Heterologous in vivo processing of human preproendothelin 1 into bioactive peptides

Endothelin (ET) is an extremely potent vasoconstrictor peptide of 21 amino acids, originally found in the supernatant of cultured vascular endothelial cells. To gain insights into its biosynthetic pathway, we expressed a synthetic RNA coding for the 212-amino acid precursor of human ET-1 (preproET-1) in Xenopus oocytes. Cell homogenates and oocyte incubation medium were tested by RIA using an anti-ET-1 serum. ET-1-like immunoreactivity was detected in oocytes injected with preproET-1 synthetic RNA but not in control oocytes and was much higher in medium than in cell homogenates. When preproET-1 was expressed in oocytes treated with monensin, a dramatic decrease in secretion of immunoreactive material was observed, indicating that secretion is mediated by the Golgi complex. ET-1-like immunoreactive material present in oocyte incubation medium was fractionated by reverse-phase HPLC into two main peaks, corresponding to the retention times of human big ET-1 and ET-1. Incubation medium of oocytes expressing the synthetic preproET-1 RNA elicited a characteristic vasoconstrictor response on rabbit vena cava, consistent with the biological activity that would be predicted from the amount of ET-1-like immunoreactivity measured. These results suggest that common pathways of ET maturation exist in widely different cells and that Xenopus oocytes may represent a useful tool in studying the cell biology of ET-1 synthesis.

Circulating and tissue endothelin immunoreactivity in advanced atherosclerosis

BACKGROUND

Atherosclerosis is characterized by endothelial injury and the proliferation of arterial smooth-muscle cells. The latter may be a result of the release of growth factors from the vessel wall; such growth factors may include an endothelium-derived vasoconstrictor for peptide with mitogenic properties. We tested the hypothesis that plasma endothelin concentrations are elevated in persons with symptomatic atherosclerosis, independently of age.

METHODS

We measured plasma endothelin levels in 100 normal subjects and in 40 patients with atherosclerosis predominantly of the following types: aortic and peripheral vascular disease (14 patients), renovascular disease (9 patients) coronary artery disease (9 patients), and carotid disease (8 patients). We also performed immunohistochemical staining for endothelin in the walls of atherosclerotic vessels.

RESULTS

In the normal subjects, the mean (+/- SD) plasma endothelin concentration was 1.4 +/- 0.2 pmol per liter, with no correlation between age and plasma endothelin concentration (r = 0.13, P = 0.2). In the patients with symptomatic atherosclerosis, the mean plasma endothelin concentration was 3.2 +/- 1.2 pmol per liter (P less than 0.001), and there was a significant correlation between plasma endothelin and the number of sites of disease involvement (r = 0.89, P less than 0.001). In the immunohistochemical studies, endothelin-1-like immunoreactivity was observed in vascular smooth muscle as well as in endothelial cells.

CONCLUSIONS

Endothelin may be a marker for arterial vascular disease. Whether it participates in the atherogenic process or is merely released from damaged endothelial cells is unclear.

Immortalization of brain capillary endothelial cells with maintenance of structural characteristics of the blood-brain barrier endothelium

Early passage bovine brain capillary endothelial cells were immortalized by transfection with the plasmid pSV3 neo. Cells from one clone, SV-BEC, expressed nuclear SV 40 large T antigen, displayed a contact-inhibited and anchorage-dependent proliferation, and a high sensitivity to the addition of exogenous basic fibroblast growth factor. SV-BEC cells are morphologically unaltered and express typical markers of endothelial cells: Factor VIII-related antigen, angiotensin-converting enzyme and Griffonia simplicifolia agglutinin binding site. Endothelium like immunoreactivity was detected in the conditioned medium from these cells. Moreover, SV-BECs present numerous intercellular tight junctions characteristic of the blood-brain barrier and possess functional beta 1- and beta 2-adrenergic receptors, as observed on isolated bovine brain capillaries.

Endothelin-1 in human skin: immunolocalization, receptor binding, mRNA expression, and effects on cutaneous microvascular endothelial cells

Endothelin-1 (ET-1), a potent vasoconstrictor peptide, has been implicated in the maintenance of systemic and peripheral vascular tone. We have therefore sought direct evidence of a role for ET-1 in the regulation of blood flow and vascular tone in the human cutaneous microvasculature. Immunostaining for ET-1 was observed in all cutaneous blood vessels of normal human skin including the capillaries of the dermal papillae. Autoradiography showed specific binding of 125I-ET-1 over capillaries and larger blood vessels as well as hair follicles and sweat glands. In situ hybridization with a 32P-labeled RNA probe for ET-1 demonstrated mRNA for ET-1 in cultured human dermal microvascular endothelial cells (HDMEC). In HDMEC, basal release of PGE2 was significantly attenuated by ET-1 (100 pM-100 nM) (p less than 0.05, n = 7) with maximum inhibition in cells incubated with 10 nM ET-1. ET-1 also increased intracellular cAMP in a dose-dependent manner with a significant increase in HDMEC incubated with 100 nM ET-1 (p less than 0.05, n = 4). In HDMEC incubated with 100 nM ET-1, inhibition of PGE2 release was unaffected by the dihydropyridine Ca++ channel antagonist nifedipine or the extracellular Ca++ chelator EGTA, whereas the intracellular Ca++ chelator TMB-8 partially blocked the action of ET-1. In contrast, cAMP accumulation was significantly attenuated by EGTA (p less than 0.05, n = 4), nifedipine (p less than 0.05, n = 4), and TMB-8 (p less than 0.05, n = 4), indicating that the endothelial cell responses to ET-1 are complex and appear to involve both Ca(++)-sensitive and -insensitive pathways. These results provide evidence of an autocrine/paracrine role for ET-1 in the human cutaneous microvasculature.

Presence of endothelin-1 and endothelin-3 in peripheral tissues and central nervous system of the pig

The distribution of endothelin (ET) peptides in the pig was studied in a variety of tissues using selective radioimmunoassays combined with reverse-phase high performance liquid chromatography (HPLC). The levels of ET-like immunoreactivity (LI) were overall relatively low. The highest levels of ET-LI were found in blood vessels, cerebral and coronary arteries containing 3190 +/- 910 and 1330 +/- 450 fmol/g, respectively. Veins generally contained higher levels of ET-LI per tissue weight than corresponding arteries. Peripheral sympathetic and sensory ganglia contained a higher concentration of ET-LI than the studied central nervous system (CNS) areas. In the CNS the highest concentration of ET-LI was found in a non-neuronal structure, the choroid plexus. The levels of ET-LI were also relatively high in the respiratory tract (100-400 fmol/g). In the heart, the endocardium contained the highest levels (190 +/- 44 fmol/g). In the kidney, the concentration of ET-LI was 3-fold higher in the medulla than in the cortex. In the gastrointestinal tract all levels were below 100 fmol/g, except for the colon which contained 120 +/- 50 fmol/g. The characterization of ET-LI in extracts of some of these tissues revealed that ET-1 dominated in the lung, spleen and hypothalamus while ET-3 and ET-1 were present in approximately equal amounts in renal medulla and thoracic spinal cord. The HPLC analysis provided no clear-cut evidence for significant presence of vasoactive intestinal contractor, ET-2 or big ET-1(1-39) in the lung, spleen, kidney, spinal cord or hypothalamus. It is concluded that mature ET-1 and ET-3 are the predominant ET peptides in peripheral tissues and CNS.

Colocalization of endothelin, vasopressin and serotonin in cultured endothelial cells of rabbit aorta

The localization and colocalization of endothelin-1, arginine-vasopressin and serotonin in the endothelial cells of rabbit aorta in primary culture were investigated by preembedding and postembedding immunocytochemistry. These three substances were localized in the same population of cells, where they appeared in high proportions (greater than 60%). These findings indicate: 1) that the cell population is heterogeneous, and 2) that these substances are colocalized in some of the cultured endothelial cells. Double labeling in single cells has demonstrated the simultaneous presence of 1) endothelin and vasopressin, 2) vasopressin and serotonin, and 3) endothelin and serotonin. The immunolabeling dominated in the cytoplasmic matrix.

Platelets stimulate expression of endothelin mRNA and endothelin biosynthesis in cultured endothelial cells

Modulation of the biosynthesis of the vasoconstrictor peptide endothelin was studied in cultured endothelial cells. Immunoreactive endothelin (irET) levels were significantly elevated in conditioned medium from bovine pulmonary artery endothelial (BPAE) or human umbilical vein endothelial cells when coincubated with washed human platelets. Platelets (approximately 200,000 cells/microliters) enhanced irET levels approximately 250% over basal levels. Stimulation of irET levels in BPAE cell-conditioned medium by platelets was time and platelet number dependent. Platelets, as well as thrombin and transforming growth factor-beta 1, stimulated the expression of preproendothelin-1 mRNA in a time-dependent manner. Coincubation of low doses of thrombin (0.1 unit/ml) and subthreshold concentrations of platelets with BPAE cells resulted in a further enhancement of irET levels in conditioned medium. Platelet-mediated stimulation of irET production was not significantly affected by indomethacin (1 microM) or the platelet-activating factor receptor antagonist WEB 2086 (1 microM); however, coincubation of endotoxin (100 ng/ml) with platelets and BPAE cells resulted in significantly higher levels of irET. Whether direct contact or adhesion between platelets and endothelial cells is necessary for stimulating irET release was studied by separating platelets from BPAE cells with a 0.4 microns permeable membrane. Under these conditions, platelets still produced significant elevations (approximately 190% over basal levels) in irET levels in BPAE cell-conditioned medium. In addition, platelet-free buffer from agonist-induced platelet aggregation also significantly enhanced irET production (200% over basal values). These data indicate that a platelet-derived regulatory factor can induce the biosynthesis of endothelin from cultured endothelial cells and also suggest that platelets might play a role in vasomotor regulation via a novel intercellular interaction with the endothelium.

Levels of endothelin in the bronchoalveolar lavage fluid of patients with symptomatic asthma and reversible airflow obstruction

We have previously demonstrated that human bronchial smooth muscle cells possess a single class of specific binding sites for the potent bronchoconstrictive peptide, endothelin 1, and that human bronchial epithelial cells constitutively release an endothelin-like material in culture, which binds to smooth muscle cell receptors with a kinetic analogous to that observed with the authentic peptide. To evaluate the potential role of endothelin in the pathogenesis of asthma, we examined in this study the release of endothelin in the airways of six patients with asthma, both at the time when they were symptomatic and had reversible airflow obstruction and during the remission phase of the disease induced by treatment. Five normal volunteers and five patients with chronic bronchitis and airflow obstruction unaffected by bronchodilators were tested as control subjects. The release of endothelin in airway mucosa was assessed by RIA with the bronchoalveolar lavage fluid recovered during bronchoscopy. Patients with asthma had increased amounts of immunoreactive endothelin in bronchoalveolar lavage fluid than normal control subjects or subjects with chronic bronchitis (p less than 0.05) in absence of any significant alteration in the levels of circulating peptide. Treatment of patients with asthma with oral corticosteroids and inhaled beta-agonists for 15 days resulted in improvement of airflow obstruction and in more than threefold reduction in the contents of endothelin in lavage fluid. Our findings indicate that the potent bronchoconstrictive substance, endothelin, may contribute to the pathogenesis of airflow obstruction in asthma.

Time course of plasma and pulmonary lymph endothelin-like immunoreactivity during sustained endotoxaemia in chronically instrumented sheep

1. Endothelin, a novel vasoconstrictor 21-residue peptide isolated from the supernatant of cultured porcine endothelial cells, has been shown to be increased in plasma in a variety of cardiovascular disease states, including acute myocardial infarction, acute renal failure and essential hypertension. We determined the time course of plasma and pulmonary lymph endothelin-like immunoreactivity in relation to the progressive deterioration of cardiopulmonary function in an ovine septic shock model leading to multi-organ failure syndrome and death within 42 h of a continuous intravenous infusion of Escherichia coli endotoxin (40 ng min-1kg-1). 2. Plasma and pulmonary lymph endothelin-like immunoreactivity were measured by r.i.a. using a specific antiserum raised in rabbits against porcine endothelin-1. Endothelin-like immunoreactivity was further determined in lung tissue and the thoracic duct lymph of endotoxin-treated sheep by reversed-phase h.p.l.c. In control instrumented conscious sheep not infused with endotoxin, there were no significant changes in any of the measured cardiopulmonary and biochemical variables, with plasma and pulmonary lymph endothelin-like immunoreactivity remaining below the detection limit (less than 1 pg/tube) throughout the 72 h study period. 3. Conscious sheep receiving endotoxin showed a major hypotensive septic syndrome, including persistently decreased systemic blood pressure, systemic vascular resistance, stroke volume, left ventricular stroke work, associated with sustained pulmonary vasoconstriction and protein-rich pulmonary oedema (greater than five-fold increase in pulmonary lymph flow and protein clearance), and marked lactic acidosis, leading to the death of animals within 14-42 h despite institution of mechanical ventilation and adequate intravascular volume replacement.(ABSTRACT TRUNCATED AT 250 WORDS)

Contribution of endogenous endothelin to the extension of myocardial infarct size in rats

Pathophysiological roles of endogenous endothelin have been studied from the viewpoint of its contribution to the extension of myocardial infarct size. A monoclonal antibody against endothelin 1 (AwETN40) suppressed changes induced by endothelin 1 and endothelin 2 but did not modify those by endothelin 3 in vivo or in vitro. Effects of AwETN40 on myocardial infarct size were investigated. Coronary ligation (1 hour) and reperfusion (24 hours) in rats caused infarction in 35% of the left ventricle. Repetitive or single administration of AwETN40 reduced the infarct size; an intravenous injection of 22.5 mg/kg of the antibody 5 minutes after coronary occlusion or 5 minutes before reperfusion reduced the size by 38% or 31% of the control, respectively. Plasma and tissue endothelin 1 and plasma big endothelin 1 in rats were measured at various stages after occlusion. Plasma endothelin 1 showed a fourfold increase 10 minutes after reperfusion (from 1.02 to 3.96 pg/ml) and had returned to the control value after 8 hours. Plasma big endothelin 1 showed changes similar to those of plasma endothelin 1. No significant changes in plasma endothelin 2 and endothelin 3 were observed. Cardiac tissue contained seven times as much endothelin 1 as the control value 1 hour after reperfusion (4.59 versus 33.1 pg/g tissue), and a high concentration (13.2 pg/g tissue) was maintained even after 48 hours. We concluded that an increase in endogenous endothelin 1 plays an important role in the extension of myocardial infarct size.

Endothelin-like immunoreactivity in rat models of diabetes mellitus

The factors associated with high concentrations of circulating plasma immunoreactive endothelin in patients with diabetes mellitus are unknown. Plasma and tissue (lung and kidney) immunoreactive endothelin levels were therefore measured by radioimmunoassay in three animal models of diabetes mellitus: dexamethasone-treated rats (2 mg/kg per day for 12 days), streptozotocin-treated rats (100 mg/kg, 4 days before being killed) and rats treated with both dexamethasone and streptozotocin. Plasma concentrations of immunoreactive endothelin in the dexamethasone-treated rats (3.13 +/- 0.28 pmol/l, mean +/- S.E.M., n = 15) were significantly (P less than 0.005) higher than those in controls (1.33 +/- 0.18 pmol/l, n = 15), while plasma concentrations of immunoreactive endothelin in streptozotocin-treated rats (n = 8) and rats treated with both dexamethasone and streptozotocin (n = 14) were undetectable (less than 0.5 pmol/l). Fast protein liquid chromatographic analysis of the plasma immunoreactive endothelin of dexamethasone-treated rats showed four peaks: one in the void volume, one eluting before endothelin-3, one eluting after endothelin-3 and before endothelin-1 and one eluting in a position identical with that of endothelin-1. Pulmonary concentrations of immunoreactive endothelin in the three groups of rats with diabetes mellitus were lower (P less than 0.005) but no significant change was found in renal immunoreactive endothelin. These findings indicate that short-term dexamethasone treatment increases plasma levels of immunoreactive endothelin while streptozotocin treatment decreases them. Thus, multiple factors may influence plasma concentrations of immunoreactive endothelin in diabetes mellitus.

Prevention of cerebral vasospasm by actinomycin D

The role of endothelin, a newly found vasoconstrictor peptide, is examined in the pathogenesis of cerebral vasospasm after experimental subarachnoid hemorrhage (SAH) in the dog. Endothelin immunoreactivity was overexpressed in the endothelium of the vasospastic basilar artery. Because endothelin synthesis is regulated at the messenger ribonucleic acid transcription level, the effect of actinomycin D, a ribonucleic acid synthesis inhibitor, was studied as a means of preventing vasospasm. It was found that treatment with intravenous actinomycin D for 5 days beginning on the day of SAH completely inhibited the development of vasospasm. This novel experimental therapy may lead not only to the elucidation of the pathogenesis of cerebral vasospasm but also to the availability of a prophylactic adjuvant therapy for patients with SAH.

Immunoreactive endothelin in human kidney

Using a sensitive and specific radioimmunoassay for endothelin, we examined immunoreactive endothelin in human kidney tissue obtained from three necropsy and three nephrectomy cases. Immunoreactive endothelin was present in high concentrations in human kidney inner medulla (necropsy cases: 1.08 +/- 0.47 pg/mg wet weight:mean +/- SE)(nephrectomy cases: 2.77 +/- 0.46). Characterization by reverse phase high performance liquid chromatography indicated that the only immunoreactive endothelin in human kidney inner medulla is endothelin-1, although immunoreactive endothelin in rat and pig kidney inner medulla comprises both isopeptides endothelin-1 and -3, suggesting that the genetic expression of endothelin differs according to species.

Endothelin-1 is an autocrine/paracrine growth factor for human cancer cell lines

We studied whether a novel vasoconstrictor peptide, endothelin-1 (ET-1), is synthesized by and released from human carcinoma cell lines, and whether ET-1 stimulates proliferation of these tumor cells. ET-1-like immunoreactivity was released from both HeLa and HEp-2 cells as a function of time. Reverse-phase HPLC of the conditioned media from HeLa cells revealed a major peak coeluting with standard ET-1. Northern blot analysis demonstrated the expression of mRNA for ET-1 precursor in both tumor cell lines. Both cell lines contained a single class of specific binding sites for ET-1. ET-1 dose-dependently induced increases in cytosolic free Ca2+ concentration in fura-2-loaded tumor cells, whose effect was completely abolished by chelating extracellular Ca2+ or by Ca(2+)-channel blocker. ET-1 stimulated proliferation of the quiescent cell lines in a dose-dependent manner, whose effect was inhibited by Ca(2+)-channel blocker. Polyclonal antibody for ET-1 inhibited proliferation of these cell lines, whereas nonimmune serum had no effect. These results demonstrate that ET-1 is synthesized by and released from human epithelial carcinoma cell lines, and that exogenous and endogenous ET-1 stimulates proliferation of the cells possibly through Ca2+ influx, suggesting its role as an autocrine/paracrine growth factor for certain tumor cells.

Presence of immunoreactive endothelin in synovial fluid: analysis of 22 cases

The endothelins are a family of recently defined active peptides with a wide range of activities, including the activation of the synthesis of prostaglandins. The concentration of endothelin in inflammatory and noninflammatory synovial fluids (SF) was measured by a sensitive radioimmunoassay. Endothelin-like immunoreactivity was detectable in all SF samples and the mean concentration of endothelin was 2.6 +/- 0.3 pg/ml, more than twice that in normal human plasma. The mean level of endothelin in SF in rheumatoid arthritis was 2.5 +/- 0.4 pg/ml (n = 11), and was not statistically different from either osteoarthritis, 3.0 +/- 0.5 pg/ml (n = 7), or acute inflammatory arthritis, 2.0 +/- 0.4 pg/ml (n = 4). Our data do not support the hypothesis that endothelin plays an important role in the pathogenesis of inflammatory arthritis.

Oxyhaemoglobin increases the production of endothelin-1 by endothelial cells in culture

Cultured endothelial cells from bovine thoracic aortas conditioned with serum-free culture media released an endothelin-1 (ET)-1-like substance. Concentrations of ET-1-like material were determined by bioassay as contractions of isolated ring segments of dog internal mammary vein and by radioimmunoassay. ET-1-like immunoreactivity (ET-1-IR) increased progressively over a 24 h conditioning period and correlated with the bioassay for the first 12 h. Oxyhaemoglobin (1-3 microM) caused a significant two-fold increase in the concentration of ET-1-IR in the medium at 6, 8 and 12 h incubation. Methaemoglobin also caused an approximate doubling of the amount of ET-1-IR at eight h of incubation. NG-Monomethyl-L-arginine (L-NMMA), a blocker of the production of endothelium-derived relaxing factor (EDRF), had no effect on the time-dependent increase in ET-1-IR in the conditioned medium. These results may have important implications for the mechanisms underlying vascular smooth muscle hyperreactivity such as cerebral spasm following subarachnoid haemorrhage.

125I-endothelin-1 and 125I-big endothelin-1 in rat tissues: autoradiographic localization and receptor binding

The potent vasoconstrictor peptide, endothelin-1 (ET-1), which exhibits a characteristically long-acting activity in vitro and in vivo, is thought to be generated in endothelial cells from a less active intermediate, big endothelin-1 (big ET-1). In addition to ET-1, big ET-1 is also present in the circulation. The autoradiographic localization of 125I-big ET-1 and 125I-ET-1 has been studied after intravenous administration in rat tissues. Highest enrichment of radioactivity was found in the kidney cortex for both peptides. Compared to blood levels, enrichment of radioactivity is also detected, in the vascular wall of the aorta. Comparing the radioactivity pattern of ET-1 and big ET-1, a nearly identical tissue distribution is observed, with the exception of the relative enrichment in the lung and the zona glomerulosa after administration of ET-1. Both radioligands show a specific and saturable binding to lung and kidney membranes. In the case of lung tissue, Ki values are 10(-10) M for endothelin-1 and 10(-8) M for big endothelin-1. This difference in affinities may account for the lack of binding of big endothelin-1 to lung tissue.

Endothelin-1 gene expression and regulation of endothelin mRNA and protein biosynthesis in avascular human amnion. Potential source of amniotic fluid endothelin

We demonstrated previously that preproendothelin mRNA is present in avascular human amnion tissue and in human amnion cells maintained in primary monolayer culture. In this investigation we sought to identify the specific endothelin (ET) gene that is expressed in amnion and to determine whether endothelin is produced by amnion. Using oligonucleotides specific for ET-1, ET-2, and ET-3 mRNA, we identified preproET-1 mRNA in human amnion tissue. By radioimmunoassay of ET we found that human amnion tissue explants and amnion cells in culture secrete immunoreactive ET into the medium. PreproET mRNA levels and immunoreactive ET production by human amnion cells in monolayer culture are increased in response to treatment with agents that are known to be present in human amniotic fluid, i.e. epidermal growth factor, interleukin-1, and tumor necrosis factor-alpha. We found that the level of preproET mRNA in amnion cells was low compared with that in human umbilical endothelial cells; treatment with cycloheximide together with a stimulus of ET-1 gene transcription led to a striking increase in the level of preproET mRNA in amnion cells compared with a much weaker response in endothelial cells. These findings suggest that protein synthesis-dependent mechanisms may be of great importance in maintaining low levels of preproET mRNA in amnion tissue and in regulating the amount of preproET mRNA in amnion exposed to stimuli of ET-1 transcription. In addition, we demonstrated that immunoreactive ET is present in human amniotic fluid at the midtrimester of pregnancy and at term. Thus, it is likely that the avascular fetal amnion is one tissue site of origin of ET in amniotic fluid during human pregnancy.

Endothelin immunoreactivity of airway epithelium in asthmatic patients

There is extensive pharmacological and physiological evidence that endothelin-1 influences airway calibre. In mammals, endothelin receptor occur on airway smooth muscle, local storage and release of the peptide have been demonstrated, and inhalation of endothelin-1 induces bronchoconstriction. To investigate the relation between endothelins and asthma the expression of this peptide in endobronchial biopsy specimens was examined immunohistochemically with an antiserum against endothelin-1. Biopsy specimens from 17 asthmatic patients and 11 atopic and non-atopic healthy controls revealed striking differences, with endothelin expression being evident in airways epithelium and vascular endothelium in 11 of the 17 asthmatic patients but in only 1 of 11 controls. These results suggest that endothelins may play a part in the exaggerated bronchomotor tone of asthma.

[Presence of the regulatory peptide endothelin in the vascular endothelium of the human nasal mucosa]

Endothelin is a 21-amino acid peptide originally isolated from cultured endothelial cells. Besides being the most potent vasoconstrictor peptide. Endothelin is known to produce a wide range of biological effects: contraction of smooth airway muscle, stimulation of cell growth and modulation of hormone and neurotransmitter release. The aim of the present study was to use immunocytochemical techniques in investigating the possible occurrence of endothelin in normal human nasal mucosa. Endothelial cells of both capacitance and resistance blood vessels of the mucosa displayed endothelin-like immunoreactivity. It is reasonable to presume that endothelin, produced and released locally by endothelial cells, may play a role in controlling blood flow, in neuromodulation and in wound healing via a paracrine mechanism.

Endothelin in human brain and pituitary gland: presence of immunoreactive endothelin, endothelin messenger ribonucleic acid, and endothelin receptors

The presence of immunoreactive (IR) endothelin, endothelin mRNA, and endothelin receptors in human brain and pituitary gland has been studied by RIA, Northern blot hybridization, and receptor assay. IR endothelin was detected in all five brain regions examined (cerebral cortex, cerebellum, brain stem, basal ganglia, and hypothalamus) (6-10 fmol/g wet wt) and spinal cord (22 +/- 6 fmol/g wet wt, n = 7, mean +/- SEM). Higher concentrations of IR endothelin were found in the pituitary gland (147 +/- 30 fmol/g wet wt). Fast protein liquid chromatographic analysis of the IR endothelin in pituitary gland showed a large IR peak in the position of endothelin-3 and a smaller peak in the position of endothelin-1, whereas IR endothelin in the hypothalamus and brain stem was mainly endothelin-1. Endothelin messenger RNA was detected by Northern blot hybridization in the pituitary but not in hypothalamus. The receptor assay showed that 125I-endothelin-1 binding sites were present in large numbers in all five brain regions but were much less abundant in the pituitary gland. Binding capacity and dissociation constant were 5052 +/- 740 fmol/mg protein and 0.045 +/- 0.007 nM in brain stem and 963 +/- 181 fmol/mg protein and 0.034 +/- 0.009 nM in hypothalamus. In the pituitary gland, there were two classes of binding sites for endothelin with dissociation constants of 0.059 +/- 0.002 nM (binding capacity = 418 +/- 63 fmol/mg protein) and 0.652 +/- 0.103 nM (binding capacity = 1717 +/- 200 fmol/mg protein). Endothelin-1, -2 and -3 were almost equipotent in displacing the binding (IC50 approximately 0.04 nM). These findings are in accord with the possibility that endothelin acts as a neurotransmitter, neuromodulator or neurohormone in man.

Immunohistochemical localization of endothelin-1 in the nervous system of the earthworm Eisenia foetida

The distribution of a substance that resembles endothelin-1 (ET-1) was examined immunohistochemically in the nervous system of the earthworm, Eisenia foetida, using antiserum against ET-1. In the cerebral ganglion, ET-1-like immunoreactivity was demonstrated in two to three pairs of neurons located in the peripheral portion. These immunoreactive neurons projected axons toward the neuropile located in the central portion of the ganglion. Immunoreactive fibers were distributed in the neuropile and proceeded posteriorly to the subesophageal ganglion through the circumpharyngeal connective. In the subesophageal ganglion, no immunoreactive cell bodies were detected, although the immunoreactive fibers were found in the neuropile. In each segmental ganglion, two to eight immunoreactive neurons were observed on each side of the caudo-ventral portion and these neurons sent axons ipsilaterally to the fiber tracts. The pattern of distribution of the immunoreactive neurons in the segmental ganglion was almost identical from one segment to the next. No immunoreactivity was detected in the nerve tracts that emerge peripherally from the cerebral, subesophageal, and segmental ganglia or in other organs, such as the digestive tract and the integument. Specific immunoreactivity to antiserum raised against corticotropin-releasing factor (1-20) was not detected in the nervous system of Eisenia.

Demonstration and nature of endothelin-3-like immunoreactivity in somatostatin and choline acetyltransferase-immunoreactive nerve cells of the neostriatum of the rat

Using a rabbit endothelin-1 (ET-1) antiserum together with a goat-anticholineacetylase antiserum or a mouse anti-somatostatin antiserum it was possible by means of double immunolabelling procedures to demonstrate ET-like immunoreactivity in striatal nerve cell bodies of the rat, which were shown to contain either cholineacetylase or somatostatin immunoreactivity. Absorption studies with ET-3, ET-1 or big ET-1 indicated that the ET-like immunoreactivity was ET-3 like. In agreement the radioimmunoassay showed that ET-3-like immunoreactivity was present in higher concentrations than ET-1-like immunoreactivity in the neostriatum and other brain areas. Characterization by reversed phase HPLC revealed, however, that a major portion of the neostriatal ET-3-like immunoreactivity was not identical to ET-3. The nature of neuronal ET in the rat may thus be more complicated than hitherto assumed.

Immunolocalization, binding, and biological activity of endothelin in rabbit uterus: effect of ovarian steroids

Specific immunostaining for endothelin 1 (ET-1) was observed in the endometrium but not myometrium of rabbits. The staining was dramatically affected by subacute treatment with ovarian steroids: epithelial cells were predominantly positive in immature rabbits, whereas, in sex steroid-primed rabbits, ET-1 was mainly localized in the stromal compartment. Binding studies were performed in myometrium of estrogen-treated rabbits using labeled ET-1 and ET-3, the corresponding unlabeled peptides, and sarafotoxin b (SRTX). Mathematical modeling of experimental results indicates that two populations of sites are present in myometrium. One site (R1 = 1 pmol/mg protein) shows approximately the same affinity for ET-1, ET-3, and SRTX [dissociation constant (Kd) 100 pM], whereas the second site (R2 = 10 pmol/mg protein) selectively binds ET-1 (Kd 400 pM). According to binding studies, ET-1 was more potent than SRTX in stimulating uterine contraction "in vitro." The subacute administration of increasing concentrations of 17 beta-estradiol (0.2-200 micrograms/kg for 4 days), but not 17 beta-estradiol (200 micrograms/kg for 4 days) plus progesterone (5 mg/kg for 4 days), stimulates a dose-dependent increase in endothelin receptors in myometrium (half-maximal effective dose = 0.7 micrograms/kg for 4 days). However, estrogen treatment does not affect the concentration of endothelin receptors in myometrial cells in primary culture. Conversely, divalent ions like calcium and magnesium enhance the binding of ET-1 to both uterine membranes and cells. Our results indicate that in rabbit uterus endothelin is present in the endometrium, whereas specific receptors are located in myometrium.

Endothelin converting enzyme of bovine carotid artery smooth muscles

This is the first report clearly demonstrating the presence of endothelin (ET) converting enzyme in vascular smooth muscle. Like cultured endothelial cells, noncultured vascular smooth muscle homogenate of bovine carotid arteries, converts human big ET- 1 to ET-1 at pH 3.0, pH 5.0 and pH 7.0, and the apparent ratio of these three activities is about 6:5:1, respectively. Peptides generated during incubation of the homogenate and big ET- 1 at the three pHs were identified as ET- 1 by radioimmunoassay and high performance liquid chromatography. The two acid enzymes are in the cytosol (103,000xg sup) and are inhibited by pepstatin A, while the neutral enzyme is sensitive to EDTA or phosphoramidon; 73% of the neutral enzyme activity was membrane-bound and the remainder (27%) cytosolic.

Structural analysis of biologically active peptides and recombinant proteins and their modified counterparts by mass spectrometry

The structural characterization of the Escherichia coli-expressed human interferon alpha-2b (rh-IFN alpha-2b) was carried out by employing the fast atom bombardment (FAB) and plasma desorption (PD) mapping methods. The mass spectral data of the rh-IFN alpha-2b and the trypsin-generated peptide mixture allowed rapid and facile confirmation of the cDNA-derived sequence and determination of the existing disulfide pattern in the protein molecule. The same PD/FAB mapping approach was successfully employed in the structural determination of the iodination reaction product of rh-IFN alpha-2b and the potent vasoconstrictor peptide endothelin.

Detection of endothelin-like immunoreactivity in epithelium and fibroblasts of the human umbilical cord

We studied tissue sections of freshly obtained full-term and premature human umbilical cords using polyclonal antibody to endothelin and immunocytochemistry. Endothelin immunoreactivity was detected in the cytoplasm of epithelial cells and primitive fibroblasts, but not in the endothelial cells of both full-term and premature umbilical cords. Immunoelectron microscopy using indirect immunogold staining technique localized endothelin immunoreactivity to the cytoplasm of the epithelial cells and fibroblasts but not confined to any particular structures. No endothelin immunoreactivity was detected in the nucleus or on the cell membrane. Pre-absorption tests with synthetic endothelin-1, -2, and -3 independently established that the immunoreactivity represented endothelin-1 and -2, but not -3. The presence of endothelin-1 and -2-like immunoreactive materials in epithelial cells and fibroblasts of human umbilical cord suggests a role of endothelin in parturition.

Immunoreactive endothelin in pheochromocytomas

The presence of endothelin (ET) in tumor tissue and plasma of patients with pheochromocytoma was studied by radioimmunoassay. Immunoreactive (ir-) ET concentrations in 12 pheochromocytomas ranged from 66 to 253 fmol per gram wet tissue (gwt) (146 +/- 20 fmol/gwt, mean +/- SEM). These values were not significantly higher than tissue ir-ET concentrations of two primary aldosteronism (66 and 132 fmol/gwt) and three normal adrenal glands (71-120 fmol/gwt) (0.05 less than p less than 0.1). However, tumor tissue ir-ET concentrations in six of the 12 pheochromocytomas were higher than 132 fmol/gwt (the upper value of the control tissues). Sephadex G-50 column chromatography and reverse-phase high-performance liquid chromatography of pheochromocytoma tumor extracts showed a major peak eluting at an identical position to synthetic ET-1. Plasma ir-ET concentrations of pheochromocytomas (1.4 +/- 0.9 fmol/ml, n = 17) were not significantly different from those of patients with essential hypertension (1.0 +/- 0.7 fmol/ml, n = 20) and normal subjects (1.0 +/- 0.4 fmol/ml, n = 18) (0.05 less than p less than 0.1). This study has shown that high concentrations of ET-1 are present in tumor tissues of 50% of pheochromocytomas.

Sandwich-enzyme immunoassays for endothelin family peptides

Sandwich-enzyme immunoassays (sandwich-EIAs) for endothelin-1 (ET-1), endothelin-3 (ET-3), big ET-1, big endothelin-2 (big ET-2), and big endothelin-3 (big ET-3) have been established using two antibodies directed against the N-terminal and C-terminal portions of each ET and big ET. These sandwich-EIAs are sensitive enough to detect 0.1-0.4 pg/well of each ET or big ET with cross-reactivity of less than 1% with other ETs and big ETs (except in the case of the EIA for ET-1, which detects immunoreactivity of ET-2 as well as ET-1). Plasma levels of immunoreactive (ir-) ET-1, big ET-1, and ET-3 in normal humans were approximately 2.0, 5.1, and 0.9 pg/ml, respectively, when corrected for recovery efficiency. In reverse-phase high-performance liquid chromatography (HPLC) analysis, immunoreactivities detected by these sandwich-EIAs were eluted at the positions of authentic ET-1, big ET-1, and ET-3, indicating that plasma levels of ET-1, big ET-1, and ET-3 were precisely measured by our methods. Levels of ir-big ET-2 and ir-big ET-3 were also detected in normal human plasma; however, further studies are needed to determine their precise values. The establishment of reliable sandwich-EIAs and the measurement of specific ETs and big ETs in normal human plasma will contribute to clarifying the biological and clinical significance of ET family peptides.

Structure of the precursor for vasoactive intestinal contractor (VIC): its comparison with those of endothelin-1 and endothelin-3

Vasoactive intestinal contractor (VIC) is a member of the endothelin (ET) peptide family, which evokes a strong contractile response in the ileum, its gene being expressed only in the intestine. Using dot blot analysis, we carried out an interspecies comparison of the nucleotide and deduced amino acid sequences of the precursor for VIC with those of ET-1 and ET-3 to investigate the physiological significance of processing of the precursor for VIC. The highly conserved amino acid sequence was observed between the big form region (big VIC, big ET-1, and big ET-3) of about 40 amino acids and the like peptide region (VIC-like peptide, ET-1-like peptide, and ET-3-like peptide) of 15 amino acids downstream from the big form region. Sequence identity of amino acids of the precursors of ET-1 and ET-3 with that of VIC was 29 and 28%, respectively. Thus, the precursors for the three peptides might have arisen from a common progenitor gene. However, apparent cleavage sites of the like peptide regions are rather unique in the VIC-like peptide, i.e., it had dibasic amino acids at the amino and carboxy termini. Therefore, we suggest that the VIC-like peptide might be liberated from its precursor protein and play some role in the intestine in vivo.

Immunoreactive endothelin in human plasma, urine, milk, and saliva

Using a highly sensitive radioimmunoassay, elevated plasma immunoreactive endothelin (ir-ET) levels were found in patients with diabetes mellitus (1.88 +/- 0.12 pmol/L, mean +/- SEM, n = 100), patients undergoing maintenance hemodialysis (4.28 +/- 0.76 pmol/L, n = 14), patients with acute myocardial infarction (3.43 +/- 1.03 pmol/L, n = 6), and patients with subarachnoid hemorrhage (4.92 +/- 0.64 pmol/L, n = 14) (normal controls: 0.54 +/- 0.05 pmol/L, n = 19). ir-ET was also present in urine (2.1 +/- 0.3 pmol/L, n = 12), breast milk (6.8 +/- 1.6 pmol/L, n = 16), and saliva (2.0 +/- 0.2 pmol/L, n = 15) obtained from healthy subjects. Chromatography studies verify the identity of endothelin. Fast protein liquid chromatography (FPLC) showed one peak in the normal plasma extract, three peaks in the plasma extracts from diabetic patients and patients undergoing maintenance hemodialysis, three peaks in the urine extract, four peaks in the milk extract, and five peaks in the saliva extract. When the materials eluting in the void volume on FPLC of urine and saliva extracts were loaded onto a Sephadex G-25 column, the ir-ET was eluted in a higher molecular weight region. Incubation of endothelin-1, endothelin-2, and endothelin-3 in urine for 5 h showed that the total amount of ir-ET decreased to less than 30% of the initial levels, suggesting that endothelins are very unstable in urine.

Development and application of three radioimmunoassays of endothelin of varying specificities

We have developed three radioimmunoassays (RIAs) of varying specificities toward the endothelin (ET) isoforms. The assays are called the endothelin-1,2[125I] assay system (RPA535), the endothelin 1-21 Specific [125I] assay system (RPA555), and the endothelin-1,2 high-sensitivity [125I] assay system (RPA545). We have fully characterized their cross-reactivities: RPA535-ED50 approximately 12 fmol/tube, ET-1 100%, ET-2 204%, ET-3 0.0024%, hBig ET 37.9%, pBig ET 32.9%; RPA545-ED50 approximately 4.8 fmol/tube, ET-1 100%, ET-2 1,300%, ET-3 less than 0.001%, hBig ET 189%, pBig ET 63%; RPA555-ED50 approximately 3.6 fmol/tube, ET-1 100%, ET-2 144%, ET-3 52%, hBig ET 0.4%, pBig ET 0.26%. These assays have also been applied to the measurement of ET immunoreactivity (ir) in normal human plasma following Amprep extraction. Further validation of the use of these assays has included the measurement of endothelin-1 (ET-1) derived from big ET by in vitro enzymatic conversion by cathepsin E, which has demonstrated that cathepsin E possesses the appropriate specificity of cleavage to be considered the endothelin-converting enzyme (ECE).

Structure-activity studies of the C-terminal region of the endothelins and the sarafotoxins

Peptides corresponding to the C-terminal 16-21 hexapeptide of the endothelins (-His-Leu-Asp-Ile-Ile-Trp) and sarafotoxins (a-c) (-His-Gln-Asp-Val-Ile-Trp) were prepared to study the role of the individual amino acids in receptor recognition and activation. Receptor binding in rabbit aorta, rabbit pulmonary artery, and rat heart ventricle is reported for all analogues. In addition, selected C-terminal hexapeptides have been evaluated functionally in two tissues (rabbit pulmonary artery and rat left atria). The C-terminal carboxylate, indole nitrogen, and nature of the aromatic residue are all important for receptor binding, but N-terminal acetylation has no effect. L-Amino acids are required in positions 19 and 21, whereas D-amino acids are tolerated in 17 and 18. D-Amino acids in positions 16 and 20 enhance the binding affinity of the hexapeptide in all three tissues. The nature of the basic residue at position 16 is important. Glu and Asn are acceptable substitutions for Asp18, although Ala leads to a substantial loss in binding. The binding of the C-terminal hexapeptide of SRTX-a, -b, and -c is less than ET[16-21] and this appears to be primarily due to the substitution of Gln for Leu17. None of the 16-21 hexapeptides showed any functional activity in the tissues studied.

Big endothelin in plasma and amniotic fluid

We previously demonstrated that endothelin-1 (ET-1) exists both in the peripheral circulation and the amniotic fluid (AF). The objects of the present study were (a) to measure the concentrations of ET-1 and big endothelin (big ET) in plasma and AF by radioimmunoassay (RIA) and (b) to characterize the molecular forms of endothelin in human AF by high-performance liquid chromatography (HPLC) coupled with RIAs. Plasma samples from healthy male and female volunteers, and AF samples from full-term and mid-trimester pregnant women were extracted by C18 cartridges. Big ET, like ET-1, exists both in plasma and in AF. Significant increases (p less than 0.01) of big ET and ET-1 in AF from mid-trimester to full-term pregnancy were observed. The reverse-phase HPLC elution profile of immunoreactive (ir-) ET-1 presented a single major peak at a position corresponding to that of the standard ET-1 in the extracted AF. Two major components of ir-big ET were revealed: one corresponded to the elution position of standard big ET; the other one to that of the standard endothelin fragment [22-38] (EF).

IN CONCLUSION

(a) Three molecular forms of ET exist in AF: ET-1 as a major form, big ET, and EF. (b) ET-1 and big ET are both present in higher concentrations in AF at full-term pregnancy than during mid-trimester.

Topographical localisation of endothelin mRNA and peptide immunoreactivity in neurones of the human brain

The distribution of endothelin mRNA and immunoreactivity in the human brain was investigated using the technique of in situ hybridization and immunocytochemistry. Cryostat sections from 22 cases of neurologically normal adult human brain, collected 3-7 h post-mortem were hybridized with 35S-labelled complementary (c)RNA probes prepared from the 3' non-coding region of endothelin-1 cDNA, and the chromosomal genes encoding endothelin-2 and -3. In situ hybridization with all three cRNA probes revealed labelled neuronal cell bodies in laminae III-VI of the parietal, temporal and frontal cortices. Labelled cells were also seen, scattered throughout the para- and periventricular, supraoptic and lateral hypothalamic nuclei, the caudate nucleus, amygdala, hippocampus, basal nucleus of Meynert, substantia nigra, raphe nuclei, Purkinje cell layer of the cerebellum and in the dorsal motor nuclei of the vagus of the medulla oblongata. The distribution of neurones immunoreactive to endothelin was similar to that of endothelin mRNA, although fewer immunoreactive cells throughout the brain, were noted. Immunoreactive fibres were present mainly in the cortex and hypothalamus, and to a lesser extent in the brain stem. Combined in situ hybridization and immunocytochemistry on the same section revealed the presence of endothelin-1 mRNA and immunoreactivity in the same cortical neuronal cell. Colocalisation studies in the cortex revealed endothelin-1 mRNA and immunoreactivity in a number of cells which also expressed neuropeptide Y mRNA and immunoreactivity. In the hypothalamus and basal nucleus of Meynert endothelin immunoreactivity was colocalised to a subset of neurophysin- and galanin-immunoreactive cell bodies respectively. Endothelin mRNA and immunoreactivity was also seen in some blood vessel endothelial cells. The findings of endothelin mRNAs and immunoreactivity in heterogenous neuronal populations further emphasises the potential role of endothelin as a neuropeptide, probably having diverse actions in the nervous system of man.

Isolation and characterization of porcine endothelin-like peptide

Two endogenous molecules possessing an endothelin-like sequence with an apparent molecular weight of 7 kDa were isolated from serum-free culture medium of porcine aortic endothelial cells, using a specific radioimmunoassay. N-terminal sequences of two molecules were identical to each other and were Ser-Leu-Lys-Asp-Leu-Phe-Pro-Ala-Lys-Ala-Ala-Asp-Arg-Arg-Asp-Arg-X-Gln-X- Ala-X- Gln-Lys-Asp, which corresponds to the sequence [94-117] of preproendothelin-1. This finding indicates that these two molecules may be closely related peptides such as the oxidized form or disulfide analogues and also suggests that the endogenous peptide possessing an endothelin-like sequence is generated by proteolytic cleavage at paired basic amino acids Arg92-Arg93. Further studies on the structure and function of new endogenous peptides possessing an endothelin-like sequence are ongoing in our laboratory.

Immunoreactive endothelin-1 contents in brain regions from spontaneously hypertensive rats

To investigate the possible role of brain endothelin-1 (ET-1) in hypertension of spontaneously hypertensive rats (SHRs), we measured immunoreactive (ir) ET-1 contents in brain regions as well as plasma ir-ET-1 levels in SHRs aged 4-5 and 12-14 weeks and age-matched Wistar-Kyoto rats (WKY) with a radioimmunoassay for ET-1. Systolic blood pressures of SHR aged 4-5 and 12-14 weeks were significantly higher than those of corresponding WKY. Significant amounts of ir-ET-1 were detectable throughout the discrete brain regions analyzed in both strains; higher ir-ET-1 contents in structures such as thalamus, hypothalamus, midbrain, pons, medulla, and cerebellum, with the lowest in cerebral cortex, were observed. A reverse-phase high-performance liquid chromatography of the brain extracts revealed the presence of both a major component identical to the elution position of synthetic ET-1 and a minor component possibly corresponding to its oxidized form. When compared, ir-ET-1 contents in all brain regions analyzed were lower in SHRs than in WKY rats. This strain-related change of ir-ET-1 contents was significant in the medulla at 4-5 weeks of age, and in all brain regions except hypothalamus at 12-14 weeks of age. Plasma ir-ET-1 levels, in contrast, were comparable between SHRs and WKY rats. These results suggest that brain ET-1 may be involved in the development and the maintenance of hypertension in SHRs.

Concentrations of endothelin-1 in human amniotic fluid at various stages of pregnancy

To examine the possible role of endothelin in the initiation of parturition, endothelin-1-like immunoreactivity (ET-1-LI) in the amniotic fluid (AF) was determined by a sensitive radioimmunoassay (RIA) system. The concentrations of ET-1-LI in AF were 24.7 +/- 6.1 pg/ml (mean +/- SD, n = 6) at the second trimester and were significantly increased to 40.4 +/- 15.1 pg/ml (n = 6) at term. These ET-1-LI concentrations are about three- to fourfold higher than those observed in the maternal plasma. The gel permeation chromatography (GPC) profile of ET-1-LI extracted from second-trimester AF indicated that the ET-1-LI consisted of only one component of 6kET, the molecular weight of which was 6,000, larger than big ET-1. In contrast, ET-1-LI in the AF at term consisted of two components, ET-1 and 6kET. These findings suggest that the level of biologically active ET-1 in the AF increases markedly from second trimester toward term. A significant amount of ET-1-LI was also detected in the supernatant of amnion cell culture. The level of ET-1-LI in the culture medium after 12 h of incubation was almost comparable with that in AF at term. Thus, it is suggested that amnion tissue may be the major source of ET-1-LI in the AF. Together with the fact that ET-1 increases cytoplasmic calcium ion in the target cell, the results of present study raise the possibility that endothelin plays an important role in the initiation of parturition by triggering the production of prostaglandins in fetal membranes.

Endothelin-like immunoreactivity in the nervous system of invertebrates and fish

There have been no reports on the distribution of immunoreactive endothelin (ir-ET) in lower vertebrates and invertebrates, except for our previous studies on the nereid Neanthes diversicolor and the earthworm Eisenia foetida. In the present study, we found ET-like immunoreactivity in five species of invertebrates and two species of fish with antiserum against synthetic endothelin-1 (ET-1). Immunoreactive perikarya and nerve fibers were observed in the central nervous system of the slug Limax marginatus, the freshwater snail Indoplanorbis exustus, and the mussel Mytilus edulis in mollusks, the field cricket Gryllus bimaculatus in insects, and the tube tunicate Ciona intestinalis in protochordates. In the medaka, Oryzias latipes, ir-ET was found in the hypothalamoneurohypophysial system, the caudal neurosecretory system, the gill, and the kidney. Immunoreactive cells were also found in the mucous gland of the slug and in the adenohypophysis of the lamprey, Lampetra japonica. The wide distribution of ET-like substances in invertebrates and fish provides evidence for the case that ET found in mammals has a long evolutionary history.

Endothelin-like immunoreactivity in human breast cyst fluid

Immunoreactive endothelin has been detected in 21 of 43 samples of breast cyst fluid (21 cases; 3.5 +/- 0.6 pmol/l, mean +/- SEM. Other 22 cases; not detectable, less than 0.5 pmol/l). Fast protein liquid chromatographic analysis of the immunoreactive endothelin of pooled breast cyst fluid showed two immunoreactive peaks; one in the void volume and the other in the position of endothelin-1. It is probable that endothelin-1 is produced by the epithelial cells lining breast cysts, but significance of the presence of endothelin-1 in breast cyst fluid remains to be elucidated.

Endothelins, peptides with potent vasoactive properties, are produced by human macrophages

Endothelins are peptides, originally isolated from endothelial cells, with potent vasoactive and mitogenic properties. In this study, we demonstrate that human macrophages synthesize and secrete endothelins. Cultured human macrophages were found by immunocytochemistry to stain positively for endothelin 1 and endothelin 3. Their capability to produce and release these peptides was confirmed by a combination of reverse-phase high-performance liquid chromatography and radioimmunoassays, specific for endothelin 1 and 3, respectively. Immunoreactive peptides were identified both in cellular extracts and in macrophage-conditioned medium. The secretion of endothelin 1, but not of endothelin 3, from macrophages could be stimulated 6-10-fold by lipopolysaccharide or phorbol myristate acetate (PMA). Northern blot analysis of total macrophage RNA using an endothelin 1 cDNA probe revealed induction of endothelin mRNA in PMA-treated macrophages. Furthermore, immunoreactive endothelin 1 and 3 were found in U937 cells, a human promonocytic line, and in freshly isolated human monocytes. In contrast, no immunoreactive endothelin was detected in cell extracts from human neutrophils and lymphocytes. The expression of endothelins in tissue macrophages was demonstrated in paraffin sections of human lung using immunohistochemistry. In conclusion, the finding that human macrophages produce endothelins suggests an important role for these peptides in the microenvironment of tissue macrophages. Macrophage-derived endothelins may have an essential function in blood vessel physiology, and aberrant production may contribute to vessel pathology.

Detection of endothelin immunoreactivity and mRNA in pulmonary tumours

Paraffin sections of 66 surgically resected lung tumours were immunostained with antisera to human endothelin-1 and to the C-terminal peptide of big endothelin. With both antisera, strong immunoreactivity was demonstrated in 11 of 15 squamous cell carcinomas and 11 of 16 adenocarcinomas. Focal immunoreactivity was seen in small cell carcinoma (2/12), large cell carcinoma (2/5), and carcinoid tumours (2/11). Four lymphomas and three sarcomas did not show endothelin immunoreactivity. Cryostat sections of 22 of the 66 tumours were hybridized with radiolabelled complementary RNA probes prepared from the 3' non-coding region of endothelin-1 cDNA, and the chromosomal genes encoding endothelin-2 and -3. In situ hybridization demonstrated the presence of endothelin mRNAs in 4 of 7 squamous cell carcinomas and in 5 of 8 adenocarcinomas, in a pattern similar to that shown by immunocytochemistry. No hybridization signals were obtained from the other types of tumours. In lung tissue adjacent to the tumours, endothelin-like immunoreactivity and mRNA were detected in pulmonary endocrine cells and, in some cases, other epithelial cells, and in alveolar capillary endothelial cells. This study demonstrates the expression of endothelin in a number of pulmonary tumours and suggests a possible role for this peptide in the growth and/or differentiation of these tumours.

[Validation of radioimmunoassay of tissue and plasma endothelin-1]

We have established a sensitive and specific radioimmunoassay for measurement of ET-1 in tissues and human plasma. Half maximal inhibition of binding of ET-1125 I was obtained at 6.6 pg/tube and the lowest concentration detectable was 0.785 pg/tube (p less than 0.001). Inter and intra-assay precisions were 14 and 9.6%, respectively. The antibody cross-reacted with ET-2 at 36.5%, ET-3 at 23.4% and Big ET at 9.9% but did not recognize non related vasoactive peptides. Immunoreactive ET-1 was extracted from human and rat tissues (lung, kidney) or human plasma using Sepak C18 columns. Human lung contains 2.3 ng/g ir-ET, corresponding mainly to synthetic ET-1 as revealed by reverse phase HPLC coupled to RIA. Rat lung and kidney ir-ET concentrations were 2.4 ng/g and 0.45 ng/g, respectively. Preliminary results indicated that the basal level of ir-ET in human plasma was 1.24 pg/ml. The RIA could be very useful to study the role of ET in various physiopathological states.

Maternal and fetal levels of a novel polypeptide, endothelin: evidence for release during pregnancy and delivery

The occurrence of endothelin (ET), a recently discovered polypeptide with potent vasoconstrictor properties, was studied in maternal and umbilical blood and amniotic fluid. The level of ET-like immunoreactivity (ET-LI) in maternal plasma was in most cases below the detection limit of the radioimunoassay, i.e. less than 2 pmol/l. The median concentration of ET-LI in the umbilical artery and vein before the initiation of breathing was 14.9 and 10.9 pmol/l, respectively. When sampling was performed after fetal breathing had begun, the arterial concentration increased to 93.7 pmol/l. Labor was not associated with increased concentrations of ET-LI, however, since neonates delivered by elective cesarean section had similar ET-LI in blood and amniotic fluid as after vaginal delivery. An approximately fivefold increase in the amniotic fluid ET-LI was seen at term as compared to early mid-trimester values. Reversed phase HPLC characterization revealed that the observed ET-LI mainly corresponded to ET-1. It is suggested that ET-1 may contribute to the fetal hemodynamic changes, e.g., closure of the umbilical vessels occurring at delivery.