Coronary vasodilator effects of BNP: mechanisms of action in coronary conductance and resistance arteries

The clinical effect of recombinant human brain natriuretic peptide on asymptomatic peri-procedural myocardial injury after percutaneous transluminal coronary angioplasty

To determine the effect of intravenous injection of recombinant human brain natriuretic peptide (rhBNP) on lowering the incidence of asymptomatic peri-procedural myocardial injury (PMI) in patients who underwent coronary stent implantation. In this retrospective observational study, data pooled from a tertiary hospital electronic medical records were used to quantify the troponin enzyme change after patients with coronary artery disease (CAD) were pretreated with rhBNP infusion one day prior to percutaneous coronary intervention (PCI). The primary end point was to analyze the incidence of the elevated high-sensitivity cardiac troponin I serum levels above the upper normal limit after PCI. A total of 156 CAD patients were enrolled into rhBNP group (n = 76) and control group (n = 80). The incidence of asymptomatic PMI was 33% in the rhBNP group versus 51% in the control group (P = 0.02) after PCI. At eight months, the incidences of composite endpoints were 25.3% in the control group and 13% in the rhBNP group (difference, 12.3 percentage points; 95% confidence interval (CI), 0.197 to 1.048; P = 0.061). There were 7 visits in the rhBNP group and 15 visits in the control group for recurrent angina (difference, 10 percentage points; 95% CI 0.168-1.147; P = 0.087). A time-to-event analysis of the composite clinical endpoints and the recurrent angina between the control group and rhBNP group showed that the hazard ratios were 2.566 (95% CI 1.187-5.551; P = 0.017) and 2.607 (95% CI 1.089-6.244; P = 0.032) respectively. The decreased incidence of asymptomatic PMI after PCI and the reduced episodes of recurrent angina at eight months follow-up were associated with the administration of rhBNP infusion prior to PCI.

B-type natriuretic peptide overexpression ameliorates hepatorenal fibrocystic disease in a rat model of polycystic kidney disease

Polycystic kidney disease (PKD) involves progressive hepatorenal cyst expansion and fibrosis, frequently leading to end-stage renal disease. Increased vasopressin and cAMP signaling, dysregulated calcium homeostasis, and hypertension play major roles in PKD progression. The guanylyl cyclase A agonist, B-type natriuretic peptide (BNP), stimulates cGMP and shows anti-fibrotic, anti-hypertensive, and vasopressin-suppressive effects, potentially counteracting PKD pathogenesis. Here, we assessed the impacts of guanylyl cyclase A activation on PKD progression in a rat model of PKD. Sustained BNP production significantly reduced kidney weight, renal cystic indexes and fibrosis, in concert with suppressed hepatic cystogenesis in vivo. In vitro, BNP decreased cystic epithelial cell proliferation, suppressed fibrotic gene expression, and increased intracellular calcium. Together, our data demonstrate multifaceted effects of sustained activation of guanylyl cyclase A on polycystic kidney and liver disease. Thus, targeting the guanylyl cyclase A-cGMP axis may provide a novel therapeutic strategy for hepatorenal fibrocystic diseases.

Efficacy and safety of nesiritide in patients with decompensated heart failure: a meta-analysis of randomised trials

OBJECTIVES

Current evidence suggests that nesiritide may have effects on renal function and decrease the incidence of mortality. However, a clear superiority using nesiritide in terms of renal toxicity and mortality in patients with heart failure was not consistently proven by previous studies. We performed a meta-analysis of all randomised trials to obtain the best estimates of efficacy and safety of nesiritide for the initial treatment of decompensated heart failure.

METHOD

We performed a meta-analysis of randomised trials of nesiritide in patients with decompensated heart failure (n=38,064 patients, in 22 trials). Two reviewers independently extracted data. Data on efficacy and safety outcomes were collected. We calculated pooled relatives risk (RRs), weighted mean difference and associated 95% CIs.

RESULTS

Compared with placebo, dobutamine and nitroglycerin, nesiritide indicated no increasing risk of total mortality. Compared with the combined control therapy, nesiritide was associated with non-significant differences in short-term mortality (RR 1.24; 95% CI 0.85 to 1.80; p=0.27), mid-term mortality (RR 0.86; 95% CI 0.60 to 1.24; p=0.42) and long-term mortality (RR 0.94; 95% CI 0.75 to 1.18; p=0.61). Nesiritide therapy increased the risk of hypotension (p<0.00 001) and bradycardia (p=0.02) when compared with control therapy. Compared with dobutamine or placebo therapy, no differences in serum creatinine, blood urea nitrogen and creatinine clearance, and no risk of the need for dialysis was observed in nesiritide therapy.

CONCLUSIONS

Our findings indicated that, in patients with heart failure, nesiritide was not associated with the risk of mortality. However, it increased the risk of cardiovascular adverse events. The change of serum creatinine and creatinine clearance had no significant difference, and no risk of the need for dialysis was observed after low-dose nesiritide treatment.

Molecular and physiological effects of nesiritide

BACKGROUND

Nesiritide (Natrecor, Janssen-Ortho Inc, Canada), or recombinant human B-type natriurtic peptide (BNP), is a molecule identical in structure to endogenous BNP-32. This peptide is secreted from cardiac myocytes in response to volume and pressure overload. While high levels of circulating BNP are measured by commercially available assays during acute decompensated heart failure (ADHF), the detection of alternate, potentially more active, but undermeasured forms of BNP needs to be considered.

AIM

The present review summarizes the molecular and physiological effects of nesiritide in the setting of hospitalized patients with ADHF. In particular, an overview of the molecular structure and circulating isoforms of BNP is given, followed by a discussion of the vasodilatory, renal, antagonistic neurohormonal, pulmonary, anti-inflammatory and cardiac remodelling effects of recombinant human BNP.

SUMMARY

Nesiritide has beneficial effects in the treatment of ADHF that go beyond the traditional goals of reducing pulmonary capillary wedge pressure, preload and afterload, and relieving symptoms of dyspnea. Therefore, the unique pharmacological profile of this medication provides an additional treatment option for Canadian patients with ADHF.

B-type natriuretic peptide in the emergency diagnosis of critical heart disease in children

OBJECTIVE

The initial presentation of congenital and acquired heart disease in children can present a diagnostic challenge. We sought to evaluate B-type natriuretic peptide as a marker of critical heart disease in children at presentation in the acute care setting.

METHODS

A cohort of 33 pediatric patients with newly diagnosed congenital or acquired heart disease had B-type natriuretic peptide levels obtained on hospital admission after evaluation in an acute care setting. Patients were admitted from March 2005 through February 2007. A noncardiac cohort of 70 pediatric patients who presented with respiratory or infectious complaints had B-type natriuretic peptide levels obtained during emergency department evaluation. A comparison of B-type natriuretic peptide results was performed.

RESULTS

Cardiac diagnoses included cardiomyopathy (14), left-sided obstructive lesions (12), anomalous left coronary artery from the pulmonary artery (4), total anomalous pulmonary venous return (2), and patent ductus arteriosus (1). Cardiac cohort mean age at presentation was 33.6 months. The 33 patients with new cardiac diagnoses had a mean B-type natriuretic peptide level of 3290 pg/mL (SD: +/-1609; range: 521 to >5000 pg/mL). The 70 noncardiac patients' mean age at presentation was 23.1 month, and mean B-type natriuretic peptide level was 17.4 pg/mL (SD: +/-20; range: <5 to 174 pg/mL).

CONCLUSIONS

B-type natriuretic peptide levels were markedly elevated at presentation in the acute care setting for all patients in this cohort of children with newly diagnosed congenital or acquired heart disease. B-type natriuretic peptide levels from noncardiac patients were significantly lower, with no overlap to the cardiac disease group. B-type natriuretic peptide level can be useful as a diagnostic marker to aid in the recognition of pediatric critical heart disease in the acute care setting.

Recent advances in natriuretic peptide research

The natriuretic peptides are a family of related hormones that play a crucial role in cardiovascular and renal homeostasis. They have recently emerged as potentially important clinical biomarkers in heart failure. Natriuretic peptides, particularly brain natriuretic peptide (BNP) and the inactive N-terminal fragment of BNP, NT-proBNP, that has an even greater half-life than BNP, are elevated in heart failure and therefore considered to be excellent predictors of disease outcome. Nesiritide, a recombinant human BNP, has been shown to provide symptomatic and haemodynamic improvement in acute decompensated heart failure, although recent reports have suggested an increased short-term risk of death with nesiritide use. This review article describes: the current use of BNP and its inactive precursor NT-proBNP in diagnosis, screening, prognosis and monitoring of therapy for congestive heart failure, the renoprotective actions of natriuretic peptides after renal failure and the controversy around the therapeutic use of the recombinant human BNP nesiritide.

Usefulness of BNP-administration in cardiac surgery: animal model

OBJECTIVE

The pharmacologic properties of Brain natriuretic peptide make it a favourable substance to use after cardiac operations. The goal of this study was to evaluate the effect of BNP following cardio-pulmonary bypass (CPB).

METHOD

Nineteen pigs were operated on using CPB. One group received BNP and the control group received placebo. A 30-minute ischemic episode was simulated. Following declamping, BNP was administered by an IV bolus, followed by an infusion for 60 minutes. Hemodynamic and clinical chemistry parameters were documented, as well as the amount of catecholamines.

RESULTS

The Cardiac output and Cardiac Index in the BNP group were significantly higher 60 minutes after ending CPB. Seven of ten animals in the control group needed catecholamines at the end of the experiment, whereas none of the animals in the BNP group did at this juncture. Creatine kinase and Lactate were significantly lower.

CONCLUSION

BNP is a well-tolerated agent that could present a new treatment option for heart failure following cardiac surgery. Hemodynamics are greatly improved with almost no need for pharmacological support.

B-type natriuretic peptide release in the coronary effluent after acute transient ischaemia in humans

BACKGROUND

The association between B-type natriuretic peptide (BNP) and coronary artery disease is not fully understood.

OBJECTIVE

To assess whether ischaemia per se is a stimulus for BNP secretion.

SETTING

University tertiary hospital, Spain (Virgen de la Arrixaca).

DESIGN

Prospective interventional study.

PATIENTS

11 patients (55 (9) years, left ventricular ejection fraction (LVEF) 45% (7%) with a non-complicated anterior myocardial infarction (MI) and isolated stenosis of the left anterior descending (LAD) coronary artery, successfully treated by primary angioplasty.

INTERVENTIONS

11.0 (0.9) days after MI, the LAD was occluded (20 min) for intracoronary infusion of progenitor cells. Blood samples were obtained from the femoral artery (peripheral circulation (PC)) and the coronary sinus (coronary circulation (CC)) immediately before and after coronary occlusion.

MAIN OUTCOME MEASURES

BNP (pg/ml) was measured and ischaemia biomarkers were monitored.

RESULTS

During coronary occlusion, all patients experienced transitory chest pain and ST-segment dynamic changes. After coronary occlusion, lactic acid levels rose in CC (1.42 (0.63) -1.78 (0.68) ng/ml, p = 0.003). Myoglobin and cardiac troponin T did not differ in CC or PC at 24 h. No differences were found in LVEF (+0.18% (2.4)%, p = 0.86) and motion score index (-0.02 (0.06), p = 0.37). Before occlusion, BNP levels did not differ significantly in CC versus PC (253 (56) vs 179 (34), p = 0.093). After occlusion, BNP showed a significant increase in CC (vs 332 (61), p = 0.004), but no change occurred in PC (vs 177 (23), p = 0.93), and circulating BNP levels were higher in CC versus PC (p = 0.008).

CONCLUSIONS

In response to acute ischaemia, BNP levels immediately increase in coronary sinus but not at the peripheral level. BNP release in the coronary effluent may exert local beneficial effects.

Lack of activation of molecular forms of the BNP system in human grade 1 hypertension and relationship to cardiac hypertrophy

We evaluated relationships among two circulating molecular forms of brain natriuretic peptide (BNP32 and NT-proBNP), severity of hypertension (HTN), and cardiac hypertrophy in subjects with mild, moderate, and severe HTN. We prospectively studied 78 patients (43 males; mean age 51.4 +/- 11 yr) with essential HTN and 28 age- and sex-matched controls. BNP32 and NT-proBNP were measured by radioimmunoassay. In grade 1 HTN, BNP32 was not elevated and NT-proBNP was reduced (P = 0.030) compared with controls. However, log-transformed values of BNP32 and NT-proBNP were both increased with severity of HTN from grade 1 to 3 (P <0.0001 and P = 0.003, respectively). By multivariate analysis, log BNP32 was independently predicted by age (beta = 0.210, P = 0.026) and HTN grade (beta = 0.274, P = 0.004), whereas log NT-proBNP was independently predicted by sex (beta = 0.235, P = 0.012) and HTN grade (beta = 0.218, P = 0.0023). Two forms of BNP were measured in normal subjects and patients with essential HTN. In grade 1 HTN, BNP32 was unchanged and NT-proBNP was significantly reduced compared with controls. As severity increased in humans with grade 1 to 3 HTN, both BNP32 and NT-proBNP levels were increased while not being affected by the presence of left ventricular hypertrophy. The lack of activation of BNP32 together with the reduction of NT-proBNP in grade 1 HTN may represent an impaired response of the BNP system in the early phase of HTN. The later activation of both forms of BNP may be a late compensatory effect, because it correlates with severity of HTN rather than cardiac hypertrophy/remodeling.

Practical application of human B-type natriuretic peptide as a therapeutic intervention in the perioperative setting

The use of human B-type natriuretic peptide (BNP, nesiritide) as a therapeutic intervention is now well established for patients with acute decompensated heart failure. Nesiritide mimics the actions of endogenous BNP by binding to and stimulating receptors in the heart, kidney, and vasculature. Postsurgical patients are typically managed with various combinations of vasodilators, diuretics, and inotropes. Many of these therapeutic interventions lack significant proof of efficacy and are potentially deleterious to these patients, despite the acute hemodynamic improvement that results from their use. Use of nesiritide may supplant some of these therapies as an equally efficacious and possibly safer alternative in patients with decompensated heart failure. Nesiritide is a unique, balanced vasodilator that markedly decreases the signs and symptoms of heart failure in perioperative patients, and also may decrease the need for inotropic agents. This review summarizes nesiritide's mechanism of action and addresses special concerns and practical considerations for cardiothoracic surgeons and anesthesiologists. Overall, nesiritide appears to be an effective and safe therapeutic option in perioperative patients with decompensated heart failure.

Acute myocardial hypoxia increases BNP gene expression

It is well established that cardiac failure increases cardiac B-type natriuretic peptide (BNP) expression due to myocardial stretching. However, patients with ischemic heart disease also display increased plasma BNP and proBNP concentrations despite preserved cardiac function. In this study, we examined whether acute myocardial hypoxia increases cardiac BNP expression. Surgical reduction of the blood flow to an area of the anterior ventricular wall in pigs reduced the myocardial oxygen tension from 46 +/- 4 to 13 +/- 5 mmHg. The tissue contents of VEGF and BNP mRNA increased 1.8-fold and 3.5-fold, respectively (n=10, P<0.005) in hypoxic compared with normoxic ventricular myocardium after 2.2 +/- 0.2 h; the magnitude of the increase in BNP mRNA expression was positively correlated with that of VEGF in hypoxic myocardium (r=0.66, P<0.05). In support of a hypoxia-induced increase of BNP gene transcription, the content of a premature BNP mRNA was increased in hypoxic myocardium (4.8-fold, P<0.005) and in freshly harvested ventricular myocytes when kept in culture flasks and oxygen-deprived for 3 h (2.2-fold, P=0.002). ProBNP peptide accumulated in the medium of freshly harvested ventricular myocyte cultures but was undetectable in ventricular myocardium, indicating rapid release of the newly synthesized proBNP peptide. Accordingly, the plasma proBNP concentration increased after 2 h of myocardial hypoxia (P=0.028). Cumulatively, the data suggest that acute hypoxia stimulates cardiac BNP expression.

B-type natriuretic peptide: spectrum of application. Nesiritide (recombinant BNP) for heart failure

The therapeutic goals for patients hospitalized with acutely decompensated heart failure are to reverse acute hemodynamic abnormalities, relieve symptoms, and to initiate heart failure therapies which will decrease disease progression and improve long-term survival. Nesiritide (recombinant B-type natriuretic peptide) is the first in a new class of therapeutic agents for the treatment of heart failure and has been demonstrated to offer a unique combination of safety and efficacy. The use of nesiritide on top of standard care including diuretic therapy, has been proven to lead to meaningful clinical benefits in a broad range of acutely decompensated heart failure patients. Nesiritide is an attractive therapeutic option because of its more rapid and sustained hemodynamic profile, more favorable effects on neurohormonal suppression, with less adverse effects than alternative intravenous heart failure treatments such as nitroglycerine, nitroprusside, dobutamine, or milrinone. The use of nesiritide is the most effective initial treatment approach among currently available strategies to reverse acutely decompensated heart failure and to facilitate optimization of the heart failure medical regimen.

B-type natriuretic peptide limits infarct size in rat isolated hearts via KATP channel opening

B-type natriuretic peptide (BNP) has been reported to be released from the myocardium during ischemia. We hypothesized that BNP mediates cardioprotection during ischemia-reperfusion and examined whether exogenous BNP limits myocardial infarction and the potential role of ATP-sensitive potassium (K(ATP)) channel opening. Langendorff-perfused rat hearts underwent 35 min of left coronary artery occlusion and 120 min of reperfusion. The control infarct-to-risk ratio was 44.8 +/- 4.4% (means +/- SE). BNP perfused 10 min before ischemia limited infarct size in a concentration-dependent manner, with maximal protection observed at 10(-8) M (infarct-to-risk ratio: 20.1 +/- 5.2%, P < 0.01 vs. control), associated with a 2.5-fold elevation of myocardial cGMP above the control value. To examine the role of K(ATP) channel opening, glibenclamide (10(-6) M), 5-hydroxydecanoate (5-HD; 10(-4) M), or HMR-1098 (10(-5) M) was coperfused with BNP (10(-8) M). Protection afforded by BNP was abolished by glibenclamide or 5-HD but not by HMR-1098, suggesting the involvement of putative mitochondrial but not sarcolemmal K(ATP) channel opening. We conclude that natriuretic peptide/cGMP/K(ATP) channel signaling may constitute an important injury-limiting mechanism in myocardium.

Effect of PDE5 inhibition on coronary hemodynamics in pacing-induced heart failure

Inhibition of phosphodiesterase type 5 (PDE5) can relax systemic and coronary vessels by causing accumulation of cGMP. Both the endothelial dysfunction with decreased nitric oxide production and increased natriuretic peptide levels in congestive heart failure (CHF) have the potential to alter cGMP production, thereby influencing the response to PDE5 inhibition. Consequently, this study examined the effects of PDE5 inhibition with sildenafil in dogs with CHF produced by rapid ventricular pacing. CHF resulted in decreases of left ventricular (LV) systolic pressure, coronary blood flow, and the maximal first time derivative of LV pressure (LV dP/dt(max)) at rest and during treadmill exercise compared with normal, whereas resting LV end-diastolic pressure increased from 10 +/- 1.4 to 23 +/- 1.4 mmHg. Sildenafil (2 and 10 mg/kg per os) caused a 5- to 6-mmHg decrease of aortic pressure (P < 0.05), with no change of heart rate, LV systolic pressure, or LV dP/dt(max). Sildenafil caused no change in coronary flow or myocardial oxygen consumption in animals with CHF at rest or during exercise. In contrast to findings in normal animals, sildenafil did not augment endothelium-dependent coronary vasodilation in response to acetylcholine in animals with CHF. Furthermore, Western blotting showed decreased PDE5 protein expression in myocardium from failing hearts. These findings demonstrate that PDE5 contributes little to regulation of coronary hemodynamics in CHF.

The therapeutic effect of natriuretic peptides in heart failure; differential regulation of endothelial and inducible nitric oxide synthases

The abnormal regulation of nitric oxide synthase activity represents an underlying feature of heart failure. Increased peripheral vascular resistance, and decreased renal function may be in part related to impaired endothelium-dependent nitric oxide (NO) synthesis. Paradoxically, the chronic production of NO by inducible nitric oxide synthase (iNOS) in heart failure exerts deleterious effects on ventricular contractility, and circulatory function. Consequently, pharmacologically improving endothelium-dependent NO synthesis and the concomitant inhibition of iNOS activity would be therapeutically advantageous. Interestingly, natriuretic peptides have been shown to differentially regulate endothelial NOS (eNOS) and iNOS activity. Moreover, in both patients and animal models of heart failure, pharmacologically increasing plasma natriuretic peptide levels ameliorated vascular tone, renal function, and ventricular contractility. Based on these observations, the following review will explore whether the therapeutic benefit of the natriuretic peptide system in heart failure may occur in part via the amelioration of endothelium-dependent NO synthesis, and the concomitant inhibition of cytokine-mediated iNOS expression.

Comparison of vasodilators in human internal mammary artery: ghrelin is a potent physiological antagonist of endothelin-1

1 The potential vasodilator function of the peptide ghrelin, recently identified as the endogenous ligand of the growth hormone secretagogue orphan receptor (GHS-R), was investigated in human endothelium-denuded internal mammary artery. The peptide endothelin-1 (ET-1) is a potent and long-lasting vasoconstrictor. Comparisons were made with established and putative endogenous vasodilators to determine if any could reverse ET-1-induced vasoconstriction in this vessel. 2 Ghrelin (0.1-300 nM) potently dilated 10 nM ET-1-induced constrictions (pD(2) 8.39+/-0.29; E(MAX) 63+/-5.6%; n=9/14, responders/total). 3 ANP (pD(2) 7.75+/-0.14; E(MAX) 106+/-2.0; n=5/5) and CGRP (pD(2) 8.08+/-0.17; E(MAX) 76+/-15% n=5/6) both produced complete reversal of the constrictor response to ET-1 (E(MAX) not significantly different from 100%, P>0.05 one-sample t-test). 4 The following caused partial reversal of the ET-1 response: Adrenomedullin (n=9/9) and two peptides derived from proadrenomedullin, PAMP-12 (n=6/7) and PAMP-20 (n=9/9) (pD(2) values 7.63+/-0.28, 7.97+/-0.23 and 8.51+/-0.29; E(MAX) 58+/-7.3, 54+/-10 and 51+/-7.8% respectively). Unexpectedly, amylin was only 2 fold less potent than CGRP, although there was less than 50% reversal of the ET-1 constriction (pD(2) 7.86+/-0.30; E(MAX) 41+/-5.4%; n=7/9). CNP (n=6/6) also partially reversed constrictions to ET-1 (E(MAX) 53+/-6.3; pD(2) 8.07+/-0.38). 5 BNP (n=4/5) and PGI(2) (n=6/8) were weak vasodilators, since concentration-response curves failed to reach a maximum within the range tested. PGE(2) caused a small dilatation in some vessels (E(MAX) 17+/-2.1%; pD(2) 8.63+/-0.36; n=4/8). 6 We have demonstrated ghrelin to be an effective, endothelium-independent vasodilator of the long-lasting constrictor ET-1 in human arteries producing responses similar to those of adrenomedullin (P>0.05, ANOVA). British Journal of Pharmacology (2002) 136, 1146-1152

Physiological antagonism of endothelin-1 in human conductance and resistance coronary artery

The ability of four endogenous vasodilators, nitric oxide (NO; 0.01 - 30 microM), atrial (ANP), brain (BNP) and C-type (CNP) natriuretic peptide (0.1 - 300 nM), to reverse endothelin-1 (ET-1; 10 nM) constrictions in human resistance and conductance coronary arteries (CA) in vitro was investigated. ET-1 (0.1 - 300 nM) constricted resistance CA more potently than conductance CA (P<0.05; EC(50) values 2.98 nM (95% CI: 1.49 - 5.95 nM and 8.58 (4.72 - 15.6 nM) respectively)). The NO-donor diethylamine NONOate fully reversed the ET-1 constriction in conductance CA (E(MAX) 127+/-9.16%), however only partial reversal was observed in resistance CA (E(MAX) 78.8+/-8.13; P<0.05). The soluble guanylate cyclase inhibitor 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (100 microM) reduced the maximum response to diethylamine NONOate to 76.9+/-14.4% in conductance CA (P<0.05), but had no effect on resistance CA (E(MAX) 77.2+/-18.4%). There was no difference between responses to ANP in conductance and resistance CA (EC(50) values 4.25 nM (0.84 - 21.4 nM) and 18.4 nM (2.92 - 116 nM), E(MAX) 53.1+/-14.7% and 48.6+/-11.8% respectively). BNP was a more potent vasodilator of conductance than resistance CA. In conductance CA the mean EC(50) value was 2.4 nM (0.74 - 7.75 nM), E(MAX) 54.5+/-14.9%. Concentration-response curves to BNP were incomplete in resistance CA. Concentration-response curves to CNP were incomplete in both conductance and resistance CA. The greater potency of ET-1 in resistance vessels may exacerbate the effects of increased circulating levels of the peptide in disease. Only NO could fully reverse ET-1 mediated constrictions in conductance CA, and none of the dilators tested could completely counteract constrictions in resistance CA.