Endothelin in human plasma and culture medium of aortic endothelial cells--detection and characterization with radioimmunoassay using monoclonal antibody

Endothelin-1 levels in plasma and cerebrospinal fluidfollowing subarachnoid haemorrhage

A serial measurement of endothelin-1(ET-1) levels in plasma, cisternal and ventricular cerebrospinal fluid(CSF) was performed in 16 patients with subarachnoid haemorrhage (SAH). The patients were classified as grade III or IV according to the clinical grade of Hunt and Hess, and computerised tomography(CT) was classified as Fisher's CT group 3. Cisternal and ventricular CSF and plasma were obtained from the patients on the day of operation days 0-3, days 5-8 and days 14-18 after SAH. ET-I concentration in each sample was quantified by sandwich-enzyme immunoassay. ET-I levels in plasma and CSF were the highest between days 0-3 and then decreased. The ET-I levels in the cisternal CSF were significantly higher during days 0-3(p<0. 01) and days 5-8(p<0. 01) than those in the ventricular CSF It is suggested that ET-I could play an important role in the early stages of the cerebral vasospasm.

Endothelin-1 as a target for therapeutic intervention in prostate cancer

The endothelins, a family of potent vasoconstricting peptides, have been implicated in the pathophysiology of advanced prostate cancer. Two endothelin receptors, ET-A and ET-B are found in normal prostate tissue. Malignant prostate cells are notable for the loss of ET-B receptors and increased levels of endothelin-1 [ET-1]; this distortion of the endothelin system may be a significant factor in the progression of prostate cancer. Proposed roles for endothelin in prostate cancer include growth promotion, apoptosis inhibition, bone formation, and stimulation of nociceptive receptors. ET-1 can act alone as a mitogen, but its effects are greatest as a comitogen with a variety of growth factors, including basic fibroblast growth factor, insulin-like growth factors, and platelet derived growth factor. Although their exact functions are unclear, ET-1, in conjunction with vascular endothelial growth factor, appears to play a major role in tumor angiogenesis. By a variety of methods, ET-1 alters the balance of osteoblast and osteoclasts to the favor new bone formation that is characteristic of metastatic disease. Several studies indicate that the refractory pain of metastatic cancer is related to the direct nociceptive effects ET-1. These findings suggest that ET receptors are promising therapeutic targets for pharmacologic intervention. Early clinical trials indicate that the ET-A receptor antagonist used in prostate cancer is reasonably well tolerated with mild but pervasive symptoms related to ET-1's vasoconstrictive effects. Results of ongoing clinical trials are eagerly awaited in order to see if the hypothetical promise of ET antagonism will result in clinical success.

Coordinate regulation of endothelin and adrenomedullin secretion by oxidative stress in endothelial cells

To elucidate the significance of oxidative stress in the modulation of endothelial functions, we examined the effects of H(2)O(2) on the expression of two endothelium-derived vasoactive peptides, endothelin (ET) and adrenomedullin (Am), and their interaction. H(2)O(2) dose dependently suppressed ET secretion and ET-1 mRNA expression in bovine carotid endothelial cells (ECs). Menadion sodium bisulfate, a redox cycling drug, also decreased ET secretion in a dose-dependent manner. Catalase, a H(2)O(2) reductase, and dl-alpha-tocopherol (vitamin E) significantly inhibited H(2)O(2)-induced suppression of ET secretion. Downregulation of ET-1 mRNA under oxidative stress was regulated at the transcriptional level. In contrast, H(2)O(2) increased Am secretion (and its mRNA expression) accompanied by the augmentation of cAMP production. Am, as well as 8-bromo-cAMP and forskolin decreased ET secretion in a dose-dependent fashion. Furthermore, an anti-Am monoclonal antibody that we developed abolished H(2)O(2)-induced suppression of ET secretion at 6-24 h after the addition of H(2)O(2). H(2)O(2) increased the intracellular Ca(2+) concentration ([Ca(2+)](i)). Moreover, treatment with ionomycin, a Ca(2+) ionophore, and thapsigargin, an inhibitor of endoplasmic reticulum ATPase, decreased ET secretion dose dependently for 3 h. These results suggest that the production of ET was decreased via activation of the Am-cAMP pathway and by the elevation of [Ca(2+)](i) under oxidative stress. These findings elucidate the coordinate expression of two local vascular hormones, ET and Am, under oxidative stress, which may protect against vascular diseases.

Endothelins: vasoactive modulators of renal function in health and disease

Vasoactive autocoids with directly opposing actions on the renal vasculature, glomerular function, and in salt and water homeostasis have been demonstrated in the kidney. In the renal cortex, endothelin (ET)-1 and angiotensin-II cause vasoconstriction, decreasing renal blood flow, and glomerular filtration rate, whereas bradykinin and atrial natriuretic peptide cause vasodilation and increase glomerular capillary permeability. ET-1 causes vasoconstriction of the afferent and efferent arteries and outer medullary descending vasa recta, thereby decreasing vasa recta and papillary blood flow, while bradykinin has the opposite effect. ET-1 stimulates cell proliferation, increasing the expression of several genes, including collagenase, prostaglandin endoperoxidase synthase, and platelet-derived growth factor. ET-1 promotes natriuresis via the ET-B receptor, causing down-regulation of the epithelial Na(+) channel in the renal tubule. Thus, ETs affect three major aspects of renal physiology: vascular and mesangial tone, Na(+) and water excretion, and cell proliferation and matrix formation.

Regulation of endothelin-1 production in cultured rat vascular smooth muscle cells

Endothelin-1 (ET-1) is secreted from all rat vascular smooth muscle cells (VSMCs) examined, in addition to endothelial cells (ECs). An average secretion rate of ET-1 from rat VSMCs was determined to be 10% that excreted from ECs. We examined the effects of 22 substances on ET-1 secretion from VSMCs and compared them with those from ECs. Transforming growth factor-beta1 (TGF-beta), acidic and basic fibroblast growth factors, epidermal growth factor, angiotensin II, and adrenaline stimulated ET-1 secretion from VSMCs, whereas forskolin, thrombin, and platelet-derived growth factor-BB reduced it. Only TGF-beta and phorbol ester elicited consistent effects on ET-1 secretion from VSMCs and ECs. Regulation of ET-1 and adrenomedullin secretion from VSMCs was distinctly different. These data suggest that ET- 1 production in VSMCs is regulated by a mechanism separate from that in ECs and from adrenomedullin production in VSMCs. Chromatographic analysis showed immunoreactive ET-1 secreted from VSMCs was mainly composed of big ET- 1, whereas approximately 90% of that from ECs was ET-1. By TGF-beta stimulation of VSMCs, the ratio of big ET-1 to ET-1 was further increased. Because big ET-1 is converted into ET-1 only on the surface of the ECs in the culture system, big ET-1 secreted from the VSMCs may function as a mediator transmitting a signal from VSMCs to ECs in vivo.

Effects of low doses of endothelin-1 on basal vascular tone and autoregulatory vasodilation in canine coronary microcirculation in vivo

The plasma level of endothelin-1 (ET-1) increases in several cardiovascular disorders. The present study examined whether threshold doses of ET-1 affect vascular tone and autoregulatory vasodilation during a reduction in perfusion pressure in the coronary microcirculation in vivo. In anesthetized open-chest dogs, arterial microvessels in the epimyocardium were observed through a microscope equipped with a floating objective. In 6 dogs, ET-1 (10(-13) to 10(-8)mol/L) was superfused onto the epimyocardium in a cumulative fashion. In another set of dogs (n= 16), the perfusion pressure of the observed vascular bed was reduced to 60 mmHg (mild stenosis) and to 40 mmHg (severe stenosis) by a hydraulic occluder, and the microvascular responses were observed in the presence (n=9) or absence (n=7) of ET-1 (10(-12) or 10(-11) mol/L). ET-1 > or =10(-11) mol/L constricted coronary arterioles (< or =100 microm in diameter) and small arteries (>100 microm in diameter) in a dose-dependent fashion. ET-1 of 10(-12) mol/L affected neither the basal diameters nor the dilation of vessels during the pressure reduction. ET-1 of 10(-11) mol/L decreased the diameters of arterioles and small arteries before and during the mild and severe stenosis. However, ET-1 did not attenuate the percentage dilation of arterioles from the baseline in response to the mild and severe stenosis. The data indicates the following: (1) ET-1 at doses > or =10(-11) mol/L similarly constricts coronary arterioles and small arteries; (2) ET-1 at 10(-11) mol/L, which is slightly higher than the pathophysiological plasma level, increases the basal vascular tone, but does not attenuate the autoregulatory vasodilation of the coronary microcirculation.

The processing pathway of endothelin-1 production

Production of endothelin (ET-1) is believed to be a three-step process, consisting of an initial proteolytic cleavage by signal peptidase of preproET-1, a second cleavage of proET-1 to big ET-1-Lys-Arg by dibasic amino acid-specific convertase and C-terminal trimming, and finally the processing of Big ET-1 to ET-1 by endothelin-converting enzyme (ECE). To clarify the relationships between the second processing step and the third, we introduced point mutation into ET-1 cDNA to replace the Arg in the -4 position of the recognition motifs of furin-like convertase in human preproET-1 (Arg49 or Arg89) by Gly. When mutant cDNAs were expressed in CHO-K1 cells, they failed to be processed at the mutated processing signal, suggesting the involvement of the enzyme with furin-like specificity in the processing at dibasic amino acid motifs. Co-transfection of mutant preproET-1 cDNA and ECE-1 cDNA revealed that cleavage at Arg92 is essential for cleavage by ECE-1 but that cleavage at Arg52 is not. Although without cleavage at Arg52 a high molecular weight form of ET-1, designated Large ET-1, is produced by processing by ECE-1, it did not evoke a Ca2+ transient in ETA receptor-expressing cells. In conclusion, the cleavage by furin-like convertase is essential for the production of active ET-1.

Endothelin-1 production and agonist activities in cultured prostate-derived cells: implications for regulation of endothelin bioactivity and bioavailability in prostatic hyperplasia

BACKGROUND

Endothelin-1 (ET-1) interacts with specific G-protein-coupled receptors to initiate short-term (contraction) and long-term (mitogenesis) events in target cells. ET-1 is an abundant prostate secretory protein that, in its biologically active form, elicits prostatic smooth muscle contraction. The present study was designed to determine the effects of ET-1 on prostate cell growth and to examine the regulation of endogenous ET-1 activity and bioavailability.

METHODS

Primary cultures of prostate secretory epithelial (PE) and prostate fibromuscular stromal (PS) cells were established from benign human prostate tissue.

RESULTS

In culture, PE cells secrete immunoreactive ET-1 (38.5 +/- 1.6 pg/ml/10(6) cells/24 hr) into the conditioned medium. Levels of immunoreactive ET-1 produced by PS cells were more than 10-fold lower. Endothelin-converting enzyme-1 (ECE-1) mRNA was detected in PE cells and not in PS cells; however, big ET-1 was the predominant immunoreactive ET-1 secretory product of PE cells. The ET(B) endothelin receptor was the predominant subtype in both PE and PS cells. In PS cells, but not PE cells, ET-1 induced significant inositol phosphate accumulation and [3H]-thymidine uptake. Agonist activity was inhibited by the ET(B) receptor selective antagonist, BQ 788. Intact PE cell monolayers secrete ET-1 through the apical surface, consistent with secretion of ET-1 into the glandular lumen in vivo.

CONCLUSIONS

On the basis of these findings, regulation of ET-1 activity and bioavailability appears to be tightly regulated. Such findings have important implications in the pathophysiology of prostate disease.

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

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

Endothelin-1 and its receptor in hypertrophic cardiomyopathy

Endothelin-1, a potent vasoconstrictor produced by vascular endothelial cells, activates the hypertrophic program in cultured heart muscle cells. However, the role of endothelin-1 in cardiac hypertrophy in humans is unknown. Therefore, we studied hypertrophic cardiomyopathy patients with normal pulmonary arterial pressure, in whom cardiac hypertrophy is a specific feature of the disease. Radioimmunoassay with a monoclonal antibody to human endothelin-1 showed that the plasma level of immunoreactive endothelin was more than twofold higher in hypertrophic cardiomyopathy patients than in control subjects (P < .005). In situ hybridization analysis of endomyocardial biopsy specimens showed positive signals of endothelin-1 type A receptor mRNA in ventricular myocytes of all specimens. The receptor expression in ventricular myocytes was similar between hypertrophic cardiomyopathy patients and control subjects. We propose that endothelin-1 might represent an important factor involved in hypertrophic cardiomyopathy. Whether endothelin-1 plays a causal role in cardiac hypertrophy or is a marker of its occurrence needs to be clarified.

Endothelin-1-like immunoreactivity and endothelin receptors in the human placenta from normotensive and hypertensive pregnancies

The levels of endothelin-1-like immunoreactivity (ET-1-LI) and characteristics of endothelin receptors in the chorionic villous tissue of human placenta were determined. The ET-1-LI level in chorionic villous tissue obtained from normal term placenta was 2,450 +/- 940 pg/g wet weight (mean +/- SD, n = 4). Further analysis using gel permeation chromatography and reverse-phase high performance liquid chromatography showed that the main ET-1-LI constituent of ET-1-LI in this tissue was ET-1. Scatchard analysis of [125I]ET-1 binding to the membrane fraction of chorionic villous tissue obtained from term placenta showed high affinity receptor sites with an apparent dissociation constant (Kd) of 23.6 +/- 11.1 pM and a Bmax value of 388 +/- 238 fmol/mg protein (n = 5). The same binding study with [125I]ET 3 showed a Kd of 13.9 +/- 3.8 pM and a Bmax value of 176 +/- 78 fmol/mg protein (n = 5). These results suggest that both ET-A and ET-B receptors (ET-AR and ET-BR) are expressed in chorionic villous tissue. This finding was further confirmed by Northern blot analysis showing the expression of both ET-AR and ET-BR mRNAs in this tissue. ET-1-LI in the umbilical venous plasma of the newborns from women with pregnancy-induced hypertension (PIH) (38.3 +/- 10.4 pg/mL, n = 5) was significantly (P < 0.05) higher than that in the normal newborns from normotensive pregnant women (26.3 +/- 5.2 pg/mL, n = 12). However, in placental chorionic villous tissue obtained from PIH women, both ET-1-LI level and ET binding profile were not different from those in chorionic villous tissue from normotensive pregnant women. These results suggest that the abundant ET-ET receptor system is present in the placental chorionic villous tissue and that this system is not the major factor of the pathogenesis of placental dysfunction occurring in PIH because these systems are similar in normotensive and hypertensive pregnancies.

Effects of anesthesia and surgery on plasma endothelin levels

To investigate the clinical significance of endothelin (ET), a potent and long-acting vasoconstrictor peptide in anesthesia and surgery, we measured plasma ET-like immunoreactivity (ET-LI) levels by using radioimmunoassay in patients undergoing various kinds of surgery under general anesthesia. No significant changes in plasma ET-LI levels were observed in patients undergoing relatively minor surgery under general anesthesia with nitrous oxide and halothane (n = 6), enflurane (n = 6), or isoflurane (n = 5). Although plasma ET-LI levels after surgery in patients undergoing total knee replacement (12.4 +/- 0.9 [mean +/- SEM] pg/mL, n = 7), hysterectomy (11.4 +/- 0.6 pg/mL, n = 8) or cholecystectomy (14.8 +/- 1.2 pg/mL, n = 9) were no different from those before surgery, plasma ET-LI levels after surgery in patients undergoing gastrectomy (20.4 +/- 1.9 pg/mL, n = 15), esophagectomy (24.7 +/- 2.5 pg/mL, n = 12), hepatectomy (27.5 +/- 3.4 pg/mL, n = 12), or heart surgery (43.1 +/- 4.1 pg/mL, n = 18) were higher than those before surgery (P < 0.05). Changes in plasma ET-LI levels during surgery had positive correlations with the duration of the operation (n = 100, r = 0.51, P < 0.01) and intraoperative blood loss (n = 100, r = 0.30, P < 0.01). In patients undergoing subtotal esophagectomy, the plasma ET-LI level did not increase during the initial 2 h, but increased gradually during surgery, reached a peak within a few hours after surgery, and declined slowly thereafter.(ABSTRACT TRUNCATED AT 250 WORDS)

Changes of endothelin concentration in cerebrospinal fluid and plasma of patients with aneurysmal subarachnoid hemorrhage

To investigate the clinical significance of endothelin (ET), a potent vasoconstrictor peptide, in subarachnoid hemorrhage (SAH) and SAH-related cerebral vasospasm, we measured the ET-like immunoreactivity (ET-LI) in plasma and cerebrospinal fluid (CSF) obtained serially from patients with SAH due to ruptured cerebral aneurysm who underwent aneurysmal surgery. The normal ET-LI levels in plasma and CSF (n = 24) were 12.4 +/- 2.0 (mean +/- s.d.) and 9.1 +/- 1.2 pg.ml-1, respectively. Plasma ET-LI levels in patients with SAH before surgery (16.8 +/- 7.8 pg.ml-1, n = 8) were higher than the normal values (P < 0.05), and became further elevated after surgery (22.5 +/- 9.4 pg.ml-1). ET-LI levels in plasma and CSF one day after surgery were 18.7 +/- 5.5 and 18.4 +/- 6.8 pg.ml-1 (P < 0.01 vs. normal values), respectively, and declined thereafter. The plasma and CSF ET-LI levels in patients who showed symptomatic vasospasm became concomitantly elevated again. These results suggest that ET is involved in SAH-related vasospasm and raise the possibility that surgical stress influences the vasospasm.

Endothelin-1 inhibits the adipose differentiation of cultured human adipocyte precursor cells

We studied the effect of endothelin-1 (ET-1) on the differentiation of adipocyte precursor cells obtained from human adipose tissue and cultured in a serum-free hormone-supplemented medium. ET-1 was found to inhibit in a dose-dependent manner the accumulation of lipid droplets and the expression of glycerol-3-phosphate dehydrogenase (GPDH), a marker of adipose differentiation. The half-maximal inhibitory effect was observed in the range of 8.5 x 10(-10) mol/L. Full inhibition required the continuous exposure of the cells to ET-1. The prevention of adipose conversion was not associated with a stimulation of mitogenesis. The presence of staurosporine, an inhibitor of the protein kinase C signaling pathway, completely prevented the inhibitory effect of ET-1 on adipose differentiation. Addition of ET-1 to newly developed fat cells also caused a suppression of GPDH activity without changing adipocyte morphology. Again, the magnitude of this effect was dependent on the exposure time. These findings suggest that ET-1 is a potent modulator of fat cell formation in man, which may act through activation of protein kinase C. Because of the close spatial relationship between fat cell precursors and blood vessels, ET-1 may exert its action in a paracrine manner.

Plasma endothelin-1 concentrations in patients with Behçet's disease

Plasma Endothelin-1 (ET-1) concentrations were determined by radio immunoassay in 30 patients with Behçet's disease at various stages and 20 healthy subjects. Mean ET-1 plasma concentrations were significantly (p < 0.001) increased in patients with active Behçet's disease (35.99 +/- 5.06 fmol/ml, mean +/- standard error) compared to concentrations found in healthy volunteers (10.98 +/- 0.84 fmol/ml). No difference in plasma ET-1 level was observed between patients with inactive Behçet's disease (12.98 +/- 1.14 fmol/ml) and volunteers. Increased plasma levels of ET-1 in patients with Behçet's disease may be attributable to increased secretion or leakage of this mitogen from injured vascular endothelial cells. These results indicate that ET-1 may play an important pathogenetic role in the development or progression of vasculitis common to Behçet's disease. Plasma concentrations of ET-1 correlates with the activity of illness.

Endothelin family peptides in human plasma and urine: their molecular forms and concentrations

Molecular forms and concentrations of endothelin (ET) family peptides in normal human plasma and urine were investigated using five different sandwich-type enzyme immunoassays (sandwich-EIAs) and reverse-phase high performance liquid chromatography (RP-HPLC). We found that immunoreactive (IR-) big ET-3 and IR-big ET-2 were the major species in both plasma and urine from normal humans. Big ET-2(1-38) was found to be the major form of IR-big ET-2 in plasma. Urinary IR-big ET-2 and plasma and urinary IR-big ET-3 were heterogeneous, and the IR-big ET-3s were larger (M(r) 6,000-12,000) than authentic big ET-3. IR-big ET-1, IR-ET-1, and IR-ET-3 were found at relatively low concentrations in human plasma and urine, and their major forms were identical to authentic big ET-1, ET-1, and ET-3, respectively. Although ET-1 and other ET family peptides have often been measured using RIAs with board-spectrum antibodies, the presence of high concentrations of IR-big ET-2 and IR-big ET-3, but not IR-ET-1, in plasma and urine indicates that the clinical significance of ET family peptides should be investigated with assay methods specific to each ET and big ET.

Involvement of cyclo-oxygenase-generated vasodilating eicosanoid(s) in addition to nitric oxide in endothelin-1-induced endothelium-dependent vasorelaxation in guinea pig aorta

This study investigates the vasodilatory effects of endothelin-1 (ET-1) in isolated guinea pig aortic rings in vitro. Cumulative dose-response curves to ET-1 were constructed and ET-1 actions on prostaglandin F2 alpha (PGF2 alpha)-precontraction were studied in both endothelium-intact and endothelium-denuded preparations, in the presence or absence of a cyclooxygenase inhibitor (indomethacin) and/or nitric oxide inhibitors (NG-nitro-L-arginine methyl ester and hemoglobin). In endothelium-intact preparations, pretreatment with indomethacin (10(-5) M, 30 min), alone or in combination with NG-nitro-L-arginine methyl ester (L-NAME, 10(-4) M), significantly augmented the constrictive responses to ET-1, whereas indomethacin, L-NAME, and hemoglobin (10(-5) M) had no significant effects in the endothelium-denuded preparations. Furthermore, in PGF2 alpha-precontracted, endothelium-intact preparations, ET-1, at a dose of 10(-9) M, induced initial relaxation followed by subsequent contraction, while it only contracted the endothelium-denuded preparations. The initial relaxation was abolished by indomethacin, but not by L-NAME or hemoglobin. In addition, this relaxation was not inhibited by a specific ETA receptor antagonist, BQ-123 (6 x 10(-6) M). In addition to the involvement of nitric oxide, these results show the involvement of cyclo-oxygenase-generated vasodilating eicosanoid(s) derived from endothelium in ET-1-induced vasorelaxation in guinea pig aorta in vitro. The results also indicate that this vasorelaxation is mediated by ETB receptor activation.

Endothelin and endothelium-derived relaxing factor control of basal renovascular tone in hydronephrotic rat kidneys

1. In order to investigate the control of renal vascular tone by endothelin (ET) and endothelium-derived relaxing factor (EDRF) under basal conditions, we infused intravenously anti-ET-1/3 antibodies (a-ET-1/3) and NG-nitro-L-arginine methyl ester (L-NAME) in split hydronephrotic rat kidneys. 2. A 25 min I.V. infusion of a-ET-1/3 (4.0 x 10(-13) mol kg-1 min-1) induced a time-dependent vasodilatation of arcuate (16.5%) and interlobular arteries (18.6%) as well as an increase of glomerular blood flow (GBF) by 32%. 3. Inhibition of EDRF synthesis by L-NAME produced a marked vasoconstriction of arcuate arteries (17.1%) and efferent (20.1%) arterioles and a decrease of GBF by 43%. 4. Co-infusion of a-ET-1/3 and L-NAME induced efferent vasoconstriction by 19.5%, whereas preglomerular vessel diameters remained unchanged. 5. The specificity of a-ET-1/3 effects was confirmed by simultaneous I.V. application of a-ET-1/3 and ET-1 (160 ng I.V.) which produced no significant vascular effects. Injection of ET-1 alone constricted arcuate arteries and decreased glomerular blood flow by 25%. 6. Experiments in normal rat kidneys with a-ET-1/3 I.V. revealed an increase of renal blood flow by 21%. 7. Our results demonstrate a physiological control of basal vascular tone in larger preglomerular arterioles by ET and EDRF. Efferent arteriolar tone is predominantly controlled by EDRF.

Enzyme immunometric assay for endothelin using tandem monoclonal antibodies

Seven distinct mouse monoclonal antibodies (mAbs) directed against human endothelin-1 (ET-1) have been obtained. On the basis of specificity studies performed with competitive immunoassays and of complementary binding studies, these mAbs were classified in two groups. mAbs of group A (Endo-4, -5, -6 and -10) were shown to be directed against the N terminal loop while those of group B (Endo-2, -8 and -18) recognized the C terminal part of the peptide. A pair of monoclonal antibodies with optimal properties for a two-site immunometric assay were selected and the test was performed in 96-well microtiter plates coated with one mAb (Endo-18), while another mAb (Endo-4) covalently labeled with enzyme acetylcholinesterase was used as tracer. Under optimal conditions, the assay appeared to be very sensitive since concentrations as low as 1 pg/ml could be significantly detected. The precision was also very good with a coefficient of variation below 10% from 3 to 250 pg/ml. The assay was specific for mature endothelin presenting no cross-reactivity with the precursor Big ET-1. On the other hand, strong cross-reactivity was observed with other ET-1-related peptides, including ET-2, ET-3, VIC peptide and sarafotoxin 6-b. The assay permitted specific determination of ET-1 in supernatants of cultured endothelial cells and the validity of the test was demonstrated by HPLC fractionation experiments. In addition, the assay also appeared to be suitable for direct determination of ET-1 in plasma. Studies performed with plasma from healthy subjects revealed that circulating levels of ET-1 are below or close to the detection limit of the method (< 8 pg/ml).

Nonlinear mixed effect modeling of the pharmacodynamics of natriuretic peptides in rats

Natriuretic peptides have not only natriuretic/diuretic but also hypotensive activities, and the decreased renal perfusion caused by the excessive hypotension is known to attenuate the diuretic actions. The present study was designed to examine the relationship between the dosing (intravenous constant infusion) rates and the diuretic actions of alpha-rat atrial natriuretic peptide (alpha-rANP) and rat brain natriuretic peptide (rBNP) in rats, and population (nonlinear mixed effect model) analysis was applied to these complicated diuretic actions. The intrinsic diuretic activities of alpha-rANP and rBNP could be analyzed, and the effects of blood pressure, heart rate, and also inhibition of degradation enzyme on the diuresis of natriuretic peptides were estimated simultaneously. The population analysis was useful for analyzing such pharmacodynamic data for which the individual analysis could not be applied easily.

Circulating levels of endothelin in cirrhosis

BACKGROUND

Current information concerning endothelin in cirrhosis is conflicting. Plasma endothelin concentration has been found to be increased in some studies and normal or reduced in others. The present study was aimed to investigate the plasma levels of endothelin in cirrhosis and to assess whether it is involved in the renal and hemodynamic disturbances and neurohumoral changes present in this condition.

METHODS

Renal function, plasma renin activity, and plasma concentration of aldosterone, norepinephrine, antidiuretic hormone, atrial natriuretic factor, and endothelin were measured in 9 healthy subjects, 7 compensated cirrhotics, and 25 cirrhotics with ascites (10 with functional renal failure).

RESULTS

Cirrhotics with ascites with and without functional renal failure showed higher endothelin levels (15.6 +/- 6.4 and 15.7 +/- 4.6 pg/mL, respectively; mean +/- SD) than compensated cirrhotics (6.4 +/- 1.8 pg/mL) and healthy subjects (3.4 +/- 1.0 pg/mL) (analysis of variance, F = 21.84; P < 0.001). These patients also showed higher plasma levels of renin, aldosterone, norepinephrine, antidiuretic hormone, and atrial natriuretic factor, although plasma endothelin levels only correlated significantly with plasma atrial natriuretic factor (r = 0.73, P < 0.001) and antidiuretic hormone concentrations (r = 0.59, P < 0.001). In 7 additional nonazotemic cirrhotics with ascites, plasma renin activity and the plasma concentration of aldosterone and endothelin were measured before and 24 hours after the intravenous administration of a saline solution of human serum albumin. Volume expansion markedly suppressed renin and aldosterone but not endothelin (21.03 +/- 7.34 vs. 23.97 +/- 14.29 pg/mL).

CONCLUSIONS

Circulating plasma levels of endothelin are elevated in cirrhosis with ascites and do not decrease following plasma volume expansion.

Suppression of endothelin-1 secretion by lysophosphatidylcholine in oxidized low density lipoprotein in cultured vascular endothelial cells

Oxidatively modified low density lipoprotein (oxidized LDL), an atherogenic lipoprotein that exists in the atherosclerotic arteries, has been shown to alter endothelial cell functions. In the present study, we examined the effects of oxidized LDL on the production of endothelin-1-like immunoreactivity (ET-1-LI) by the cultured vascular endothelial cells from porcine aorta and human umbilical vein. Incubation with oxidized LDL resulted in a dose-dependent suppression of ET-1-LI release by both endothelial cells. Oxidized LDL also inhibited thrombin-mediated stimulation of ET-1-LI secretion. However, native LDL had no effects on ET-1-LI secretion. A lipid extract from oxidized LDL, but not from native LDL, inhibited ET-1-LI secretion, indicating that the lipid component of oxidized LDL was required for the inhibition of ET-1-LI secretion. Oxidative modification of LDL was associated with degradation of a substantial amount of phosphatidylcholine to lysophosphatidylcholine (LPC). Pretreatment with defatted albumin, which is an acceptor for hydrophilic lipids including LPC, reduced LPC concentration in oxidized LDL to that in native LDL and simultaneously prevented the inhibitory effects of oxidized LDL on ET-1-LI secretion. Incubation with synthetic LPC (palmitoyl), but not with synthetic phosphatidylcholine (dipalmitoyl), suppressed ET-1-LI secretion by the endothelial cells. No cell death was observed during the incubations as judged by the trypan blue exclusion test, and protein synthesis of the endothelial cells was not affected by lipids or lipoproteins at a concentration at which suppression of ET-1-LI was observed. We concluded that LPC in oxidized LDL causes suppression of ET-1-LI release, which may counteract the vasoconstrictive properties of atherosclerotic arteries.

Endothelin peptides: biological activities, cellular signalling and clinical significance

Endothelins (ET-1, ET-2 and ET-3) are a family of 21 amino acid peptides produced by endothelial cells. They are thought to regulate the local vasomotor tone with endothelium-derived relaxing factors. ETs are the most potent vasoconstrictor substances yet identified and veins and renal vasculature are the most sensitive targets. They reduce cardiac output and have positive inotropic and chronotropic effects. ETs increase the secretion of atrial natriuretic peptide (ANP), aldosterone and catecholamines but reduce renal blood flow and glomerular filtration and they also have mitogenic properties. ETs bind to receptors (ETA and ETB), activate phospholipase C, modulate intracellular Ca2+ concentration and open Ca2+ channels. Vasoactive agents (adrenaline, angiotensin, vasopressin, thrombin, endotoxins) and hypoxia stimulate the release of ET and also ET gene expression. Raised concentrations of plasma ET have been found to occur in several clinical conditions such as hypertension, myocardial infarction, cardiogenic shock, pregnancy induced hypertension, arteriosclerosis, Raynaud's disease, subarachnoid haemorrhage, uraemia, ulcerative colitis, Crohn's disease and surgical operations suggesting that ETs have a role in several patophysiological processes.

Characterization of immunoreactive endothelin in human urine

We developed three antibodies, specific and sensitive to endothelin-1 (ET-1), and established two sandwich and three competitive enzyme immunoassays (EIAs). By using these EIAs, large immunoreactive ET (IR-ET) of molecular weight 10 k Da was identified as a main component of IR-ETs in human urine. This large IR-ET, which reacted with two antibodies specific for N-terminal region of ET-1 but not with the antibody against C-terminal peptide of ET-1, was partially purified by six-step procedure and examined by Western blotting after SDS polyacrylamide gel electrophoresis. The large IR-ET was detected as a single band at molecular weight of 10 k Da both in reduced and non-reduced conditions. From these results, the large IR-ET was thought to consist of a single polypeptide chain and possess the steric restricted N-terminal region of ET-1.

Plasma endothelin concentrations in patients with pulmonary hypertension associated with congenital heart defects. Evidence for increased production of endothelin in pulmonary circulation

BACKGROUND

To elucidate the pathophysiological significance of endothelin in pulmonary hypertension associated with congenital heart defects, we measured plasma endothelin-like immunoreactivity (ET-LI) concentrations by using radioimmunoassay in 18 patients with pulmonary hypertension (PH group; age, 6 months to 12 years) in comparison with 27 patients without pulmonary hypertension (non-PH group; age, 6 months to 12 years).

METHODS AND RESULTS

Blood samples were obtained from the vena cava, right atrium, right ventricle, left or right pulmonary artery, and pulmonary vein or the pulmonary arterial wedge position (pulmonary venous blood) during cardiac catheterization. Plasma ET-LI concentrations in the PH group were significantly higher than those in the non-PH group at all sampling sites. In the PH group, plasma ET-LI concentration showed a significant increase between the right ventricle and pulmonary artery and between the pulmonary artery and pulmonary vein. The increment of plasma ET-LI concentrations from the right ventricle to the pulmonary vein was significantly larger in the PH group than in the non-PH group and was significantly correlated with pulmonary artery pressure.

CONCLUSIONS

Plasma ET-LI concentrations were elevated in patients with pulmonary hypertension; the elevation was due to the increased production of ET-LI in pulmonary circulation, indicating the possible involvement of endothelin in the pathophysiology of pulmonary hypertension.

Radio-immunoassay of endothelin in human plasma

Endothelin (ET) is a newly described endothelium-derived 21-amino-acid peptide with potent vasoconstrictive properties. The present study describes a radio-immunoassay utilizing an antibody without cross-reactivity with big endothelin, produced after immunization of rabbits with endothelin-1 (ET-1). Measurement of endothelin in human plasma was performed after prior extraction on Sep-pak C18 cartridges. Recovery of unlabelled endothelin-1 added to human plasma (3.5 pg ml-1) was 84.8 +/- 11.1% (mean +/- SD, n = 12). The minimum detectable level in plasma was 50 fmol 1-1. High-pressure liquid chromatography on reverse-phase C18 column established that the measured irET eluted identically to ET-1. The concentration of irET in plasma from healthy control subjects was 1.11 +/- 0.2 pmol-1 (mean +/- SD, n = 30). Agarose electrophoresis of plasma with [125I]-ET-1 indicated a reversible binding to albumin. It is concluded that ET-1 is present in measurable amounts in human plasma. It is suggested that ET-1 in plasma is associated with albumin. The importance of an adequate extraction procedure is stressed.

Increased plasma level of endothelin-1-like immunoreactivity during coronary spasm in patients with coronary spastic angina

To examine the role of endothelin in coronary spasm, the plasma endothelin-1-like immunoreactivity in the coronary sinus and the aortic root was measured before and during spasm of the left coronary artery induced by injection of acetylcholine (20 to 100 micrograms) into the left coronary artery in 26 patients with coronary spastic angina. The plasma level of endothelin-1-like immunoreactivity was measured by the radioimmunoassay with a monoclonal antibody against endothelin-1. Plasma lactate levels in the coronary sinus and the aortic root were also measured to evaluate myocardial lactate metabolism during spasm. In 13 patients who had myocardial lactate production during spasm, the plasma level of endothelin-1-like immunoreactivity in the coronary sinus increased from 19.8 +/- 3.0 to 25.7 +/- 6.4 pg/ml (p less than 0.01), while that in the aortic root remained unchanged (from 20.2 +/- 5.9 to 21.3 +/- 5.8 pg/ml). No significant changes in the plasma levels of endothelin-1-like immunoreactivity in the coronary sinus (from 21.1 +/- 7.3 to 19.7 +/- 5.2 pg/ml) and the aortic root (from 21.1 +/- 5.7 to 19.7 +/- 5.6 pg/ml) were observed in 13 patients who did not show myocardial lactate production during spasm. On the other hand, 16 patients without ischemic heart disease showed no significant changes in the plasma levels of endothelin-1-like immunoreactivity in the coronary sinus (from 24.4 +/- 9.7 to 25.8 +/- 6.9 pg/ml) and the aortic root (from 23.0 +/- 7.1 to 23.4 +/- 5.8 pg/ml) by acetylcholine injection (100 micrograms).(ABSTRACT TRUNCATED AT 250 WORDS)

Serum platelet-derived growth factor and endothelin concentrations in human hypercholesterolaemia

Platelet-derived growth factor (PDGF) and endothelin are both smooth muscle cell mitogens, and may have an important role in mediation of the proliferative phase of atherogenesis. Since hypercholesterolaemia is an important risk factor for atherosclerosis, we have measured serum endothelin and PDGF concentrations in matched pairs of hypercholesterolaemic patients and control subjects. Both endothelin and PDGF concentrations were higher in the hypercholesterolaemic patients (23.8 +/- 4.3 pM vs. 21.7 +/- 2.4 pM, P = 0.019, median difference 3.0, 95% confidence limits 0.6-7.3, and 115.4 +/- 60.3 pM vs. 64.7 +/- 22.7 pM P = 0.033, median difference 27.2, 95% confidence limits 1.3-82.5, respectively), while serum endothelin and PDGF concentrations were positively correlated with each other (r = 0.764, P less than 0.0001, 95% confidence limits 0.505-0.897). PDGF concentrations were correlated with the peripheral blood platelet count (r = 0.560, P = 0.007, 95% confidence limits 0.180-0.794). These findings suggest that PDGF, and possibly endothelin, may be involved in hypercholesterolaemia-related atherogenesis.

Natriuretic peptide receptors regulate endothelin synthesis and release from parathyroid cells

Cloned rat parathyroid cells (PTr cell line) that produce parathyroid hormone-related peptide plus endothelin 1 and primary cultures of human parathyroid cells were tested for growth and differentiation responses to atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP). High- and low-affinity binding sites for ANP were found on PTr cells; BNP appeared to bind to the same receptors with similar affinities. Either ANP or BNP stimulated production of cGMP and caused a 30% decrease in Na(+)-K(+)-Cl- cotransport. Each peptide increased synthesis and secretion of endothelin 1 by PTr cells in a dose-dependent fashion, but cell growth was not affected. Human parathyroid cells (normal and pathological) also responded to ANP or BNP with an increase in cGMP production. The finding of receptors for natriuretic hormones on parathyroid cells with consequent effects on release of endothelin 1 might be of relevance in understanding the clinical association between hyperparathyroidism and hypertension.

Plasma immunoreactive endothelin-1 in experimental malignant hypertension

We measured plasma concentrations of immunoreactive endothelin-1 (irET-1) in the prehypertensive and hypertensive phases in spontaneously hypertensive rats (SHR) and in malignant hypertension caused by deoxycorticosterone acetate (DOCA)-salt administration in SHR. We also measured concentrations of this peptide in another model of malignant hypertension, the two-kidney, one clip (2K1C) renovascular hypertensive rats chronically given caffeine. Plasma irET-1 concentrations in young (6-week-old) and mature (18-week-old) SHR did not differ from those of age-matched Wistar-Kyoto (WKY) rats. Four weeks of treatment with DOCA-salt increased blood pressure, blood urea nitrogen, serum creatinine, and plasma irET-1 in SHR but not in WKY rats. Eight weeks of DOCA-salt treatment further increased these values in SHR. Plasma irET-1 concentrations were not increased in the 2K1C rats. Six weeks of caffeine administration increased blood pressure, blood urea nitrogen, serum creatinine, plasma renin activity, and plasma irET-1 in the 2K1C rats but not in the sham-operated rats. High-performance liquid chromatographic profiles of plasma extracts pooled from these rats with malignant hypertension showed that a major component of irET-1 eluted in the position of synthetic ET-1 (1-21). Furthermore, acute hypertension induced by angiotensin II or phenylephrine did not affect the plasma irET-1 concentration in rats. The results suggested that the plasma ET-1 concentration is increased in rat models of malignant hypertension and that the high blood pressure itself is not the main factor involved in the increase of plasma ET-1.

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.

Beagle pup germinal matrix maturation studies

Intraventricular hemorrhage, or hemorrhage into the germinal matrix tissues of the developing brain, remains a common problem of preterm infants. The "risk period" for this insult is the first 3-4 postnatal days. We hypothesized that this risk period for hemorrhage is related to rapid perinatal maturation of the germinal matrix vasculature and employed the newborn beagle pup model for the study of this maturation. Newborn beagle pups (n = 30) were anesthetized and systemically perfused with buffered formalin; the brains were removed and prepared for immunohistochemical study. Sections stained with Bandeiraea lectin demonstrated that there was no difference in germinal matrix vessel density between postnatal days 1 and 4. Germinal matrix sections were also stained for antibodies to alpha-smooth muscle actin, collagen IV, collagen V, desmin, factor VIII-related antigen, fibronectin, glial fibrillary acidic protein, laminin, transferrin, and vimentin. Vasculature staining by alpha-smooth muscle actin was not noted until postnatal day 10, and differential staining was detected for antibodies to laminin and collagen V. Quantification of staining intensity by confocal microscopy demonstrated a significant increase in both extracellular matrix components at postnatal day 4 compared with day 1 (p less than 0.05 for both). These basement membrane proteins may add sufficient structural integrity to germinal matrix vessels to prevent capillary rupture and thus intraventricular hemorrhage.

Endothelin and atrial natriuretic peptide after exercise performed until exhaustion in the rat

Endothelin-1(ET) is a recently discovered endothelium-derived vasoconstrictor peptide. Plasma concentrations of immunoreactive (IR-) endothelin were investigated in rats by radioimmunoassay after extraction of endothelin on Sep-Pak Cartridges. In control rats, a mean concentration of 1.03 +/- 0.2 pg/ml was found. After exercise performed until semi-exhaustion or exhaustion, the mean plasma concentration of IR-endothelin decreased. An increase of Atrial Natriuretic Peptide plasma was observed immediately after exercise. There was a negative correlation between Endothelin and Atrial Natriuretic Peptide (r = -0.73, p less than 0.001). This is the first time that this increase following exercise is shown in normotensive rat. The mechanisms of the decrease of Endothelin are unclear. One hypothesis could be that the decrease in Endothelin is related to its rapid removal by the different tissues, specially the lungs.

Acute pulmonary alveolar hypoxia increases lung and plasma endothelin-1 levels in conscious rats

To investigate the effect of pulmonary alveolar hypoxia on the synthesis and release of endothelin (ET)-1, ET-1-like immunoreactivity (-LI) levels of the lung and plasma were measured in conscious unrestrained rats under hypoxic conditions. Sixty-min exposure to alveolar hypoxia (10% O2 or 5% O2) increased the ET-1-LI level in the lung. The plasma ET-1-LI level in hypoxic rats also increased significantly. The increase of plasma and lung ET-1-LI levels were parallel to the severity of hypoxia. These results demonstrates that acute pulmonary alveolar hypoxia increases lung and plasma ET-1-LI levels in conscious unrestrained rats, suggesting a possible physiological or pathophysiological significance of ET in alveolar hypoxia.

Cerebrospinal fluid endothelin-1 and endothelin-3 levels in normal and neurosurgical patients: a clinical study and literature review

Endothelins are a family of structurally related, potent, long-lasting vasoconstrictor peptides. There are no established normal human levels of endothelin-1 or endothelin-3 in the cerebrospinal fluid. We measured cerebrospinal fluid endothelin-1 and endothelin-3 levels in five groups of patients: normal controls, patients with subarachnoid hemorrhage and cerebral vasospasm, patients with severe head injuries, patients undergoing temporal lobectomy for intractable epilepsy, and a patient with a gunshot injury to the thoracic spine. Endothelin-3 levels were significantly elevated in patients with subarachnoid hemorrhage and may participate in cerebral vasospasm and subsequent neurologic deterioration.

Endothelin stimulates PDGF secretion in cultured human mesangial cells

Endothelin, a 17-DKa peptide originally described as a potent vasoconstrictor, also stimulates the release of important regulators of glomerular hemodynamics such as atrial natriuretic factor and renin. In the present study we investigated the role of endothelin in the release of another potent vasoconstrictor and mitogen of human mesangial cells, the platelet-derived growth factor. Endothelin stimulated PDGF release at 12 hours and the effect was sustained for 36 hours. This effect was associated with the enhanced induction of mRNAs encoding PDGF A- and B-chain. Endothelin also induced mitogenesis in human mesangial cells which was accompanied by activation of phospholipase C with increased inositol phosphate turnover. These data suggest a mechanism by which endothelin may regulate mesangial cell function in disease states.

[Plasma endothelin in normal probands and patients with nephrologic-rheumatologic and cardiovascular diseases]

Plasma concentrations of the recently isolated potent vasoconstrictory peptide endothelin were measured in 382 patients. The investigations were performed by means of a sensitive radioimmunoassay specific for Endothelin-1, 2. The results from 110 healthy volunteers displayed a normal range of 44.67 +/- 3.51 pg/ml. Significantly raised levels were found in 33 patients with chronic end-stage renal failure both before and after hemodialysis. In contrast, 35 patients with compensated renal insufficiency did not differ from the normals. Sixty-five patients after kidney transplantation revealed significantly elevated levels, as did 27 patients with acute myocardial infarction, 8 after coronary bypass surgery, and 5 with liver cirrhosis. The mean values of 27 patients with untreated hypertension, 22 with secondary hypertension, of various causes and 16 with coronary artery disease were comparable to the normal population. The values were significantly decreased in 9 pregnant women with hypertension and proteinuria. A marked decline was found in 5 patients with systemic lupus erythematodes, while 20 patients with rheumatoid arthritis demonstrated only a slight decrease. The pathophysiological role of endothelin as a local or circulating hormone in regulating systemic blood pressure or release of other hormones remains to be determined.

Application of monoclonal antibodies for endothelin to hypertensive research

We developed six kinds of monoclonal antibodies against endothelin (ET)-1 recognizing different epitopes with high affinities (5 x 10(10) M-1 to 5 x 10(11) M-1). Using these monoclonal antibodies, we developed radioimmunoassays for ET-1 with different specificities. Cross-reactivities with ET-2 ranged from 80% to 100%, and those with ET-3 ranged from 3% to 60%. Patients with essential hypertension (n = 20) showed a significant elevation in the plasma ET-1-LI level compared with age-matched control subjects (n = 12) (30.1 +/- 1.4 pg/ml versus 18.5 +/- 0.9 pg/ml, p less than 0.01). The plasma ET-1-LI level in hypertensive patients in stages II and III (World Health Organization classification) was significantly higher than that in those patients in stage I. There was no significant correlation between the plasma ET-1-LI level and systolic blood pressure (r = 0.11), diastolic blood pressure (r = -0.13), or age (r = 0.24) in all patients studied who had essential hypertension. In the neutralization experiment, monoclonal antibodies attenuated ET-1-induced contraction of rat aortic rings and the pressor action of ET-1 in pithed rats in vivo. The present study demonstrates the elevated plasma ET-1-LI level in patients with essential hypertension. Monoclonal antibodies developed in this study can become powerful tools to investigate the pathophysiological significance of ET in essential hypertension.

Chronic hypertension produced by infusion of endothelin in rats

Endothelin, a potent vasoconstrictor peptide synthesized by the vascular smooth muscle endothelium, was chronically infused into male Sprague-Dawley rats to determine whether a long-term increase in circulating endothelin levels would cause a sustained elevation in mean arterial pressure. Rats were catheterized, housed in metabolic cages, and maintained on a fixed 6 meq/day sodium intake throughout the experiment with daily measurements including mean arterial pressure, heart rate, water intake, urine output, urinary sodium excretion, urinary potassium excretion, cardiac output, total peripheral resistance, and stroke volume. Infusion of endothelin-1 (ET-1) at rates of 3, 5, or 7.5 pmol/kg/min for 7 days was associated with significant, sustained, and dose-dependent increases in mean arterial pressure and smaller less consistent elevations in total peripheral resistance. Other parameters were unaffected. Similar results were observed in rats receiving endothelin-3 (ET-3), except that a higher dose of ET-3 was required. These results indicate that elevated blood levels of endothelin could produce a maintained hypertension without sodium or water retention and that the hemodynamic basis for the increased mean arterial pressure is similar to that seen in most other forms of experimental and clinical hypertension.

Regional distribution of endothelin receptor in porcine cardiovascular tissues

To clarify effecting sites of endothelin (ET) in a circulation system, we have identified specific receptors for porcine ET(ET-1) and investigated the distribution in the porcine cardiovascular tissues. Scatchard analysis of 125I-porcine ET binding indicated the presence of a single class of high-affinity binding sites. The binding was highly specific for ET-1, because (1) none of the other various peptides or Ca2+-channel antagonists affected the binding, (2) the scission of disulfide bonds, the digestion of the C-terminal 6-amino acid residues, or nitrophenylsulfenylization of the C-terminal Trp21 of ET-1 markedly reduced the binding ability and, (3) ET-1 showed the highest affinity for the vascular receptor among three ET isopeptides. Cardiac atria possessed the highest density (2.7 pmol/mg protein) of ET receptors of all the tissues examined, including thoracic aorta, cardiac atria and cardiac ventriculi, basilar, renal, coronary and pulmonary branch arteries, coronary, renal and jugular veins, and small vessels of pia mater encephali. Small vessels, renal and coronary arteries also showed relatively high density (0.8-1.4 pmol/mg protein). Various veins examined also showed considerable density (0.45-0.74 pmol/mg protein). The apparent Kd of cardiac ET receptors (0.76 nM) was significantly greater than that of the receptors of the other tissue (0.06-0.14 nM). The extensive distribution and the local enrichment of ET receptor in a cardiovascular system strongly suggests that ET is one of the essential endogenous substances to control the tone of the vasculature.

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.

Detection and characterization of endothelin-1-like immunoreactivity in rat plasma

Using two radioimmunoassays (RIAs) for endothelin-1 (ET-1) with and without a substantial cross-reactivity with ET-3, we have measured the plasma ET-1-like immunoreactivity (-LI) level in rat plasma. ET-1-LI was detected in plasma from male Wistar rats. ET-1-LI in rat plasma consisted of three components with molecular weights of 6K, 4K and 2.5K daltons by gel permeation chromatography. Two of the components were eluted at positions of big ET (4K) and synthetic ET-1 (2.5K). The remaining component was eluted at the preceding fraction (6K). No difference was observed in ET-1-LI of the small molecular form of ET (2.5K) between the two RIAs. Thus, there is little or no ET-3 in rat plasma, which has the sequence found originally in the rat genome. The concentration of the small molecular form of ET, presumably ET-1, in rat plasma was about 4 pg/ml.

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.