Endothelin in human congestive heart failure

The effects of endothelin-A receptor blockade during the progression of pacing-induced congestive heart failure

OBJECTIVES

We sought to identify the effects of endothelin (ET) subtype-A (ET(A))) receptor blockade during the development of congestive heart failure (CHF) on left ventricle (LV) function and contractility.

BACKGROUND

Congested heart failure causes increased plasma levels of ET and ET(A) receptor activation.

METHODS

Yorkshire pigs were assigned to four groups: 1) CHF: 240 beats/min for 3 weeks; n=7; 2) CHF/ET(A)-High Dose: paced for 2 weeks then ET(A) receptor blockade (BMS 193884, 50 mg/kg, b.i.d.) for the last week of pacing; n=6; 3) CHF/ET(A)-Low Dose: pacing for 2 weeks then ET(A) receptor blockade (BMS 193884, 12.5 mg/kg, b.i.d.) for the last week, n=6; and 4) CONTROL: n=8.

RESULTS

Left ventricle fractional shortening decreased with CHF compared with control (12+/-1 vs. 39+/-1%, p < 0.05) and increased in the CHF/ET(A) High and Low Dose groups (23+/-3 and 25+/-1%, p < 0.05). The LV peak wall stress and wall force increased approximately twofold with CHF and remained increased with ET(A) receptor blockade. With CHF, systemic vascular resistance increased by 120%, was normalized in the CHF/ET(A) High Dose group, and fell by 43% from CHF values in the Low Dose group (p < 0.05). Plasma catecholamines increased fourfold in the CHF group and were reduced by 48% in both CHF/ET(A) blockade groups. The LV myocyte velocity of shortening was reduced with CHF (32+/-3 vs. 54+/-3 microm/s, p < 0.05), was higher in the CHF/ET(A) High Dose group (39+/-1 microm/s, p < 0.05), and was similar to CHF values in the Low Dose group.

CONCLUSIONS

ET(A) receptor activation may contribute to the progression of LV dysfunction with CHF.

Value of cardiopulmonary exercise testing and big endothelin plasma levels to predict short-term prognosis of patients with chronic heart failure

OBJECTIVES

We tested the hypothesis that, in patients with stable heart failure, measuring big endothelin-1 (ET-1) plasma level at rest predicts short-term prognosis better than peak oxygen consumption (VO2max) at exercise.

BACKGROUND

Cardiopulmonary exercise testing and evaluation of neurohumoral plasma factors are established tools to estimate survival in patients with heart failure. No data, however, exist comparing the prognostic value of both marker categories simultaneously.

METHODS

Two hundred twenty-six heart failure patients were studied in regard to a combined end point of death and prioritization for urgent cardiac transplantation within 1 year follow-up.

RESULTS

During the study period 149 patients were without cardiac events (group A), 69 patients died or were urgently transplanted (group B) and 8 patients were alive after a nonurgent heart transplant operation. Norepinephrine (p < 0.0001), atrial natriuretic peptide (p < 0.001), big endothelin plasma levels (p < 0.0001 as well as workload, VO2max and achieved percentage of predicted peak oxygen consumption (pVO2max) (all p < 0.0001) differed significantly between groups A and B. In multivariate stepwise regression analysis, however, only big ET-1 plasma concentration (chi2=74.4, p < 0.0001), New York Heart Association function class (chi2=33.9, p < 0.0001), maximal workload (chi2=7.2, p < 0.01, and plasma atrial natriuretic peptide (ANP) concentration (chi2=4.6, p < 0.05) were independently related to outcome. Peak oxygen consumption or pVO2max did not reach statistical significance in this model. Event-free survival rates were significantly lower in patients with a big ET-1 level of 4.3 fmol/ml or more than with lower big ET-1 levels (p < 0.0001).

CONCLUSION

We conclude that in patients with chronic heart failure who are stable on oral therapy measuring big ET-1 and ANP plasma levels may be a valuable noninvasive adjunct to improve the prognostic accuracy of detecting high risk patients compared with exercise testing alone.

Antiplatelet and anticoagulant therapy in the prevention of thromboemboli in chronic heart failure

Thromboembolism is an important complication in patients with heart failure. Several recent clinical trials have established the efficacy of anticoagulant therapy in patients with heart failure and atrial fibrillation. There is renewed interest in examining the role of antiplatelet and anticoagulation therapy in patients with heart failure in sinus rhythm. There is a need to identify patients at risk for thromboembolism in heart failure. However, there are data to suggest that occult thromboembolic events may contribute to disease progression, ischemic events, and sudden cardiac death. This review summarizes the incidence, potential mechanism, and therapeutic approaches for management of thromboembolism in heart failure.

Discovery and development of an endothelin A receptor-selective antagonist PD 156707

PD 156707 is a highly potent, selective antagonist of the ETA receptor that has demonstrated efficacy in a number of different disease models. The next few years will be exciting in the field of ET research as several compounds progress through clinical development. It is our hope that the efficacy that data demonstrated to date with PD 156707 will some day be translated into real hope for the patients who are waiting beyond the confines of our research laboratories.

Changes of neurohumoral parameters and endothelin-1 in response to exercise in patients with mild to moderate congestive heart failure

Plasma endothelin levels are increased in patients with moderate and severe CHF. Conflicting data exist about the endothelin-1 (ET) level in patients with mild to moderate CHF and the effect of maximal exercise on plasma ET levels.

METHODS AND RESULTS

We determined the plasma levels of ET and various neurohumoral parameters in 93 patients with CHF in functional class II and III of the NYHA classification at rest and after maximal bicycle exercise. Baseline ET level was increased compared to an age-matched healthy volunteer group (6.95+/-0.31 vs 3.29+/-0.17 pg/ml, mean+/-S.E.M., P<0.05), without significant differences between NYHA class II and III patients. Maximal exercise did not increase the ET level. In contrast, the neurohumoral parameters were significantly increased with maximal exercise. In conclusion, plasma levels of ET are increased in patients with mild to moderate CHF. However, no further increase in response to exercise was observed. Thus, it is highly unlikely that exercise capacity may be limited by ET-mediated peripheral vasoconstriction.

Fibrosis and inflammatory cells in human chronic chagasic myocarditis: scanning electron microscopy and immunohistochemical observations

The present study deals with both pathologic fibrosis and matrix connective tissue in chronic chagasic myocarditis. A total of 12 hearts were obtained at autopsy. Eight cases of chronic chagasic myocarditis were selected. Four cases without evidence of cardiac disease were used as controls. The diagnosis of chronic Chagas' heart disease was based on previously established criteria. A cell-maceration method was utilized to evaluate the spatial organization of the fibrillar collagen accumulation after removal of the myocardial tissue non-fibrous elements. The relationship between inflammatory cells identified by monoclonal antibodies and interstitial fibrosis stained with picrosirius red was assessed. Striking structural alterations of the collagen matrix in the perimysium were detected: increase in number and thickness of tendon-like structures, and markedly thickened and aggregated collagen strands. Besides, a diffuse increase in the thickness of collagen fibers surrounding individual myocytes, consisting of the endomysial matrix, mainly adjacent to the perimysium, could be observed. The dense-weave endomysial meshwork was composed of fine collagen fibrils, and it was continuous with those of adjacent myocytes, obscuring the lateral struts. Sometimes, thicker struts tethering myocytes to myocytes could be seen. These changes were associated with scattered dense scar-like foci, probably reflecting repair fibrosis associated with myocyte necrosis. Furthermore, the present results clearly showed the colocalization of foci of myocyte necrosis and degeneration and associated fibrosed areas and fibroblasts with T lymphocytes and macrophages. The accumulation of interstitial collagen fibers in chronic chagasic myocarditis may be expected to decrease myocardial compliance and disrupt synchronous contraction of the ventricles during systole, contributing to a spectrum of ventricular dysfunction that involve either the diastolic or systolic phase of the cardiac cycle or both. Myocardial fibrosis can be also implicated in the genesis of malignant ventricular tachyarrhythmias, major causes of sudden death among chronic chagasic patients. The increase in myocardial fibrosis could be directly related to an inflammatory reaction mainly composed of T lymphocytes and macrophages.

The influence of basal nitric oxide activity on pulmonary vascular resistance in patients with congestive heart failure

Increased pulmonary resistance may reduce survival and treatment options in patients with congestive heart failure. Nitric oxide (NO) is a determinant of normal pulmonary resistance vessel tone. We tested the hypothesis that loss of NO function contributes to increased pulmonary vascular resistance index (PVRI) in congestive heart failure. Pulmonary arterial resistance vessel function was studied in 25 conscious adults. Three groups were studied: 8 controls, 9 patients with congestive heart failure and normal PVRI, and 8 patients with congestive heart failure and raised PVRI. Segmental arterial flow was determined with a Doppler wire and quantitative angiography. NG-monomethyl-L-arginine (L-NMMA) was used to inhibit NO, whereas phenylephrine was used as an endothelium-independent control. The response to inhibition of NO with L-NMMA was less in patients with congestive heart failure and elevated PVRI than in patients with congestive heart failure and normal PVRI (p <0.05). The difference in response between the congestive heart failure groups was specific to NO-dependent regulation because the response to the endothelium-independent constrictor phenylephrine was not different (p = 0.92). There was no difference in response to L-NMMA between controls and patients with congestive heart failure and normal PVRI. The response to L-NMMA correlated to PVRI. In adults with congestive heart failure, NO appears to play an important role in maintaining normal pulmonary resistance.

Aggravation of left ventricular remodeling by a novel specific endothelin ET(A) antagonist EMD94246 in rats with experimental myocardial infarction

An endothelin (ET(A)) antagonist reduced mortality and an ET(A) + ET(B) antagonist prevented left ventricular dilatation in rats with large myocardial infarction. This study tested the hypothesis that long-term blockade of the ET(A) receptor would have beneficial effects on left ventricular function and remodeling. Three hours after coronary artery ligation or sham operation in rats, EMD94246 (100 mg/kg/day, n=62) or placebo (n=62) was given by gavage. Eight weeks later, left ventricular hemodynamic measurements were performed and left ventricular volume determined with a double-lumen catheter after KCl-induced cardiac arrest. EMD94246 treatment had no effects on mortality or hemodynamic parameters. In rats with large infarcts, EMD94246 significantly increased left ventricular volume (2.5+/-0.1 vs. 2.2+/-0.1 ml/kg; p < 0.05). The nonpeptide ET(A)-selective antagonist EMD94246 promoted chronic left ventricular dilatation in rats with large myocardial infarction.

A role for endothelin in the pathogenesis of hypertension: fact or fiction?

Endothelin-1 (ET-1) was discovered 10 years ago. Because it is one of the most potent vasoconstrictors in vivo, a pathophysiological role for the peptide as a mediator of hypertension has been postulated. Several clinical studies, however, have been unable to identify elevated ET levels in the plasma of hypertensive patients, suggesting that it does not play a prominent role in this disease. More recently, evidence has been presented that ETs act predominantly at the autocrine/paracrine level and that measurements of plasma levels can give only an indirect view of the activity of the system. In addition, transgenic technology has uncovered new actions of the peptide systems in recent years, which point to a key function of the system in prenatal development. Moreover, investigation of conditions associated with hypertensive end-organ damage, such as chronic renal failure, has led to a re-evaluation of the role of the ET system in hypertension. This article discusses this recent evidence and defines the exact role of the ET system in hypertension and hypertensive end-organ damage.

Whole-body cooling increases plasma endothelin-1 levels in women with primary Raynaud's phenomenon

To understand better the role of endothelin-1 (ET-1) in the pathogenesis of primary Raynaud's phenomenon (PRP), we investigated the basal ET-1 plasma levels and changes after whole-body cooling in healthy women and those with PRP. The study was performed as an open parallel-group comparison during the month of February. The Raynaud group included 21 female patients (mean age 45.3 years, range 21-57 years) who had had disabling Raynaud's phenomenon for a mean period of 17 years (range 2-26 years). The control group consisted of 25 healthy women (mean age 43.6 years, range 27-56 years). Plasma levels of ET-1 were measured on two separate occasions: once after 30 min of rest at room temperature and after 40 min of whole-body cooling. There were no significant differences in baseline plasma ET-1 levels between the two groups of women. The plasma ET-1 levels increased significantly in the PRP group after cold exposure (mean difference 0.11 pmol l-1, 95% CI 0.005-0.214, P = 0.012). In contrast, the levels of plasma ET-1 in the control group did not change significantly after cold provocation. In conclusion, no differences in plasma basal levels of ET-1 were observed between the two groups. However, women suffering from Raynaud's phenomenon responded with a slight but significant elevation in plasma levels of ET-1 after whole-body cooling, whereas the healthy control subjects did not. The results from the present study confirm previous observations that endothelial dysfunction may be of aetiological importance in PRP.

Endothelin as a regulator of cardiovascular function in health and disease

The endothelins are a family of endothelium-derived peptides that possess characteristically sustained vasoconstrictor properties. Endothelin-1 appears to be the predominant member of the family generated by vascular endothelial cells. In addition to its direct vascular effects, endothelin-1 has inotropic and mitogenic properties, influences homeostasis of salt and water, alters central and peripheral sympathetic activity and stimulates the renin-angiotensin-aldosterone system. Studies with endothelin receptor antagonists have indicated that endothelin-1 probably has complex opposing vascular effects mediated through vascular smooth muscle and endothelial ET(A) and ET(B)receptors. Endogenous generation of endothelin-1 appears to contribute to maintenance of basal vascular tone and blood pressure through activation of vascular smooth muscle ET(A)receptors. At the same time, endogenous endothelin-1 acts through endothelial ET(B) receptors to stimulate formation of nitric oxide tonically and to oppose vasoconstriction. In view of the multiple cardiovascular actions of endothelin-1, there has been much interest in its contribution to the pathophysiology of hypertension. Results of most studies suggest that generation of, or sensitivity to, endothelin-1 is no greater in hypertensive than it is in normotensive subjects. Nonetheless, the deleterious vascular effects of endogenous endothelin-1 may be accentuated by reduced generation of nitric oxide caused by hypertensive endothelial dysfunction. It also appears likely that endothelin participates in the adverse cardiac and vascular remodelling of hypertension, as well as in hypertensive renal damage. Irrespective of whether vascular endothelin activity is increased in hypertension, anti-endothelin agents do produce vasodilatation and lower blood pressure in hypertensive humans. There is more persuasive evidence for increased endothelin-1 activity in secondary forms of hypertension, including pre-eclampsia and renal hypertension. Endothelin-1 also appears to play an important role in pulmonary hypertension, both primary and secondary to diseases such as chronic heart failure. The hypotensive effects of endothelin converting enzyme inhibitors and endothelin receptor antagonists should be useful in the treatment of hypertension and related diseases. Development of such agents will increase knowledge of the physiological and pathological roles of the endothelins, and should generate drugs with novel benefits.

Abnormal vascular responses in human chronic cardiac failure are both endothelium dependent and endothelium independent

OBJECTIVE

To study underlying vascular responses in chronic heart failure in patients without ACE inhibitor treatment, and to compare them with age matched controls.

DESIGN

Forearm blood flow was studied using venous occlusion plethysmography in patients with chronic heart failure (n = 12) and matched controls (n = 13), after infusion of L-NMMA (a nitric oxide synthase inhibitor), glyceryl trinitrate (an endothelium independent vasodilator), and serotonin (an endothelium dependent vasodilator).

RESULTS

L-NMMA produced significant vasoconstriction in normal subjects (forearm blood flow reduced by 24%), but not in patients (6%; difference between groups p < 0.03). The vasodilator responses to glyceryl trinitrate were impaired in patients (p < 0.02). In normal controls, serotonin produced initial dilatation, followed by vasoconstriction at high doses. In patients, no vasodilator responses were observed, only late vasoconstriction (p < 0.03).

CONCLUSIONS

The vascular responses of patients are confirmed as being abnormal. The lack of response to L-NMMA suggests that nitric oxide does not contribute to basal vascular tone in patients with chronic heart failure. The responses to glyceryl trinitrate and to serotonin suggest that there is both smooth muscle and endothelial dysfunction in patients with chronic heart failure.

Estrogen and postmenopausal estrogen/progestin therapy: effect on endothelium-dependent prostacyclin, nitric oxide and endothelin-1 production

It is well documented that postmenopausal estrogen/progestin therapy (HRT) protects women against cardiovascular disorders. However, the mechanism(s) by which this protection is mediated remains largely unresolved, because beneficial effects of estrogen on the blood lipid profile account for only 20-30% of the overall protection. Growing evidence suggests that estrogen has direct effects on the blood vessel wall indicating that vascular endothelium may play a key role in mediating these effects by producing vasoactive factors, such as prostacyclin (PGI2), nitric oxide (NO) and endothelin-1 (ET-1). In vitro estrogen stimulates endothelial PGI2 and NO production, whereas ET-1 production is not affected. Moreover, in vivo studies indicate that estrogen and HRT increase PGI2 and NO production, whereas ET-1 production decreases. These effects are evidently mediated through estrogen receptors in endothelial cells. Thus, estrogen and HRT lead to the dominance of vasodilatory and antiaggregatory agents released by the endothelial cells. This may be an important new mechanism in the cardiovascular protection mediated by estrogen and HRT.

Effects of phosphoramidon, BQ 788, and BQ 123 on coronary and cardiac dysfunctions of the failing hamster heart

Coronary dysfunctions identified in the presence of chronic heart failure are an important pathophysiologic abnormality that influences the prognosis of the disease. Because the endothelin pathway plays a significant role in the increased peripheral vascular tone associated with heart failure, we hypothesized that the endothelin pathway may be involved in the abnormal coronary vasomotion associated with this pathologic condition. Experiments were carried out in failing hearts (UM-X7.1 cardiomyopathic hamsters, aged 225-250 days) and normal hearts (Syrian LVG hamsters, also aged 225-250 days). Isolated hearts were perfused at constant flow and exposed to the blocker of the generation of endothelin-1 (ET-1), phosphoramidon (10 microM infusion), as well as to the selective ET(A)-receptor antagonist BQ 123 (10 microM infusion) and to a selective ET(B)-receptor antagonist BQ 788 (1 microM infusion). Coronary and cardiac effects of exogenous ET-1 (0.01-100 pmol) were also studied. Phosphoramidon, BQ 788, and BQ 123 did not altered coronary perfusion pressure either in normal or in failing hearts, whereas cardiac contractility was significantly impaired in the presence of phosphoramidon and BQ 123. Coronary sensitivity to exogenous ET-1 did not demonstrate a significant difference between normal and failing hearts [median effective concentration (EC50), 7 pmol in failing hearts vs. 12 pmol in normal hearts; p = NS]. In the presence of exogenous ET-1, cardiac contractility was significantly increased in both groups. In normal hearts, the exogenous ET-1-induced increase in coronary perfusion pressure was completely antagonized by BQ 123, whereas combined administration of BQ 788 and BQ 123 was necessary to induce complete inhibition in failing hearts. The positive inotropic effect elicited by exogenous ET-1 (EC50) was completely abolished in the presence of BQ 123, whereas BQ 788 had no significant effect. Results indicate that the endothelin pathway does not play a significant role in the altered coronary vasomotion observed in this model of chronic heart failure. On the contrary, the endothelin pathway appears to participate in the maintenance of myocardial contractility. According to these observations, administration of an inhibitor of ET-1 synthesis, as well as the use of an ET(A)-receptor antagonist, may be contraindicated in the presence of poor left ventricular function because the endothelin pathway contributes significantly to the maintenance of cardiac contractility.

Expression of endothelin-1 and endothelin-converting enzyme-1 mRNAs and proteins in failing human hearts

Accumulating evidence suggests that endogenous endothelin-1 (ET-1) may contribute to the development of heart failure. In this study we determined sites of ET-1 synthesis and production in the failing human myocardium by immunohistochemistry and in situ hybridization for ET-1 and endothelin-converting enzyme-1 (ECE-1). Myocardial tissues were obtained from 19 patients with heart failure and from four noncardiac patients as controls. In both failing and nonfailing hearts, apparent immunoreactivity for ET-1 and ECE-1 was consistently seen in cardiac myocytes. Endothelial cells of intramyocardial coronary arteries and veins had only weak or focal ET-1 and apparent ECE-1 immunoreactivities. On the other hand, in situ hybridization showed strong signals for ET-1 and ECE-1 mRNAs in vascular endothelial cells but a lesser intensity of signals in cardiac myocytes. Apparent immunoreactivity and strong hybridization signals for both ET-1 and ECE-1 were seen in macrophages, which were abundant in infarcted regions of ischemic cardiomyopathy and in myocardium of septic patients but were rare in healthy hearts. These results suggest that, in failing human heart, vascular endothelial cells and macrophages rather than cardiac myocytes appear to be the principal ET-1 synthetic sites, although ET-1 peptides are abundantly present in cardiac myocytes of both failing and nonfailing hearts. Endogenous ET-1 may play a pathophysiologic role in human heart failure.

Renal endothelin-converting enzyme in rats with congestive heart failure

The expression and immunoreactivity of endothelin-converting enzyme (ECE) were examined in the renal tissue of rats with experimental congestive heart failure (CHF). Reverse transcriptase polymerase chain reaction (RT-PCR) revealed that ECE mRNA was more abundant (about twofold) in the renal medulla than in the cortex. Induction of heart failure caused a significant enhancement in the expression of this key enzyme in the renal cortex of rats with compensated CHF (delta + 28%) and in animals with decompensated heart failure (delta + 58%). An identical trend was also observed in the renal medulla, although these increases were moderate compared to those in the cortex. Similar findings were observed with Western blot techniques applying two monoclonal antibodies to rat ECE (AEC32-236 and AEC27-121). Taken together, these data suggest that upregulation of ECE is an important component in the activated renal ET system in CHF.

Endothelin: receptor subtypes, signal transduction, regulation of Ca2+ transients and contractility in rabbit ventricular myocardium

Endothelin (ET) isopeptides, ET-1, ET-2 and ET-3, elicit a positive inotropic effect (PIE) in association with a negative lusitropic effect, essentially with identical efficacies and potencies in the isolated rabbit papillary muscle, but with different concentration-dependent properties. Pharmacological analysis indicates that the PIE of ET-1 is mediated by an ETA2 subtype that is less sensitive to BQ-123 and FR139317, whereas the PIE of ET-3 is mediated by an ETA1 subtype that is highly sensitive to these ETA antagonists. ETs increased the amplitude of intracellular Ca2+ transient (CaT) in indo-1 loaded rabbit ventricular myocytes, but the increase was much smaller than that produced by elevation of [Ca2+]o or isoproterenol for a given extent of PIE, an indication of increased myofibrillar Ca2+ sensitivity. ETs stimulate phosphoinositide (PI) hydrolysis, which leads to production of inositol 1,4,5-trisphosphate (IP3) and diacylglycerol (DAG). Evidence for the role of IP3-induced Ca2+ release in cardiac E-C coupling is tenuous. Generation of IP3 induced by ET-1 was transient and returned to the baseline level when the PIE reached an elevated steady level. Protein kinase C (PKC) that is activated by DAG and also via other pathways triggered by ETs stimulates Na+-H+ exchanger to lead to an increased [Na+]i and alkalinization. The former may contribute to an increase in the amplitude of CaT through Na+-Ca2+ exchanger, and the latter, to an increase in myofibrillar Ca2+ sensitivity. A number of PKC inhibitors, such as staurosporine, H-7, calphostin C and chelerythrine, consistently and selectively inhibited the PIE of ET-3 without affecting the PIE of isoproterenol and Bay k 8644. The maximum inhibition was 20-30% of the total response. A Na+-H+ exchange inhibitor, [5-(N-ethyl-N-isopropyl) amiloride (EIPA)] or a Ca2+ antagonist, verapamil, could not completely inhibit the PIE of ET-3, but the combination of both inhibitors totally abolished the PIE of ET-3. These findings indicate that activation of PKC and subsequent activation of Na+-H+ exchanger and/or L-type Ca2+ channels may play a crucial role in the cardiac action of ET isopeptides in the rabbit ventricular myocardium.

Innovations in the pharmacologic management of heart failure

Improved understanding of the pathophysiologic course of heart failure has led to many advances in pharmacologic therapy. Angiotensin-converting enzyme inhibitors represent the first effort at targeting neurohormonal activation in chronic heart failure. More recently, beta-adrenergic receptor antagonists have been shown effective in blocking chronic sympathetic nervous system activation. The roles of digoxin and the newer, vasoselective calcium channel blockers in heart failure have been better defined. Other agents targeting the neurohormonal system are under investigation. These include angiotensin-receptor antagonists, aldosterone inhibitors, and endothelin antagonists. Experience with phosphodiesterase inhibitors and adrenergic agents has confirmed the importance of neurohormonal activation in progression of heart failure. Despite angiotensin-converting enzyme inhibitor, diuretic, and digoxin therapy, mortality in heart failure remains high. Careful manipulation of the neurohormonal response to heart failure holds promise for altering the course of the disease.

Oestrogen and progesterone inhibit the stimulated production of endothelin-1

Important vascular proteins such as endothelin-1 (ET-1) promote the development of cardiovascular diseases. Oestrogen, and perhaps progesterone, prevent the development of vascular disease in women through incompletely understood cellular mechanisms. We hypothesized that oestradiol or progesterone might regulate the production of ET-1 as a potential novel mechanism. We found that serum and angiotensin II (AII) significantly stimulated ET-1 secretion from cultured bovine aortic endothelial cells, inhibited 50-75% by oestradiol or by progesterone. Serum and AII stimulated ET-1 mRNA levels, inhibited at least 70% by oestradiol and by progesterone. Serum stimulated ET-1 transcription mainly through the first 43 nucleotides of the ET-1 promoter, but oestradiol and progesterone did not inhibit this. In contrast, AII stimulated ET-1 transcription through nucleotides -143 to -98, specifically involving an activator protein-1 (AP-1) site at -102. Oestradiol and progesterone caused a 60-70% inhibition of AII-stimulated wild-type construct -. 143ET-1/CAT activity (CAT is chloramphenicol acyltransferase). AII-stimulation of ET-1 transcription was critically dependent on stimulation of mitogen-activated protein kinase (erk) activity, inhibited by oestradiol and progesterone. In summary, we found that sex steroids inhibit AII-induced erk signalling to the ET-1 transcriptional programme. This novel mechanism of negative transcriptional regulation by oestradiol and progesterone decreases the production of ET-1, potentially contributing to the vascular protective effects of these steroids.

Coronary constriction and consequent cardiodepression in pulmonary embolism are mediated by pulmonary big endothelin and enhanced in early endothelial dysfunction

OBJECTIVES

Myocardial ischemia plays a central role in the development of right ventricular failure after acute pulmonary embolism. This study investigates whether pulmonary mediators act specifically on coronary tone and cardiac contractile function in acute pulmonary microembolization and whether such effects are altered in the case of early systemic atherosclerosis. We employ a novel model of serial perfusion in which an isolated rabbit heart is perfused with the effluent of the same animal's isolated lung.

DESIGN

Controlled experiment using isolated organs.

SETTING

Experimental laboratory.

SUBJECTS

Male New Zealand White rabbits (controls). Age-matched, male Watanabe rabbits (hypercholesterolemic, development of accelerated atherosclerosis).

INTERVENTIONS

Seven isolated control and seven isolated Watanabe hearts were perfused with the saline effluent of the same animal's isolated lung. After the assessment of the baseline data, the lungs were gradually embolized with glass beads measuring 100 microm in diameter to induce an increase in mean pulmonary arterial pressure from 6 to 8 mm Hg, at baseline, up to 25 mm Hg.

MEASUREMENTS AND MAIN RESULTS

Pulmonary embolization to 25 mm Hg evoked a coronary constriction, measured as coronary flow decrease to 89 +/- 7% of the baseline value in controls. In the Watanabe group, coronary constriction was significantly enhanced, compared with controls, with coronary flow decreasing to 76 +/- 6% of the baseline value. In both groups, coronary constriction was followed by a deterioration in cardiac contractile performance. This cardiodepression was significantly deeper in Watanabe hearts with respect to both maximum ventricular pressures and maximum rates of pressure development and decline. Coronary constriction and cardiodepression were prevented by coronary infusion of the nonselective endothelin antagonist PD-145065, the endothelinA antagonists A-127722 and BQ-123, and the endothelin-converting enzyme inhibitor phosphoramidon. Concentration of big endothelin in pulmonary effluent increased from 5.6 +/- 0.3 pmol/L in controls and 5.6 +/- 0.2 pmol/L in the Watanabe group, at baseline, to 8.8 +/- 0.4 pmol/L in controls and 8.9 +/- 0.4 pmol/L in the Watanabe group, at 25 mm Hg pulmonary arterial pressure. Endothelin was not detectable at any time during the experiment in pulmonary effluent. The coronary gradient, calculated as a difference in concentration between coronary and pulmonary effluent, was negative for big endothelin and positive for endothelin in both groups.

CONCLUSIONS

We have demonstrated that an increase in pulmonary release of big endothelin occurs during lung embolism, which, in turn, results in coronary constriction and consequent cardiodepression. This action of big endothelin is based on its local coronary conversion into endothelin. In addition, coronary endothelial dysfunction, attributed to early systemic atherosclerosis, was shown to represent a specific risk factor in these events.

Direct enzyme immunometric measurement of plasma big endothelin-1 concentrations and correlation with indicators of left ventricular function

Recent studies have suggested that the plasma concentrations of endothelin-1, a potent vasoconstrictive peptide, are increased in patients with congestive heart failure. This study aimed to evaluate a new direct ELISA for big endothelin-1 (the precursor of endothelin-1), in comparison with a big endothelin-1 ELISA using plasma sample extraction, and to investigate whether plasma big endothelin-1 concentrations correlate with indicators of left ventricular function. The direct ELISA yielded significantly (P &lt;0.001) lower results than the assay with extracted samples (0.9 ± 0.5 pmol/L vs 2.7 ± 1.9 pmol/L; n = 90); however, the results of the two assays were closely correlated (r = 0.86, P &lt;0.001). Plasma big endothelin-1 concentrations exhibited a significant (P &lt;0.001) negative correlation (r = −0.46, r = −0.40) with the left ventricular ejection fraction and a significant positive correlation (r = 0.40, P &lt;0.001; r = 0.36, P &lt;0.01) with the left ventricular end-diastolic pressure and the left ventricular end-diastolic (r = 0.42, r = 0.38, P &lt;0.001) and end-systolic (r = 0.52, r = 0.47, P &lt;0.001) volume indices. Plasma big endothelin-1 concentrations were notably greater in patients with New York Heart Association (NYHA) class II–IV symptoms than in patients without cardiac disease or in patients categorized to NYHA class I. These data suggest that plasma big endothelin-1 concentrations, measured by a direct ELISA, correlate with hemodynamic indicators and symptoms of left ventricular dysfunction.

Cardiovascular actions of ET-B activation in vivo and modulation by receptor antagonism

The endothelin (ET)-B receptor subtype is expressed on vascular endothelial and smooth muscle cells and participates in vasodilatation and vasoconstriction. Controversy exists regarding the role of the ET-B receptor as a mediator of systemic, pulmonary, and renal vasoconstriction in states of marked ET-1 activation. Moreover, the potential activation of endogenous ET-1 with secondary stimulation of the ET-A receptor in response to sarafotoxin S6c (S6c) remains unclear. This study was designed to assess the cardiovascular actions of ET-B activation with S6c in the presence and absence of selective ET-A antagonism with FR-139317 and dual ET-A/ET-B antagonism with SB-209670 in the anesthetized dog. Compared with time control (n = 5), S6c increased from baseline systemic vascular resistance (SVR) [28 +/- 7 vs. 14 +/- 3 resistance units (RU), P < 0.05] and pulmonary vascular resistance (PVR) (3.2 +/- 0.7 vs. 0.9 +/- 0.3 RU, P < 0.05) and decreased cardiac output (CO) (-1.7 +/- 0.3 vs. -0.5 +/- 0.1 l/min, P < 0.05), with no differences in renal vascular resistance in association with increases in plasma ET-1. S6c also decreased mixed venous oxygen saturation (SVO2) (56 +/- 6 vs. 76 +/- 5%, P < 0.05). Selective ET-A receptor antagonism did not affect the actions of S6c, with the exception that ET-A receptor antagonism blocked the increase in SVR to high-dose S6c. Dual ET-A/ET-B receptor antagonism attenuated the increase from baseline in SVR (7 +/- 1 vs. 28 +/- 7 RU, P < 0.05) and PVR (0.7 +/- 0.2 vs. 3.2 +/- 0.7 RU, P < 0.05) and decrease from baseline in CO (-0.9 +/- 0.1 vs. -1.7 +/- 0.3 l/min, P < 0.05) and SVO2 (-7 +/- 3 vs. -20 +/- 3%, P < 0.05) observed with S6c alone. In summary, this study demonstrates an important role of ET-B receptor activation in vivo, which results in increases in plasma ET-1 and systemic and pulmonary vasoconstriction and reductions in CO and SVO2. This study also supports a modest role for the ET-A receptor in mediating the systemic vasoconstrictor response to high-dose S6c.

The molecular and cellular pathophysiology of heart failure

In the United States, it is estimated that heart failure develops in 465,000 people each year. Heart failure occurs in both men and women and is associated with a high morbidity and mortality rate in both sexes and in all races. Our knowledge of the pathophysiology of heart failure has advanced beyond the cardiorenal-neurohumoral model and now includes changes in myocyte structure and function. Cellular changes in heart failure include myocyte hypertrophy, abnormalities in calcium homeostasis, excitation-contraction coupling, cross-bridge cycling, and changes in the cytoskeletal architecture. Data also indicate that some of these changes are found during the compensated stage of heart failure; whereas other changes are found during overt decompensation and are associated with changes in systolic and diastolic function. The transition from compensated to decompensated heart failure is more than likely related to the overexpression of neurohormones and peptides such as norepinephrine, angiotensin II, and proinflammatory cytokines. The purpose of this article is to review the epidemiology and cellular pathophysiology of heart failure.

Pulmonary hemodynamics and endothelin levels in pacing-induced heart failure: during rest and exercise

Elevated plasma levels of endothelin (ET) have been reported to accompany the development of heart failure (HF), and therefore, this potent vasoconstrictive peptide has been postulated to contribute to the altered pulmonary hemodynamics that occur in this disease process. The overall goal of this study was to examine more carefully the relationship between ET levels in the pulmonary system and pulmonary hemodynamics in the normal and HF states, during both rest and exercise. This study used a porcine model of chronic rapid pacing that has been shown in previous studies to produce left ventricular dysfunction and neurohormonal system activation consistent with the syndrome of HF. Pigs (n = 10) were chronically instrumented to measure pulmonary and systemic hemodynamics, parenchymal flow, and ET content and to obtain blood samples from the pulmonary circuit in the conscious state. Measurements were performed in the normal control state and again following the development of pacing-induced HF (240 beats/min per 21 days), both at rest and during treadmill exercise (3 mph, 15 degrees incline, 12 minutes). With HF, under ambient resting conditions, a threefold increase in pulmonary plasma ET occurred and was accompanied by a fivefold increase in pulmonary vascular resistance. During treadmill exercise, pulmonary plasma ET and pulmonary vascular resistance remained elevated in the HF group when compared with the normal state and were associated with a sixfold decrease in pulmonary parenchymal flow. Pulmonary parenchymal ET content was increased with HF when compared with values for normal control subjects (8.5 +/- 0.6 vs 5.6 +/- 0.8 fmol ET/mg protein, P < .05). Thus, the findings of this study suggest that in this model of HF, increased ET within the pulmonary circuit contributed to abnormalities in resistive properties and parenchymal flow.

Transient, isopeptide-specific induction of myocardial endothelin-1 mRNA in congestive heart failure in rats

Increased myocardial expression of preproendothelin-1 (ppET-1) mRNA has been associated with congestive heart failure (CHF) in rats. However, the time course and isoform pattern of ppET mRNA induction and the cellular localization of ET in failing hearts are unknown. Thus our aim was to investigate myocardial ppET mRNA expression in CHF rats during the first 6 wk after induction of myocardial infarction. Furthermore, performing immunohistochemical analysis, we also investigated the origin and localization of immunoreactive endothelin (ET) in different regions of the failing heart. Ribonuclease protection assays revealed a marked increase in ppET-1 mRNA levels in rat myocardial tissues during CHF. The induction of ppET-1 mRNA was isopeptide specific and transient. The most substantial upregulation was observed in the infarcted area, where maximal expression of ppET-1 mRNA was observed after 7 days (25-fold increase, P < 0.05). However, a marked and statistically significant induction of ppET-1 mRNA was also observed in the nonischemic myocardium. Immunohistochemical analysis revealed ET-1-like immunoreactivity in cardiomyocytes, vascular endothelial cells, macrophages, and proliferating fibroblasts. Thus immunohistochemistry revealed the structural basis for the dramatic upregulation of the myocardial ET system in the infarcted region, suggesting a role for ET in the healing process after myocardial infarction. However, the global upregulation of ppET-1 mRNA in the heart also suggests an autocrine/paracrine regulatory mechanism in the nonischemic myocardium during CHF.

Endothelin-1 in heart and pulmonary tissue in experimental heart failure

We studied the effect of congestive heart failure (CHF) on the tissue levels of endothelin 1 (ET-1) and of the mRNA of prepro-ET-1 in the rat. Congestive heart failure was produced by ligation of the left coronary artery. The rats were killed 3 weeks after the ligation. Congestive heart failure was determined by elevated plasma atrial natriuretic peptide and by a myocardial infarction scar covering more than 30% of the left ventricular circumference. Both ET-1 and prepro-ET-1 mRNA were measured in cardiac ventricles and lungs by radioimmunoassay and quantitative polymerase chain reaction. The rats with CHF had an increased heart weight/body weight ratio and elevated plasma atrial natriuretic peptide levels. In rats with CHF, as compared to controls, the concentration of ET-1 was elevated 3.6-fold in pulmonary tissue and 1.4-fold in the right ventricle, respectively, but not in the left ventricle. The concentration of mRNA showed a similar pattern, but due to methodological limitations this was assumed to represent a rough estimate only. The enhanced production of ET-1 in the right ventricle and in the pulmonary tissue may be of pathophysiological importance for the development of high pulmonary vascular resistance in CHF.

Detection of endothelin receptors in human coronary artery vascular smooth muscle cells but not endothelial cells by using electron microscope autoradiography

Endothelin A (ET(A)) and ET(B) receptors located on vascular smooth-muscle cells mediate potent vasoconstriction in animal and human blood vessels. Although vascular endothelial ET(B) receptors mediate vasodilatation through release of nitric oxide, prostacyclin, or an endothelium-derived hyperpolarizing factor in animal vessels, there is less evidence to support ET-mediated endothelium-dependent relaxation in human arteries. We investigated the regional and subcellular localization of ET-receptor subtypes in human epicardial coronary arteries obtained from patients with congestive heart failure undergoing cardiac transplantation. Radioligand-binding studies revealed a predominance of the ET(A)-receptor subtype in the coronary artery. ET(A) and ET(B) receptors were located in the media and in perivascular structures by using macroautoradiography. Specific binding in the intimal layer was low. Autoradiography at the ultrastructural level revealed the presence of ET(A) and ET(B) receptors on medial vascular smooth-muscle cell plasmalemma and plasmalemmal vesicles with a predominance of the ET(A) subtype. ET receptors were not detected in either luminal endothelial cells of the coronary arteries or endothelial cells lining small adventitial blood vessels. This study is the first to identify the subcellular localization of ET receptors in human coronary artery vascular smooth-muscle cells. These receptors probably mediate the well-established vasoconstrictor response to ET-1. The inability to detect ET receptors on endothelial cells suggests a minor role for endothelial cells in ET-mediated vasodilatation of the coronary vasculature.

Involvement of endothelin (ET)A and ETB receptors in the hypertrophic effects of ET-1 in rabbit ventricular cardiomyocytes

The question was addressed whether endothelin-1 (ET-1) exerts hypertrophic effects in cardiomyocytes isolated from ventricles of adult rabbits and maintained in short-term (24 h) serum-free primary culture providing mechanical quiescence. ET-1 (> or =100 pM) increased significantly total mass of cellular protein and incorporation of L-U-[(14)C]phenylalanine and 2-[(14)C]uridine into cellular protein and RNA, respectively. Cycloheximide (35 microM), an inhibitor of protein synthesis, significantly reduced the incorporation of L-U-[(14)C]phenylalanine and 2-[(14)C]uridine into cellular protein and RNA, respectively, under control conditions and in response to ET-1. Actinomycin D (5 microM), a selective inhibitor of transcription, abolished the incorporation of 2-[(14)C]uridine into cellular RNA and significantly reduced the incorporation of L-U-[(14)C]phenylalanine into cellular protein under control conditions and in response to ET-1. The selective antagonists at the ET(A) receptor [BQ123 (100 nM) and PD155080 (100 nM)] and the selective antagonist at the ET(B) receptor [BQ788 (100 nM)] significantly reduced the incorporation of L-U-[(14)C]phenylalanine into cellular protein in response to ET-1 (10 nM). The selective inhibitor of protein kinase C (PKC), bisindolylmaleimide (BIM) (5 microM), reduced markedly the incorporation of 2-[(14)C]uridine into cellular RNA and, to a lesser degree, the incorporation of L-U-[(14)C]phenylalanine into cellular protein in response to ET-1 (100 pM to 10 nM). ET-1 exerts hypertrophic effects directly in vitro in ventricular cardiomyocytes isolated from the hearts of adult rabbits. These effects are (a) due to de novo synthesis since total mass of cellular protein and incorporation of L-U-[(14)C]phenylalanine and 2-[(14)C]uridine into cellular protein and RNA, respectively, were increased; (b) mediated by both the ET(A) and ET(B) receptor subtypes; and (c) may be associated, at least partly, with the activation of PKC.

Determinants of pulmonary hypertension in left ventricular dysfunction

OBJECTIVES

This study sought to analyze the determinants of pulmonary hypertension in patients with left ventricular dysfunction.

BACKGROUND

Pulmonary hypertension in patients with left ventricular dysfunction is a predictor of poor outcome. The independent role of cardiac functional abnormalities in the genesis of pulmonary hypertension is unclear.

METHODS

In 102 consecutive patients with primary left ventricular dysfunction (ejection fraction < 50%), systolic pulmonary artery pressure was prospectively measured by Doppler echocardiography (using tricuspid regurgitant velocity), and left ventricular systolic and diastolic function, functional mitral regurgitation, cardiac output and left atrial volume were quantified.

RESULTS

Systolic pulmonary artery pressure was elevated in patients with left ventricular dysfunction (51 +/- 14 mm Hg [mean +/- SD]), but the range was wide (23 to 87 mm Hg). Of the numerous variables correlating significantly with systolic pulmonary artery pressure, the strongest were mitral deceleration time (r = -0.61, p = 0.0001; odds ratio of pulmonary pressure > or = 50 mm Hg [95% confidence interval] if < 150 ms, 48.8 [14.8 to 161]) and mitral effective regurgitant orifice (r = 0.50, p = 0.0001; odds ratio [95% confidence interval] if > or = 20 mm2, 5.9 [2.3 to 15.5]). In multivariate analysis, these two variables were the strongest predictors of systolic pulmonary artery pressure in association with age (p = 0.005). Ejection fraction or end-systolic volume was not an independent predictor of pulmonary artery pressure.

CONCLUSIONS

Pulmonary hypertension is frequent and highly variable in patients with left ventricular dysfunction. It is not independently related to the degree of left ventricular systolic dysfunction but is strongly associated with diastolic dysfunction (shorter mitral deceleration time) and the degree of functional mitral regurgitation (larger effective regurgitant orifice). These results emphasize the importance of assessing diastolic function and quantifying mitral regurgitation in patients with left ventricular dysfunction.

Increased renal formation of thromboxane A2 and prostaglandin F2 alpha in heart failure

Renal formation of the vasoconstrictor prostaglandins thromboxane A2 (TXA2) and prostaglandin F2 alpha (PGF2 alpha) was investigated in 25 patients with cardiac failure, divided into New York Heart Association functional classes I to IV, and in eight healthy control subjects. Plasma renin activity (PRA) and hemodynamic parameters were also investigated. Renal vasoconstrictor eicosanoid formation, measured in urinary daily excretion, was not different between patients in class I and control subjects. Class II to IV patients showed progressively increasing production of PGF2 alpha (F = 49.8, p < 0.001, analysis of variance) and TXA2 (F = 37.8, p < 0.002). PGF2 alpha excretion peaked in class IV (+ 1266% vs class I, p < 0.001). Compared with class I, urinary excretion of thromboxane B2 was + 816% in class III and + 1561% in class IV (both p < 0.001). PRA was significantly increased only in class IV (+ 1558%, p < 0.001). The current results indicate a progressive increase in renal production of vasoconstrictor eicosanoids directly related to New York Heart Association class and suggest that these prostanoids may have a role in deterioration of renal function.

Acute and short-term effects of the nonpeptide endothelin-1 receptor antagonist bosentan in humans

In recent years, evidence from various animals experiments has accumulated that emphasizes the role of endothelin-1 in the pathophysiology of several cardiovascular diseases, including congestive heart failure. The recent advent of potent antagonists of this system now allows the assessment of the involvement of endothelin-1 in the maintenance of vascular tone in animals and humans. We report hemodynamic data from two trails in patients with chronic severe congestive heart failure (i.e., reduced left ventricular ejection fraction of < 30%, elevated resting pulmonary capillary wedged pressure > 15 mmHg, and/or reduced cardiac index of 2.5 L/min/m2 or less) who were treated with the mixed endothelin-type A and type B-receptor antagonist bosentan. In the first study, the acute effect of bosentan (300 mg, intravenous) on hemodynamics and neurohormones was investigated. Bosentan was well tolerated and significantly improved impaired hemodynamics due to systemic and venous vasodilation. In the second, trial, bosentan was given orally (0.5 g bid) for 14 days, in addition to conventional triple treatment for congestive heart failure, including digitalis, angiotensin-converting enzyme inhibitors, and diuretics. Cardiac hemodynamics were monitored during the first 24 hours of treatment, and measurements were repeated during the last day of bosentan therapy. Bosentan was well tolerated in these patients as well, and hemodynamic measures were compatible with an additional effect of bosentan after 2 weeks. However, there was a slight increase in heart rate as well. Our result underline the importance of endogenously generated endothelin-1 in congestive heart failure and suggest a potential benefit of endothelin antagonism in such patients. However, long-term studies are needed to establish whether chronic endothelin antagonism has beneficial clinical effects and is capable of improving survival and/or symptoms in severe heart failure patients who remain symptomatic despite standard triple therapy.

Ca(2+)-dependent and Ca(2+)-independent regulation of contractility in isolated human myocardium

Changes in contractile force of the myocardium may depend on changes in the intracellular Ca2+ concentration, changes in the responsiveness of the myofibrils for Ca2+, or a combination of both. We investigated in isolated muscle strip preparations from human nonfailing and endstage failing hearts the influence of physical (changes in preload, stimulation rate, or rhythm), and pharmacological interventions (alpha- or beta-adrenoceptor-stimulation, endothelin) on developed force of contraction and the corresponding intracellular Ca2+ transients.

METHODS

Isometric contraction, electrical stimulation, 37 degrees C. Simultaneous registration of force of contraction and intracellular Ca2+ transients (aequorin method).

RESULTS

Increases in preload, alpha- and endothelin-receptor stimulation resulted in increases in force of contraction without increasing aequorin light emission. Increasing stimulation rate or increasing rest intervals resulted in parallel increases (nonfailing myocardium) or decreases (failing myocardium) of force of contraction and aequorin light emission. beta-Adrenoceptor-stimulation exerted inotropic and lusitropic effects in human failing myocardium associated with a large, overproportional increase in aequorin light emission.

CONCLUSION

The human heart regulates intrinsic contractility via several subcellular mechanisms. Increases in preload (Frank-Starling-mechanism) and alpha- or endothelin-receptor-stimulation enhance myocardial contractility by increasing the Ca2+ responsiveness of the myofilaments; rate- and rhythm-dependent modulation of the contractile state directly depend on changes in the intracellular Ca(2+)-transients; beta-adrenoceptor stimulation results in an overproportional large increase in intracellular Ca2+ transients, probably due to additional cAMP-dependent Ca(2+)-desensitizing effects on the level of the myofibrils.

Endothelins and cardiac hypertrophy

Cardiac hypertrophy is a commonly observed complication of a variety of cardiovascular diseases. As well as mechanical stresses such as pressure overload, several humoral factors may contribute to the development of cardiac hypertrophy. In the early 1990s, endothelin-1 (ET-1) was found to induce cardiomyocyte hypertrophy in cultured neonatal rat cardiomyocytes. Furthermore, evidence is accumulating to date to support the postulate that ET-1 may function as an autocrine/paracrine factor in the development of cardiac hypertrophy in vivo as well as in vitro In this review article, I discuss physiological and pathophysiological roles of ET-1 and its related peptides in cardiac hypertrophy associated with various cardiovascular diseases.

Effects of endothelin-receptor antagonism with PD156707 on myocardial stunning in swine

Endothelin (ET) has been proposed to play a role in pathogenesis of myocardial ischemia/reperfusion injury. The potential role of ET in myocardial stunning has not been examined. Therefore we tested the hypothesis that selective blockade of ETA receptors with PD156707 {sodium 2-benzo[1,3]dioxol-5-yl-4-(4-methoxy-phenyl) -4-oxo-3-(3,4,5-trimethoxy-benzyl)-but-2-enoate} could improve postischemic contractile dysfunction in open-chest pigs. Myocardial stunning was achieved by a sequence of three 10-min left anterior descending (LAD) occlusions interspersed with 15 min of reperfusion. All pigs received either an intravenous saline vehicle (n =6) or PD156707 (n = 6) at a loading dose infusion of 10 mg/kg/h for 1 h before the first occlusion followed by a maintenance dose of 7 mg/kg/h for 4 h. Systolic wall thickening (percentage of baseline) was measured with sonomicrometers. There was no significant difference in systolic thickening between groups at baseline, at the end of the final stunning occlusion, or at any of the time points during reperfusion. PD156707 significantly reduced arterial blood pressure before myocardial ischemia and throughout reperfusion. There was no significant difference in size of the region at risk between groups. In conclusion, selective blockade of ETA receptors with PD156707 did not significantly alter postischemic contractile function in open-chest pigs. These results suggest that activation of ETA receptors by endogenous ET does not play a significant role in the pathogenesis of myocardial stunning.

Captopril does not acutely modulate plasma endothelin-1 concentration in human congestive heart failure

Congestive heart failure (CHF) is a syndrome characterized by increased levels of angiotensin II (Ang II) and endothelin-1 (ET-1). In vitro, Ang II stimulates ET-1 release. The purpose of the study was to assess the effect of a single dose of an angiotensin-converting enzyme inhibitor (ACEI) captopril versus placebo on plasma endothelin concentration in human congestive heart failure. Captopril (25 mg, given orally) was compared with placebo in a group of 20 patients with systolic dysfunction in a double-blind randomized study. Plasma irET concentration was significantly increased in CHF patients compared with normal subjects (5.59 pg/ml +/- 0.35 vs. 3.58 pg/ml +/- 0.99, p < 0.0002). Despite the decrease in systolic blood pressure and the increase in plasma renin activity, suggesting a significant blockade of the renin-angiotensin system, no difference in plasma irET-1 was observed between captopril and placebo. Our results suggest that captopril does not acutely influence irET-1 plasma concentration in human CHF. These data do not support the hypothesis that the acute vasodilator effect of a single dose of 25 mg of captopril given daily orally involves modulation of the increased plasma concentration of endothelin observed in CHF.

Blunted cGMP response to agonists and enhanced glomerular cyclic 3',5'-nucleotide phosphodiesterase activities in experimental congestive heart failure

The natriuretic peptide (NP) and nitric oxide (NO) systems are activated in congestive heart failure (CHF), resulting in increased synthesis of cGMP, which serves as a second messenger for both humoral systems. These two regulatory systems play functional roles in the preservation of glomerular filtration rate (GFR) and sodium excretion in both acute and chronic CHF. A progressive decline in glomerular responsiveness to atrial natriuretic peptide (ANP) characterizes the terminal stage of chronic CHF despite elevation of plasma ANP. Phosphodiesterase isozymes (PDEs) are integral factors in determining cellular content and accumulation of cGMP, and up-regulation of PDE activity could participate in the glomerular resistance to ANP in severe CHF. To date, characterization of possible alteration of glomerular PDE isozyme activities in CHF is unknown, as is the in vitro glomerular response to the nitric oxide-soluble guanylyl cyclase pathway. We, therefore, first determined cGMP generation in response to particulate and soluble guanylyl cyclase activation by ANP and sodium nitroprusside (SNP) in isolated glomeruli from normal (N = 6) and CHF dogs (N = 5) in which CHF was induced by rapid ventricular pacing for 18 to 28 days. Secondly, we explored the presence of major PDE isozymes in glomeruli isolated from the control and CHF dogs. When ANP or SNP (10(-10) to 10(-4) M) were incubated with the suspension of isolated glomeruli, cGMP accumulation was lower by -72 to -96% with ANP and -42 to -77% with SNP in all glomerular medias obtained from CHF compared to controls. PDE hydrolyzing activity of both cAMP and cGMP were higher in the glomerular homogenates obtained from the kidneys of the CHF group (N = 5) compared to those of the control group (N = 5). We conclude that in severe chronic experimental CHF, glomerular cGMP accumulation decreases in response to both ANP and SNP, and CHF is characterized by enhanced cGMP- and cGMP-PDE activities that may participate in glomerular maladaptation to this cardiovascular syndrome.

Endothelins in chronic liver disease

This review describes recent progress in the accumulation of knowledge about the endothelins (ETs), a family of vasoactive 21-amino acid polypeptides, in chronic liver disease. Particular prominence is given to the dynamics of ET-1 and ET-3 and their possible relation to the disturbed circulation and neurohumoral dysregulation found in cirrhosis. Recent studies have shown that the ET system is highly activated in most cirrhotic patients. Circulating ET-1 and ET-3 levels have a positive relation to the severity of the disease and fluid retention, with the highest values recorded in patients with functional renal failure. Studies on liver biopsies have revealed synthesis of ET-1 in hepatic endothelial and other cells, and recent investigations have identified the hepatosplanchnic system as a major source of ET-1 and ET-3 spillover into the circulation, with a direct relation to portal venous hypertension. In addition, marked associations with disturbance of systemic haemodynamics and with abnormal distribution of blood volume have been reported. Although the pathophysiological importance of the ET system in chronic liver disease is not completely understood, similarities to other vasopressive and antinatriuretic regulatory systems (i.e. the sympathetic nervous system, renin-angiotensin-aldosterone and vasopressin) are apparent, with respect to kinetics and haemodynamic dysregulation. Cirrhosis seems to be a pathophysiological condition with indications of the occurrence of ETs, not only as local modulators, but also as a system with potential importance for systemic regulation.

Basic mechanisms in heart failure: the cytokine hypothesis

Although the development and progression of heart failure have traditionally been viewed as hemodynamic disorders, there is now an increasing awareness that the syndrome of heart failure cannot be simply and/or precisely defined solely in hemodynamic terms. The inability of the so-called hemodynamic hypothesis to explain the progression of heart failure has given rise to the notion that heart failure may progress as a result of the overexpression of an ensemble of biologically active molecules referred to generically as neurohormones. More recently, it has become apparent that in addition to neurohormones, another portfolio of biologically active molecules, termed cytokines, are also expressed in the setting of heart failure. This article reviews recent clinical and experimental material that suggests that the cytokines, much like the neurohormones, may represent another class of biologically active molecules that are responsible for the development and progression of heart failure.

Bosentan improves renal regional blood flow in rats with experimental congestive heart failure

The effects of the mixed endothelin receptor antagonist bosentan on renal regional haemodynamics were investigated in rats with aorto-caval fistula, an experimental model of congestive heart failure. A matched group of normal rats served as control. Injection of bosentan (10 mg/kg i.v.) to the rats with decompensated congestive heart failure produced an increase in cortical (+20%) and medullary (+12%) blood flow, and a decrease in vascular resistance in the cortex (-30%) and medulla (-23%), while reducing mean arterial pressure by approximately 10 mm Hg. In rats with compensated congestive heart failure and in normal animals, infusion of bosentan did not affect blood pressure and cortical perfusion. These findings indicate that 1) endothelin receptor blockade produces beneficial effects on renal haemodynamics in rats with experimental congestive heart failure and 2) endothelin-1 may be involved in the pathogenesis of renal hypoperfusion only in decompensated congestive heart failure.

Endogenous cardiac vasoactive factors modulate endothelin production by cardiac fibroblasts in culture

Endothelin, a potent vasoconstrictor, is produced by cardiac fibroblasts in culture and induces hypertrophy in cardiac myoctes. The purpose of this study was to determine whether vasoactive factors endogenous to the heart affect the production of endothelin by cultured cardiac fibroblasts. Vasoactive factors have been shown to play multiple roles in the adaptation of the heart to chronic overload, affecting both vascular tone and cell growth. Both atrial (ANP) and brain (BNP) natriuretic peptides are endogenous cardiac vasodilators and are produced by cultured myocytes in response to stimulation with endothelin. Treatment of cardiac fibroblasts with these peptides decreased endothelin production. Nitroprusside, an activator of guanylyl cyclase, decreased endothelin production indicating the involvement of cGMP in the response. Carbaprostacyclin, a stable derivative of prostacyclin, another endogenous cardiac vasodilator, also decreased endothelin production by fibroblasts. The combination of BNP and carbaprostacyclin was additive in decreasing endothelin production. In contrast, PGF2α and angiotensin II, both endogenous cardiac vasoconstrictors, increased endothelin production and overcame the inhibition induced by BNP and carba-prostacyclin. In summary, endothelin production by cardiac fibroblasts was decreased by the endogenous cardiac vasodilators ANP, BNP, and prostacyclin and increased by the endogenous vasoconstrictors PGF2α and angiotensin II.

Pharmacokinetics and pharmacodynamics of the endothelin-receptor antagonist bosentan in healthy human subjects

INTRODUCTION

Bosentan (Ro 47-0203) is a potent and mixed ETA-and ETB-receptor antagonist. Its activity has been studied in a variety of preclinical disease models.

METHODS

Two double-blind placebo-controlled studies were performed to investigate the pharmacokinetics and pharmacodynamics of bosentan after single oral and intravenous doses in healthy volunteers; doses of 3, 10, 30, 100, 300, 600, 1200, and 2400 mg were given in a single ascending oral dose study, and doses of 10, 50, 250, 500, and 750 mg were given in a single ascending intravenous dose study (six subjects received active drug and two received placebo at each dose level). In an open-label crossover added to the second study, six subjects received a single oral dose of 600 mg and a single intravenous dose of 250 mg in randomized order. At regular intervals, blood pressure, pulse rate, and skin responses to intradermally injected endothelin-1 (ET-1) were recorded, and plasma levels of ET-1, proendothelin-1 (big ET-1), and ET-3, and drug and urinary levels of ET-1 and drug were determined.

RESULTS

Systemic plasma clearance and volume of distribution decreased with increasing dose to limiting values of around 6 L/hr and 0.2 L/kg, respectively. The absolute bioavailability was 50% and appeared to decrease with doses above 600 mg. Plasma ET-1 increased maximally twofold (oral) and threefold (intravenous), and this increase was directly related to bosentan plasma concentrations according to an Emax model. Bosentan reversed the vasoconstrictor effect of ET-1 measured in the skin microcirculation. There was a tendency toward decreased blood pressure (approximately 5 mm Hg) and increased pulse rate (approximately 5 beats/min), neither was clearly dose dependent. Oral bosentan was well tolerated. Vomiting and local intolerability was observed at the higher intravenous doses.

CONCLUSION

Bosentan is an orally bioavailable, well-tolerated, and active ET-1 antagonist with a low clearance and a moderate volume of distribution. Its intravenous use is limited because of local intolerability.