Circulating and tissue endothelin immunoreactivity in advanced atherosclerosis

Endothelin in human congestive heart failure

BACKGROUND

Although recent investigations report the elevation of plasma endothelin (ET) in congestive heart failure (CHF), it remains unclear if this elevation is that of the biologically active peptide ET-1 or of its precursor big-ET. Furthermore, it is unclear if such elevation is associated with increased myocardial ET and if the molecular form from cardiac tissue is altered ET. Last, it remains to be established whether circulating ET is increased at the earliest stage of CHF in patients with asymptomatic left ventricular dysfunction and correlates with the magnitude of ventricular dysfunction.

METHODS AND RESULTS

The present study was designed to investigate concentrations and molecular forms of ET in plasma and cardiac tissue in healthy subjects and CHF patients with New York Heart Association (NYHA) class I through IV using cardiac radionuclide angiogram, cardiac myocardial biopsy, radioimmunoassay, gel permeation chromatography (GPC), and immunohistochemical staining (IHCS). Plasma ET was increased only in patients with moderate (NYHA class III) or severe (NYHA class IV) CHF compared with healthy subjects and individuals with asymptomatic (NYHA class I) or mild (NYHA class II) CHF. The elevation of circulating ET in CHF showed a negative correlation with left ventricular ejection fraction and cardiac index and a positive correlation with functional class and left ventricular end-diastolic volume index. GPC demonstrated that immunoreactive plasma ET was ET-1 in healthy subjects and both mature ET-1 and its precursor big-ET in severe CHF patients, with big-ET the predominant molecular form. Cardiac tissue concentrations and IHCS revealed ET presence in healthy atrial and ventricular tissue, which were not different in severe CHF. GPC revealed that the molecular form of cardiac ET was ET-1 in both healthy and CHF hearts.

CONCLUSIONS

The present study establishes for the first time that the elevation of plasma ET in severe human CHF represents principally elevation of big-ET. Second, ET is present in healthy and failing myocardia, and its activity by both immunohistochemistry and radioimmunoassay is not changed in CHF. Furthermore, the elevated plasma ET is characteristic of severe CHF and not asymptomatic or mild CHF. In addition, the degree of plasma elevation of ET correlates with the magnitude of alterations in cardiac hemodynamics and functional class. The present study confirms and extends previous investigations of ET in human CHF and establishes the evolution of circulating and local cardiac ET in the spectrum of human CHF.

Does endothelin-1 play a role in the pathogenesis of cerebral vasospasm?

BACKGROUND

Endothelin-1 is a very powerful endogenous vasoconstrictor substance produced by endothelial cells. Its long-lasting vasoconstrictor and hypertensive action has been well documented in several species, including humans.

SUMMARY OF REVIEW

It is generally accepted that endothelin-1 may contribute to the pathogenesis of a number of cardiovascular diseases. In the cerebral vasculature, endothelin-1 has been proposed as a key mediator of cerebral vasospasm following subarachnoid hemorrhage. Availability of endothelin-1 antagonist provided a pharmacologic tool to test the role of endothelin in the development of vasospasm.

CONCLUSIONS

This brief review is focused on the controversial results reported by different groups concerning the possible role of endothelin-1 in narrowing of cerebral arteries exposed to autologous blood.

Plasma endothelin following cardiac arrest: differences between survivors and non-survivors

Cardiac arrest is associated with major metabolic disturbances, including severe hypoxia and large increases in circulating catecholamines, both of which are known to stimulate generation of the potent endothelium-derived vasoconstrictor peptide endothelin-1. We have, therefore, examined plasma immunoreactive endothelin concentrations following cardiac arrest. Blood was sampled at 10-min intervals from a central venous catheter inserted at onset of resuscitation in 38 patients (13 female; mean age, 67 years) presenting with cardiac arrest to the Accident and Emergency Department at the Royal Infirmary of Edinburgh. Plasma immunoreactive endothelin concentrations (mean +/- S.D.) in patients following cardiac arrest (5.4 +/- 2.3 pg/ml) were no different from those in healthy subjects (5.1 +/- 1.2 pg/ml). There was no significant difference between endothelin concentrations at presentation in survivors and non-survivors of cardiac arrest. However, non-survivors had a significant fall in endothelin concentrations with time from onset of resuscitation from 5.4 +/- 2.2 pg/ml to 3.5 +/- 1.8 pg/ml (P = 0.002), while survivors had a non-significant increase in concentrations. On multiple regression analysis there was a significant association between higher plasma endothelin concentration and survival (r = 0.37; P = 0.009). The failure of plasma endothelin to increase after cardiac arrest is unexpected. Although the fall in plasma endothelin with time in non-survivors may reflect the adverse physiological milieu that occurs during cardiac arrest, it is also possible that low endothelin concentrations contribute to the poor prognosis in this condition.

Both ETA and ETB receptors mediate contraction to endothelin-1 in human blood vessels

BACKGROUND

Endothelin (ET)-1 has potent vascular effects. Two endothelin receptors have been cloned, namely, the ETA receptor, which preferentially binds ET-1, and the ETB receptor, which equally binds ET-1 and ET-3 and preferentially sarafotoxin S6c. We characterized endothelin receptor subtypes on vascular smooth muscle and endothelium of isolated human internal mammary artery (IMA) and vein (IMV) and porcine coronary artery (PCA) using the ETA antagonists FR139317 and BQ-123, the ETB ligand sarafotoxin S6c, and the ETA/ETB antagonist Ro 47-0203 (bosentan).

METHODS AND RESULTS

In endothelium-denuded IMA and PCA and less so in IMV, FR139317 and BQ-123 (in PCA only) shifted the concentration-contraction curves to ET-1 parallel to the right. However, even at 10(-5) mol/L, FR139317 did not inhibit a high-sensitivity portion of the concentration-contraction curve. Moreover, the ETB receptor agonist sarafotoxin S6c induced contraction in vessels preincubated with FR139317. IMV was significantly more sensitive to the contractile effect of ET-1 and sarafotoxin S6c than was IMA (P < .05). Prolonged incubation with sarafotoxin S6c (to downregulate ETB receptors) and FR139317 eliminated the contraction resistant to FR139317. The ETA/ETB receptor antagonist bosentan caused a parallel shift of the concentration-contraction curve to the right at all concentrations of endothelin. ETB receptor mRNA was detected by Northern blot analysis in IMA and aortic smooth muscle cells. In precontracted IMA and PCA with endothelium, sarafotoxin S6c did not cause endothelium-dependent relaxations, whereas transient responses occurred in IMV.

CONCLUSIONS

Vascular smooth muscle cells of human IMA, IMV, and PCA contain both ETA and ETB receptors, whereas the endothelium of IMA and PCA does not express functional ETB receptors linked to nitric oxide and/or prostacyclin production. Hence, inhibition of endothelin-induced contraction in patients requires the use of combined ETA/ETB antagonists.

Effect of angiotensin converting enzyme inhibition on plasma endothelin in congestive heart failure

The influence of angiotensin converting enzyme inhibitor therapy on elevated plasma endothelin concentrations in chronic heart failure was investigated by measuring plasma endothelin immunoreactivity in 22 patients with severe but stable chronic heart failure before and after 16 weeks of therapy with quinapril (n = 12) or captopril (n = 10). Plasma endothelin immunoreactivity in the patients (10.2 +/- 34 pg/ml) was significantly higher than a control group (5.9 +/- 1.8 pg/ml). Quinapril improved symptoms and haemodynamics but did not affect plasma endothelin immunoreactivity (11.9 +/- 2.9 pg/ml at baseline and 12.3 +/- 3.4 pg/ml after 16 weeks of quinapril). Captopril also had no effect on endothelin levels (8.1 +/- 2.9 at baseline and 8.1 +/- 3.8 pg/ml after 16 weeks of captopril). The vasodilatory effects of angiotensin converting enzyme inhibitors in heart failure are not mediated by, or associated with, changes in plasma endothelin immunoreactivity.

Endothelin-1-selective receptor in the arterial intima of patients with hypertension

Endothelin-1 is a potent vasoconstrictor produced by vascular endothelial cells. A recently cloned endothelin-1-selective receptor, the endothelin-A receptor, mediates the vasoconstrictive action of endothelin-1. Because endothelin-1 also possesses mitogenic properties, it may play a role in regulating the proliferation of intimal smooth muscle cells. In this study, we analyzed the expression of endothelin-A receptor gene in the thickened arterial intima of patients with hypertension. Internal mammary artery specimens obtained from 12 patients undergoing cardiovascular surgery were subjected to in situ hybridization using a digoxigenin-labeled cRNA probe. High, homogeneous signals of endothelin-A receptor mRNA were observed in the medial smooth muscle cells of all vessels examined but not in the endothelial cells. Patients with hypertension displayed more severe intimal thickening than those without hypertension. Immunohistochemical analysis suggested that almost all of the intimal proliferative cells originated from smooth muscle cells. In contrast to media, endothelin-A receptor mRNA signals in intimal smooth muscle cells were low and heterogeneous. In the thickened arterial intima of hypertensive patients, the signals were detected just beneath the luminal endothelium but not deep in the intimal smooth muscle cell layer. By contrast, staining with anti-alpha-smooth muscle actin antibody was more intense in the deep layer than in the subendothelium. These findings suggest that the modulation of endothelin-A receptor gene expression in smooth muscle cells differs between the intima and media. Its regulated expression in intimal smooth muscle cells might affect the proliferative activity of these cells in patients with hypertension.

Inhibitory effect of atrial natriuretic peptide on accelerated endothelin secretion from cultured human endothelial cells

This study investigated the effect of atrial natriuretic peptide (ANP) on endothelin (ET) secretion from cultured human endothelial cells. Confluent umbilical venous endothelial cells were incubated with experimental agents in multi-well plates, and the level of immunoreactive ET in the medium was measured by radioimmunoassay. There was no significant effect of ANP (10(-8), 10(-7) and 10(-6) M) on ET secretion after a 3- or 6-hour incubation. However, with 24-hour incubation, ANP significantly inhibited ET secretion from cultured human endothelial cells (control, 139.0 +/- 7.2 fmol/well; 10(-7) M, 89.4 +/- 4.7 fmol/well; 10(-7) M, 79.4 +/- 8.2 fmol/well; 10(-6) M, 71.0 +/- 10.1 fmol/well, P < 0.01). Furthermore, the addition of 8-bromo-cyclic GMP to the medium inhibited ET secretion (control, 147.2 +/- 2.9 fmol/well; 10(-5) M, 140.9 +/- 2.3 fmol/well; 10(-4) M, 143.0 +/- 1.0 fmol/well; 10(-3) M, 96.6 +/- 6.3 fmol/well, P < 0.01). These findings demonstrate that ANP inhibits accelerated ET secretion from cultured human endothelial cells, probably due to augmentation of intracellular cyclic GMP levels by ANP-activated guanylate cyclase.

Effects of calcium- and ETA-receptor antagonists on endothelin-induced vasoconstriction and levels of endothelin in the human internal mammary artery

1. The effects of the ETA receptor antagonist BQ123 and dihydropyridine calcium antagonists on the vasoconstrictor effect of endothelin-1 (ET-1) were studied in human isolated internal mammary artery (IMA). The effect of the calcium antagonist, nisoldipine, on ET-1 levels has also been examined in cultured IMA endothelial cells (IMAEC). 2. The results showed that BQ123 and the calcium antagonists nisoldipine, isradipine, nitrendipine and nifedipine fully relaxed IMA precontracted with 3 nmol/L ET-1 with the EC50 values of 7.18 +/- 0.09 (-log mol/L) for BQ123, and 7.68 +/- 0.07, 7.02 +/- 0.12, 6.96 +/- 0.08 and 6.89 +/- 0.09 for the calcium antagonists, respectively. 3. Pretreatment of IMA with 10, 30, 100 and 300 nmol/L nisoldipine significantly depressed the maximal response (Max; 88.3 +/- 5.1, 75.2 +/- 4.9, 59.3 +/- 5.6 and 56.2 +/- 4.8% of maximal noradrenaline response versus 99.1 +/- 13.2% in control, P < 0.01) of IMA to ET-1 without a significant change in the EC50 values. 4. Pretreatment of IMA with 300 nmol/L BQ123 significantly increased both the EC50 (7.97 +/- 0.09 vs 8.36 +/- 0.08 in the control, P < 0.05) and the Max (138.1 +/- 10.2% vs the control, P < 0.01) of IMA to ET-1. 5. Incubation of IMAEC with nisoldipine for 7 h resulted in a dose-dependent (10(-8)-10(-5) mol/L) reduction up to 93.1% in ET levels in the conditioned media.(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of lipoproteins on endothelial function

The endothelium is a physical barrier between the blood and vascular smooth muscle, a source of enzymes activating and deactivating cardiovascular hormones and a site of production of relaxing and contracting factors. Nitric oxide is a potent vasodilator and inhibitor of platelet function which under most circumstances is released together with prostacyclin which exerts similar effects. Both substances play an important protective role in the coronary circulation in that they cause continuous vasodilation and inhibition of platelet function. In addition, the endothelium is a source of contracting factors such as endothelin-1, thromboxane A2 and endoperoxides. Due to its strategic anatomic position, the endothelium is a primary target of injuries and cardiovascular risk factors. Besides other risk factors such as hypertension and diabetes, low density lipoproteins alter endothelial function. A reduced release of endothelium-derived relaxing factors and an enhanced liberation of endothelium-derived contracting factors are common in the presence of lipoproteins. These alterations in endothelial function are likely to contribute to the pathogenesis as well as progression and complications of coronary artery disease such as vasospasm and thrombus formation. This review will focus on the influence of lipoproteins on endothelial function.

Effect of percutaneous transluminal coronary angioplasty on circulating endothelin levels

Percutaneous transluminal coronary angioplasty (PTCA) is frequently associated with vasoconstriction involving large vessels as well as microcirculation, but the potential mechanisms remain poorly defined. In this study, we tested the hypothesis that endothelial disruption during PTCA is associated with an increase in circulating levels of endothelin, a potent endothelium-derived vasoconstrictor peptide. Circulating levels of endothelin and other potential vasoactive mediators such as atrial natriuretic factor, epinephrine and norepinephrine were measured immediately before and after PTCA in 23 patients with coronary artery disease. Although there was no change in the endothelin levels after angiography alone (43 +/- 5 vs 44 +/- 7 pg/ml, p = 0.5), there was a significant increase after PTCA (32 +/- 8 to 37 +/- 10 pg/ml, p < 0.005). The increase in endothelin was associated with a significant increase in atrial natriuretic factor (78 +/- 57 to 129 +/- 131 ng/ml, p = 0.01) and a decrease in epinephrine and norepinephrine levels (111 +/- 64 to 59 +/- 36 pg/ml, p = 0.005, and 1,131 +/- 500 to 811 +/- 311 pg/ml, p = 0.003, respectively). Circulating levels of endothelin did not correlate with the percent coronary stenosis before or after PTCA or the presence or absence of angiographically visible thrombus. These findings suggest that endothelial injury during PTCA may be associated with increased circulating levels of endothelin and its counter-regulatory hormone, atrial natriuretic factor, and also with a reciprocal decrease in epinephrine and norepinephrine levels. Thus, these humoral changes may modulate changes in coronary vascular tone after PTCA.

Circulating and tissue endothelin immunoreactivity in hypercholesterolemic pigs

BACKGROUND

Hypercholesterolemia is characterized by a coronary vasoconstrictive response to the endothelium-dependent vasodilator acetylcholine. This abnormality may be due to reduced synthesis of endothelium-derived relaxing factor and/or enhanced synthesis and release of an endothelium-derived contracting factor. Endothelin is an endothelium-derived vasoconstrictor and mitogenic peptide that is present in normal plasma, and its circulating concentrations are elevated in disease states that are characterized by abnormal endothelium-dependent relaxation to acetylcholine. The current studies were designed to test the hypotheses that experimental hypercholesterolemia results in elevation of plasma and tissue endothelin immunoreactivity and that the abnormal acetylcholine-evoked coronary vasoconstriction in the hypercholesterolemic animals is associated with further elevation of plasma endothelin.

METHODS AND RESULTS

Plasma concentrations and molecular forms of endothelin immunoreactivity were determined following 2% cholesterol diet for 4 months in pigs and during intracoronary acetylcholine administration. Second, we assessed the presence of endothelin in the coronary vascular wall by using immunohistochemistry. Hypercholesterolemia elevated plasma endothelin concentration and enhanced coronary artery tissue endothelin immunoreactivity. The endothelium-dependent vasodilator acetylcholine further increases plasma endothelin in hypercholesterolemia in association with coronary vasoconstriction. The predominant molecular form of endothelin in hypercholesterolemia is the biological active endothelin-1.

CONCLUSIONS

This study suggests a role for endothelin as an early participant and a marker for the endothelial dysfunction in hypercholesterolemia as well as a participant in the atherogenic process.

Increased endothelin plasma concentrations in patients with coronary artery disease or hyperlipoproteinemia without coronary events

Endothelins are made by endothelial cells, macrophages, and vascular smooth muscle cells, among others, and are the most potent endogenous vasoconstrictors yet discovered, with additional growth-promoting properties. A locally increased endothelin production in coronary artery disease or other atherosclerotic diseases may increase circulating endothelin plasma concentrations before symptoms of disease are manifest. We determined endothelin plasma concentrations (1) in 43 patients suffering from coronary artery disease (CAD); (2) in 43 patients with hyperlipoproteinemia without coronary artery disease (HLP); (3) in 29 healthy control subjects (C), by means of a novel extraction procedure and radioimmunoassay followed by chromatographic separation. Plasma concentrations in HLP and C overlapped, but were still significantly different (29 +/- 10 vs 21 +/- 8 fmol/ml, ANOVA and Duncan's test). Significantly increased plasma concentrations were also found in patients with CAD, with the highest levels in a subgroup of 8 patients presenting with unstable angina (43 +/- 12 vs 53 +/- 15 fmol/ml). There were no statistically significant differences between CAD groups with (n = 28) or without hyperlipoproteinemia (n = 15) (42 +/- 14 vs 41 +/- 16 fmol/ml; n.s.). Likewise there was no relationship between endothelin plasma concentration in any of the patients studied and lipid fractions in serum. Increased endothelin plasma concentrations in HLP patients without evidence of coronary artery disease are thus not related to the hyperlipidemic state per se, but may rather indicate presence of an increased vasoconstrictor tonus, pre-clinical or silent atherosclerotic disease.

Polyclonal 111In-IgG, 125I-LDL and 125I-endothelin-1 accumulation in experimental arterial wall injury

To test iodine-125 labelled low-density lipoprotein (125I-LDL), polyclonal indium-111 labelled immunoglobulin G (111In-IgG) and iodine-125 labelled endothelin-1 uptake in metabolically active atheromatous plaques after arterial wall injury, we performed balloon de-endothelialization of carotid arteries or abdominal aortas in 24 New Zealand male rabbits which were fed with a normal diet (n = 14) or a hypercholesterolaemic diet (n = 10) after surgery. Six weeks later the animals were injected with 200 microCi of 125I-LDL and/or with 100 microCi of 111In-IgG or with 9 microCi of 125I-endothelin-1. Forty-eight hours later the animals were sacrificed. Carotid arteries and aortas were removed, counted and fixed for autoradiography and light microscopy examination. Contralateral carotid arteries and thoracic aortas served as controls. Significant 111In-IgG uptake was observed in the injured arteries at autoradiography, with localization mainly in the healing edges, and at well counting. The percentage of the injected dose per gram (%D.inj/g) was 0.0188 +/- 0.06 versus 0.0059 +/- 0.003 in controls (P < 0.05). There was no difference in 111In-IgG uptake between arteries with injury alone and those with active atheroma formation at the site of the injury. Significant 125I-LDL uptake was observed only when lipid deposition was present at light microscopy (%D.inj/g of 0.0024 +/- 0.0005 vs. 0.0010 +/- 0.0003 in controls, P < 0.05). 125I-endothelin-1 accumulation was observed in four of five injured aortas both at autoradiography, with diffuse localization, and at well counting (%D.inj/g of 0.0012 +/- 0.0004 in the abdominal aortas vs 0.0008 +/- 0.0003 in the thoracic aortas).(ABSTRACT TRUNCATED AT 250 WORDS)

Role of the leucocyte in the pathogenesis of vascular disease

The leucocyte plays a key role in the local and systemic tissue injury that results from peripheral arterial disease and chronic venous insufficiency. Despite the apparent dissimilarities between limb ischaemia and chronic venous ulceration, in both diseases macrovascular abnormalities lead to microvascular leucocyte trapping and activation. Activated leucocytes adhere to and damage adjacent endothelium by expressing adhesion molecules and releasing harmful moieties such as proteases and free radicals. Subsequent loss of endothelial integrity and the migration of activated leucocytes outwith the circulation leads to destruction of surrounding tissue. Leucocytes and their products are also involved in the systemic manifestations of ischaemia such as multiple organ failure and coagulopathy. An overview of leucocyte biology as it pertains to peripheral arterial and venous disease is presented. The opportunities for novel therapeutic interventions based on a better understanding of this biology are also discussed.

In vitro characterization of Ro 46-2005, a novel synthetic non-peptide endothelin antagonist of ETA and ETB receptors

Ro 46-2005 is a new synthetic non-peptide endothelin (ET) receptor antagonist. In binding experiments, Ro 46-2005 proved to be equipotent (IC50 200-500 nM) for inhibition of [125]ET-1 binding on the two known ET receptor subtypes (ETA and ETB). Scatchard analysis was consistent with a competitive binding mode. Ro 46-2005 also inhibited the functional consequences of ET-1 stimulation: the ET-1 induced release of arachidonic acid from rat mesangial cells was inhibited with an IC50 of 1.8 microM.

Pathophysiological role of endothelin revealed by the first orally active endothelin receptor antagonist

Since its discovery, endothelin-1 has attracted considerable scientific interest because of its extremely potent and long-lasting vasoconstrictor effect and its binding to G-protein-coupled receptors. Plasma concentrations of endothelin-1 are low and its release by endothelial cells is polarized towards the basolateral side, suggesting that it is a paracrine factor and not a hormone. Consequently, the effect of injected endothelin-1 may not reflect the effect of endogenous endothelin-1. In contrast, blockade of the action of endogenous endothelin-1 using receptor antagonists should be a valuable means of investigating its physiological and pathological effects. We report here evidence for the pathophysiological role of endothelin-1 as brought by the first synthetic orally active nonpeptide antagonist of endothelin receptors, Ro 46-2005.

Endothelins in the kidney: physiology and pathophysiology

In summary, ET may be important in the pathogenesis of multiple diseases of the kidney. Alterations in ET-1 production and action may lead to severe vasoconstriction, mesangial cell contraction, glomerular cell proliferation, and enhanced sodium and water retention. It is not surprising, therefore, that intense investigations are under way in an effort to develop specific inhibitors of ET action, including ECE inhibitors and ET receptor blockers. It is likely that with the development of these agents, we will uncover even more diseases in which ET mediates renal dysfunction and in which, hopefully, blockers of ET action will be of therapeutic benefit.

High frequency rotational ablation: an alternative in treating coronary artery stenoses and occlusions

OBJECTIVE

To prove the safety and effectiveness of high frequency rotational ablation of coronary artery stenoses and occlusion in humans.

SUBJECTS

106 patients with symptoms (91 men, 15 women) who had 67 significant stenoses, mainly types B and C, and 46-chronic occlusions.

MAIN OUTCOME MEASURES

Mean change in diameter stenosis after rotational angioplasty alone and in combination with percutaneous transluminal coronary angioplasty immediately after treatment and 24 hours and six months later; restenosis rates at six months; complication of treatment.

RESULTS

Rotational ablation could not be used in five stenoses and 16 chronic occlusions because of inability to reach or cross the lesion with the Rotablator guide wire. In four cases rotational ablation failed. Initial angiographic and clinical success by rotational ablation was achieved in 40 of the 67 stenoses (60%) and in 18 of the 46 chronic occlusions (39%). Additional balloon angioplasty was performed in 45 patients, increasing the success rates to 79% and 54%, respectively. In the 62 stenoses treated by rotational ablation the angiographic diameter stenoses were reduced from 76% (SD 14%) to 32% (14%) after Rotablator treatment alone and from 75% (11%) to 33% (17%) with additional balloon angioplasty. In the 30 chronic occlusions treated by rotational ablation the angiographic diameter stenoses were reduced to 38% (18%). At six months angiographic restenosis was evident in nine of the 25 (36%) stenoses treated with rotational ablation alone, in seven of the 22 (32%) stenoses treated with rotational and balloon angioplasty, and in 14 of the 24 (58%) chronic occlusions. There were no procedural deaths and two patients (2%) underwent emergency coronary artery bypass grafting. Although no transmural infarction occurred, there were five (6%) non-Q wave infarctions (two embolic side branch occlusions, two subacute occlusions, and one acute occlusion). Clinically insignificant slight increases in creatine kinase activity were seen in five patients (6%). Severe coronary artery spasm unresponsive to medical treatment was provoked in seven cases (8%).

CONCLUSIONS

High frequency rotational ablation is a safe and effective method for treating type B and C coronary artery lesions with results comparable to percutaneous transluminal coronary balloon angioplasty. The combined use of rotational ablation and balloon angioplasty is feasible and is necessary in about half of all procedures, in most cases because the lumen created by the biggest burr is too small.

Effect of endothelin-1 on neutrophil adhesion to endothelial cells and perfused heart

BACKGROUND

Based on recent evidence showing that endothelin-1 stimulates several activation mechanisms on neutrophils, the aim of the present study was to analyze the effects of endothelin-1 on neutrophil adhesion to endothelial cells and neutrophil accumulation in the heart.

METHODS AND RESULTS

The experiments included (1) adhesion of 51Cr-labeled human neutrophils to bovine endothelial cells in culture both in the presence and absence of monoclonal antibodies against the alpha- and beta-subunits of integrins; (2) surface expression of the alpha- and beta-integrin antigens; (3) accumulation of 51Cr-labeled neutrophils on the isolated perfused rabbit heart; (4) in vivo accumulation of autologous neutrophils in the heart, as assessed by myeloperoxidase activity. Endothelin-1 stimulated neutrophil adhesion to endothelial cells (increase of 1 x 10(5) +/- 1 x 10(4) neutrophils per well). The endothelin-1-induced adhesion was blocked (83 +/- 6%) by the anti-CD18 antibody TS1/18 and by several anti-alpha-subunit antibodies. The expression of CD18 and CD11b on the neutrophil surface was also increased by endothelin-1. Endothelin-1 enhanced neutrophil accumulation in the isolated rabbit heart by 4.2 times throughout a TS1/18-inhibitable mechanism. Myeloperoxidase activity increased by 4.2 times in hearts infused in vivo with endothelin-1.

CONCLUSIONS

Endothelin-1 stimulates neutrophil adhesion to endothelial cells by an effect on the expression of adhesive molecules on the neutrophil surface. Endothelin-1 stimulates neutrophil accumulation in vivo and in vitro in the heart. Antibodies against the integrin complex block the endothelin-1-dependent neutrophil adhesion. These findings have potential importance in the pathophysiology of endothelin-1-increased states.

Platelet-vessel wall interaction: role of nitric oxide, prostaglandins and endothelins

Platelets can interact with the blood vessel wall in numerous ways. By releasing vasoactive substances such as adenosine tri- and diphosphate as well as serotonin, platelets can stimulate the formation of nitric oxide and prostacyclin within endothelial cells. Under physiological conditions, this may provide an important protective mechanism providing platelet inhibition and increased local blood flow at sites of platelet activation. In addition, platelets also can stimulate the formation of the vasoconstrictor peptide endothelin-1 within endothelial cells. On the other hand, platelet-derived substances such as thromboxane and serotonin can activate vascular smooth muscle cells and cause profound vasoconstriction. Platelet-vessel wall interaction is normally very low due to protective mechanisms. In disease states, however, endothelial dysfunction increases platelet-vessel wall interaction. Low-density lipoproteins markedly reduced endothelium-dependent relaxations to aggregating platelets and serotonin. Even more marked changes in endothelial function occur in atherosclerosis. These functional alterations of platelet-vessel wall interaction may play an important role in the pathogenesis of cardiovascular disease.

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

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

A new model of transient complete obstruction of retinal vessels induced by endothelin-1 injection into the posterior vitreous body in rabbits

Endothelin-1 (ET-1) is a potent vasoconstrictor peptide produced by vascular endothelial cells. In order to investigate the effects of ET-1 on retinal vessels, ET-1 (1-1000 pmol) was injected into the posterior vitreous body in rabbits. A high dose of ET-1 induced transient complete obstruction of the retinal vessels. In this experimental model of transient complete obstruction of the retinal vessels, the effects of ET-1 on retinal function were further analyzed by means of electroretinograms. The scotopic a-wave was not affected, but the amplitude of the scotopic b-wave was significantly elevated. The amplitude of oscillatory potentials was significantly reduced. These phenomena suggested that retinal ischemia without choroidal ischemia was brought about due to severe vasoconstriction of the retinal arteries. These findings indicate that intravitreal injection of ET-1 causes a transient cessation of blood supply from retinal vessels and that oscillatory potentials in electroretinograms appear to be sensitive for detecting changes of retinal circulation. This new model of transient complete obstruction of retinal vessels might be useful for studying the pathophysiology of severe retinal ischemia.

Circulating immunoreactive endothelin-1 in children with pulmonary hypertension. Association with acute hypoxic pulmonary vasoreactivity

To determine whether circulating levels of endothelin-1 (ET-1), a potent vasoconstrictor peptide, are elevated in children with pulmonary hypertension and related to the degree of hypoxic pulmonary vasoconstriction, we measured arterial and mixed venous plasma concentrations of immunoreactive ET-1 (irET-1) in 13 children during cardiac catheterization. Clinical diagnoses in seven children with pulmonary hypertension (PH) included chronic lung disease (four children), congenital heart disease after surgical repair (two children), and primary ("reactive") pulmonary hypertension (one child). Blood samples were simultaneously obtained from pulmonary artery (venous) and systemic arterial sites during baseline conditions. Plasma irET-1 was elevated in children with PH (12.3 +/- 3.4 versus 3.6 +/- 0.7 pg/ml, PH versus non-PH; p < 0.01). Arterial/venous irET-1 ratios in the PH group (1.1 +/- 0.2) were not different from those in the non-PH group. During acute hypoxia, mean Ppa increased from 27 +/- 3 to 40 +/- 5 mm Hg. Basal irET-1 correlated strongly with the degree of elevation of mean Ppa during acute hypoxia (r = 0.69; p < 0.02). We conclude that irET-1 levels are often elevated in children with PH, and they are strongly correlated with pulmonary vasoreactivity during acute hypoxia. Whether elevated irET-1 levels contribute directly to or are markers of altered pulmonary vascular tone and reactivity in children with PH remains speculative.

Hypercholesterolemia promotes endothelial dysfunction in vitamin E- and selenium-deficient rats

Abnormal regulation of local vascular tone occurs early in human and experimental atherosclerosis. Impaired endothelium-dependent vascular relaxations mediated by endothelium-derived relaxing factor are an important contributor to these abnormalities. Endothelium-derived relaxing factor is nitric oxide released as such or attached to a carrier molecule. Oxidized lipoproteins impede endothelium-derived relaxing factor-mediated responses in vitro. We designed in vivo experiments to determine whether hypercholesterolemia with and without deficiency of two endogenous lipid antioxidants, vitamin E and selenium, would result in endothelial dysfunction. Vitamin E and selenium deficiencies were induced in a group of hypertension-prone Dahl salt-sensitive rats fed a diet high in cholesterol (4%) but low in NaCl (0.5%) for 18 weeks. Two other groups of Dahl salt-sensitive rats received diets sufficient in vitamin E and selenium but containing either high or normal cholesterol levels (control group). Serum cholesterol levels increased approximately 10-fold in the two groups of rats fed high-cholesterol diets. Systolic blood pressure was 143 +/- 3 mm Hg in high-cholesterol/vitamin E- and selenium-sufficient rats and 142 +/- 5 mm Hg in high-cholesterol/vitamin E- and selenium-deficient rats (P = NS). Mild intimal thickening and occasional mononuclear cell infiltration were observed in both of these groups. Serum vitamin E levels were decreased, whereas serum thiobarbituric acid-reactive substances and exhaled pentane (two indicators of endogenous lipid oxidation) were significantly increased in high-cholesterol/vitamin E- and selenium-deficient rats compared with high-cholesterol/vitamin E- and selenium-sufficient rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Stimulation of endothelin-1 release by low density and very low density lipoproteins in cultured human endothelial cells

To examine the effects of lipoproteins on the secretion of endothelin-1 from endothelial cells, we measured immunoreactive (ir) endothelin-1 release from cultured human umbilical vein endothelial cells in the presence or absence of various concentrations of native low density lipoprotein (LDL), oxidized LDL, and very low density lipoprotein (VLDL). Cultured endothelial cells secreted ir-endothelin-1 into serum-free medium in a time-dependent manner, and the secretion was clearly stimulated following a 15-24-h incubation with 10 micrograms/ml oxidized LDL. The secretion of ir-endothelin-1 increased in a dose-dependent manner after a 24-h incubation with oxidized LDL, while only a high dose of native LDL and VLDL significantly increased ir-endothelin-1 secretion. The release of ir-endothelin-1 stimulated by 20 micrograms/ml oxidized LDL was reproduced by the same concentration of acetylated LDL but not native LDL. These observations indicate that the release of ir-endothelin-1 from endothelial cells is stimulated by lipoproteins, in particular by oxidized LDL, probably through the endothelial scavenger receptor. This increase in ir-endothelin-1 release induced by oxidized LDL may contribute to the development of atherosclerotic vascular lesions.

Expression of endothelin-1 in the lungs of patients with pulmonary hypertension

BACKGROUND

Pulmonary hypertension is characterized by an increase in vascular tone or an abnormal proliferation of muscle cells in the walls of small pulmonary arteries. Endothelin-1 is a potent endothelium-derived vasoconstrictor peptide with important mitogenic properties. It has therefore been suggested that endothelin-1 may contribute to increases in pulmonary arterial tone or smooth-muscle proliferation in patients with pulmonary hypertension. We studied the sites and magnitude of endothelin-1 production in the lungs of patients with various causes of pulmonary hypertension.

METHODS

We studied the distribution of endothelin-1-like immunoreactivity (by immunocytochemical analysis) and endothelin-1 messenger RNA (by in situ hybridization) in lung specimens from 15 control subjects, 11 patients with plexogenic pulmonary arteriopathy (grades 4 through 6), and 17 patients with secondary pulmonary hypertension and pulmonary arteriopathy of grades 1 through 3.

RESULTS

In the controls, endothelin-1-like immunoreactivity was rarely seen in vascular endothelial cells. In the patients with pulmonary hypertension, endothelin-1-like immunoreactivity was abundant, predominantly in endothelial cells of pulmonary arteries with medial thickening and intimal fibrosis. Likewise, endothelin-1 messenger RNA was increased in the patients with pulmonary hypertension and was expressed primarily at sites of endothelin-1-like immunoreactivity. There was a strong correlation between the intensity of endothelin-1-like immunoreactivity and pulmonary vascular resistance in the patients with plexogenic pulmonary arteriopathy, but not in those with secondary pulmonary hypertension.

CONCLUSIONS

Pulmonary hypertension is associated with the increased expression of endothelin-1 in vascular endothelial cells, suggesting that the local production of endothelin-1 may contribute to the vascular abnormalities associated with this disorder.

Hypertension, hyperlipidemia, and renal damage

Experimental studies have demonstrated that a number of factors participate in the progression of renal disease. Systemic and glomerular hypertension have been shown to be critical factors in renal injury. Hyperlipidemia that frequently coexists with renal disease also has been suggested as an important participatory factor in nephron damage. Interestingly, both hypertension and hyperlipidemia seem to evoke glomerular growth, a factor that has also been postulated to be involved in glomerular and tubular destruction. Recently, experimental and clinical data suggest that an important interaction occurs between hyperlipidemia and hypertension. Not only do they frequently coexist, but hypertension dramatically exaggerates hyperlipidemic injury, and hyperlipidemia alters systemic and glomerular vascular production of vasoactive substances which maintain basal vascular tone. Thus, these recent observations underscore the interactive potential of the various risk factors that participate in progression of renal disease. They also suggest that multiple interventional strategies may be needed to optimally prevent progressive nephron loss.

Recombinant human erythropoietin (rHuEPO) increases endothelin-1 release by endothelial cells

Hypertension is a major complication of rHuEPO therapy in hemodialysis (HD) patients. We have previously reported that patients receiving rHuEPO intravenously (i.v.) had higher mean arterial pressure (MAP) and plasma endothelin-1 (ET-1) levels than those in which the hormone was administered subcutaneously (s.c.). To test whether the increased serum ET-1 levels associated with i.v. rHuEPO administration are the result of a direct effect of the hormone on ET-1 release by the endothelial cells (EC), we examined the effects of rHuEPO in vitro. Bovine pulmonary artery endothelial cells (BPAEC) were exposed to doses of rHuEPO of 0.8; 1.6; 3.3 and 6.6 U/ml. A 24 hour-time course showed maximal ET-1 production at 12 hours for all the doses tested. A significant increase in cell proliferation over controls was observed at 24 hours, for all rHuEPO doses, and no correlation was found between ET-1 values and cell proliferation. Inhibition of protein synthesis by cycloheximide (10 micrograms/ml) abolished the stimulation of ET-1 release by rHuEPO. Thrombin (4 U/ml) and angiotensin II (10(-7) M), two potent stimulators of ET-1 release, had additive effects to those of rHuEPO. Specific thrombin and angiotensin II antagonists blocked these additive effects, reducing ET-1 release to the level of rHuEPO stimulation alone. In summary, rHuEPO stimulates vascular EC in culture to increase ET-1 release through an increase in synthesis and in a time dependent fashion. The routes of stimulation seem to differ from other known ET-1 secretogoges. Our data also confirm a significant mitogenic effect of rHuEPO on the endothelial cell.

Endothelin-converting enzyme activity in human serum lipoprotein fraction

Endothelin-1 (ET-1)-converting enzyme (ECE) activity in the human serum lipoprotein fraction was studied using a sensitive enzyme immunoassay and reverse-phase high performance liquid chromatography. The ECE activity of cleaving synthetic human big ET-1 into ET-1 by the serum lipoprotein fraction was about 14-times greater than that by whole serum, and the activity was closely associated with lipoprotein itself. The lipoprotein ECE activity, which was optimal at pH 7.0, was inhibited by EDTA, o-phenanthroline, phosphoramidon, thiorphan, phenylmethanesulfonyl fluoride and chymostatin, but not by cysteine or aspartic proteinase inhibitors, suggesting metalloproteinase- and chymotrypsin-like properties. These results suggest that the serum lipoprotein ECE may be involved in the processing of big ET-1 to ET-1 in the circulatory system.

[Endothelin: the vasoconstrictor of the 1990's?]

Endothelin is a recently isolated 21 amino acid peptide with vasoconstrictor activity. It seems to be part of the "hormonal" production by the vascular endothelium and might play a key role in the regulation of vasomotricity. The principal property of endothelin is that it induces an intense and prolonged arterial and venous contraction. Endothelin is secreted by endothelial cells under the influence of various stimuli (thrombin, adrenaline, shearing stress, hypoxia, etc.), then binds to specific membrane receptors thereby increasing the intracellular free calcium concentration. Endothelin has many other vascular and extravascular properties: it has positive inotropic and chronotropic effects, increases renal vascular resistances and reduces the glomerular filtration rate, contracts bronchial and gastrointestinal smooth muscle, induces proliferation of the vascular smooth muscle cells as well as that of fibroblasts and glomerular mesangial cells. Compared with experimental data in animals, human data are still scantly. Plasma endothelin concentration rises in acute renal failure and in chronic renal failure treated by dialysis, diabetes mellitus, essential arterial hypertension, pre-eclampsia and asthma. The development of specific antagonists and endothelin in synthesis inhibitors should soon enable us to specify the modes of regulation of endothelin production before considering applications to therapy.

Growth regulatory properties of endothelins

Endothelins are produced by endothelial and epithelial cells, macrophages, fibroblasts, and many other types of cells. Their receptors are present in numerous cells, including smooth muscle cells, myocytes, and fibroblasts. Evidence now suggests that the three isoforms of endothelins (ET-1 and the other two related isopeptides, ET-2 and ET-3) regulate growth in several of these cells. Endothelin-1 influences DNA synthesis, the expression of protooncogenes, cell proliferation, and hypertrophy. The participation of ET in mitogenesis involves activation of multiple transduction pathways, such as the production of second messengers, the release of intracellular pools of calcium, and influx of extracellular calcium. Moreover, ET-1 acts in synergism with various factors, such as EGF, PDGF, bFGF, TGFs, insulin, etc., to potentiate cellular transformation or replication. Several of these factors may in turn stimulate the synthesis and/or the release of endothelins. The production and release of endothelins are also increased in acute and chronic pathological processes, e.g., atherosclerosis, postangioplastic restenosis, hypertension, and carcinogenesis. It is postulated that endothelins act in a paracrine/autocrine manner in growth regulation and play an important role mediating vascular remodeling in some cardiovascular diseases. The present review analyses the implication of endothelins (ET-1, -2, and -3) in physiopathology related to their growth regulatory properties.

The structure and specificity of endothelin receptors: their importance in physiology and medicine

In addition to involvement in vascular endothelium-smooth muscle communication, the secretion of and receptors for, endothelins are widely distributed. Two cloned receptor subtypes are G-protein-coupled to several intracellular messengers, predominantly inositol phosphates. From a knowledge of structure-activity relationships and peptide conformations, details of receptor architecture and selective agents, including nonpeptides and antagonists, have been discovered. From the nature of the actions of endothelins, receptor distributions (including CNS) and plasma levels, it is concluded that they are paracrine factors normally involved in long-term cellular regulation, but which may be important in several pathologies, many of which are stress-related.

Preventive effect of nicardipine on hyperplastic changes in venous bypass grafts

Nicardipine is a relatively new calcium channel blocker with important properties that could result in attenuation of the adverse proliferative changes in autogenous vein bypass grafts. In this experimental, randomized, controlled study, the effect of nicardipine on the pathologic findings in aortoaortic bypass graft was assessed. Forty-two male rabbits (Orycytolagus cuniculus) were randomized to three groups: group 1 received nicardipine and groups 2 and 3 placebo for 4 weeks, after which an aortaortic bypass was realized with an autogenous inferior vena cava segment. During the following 4 weeks, groups 1 and 2 received nicardipine, and placebo was continued in group 3. The animals were sacrificed at the end of the study to permit removal and evaluation of the bypass grafts. The mean intimal and medial thickness values for groups 1 and 2 were lower than those for group 3, indicating that nicardipine has a significant preventive effect on the hyperplastic changes in venous bypass grafts compared to placebo. The mean intimal and medial thickness values of group 1 were also lower than those of group 2, and the differences carried statistical relevance, suggesting that the use of nicardipine before grafting could potentiate its protective effect. To provide stimulus for further research, an attempt is made to relate the hyperplasia-preventing effect of nicardipine to possible mechanisms.