Dexamethasone down-regulates the expression of endothelin receptors in vascular smooth muscle cells

Association of endothelin receptor type A rs5333 gene polymorphism with steroid response in Egyptian children with idiopathic nephrotic syndrome

Aim: To investigate ENDRA rs5333 gene polymorphism distribution in idiopathic nephrotic syndrome (INS) and to analyze their association with response to steroid therapy, and biochemical markers of INS. Subjects & methods: The PCR-restriction fragment length polymorphism was used to analyze ENDRA rs5333 polymorphism in 100 children with idiopathic nephrotic syndrom (INS) and 100 healthy children. Plasma endothelin-1 were measured by ELISA. Results: The ENDRA rs5333 gene polymorphism was not associated with risk of INS. The frequency of minor allele (C) was significantly higher in the steroid resistant nephrotic syndrome group than the steroid sensitive group. The CC and TC mutant variants were associated with higher plasma levels of cholesterol, albumin, urea and 24-h urinary protein, but were not associated with risk of hypertension. The endothelin-1 plasma level was higher in INS than control and in steroid resistant nephrotic syndrome group when compared with steroid sensitive group cases. Conclusion: The ENDRA rs5333 gene polymorphism may be associated with genetic predisposition to steroid resistance in INS Egyptian children.

Endothelin and the heart in health and diseases

Endothelin-1 (ET-1), a 21-amino acid peptide, was initially identified in 1988 as a potent vasoconstrictor and pressor substance isolated from the culture supernatant of porcine aortic endothelial cells. From human genomic DNA analysis, two other family peptides, ET-2 and ET-3, were found. They showed different effects and distribution, suggesting that each peptide may play separate roles in different organs. In the heart, ET-1 also causes positive inotropic and chronotropic responses and hypertrophic activity of the cardiomyocytes. ETs act via activation of two receptor subtypes, ET_A and ET_B receptors, both of which are coupled to various GTP-binding proteins depending on cell types. Endogenous ET-1 may be involved in progression of various cardiovascular diseases. ET antagonists are currently used clinically in the treatment for patients with pulmonary hypertension, and are considered to have further target diseases as heart failure, cardiac hypertrophy and other cardiac diseases, renal diseases, systemic hypertension, and cerebral vasospasm.

Dexamethasone stimulates endothelin-1 gene expression in renal collecting duct cells

Aldosterone stimulates the endothelin-1 gene (Edn1) in renal collecting duct (CD) cells by a mechanism involving the mineralocorticoid receptor (MR) and the glucocorticoid receptor (GR). The goal of the present study was to determine if the synthetic glucocorticoid dexamethasone affected Edn1 gene expression and to characterize GR binding patterns to an element in the Edn1 promoter. Dexamethasone (1μM) induced a 4-fold increase in Edn1 mRNA in mIMCD-3 inner medullary CD cells. Similar results were obtained from cortical collecting duct-derived mpkCCD(c14) cells. RU486 inhibition of GR completely blocked dexamethasone action on Edn1. Similarly, 24h transfection of siRNA against GR reduced Edn1 expression by approximately 50%. However, blockade of MR with either spironolactone or siRNA had little effect on dexamethasone induction of Edn1. Cotransfection of MR and GR siRNAs together had no additive effect compared to GR-siRNA alone. The results indicate that dexamethasone acts on Edn1 exclusively through GR and not MR. DNA affinity purification studies revealed that either dexamethasone or aldosterone resulted in GR binding to the same hormone response element in the Edn1Edn1 promoter. The Edn1 hormone response element contains three important sequence segments. Mutational analysis revealed that one of these segments is particularly important for modulating MR and GR binding to the Edn1 hormone response element.

Effect of preoperative single-dose corticosteroid administration on postoperative morbidity following esophagectomy

BACKGROUND

Eight clinical trials involving the administration of preoperative i.v. methylprednisolone have been undertaken in order to decrease the considerable inflammatory response to esophageal resection, in an effort to decrease the supposedly associated morbidity and mortality

METHOD

A meta-analysis was performed for eight clinical end-points. Due to quality problems in seven of the eight included studies, a Bayesian meta-analysis using a skeptical prior derived from the results of the classical analysis was also performed.

RESULTS

The end-points including any organ dysfunction (OR = 0.30), respiratory complication (OR = 0.41), sepsis (OR = 0.37), liver dysfunction (OR = 18), cardiovascular dysfunction (OR = 0.28), and surgical anastomotic leak (OR = 0.42) were significantly decreased by methylprednisolone pretreatment. Following the Bayesian analysis, despite the use of skeptical priors, there is a 95% probability to obtain a relative risk reduction of at least 23% to 54%, depending of the end-point, by methylprednisolone pretreatment.

CONCLUSION

We are in the presence of a potential benefit that cannot be accepted at face value due to the quality problems of the included studies. But in the presence of a remaining potential benefit after a Bayesian analysis starting from a skeptical prior, the best option would be the planning of a large multicenter prospective randomized study.

Thermographic study of in vivo modulation of vascular responses to phenylephrine and endothelin-1 by dexamethasone in the horse

REASONS FOR PERFORMING STUDY

In vitro, glucocorticoids potentiate vasoconstriction of equine digital vessels to catecholamines and this has been implicated as a mechanism of glucocorticoid-induced laminitis. This observation has never been confirmed in vivo.

OBJECTIVES

To study the effects of glucocorticoid therapy on vasoconstrictor responsiveness in the horse in vivo.

METHODS

In a blinded, randomised cross-over experiment, 9 horses were treated with either dexamethasone (0.1 mg/kg bwt i.v. q. 24 h) or saline i.v. for 6 days. The changes in local average skin temperature before (baseline) and after intradermal injections of the alpha1-adrenoceptor agonist phenylephrine (PHE; 10(-4), 10(-5), 10(-6), 10(-7) and 10(-8) mol/l), endothelin-1 (ET-1; 10(-5), 10(-6), 10(-7), 10(-8) and 10(-9) mol/l) or ET-1 plus a blocker (BQ-123 10(-6) mol/l; RES-701 10(-6) mol/l; and L-NAME 10(-4) mol/l) were investigated with a thermograph.

RESULTS

Dexamethasone (DEX) decreased baseline skin temperatures, suggesting reduced blood flow as a consequence of an increase in vasomotor tone. This was accompanied by potentiation of the response to PHE as demonstrated by a left shift in the dose-response curve and a decrease in the EC50. Dexamethasone did not potentiate ET-1, but the interplay with the lower baseline temperature resulted in a significantly lower skin temperature for this vasoconstrictor after DEX. The different ET-1 blockers had no effect on ET-1 modulated skin temperatures.

CONCLUSIONS

Dexamethasone decreases skin perfusion. This is accompanied by a potentiated alpha1-adrenoceptor agonist response and a greater response to ET-1.

POTENTIAL RELEVANCE

Glucocorticoid therapy probably decreases perfusion of the equine hoof. During disease states that already are characterised by hypoperfusion and/or increased levels of circulating catecholamines, glucocorticoid therapy could, according to the vascular model of laminitis, tilt the balance in favour of laminitis.

Expression of endothelin-1 system in a pig model of endotoxic shock

Endothelin (ET)-1 is a potent vasoconstrictive peptide and it is involved in the pathogenesis of septic shock. Blockade of ET-1 receptors abolishes the LPS-induced pulmonary hypertension and worsens the LPS-dependent systemic hypotension, but the role of ET-1 in sepsis remains uncertain. To determine the role of ET-1 in cardiovascular and respiratory derangement in a porcine model of endotoxemic shock we evaluated ET-1 plasma levels and ET-1 mRNA and protein levels in lung, liver, and heart as well as Endothelin Converting Enzyme-1, ET(A) and ET(B) receptors mRNA in the same tissues. Twelve piglets were randomised to sham operated or to LPS-treated (40 microg/kg/h for 4 h) groups. During the experiment, respiratory and circulatory parameters have been recorded and blood samples collected. At the end of the experiment the animals were sacrificed and tissue samples collected for real-time quantitative PCR and ELISA test. LPS infusion evokes a large increase in ET-1 plasma concentration, and in tissues mRNA levels, associated with an increase in pulmonary arterial pressure, as well as in pulmonary and systemic vascular resistances, and a decrease in stroke volume. LPS infusion caused also a derangement of respiratory mechanics, evidenced by an increase in resistance and a decrease in compliance of the respiratory system. ET(A) and ET(B) receptor mRNA levels were markedly decreased in liver and lung and slightly increased in heart, evidencing that ET receptor subtypes were differentially regulated in the major organs of endotoxin treated pigs. In conclusion our data show the presence of a continuative and differentially regulated stimulating mechanism of ET-1 expression during pig endotoxaemia as well as a fundamental role of ET-1 system in the cardiovascular and respiratory derangement.

Interleukin-18 Induces Mechanical Hypernociception in Rats via Endothelin Acting on ETBReceptors in a Morphine-Sensitive Manner

Interleukin (IL)-18 has an important role in the pathogenesis of arthritis, which is accompanied by movement limitation secondary to inflammatory articular nociception. Therefore, we investigated the possible mechanical hypernociceptive effect of IL-18 in rats using the paw constant pressure and the electronic pressure-meter tests. In both tests, intraplantar administration of IL-18 (20-60 ng paw(-1)) caused a dose- and time-dependent mechanical hypernociception, which peaked 3 h and reached control levels 24 h after injection. Pretreatments with indomethacin (2.5 mg kg(-1)), atenolol (1 mg kg(-1)), or 3-[1-(p-chlorobenzyl)-5-(isopropyl)-3-t-butylthioindol-2-yl]-2;2-dimethylpropanoic acid; Na (MK886) (5-lipoxygenase-activating protein inhibitor; 1 mg kg(-1)) did not inhibit IL-18-evoked hypernociception (40 ng paw(-1)), whereas dexamethasone (2 mg kg(-1)) inhibited the process. IL-18-evoked hypernociception was not inhibited by pretreatment with antiserum to rat tumor necrosis factor-alpha (50 microl paw(-1)) or IL-1 receptor antagonist (300 pg paw(-1)). Pretreatment with N-cys-2,6 dimethylpiperidinocarbonyl-l-gamma-methylleucyl-d-1-methoxycarboyl-d-norleucine (BQ788) (ET(B) receptor antagonist; 3-30 nmol paw(-1)), but not with cyclo[(D)Trp-(D)Asp-Pro-(D)Val-Leu] (BQ123) (ET(A) receptor antagonist; 30 nmol paw(-1)), dose dependently inhibited the IL-18-induced hypernociception. Pretreatment with morphine (3-12 microg paw(-1)) also dose-dependently inhibited the IL-18-induced hypernociception. Moreover, endothelin-1-induced mechanical hypernociception also was inhibited by BQ788, but not by BQ123, indomethacin, or atenolol. In conclusion, we demonstrated for the first time that IL-18 is a prohypernociceptive cytokine that induces mechanical hypernociception mediated by endothelin, via ET(B) receptor. Therefore, inhibition of the endothelin ET(B) receptor could be beneficial on controlling inflammatory hypernociception of diseases in which IL-18 plays a role in their pathogenesis.

Corticosteroids and fetal vasculature: effects of hydrocortisone, dexamethasone and betamethasone on human umbilical artery

OBJECTIVE

To investigate the direct effects of corticosteroids on human umbilical artery resistance, in vitro.

DESIGN

Prospective laboratory study.

SETTING

University teaching hospital.

SAMPLES AND METHODS

Umbilical artery samples were obtained following normal, term deliveries (n = 50) and dissected rings were suspended for isometric recording under physiological conditions. The effects of hydrocortisone (10(-9) - 10(-4) M), dexamethasone (10(-9) - 10(-4) M) and betamethasone (10(-9) - 10(-4) M) on umbilical artery resistance were measured in vitro.

MAIN OUTCOME MEASURES

Changes in umbilical artery resistance, in vitro.

RESULTS

Hydrocortisone (n = 12) exerted a vasodilatory effect on human umbilical artery at all concentrations studied compared with vehicle control experiments (n = 12) (P < 0.0001). The mean net relaxant effect of hydrocortisone ranged from 11.77% (10(-9) M) to 57.01% (10(-4)). Both exogenous compounds, dexamethasone (n = 12) and betamethasone (n = 12), similarly exerted a significant relaxant effect on human umbilical artery tone (P < 0.05-0.01), compared with vehicle control experiments (n = 12). The mean net relaxant effect of dexamethasone ranged from 14.43% (10(-9) M) to 38.12% (10(-4)) and that of betamethasone ranged from 6.02% (10(-9) M) to 42.30% (10(-4)), in a cumulatively increasing fashion. There was a non-significant trend towards a greater vasodilatory effect of dexamethasone than betamethasone at lower bath concentrations studied.

CONCLUSION

Corticosteroids exert a direct and potent vasodilatory effect on human umbilical artery resistance in vitro, thus providing an explanation for the previously unexplained vascular effects associated with antenatal administration of corticosteroids.

Effect of in vivo fetal infusion of dexamethasone at 0.75 GA on fetal ovine resistance artery responses to ET-1

At 110-111 days gestation, instrumented fetal sheep were administered saline or dexamethasone (2.2 microgram. kg(-1). h(-1) iv) for 48 h. Measurement of fetal blood pressure showed a greater increase in dexamethasone-treated (n = 6) compared with control (n = 5) fetuses (7.3 +/- 2.3 vs. 0.6 +/- 2.3 mmHg, P < 0.05). Fetuses were delivered by cesarean section, and the femoral muscle and brain were obtained under halothane anesthesia. Femoral and middle cerebral arteries (approximately 320-micrometer internal diameter) were evaluated using wire myography. Sensitivity to KCl (2.5-125 mM) and the magnitude of the maximal vasoconstriction to 125 mM K(+) were similar in femoral and middle cerebral arteries from dexamethasone-treated vs. control fetuses. Acetylcholine-induced vasorelaxation was similar in femoral arteries from control and dexamethasone-treated fetuses. Middle cerebral arteries did not relax to acetylcholine. Sensitivity to endothelin-1 (ET-1; 0.1 pM-0.1 microM) and magnitude of the ET-1-induced vasoconstriction were greater in femoral arteries from dexamethasone-treated vs. control fetuses (P < 0.05). Autoradiographical studies with receptor-specific ligands demonstrated increased ET(A)-receptor binding, the principal receptor subtype, in femoral muscle vessels (P < 0.001) but decreased ET(A)-receptor binding in middle cerebral arteries (P < 0.01) from dexamethasone-treated compared with control fetuses. Relatively little ET(B)-receptor binding was evident in all tissues examined. We conclude that hyperreactivity to ET-1, due to increased ET(A)-receptor binding, may be involved in the dexamethasone-induced increase in peripheral vascular resistance in fetal sheep in vivo.

Role of endothelin-1/endothelin receptor system in endotoxic shock rats

Endothelin (ET)-1, a potent vasoconstrictor peptide derived from the endothelium, is markedly increased in endotoxic shock, although the pathophysiological role of ET-1 under septic conditions remains obscure. To delineate the role of ET-1 and its receptor subtype in endotoxic shock, we here attempted to determine the changes of circulating levels of ET-1 and its biosynthetic intermediate big ET-1 in endotoxic shock rats, to evaluate the gene expression of ET-1 as well as the ET-1 receptor subtypes (ETA and ETB) in the heart, lung and liver, and to study the effects of ET receptor antagonists on systemic arterial blood pressure, heart rate and survival rate. Administration of bacterial lipopolysaccharide (LPS) caused profound hypotension, increased heart rate and death, and these effects were blocked by a nonselective ETA/ETB receptor antagonist (TAK044), but not by an ETA selective antagonist (BQ123). Administration of exogenous ET-1 caused a profound pressor response in control rats, but not in the LPS-pretreated rats. Injection of LPS caused marked elevation of plasma levels of both ET-1 and big ET-1, which were not affected by treatment with either ET receptor antagonist. Administration of LPS caused up-regulation of ET-1 and ETB receptor mRNA in the heart, whereas ETA receptor mRNA was markedly down-regulated in the heart, lung and liver. These data suggest differential gene regulation of ET-1 and its receptor subtypes in various organs from endotoxic shock rats, and that nonselective ETA/ETB receptor antagonist, but not ETA receptor antagonist, ameliorates endotoxin-induced hypotension and death.

Differential regulation of endothelin secretion and endothelin receptor mRNA levels in JAR, JEG-3, and BeWo choriocarcinoma cell lines and in human trophoblasts, their nonmalignant counterpart

Endothelin (ET) secretion and expression of both ET-A and ET-B receptor subtypes have been found in a number of primary cancers. The present study tested (1) whether choriocarcinoma cells and their nonmalignant counterpart, the trophoblast, secrete ET-1 and express ET-A and ET-B receptors; (2) whether ET-1 secretion and receptor mRNA levels are regulated by the same factors in nonvascular tissues as in vascular tissues; and (3) whether such regulation is similar in malignant and nonmalignant cells. All cells secreted ET-1 in similar amounts (approximately 0.8 fmol/10(6) cells per 24 h) and secretion was unaffected by culture and treatment. Whereas ET-B accounted for almost all (>98%) ET receptor transcripts in the choriocarcinoma cells, the trophoblasts expressed about 20% ET-A receptor mRNA. During control cultures, ET-B mRNA levels rose in choriocarcinoma, with the greatest relative increase (6-fold; P < 0.05 vs 0 h) in BeWo, whereas in trophoblasts, ET-A mRNA transiently changed after 24 and 48 h. Treatment with dexamethasone and glucose did not alter the mRNA levels in all cells. Insulin induced changes (P < 0.05) in ET-B mRNA levels in BeWo (+90 and +60% after 24 and 48 h, respectively) and JEG-3 (-70%), but not in JAR and trophoblast cells. We conclude that malignant transformation affects the responsiveness of the endothelin receptor system to external stimuli and that the regulation of the endothelin system differs in vascular and nonvascular tissues.

Effect of CGS 26303, an endothelin-converting enzyme-neutral endopeptidase inhibitor, on nitrofen-induced congenital diaphragmatic hernia in the rat

BACKGROUND/PURPOSE

The pathophysiology of congenital diaphragmatic hernia (CDH) associated with lung hypoplasia and pulmonary hypertension is not understood fully. Endothelins (ETs) are the most potent vasoconstrictors that also act as promitogenic agents. They may play a role during pregnancy in leading to the condition found at birth and ongoing mortality in CDH. Therefore, the authors studied the effect of CGS 26303, a nonselective endothelin-converting enzyme and neutral endopeptidase inhibitor, in the rat model of CDH.

METHODS

Pregnant Sprague-Dawley rats were divided into 3 groups: group 1 (n = 4) received CGS 26303 (50 mg/kg, subcutaneously, twice a day), from gestational day 12 until term (21 to 23 days); group 2 (n = 8) received nitrofen (100 mg/kg, orally) at gestational day 11.5; group 3 (n = 8) received both nitrofen and CGS 26303. The survival of the newborn rats was monitored up to 240 minutes. After natural death or euthanasia, they were weighed and microdissected. The degree of hernia was quantified as small, moderate, or severe, and lungs and liver were harvested and weighed.

RESULTS

Newborn rats from mothers of group 3 (n = 81) survived 196 +/- 8 minutes compared with 173 +/- 9 minutes of those of group 2 (n = 97). Severe CDH from group 3 (n = 20) had a mean survival time of 66 +/- 13 minutes compared with 26 +/- 4 minutes for those of group 2 (n = 27). Lung index in severe CDH pups of group 3 was increased by 13% compared with those from group 2 (P < .0001), whereas their liver index went down by 8% (P < .05).

CONCLUSIONS

These results suggest that CGS 26303 might have a beneficial effect when given during pregnancy in increasing survival at birth and reducing the severity of the pulmonary hypoplasia in newborn rats with nitrofen-induced CDH.

Endothelins and the lung

Since endothelins were discovered by Yanasigawa in 1988 it has been recognised that they may have an important role in lung pathophysiology. Despite their biological importance as vasoconstrictors the physiological role of endothelin has not yet been defined within the lungs. This review explores their role in acute and chronic disease. During acute inflammation and ischaemia-reperfusion injury cytokines may induce release of endothelin. This is important in the realm of acute lung injury and during surgical procedures such as cardiopulmonary operations including lung resections and transplantation. Complications of surgery including primary organ failure resulting in poor gas exchange as well as increased pulmonary vascular resistance have been linked to the presence of excessive endothelin. Endothelin may have an important role in transplantation biology. The complex process leading to successful lung transplantation includes optimising the donor with brain death, harvesting the lungs, managing acute and chronic rejection, and protecting the vital organs from toxic effects of immunosuppressants. During chronic disease processes, the mitotic action of endothelin may be important in vascular and airway remodelling by means of smooth muscle cell proliferation. We also explore recent advances in drug development, animal models and future directions for research.

Pneumadin-evoked intracellular free Ca2+ responses in rat aortic smooth muscle cells: effect of dexamethasone

The direct vascular effect of pneumadin (PN) was determined by studying the changes in intracellular free calcium ([Ca2+]i) levels in cultured rat aortic smooth muscle cells maintained between the second and fifth passages. PN evoked a rapid, concentration-dependent, biphasic increase in [Ca2+]i. The [Ca2+]i level rose from a basal value of 108 nM to a maximum increase in peak value of 170 nM. Although the level of maximal [Ca2+]i response evoked by PN was less than with other vasoactive agonists, it was more potent (EC50 0.5 nM) than even endothelin-1 (EC50 3.1 nM). At concentrations > 100 nM, [Ca2+]i elevations induced by PN above basal levels were no longer observed. Pretreatment with dexamethasone (100 nM for 24 hr) resulted in a significant increase (P < 0.01) in the peak [Ca2+]i response (310 nM) to PN. However, the biphasic pattern in the peak [Ca2+]i responses encountered with increasing concentrations of PN remained unaffected. The exaggerated [Ca2+]i response to PN was abolished by preincubation of cells with either the glucocorticoid antagonist mifepristone (RU 486) or the protein synthesis inhibitor cycloheximide. Inclusion of either an AT1 antagonist (losartan), a V1 selective vasopressin antagonist (d(Ch2)5 Tyr (Me) AVP), or an alpha-adrenoceptor antagonist (phentolamine) failed to affect the increases in [Ca2+]i induced by PN. PN-evoked increases in inositol 1,4,5-trisphosphate levels paralleled the [Ca2+]i changes. These data suggest that PN increases Ca2+ mobilization in rat aortic smooth muscle cells via activation of phospholipase C coupled receptors. This effect is up-regulated by dexamethasone.

Gene expression of the renal endothelin system in renal transplant recipients on cyclosporine A based immunosuppression

BACKGROUND

Immunosuppressive therapy based on cyclosporine A (CsA) is potentially nephrotoxic, and each dose of CsA is followed by a transient increase in plasma endothelin (ET)-1. The aim of this study was to investigate the effect of CsA based immunosuppressive therapy on renal gene expression of the ET(A) and ET(B) receptor subtypes and preproET-1 in human transplant needle biopsies.

METHODS

Twelve living donor renal transplant recipients, median age 51.5 years (range 24-63 years) were included in the study. Immunosuppressive therapy consisted of CsA, azathioprine, and prednisolone. Baseline renal cortical needle biopsies from the living donor kidneys were obtained just before nephrectomy. Follow-up biopsies were obtained from the same transplanted kidneys after 2-6 weeks of immunosuppressive therapy. We used a quantitative, competitive reverse transcriptase polymerase chain reaction assay to measure renal ET(A) and ET(B) receptor subtype mRNAs as well as preproET-1 mRNA levels in each of the biopsies.

RESULTS

The renal ET system was not significantly altered by CsA-based immunosuppressive therapy. Median ET(A) mRNA level was 185 (range 35-244) at baseline, and 120 (11-189) amol/microg total RNA after CsA based immunosuppressive therapy (P=0.11). ET(B) mRNA level was 506 (209-1411) at baseline, and 463 (267-1609) amol/microg total RNA at follow-up (P=0.44) and preproET-1 mRNA level was 160 (112-392) before and 221 (187-361) amol/microg total RNA after immunosuppressive therapy based on CsA (P=0.58).

CONCLUSION

This study indicates that 2-6 weeks of CsA-based immunosuppression neither significantly influences renal gene expression of the ET(A) or ET(B) receptor subtypes nor preproET-1 in living donor renal transplant kidneys.

Pathophysiology of endothelin in the cardiovascular system

In this article, we review the basic pharmacological and biochemical features of endothelin and the pathophysiological roles of endothelin in cardiovascular diseases. Development of receptor antagonists has accelerated the pace of investigations into the pathophysiological roles of endogenous endothelin-1 in various diseases, e.g. chronic heart failure, renal diseases, hypertension, cerebral vasospasm, and pulmonary hypertension. In chronic heart failure, the expression of endothelin-1 and its receptors in cardiomyocytes is increased, and treatment with an endothelin receptor antagonist improves survival and cardiac function. Endothelin receptor antagonists also improve other cardiovascular diseases. These results suggest that the interference with endothelin pathway either by receptor blockade or by inhibition of endothelin converting enzyme may provide novel therapeutic drugs strategies for multiple disease states.

Appearance of contractile endothelin-B receptors in rat mesenteric arterial segments following organ culture

The aim of this study was to examine how different procedures for organ culture affect the expression of contractile endothelin(ET)-B receptors in a branch of the rat mesenteric artery. In fresh segments, ET-1 and ET-3 induced similar strong contractions, ET-1 being 20-fold more potent, whereas neither of the selective ETB receptor agonists, sarafotoxin 6c (S6c) nor IRL 1620, induced significant contractions. In segments cultured for 1 day, ET-3 was only 3-fold less potent as ET-1, and S6c and IRL 1620 induced concentration-dependent contractions which were about 60% of the ET-1 induced contraction. The maximum contractile response to S6c was not altered in segments cultured with foetal calf serum or in buffer solution, but was reduced to about 20% of the control value when cultured in glucose-free buffer solution. The contraction to S6c was abolished in segments placed in cold (4 degrees C) buffer solution. Removal of the endothelium had no effect on the S6c-induced contractions. Arteries cultured at isometric tension (at 2 mN) for 1 day achieved the same contractile response for ETB agonists as resting segments. Pressurized arteries (60 mmHg) did not constrict to S6c when mounted as a fresh segment but demonstrated a strong contraction after 1 day at this transmural pressure. This study suggests that the appearance of ETB receptor mediated contraction following organ culture is not dependent on specific nutrients, endothelial factors or absence of intrinsic tension, but is a metabolically active process.

Endothelin receptor mRNAs in human fetal membranes, chorionic vessels, and decidua parietalis

Endothelin-1 (ET-1) is synthesized in avascular human amnion; and, immunoreactive ET-1 is present in amniotic fluid in concentrations 10 to 100 times those in blood. ET-1 acts, most commonly, in a local or paracrine manner; therefore, it is possible that amnion/amniotic fluid ET-1 acts on contiguous tissues, namely chorion laeve or placental surface (chorionic) vessels, or in an autocrine fashion on amnion cells. To address these possibilities, the levels of ET(A) and ET(B) receptor mRNAs were evaluated in amnion, chorion laeve, decidua parietalis, placenta, and chorionic vessel tissues. By Northern analysis of total RNA (20 microg), ET(A) and ET(B) receptor mRNAs were detected in decidua (n = 18), placenta (n = 14), and chorionic vessels (n = 13). In chorion laeve (n = 24), ET(B) receptor mRNA but not ET(A) receptor mRNA was detected by Northern analysis of total RNA. Northern analysis of chorion laeve poly(A)+ mRNA (1.5-2.5 microg) revealed ET(A) receptor mRNA at low levels. Neither ET(A) nor ET(B) receptor mRNAs were detected in amnion tissue by Northern analysis of total RNA (n = 30; placental and reflected amnion from 15 pregnancies) or by Northern analysis of poly(A)+ mRNA (1.5-2.5 microg). Moreover, there was no demonstrable dose-dependent effect of ET-1 on prostaglandin E2 production or DNA synthesis in amnion epithelial cells in primary culture. The findings of this investigation are indicative that ET-1 in amniotic fluid or secreted from amnion may act in a paracrine fashion on chorion laeve by way of the ET(B) receptor and on chorionic vessels by way of ET(A) and ET(B) receptors.

Molecular pharmacology and pathophysiological significance of endothelin

Since the discovery of the most potent vasoconstrictor peptide, endothelin, in 1988, explosive investigations have rapidly clarified much of the basic pharmacological, biochemical and molecular biological features of endothelin, including the presence and structure of isopeptides and their genes (endothelin-1, -2 and -3), regulation of gene expression, intracellular processing, specific endothelin converting enzyme (ECE), receptor subtypes (ETA and ETB), intracellular signal transduction following receptor activation, etc. ECE was recently cloned, and its structure was shown to be a single transmembrane protein with a short intracellular N-terminal and a long extracellular C-terminal that contains the catalytic domain and numerous N-glycosylation sites. In addition to acute contractile or secretory actions, endothelin has been shown to exert long-term proliferative actions on many cell types. In this case, intracellular signal transduction appears to converge to activation of mitogen-activated protein kinase. As a recent dramatic advance, a number of non-peptide and orally active receptor antagonists have been developed. They, as well as current peptide antagonists, markedly accelerated the pace of investigations into the true pathophysiological roles of endogenous endothelin-1 in mature animals; e.g., hypertension, pulmonary hypertension, acute renal failure, cerebral vasospasm, vascular thickening, cardiac hypertrophy, chronic heart failure, etc. Thus, the interference with the endothelin pathway by either ECE-inhibition or receptor blockade may provide an exciting prospect for the development of novel therapeutic drugs.

Regulation of histamine H1 receptor coupling by dexamethasone in human cultured airway smooth muscle

1. The regulation of histamine-induced [3H]-inositol phosphate and intracellular calcium responses in human cultured airway smooth muscle cells was studied. 2. Histamine induced concentration-dependent [3H]-inositol phosphate formation (EC50 4 microM). This response was inhibited by a range of selective H1 receptor antagonists but not by the H2-selective antagonist, tiotidone or the H3 receptor-selective antagonist, thioperamide, indicating that an H1 receptor is involved in this response in human cultured airway smooth muscle cells. 3. Preincubation of human cultured airway smooth muscle cells with concentrations of dexamethasone > 10 nM for 22 h produced concentration-dependent inhibition of histamine-induced inositol phosphate formation. The maximum inhibition observed was 45% of the response in control cells. The inhibitory effect of dexamethasone was itself reversed by prior exposure to the glucocorticoid receptor antagonist, RU38486 (10 microM). Preincubation for 22 h with 1 microM dexamethasone produced inhibition of the inositol phosphate response to histamine to all concentrations of histamine inducing significant inositol phosphate formation in these cells. In contrast, the response to the G protein activator, NaF (0.1-20 mM) was unaltered by preincubation with dexamethasone. 4. Preincubation of human airway smooth muscle cells with 1 microM dexamethasone for time periods of < 6 h failed to inhibit histamine-induced inositol phosphate formation in human airway smooth muscle cells. 5. Histamine also induced concentration-dependent elevation of intracellular calcium levels in Fura 2-loaded human airway smooth muscle cells. This response was inhibited by preincubation with 1 microM dexamethasone. 6. We conclude that signal transduction through the H1 receptor in human airway smooth muscle is subject to regulation by dexamethasone and that this may in part account for the protective effect of dexamethasone against spasmogen-induced contractile responses in the airways.

Endothelin in organ transplantation

Solid organ allografts are often compromised by ischemia, acute rejection episodes associated with hemodynamic changes, and chronic rejection typically characterized by the development of obliterative vasculopathy, and in the case of the kidney, and glomerulosclerosis. Recent in vivo data indicate that endothelin (ET) production is locally upregulated in rejecting allografts, and that, in addition to endothelial cells, ET is also produced by graft-infiltrating mononuclear cells (monocytes/macrophages). In vitro data also indicate that ET production is regulated, at least in part, by certain T cell-and monocyte/macrophage-derived cytokines, which are abundant in rejecting allografts. These data and the findings of elevated plasma levels of ET after transplantation (in particular during rejection processes), the effects of immunosuppressive drugs (cyclosporine and tacrolimus in particular) on ET production, and the profound vasoconstrictive and mitogenic properties of this peptide suggest that endothelin may be involved in the initiation and propagation of posttransplantation complications; including systemic hypertension, acute allograft dysfunction, and perhaps most importantly, chronic allograft dysfunction. These observations provide the rational to use ET receptor antagonists to formally address the potential role of ET in these processes, and to develop therapeutic strategies that ameliorate or possibly prevent these complications.

Dexamethasone down-regulates the expression of endothelin B receptor mRNA in the rat brain

The present study was designed to examine effects of dexamethasone on the steady state level of endothelin B(ETB) receptor mRNA in in vivo the rat brain. ETB receptor mRNA was very high at the hypothalamus and cerebellum but was comparatively low at the striatum and amygdala. Dexamethasone, 1 and 7 mg/kg, i.p., markedly and dose-relatedly decreased ETB receptor mRNA level with slow onset of 8hr at the hypothalamus and cerebellum, but did not induced a marked decrease at other areas. On the contrary, dexamethasone produced an increase of ET-1 mRNA which preceded to the decrease of ETB receptor mRNA at the same brain areas. Phosphoramidon, a endothelin-converting enzyme inhibitor, did not antagonized but potentiated the effect of dexamethasone. Besides, phosphoramidon per se markedly stimulated the expression of ET-1 mRNA. The results suggested that dexamethasone down-regulates ETB receptor mRNA level at the hypothalamus and cerebellum of rat brain and these effects may be involved in the increase of ET-1 peptide gene transcription.

Regulation of alpha 2-adrenergic receptor expression and signaling in pancreatic beta-cells

Activation of alpha 2-adrenergic receptors (alpha 2-AR) in pancreatic beta-cells inhibits insulin secretion in response to various stimuli, and acute or long-term regulation of alpha 2-AR receptor-mediated effects may influence the tissue response to glucose dishomeostasis. As an initial approach to this issue, we determined the effect of various metabolic and hormonal treatments on alpha 2-AR expression and coupling in the pancreatic beta-cell lines HIT-T15 and RIN-5AH. Radioligand binding studies ([3H]RX-821002) and RNA blot analysis indicate that both pancreatic beta-cell lines express the alpha 2A/D-AR subtype [for HIT-T15 the maximum binding (Bmax) = 113 +/- 28; for RIN-5AH Bmax = 93 +/- 18 fmol/mg of cellular protein]. Treatment of HIT-T15 or RIN-5AH cells with glucocorticoids [dexamethasone, hydrocortisone, or prednisolone (1 microM)] increased alpha 2-AR mRNA level and receptor protein density three- to fivefold. The glucocorticoid-induced increase in receptor density in HIT-T15 cells was associated with 1) an increase in the amount of receptors coupled to G protein as determined by analysis of high-affinity 5'-guanylyl imidodiphosphate-sensitive binding of [3H]UK-14304, a selective alpha 2-AR agonist, and 2) a greater inhibition of forskolin-induced elevation of cellular adenosine 3',5'-cyclic monophosphate after receptor activation. Receptor density in HIT-T15 cells was not altered by different growth conditions, insulin (1 microM), phorbol 12-myristate 13-acetate (1 microM), or the sex steroids testosterone and progesterone (1 microM). These data indicate that glucocorticoids upregulate alpha 2-AR expression and signaling in pancreatic beta-cells. Such regulation may operate in a cell-specific manner, allowing discrete modulation of tissue responses to glucose dishomeostasis.

Modulation of endothelin receptor expression in human vascular smooth muscle cells by interleukin-1 beta

Endothelin may play a role in atherosclerosis as it causes smooth muscle cell proliferation and its levels are elevated in patients with atherosclerosis. We report that interleukin-1 beta is a potent inducer of endothelin receptor expression in cultured human vascular smooth muscle cells. The effect is dose- and time-dependent and is due to an increase in receptor number. Endothelin receptor mRNA levels are also elevated. Interleukin-1 beta is a major regulator of endothelin release so, together with its effects on endothelin receptors, it may be responsible for a generalized activation of the endothelin system in diseased vessels.

Glucocorticoids but not mineralocorticoids modulate endothelin-1 and angiotensin II binding in SHR vascular smooth muscle cells

Both glucocorticoids and mineralocorticoids are involved in circulatory homoeostasis and blood pressure control. In recent years direct effects of both steroid classes on vascular smooth muscle cells (VSMC) have been reported. We have thus examined the effects of RU 28362, a pure glucocorticoid agonist, and aldosterone, the physiologic mineralocorticoid, on the binding to VSMC from spontaneously hypertensive rats (SHR) of two key vasoactive peptides, endothelin-1 and angiotensin II. Binding of angiotensin II rose, and that of endothelin-1 declined, in a time- and dose-dependent fashion with maximal effects observed at 24 h and half-maximal effects for each at 2-3 nM RU 28362. Scatchard analysis showed that for both endothelin-1 and angiotensin II, RU 28362 alters receptor number but not affinity; competition studies with receptor-selective ligands (BQ123, S6C, DuP753 and PD123319) show that glucocorticoids specifically elevate (X2) AT-1 receptors and specifically lower (to approximately 30%) levels of ETA receptors. Treatment of VSMC with the antiglucocorticoid RU 38486 reversed the effect of glucocorticoids on endothelin-1 and angiotensin II binding, confirming the Type II (glucocorticoid) receptor mediated effect of the glucocorticoids. Aldosterone (100 nM) also lowers endothelin-1 binding and increases angiotensin II binding in VSMC; that this effect reflects aldosterone occupancy of classical glucocorticoid receptors is shown by the blockade of the aldosterone effect by an equal concentration (100 nM) of RU 38486--i.e. there is no evidence for an action of aldosterone via mineralocorticoid receptors. We interpret our results as evidence for a complex modulation of receptors for vasoactive peptides in VSMC by glucocorticoid but not mineralocorticoid hormones.

Endothelin-1 induction of cyclooxygenase-2 expression in rat mesangial cells

Prostaglandin E2 (PGE2) may be an important negative feedback modulator of endothelin-1 (ET-1)-stimulated mesangial cell proliferation and contraction. Recent studies suggest that ET-1 may induce prolonged mesangial cell PGE2 production, however the mechanism of this effect is unknown. The current study was undertaken, therefore, to examine the long-term effect of ET-1 on mesangial cell PGE2 synthesis. ET-1 markedly increased PGE2 release by rat mesangial cells for at least six hours. Cyclooxygenase (COX) activity was increased by one hour and persisted for at least six hours. ET-1 increased COX-2, but not COX-1, protein and mRNA levels. Actinomycin D reduced ET-1-stimulated PGE2 synthesis and COX-2 mRNA expression, while cycloheximide superinduced COX-2 mRNA. Dexamethasone decreased ET-1-stimulated PGE2 release and COX-2 protein and mRNA levels. ET-1-stimulated PGE2 release was prevented by BQ-123, an endothelin receptor A antagonist. We conclude that ET-1, via activation of the endothelin A receptor, causes a prolonged increase in mesangial cell PGE2 production that is partially dependent on induction of dexamethasone-inhibitable COX-2.

Glucocorticoids enhance the potency of Schwann cell mitogens

Previous studies have documented that cultured Schwann cells require serum-containing medium to respond maximally to mitogens. We now report that Schwann cells are able to proliferate to a mitogenic response in a serum-free defined medium termed oligodendrocyte defined media (ODM). Glucocorticoids are the essential component of ODM which allow Schwann cell proliferation in the serum-free medium. Charcoal treatment of the fetal calf serum decreases the mitogenic potency of the axolemma-enriched fraction (AEF) by 50%. The addition of 2 microM hydrocortisone to charcoal-treated fetal calf serum restores 75% of the lost mitogenicity. These observations are consistent with the view that glucocorticoids present in fetal calf serum are potent co-mitogens essential for AEF-induced Schwann cell proliferation. The synthetic glucocorticoid, dexamethasone, is a more potent co-mitogen than hydrocortisone, with a maximal effect at concentrations less than 10 nM. In contrast, other steroids including aldosterone, progesterone, testosterone, and 17 beta-estradiol have no effect on enhancing the mitogenic response of Schwann cells to the AEF. The glucocorticoid antagonists RU 486 and dehydroepiandrosterone (DHEA), but not the antiestrogenic compound tamoxifen, block AEF-induced Schwann cell proliferation. These results suggest that glucocorticoid-induced Schwann cell proliferation is mediated through a glucocorticoid receptor (GR) mechanism. We detected immunoreactivity to the GR in the cytoplasm, but not in the nuclei of Schwann cells grown in ODM lacking dexamethasone. The addition of 100 nM dexamethasone to these cultures resulted in immunoreactivity in the nucleus. This data suggests that glucocorticoids working through the GR are potent co-mitogens for Schwann cell proliferation.

C-type natriuretic peptide upregulates vascular endothelin type B receptors

Cultured rat vascular smooth muscle cells (VSMCs) possess receptors for potent vasoconstrictor endothelin-1 (ET-1) as well as potent vasodilator natriuretic peptides (atrial, brain, and C-type natriuretic peptides [ANP, BNP, and CNP, respectively]). However, little is known about molecular interactions between endothelin receptors and natriuretic peptides in VSMCs. To elucidate whether natriuretic peptides regulate vascular endothelin receptors, we studied the effects of three natriuretic peptides on the capacity of 125I-ET-1 binding and expression of endothelin type A (ETA) and type B (ETB) receptor mRNAs in cultured rat VSMCs. CNP (10(-6) mol/L) increased 125I-ET-1 binding capacity in a time-dependent manner (6 to 48 hours) and stimulated cyclic GMP (cGMP) generation in a dose-dependent manner (10(-8)) to 10(-6) mol/L). Pretreatment with CNP (10(-8) to 10(-6) mol/L) and 8-bromo-cGMP (10(-5) to 10(-3) mol/L) for 24 hours resulted in dose-dependent increases in 125I-ET-1 binding in VSMCs. The three natriuretic peptides at the highest concentration (10(-6) mol/L) increased 125I-ET-1 binding and stimulated cGMP generation with almost the same rank order of efficacy (CNP > BNP > ANP). Scatchard analysis of binding studies revealed that CNP (10(-6) mol/L) and 8-bromo-cGMP (10(-3) mol/L) increased vascular endothelin receptor number by 28% and 88%, respectively, without changing its affinity. Pretreatment with both CNP and 8-bromo-cGMP increased ET-1-stimulated inositol 1,4,5-trisphosphate formation.(ABSTRACT TRUNCATED AT 250 WORDS)

Vasoconstrictive peptides induce endothelin-1 and prostanoids in human cerebromicrovascular endothelium

Vasoconstrictive peptides and prostanoids have been implicated in the pathogenesis of hypertension and vasospasm. Recently, we have shown that human cerebromicrovascular endothelium [human brain endothelial cells (HBEC)] constitutively produces both endothelin-1 (ET-1) and prostanoids. The vasoactive peptides, arginine vasopressin (AVP) or angiotensin II (ANG II), stimulated secretion of both immunoreactive ET-1 and prostanoids from HBEC by a receptor-mediated induction of phospholipase C (PLC) and PLA2. The release of constitutive or AVP- or ANG II-induced ET-1 occurred at different rates during the 24-h incubation of HBEC in serum-free medium. The temporal profile of AVP-stimulated production of prostanoids differed from that of ANG II. AVP-induced release of prostaglandin D2 (PGD2) persisted for 24 h, whereas ANG II-stimulated PGD2 was only seen during the first 4 h of incubation. ANG II maximally stimulated PGI2 secretion during the 4- to 8-h interval, whereas AVP did not stimulate PGI2 secretion. Dexamethasone (Dxm), indomethacin (Indo), and nordihydroguaiaretic acid, the respective inhibitors of PLA2-cyclooxygenase II, cyclooxygenase, and lipoxygenase, increased both constitutive and AVP- or ANG II-stimulated secretion of ET-1. Dxm also decreased AVP- or ANG II-stimulated production of PGD2 and PGF2 alpha. These results indicate an interrelationship between HBEC production of ET-1 and prostanoids, which may play a role in regulating cerebral microcirculation.