Endothelin: 30 Years From Discovery to Therapy

Discovered in 1987 as a potent endothelial cell-derived vasoconstrictor peptide, endothelin-1 (ET-1), the predominant member of the endothelin peptide family, is now recognized as a multifunctional peptide with cytokine-like activity contributing to almost all aspects of physiology and cell function. More than 30 000 scientific articles on endothelin were published over the past 3 decades, leading to the development and subsequent regulatory approval of a new class of therapeutics-the endothelin receptor antagonists (ERAs). This article reviews the history of the discovery of endothelin and its role in genetics, physiology, and disease. Here, we summarize the main clinical trials using ERAs and discuss the role of endothelin in cardiovascular diseases such as arterial hypertension, preecclampsia, coronary atherosclerosis, myocardial infarction in the absence of obstructive coronary artery disease (MINOCA) caused by spontaneous coronary artery dissection (SCAD), Takotsubo syndrome, and heart failure. We also discuss how endothelins contributes to diabetic kidney disease and focal segmental glomerulosclerosis, pulmonary arterial hypertension, as well as cancer, immune disorders, and allograft rejection (which all involve ET_A autoantibodies), and neurological diseases. The application of ERAs, dual endothelin receptor/angiotensin receptor antagonists (DARAs), selective ET_B agonists, novel biologics such as receptor-targeting antibodies, or immunization against ET_A receptors holds the potential to slow the progression or even reverse chronic noncommunicable diseases. Future clinical studies will show whether targeting endothelin receptors can prevent or reduce disability from disease and improve clinical outcome, quality of life, and survival in patients.

UVB Stimulates the Expression of Endothelin B Receptor in Human Melanocytes via a Sequential Activation of the p38/MSK1/CREB/MITF Pathway Which Can Be Interrupted by a French Maritime Pine Bark Extract through a Direct Inactivation of MSK1

Melanogenesis is the physiological process by which melanin is synthesized to protect the skin from UV damage. While paracrine interactions between keratinocytes and melanocytes are crucial for regulating epidermal pigmentation, the endothelin (EDN)-endothelin B-receptor (EDNRB) interaction is one of the key linkages. In this study, we found that a single exposure of normal human melanocytes (NHMs) with UVB stimulates the expression of EDNRB and its upstream transcription factor microphthalmia-associated transcription factor (MITF) at the transcriptional and translational levels. That stimulation can be abrogated by post-irradiation treatment with a French maritime pine bark extract (PBE). UVB stimulated the phosphorylation of p38 and c-jun N-terminal kinase (JNK), but not ERK, followed by the increased phosphorylation of MSK1 and CREB. The post-irradiation treatment with PBE did not affect the increased phosphorylation of p38 and JNK, but distinctly abrogated the phosphorylation of MSK1 and CREB. Post-irradiation treatment with the MSK1 inhibitor H89 significantly down-regulated the increased gene expression of MITF and EDNRB in UVB-exposed NHMs. Our findings indicate for the first time that the increased expression of MITF that leads to the up-regulation of melanocyte-specific proteins in UVB-exposed NHMs is mediated via activation of the p38/MSK1/CREB pathway but not the ERK/RSK/CREB pathway. The mode of action by PBE demonstrates that interrupting MSK1 activation is a new target for antioxidants including PBE which can serve as anti-pigmenting agents in a reactive oxygen species-depletion-independent manner.

Modulation of Calcium Signaling of Angiotensin AT1, Endothelin ETA, and ETB Receptors by Silibinin, Quercetin, Crocin, Diallyl Sulfides, and Ginsenoside Rb1

Angiotensin II and endothelin-1 are potent vasoconstrictive peptides that play a central role in blood pressure regulation. Both peptides exert their pleiotropic effects via binding to their respective G-protein-coupled receptors, i.e., angiotensin AT1 and endothelin type A and type B receptors. In the present study, we have selected six structurally different plant-derived compounds with known cardioprotective properties to evaluate their ability to modulate calcium signaling of the above-mentioned receptors. For this purpose, we used and validated a cellular luminescence-based read-out system in which we measured intracellular calcium signaling in Chinese hamster ovary cells that express the calcium sensitive apo-aequorin protein. Firstly, silibinin, a flavanolignan that occurs in milk thistle (Silybum marianum), was investigated and found to be an antagonist for the human angiotensin AT1 receptor with an affinity constant of about 9 µM, while it had no effect on endothelin type A or type B receptor activation. Quercetin and crocin partially impeded intracellular calcium signaling resulting in a non-receptor-related reduction of the responses recorded for the three investigated G-protein-coupled receptors. Two organosulfur compounds, diallyl disulfide and diallyl trisulfide, as well as the triterpene saponin ginsenoside Rb1 did not affect the activation of the angiotensin AT1 and endothelin type A and type B receptors. In conclusion, we were able, by using a nonradioactive cellular read-out system, to identify a novel pharmacological property of the flavanolignan silibinin.

[Effects of propofol pretreatment on endothelin in oleic acid-induced acute lung injury]

INTRODUCTION

Acute lung injury (ALI) is a pathological condition characterized by injury in the alveolar-capillary membrane that triggers local and systemic inflammation. Endothelin (ET) is a protein that regulates immune response and constricts blood vessels; when it is over-expressed, it may contribute to high blood pressure and lung injury. This work tries to determine if propofol may decrease hemodynamic, gasometric, microscopic, ET-1 plasmatic concentration, and immuno-histochemical alterations in an experimental model of oleic acid-induced acute lung injury. MATERIALS AND METHODS. Animals were classified into three groups (n = 6): group I was the control group; in group II, there was oleic acid-induced ALI with no treatment, and group III with propofol pre-treatment and oleic acid-induced ALI.

RESULTS

All animals survived until the end of the study, and 100% of group II and group III developed ALI, with hemodynamic, gasometric and gravimetric alterations. However, group III showed less inflammatory infiltration and lower ET-1 expression in lung tissue.

CONCLUSIONS

Pretreatment with propofol in a canine model of OA-induced ALI indicates that the drug has anti-inflammatory action, with a potential therapeutic role against progression of anti-inflammation and lung damage.

Endothelium-dependent contractions and endothelial dysfunction in human hypertension

The endothelium is a crucial regulator of vascular physiology, producing in healthy conditions several substances with a potent antiatherosclerotic properties. Accordingly, the presence of endothelial dysfunction is associated with subclinical atherosclerosis and with an increased future risk of cardiovascular events. A large body of evidence supports the fundamental role of nitric oxide (NO) as the main endothelium-derived relaxing factor. However, in the presence of pathological conditions, such as hypertension, endothelial cells, in response to a number of agents and physical stimuli, become also a source of endothelium-derived contracting factors (EDCFs), including endothelins and angiotensin II and particularly cyclooxygenase-derived prostanoids and superoxide anions. These latter were at first identified as responsible for impaired endothelium-dependent vasodilation in patients with essential hypertension. However, cyclooxygenase-dependent EDCFs production is characteristic of the aging process, and essential hypertension seems to only anticipate the phenomenon. It is worth noting that both in aging and hypertension EDCF production is associated with a parallel decrease in NO availability, suggesting that this substance could be oxygen free radicals themselves. Accordingly, in hypertension both indomethacin, a cyclooxygenase inhibitor, and vitamin C, an antioxidant, increase the vasodilation to acetylcholine by restoring NO availability. In conclusion, hypertension is characterized by a decline in endothelial function, associated with a progressive decrease in NO bioavailability and increase in the production of EDCF. The mechanisms that regulate the balance between NO and EDCF, and the processes transforming the endothelium from a protective organ to a source of vasoconstrictor, proaggregatory and promitogenic mediators remain to be determined.

The peroxisome proliferator-activated receptor-gamma agonist pioglitazone represses inflammation in a peroxisome proliferator-activated receptor-alpha-dependent manner in vitro and in vivo in mice

OBJECTIVES

Our aim was to investigate if the peroxisome proliferator-activated receptor (PPAR)-gamma agonist pioglitazone modulates inflammation through PPARalpha mechanisms.

BACKGROUND

The thiazolidinediones (TZDs) pioglitazone and rosiglitazone are insulin-sensitizing PPARgamma agonists used to treat type 2 diabetes (T2DM). Despite evidence for TZDs limiting inflammation and atherosclerosis, questions exist regarding differential responses to TZDs. In a double-blinded, placebo-controlled 16-week trial among recently diagnosed T2DM subjects (n = 34), pioglitazone-treated subjects manifested lower triglycerides and lacked the increase in soluble vascular cell adhesion molecules (sVCAM)-1 evident in the placebo group. Previously we reported PPARalpha but not PPARgamma agonists could repress VCAM-1 expression. Since both triglyceride-lowering and VCAM-1 repression characterize PPARalpha activation, we studied pioglitazone's effects via PPARalpha.

METHODS

Pioglitazone effects on known PPARalpha responses--ligand binding domain activation and PPARalpha target gene expression--were tested in vitro and in vivo, including in wild-type and PPARalpha-deficient cells and mice, and compared with the effects of other PPARgamma (rosiglitazone) and PPARalpha (WY14643) agonists.

RESULTS

Pioglitazone repressed endothelial TNFalpha-induced VCAM-1 messenger ribonucleic acid expression and promoter activity, and induced hepatic IkappaBalpha in a manner dependent on both pioglitazone exposure and PPARalpha expression. Pioglitazone also activated the PPARalpha ligand binding domain and induced PPARalpha target gene expression, with in vitro effects that were most pronounced in endothelial cells. In vivo, pioglitazone administration modulated sVCAM-1 levels and IkappaBalpha expression in wild-type but not PPARalpha-deficient mice.

CONCLUSIONS

Pioglitazone regulates inflammatory target genes in hepatic (IkappaBalpha) and endothelial (VCAM-1) settings in a PPARalpha-dependent manner. These data offer novel mechanisms that may underlie distinct TZD responses.

Cardioprotective effect of salvianolic acid B on large myocardial infarction mediated by reversing upregulation of leptin, endothelin pathways, and abnormal expression of SERCA2a, phospholamban in rats

AIM

To study the cardioprotective effect of salvianolic acid B (Sal B) on cardiac dysfunction. We hypothesized that hyperleptinemia may correlate with abnormal expression of sarco/endoplasmic reticulum ATPase 2a (SERCA2a), phospholamban (PLB) and endothelin-reactive oxygen species (ET-ROS) pathways in rats with large myocardial infarction (MI).

METHODS

Large MI was produced by coronary artery ligation for 4 weeks in rats. The rats were divided into four groups: sham, MI, MI+l-Sal B (50 mg/(kg d)), p.o. for 4 weeks), and MI+h-Sal B (100 mg/(kg d)), p.o. for 4 weeks).

RESULTS

In MI rats, hemodynamic and echocardiographic abnormalities, cardiac remodeling, and histological changes with features of cardiac failure were associated with hyperleptinemia accompanied by oxidative stress and upregulated OB-Rb, ET pathway mRNA expression and downregulated SERCA2a and PLB mRNA and protein expressions in the myocardium.

CONCLUSIONS

The studies demonstrated that an activated leptin pathway correlated with abnormal expression of SERCA2a, PLB and an activated ET-ROS system in the affected myocardium. Sal B exerts beneficial actions on cardiac function in rats with large MI, mainly suppressing upregulation of leptin and ET pathways and oxidative stress, and recovering the normal expressions of SERCA2a and PLB in myocardium.

Effect of lifestyle and/or statin treatment on soluble markers of atherosclerosis in hypertensives

OBJECTIVES

To investigate the independent and combined effects of lifestyle changes and statin treatment on soluble markers of atherosclerotic activity.

DESIGN

The study was a randomised, 2 x 2 factorial 1 year intervention trial. Participants (n=177) were sedentary, drug-treated, hypertensive men (aged 40-74 years). They were randomised to placebo, lifestyle intervention (diet and physical activity), fluvastatin 40 mg, or the combination of lifestyle and fluvastatin.

RESULTS

Lifestyle intervention significantly reduced intercellular adhesion molecule-1 (sICAM-1) compared to usual care (p=0.003). Thrombomodulin level remained higher among individuals receiving lifestyle intervention (p=0.025). sICAM-1 was less reduced among fluvastatin treated participants compared to the placebo treated (p=0.029). Changes of blood pressure, weight or waist circumference were not significantly different between treatment groups. Individuals who achieved improvement of classical risk factors also had a significant reduction of endothelial markers (E-selectin, von Willebrands factor, tissue plasminogen activator antigen).

CONCLUSIONS

One year of lifestyle intervention reduced the level of sICAM-1 in sedentary, drug-treated hypertensives, in spite of no impact on traditional risk factors. Low dose fluvastatin had no beneficial effect on the measured markers.

A retrospective study of bosentan in pulmonary arterial hypertension associated with congenital heart disease

BACKGROUND

Pulmonary Arterial Hypertension (PAH) plays a significant role in morbidity and mortality of patients with congenital heart disease (CHD). Bosentan, a dual endothelin receptor antagonist has been approved for PAH patients with Eisenmenger physiology (EP). The authors retrospectively reviewed the efficacy and safety of bosentan in Thai PAH patients associated with CHD.

MATERIAL AND METHOD

The study population was obtained from the databases of the CHD patients at Siriraj Hospital from October 2004 to April 2007 who received 6 months of bosentan treatment. Inclusion criteria are: CHD with Eisenmenger physiology (EP) or those with severe PAH after surgical repair or interventional cardiac catheterization. Clinical characteristics including the 6-- minute walk test (6MWT) distances, oxygen saturation (O2 sat), New York Heart Association (NYHA) functional class, and right ventricular systolic pressure (RVSP) at baseline were compared with those at 1, 3, and 6 months post bosentan treatment. Signs and symptoms of adverse events were also recorded.

RESULTS

There were 11 patients from among those who fitted the inclusion criteria and whose records were examined. Their average age was 51.1 +/- 10.1 years old (13-61 years old). Patients were divided into 2 groups; Group A (6 patients) was PAH with EP and Group B (5 patients) was PAH post intervention. In group A, the 6MWT increased from 151 +/- 69 meters to 293 +/- 61 meters (p = 0.001) with the average increase of 38 +/- 61 meters. The 2O sat increased from 83 +/- 12.7% to 91.8 +/- 5.6% (p = 0.038) with an average increase of 1.4 +/- 0.07%. There was no significant change in right ventricular systolic pressure (RVSP). In group B, there was a trend in 6MWT improvement from 274 +/- 69 meters to 312 +/- 38 meters but this was not statistically different. There were improvements in the NYHA functional class in both groups. There was no significant increase in serum aminotransferase at the end of 6 months in each patient.

CONCLUSION

There are benefits of bosentan for treatment of severe PAH in CHD, especially in patients with Eisenmenger physiology. Obvious benefits are an improvement of 6MWT and O2 sat.

Plasma endothelin response to acute hypoglycaemia in adults with Type 1 diabetes

AIMS

To determine whether acute insulin-induced hypoglycaemia provokes a detectable alteration in peripheral plasma endothelin (ET) concentrations in humans with Type 1 diabetes.

METHODS

Serial plasma concentrations of ET were measured in 20 patients with Type 1 diabetes during controlled hypoglycaemia induced by intravenous infusion of soluble insulin.

RESULTS

A significant increase was observed in plasma ET concentrations, from 3.80 +/- 0.31 pg/ml at baseline to 6.72 +/- 1.47 pg/ml at 60 min after the onset of the hypoglycaemic reaction (P < 0.05).

CONCLUSIONS

Acute insulin-induced hypoglycaemia induces a rise in plasma endothelin concentrations in people with Type 1 diabetes. This finding is consistent with a putative role for ET in the mediation of hypoglycaemia-induced vasoconstriction, and the possible precipitation of macrovascular or microvascular events.

Nicotine inhibits large conductance Ca(2+)-activated K(+) channels and the NO/-cGMP signaling pathway in cultured human endothelial cells

OBJECTIVE

The effects of nicotine on endothelium-dependent vasorelaxation mediated by nitric oxide (NO) are controversial. Since endothelial NO synthesis has been shown to depend on the activity of large conductance Ca(2 + )-activated K(+) channels (BK(Ca)), the present study investigated whether nicotine alters BK(Ca) single channel activity induced by the K(+) channel opener NS1619, and to examine a possible interaction with the endothelial NO generation.

DESIGN

The patch-clamp technique was used to examine the BK(Ca) activity. NO production was measured indirectly using a [(3)H]-cGMP-radioimmunoassay. All experiments were performed using cultured endothelial cells derived from human umbilical cord veins.

RESULTS

The BK(Ca) opener NS1619 (10 micromol/l) significantly increased the BK(Ca) open-state probability (NPo) from 0.011+/-0.007 (control) to 0.052+/-0.019. Co-perfusion with nicotine (1 micromol/l) significantly decreased NS1619 induced NPo (n = 14, p < 0.05). Intracellular cGMP levels were significantly increased, if cells were stimulated with NS1619 (+ 225%; n = 10, p < 0.05), which was blocked by Nicotine (1 micromol/l).

CONCLUSIONS

The results of the present study demonstrate that BK(Ca) activation by NS1619 plays an important role in the regulation of the NO-/cGMP-signaling-pathway. Endothelial dysfunction caused by nicotine may be connected with a decrease in BK(Ca)-activity.

The endothelin/nitric oxide balance determines small-for-size liver injury after reduced-size rat liver transplantation

Small-for-size (SFS) liver graft injury is probably related to microcirculatory disorders due to an imbalance of vasoconstricting, e.g. endothelin (ET)-1, and vasorelaxing mediators, e.g. nitric oxide (NO). We studied the role of ET-1/NO balance and the effect of an endothelin A receptor (ETAR) antagonist on SFS injury after liver resection and reduced-size liver transplantation (RSLT). One hundred twenty-six Lewis rats were divided into five groups: (I) 70% liver resection, (II) 70% liver resection treated with the ETAR antagonist LU 135252 (1 mg/kg b.w. i.v.), (III) RSLT (30% residual liver volume), (IV) RSLT treated with the ETAR antagonist, (V) sham operation. Liver microcirculation was measured by intravital microscopy. ET-1, ETAR, endothelial NO-synthase (eNOS), activation of Kupffer cells (KCs) and parenchymal injury were studied by immunohistology. Survival and liver function were followed up to 14 days. RSLT led to increased ET-1, ETAR and decreased eNOS protein expression, accompanied by activation of KC, reduced perfusion rate, vasoconstriction and elevated sinusoidal blood flow, as well as hepatocellular damage, impaired liver function and impaired survival. ETAR blockade (groups II + IV) improved the ET-1/NO balance, attenuated microcirculatory disorders and improved hepatocellular apoptosis and liver function. Microcirculatory disorders related to an ET-1/NO imbalance may contribute to SFS liver injury. Maintenance of ET-1/NO balance by blocking ETAR reduces SFS injury by protecting liver microcirculation, thus reducing hepatocellular damage.

Endothelin-Induced Increased Aldosterone Activity Mediates Augmented Distal Nephron Acidification as a Result of Dietary Protein

The hypothesis that increased dietary protein augments distal nephron acidification through endothelin-mediated increased aldosterone activity was tested. Munich-Wistar rats were studied after 3 wk of diets with 50% high protein (HiPro) and 20% control (CON) casein-provided protein, the latter comparable to standard diet. HiPro versus CON rats had higher distal nephron H+ secretion by in vivo microperfusion as shown previously. Perfusion with inhibitors of Na+/H+ exchange (EIPA, 10(-5) M), H+-ATPase (bafilomycin, 10(-7) M), and H+-K+-ATPase (Sch 28080 [10(-5) M] and ouabain [10(-3) M]) support that higher Na+/H+ exchange and higher H+-ATPase but not higher H+-K+-ATPase activity mediated increased H+ secretion in HiPro rats. Oral bosentan, an endothelin A/B receptor antagonist, decreased distal nephron H+ secretion in HiPro rats as a result of reduced Na+/H+ exchange and H+-ATPase activity as shown previously by the authors' laboratory. HiPro versus CON rats had higher plasma aldosterone (60.9 +/- 5.9 versus 42.2 +/- 4.4 pg/ml; P < 0.024) and higher urine aldosterone excretion (21.9 +/- 3.9 versus 10.5 +/- 2.8 ng/d; P < 0.04) in the absence but not presence of bosentan, consistent with endothelin-mediated increased aldosterone secretion. HiPro rats that did versus did not ingest the aldosterone antagonist spironolactone had lower distal nephron H+ secretion (29.2 +/- 3.3 versus 42.1 +/- 3.8 pmol/mm per min; P < 0.05) as a result of lower H+-ATPase activity without differences in Na+/H+ exchange or H+-K+-ATPase activity. The data support that dietary protein provided as casein increases distal nephron acidification through endothelin-stimulated Na+/H+ exchange and endothelin-stimulated aldosterone secretion that increases H+-ATPase activity.

[Inorganic lead stimulates endothelin secretion in the MDCK cell line]

BACKGROUND

Lead (Pb) is an environmental toxin whose acute intoxication causes haematological, gastrointestinal and neurological dysfunctions. Moreover it is well-established that prolonged exposure to low levels of inorganic Pb compounds is closely related to hypertension in experimental animals and occupationally exposed humans. Previous reports have suggested that endothelins (ETs), a family of peptides with potent vasoconstrictive properties, might be involved in the pathogenesis of lead-induced hypertension. In vivo studies demonstrated that rats chronically exposed to Pb low levels exhibited blood pressure elevation coupled with an increase of ET-3 concentration in plasma and urine in comparison with control animals.

OBJECTIVE

Since kidney is one of the target organs of lead injury, as well as the site of production/action of ETs, we investigated the effects of an inorganic Pb compound (Pb chloride) on the synthesis and secretion of these peptides, using, as in in vitro model, a renal-derived cell line (MDCK).

METHODS

The ETs assays in culture media of sub-confluent cell cultures exposed to different concentration of PbCl2 were performed by Enzyme linked Immunoassay (EIA), using two experimental procedures: a) cultures were exposed to 1100 and 200 microM PbCl2 for 30 min, next cells received Pb-free culture medium up to 24 h (pulse/chase experiment); b) cultures were fed continuously up to 24 h with treatment media containing the same PbCl2 concentrations (pulse experiment). Concomitantly, the Pb influence on cell viability was evaluated by different cytotoxicity assays (LDH release, DAPI staining and cell density assays). The mRNA expression of ET-1 was evaluated in pulse experiments by RT-PCR analysis before and after cell exposure to PbCl2. The Pb2+ cellular content of parallel MDCK cell cultures was assessed by AAS analysis.

RESULTS

In our experimental conditions, the administration of PbCl2 to sub-confluent MDCK cell cultures did not significantly affect cell viability. Either in pulse or in pulselchase experiments, the ETs content, evaluated in culture media of cells exposed to 100 microM PbCl2, significantly increased. On the contrary, cell treatment with 1 or 200 microM PbCl2 did not modify the ETs secretion. Because the amounts of ETs released in culture media were similar in both kinds of experiment, our results suggest that the metal induces the ETs secretion already after 30 min of cell exposure to the toxicant. Moreover, the ET-3 EIA specific assay did not reveal any immunoreactivity, excluding the involvement of this isoform in the Pb-induced secretion of ETs. Additionally, our results seem to exclude any Pb-induced up-regulation of ET-1 transcripts. The Pb2+ quantification in cell extracts demonstrated that the uptake of the metal is dose- and time-dependent and, in pulse experiments, it was maximum after six hours from the beginning of treatments, then the intracellular Pb2+ content decreased. This last phenomenon suggests the involvement of an ATP-dependent transporter in the mechanism of Pb cell excretion. Moreover, the ETs cell release in culture media of MDCK cells appears to depend on the intracellular content of Pb ions reached within 30 min of treatment.

CONCLUSION

Our results indicate that there is a range of PbCl2 doses (100 microM) at which MDCK cells enhance their ETs secretion. Lower doses (1 microM) of Pb salt seem to be ineffective to stimulate ETs release, while, doses equivalent to 200 microM seem to inhibit this phenomenon.

Endothelin and pulmonary arterial hypertension

BACKGROUND AND OBJECTIVES

Pulmonary arterial hypertension (PHT) is a potentially fatal disease. The purpose of this article is to review the current knowledge of the role played by endothelin (ET) in PHT and the relevant drug regimens used in the treatment of this condition.

METHODS

A detailed search via MEDLINE (PubMed) was performed by using PHT and ET as the key terms.

RESULTS

PHT could be a primary or a secondary diagnosis associated with various heart and lung diseases. PHT appears during the late stage of systemic sclerosis and may complicate other systemic diseases such as systemic lupus erythematosus. The vascular endothelium and activation of various mediators and growth factors such as the ET system are thought to play a crucial role in the development of this condition. The pathologic process progresses very rapidly from vasoconstriction to widespread pulmonary vascular obstruction. The use of high doses of calcium channel blockers is of limited value. Life-long anticoagulant therapy is recommended for the treatment of PHT. Currently, the drug being used in PHT therapy is continuous central-venous prostacyclin infusion. Prostacyclin is a strong vasodilator with antiaggregate and antifibrotic properties and has the potential to reduce endothelial injury and to induce vasculature remodeling. This treatment results in improved functional status and increased life span. Unfortunately, its use is accompanied by various side effects, technical difficulties, and high cost. The role of other therapeutic modalities (inhaled prostacyclin, subcutaneous treprostinil, oral beraprost, sildenafil) in vascular remodeling, and the improvement in functional capacity and survival of patients with PHT, are currently under investigation. Bosentan, administered orally, is a recently developed active ET receptor antagonist. It is a promising new therapeutic tool in the treatment of PHT because of its potent vasodilator, antiproliferative, and vascular remodeling activity.

CONCLUSIONS

The revolutionary conceptual shift in understanding the pathogenesis of PHT from a vasoconstrictive process to a vasoproliferative one, has led to a modification in the treatment of this disease from the use of vasodilators to the use of drugs with antiproliferative and vascular remodeling activity. Until now, prostacyclin was the only drug of this type available for the treatment of PHT. ET blockade seems to be a reasonable and potential therapeutic option.

Hemodynamic and hormonal actions of adrenomedullin

Adrenomedullin, a 52-amino acid residue peptide, has numerous biological actions which are of potential importance to cardiovascular homeostasis, growth and development of cardiovascular tissues and bone, prevention of infection, and regulation of body fluid and electrolyte balance. Studies in man using intravenous infusion of the peptide have demonstrated that, at plasma levels detected after myocardial infarction or in heart failure, adrenomedullin reduces arterial pressure, increases heart rate and cardiac output, and activates the sympathetic and renin-angiotensin systems but suppresses aldosterone. The thresholds for these responses differ, being lower under some experimental circumstances for arterial pressure than for the other biological effects. Adrenomedullin administration inhibits the pressor and aldosterone-stimulating action of angiotensin II in man. By contrast, the pressor effect of norepinephrine is little altered by concomitant adrenomedullin administration. Although in the absence of a safe, specific antagonist of the actions of endogenous adrenomedullin it is difficult to be certain about the physiological and pathophysiological importance of this peptide in man, current evidence suggests that it serves to protect against cardiovascular overload and injury. Hope has been expressed that adrenomedullin or an agonist specific for adrenomedullin receptors might find a place in the treatment of cardiovascular disorders.

[Endothelin system and heart failure: a potential therapeutic target]

Neurohormonal activation is a marker and one of the most important pathophysiologic aspects of heart failure. The hyperactivation and participation of the endothelin system in several manifestations of this syndrome have been widely documented in the last few years. These data support attempts to view the endothelin system as a potential pharmacological target in order to reduce the high morbidity and mortality associated with heart failure. This is a short review of the main aspects of endothelin biology, its mechanisms of action, including those at the molecular level, and its pathophysiological role in heart failure. Finally, the potential benefits of the pharmacological manipulation of the endothelin system as well as some results of clinical trials in this context will be presented.

Changes of brain endothelin levels and peripheral endothelin receptors by chronic cigarette smoke in spontaneously hypertensive rats

The present study was conducted to evaluate the contribution of endothelin (ET) to the pharmacodynamic response to chronic cigarette smoke in spontaneously hypertensive rats (SHR). The contribution of ET was studied consequent to the hemodynamic response following 8 weeks of cigarette smoke by determining the changes in tissue ET-1 content and ET receptors. The blood pressure (BP) at the early phase of smoking and the heart rate (HR) 24 h later were apparently reduced in SHR, while the HR at the early phase was transiently elevated in normotensive Wistar Kyoto (WKY) rats. Tissue ET-1 levels in the hypothalamus, striatum, and cortex of SHR were higher than those in WKY rats, and these higher levels in SHR were reduced by exposure to chronic cigarette smoke. The ET-1 contents in the medulla oblongata and midbrain of both strains were clearly increased by smoke exposure, although the levels of SHR and WKY rats were not different. In addition, the immunoreactivity of the ET type A receptor in the adrenal glands and type B receptor in the kidneys of SHR showed a different response to smoke exposure as compared to WKY rats. Our present findings suggest that the changes of ETs may relate to the pharmacodynamic effects of chronic cigarette smoke.

Elevation of serum endothelins and cardiotoxicity induced by particulate matter (PM2.5) in rats with acute myocardial infarction

Epidemiological studies have defined a significant positive association of acute exposure to ambient concentrations of particulate matter (PM) with increased daily mortality and hospital admission for cardiovascular diseases. Experimental studies have shown that animals with pre-existing cardiovascular diseases are more susceptible to the cardiac effect of PM exposure. The present study was undertaken to investigate possible involvement of upregulation of the endothelin system in PM exposure-induced cardiotoxicity in rats with acute myocardial infarction (MI). Adult male Sprague Dawley rats were subjected to occlusion of the left coronary artery and displayed myocardial infarction 12 h after the surgery. The heart rate significantly decreased and premature ventricular complexes of the electrocardiogram occurred in the myocardial infarct animals. Exposure to PM(2.5) via intratracheal instillation with 2.0 mg in 0.3 mL normal saline significantly worsened the ventricular arrhythmia along with a further decrease in heart rate. The same PM exposure only caused slight cardiac changes in the sham-operated animals. Serum total endothelin concentrations were significantly elevated in both myocardial infarct rats and shamoperated controls in response to PM exposure. However, increased numbers of the endothelin receptor type A on the cardiomyocytes were observed only in the infarct myocardium. This study thus suggests that upregulation of the endothelin system in rats with MI is likely involved in the PM exposure-induced cardiotoxicity.

Hemorrhage-induced vascular hyporeactivity to norepinephrine in select vasculatures of rats and the roles of nitric oxide and endothelin

Hemorrhage-induced vascular hyporeactivity to norepinephrine (NE) and the possible effector roles of nitric oxide (NO) and endothelin (ET) were investigated in different vascular beds of rats. Under urethane anesthesia, rats (n = 7 per group) were hemorrhaged to a mean arterial pressure (MAP) of 50 mm Hg for 60 min. A group of rats was pretreated with either NG-nitro-L-arginine methyl ester (10 mg/kg), an NO synthase inhibitor, or PD142893 (0.1 mg/kg), an ET receptor antagonist 15 min before the end of the hypotensive period. Operated, euvolemic rats served as controls. The responses of MAP and the blood flow of the superior mesenteric (SMA), celiac (CA), left renal (LRA), and left femoral arteries (LFA) to NE (3 microg/kg, i.v.) were measured at baseline (prehemorrhage), at the end of the hypotensive period (0 h), and at 1, 2, and 4 h after the end of the hypotensive period. The pressor responses to NE on MAP at 0, 1, 2, and 4 h in the 60-min hemorrhage groups were reduced to 45.9%, 37.8%, 29.2%, 18.4% of baseline pressor response, respectively. At these same times, the fall in blood flow in response to NE in SMA, CA, LRA, and LFA was significantly blunted (P < 0.01). This loss of responsiveness in CA and LFA was more severe than in SMA and LRA (P < 0.05-P < 0.01). Pretreatment with L-NAME or PD142893 significantly improved the pressor response of MAP and the blood flow responses of the four arteries to NE (P < 0.01). Hypotension at 50 mm Hg for 60 min resulted in an apparent loss of vascular reactivity to NE, and the four vasculatures studies were not affected to the same extent. In addition, NO and ET appear to contribute to the loss of vascular reactivity in different vasculatures in hemorrhagic shock.

Medroxyprogesterone acetate versus norethisterone: effect on estradiol-induced changes of markers for endothelial function and atherosclerotic plaque characteristics in human female coronary endothelial cell cultures

OBJECTIVE

Progestin addition to estradiol (E(2)) replacement therapy may lead to a deterioration of beneficial effects on the vasculature. The effect of the two clinically most common progestins, medroxyprogesterone acetate (MPA) and norethisterone (NET), during continuous combination with E(2) on the synthesis of markers for coronary endothelial function, atherosclerotic plaque initiation, and plaque formation was investigated in human female vascular cell cultures and compared with that of E(2) alone.

DESIGN

Endothelial cell cultures from human female coronary arteries were used to evaluate the effect of progestin addition to E(2) on the production of the following endothelial markers: prostacyclin, endothelin, plasminogen activator inhibitor-1, E-selectin, intercellular adhesion molecule-1, monocyte chemoattractant protein-1 (MCP-1), and the precursor of matrix metalloproteinase-1 (pro-MMP-1). E(2) was tested at 0.1 microM, 1 microM, and 10 microM alone and in equimolar combinations with MPA or NET. The markers were determined by enzyme immunoassays in the cell supernatant.

RESULTS

E(2) induced a significant increase of endothelial prostacyclin production and was able to significantly decrease the synthesis of endothelin, plasminogen activator inhibitor-1, E-selectin, and intercellular adhesion molecule-1. Neither MPA nor NET addition negatively interfered with these E(2)-induced benefits. However, MPA antagonized the E(2)-induced significant reduction of MCP-1 synthesis, with the difference between both progestins being significant (p < 0.01). Interestingly, an enhancement of the positive E(2)-effect on pro-MMP-1 production was observed by the addition of both MPA and NET (p < 0.01).

CONCLUSION

E(2) can positively influence various markers of endothelial function. Addition of MPA or NET can elicit different effects, which has been demonstrated for the first time in human coronary cell cultures. No impact was found on markers representing primarily vasotonus and thrombogenicity. In terms of MMP-1, which is crucial for atherosclerotic plaque stability, an enhancement of the beneficial E(2) effect was observed. However, regarding MCP-1, contrary effects of progestins cannot be excluded. This indicates that progestins may differ in their effects, particularly in the early stages of atherosclerosis, which has also been supported by other studies.

Role of selenium in cytoprotection against cholesterol oxide-induced vascular damage in rats

Wistar rats were fed Se-deficient (0.038 mg/kg diet) and adequate (0.326 mg/kg diet) diets for 13 weeks. The blood Se content, blood and vascular wall glutathione peroxidase (GPx) activity, serum high-density lipoprotein cholesterol (HDL-C) level and plasma prostacyclin (PGI(2)) concentration were decreased significantly, and the blood lipid peroxide (LPO) concentration, serum low-density lipoprotein cholesterol (LDL-C), total cholesterol (TC) level and plasma thromboxane A(2) (TXA(2)), content were increased significantly in Se-deficient rats compared with Se-adequate group, respectively. Furthermore the Se-deficient and adequate rats were given 5 mg/kg of cholestane-3 beta, 5 alpha, 6 beta -triol (3-triol) or vehicle only. Twenty four hours after treatment, the plasma PGI(2) level was decreased in Se-adequate rats infused 3-triol (+3 triol), meanwhile, the level in Se- deficient +3-triol group was much lower than that in Se-adequate +3-triol group. Compared with Se-adequate group, plasma TXA(2) content in Se-adequate +3-triol group had no significantly difference, but in Se- deficient rats infused 3-triol, plasma TXA(2) content was much higher than that in Se-adequate +3-triol group. The plasma ET concentration in Se-deficient group decreased slightly, but the concentration in Se-adequate +3-triol group increased significantly with respect to Se-deficient group. Although plasma ET concentration in Se-deficient group +3-triol did not increase, it was significantly lower than that in Se-adequate +3-triol group. The luminal surfaces of aorta thoracica of experimental rats were examined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Observed by SEM, the luminal surface of aorta of Se-deficient rats showed few crater-like defects due to the disruption of endothelial cell. Se-adequate +3-triol group showed some crater-like defects on the their aorta luminal surface, but the luminal surface of Se-deficient +3-triol group exhibited numerous crater-like defects and appeared sponge-like as well as platelets adhering followed by thrombus formation in focal area of extensive endothelial damage. TEM studies also showed that the endothelium of aorta of Se deficient +3-triol group had more frequent lesion where endothelial cell plasma were swelling with profuse intracellular edema and some vacuoles were seen in cytoplasm. In severely injured areas, endothelial integrity was completely destroyed and smooth muscle cells were proliferating and migrated to the endomembrane. Thus, we can conclude that Se or selenoproteins in the vascular wall plays an important role in cytoprotection against cholesterol oxide-induced vascular damage in rats.

Effects of ibuprofen on plasma endothelin levels and some vital parameters during endotoxin shock in rabbits

BACKGROUND

There is evidence that septic shock results from breakdown in the balance between vasodilators such as prostacyclin, prostaglandin E(2), and nitric oxide, and the vasoconstrictors thromboxane A(2), serotonin, and endothelin. Increased plasma endothelin (ET) concentrations during septic shock were found. Inducing phospholipase A(2), ET causes release of arachidonic acid and production of prostaglandins. Ibuprofen is nonsteroidal anti-inflammatory drug inhibiting prostaglandin synthesis. There are no any information about the effects of ibuprofen on ET production in endotoxemia. In the present study we aimed to determine the effects of ibuprofen on plasma ET concentrations in an animal model of endotoxin shock.

METHODS

A total of 28 rabbits were randomly allocated into four groups. The first group only received saline and served as controls. The rest of the animals (groups 2, 3, and 4) were injected intravenously with endotoxin at a dose of 2 mg/kg. To the third group, ibuprofen at 30 mg/kg dosage was given, 30 min following endotoxin administration, whereas in the fourth group animals, ibuprofen was administered 30 min before endotoxin administration. Animals were monitored through the canulation of femoral arteries and venules under the complete anaesthesia. At 0, 30, 60, 90, 120, 180, and 240 min, arterial blood pressure, heart rate, and ET determinations were carried out.

RESULTS

Ibuprofen before the endotoxin administration was more effective in controlling the increase in heart rate. Ibuprofen was also effective in inhibiting the sudden reductions in blood pressure if administered before endotoxin. However, if administered after endotoxin injection, ibuprofen precipitated the reduction in blood pressure further. Ibuprofen reduced the ET production which was induced by the endotoxin administration.

CONCLUSIONS

Ibuprofen administration during endotoxin shock seems to decrease the elevated ET concentrations, and increase the blood pressure.

Involvement of proteasome in endothelin-1 production in cultured vascular endothelial cells

We examined whether the proteasome could regulate endothelin (ET)-1 production in vascular endothelial cells (ECs). A proteasome inhibitor N-benzyloxycarbonyl-Ile-Glu (O-t-Bu)-Ala-leucinal (PSI) significantly decreased ET-1 release from ECs by about 25% of the basal release. PSI also suppressed tumor necrosis factor (TNF)-alpha-induced ET-1 release from ECs in a dose-dependent manner. Similar inhibitory effects were observed using another proteasome inhibitor lactacystin, whereas a calpain inhibitor calpeptin had no apparent effect on ET-1 release. Furthermore, PSI significantly attenuated prepro ET-1 mRNA expression under basal and TNF-alpha-stimulated conditions. Electrophoretic mobility shift assay showed that proteasome inhibitors diminished TNF-alpha-stimulated nuclear factor-kappa B (NF-kappaB) activation in ECs. Pretreatment with antioxidants, pyrrolidine dithiocarbamate and alpha-lipoic acid, both of which are known to be suppressors of NF-kappaB activation, effectively attenuated basal and TNF-alpha-induced ET-1 release. Thus, a proteasome-dependent proteolytic pathway is at least partly involved in ET-1 production under basal conditions, and this proteolytic pathway seems to have a crucial role in ET-1 production enhanced by TNF-alpha. The reduction of NF-kappaB activation may be involved in the mechanisms for suppressive effects of proteasome inhibitors on ET-1 gene transcription and the consequent decrease in ET-1 mRNA expression and ET-1 release.

Sex-specific acute effect of estrogen on endothelium-derived contracting factor in the renal artery of hypertensive Dahl rats

OBJECTIVE

To determine whether estrogen rapidly affects endothelium-derived contracting factor (EDCF) in the renal artery of hypertensive Dahl rats, and whether factors other than nitric oxide (NO) contribute to the effect of estrogen.

DESIGN

Acute effects of estrogen on the acetylcholine-induced vasomotor responses and on prostaglandin H2/thromboxane A2 mimetic, U46619,-induced contraction were examined in isolated arterial rings.

METHODS AND RESULTS

Dahl salt-sensitive male and female rats were fed an 8% NaCl diet for 4 weeks. The blood pressure increased more rapidly and to a greater extent in males than in females. Renal arterial rings were prepared for isometric tension recording. 17beta-Estradiol, but not the biologically less active stereoisomer, 17alpha-estradiol, improved the relaxation response to acetylcholine in renal arteries from females. Estrogen also rapidly decreased the contraction evoked by acetylcholine (10(-6) to approximately 10(-4) mol/l) in renal arteries from females and it was effective at a physiological concentration (10(-9) mol/l) in the presence of Nomega-nitro-l-arginine methyl ester (an NO synthase inhibitor). The estrogen receptor antagonist, ICI 182,780, abolished the effect of estrogen, whereas the cytochrome P450 inhibitor, miconazole, had no effect. The contraction induced by U46619 was also suppressed by estrogen, without any contribution from NO. Estrogen had no effect on either relaxation or contraction responses in renal arteries from males.

CONCLUSION

17beta-Estradiol antagonizes increases in vascular tone in hypertensive females by enhancing NO-dependent relaxation, and by suppressing EDCF-mediated mechanisms in an NO-independent manner.

Antioxidants block angiotensin II-induced increases in blood pressure and endothelin

Chronically infusing a subpressor dose of angiotensin (Ang) II increases blood pressure via poorly defined mechanisms. We found that this hypertensive response is accompanied by increased oxidant stress and is prevented by blocking endothelin (ET) receptors. Thus, we now tested whether blocking oxidant stress decreases both blood pressure and ET levels. We infused Sprague-Dawley rats (via osmotic pumps) with either vehicle (group 1) or Ang II (5 ng. kg(-1). min(-1); groups 2 to 4) for 15 days. Groups 3 and 4 also received either tempol in the drinking water (1 mmol/L) or vitamin E (5000 IU/kg diet), respectively, for 15 days. We measured systolic blood pressure (SBP) and urinary nitrite excretion every 3 days, and on day 15 we measured systemic and renal venous plasma levels of ET, isoprostanes, and thiobarbituric acid reactive substances (TBARS). SBP in Group 1 did not change throughout the study, whereas Ang II increased SBP (from 132+/-5 to 151+/-7 mm Hg). In addition, Ang II increased the systemic and renal venous levels of isoprostanes, TBARS, and ET and caused a transient decrease in urinary nitrites (that returned to control levels by day 9). Both tempol and vitamin E prevented Ang II-induced hypertension and either prevented or tended to blunt the increase in systemic and renal isoprostanes, TBARS, and ET. Finally, both antioxidants abolished the transient decrease in urinary nitrites. These results together with our previous study suggest that subpressor-dose Ang II increases oxidant stress (and isoprostanes). This in turn increases ET levels, which participate in the hypertensive response to Ang II.

Effects of the endothelin receptor antagonist Bosentan on ischaemia/reperfusion injury in rat skeletal muscle

We examined the role of endothelin in ischaemia/reperfusion injury in skeletal muscle, using the endothelin receptor antagonist Bosentan. In the rat hindlimb tourniquet ischaemia model, one hindlimb was rendered ischaemic for 2 h at 36 degrees C, then blood flow was re-established for either 24 h to assess muscle survival or 1.5 h for a study of capillary perfusion. In the first set of rats, the gastrocnemius muscle was removed from the postischaemic limb and assessed for viability histochemically using the nitro blue tetrazolium stain. Tissue water content (a measure of oedema) and myeloperoxidase activity (a measure of neutrophil accumulation) were also assessed in the ischaemic muscle, the contralateral non-ischaemic muscle and the lungs. In the second set of rats, the hind limb was infused with India ink after 2-h ischaemia and 1.5-h reperfusion and the muscle was harvested, fixed and cleared. In control rats, muscle viability was 17+/-2% (S.E.M.). In rats treated with Bosentan (10 mg/kg, i.p.) 30 min before release of the tourniquet, muscle viability (48+/-7%) was significantly increased compared to the control group (P<0.01). Bosentan treatment had no significant effect on tissue water content or myeloperoxidase activity in the ischaemic muscle, the contralateral non-ischaemic muscle or the lung. Immunoreactive endothelin levels in serum increased to a peak at 90 min of reperfusion and returned to control levels by 24-h reperfusion. India ink studies demonstrated a significantly increased functional capillary density in postischaemic Bosentan-treated muscles compared with postischaemic control muscles (P<0.05). These results suggest that endothelin plays an important role in the necrosis which results from a period of ischaemia and reperfusion in skeletal muscle, by mediating a decrease in postischaemic microvascular perfusion.

The role of endothelins and their receptors in heart failure

Endothelin (ET) is a peptide composed of 21 amino acids, derived from a larger precursor, the big-endothelin, by action of the endothelin-converting enzyme (ECE) family; three isoforms of endothelin, named ET-1, ET-2 and ET-3, have been identified. Endothelin-1 is generated mainly by vascular endothelial cells and exerts various important biological actions, mediated by two receptor subtypes, ET-A and ET-B, belonging to the G protein-coupled family that have been identified in various human tissues such as the cardiac tissue. Endothelin-1 is a potent vasoconstrictive agent, has inotropic and mitogenic actions, modulates salt and water homeostasis and plays an important role in the maintenance of vascular tone and blood pressure in healthy subjects. Endothelin-1, as well as ET-A and ECE-1, also has an important role in cardiovascular development, as observed by the variety of abnormalities related to neural crest-derived tissues in mouse embryos deficient of a member of the ET-1/ECE-1/ET-A pathway. Various evidence indicates that endogenous endothelin-1 may contribute to the pathophysiology of conditions associated with sustained vasoconstriction, such as heart failure. In heart failure, elevated circulating levels of both endothelin-1 and big-endothelin-1 are observed; in failing hearts an activation of the endothelin system is found: tissue level of ET-1 is increased with respect to non-failing hearts as well as receptor density, due mainly to an upregulation of the ET-A subtype, the prevalent receptor subclass in cardiac tissue. Finally, studies in both humans and animal models of cardiovascular disease show that inhibition of the endothelin function (anti-endothelin strategy) is associated with an improvement of haemodynamic conditions; these observations indicate that endothelin receptor antagonists or endothelin-converting enzyme inhibitors may constitute a novel and potentially important class of agents for the treatment of this disease.

Conversion of big endothelin-1 and characterization of its contractile effects on isolated human placental arteries

OBJECTIVES

To study the conversion of human big endothelin-1 (bigET-1) to endothelin-1 (ET-1) and to characterize contractile ET-1 receptors in human placental arteries.

METHODS

BigET-1 was incubated with artery membranes and the formation of ET-1 was investigated. ET-1 and bigET-1-induced contractile responses were studied in the absence or presence of the metalloprotease inhibitor phosphoramidon, the ET(A)-receptor antagonist BQ 123, or the ETB-receptor antagonists IRL 1038 and RES 701-1.

RESULTS

The artery membranes hydrolysed bigET-1 to ET-1 through a partly phosphoramidon-sensitive pathway. The contractile responses to ET-1 and bigET-1 were similar, with pEC50% values of 8.1 +/- 0.2 and 7.8 +/- 0.1, respectively (NS; n = 17). Phosphoramidon decreased pEC50% for bigET-1-evoked contractions (p < 0.05; n = 8), without affecting the response to ET-1. A Schild plot of BQ 123 effects on ET-1 and bigET-1-induced contractions resulted in identical pA2 values and a slope of 0.56 +/- 0.2 and 0.47 +/- 0.01, respectively. IRL 1038 and RES 701-1 did not affect the contractile responses.

CONCLUSION

BigET-1-evoked contractions in isolated human placental arteries depend on a rapid and metalloprotease-dependent hydrolytic conversion to ET-1, which in turn causes a, mainly ETA-receptor-mediated, contraction.

[The role of endothelium-dependent factors in realizing cardiogenic reflexes under normal and pathological conditions]

We have investigated the role of NO-dependent mechanisms in the realization of cardiogenic reflexes (pressor and depressor) during the action of veratrin and serotonin on cardiac receptors, adrenergic changes of the myocardial contractile activity or the short-term period of myocardial ischemia on anaesthetized dogs cats and rats. NO take place in the development of cardiogenic depressor reflexes and decreases pressor reflexes from the cardiac receptors in dogs. Specific characteristics of these influences were asserted: the depressor reflexes decrease after systemic inhibition of NOS by L-NNA in dog but they are increased or are not altered in rats. The depressor reaction in rats diminished after inhibition of nNOS performing by 7-nitroindazole. We affirm that NO-dependent influences have a compensatory effect in the course of acute alterations of the coronary blood flow and our statement concerning the advantageous role of NO-dependent mechanisms in the realization of self-regulatory reactions of circulation that connected with vagus nerve.

Effect of atorvastatin on endothelium-dependent constrictor factors in dyslipidemic rabbits

Relaxations to acetylcholine and contractions to acetylcholine in the presence of the nitric oxide (NO) synthesis inhibitor (L-N(G)-nitroarginine methyl ester, L-NAME) were studied in aortic rings from rabbits fed either a control or a diet containing 0.5% cholesterol+14% coconut oil for 14 weeks and treated or not with atorvastatin (2.5 mg kg(-1) day(-1)). Rings were incubated with the endothelin (ET(A)) receptor antagonist BQ123, and/or the thromboxane A(2) (TXA(2))/prostaglandin H(2) (PGH(2)) receptor antagonist ifetroban. In rabbits, high cholesterol and triglyceride plasma levels were associated with intimal thickening and blunted acetylcholine-relaxation as compared with controls. By contrast, acetylcholine+L-NAME response was higher. Incubation with either ifetroban or BQ123 increased acetylcholine-relaxation in both diet groups and it reduced the constrictor response only in dyslipidemic rabbits. Removal of endothelium reduced acetylcholine+L-NAME contraction in dyslipidemic rabbits, although increased it in control animals. Atorvastatin treatment reduced plasma lipid levels and lesion size in dyslipidemic animals. Likewise, it prevented acetylcholine-relaxation reduction. In addition, atorvastatin reduced constrictor response in dyslipidemic rabbits but only in rings with endothelium. Incubation with either ifetroban or BQ123 did not further modify these responses in atorvastatin-treated animals in any group. These data suggest that ET and TXA(2) availabilities seem to participate in the endothelial dysfunction associated with dyslipidemia. Atorvastatin treatment reduces intimal thickening and improves endothelial dysfunction in rabbits. This effect seems to be a consequence of its ability to act on ET and TXA(2) systems.

Low-dose nitro-L-arginine administration in baboon (Papio hamadryas) pregnancy

1. The purpose of the present study was to examine the effect of nitric oxide (NO) inhibition on mean arterial pressure (MAP), endothelin (ET) and the renin-aldosterone system in pregnancy in the non-human primate (baboon). 2. Twenty pregnant baboons (Papio hamadryas) were examined prospectively after the administration of an oral NO inhibitor in different phases of pregnancy. Haemodynamic responses to NO inhibition, evidence of pre-eclampsia and the renin-aldosterone system were examined under anaesthesia. 3. Oral NL-nitro-L-arginine (NOLA; 5 or 10 mg/kg) was given for 1 week in early (6-8 weeks gestation), middle (14-16 weeks gestation) and late (22-24 weeks gestation) pregnancy and while non-pregnant. Mean arterial pressure, heart rate, haematology, biochemistry, ET, plasma renin activity (PRA) and aldosterone were measured. Foetal effects of NOLA were also examined by ultrasound and neonatal measurements. 4. Nitric oxide inhibition led to an increase in MAP in non-pregnant animals (9 mmHg) and in middle and later pregnancy (6 and 7 mmHg, respectively). Mean arterial pressure in early pregnancy was not affected. A reduction in PRA occurred after NO inhibition in all stages of pregnancy. Significant proteinuria occurred only in late pregnancy. 5. Nitric oxide is involved in the maintenance of lower blood pressure in late pregnancy and inhibition leads to an increase in blood pressure and proteinuria in the baboon. Nitric oxide insufficiency may contribute to the clinical manifestations of human pre-eclampsia. Nitric oxide was not involved in the normal vasodilation of early primate pregnancy.

Fluvastatin reduces endothelin secretion of cultured human umbilical vein endothelial cells

OBJECTIVE

Fluvastatin is an agent of a new lipid lowering drug class, the 3-hydroxy-3-methylglutaryl-coenzyme A reductase inhibitors, which seems to elicit direct effects on the vasculature.

METHODS

The effect of fluvastatin on endothelin secretion in endothelial cell cultures from human umbilical veins was investigated.

RESULTS

Fluvastatin significantly reduced endothelin secretion by 13% at a concentration of 10(-8) M, by 41% at 10(-7) M and by 62% at 10(-6) M.

CONCLUSION

Since endothelin is a potent vasoconstrictor which may be associated with the aetiology of cardiovascular diseases, the reduction of its synthesis by fluvastatin may contribute to the beneficial effects of this substance on the cardiovascular system.

Decrease of serum endothelin levels with postmenopausal hormone replacement therapy or tibolone

Endothelin is the most potent vasoconstrictor peptide known to date. Hormone replacement therapy (HRT) with estrogen reduces plasma endothelin levels. We measured endothelin in 51 postmenopausal patients before and during HRT. Patients were randomly allocated to receive either oral tibolone, oral or transdermal 17 beta-estradiol. A group of comparable volunteers served as controls. After 24 months, endothelin levels decreased in all treatment groups: tibolone, 18.2%; oral 23.1%; transdermal, 20.8%. Endothelin levels increased in the controls by 36.6% (p < 0.01). Tibolone decreases endothelin levels to a similar degree as conventional estrogen-progestogen-replacement therapy. These data provide another potential mechanism supporting the cardioprotective effects of tibolone.

Ischemia-reperfusion-induced delay in intestinal transit. Role of endothelins

BACKGROUND/AIMS

To evaluate the involvement of ET-1 in ischemia-reperfusion (I/R) injury.

METHODS

Superior artery occlusion was performed in Wistar albino rats for 30 min followed by 2-hour (early reperfusion; ER) or 24-hour (late reperfusion; LR) reperfusion periods.

RESULTS

Intestinal transit was found to be reduced in the ER and LR groups (19.0 +/- 2.5%; p < 0.001 and 72.7 +/- 6.0%; p < 0.05, respectively) compared to the control group (85. 8 +/- 2.5%), while treatment with the ET receptor antagonist bosentan (BOS; 10 mg/kg i.v.) abolished this delay in LR. Myeloperoxidase activity showed a significant increase in ER (7.07 +/- 85.70 U/g; p < 0.001) compared to control (281.16 +/- 43.23 U/g), but BOS had no effect on this increase. The protein oxidation level was found to be higher in LR (5.92 +/- 0.77 nmol/mg protein; p < 0. 05) compared to the control (3.77 +/- 0.45 nmol/mg protein), and was reversed by BOS treatment.

CONCLUSION

The results of the present study imply that I/R delays intestinal transit involving an endothelin-dependent mechanism.

[Endothelin and arterial hypertension]

Endothelins (ETs) are peptides of 21 amino acids synthesized and released by variety of cells. Endothelin (now this peptide is called endothelin-1 (ET-1)) was isolated and identified in 1988 by Yanagisawa et al. Following studies revealed two other isoforms of endothelin': Endothelin-2 (ET-2) and endothelin-3 (ET-3). All of them bind to two types of receptors (A and B (ET-A r, ET-Br). ET-A r are responsible for concentration mediating. Two subtypes of ET-B r are known. ET-B1 r mediates vasorelaxation; ET-B2 vasoconstriction. ETs (especially ET-1) have variety of biological actions but the most important are vasoconstrictor and mitogenic action. Through these two mechanism ETs may participate in the pathogenesis and/or in the maintenance of hypertension in both experimental animal models and human essential hypertension. The intravenous infusion of synthetic ET induces a long-lasting elevation of blood pressure in experimental animals and in healthy humans. Number of studies have shown enhanced responses to ET in hypertensive subjects but decreased responses have also been reported. Similarly, plasma levels of ET-1 are either normal or elevated in experimental and human essential hypertension. Numerous investigators have suggested an interaction between ET and angiotensin-converting enzyme inhibitors through the renin-angiotensin system or through the accumulation of endogenous bradykinin. Also calcium antagonists of different classes prevent endothelin-induced contractions. Endothelin- converting enzyme inhibitor (phosphoramidon) and ET-A/B r antagonists (bosentan, BQ-123, FR139317) may have potential role as vasodilators in the treatment of hypertension.

Treatment of congestive heart failure in the elderly: emphasis on renal functional changes and impact of therapy

Congestive heart failure (CHF) is a syndrome in which the kidney plays a fundamental role, as sodium retention is a hallmark of the syndrome. An additional hallmark of CHF is that it affects the elderly disproportionately. This high incidence of CHF in the elderly is complicated by age-related alterations in renal hemodynamics and tubular function. In view of these age-related renal alterations, pharmacologic therapy for CHF in the elderly needs to be closely monitored. In addition, recent understanding of neurohumoral mechanisms of CHF has led to new therapeutic options for the treatment of CHF, which are reviewed here.

Protein kinase C mediates angiotensin II-induced contractions and the release of endothelin and prostacyclin in rat aortic rings

Angiotensin II (Ang II) stimulation of vascular smooth muscle results in a myriad of intracellular signals that interact to produce the final physiologic response of the cell. We used rat aortic rings to investigate the role of protein kinase C (PKC) in Ang II-induced contractions and in the concomitant release of endothelin (ET) and prostacyclin (PGI2). Ang II (10(-9) M) produced a rapid contraction which was sustained for 10 min. When aortic rings were pretreated with graded concentrations of each of the four different inhibitors of PKC, that is, (i) 1-(5-isoquinolinesulfonylmethyl) piperazine (H7); (ii) 1-(5-isoquinolinesulfonyl) piperazine(CL); (iii) staurosporine; or (iv) calphostin C, inhibition of Ang II-induced contractions began at 10(-9) M, and was nearly complete at 10(-6) M. Ang II-induced contractions were associated with a 10-fold increase in the release of both ET and PGI2. Pretreatment with 10(-6) M of any one of the same four PKC inhibitors blocked Ang II-induced release of both ET and PGI2. Pretreatment with a blocker of the endothelin-A receptor, BQ123 (10(-6) M), inhibited, by approximately 50%, Ang II-induced contractions, and the release of both ET and PGI2. In aortic rings denuded of endothelium, Ang II-induced contractions, and the release of both ET and PGI2 were significantly reduced, compared to intact rings. We conclude that PKC mediates Ang II-induced contractions in rat aortic rings and that the secondary release of both ET and PGI2 during Ang II-induced contractions is mediated, at least in part, by PKC. In addition, approximately half of Ang II-induced contractile force and of PGI2 release is dependent upon the ET released from endothelial cells.

DNA antisense strategies in the study of receptors for vasoactive peptides, and of growth and wound-healing factors

Antisense oligodeoxynucleotide technology has contributed greatly to the overall understanding of both mRNA stability as well as translational processes leading to protein synthesis. Arrest of translational processes by DNA antisense strands usually reduces maximal effects of agonists without affecting their apparent affinities in treated isolated vascular or nonvascular preparations. In the present study, examples are given of DNA antisense oligonucleotide-induced repression of receptors for endothelins, kinins as well as of the platelet-derived growth factor. Furthermore, the efficiency of this technology illustrates the roles of protooncogenes (c-myc and c-myb) in wound-healing mechanisms. The overall mechanism of action of these oligomers is described and the relevance of size, chemical alterations and mode of delivery are illustrated. Release of oligophosphorothioates from polymer matrices and gels can produce a prolonged effect in vivo. Antisense oligonucleotides remain essential in experimental models for which receptor antagonists or selective inhibitors of intracellular components are currently unavailable.

Effects of insulin infusion on endothelium-derived vasoactive substances

An association between insulin resistance and hypertension has been reported in several studies. In apparent contradiction, insulin infusion in healthy volunteers is associated with vasodilatation. Furthermore, there is evidence that some insulin effects may differ between the sexes. We performed three-step hyperinsulinaemic-euglycaemic clamp studies in six men and six women to test the hypotheses that: 1) insulin might affect the release of vasoactive substances by the endothelium, and 2): this putative effect on vasoactive substances might differ between men and women. Six other women and six men served as control subjects, receiving 154 mmol/l NaCl (saline) infusion. Plasma levels of insulin, immunoreactive endothelin, L-arginine (precursor of nitric oxide), L-citrulline (by-product of nitric oxide synthesis) and cyclic GMP (second messenger of nitric oxide) were measured during infusion of insulin or 154 mmol/l NaCl (saline), respectively. We also assessed urinary excretion of 6-keto PGF-1 alpha (a degradation product of prostacyclin reflecting prostacyclin production). Blood pressure was monitored in all subjects throughout the experiment. In women plasma levels of immunoreactive endothelin decreased from (mean +/- SD) 2.58 +/- 0.96 to 1.7 +/- 0.72 pmol/l during insulin infusion (p < 0.01), while remaining constant in female control subjects (p < 0.02). No changes in levels of endothelin were observed in men during infusion of insulin or saline. In women levels of cGMP rose and levels of L-arginine decreased significantly during insulin infusion, consistent with an increase in nitric oxide production. Excretion of 6-keto PGF-1 alpha also increased significantly in women during insulin infusion. No such effects were observed in men, or in women during infusion of saline. Blood pressure remained constant in all subjects during hyperinsulinaemia. We conclude that sex differences exist in the effects of insulin on the endothelium. Short-term hyperinsulinaemia in women is associated with a decline in levels of immunoreactive endothelin, and possibly with a rise in production of nitric oxide and prostacyclin. In contrast, levels of vasoactive substances remained constant in men during hyperinsulinaemia. Our findings may partly explain insulin's vasodilatory effects in healthy individuals. It remains to be investigated whether these effects are lost in insulin-resistant states. Our observation that there is a sex difference in insulin effects on the endothelium may help explain why the link between hyperinsulinaemia and cardiovascular disease appears to be clearer in men than in women.

Comparison of effect of endothelin antagonism and angiotensin-converting enzyme inhibition on blood pressure and vascular structure in spontaneously hypertensive rats treated with N omega-nitro-L-arginine methyl ester. Correlation with topography of vascular endothelin-1 gene expression

Inhibition of nitric oxide synthase by L-arginine analogues such as N omega-nitro-L-arginine methyl ester (L-NAME) in spontaneously hypertensive rats (SHR) is associated with malignant hypertension and enhanced expression of the endothelin-1 gene in some blood vessels. In this study, SHR treated chronically with L-NAME (SHR-L-NAME) were given the angiotensin I-converting enzyme inhibitor cilazapril or the endothelin-A/endothelin-B receptor antagonist bosentan for 3 weeks. Systolic pressure was lowered slightly by cilazapril (213 +/- 2 versus 229 +/- 2 mm Hg in untreated SHR-L-NAME, P < .01) but was not significantly lowered by bosentan (223 +/- 2 mm Hg). Hypertrophy of aorta and small arteries (coronary, renal, mesenteric, and femoral) was decreased by cilazapril treatment and unaffected by bosentan. Expression of the endothelin-1 gene was evaluated in SHR-L-NAME by in situ hybridization histochemistry, which showed that endothelin-1 expression was enhanced in the endothelium of aorta but not in small mesenteric arteries in these rats. The absence of enhancement of endothelin-1 gene expression in small arteries may account for the absence of increased severity of hypertrophy of small vessels in SHR-L-NAME and may be a mechanism whereby L-NAME inhibits cardiovascular growth. These results suggest that in the absence of enhanced small-artery endothelin-1 expression, endothelin antagonism does not lower blood pressure. The blood pressure-lowering effect of angiotensin I-converting enzyme inhibition suggests a role for the renin-angiotensin system in the malignant form of hypertension that develops in SHR treated with L-NAME.

Increase in number of Weibel-Palade bodies and endothelin-1 release from endothelial cells in the cadmium-treated rat thoracic aorta

Male rats received daily intraperitoneal injections of cadmium sulphate (2.0 mg/kg) for 3 (Cd-3 group), 6 (Cd-6 group) and 8 days (Cd-8 group). The blood samples were prepared for endothelin (ET)-1 assay, and the thoracic aorta was investigated by both electron microscopy and immunoelectron microscopy using anti ET-1 sera. The plasma ET-1 concentrations of both Cd-6 and Cd-8 groups increased significantly in a cumulative dose-dependent manner. The cadmium-treated rat aorta showed an increase in the number of Weibel-Palade (WP) bodies in endothelial cells, and degranulation and exocytosis of WP bodies occurred exclusively in the Cd-8 group. Immunoreaction for ET-1 was localized preferentially in WP bodies of both cadmium-treated and control groups, and in the rough endoplasmic reticulum of the cadmium-treated groups only. Reactivity was also found on the WP bodies undergoing exocytosis in the Cd-8 group. Cadmium intoxication induces an increase in number of ET-1-storing WP bodies in the rat aorta endothelium. The enhancement of extracellular release of their contents by exocytosis results in elevation of the plasma ET-1 concentration.

Effects of cloricromene on the levels of endothelin and on the microcirculatory function in peripheral atherosclerotic arteriopathies

The effects of cloricromene on plasma endothelin-1 (ET-1) levels and on microcirculatory function in 9 patients with peripheral atherosclerotic arteriopathy (PAA) and in healthy control subjects were studied. ET-1 levels and microcirculatory function were evaluated both under basal conditions and 30, 60, and 90 min after acute administration of cloricromene (30 mg i.v.). PAA patients had significantly increased levels of ET-1 and impaired vascular parameters (studied by means of Winsor's Index, Gosling's Index, postischemic perfusion index and recovery time) when compared to control subjects. The acute administration of cloricromene (30 mg i.v.) did not change plasma ET-1 both in control subjects and in patients with PAA. In contrast, cloricromene produced a significant improvement in the postischemic perfusion index and in recovery time in arteriopathic patients. Control subjects and patients with PAA also underwent a cold pressor test (CPT) under basal conditions and (72 h later) 30 min after an acute intravenous administration of cloricromene (30 mg i.v.). CPT caused a higher increase in ET-1 in the patients with PAA compared to the control group, and a reduction in the vascular flow at the femoral level, while the pretreatment with cloricromene prevented both the increase in the levels of ET-1 and the reduction of the femoral vascular flow observed after the cold stimulus in patients with PAA. Our data show that cloricromene, besides ameliorating the microcirculatory function, is able to interfere with dynamic mechanisms, such as those induced by the CPT, capable of stimulating the release of ET-1 at the vascular level.