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

The mechanism of action of endothelin-1 on small pulmonary arterial vessels

The effect of endothelin-1, a recently isolated vasoconstrictor peptide, was studied in preparations of pulmonary arterial vessels from the rat. Contraction was measured in large (1-2 mm diameter) and small (150-350 microns diameter) vessels on a Mulvany-Halpern myograph. Endothelin-1 was found to be one of the most potent vasoconstrictors yet described in these isolated pulmonary vessels. The contraction elicited was dose dependent, of slow onset, and prolonged. There was significant difference in sensitivity between the two vessel types, with an EC50 of 8.9 nM for the artery, and 33.1 nM for the smaller vessels. The endothelin-1 stimulated contraction was predominantly dependent on extracellular [Ca2+]. However 34.7% of the contraction in the pulmonary artery and 18.5% in the resistance vessel could be obtained in Ca2+ free (EGTA containing) solution. This extracellular Ca2+ independent fraction was sensitive to depletion of intracellular stores by pretreatment with caffeine or noradrenaline in the artery but not the arteriole. The extracellular Ca2+ dependent fraction was not affected by Ca2+ channel blockade with dihydropydridines or verapamil, but was inhibited by application of cadmium or lanthanum. The contraction was not altered by inhibition of Na+/H+ exchange.

Rat mesenteric artery endothelial cells in culture secrete ET-1

Endothelial cells were harvested by the collagenase perfusion of isolated mesenteric arteries of rats and cultured. An endothelin peptide was detected in the supernatant of these cells by an antibody which recognizes ET-1 but not "rat" endothelin (ET-3). Culture media was extracted using a C-8 solid phase column and subjected to reverse phase HPLC using a system that separates all known endothelins and immunoreactive endothelins measured using another antibody which recognizes all endothelins. The main immunoreactive peak co-eluted with ET-1. We could not detect any ET-2, ET-3 or Vasoactive Intestinal Contractor. A smaller immunoreactive peak of unknown structure that eluted earlier than ET-1 was also detected. In conclusion, rat endothelial cells secrete a peptide of similar chromatographic and immunoreactive properties as ET-1.

Endothelium-derived contractile factors

1. Vascular endothelium releases different substances (endothelium-derived contractile factors, EDCFs), which mediate vasoconstrictor responses induced by several agents. 2. Clear differences have been reported in endothelium-dependent contractions, which suggest at least three distinct EDCFs, named EDCF1, EDCF2 and EDCF3, respectively. 3. EDCF1 is a cyclooxygenase metabolite(s) of arachidonic acid. EDCF2 is a polypeptide released from cultured endothelial cells. It has been isolated and identified as a 21-amino acid peptide called endothelin, which is described as the most potent vasoconstrictor agent known to date. EDCF3 is an unidentified contractile factor(s), which is neither EDCF1 nor EDCF2. 4. The physiological role of these endothelial contractile factors is not yet clear. However, they have been implicated in the local mechanisms involved in blood flow regulation, as well as in some pathological conditions, such as hypertension or cerebral vasospasm.

Chromatographic characterization of immunoreactive endothelin in rat lung

Using a specific and sensitive radioimmunoassay for endothelin, combined with gel filtration and reverse phase high performance liquid chromatography, the molecular form of immunoreactive endothelin in the rat lung was investigated. On reverse phase high performance chromatography, the major immunoreactive endothelin in the rat lung emerged at a position identical to that of authentic endothelin-1. After oxidation of the immunoreactive endothelin by H2O2, the immunoreactivity migrated to a position identical to that of Met-sulfoxide endothelin-1. These data indicate that the major immunoreactive endothelin in the rat lung is not endothelin-3 (putative rat/human endothelin), but is identical or very similar to endothelin-1 (porcine/human endothelin).

Immunoreactive endothelin concentrations in maternal and fetal blood

Immunoreactive-endothelin (ir-ET) concentrations were determined in peripheral maternal blood and in umbilical cord blood just after delivery. The concentrations in both the umbilical artery (2.83 +/- 1.36 pmol/l plasma, Mean +/- SD) and vein (3.37 +/- 1.53 pmol/l) were significantly higher than those found in maternal venous blood (1.43 +/- 1.02 pmol/l). On the other hand, ir-ET levels in maternal blood were not significantly different when compared with those found in non-pregnant women (1.50 +/- 0.83 pmol/l). No significant difference of ir-ET levels between the umbilical artery and vein was observed. A highly significant correlation (r = 0.60, p less than 0.01) of ir-ET levels between the umbilical artery and vein was observed. Also, a significant correlation (r = 0.48, p less than 0.01) between umbilical vein and maternal vein ir-ET levels with a weaker correlation (r = 0.36, p less than 0.05) between umbilical artery and maternal vein ir-ET levels was demonstrated. The present study indicates that ir-ET may be actively secreted in fetal circulation and the plasma levels in maternal and fetal circulation may have a possible relation.

Increased pressor effect of repeated doses of rat or porcine endothelin in the anaesthetised rat

Rat and porcine endothelin differ by 6 amino acids. Porcine and rat endothelin were equiactive at producing the transient fall in blood pressure in the anaesthetised rat but porcine endothelin was three times more potent at producing the subsequent sustained rise. Repeated doses of either peptide in the same rat produced a larger pressor response with each repetition, the peak response being reached more rapidly. The magnitude of the blood pressure fall did not change significantly but the first response in each rat was of longer duration than subsequent responses, especially with rat endothelin.

Endothelin-like pulmonary vasoconstrictor peptide release by alpha-thrombin

The endothelial cells lining the vessel wall can modulate vasomotor tone by releasing vasoactive factors, such as endothelial-derived constricting factors. We observed that alpha-thrombin, but not catalytically inactivated alpha-thrombin, mediated the release of two pulmonary vasoconstrictor peptides into the venous effluent of guinea pig lungs. These peptides elicited a slow-onset, long-lasting pulmonary vasoconstriction similar to the effect of endothelin, an endothelial-derived 21-amino acid vasoconstrictor peptide previously isolated from cells in culture. One of the isolated peptides coelutes with endothelin upon reverse-phase HPLC with an acetonitrile gradient and has a molecular weight comparable to endothelin as determined by gel-permeation HPLC. The other vasoconstrictor peptide elutes earlier than endothelin on reverse-phase HPLC and exhibits a lower molecular weight. The studies show the release of endothelin-like pulmonary vasoconstrictor peptides in the intact lung by alpha-thrombin, a central regulatory enzyme in hemostasis.

Two different forms of endothelin receptors in rat lung

We provided evidence for the presence of two distinct types of rat endothelin (ET) receptors having different molecular masses by affinity labelling of rat lung membranes with 125I-ET-1, ET-2 and ET-3 and SDS-PAGE followed by autoradiography. One type, which is 44 kDa has a higher affinity for ET-1 and -2 than ET-3, whereas the other type, which is 32 kDa, preferably interacts with ET-3 rather than ET-1 and -2.

Renal vasoconstriction by the endothelial cell-derived peptide endothelin in spontaneously hypertensive rats

The effects of endothelin on systemic and renal hemodynamics in anesthetized spontaneously hypertensive rats (SHR) and Wistar-Kyoto rats were examined. Endothelin (500 ng i.v. +1,000 ng/hr per 300-g rat) elevated mean blood pressure by 13% (p less than 0.02) and decreased renal blood flow by 71% and glomerular filtration rate by 66% (both p less than 0.01), resulting in a 430% (p less than 0.05) increase in renal vascular resistance (RVR) in SHR. This rise in blood pressure was associated with a significant increase in hematocrit (+8%), but a decrease in urinary sodium excretion (-51%). This dose of endothelin reduced cardiac output by 40% (p less than 0.001) and brought about a 96% (p less than 0.01) rise in systemic vascular resistance (SVR). However, the SVR increase was significantly smaller than the RVR increase. These changes in systemic and renal hemodynamics were observed in a dose-dependent manner, and the degrees of change did not differ between the two strains. Additional infusion of atrial natriuretic peptide (0.33 microgram/kg/min) into SHR completely reversed the changes in blood pressure and renal hemodynamics caused by endothelin, resulting in pronounced natriuresis (+760%). The renal vascular casting study revealed that endothelin mainly constricted the arcuate and interlobular arteries, as well as afferent arterioles. These results suggest that endothelin may be involved in blood pressure and body fluid volume regulation through systemic and renal vasoconstriction.

Effects of endothelin on the coronary vascular bed in open-chest dogs

The goal of the present study was to evaluate the effects of endothelin, a newly discovered very potent vasoconstrictor secreted by endothelial cells, on the coronary vascular bed. For this purpose, the effects of endothelin injected intracoronarily were tested in open-chest anesthetized dogs with the circumflex coronary artery cannulated and perfused at a constant pressure of 100 mm Hg. Circumflex blood flow, transmural distribution of coronary blood flow (radioactive microspheres), circumflex coronary artery diameter (piezoelectric crystals), and circumflex luminal surface area were measured. Endothelin decreased coronary blood flow by 30% and 61% with doses of 1 and 3 micrograms, respectively. A dose of 10 micrograms was lethal. The decrease of coronary blood flow was larger in the subepicardium than in the subendocardium, which explains that the endocardial-epicardial blood flow ratio increased from 1.27 +/- 0.05 to 1.98 +/- 0.23 (p less than 0.001) with a dose of 3 micrograms endothelin. Circumflex surface area decreased by 7% (p = NS) and 20% (p less than 0.01) with doses of 1 and 3 micrograms endothelin, respectively. The action of endothelin was not modified by the concomitant alpha-adrenergic blockade, serotonergic blockade, angiotensin converting enzyme inhibition, or cyclooxygenase inhibition. We conclude that endothelin is a potent coronary vasoconstrictor with a selective effect on the subepicardium. At least part of the increase of coronary vascular resistance is due to a constriction of the large coronary arteries. Further studies are required to determine the physiopathological role of endothelin, especially in coronary vasospasm.

Endothelin acts in feline and canine cerebral arteries from the adventitial side

We investigated the in vivo vasoconstrictor effect of endothelin, a recently characterized vasoconstrictor peptide from vascular endothelium, in the basilar arteries of five cats and five dogs. Basilar artery caliber was angiographically measured under anesthesia before (control) and after either vertebral artery infusion or cisternal injection of the peptide. In cats, 5-500 pmol endothelin induced a dose-dependent basilar artery contraction in vivo when injected intracisternally; within 3 minutes after injection of 500 pmol endothelin, basilar artery caliber was decreased by 73 +/- 4% compared with control diameter before injection. The vasoconstriction was extremely long-lasting; no significant recovery of basilar artery caliber was observed for up to 2 hours after injection. In contrast, infusion of up to 3,000 pmol endothelin into the vertebral artery had no appreciable effect on basilar artery caliber. Similar results were obtained in dogs; vasoconstriction was maintained for as long as 12 hours. Our observations suggest that endothelin acts in cerebral vessels from the adventitial side, not from the luminal side, possibly due to the presence of the blood-arterial wall barrier. The long-lasting nature of endothelin-induced constriction of the cerebral arteries in vivo suggests that the peptide might be involved in the pathogenesis of cerebral vasospasm.

Immunohistochemical localization of endothelin in human vascular endothelial cells

The cellular localization of endothelin (ET), a novel vasoconstrictor peptide, was studied in human vascular tissues by immunohistochemistry. Distinct and diffuse staining for ET-like immunoreactivity was demonstrated in the cytoplasm of vascular endothelial cells, but not in smooth muscle cells or adventitial fibroblasts. The specificity was confirmed by the negative results following immunoabsorption. These findings suggest that human vascular endothelial cells function as an endocrine and/or paracrine cells for ET secretion.

Endothelin-1 induces potent constriction of lymphatic vessels in situ

The response of lymph vessels, arterioles and venules in the exteriorized rat mesentery to endothelin-1, vasopressin and norepinephrine was examined with the aid of high-resolution television microscopy. On a molar basis, endothelin-1 was more potent than vasopressin to contract the three types of vessels. Norepinephrine, which could constrict blood microvessels, did not act on lymph vessels. Acetylcholine, sodium-nitroprusside and isoproterenol were ineffective to block the constrictive responses of lymph vessels to endothelin-1 and vasopressin. At the same concentrations, however, acetylcholine and sodium-nitroprusside antagonized the responses of arterioles and venules to endothelin-1 and norepinephrine, whereas the responses of blood microvessels to vasopressin remained unaffected. Isoproterenol, at doses capable of blocking the response of the arterioles and venules to norepinephrine, did not interfere with the constriction induced by endothelin-1 and vasopressin on these vessels. It is suggested that endothelin-1 might play a role in the regulation of lymphatic contractility apart from its vasoconstrictor activity on blood vessels.

Solution conformation of endothelin determined by nuclear magnetic resonance and distance geometry

The solution conformation of endothelium-derived vasoconstrictor peptide, endothelin, has been determined by two-dimensional 1H-NMR spectroscopy and distance geometry. Conformation in the N-terminal core region (residues 1-15) is well-defined and a characteristic is the helix-like conformation in the segment from Lys9 to Cys15. Contrarily, the C-terminal tail region (residues 16-21) does not assume a defined conformation and there are no specific interactions between the core and the tail regions.

Abundance of endothelin-3 in rat intestine, pituitary gland and brain

We established a highly sensitive and specific sandwich-enzyme immunoassay (EIA) for endothelin-3 (ET-3), which showed no crossreactivity with endothelin-1 (ET-1), endothelin-2 (ET-2) and big-endothelin-1 (big-ET-1). We had previously established a sensitive sandwich-EIA for ET-1, which fully crossreacted with ET-2, but not with ET-3 or big-ET-1. These EIAs were used to examine the tissue distribution of immunoreactive (ir-) ET-3 and compare them with those of ir-ET-1 (including ir-ET-2) in Sprague-Dawley rats. High concentrations of ir-ET-3 were found in the intestine, lung, pituitary gland and brain (greater than 100 pg/g wet tissue), ir-ET-1(ET-2) showed widespread distribution, with large amounts in the lung and colon (greater than 1000 pg/g wet tissue). The pituitary gland was the only organ containing higher amounts of ir-ET-3 than ir-ET-1 (ET-2). In reverse phase-high performance liquid chromatography coupled with EIAs, the ir-ET-3 was exclusively eluted at the position of synthetic ET-3, indicating that the ir-ET-3 was identical to ET-3. The abundance of ET-3 in the intestine, pituitary gland and brain indicates that ET-3 is a new brain-gut peptide which may have a physiological function in nervous and endocrine systems.

Characterization of renal glomerular endothelin receptors in the rat

Specific receptors for Endothelin (Et) have been identified in the glomerulus of rat kidney. Human 125I-ET binds to a single population of high affinity receptors in glomerular membranes from normal rats with a mean equilibrium dissociation constant of 200 pM. The binding was time and temperature-dependent, saturable and reversible. The Et-receptor complex was not affected by either vasopressin, atrial natriuretic factor or angiotension II.

Endothelin 1, an endothelium-derived peptide, is expressed in neurons of the human spinal cord and dorsal root ganglia

The localization of endothelin 1 mRNA and endothelin-like immunoreactivity was investigated in samples of neurologically normal nervous system tissue from 10 adults by using in situ hybridization and immunocytochemistry. Tissue sections of spinal cord and dorsal root ganglia were hybridized with an 35S-radiolabeled endothelin 1 complementary RNA probe. Autoradiograms showed labeled neurons in the spinal cord (laminae IV-VI and many motoneurons) and numerous small and large neurons in the dorsal root ganglia. Endothelin 1 transcripts were also found in association with the endothelial layer of some blood vessels in the white matter of the spinal cord. A similar distribution of immunoreactivity was seen using three antisera to endothelin 1, but fewer cells were immunostained than were labeled after the hybridization. Two other endothelin 1 antisera immunostained the endothelial lining of blood vessels in the spinal cord white matter but not neurons. In the ganglia, endothelin 1 transcripts were localized to all cells expressing beta-preprotachykinin and most expressing calcitonin gene-related peptide mRNAs; in the majority of the motoneurons, coexistence of endothelin 1 and calcitonin gene-related peptide mRNAs was noted. There was a similar pattern of coexistence for respective peptide immunoreactivities in the ganglia and spinal cord. The expression of endothelin 1 mRNA in distinct neuronal cell types suggests that this peptide plays a part in neural transmission/modulation and adds a further dimension to the known vascular-related actions of endothelin 1.

Endothelin: visualization of mRNAs by in situ hybridization provides evidence for local action

Endothelin (ET) is a recently identified vasoactive peptide with three isoforms for which three genes have been cloned. The cellular sites of synthesis of this peptide have not yet been identified in vivo. Using Northern blot analysis, we have detected two forms of ET mRNA in rat tissues: a 3.7-kilobase form in the kidney, eye, and brain, a 2.5-kilobase form in the intestine, and both forms in the lung. We have localized these forms of ET mRNA in several rat tissues using in situ hybridization. In the 19-day rat fetus, ET mRNA is highest in the lung, intestine, and meninges. At high resolution, ET mRNA is localized in the lung to respiratory epithelial cells of bronchioles and apparently in blood vessels. In adult tissues, ET mRNA is present throughout the lung, in the renal medulla vasa recta, and in the iris of the eye. ET mRNA is synthesized in close proximity to ET binding sites in many organs (e.g., lung, kidney, intestine, and eye), suggesting a local action of this peptide. However, in other areas (e.g., heart and renal cortex), ET binding sites are present in the absence of ET mRNA, suggesting an action of ET from the bloodstream or from neurons. Northern blot analysis of ET mRNA in microvascular endothelial cells in culture indicates that ET is synthesized in small blood vessels and regulated similarly to its regulation in large vessels. Our results provide evidence that ET, like other regulatory peptides, may serve in several tissues as a neuromodulator or local hormone.

Endothelin binding to cultured calf adrenal zona glomerulosa cells and stimulation of aldosterone secretion

Endothelins are a group of potent vasoconstrictors whose structure was deduced from genomic DNA. ET-1 was first isolated from culture supernatants from porcine endothelial cells and ET-3 was identified from a rat DNA library. We report on the binding of 125I-ET-1 to zona glomerulosa cells in culture and on its ability to stimulate aldosterone secretion. Cultured calf adrenal zona glomerulosa cells have saturable, high affinity [Kd = 1.00 +/- 0.17 X 10(-10) M (SEM)] receptors which bind ET-1 in a temperature and time dependent manner. Binding was specific and angiotensin II, vasopressin, ANP, BNP, apamin, calcium channel agonists or antagonists did not interact with the receptor. ET-3 displaced 125I-ET-1 from the receptor with a relative potency of 0.39 +/- 0.1% (SEM) that of ET-1. ET-1 incubated with cultured glomerulosa cells stimulated aldosterone secretion in a dose dependent manner but it was less potent than angiotensin II. ET-3 had less than 1% the relative potency of ET-1 stimulating aldosterone secretion. This data suggest that ET-1 is an independent stimulator of aldosterone secretion and we are speculating that it might be important in those situations, like in malignant hypertension, where endothelial damage might result in increased ET-1 production.

Endothelin produces systemic vasodilation independent of the state of consciousness

The effects of endothelin, ET-1, on pulmonary and systemic hemodynamics were studied in the open chest dog and changes in systemic arterial pressure in dogs under conscious and anesthetized states were compared. Rapid intravenous (IV) bolus injections of ET-1, 100-1,000 nanograms/kg, significantly decreased systemic arterial pressure, and significantly decreased systemic vascular resistance whereas left atrial pressure and pulmonary vascular resistance were not altered. Reductions in systemic arterial pressure in response to bolus injection of ET-1, 100 and 300 nanograms/kg IV, during conscious state and during anesthesia were similar, respectively. The present data suggest that ET-1 dilates the systemic vascular bed independent of the animal's state of consciousness. The present data also suggest that when compared to the systemic vascular bed, the pulmonary vascular bed is less responsive to bolus administration of ET-1.

Structure-activity relationship of endothelin: importance of charged groups

Endothelin (ET)-related peptides including ET-1 (1-39) were synthesized, and their constricting activity in rat pulmonary artery rings and pressor activity in unanesthetized rat were measured to elucidate their structure-activity relationship. The vasoconstrictor activities of ET-2, ET-3 and sarafotoxin S6b were one-half, one-60th and one-third that of ET-1, respectively. Such differences in biological activities should mainly arise from sequence heterogeneity at the N-terminal portion, especially at positions 4 to 7. All of the blocked ETs at the amino or carboxyl termini showed greatly decreased activities. A monocyclic analog, in which Cys3 and Cys11 were replaced by Ala, showed one-third the activity of ET-1; however, its deamino dicarba analog was almost completely inactive. Significant activities were retained even with replacement of amino acids at positions Ser4, Ser5, Leu6, Met7, Lys9, Tyr13, and Trp21 by Ala, Ala, Gly, Met(0), Leu, Phe, and Tyr or Phe, respectively. On the other hand, replacement of Asp8, Glu10 and Phe14 by Asn, Gln and Ala, respectively, resulted in complete loss of the biological activity. These results indicated that two disulfide bonds in ET molecule were not essential for the expression of vasoconstricting activity. Both terminal amino and carboxyl groups, carboxyl groups of Asp8 and Glu10, and the aromatic group of Phe14 seemed to be contributing, more or less, to the expression of the biological activities.

Analysis of endothelin related peptides in culture supernatant of porcine aortic endothelial cells: evidence for biosynthetic pathway of endothelin-1

We investigated the molecular forms of endothelin (ET) related peptides in culture supernatant of porcine aortic endothelial cells by high performance liquid chromatography coupled with radioimmunoassays for ET related peptides. We isolated and sequenced a C-terminal peptide (big ET-1(22-39] of big ET-1(1-39) and its N-terminal truncated form (big ET-1(23-39] in addition to ET-1(1-21) and its oxidized form, [Met7 (0)]ET-1(1-21). The total contents of the two C-terminal peptides of big ET-1(1-39) are approximately equal to those of ET-1(1-21) and its oxidized form on a molar basis in the culture supernatant. Furthermore, we isolated big ET-1(1-39) although its content is approximately 2% of that of ET-1(1-21). These results strongly suggest that ET-1(1-21) and big ET-1(22-39) are generated from big ET-1(1-39) by specific processing between Trp21-Val22.

Immunological and structural characterization of sarafotoxin/endothelin family of peptides

A highly specific and sensitive radioimmunoassay (RIA) was developed for the potent vasoconstrictor peptides, sarafotoxin-b and human endothelin. The antigenic determinants of the antibodies employed in studies with these assays were found to be localized within the amino acid sequence at positions 4-7. This was confirmed by CNBr cleavage of the methionyl residue at position 6 in the sarafotoxin and at position 7 in the endothelin. The chemically characterized modified peptides showed very low cross reactivity in the RIAs. On the other hand, the binding properties as well as the ability to induce phosphoinositide hydrolysis were very similar in the modified and native peptides, indicating that despite cleavage of the peptide bond the biologically active conformation responsible for either binding or phosphoinositide hydrolysis is retained, probably because of the disulfide bonds. Thus, structural alteration might be a valuable means of curtailing some of the various activities induced by the sarafotoxin/endothelin family of peptides.

The pharmacological properties of the peptide, endothelin

1. The effect of endothelin (ET-1) has been studied on isolated vascular and non-vascular preparations, using both functional and competition radioligand binding techniques. The effects of endothelin on blood pressure were studied in both anaesthetised, chemically denervated normotensive and spontaneously hypertensive rats (SHR). 2. Endothelin elicited contractile responses in the rat thoracic aorta, perfused mesenteric bed, rabbit mesenteric artery and portal vein. The maximal responses in the rat aorta were enhanced by removal of the endothelium, and were reduced in the presence of either a cyclo-oxygenase inhibitor (indomethacin) or a thromboxane receptor antagonist (SQ 29,548). In terms of potency, the most sensitive preparation was the rat endothelium-denuded aorta and rat perfused mesenteric bed (-log EC50 values = 8.2 +/- 0.07 and 8.2 +/- 0.12, mean +/- s.e.mean, n = 4, respectively). In the perfused mesenteric bed of the rat the maximum response to endothelin (219 +/- 12 mmHg, n = 4) was greater than that to either phenylephrine (maximal response = 67 +/- 9 mmHg; n = 4) or KCl (maximal response = 110 +/- 6 mmHg, n = 4). 3. Endothelin elicited contractile responses of the guinea-pig isolated ileum, oesophageal muscularis mucosae and uterus. Responses were also observed in the rat fundic strip and paced left atria. The guinea-pig urinary bladder, trachea, rat vas deferens and anococcygeus exhibited little or no response to endothelin at the concentrations studied (1 x 10(-12)-3.2 x 10(-8) M). Of the above preparations, the ileum and oesophageal muscularis mucosae were the most sensitive to endothelin (-log EC50 = 8.5 +/- 0.11 and 8.4 +/- 0.06, n = 6, respectively), exhibiting potencies similar to those observed in the endothelium-denuded aorta of the rat. 4. In competition-radioligand binding studies, endothelin did not displace either [3H]-PN 210-100 or [125I]-(-)-omega-conotoxin GVIA from binding sites in membranes from rat cerebral cortex and, skeletal muscle or from guinea-pig cerebral cortex and hippocampus, respectively. This indicates a lack of direct interaction of endothelin at the dihydropyridine binding site and the N-type calcium channel, respectively. However, in functional studies, contractile responses to endothelin (1 x 10(-8) M) in the endothelium-denuded aorta of the rat were potently reversed by nifedipine, verapamil, and prenylamine (-log IC50 values = 8.0 +/- 0.13, 7.2 +/- 0.09 and 6.6 +/- 0.08, n = 4-8, respectively). In addition, the responses to endothelin were virtually abolished in the presence of Krebs physiological salt solution containing no calcium but with 1 x 10-M EDTA added. Preequilibration with either (-)-w-conotoxin (1 x 10-6M) or tetrodotoxin (1 x 10-6M) did not affect responses to endothelin. 5. In chemically denervated rats, endothelin (1pmolkg-'-10nmolkg- , i.v.) exhibited pressor responses, which were unaffected by a 3 h pretreatment with indomethacin. In the SHR, the effects on blood pressure were not significantly different from those observed in normotensive animals at any of the doses studied. A transient (duration < 30 s) depressor response was also observed in all groups studied at a dose of 0.1-1 nmol kg-1 i.v. 6. In conclusion, endothelin is a potent contractile agonist in both vascular and non-vascular muscle. It appears to elicit responses partly via the entry of extracellular calcium (by a mechanism distinct from that of other calcium facilitators) and partly by release of endoperoxides.

Synthesis of human endothelin-1 precursors in Escherichia coli

Endothelin, the most potent vasoconstrictor found in nature, is thought to be important in the regulation of blood pressure and/or local blood distribution. Human placenta cDNA fragment encoding preproendothelin-1 (preproET-1) and its carboxyl terminal mature precursor (C-matured precursor) was expressed in E. coli. These products were characterized by both enzyme immunoassay and Western blot analysis.

Immunoreactive endothelin in rat kidney inner medulla: marked decrease in spontaneously hypertensive rats

Using a specific and sensitive radioimmunoassay for endothelin, the regional distribution and molecular form of endothelin was investigated in rat tissue. The highest concentration was observed in the inner medulla of the kidney (8.7 +/- 2.2 pg/mg wet weight). On two kinds of reverse phase high performance liquid chromatography, immunoreactive endothelin in the inner medulla of the kidney was separated into two peaks at positions where authentic porcine/human and putative rat/human endothelin eluted. Furthermore, the concentration of immunoreactive endothelin in the inner medulla of the kidney was remarkably decreased in spontaneously hypertensive rats (SHR) compared with normotensive control Wistar Kyoto rats (WKY) but no difference was observed in lung immunoreactive endothelin.

Concomitant secretion of big endothelin and its C-terminal fragment from human and bovine endothelial cells

A specific radioimmunoassay (RIA) for the carboxyl-terminal fragment (CTF) of big porcine endothelin (pET), an intermediate form of pET, was established to characterize big ET-like and its CTF-like immunoreactivity (LI) secreted from cultured bovine and human endothelial cells (EC). The antibody used crossreacted equally with big pET(1-39) and its CTF(22-39), but not with pET(1-21). Serial dilution curves of the culture media from bovine and human EC were parallel to that of standard CTF. Reverse-phase HPLC coupled with RIAs for big ET and ET of the culture media from bovine and human EC revealed essentially the same elution profiles: two major CTF-LI components, one corresponding to big pET(1-39) and the other to its CTF(22-39), in addition to one major ET-LI component corresponding to pET(1-21). The amounts of CTF-LI were almost equal to that of ET-LI on a molar basis. These data suggest that big ET is processed by a putative ET converting enzyme to yield its CTF and the mature ET(1-21) in EC.

Specific platelet mediators and unstable coronary artery lesions. Experimental evidence and potential clinical implications

We have speculated previously that the abrupt conversion from chronic stable to unstable angina and the continuum to acute myocardial infarction may result from myocardial ischemia caused by progressive platelet aggregation and dynamic vasoconstriction themselves caused by local increases in thromboxane and serotonin at sites of coronary artery stenosis and endothelial injury. Platelet aggregation and dynamic coronary artery vasoconstriction probably result from the local accumulation of thromboxane and serotonin and also relative decreases in the local concentrations of endothelially derived vasodilators and inhibitors of platelet aggregation, such as endothelium-derived relaxing factor (EDRF) and prostacyclin. With severe reductions in coronary blood flow caused by these mechanisms, platelet aggregates may increase, and an occlusive thrombus composed of platelets and white and red blood cells in a fibrin mesh may develop. When coronary arteries are occluded or narrowed for a sufficient period of time by these mechanisms, myocardial necrosis, electrical instability, or sudden death may occur. We believe that unstable angina and acute myocardial infarction are a continuum in relation to the process of coronary artery thrombosis and vasoconstriction. When the period of platelet aggregation or dynamic vasoconstriction at sites of endothelial injury and coronary artery stenosis is brief, unstable angina or non-Q wave infarction may occur. However, when the coronary artery obstruction by these mechanisms is prolonged for several hours, Q wave myocardial infarction results. Chronic endothelial injury and coronary artery stenosis are probably associated with the accumulation of platelets, white and red blood cells, and a fibrin mesh at the site of stenosis and endothelial injury.

Endothelin- and neuropeptide Y-induced vasoconstriction of human epicardial coronary arteries in vitro

1. The effects of the recently discovered peptide endothelin and neuropeptide Y (NPY) on human epicardial coronary arteries were studied in vitro. 2. Endothelin induced a concentration-dependent, endothelium-independent, long-lasting vasoconstriction regardless of vessel size. NPY evoked contractions of small coronary arteries with a similar potency to that of endothelin, although to a significantly lower degree. Large coronary arteries did not respond to NPY. Endothelin did not relax coronary arteries precontracted with potassium. 3. The effect of endothelin was dependent on extracellular Ca2+ and, like NPY, significantly reduced by the Ca2+-antagonist nifiedipine. 4. In conclusion, endothelin is a potent human vasoconstrictor in vitro. It is suggested that endothelin may be involved in the regulation of coronary blood flow.

Regional distribution of immunoreactive endothelin in rats

By use of a specific radioimmunoassay for endothelin (ET), the regional distribution of ET-like immunoreactivity (LI) was studied in rats. The antiserum used cross-reacted equally with synthetic porcine and rat ET. Significant amounts of ET-LI are detectable not only in aorta, but also in kidney, lung, heart, liver and central nervous system. Gel chromatography of the tissue extracts revealed size heterogeneity of ET-LI; one major component eluting close to, but slightly larger than standard rat ET and the other minor component with a larger molecular weight. These data indicate that ET-LI is widely distributed throughout the various rat tissues, suggesting its possible involvement in a variety of organ functions.

Two distinct types of endothelin receptors are present on chick cardiac membranes

Competitive displacement experiments of 125I-endothelin (ET)-1, -2, or -3 binding to chick cardiac membranes were performed with unlabeled ET-1, -2, -3, and sarafotoxin S6b (STX) as competitors. 125I-ET-1 and -2 binding was competitively inhibited by increasing concentrations of these unlabeled peptides in the same order; i.e. ET-2 greater than or equal to ET-1 greater than ET-3 greater than STX. In contrast, the order of potency in displacing 125I-ET-3 binding was ET-3 greater than ET-2 greater than or equal to ET-1 greater than STX. Affinity labeling of the membranes by cross-linking with 125I-ET-1 and -2 via disuccinimidyl tartarate yielded one major specific band with an apparent Mr = 53,000 by sodium dodecyl sulfate-polyacrylamide gel electrophoresis followed by autoradiography. On the other hand, affinity labeling with 125I-ET-3 showed that two major and one minor bands of Mr = 34,000, 46,000, and 53,000, respectively, were specifically labeled. These results indicate the presence of two distinct types of ET receptors, one of which has higher affinity for ET-1 and -2 than ET-3 and the other is conversely ET-3-preferring.

Endotoxin stimulates endothelin-release in vivo and in vitro as determined by radioimmunoassay

A marked increase in immunoreactive endothelin was observed in rat serum collected within 10-15 min after infusion of endotoxin. Endothelin level was 117 +/- 11.5 pg/ml (mean +/- S.E., N = 4) in rats exposed to endotoxin as compared with undetectable levels (less than 2 pg/ml, N = 4) in controls. We have also observed a significant stimulation of endothelin-release by endotoxin from cultured bovine transformed thoractic aortic endothelial cells at concentrations of endotoxin ranging between 0.1 and 10.0 micrograms/ml. Serum was indispensable for the stimulating effect of endotoxin, although serum itself did not show any effect at the concentration used (1%). These results suggest that endothelin plays an important role in mediation of pathophysiological responses caused by endotoxin. The levels of endothelin were measured by radioimmunoassay with high sensitivity.

Differential effects of rat endothelin on regional blood flow in the cat

Regional vascular responses to rat endothelin were investigated in the anesthetized cat. Intravenous injection of the peptide in doses of 0.1-1 nmol/kg decreased arterial pressure and increased distal aortic blood flow with a small secondary reduction in flow at the high dose. Mesenteric blood flow was decreased, and the decreases in flow were proportionately greater than the decreases in pressure so that mesenteric resistance increased at all doses. The rat peptide increased blood flow or caused biphasic changes in flow in the renal vascular bed. At 0.1 and 0.3 nmol the peptide decreased renal resistance, whereas at 1 nmol a biphasic change occurred. The present data suggest that responses to rat endothelin are dependent on dose and the vascular bed studied and indicate that the peptide can cause both vasodilation and vasoconstriction.

Detection of immunoreactive endothelin in plasma of hemodialysis patients

Two types of radioimmunoassay (RIA) methods for measuring endothelin (ET) in human plasma were developed. One was an extraction procedure using a Sep-Pak C18 cartridge, the other being a direct method. By the extraction method, plasma ET levels were lower than the detectable limit (7 pg/ml) in normal subjects and elevated in hemodialysis patients. The absolute values obtained via the direct method were 20-times higher than those from extraction. Gel-filtration experiments revealed that this discrepancy was mainly due to immunoreactive (IR-) endothelin-like substances of high molecular mass near 11.6 kDa (large IR-ET). Extraction of the peptide by the C18 cartridge could eliminate interference by large IR-ET and is important in the accurate measurement of ET concentrations in plasma.

Endothelin binding sites in porcine aortic and rat lung membranes

High-affinity binding sites for endothelin were identified on porcine aortic and rat lung membranes. Interaction of 125I-labelled endothelin with its binding site was specific, saturable, time- and temperature-dependent but dissociation of receptor-bound ligand was minimal. Maximal binding was observed at pH 7.0 in porcine aorta and at pH 3.1 in the rat lung. Treatment of membranes with trypsin destroyed the binding site in both tissues. Porcine endothelin showed a higher affinity for receptors in both tissues compared to rat endothelin. Vasoactive peptides and Ca2+ channel antagonists did not interact with this site suggesting high specificity of binding. Analysis of saturation binding showed that the number of binding sites was 1250 +/- 104 and 1650 +/- 170 fmol/mg protein and the affinity of binding sites was 0.47 +/- 0.15 and 0.16 +/- 0.07 nM in the aorta and the lungs respectively (n = 5). Presence of protease inhibitors did not alter binding suggesting that the label was stable under the incubation conditions. This was further confirmed by HPLC. Removal of the endothelium from the aorta did not change the binding characteristics of this tissue. Ca2+ and Mg2+ ions caused an increase in binding by increasing the affinity. Binding was completely abolished in the presence of Triton and dithiothreitol. The binding sites identified in this study may be responsible for the actions of endothelin in the aorta and the lung.

Effects of porcine and rat endothelin and an analog on blood pressure in the anesthetized cat

Arterial responses to a wide range of doses of porcine and rat endothelin and a monocyclic analog were compared in the anesthetized cat. Injections of the porcine peptide in doses of 0.01-0.1 nmol/kg i.v. decreased systemic arterial pressure in a dose-related manner, whereas doses of 0.3 and 1 nmol/kg i.v. elicited biphasic responses. The rat peptide, in doses of 0.03-1 nmol/kg i.v., also decreased arterial pressure in a dose-related fashion, whereas injection at 3 nmol/kg i.v. caused a biphasic response. With both peptides the biphasic response was characterized by an initial short-lived decrease followed by a secondary sustained increase in pressure. The monocyclic porcine analog in doses of 3-30 nmol/kg i.v. had no significant effect on arterial pressure. Both peptides increased cardiac output, and changes in peripheral vascular resistance in response to both peptides were not altered by sodium meclofenamate. These data suggest that arterial depressor responses to porcine and rat endothelin are similar and dose-dependent. However, the porcine peptide has 3-fold greater pressor activity in the cat. The lack of effect with the monocyclic porcine analog suggests that the two disulfide linkages are necessary for activity.

Synthesis of the vasoconstrictor peptide endothelin in kidney cells

The expression plasmid containing human prepro-endothelin cDNA was constructed and introduced into COS-7 cells. Mature endthelin, consisting of 21 amino acid residues, was secreted into the culture medium of the transfected cells and was also synthesized by non-transfected COS-7 cells. Normal kidney cells derived from other species also synthesized and secreted endothelin. Partial characterization of endothelins produced by kidney cells suggested that existence of new types of endothelin. This is the first report of the vasoconstrictor peptide endothelin being synthesized in kidney cells.

Plasma endothelin levels in patients with uraemia

Plasma immunoreactive endothelin concentrations were measured in patients with uraemia and in non-uraemic controls. Concentrations were beneath the detection limit of the assay in most patients without uraemia but were readily detectable in those undergoing haemodialysis. Plasma endothelin concentrations in patients with uraemia who were not undergoing haemodialysis were lower than in those on maintenance dialysis.

Specific binding of endothelin on human vascular smooth muscle cells in culture

Endothelin is a newly discovered, potent vasoconstrictor peptide secreted by endothelial cells. The binding of endothelin was studied on cultured human vascular smooth muscle cells obtained from umbilical veins. A single specific binding site for 125I-endothelin was identified, with an apparent Kd of 126 pM and a maximal binding capacity of approximately 10,000 sites per smooth muscle cell. At room temperature the binding was saturable, reached equilibrium at 2 h (using 20 pM endothelin), and was slowly and only partially reversed by unlabeled endothelin. The calcium antagonists nifedipine, nicardipine, and diltiazem did not compete for the same binding site. Conditioned medium from cultured human umbilical vein endothelial cells inhibited the binding of 125I-endothelin dose dependently. This effect was antagonized by anti-endothelin antiserum. We conclude that human umbilical vein smooth muscle cells possess specific binding sites for endothelin, and that human endothelial cells secrete an endothelinlike material.

Endothelin activates the dihydropyridine-sensitive, voltage-dependent Ca2+ channel in vascular smooth muscle

Endothelin is a potent endothelium-derived vasoconstrictor peptide recently characterized from porcine and human vascular endothelial cells. Here we provide evidence that endothelin activates the dihydropyridine-sensitive, voltage-dependent Ca2+ channel in porcine coronary artery smooth muscle. The vasoconstrictor action of endothelin is efficiently antagonized by low doses of the dihydropyridine Ca2+-channel blocker nicardipine. Endothelin augments the Ca2+-induced contraction in a high-K+ depolarizing solution, markedly enhances high-threshold Ca2+-channel current on the whole-cell patch clamp recording, and causes a sustained increase in the intracellular Ca2+ that is largely dependent on extracellular Ca2+. These findings suggest that endothelin exerts its vasoconstrictor effect by either directly or indirectly activating the voltage-dependent Ca2+ channel.