET(B) receptors on endothelial cells (n=5). 6. Using autoradiography, specific high density binding of the non-selective, ET(A)/ET(B) ligand [125I]-ET-1 and selective ET(A) ligand [125I]-PD151242 was detected on the vascular smooth muscle layer of small intramyocardial coronary arteries (n=5). In contrast, little or no binding of the selective ET(B) receptor ligand [125I]-BQ3020 was observed (n=5). Similarly, [125I]-ET-1 binding to vascular smooth muscle was absent in the presence of the selective ET(A) receptor antagonist PD156707. 7. We conclude that human small epi- and intramyocardial coronary arteries express predominantly ET(A) receptors and it is these receptors which mediate ET-induced contractions. A constrictor ET(B) receptor population may exist in some patients. However, these receptors may have a limited role as contractions to ET-1 can be blocked fully by the selective ET(A) receptor antagonist PD156707.

Endothelin receptors in the failing and nonfailing human heart

BACKGROUND

In patients with chronic heart failure (CHF), plasma endothelin-1 (ET-1) levels are increased. We studied whether the cardiac ET-receptor system is altered in CHF patients.

METHODS AND RESULTS

We assessed ET-evoked inositol phosphate (IP) formation in slices from right atria and left ventricles from 6 potential heart transplant donors (NFH) and 15 patients with end-stage CHF; in membranes from the same tissues, we studied ET-induced inhibition of isoprenaline- and forskolin-stimulated adenylyl cyclase and ET-receptor density. ET (10[-9] to 10[-6] mol/L, ET-1 >>> ET-3) increased IP formation in right atria and left ventricles through ET(A)-receptor stimulation in a concentration-dependent manner; no difference in potency or efficacy between NFH and CHF hearts was observed. ET-1 (10[-10] to 10[-6] mol/L), via ET(A)-receptor stimulation, inhibited isoprenaline- and forskolin-stimulated adenylyl cyclase in right atria but not in left ventricles, whereas carbachol inhibited adenylyl cyclase in both tissues; again, the potency and efficacy of ET- or carbachol-induced adenylyl cyclase inhibition was not different between NFH and CHF hearts. [125I]ET-1 binding revealed the coexistence of ET(A) and ET(B) receptors in both tissues; however, the density of ET(A) receptors was not significantly different between NFH and CHF hearts. Finally, the immunodetectable amount of left ventricular Gq/11 protein did not differ between NFH and CHF hearts.

CONCLUSIONS

In the human heart, ET(A) and ET(B) receptors coexist; however, only ET(A) receptors are of functional importance. In right atria, ET(A) receptors couple to IP formation and inhibition of adenylyl cyclase; in left ventricles, they couple only to IP formation. In end-stage CHF, the functional responsiveness of the cardiac ET(A)-receptor system is not altered.

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.

Endothelin-3 reduces C-type natriuretic peptide-induced cyclic GMP formation in C6 glioma cells

The effect of endothelin-3 (ET-3) on C-type natriuretic peptide (CNP)-induced guanosine 3',5'-cyclic monophosphate (cGMP) was examined in C6 glioma cells, CNP-induced cGMP formation was both time- and dose-dependent, with an EC50 value of about 10 nM. While ET-3 and phorbol 12-myristate 13-acetate (PMA) had no effect on basal cGMP production, both compounds were potent inhibitors of CNP-induced cGMP formation, with IC50 values of approximately 10 and 2 nM, respectively. Although protein kinase C (PKC) inhibitors had no effect on basal cGMP formation, Ro 31-8220, a PKC inhibitor, reversed the ET-3 inhibition on CNP-induced cGMP formation by 63% and that of PMA almost completely. Our findings suggest that stimulation of cGMP formation by CNP in C6 glioma cells is negatively modulated by PKC activation, and that the inhibitory action of ET-3 on CNP-stimulated cGMP formation is mediated partly by PKC.

Plasma endothelin-1 levels in adult patients undergoing coronary revascularization

Cardiopulmonary bypass is thought to injure all endothelial cells, mainly by cell-to-cell interaction with activated granulocytes which, augmented by endothelin-1 (ET-1), enhance the generation of superoxide radicals. These radicals on the other hand, may sustain and prolong endothelial injury. In the present study, by means of a magnetic separation radioimmunoassay procedure, ET-1 levels were measured in 10 adult patients undergoing coronary artery bypass surgery, in 10 perioperative phases, in order to reconfirm and further elucidate the effect of cardiopulmonary bypass on endothelial secretion of ET-1. ET-1 levels before cardiopulmonary bypass showed a definite rising trend, especially after median sternotomy. After induction of cardiopulmonary bypass, ET-1 levels increased significantly compared with preoperative values (P < 0.01). ET-1 levels in stable angina patients during and after aortic cross-clamping were strongly and positively correlated with preoperative mean pulmonary artery pressure (r = 0.79, n = 7, P < 0.05 and r = 0.92, n = 7, P = 0.05) respectively. After the first hour in the intensive care unit, ET-1 levels in three patients with unstable angina were considerably higher than in those with stable angina, a fact that deserves further consideration and study.

Differential distribution of endothelin peptides and receptors in human adrenal gland

Sub-type selective ligands revealed a differential distribution of endothelin (ET) receptors within human adrenal glands. High densities of ETA receptors were localized, using [125I]-PD151242, to the smooth muscle layer of the arteries, smaller vessels within the capsular plexus and to the secretory cells of zona glomerulosa (KD = 139.8 +/- 39.7, Bmax = 69.7 +/- 9.1 fmol mg-1 protein, mean of 3 individuals+/-sem). ETB receptors were present in the medulla (KD = 145.2 +/- 16.4, Bmax = 75.5 +/- 12.3), zona glomerulosa (KD = 100.6 +/- 35.1, Bmax = 63.1 +/- 10.0), fasiculata (KD 145.1 +/- 16.2, Bmax = 67.9 +/- 6.9) and reticularis (KD = 118.2 +/- 18.6, Bmax = 71.9 +/- 6.5). ETB receptors were not detected within the smooth muscle of the vasculature. Messenger RNA encoding both sub-types was present in adrenals. ET-like immunoreactivity was localized to the cytoplasm of the endothelial cells from arteries supplying the gland and resistance vessels within the capsular plexus. Staining was also detected in these cells using anti-big ET-1 and less intensely with anti-big ET-2 antisera but not within cells within the cortex or medulla. Big ET-3-like immunoreactivity was localized to secretory cells of the medulla. Staining was not found using antiserum that could detect ET-3, suggesting further processing of big ET-3 may occur within the plasma, and that the adrenals could be a source of ET-3. The presence of ET-1 was confirmed by high performance liquid chromatography and radioimmunoassay although ET-3 was not detected. The results suggest that ET-1 is the predominant mature isoform, which is localized mainly to adrenal vasculature, particularly the capsular plexus, and may contribute to blood flow regulation in the gland.

Mechanisms underlying the vascular activity of beta-amyloid protein fragment (beta A(4)25-35) at the level of skin microvasculature

Deposition of beta-amyloid protein (beta A4) in extracellular senile plaques is a pathologic hallmark of Alzheimer's disease (AD). The neurotoxic effect of beta A4 has been ascribed to a discrete 11-amino acid internal sequence (beta A(4)25-35). Substance P (SP) has been found to be depleted in the brain of AD patients while its presence was found to protect against the neurodegenerative effect of beta A(4)25-35. Our previous studies, in vivo, in aged rats showed that beta A(4)25-35 exhibits a potent vasoconstrictor (VC) effect in rat skin microvasculature and can prevent SP but not calcitonin gene-related peptide (CGRP) from inducing a vasodilator (VD) response. It was postulated that beta A(4)25-35 might be interacting with SP at the level of the second messenger system via the phosphoinositide pathway. Using a blister model of inflammation in the rat hind footpad, we examined the ability of beta A(4)25-35 to modulate the vascular activity of bradykinin (BK) and serotonin (5-HT) which also activate the phosphoinositide pathway. In addition, the role of nitric oxide (NO), endothelin (ET, an endothelium-derived constrictor factor) and protein kinase C (PKC) in the vascular effects of beta A(4)25-35 were examined using the NO synthase inhibitor, NG-nitro-L-arginine (L-NOARG), the ET-receptor antagonist, BQ-123, and the PKC inhibitor, bisindolylmaleimide (BIM) respectively. Changes in microvascular blood flow were monitored using laser Doppler flowmetry and the area within the response curve measured. The results showed that beta A(4)25-35 (10 microM) induced a VC effect and inhibited the subsequent VD response to BK (10 microM) and 5-HT (1 microM) in a similar fashion to its effect on SP (1 microM). In the presence of L-NOARG (100 microM), the VD effect of SP was reduced and further attenuated after perfusion of beta A(4)25-35. Superfusion of the blister base with BQ-123 (10 microM) or BIM (1 microM) prior to and during perfusion with beta A(4)25-35 abolished its VC effect and allowed SP to induce a normal VD response in both young and old rats. Based on these results, we suggest that the vascular activity of the active fragment, beta A(4)25-35, is mediated by ET via activation of PKC. This study provides new findings which may help to elucidate the signal transduction mechanisms involved in the vascular activity of beta A(4)25-35. The relevance of these mechanisms to those underlying the pathological effects of beta A4 and their significance in AD remains to be determined.

Molecular characterization of a novel human endothelin receptor splice variant

Endothelin receptors are widely distributed throughout a number of tissues. A novel ETB receptor splice variant (ETB-SVR) was identified from a human placental cDNA library. Sequence analysis indicated that the ETB-SVR is 436 amino acids long and shares 91% identity to the human ETB-R. Northern blot analysis indicated an mRNA species of 2.7 kilobases, which is expressed in the lung, placenta, kidney, and skeletal muscle. Ligand binding studies of the cloned ETB-SVR and ETB-R receptors expressed in COS cells showed that ET peptides exhibited similar potency in displacing 125I-ET-1 binding. Functional studies showed that ET-1, ET-3, and sarafotoxin 6c displayed similar potencies for inositol phosphates accumulation in ETB-R-transfected COS cells, whereas no increase in inositol phosphate accumulation was observed in ETB-SVR-transfected cells. In addition, exposure of ETB-R-transfected cells to ET-1 caused an increase in the intracellular acidification rate whereas ETB-SVR-transfected cells did not respond to ET-1. These data suggest that the ETB-SVR and ETB-R are functionally distinct and the difference in the amino acid sequences between the two receptors may determine functional coupling. Availability of cDNA clones for endothelin receptors can facilitate our understanding of the role of ET in the pathophysiology of various diseases.

Endothelins in chronic liver disease

This review describes recent progress in the accumulation of knowledge about the endothelins (ETs), a family of vasoactive 21-amino acid polypeptides, in chronic liver disease. Particular prominence is given to the dynamics of ET-1 and ET-3 and their possible relation to the disturbed circulation and neurohumoral dysregulation found in cirrhosis. Recent studies have shown that the ET system is highly activated in most cirrhotic patients. Circulating ET-1 and ET-3 levels have a positive relation to the severity of the disease and fluid retention, with the highest values recorded in patients with functional renal failure. Studies on liver biopsies have revealed synthesis of ET-1 in hepatic endothelial and other cells, and recent investigations have identified the hepatosplanchnic system as a major source of ET-1 and ET-3 spillover into the circulation, with a direct relation to portal venous hypertension. In addition, marked associations with disturbance of systemic haemodynamics and with abnormal distribution of blood volume have been reported. Although the pathophysiological importance of the ET system in chronic liver disease is not completely understood, similarities to other vasopressive and antinatriuretic regulatory systems (i.e. the sympathetic nervous system, renin-angiotensin-aldosterone and vasopressin) are apparent, with respect to kinetics and haemodynamic dysregulation. Cirrhosis seems to be a pathophysiological condition with indications of the occurrence of ETs, not only as local modulators, but also as a system with potential importance for systemic regulation.

Plasma endothelin-1 levels in patients with aldosterone-producing adenoma and pheochromocytoma

The aim of the study was to evaluate possible changes of plasma endothelin-1 levels (ET-1) in patients with hypertension secondary to primary aldosteronism and pheochromocytoma. We enrolled in the study: 12 patients affected by aldosterone-producing adenoma (5 M and 7 W; mean age 42.1 +/- 17.2 years); 8 patients with pheochromocytoma (5 M, 3 W; mean age 36.2 +/- 17.1 years); 15 patients with essential hypertension (9 M, 6 W; mean age 48.5 +/- 10 years). We also enrolled a normal control group (8 M, 12 W; mean age 34.2 +/- 11 years). The mean plasma ET-1 concentrations in patients with pheochromocytoma were significantly higher (23.9 +/- 5.2 pg/ml) than those in normal subjects (7.3 +/- 1.9 pg/ml), in patients with primary aldosteronism (12.1 +/- 3.8 pg/ml) and in patients with essential hypertension (9.2 +/- 3 pg/ml); p < 0.001, respectively. The present investigation demonstrates that in human adrenal hypertension patients with pheochromocytoma have increased circulating ET-1 levels respect to patients with aldosterone-producing adenoma.

Pre- and postjunctional modulation by endothelin-1 of the adrenergic neurogenic response in canine mesenteric arteries

Transmural electrical stimulation (5-30 Hz) produced a frequency-dependent increase in the perfusion pressure of isolated, perfused dog mesenteric artery segments, which was suppressed by prazosin and abolished by tetrodotoxin. Treatment with endothelin-1 in low concentrations (10(-10) and 3 x 10(-10) M) inhibited the response to electrical nerve stimulation. The effect was not affected by NG-nitro-L-arginine, indomethacin and removal of the endothelium. The endothelin-1-induced inhibition was antagonized by 10(-7) M BQ123[cyclo(D-Trp-D-Asp-L-Pro-D-Val-L-Leu-)sodium], an endothelin ETA receptor antagonist, but not by 10(-5) M BQ788 [N-cis-2,6-dimethyl-piperidinocarbonyl-L- gamma-methylleucyl-D-1-methoxycarbonyltryptophanyl-D-norleuc ine], an antagonist of endothelin ETB1 and ETB2 receptors. IRL1620 [Suc-[Glu9, Ala11,15]endothelin-1-(8-21)], a selective endothelin ETB1 receptor agonist, did not alter the response to electrical stimulation. However, raising the concentration of endothelin-1 to 10(-9) M or higher potentiated the response. Similar results were also obtained in mesenteric artery strips in response to electrical stimulation. Endothelin-1 at low concentrations did not alter the contraction caused by exogenous norepinephrine in the artery strips, whereas the peptide at high concentrations potentiated the response. 3H-overflow evoked by transmural electrical stimulation from tissues prelabeled with [3H]norepinephrine was decreased by endothelin-1 (3 x 10(-10) M) in the superfused dog mesenteric arteries. It is concluded that endothelin-1 at low concentrations activates prejunctional endothelin ETA receptors and inhibits adrenergic nerve-mediated contractions by an inhibition of amine release, whereas the peptide at high concentrations potentiates the neurally induced contractions by a postjunctional enhancement, via endothelin ETA receptors, of the action of norepinephrine. Low concentrations of endothelin-1 appear to act as a vasodilator in adrenergically innervated mesenteric artery

Modulation of autotransplanted adrenal gland by endothelin-1: a morphological and biochemical study

BACKGROUND

Adrenal gland autotransplantation, a model of cortical tissue regeneration, provides the reconstruction of distinct functional and morphological zonae. A morphological and biochemical study of the adrenal gland of adult male rats after autotransplantation and endothelin-1 (ET-1) administration was made.

METHODS

The technique involved bilateral adrenalectomy and placement of pieces of the adrenal gland in a dorsal plane between the skin and muscle. The animals were killed 90 days after the autotransplantation and 1 hr after intravenous ET-1 administration (0.5 microgram/kg body weight). The autotransplanted pieces were removed, fixed, and processed for light and electron microscopic morphologic studies. Trunk blood was collected for steroid assay.

RESULTS

Saline-treated control autotransplanted animals showed no remarkable differences in adrenal organization; grafts exhibiting a mass of regenerated cortical tissue were arranged in nests of glandular cells surrounded by a fibrous capsule and intersected by layers of connective tissue. The adrenal medulla was systematically absent. Ultrastructure of ET-1-treated animals revealed an inner area in the graft, consisting mainly of fasciculatalike cells. Cytoplasmic changes were evident, with high variations in mitochondrial size and arrangement. Profiles of smooth endoplasmic reticulum sometimes exhibited evidence of hypertrophy. Glandular cells in the graft outer area (subcapsular) were almost invariably like glomerulosa; however, some of them showed mitochondria with a peculiar arrangement of the cristae. "Hybrid" cells with mitochondria resembling those of the zona reticularis were also observed in the subcapsular environment. ET-1-stimulated animals showed significant increases in plasma corticosterone and aldosterone concentrations.

CONCLUSIONS

Endothelin-1, previously reported to stimulate acutely the aldosterone secretion by the adrenal zona glomerulosa in the rat, seems to exert a modulator role on the physiology of adrenal autotransplants, their regeneration and secretion.