Positive inotropic and vasoconstrictive effects of endothelin-1 in in vivo and in vitro experiments: characteristics and the role of L-type calcium channels

Endothelium, lipoproteins and atherosclerotic vascular disease

The endothelium modulates vascular tone by releasing nitric oxide, which is a potent vasodilator and inhibitor of platelet aggregation. Together with prostacyclin, the endogenous nitrate nitric oxide has an important protective role in preventing vasospasm and thrombus formation. In addition, the endothelium is a source of contracting factors such as endothelin-1, thromboxane A2 and endoperoxides. Due to its strategic anatomical position, the endothelium is a primary target for injurious stimuli and cardiovascular risk factors. Low density lipoproteins reduce endothelium-dependent relaxation and enhance endothelium- dependent contraction. The same pattern of endothelial dysfunction occurs in hypercholesterolaemia and atherosclerosis. These alterations of endothelial function may contribute to vasospasm, ischaemia and thrombus formation, which are common events in patients with atherosclerotic vascular disease.

Modulation of myocardial contraction by endocardial and coronary vascular endothelium

Endothelial cells in the heart, both endocardial endothelium and coronary vascular endothelium, influence myocardial contraction in isolated tissue and pump function in intact hearts by releasing diffusible agents that affect subjacent myocardium. Endocardial endothelium releases both nitric oxide (NO) and an unidentified "contraction-prolonging substance" ("endocardin") that respectively decrease and increase the duration of twitch contraction, probably by altering myofibrillar calcium sensitivity. These agents modulate the duration of ejection and the timing of relaxation, but without significantly altering early systolic behavior. Coronary vascular endothelium also releases NO, with similar effects on contraction, and in addition probably releases several other agents. Current work is aimed at identifying all of the agents involved in these novel endothelial influences and studying their potential physiologic and pathophysiologic roles in cardiac contractile and other functions.

Clinical trials with endothelin receptor antagonists: what went wrong and where can we improve?

In the early 1990s, within three years of cloning of endothelin receptors, orally active endothelin receptor antagonists (ERAs) were tested in humans and the first clinical trial of ERA therapy in humans was published in 1995. ERAs were subsequently tested in clinical trials involving heart failure, pulmonary arterial hypertension, resistant arterial hypertension, stroke/subarachnoid hemorrhage and various forms of cancer. The results of most of these trials - except those for pulmonary arterial hypertension and scleroderma-related digital ulcers - were either negative or neutral. Problems with study design, patient selection, drug toxicity, and drug dosing have been used to explain or excuse failures. Currently, a number of pharmaceutical companies who had developed ERAs as drug candidates have discontinued clinical trials or further drug development. Given the problems with using ERAs in clinical medicine, at the Twelfth International Conference on Endothelin in Cambridge, UK, a panel discussion was held by clinicians actively involved in clinical development of ERA therapy in renal disease, systemic and pulmonary arterial hypertension, heart failure, and cancer. This article provides summaries from the panel discussion as well as personal perspectives of the panelists on how to proceed with further clinical testing of ERAs and guidance for researchers and decision makers in clinical drug development on where future research efforts might best be focused.

Cardiac effects of endothelin receptor antagonism in endotoxemic pigs

Myocardial depression in sepsis is frequently encountered clinically and contributes to morbidity and mortality. Increased plasma levels of endothelin-1 (ET-1) have been described in septic shock, and previous reports have shown beneficial effects on cardiovascular performance and survival in septic models using ET receptor antagonists. The aim of the current study was to investigate specific cardiac effects of ET receptor antagonism in endotoxicosis. Sixteen domestic pigs were anesthetized and subjected to endotoxin for 5 h. Eight of these pigs were given tezosentan (dual ET receptor antagonist) after 3 h. Cardiac effects were evaluated using the left ventricular (LV) pressure-volume relationship. Endotoxin was not associated with any effects on parameters of LV contractile function [end-systolic elastance (Ees), preload recruitable stroke work (PRSW), powermax/end-diastolic volume (PWRmax/EDV) and dP/d tmax/end-diastolic volume (dP/d tmax/EDV)] but with impairments in isovolumic relaxation (time constant for pressure decay, tau) and mechanical efficiency. Tezosentan administration decreased Ees, PWRmax/EDV, and dP/d tmax/EDV, while improving tau and LV stiffness. Thus, dual ET receptor antagonism was associated with a decline in contractile function but, in contrast, improved diastolic function. Positive hemodynamic effects from ET receptor antagonism in acute endotoxemia may be due to changes in cardiac load and enhanced diastolic function rather than improved contractile function.

FLOW MOTION IN THE INTESTINAL VILLI DURING HEMORRHAGIC SHOCK: A NEW METHOD TO CHARACTERIZE THE MICROCIRCULATORY CHANGES

Conventional parameters are often inadequate to describe the dynamic flow changes in microcirculation. We used a novel approach to characterize oscillatory flow conditions in a canine model of hemorrhagic shock. Microcirculation in the ileal mucosal villi was visualized using intravital microscopy with the orthogonal polarization spectral imaging technique. The distribution of red blood cell velocity (RBCV) was estimated from the relative time periods of observed RBCV, and the average RBCV (A-RBCV) and its SD were then computed from the first and second moments of the RBCV distribution, respectively. Hemorrhagic shock (for 60 min) was followed by resuscitation with saline, hypertonic saline-Dextran solution (HSD, 7.2% NaCl-10% Dextran, 4 mL/kg), or HSD supplemented with the selective endothelin-A receptor antagonist ETR-p1/fl peptide (100 nmol/kg), respectively. The macrohemodynamic derangement (70% decrease in cardiac index and ileal blood flow) during shock was associated with the appearance of flow motion in the villi and an enhanced endothelin-1 release. The calculated A-RBCV was decreased by 40%. At resuscitation onset, continuous flow periods were transiently seen in 33%, 40%, and 50% of the experiments after saline, HSD, and HSD + ETR p1/fl treatment, respectively. HSD with or without endothelin-A antagonist treatment resulted in an increased relative duration of high-flow periods (by 20%) and a significant, 20% to 40% rise in A-RBCV. These results demonstrate that time-wise variability of RBCV should be used for the analysis of oscillatory flow conditions. The probabilistic estimation of A-RBCV provides a quantitative basis for comparison of the effectiveness of different resuscitation or vasoactive strategies.

Functional endothelin receptors are present on nuclei in cardiac ventricular myocytes

Endothelins are thought to act through two specific, plasmalemmal G protein-coupled receptor subtypes, ETAR and ETBR. However, in subfractionated cardiac membranes, ETAR immunoreactivity was detected only in the plasma membrane whereas ETBR immunoreactivity was detected predominantly in membranes of intracellular origin. Confocal microscopy demonstrated the presence of intracellular ETAR and ETBR in ventricular myocytes. ETAR were primarily on plasma membrane (surface membranes and transverse-tubules) and to a lesser extent on the nucleus while ETBR localized primarily to the nuclei. Western blot analysis of nuclei isolated from the heart indicated the presence of endothelin receptors: both ETAR and ETBR copurified with nucleoporin 62, whereas markers of endoplasmic reticulum and Golgi membranes were depleted. Radioligand binding studies revealed that isolated nuclei contain specific [125I]ET-1 binding sites. Specific [125I]ET-1 binding was reduced by 70-80% using the ETAR-selective antagonist BQ610 and 20-30% using the ETBR-specific antagonist BQ788. IRL-1620, an ETBR-specific agonist, also reduced [125I]ET-1 binding. Furthermore, ET-1 and IRL-1620 altered the incorporation of 32P into nuclear proteins and caused a transient increase in nuclear Ca2+ concentration. Hence, cardiac nuclei possess both ETAR and ETBR subtypes, which are functional with respect to ligand binding and are coupled to signaling mechanisms within the nuclear membrane.

Endothelin-1 during and after cardiopulmonary bypass: association to graft sensitivity and postoperative recovery

OBJECTIVE

Our objectives are 2-fold: (1) to serially measure the release of endothelin and graft-conduit endothelin sensitivity during and after coronary artery bypass grafting and (2) to define potential relationships of changes in endothelin levels to perioperative parameters.

METHODS

Endothelin plasma content was measured in patients (n = 105) undergoing bypass grafting from select vascular compartments before operations and at specific intervals up to 24 hours postoperatively. Endothelin sensitivity was determined in isolated internal thoracic artery segments.

RESULTS

Systemic arterial and pulmonary arterial endothelin levels were increased by approximately 50% immediately after bypass grafting and increased by another 85% during the first 24 hours postoperatively. Endothelin levels were highest in patients with prolonged ventilatory requirements and extended stays in the intensive care unit (10.2 +/- 0.8 vs 13.2 +/- 1.1 fmol/mL, P =.02, and 9.8 +/- 0.7 vs 13.9 +/- 1.2 fmol/mL, P =.01, respectively. Endothelin sensitivity of the internal thoracic artery was increased in patients requiring prolonged vasodilator support with nitroglycerin.

CONCLUSIONS

Systemic and pulmonary arterial endothelin levels remained increased for at least 24 hours postoperatively. Prolonged pharmacologic management and increased intensive care unit stay were associated with increased systemic endothelin release and heightened graft-conduit sensitivity to endothelin.

Role of endothelin-1 receptors in healthy anaesthetized rabbits

1. Many diseases are associated with elevated endothelin (ET)-1 plasma concentrations. In order to understand the consequence of this elevation, in the present study the effects of exogenous ET-1 on the entire organsim were investigated, in particular with respect to the role of ETA and ETB receptors in the cardiovascular system. In open-chest rabbits, left ventricular (LV) pressure (LVPmax, LVPed), dP/dtmax and dP/dtmin were recorded in ejecting and isovolumically beating hearts to determine cardiac function. In addition, heart rate (HR), aortic pressure (AoP) and aortic flow (AoF) were measured. Total peripheral resistance (TPR) was calculated from mean AoP and AoF. 2. In the first series of experiments (n = 11), ET-1 (0.5 nmol/kg; bolus) produced a non-significant reduction in HR. Systolic function, in terms of AoF, LVPmax and dP/dtmax, was improved; for example, LVPmax was increased significantly (69 +/- 10 vs 106 +/- 20 mmHg for control and ET-1, respectively; P < 0.05). Similarly, early relaxation (dP/dtmin) was improved. In parallel, TPR rose significantly (0.25+/-0.07 vs 0.35+/-0.1 mmHg/min per mL for control and ET-1, respectively; P < 0.05). Isovolumic measurements showed corresponding responses. 3. In the second series of experiments (n = 7), animals were pretreated with an ETA receptor antagonist (330 nmol/min per kg FR 139317). After ETA receptor blockade, the administration of ET-1 had no significant effect on cardiac function or vasomotion. 4. In the third series of experiments (n = 6), animals were pretreated with an ETB receptor antagonist (10 nmol/min per kg BQ 788). In this series of experiments, the effects of ET-1 on cardiac function and vasomotion were the same as in the first series of experiments, except for the effect on HR, which decreased by 35% after ET-1. 5. In our experimental model, exogenous ET-1 exerted a clear-cut positive inotropic effect, together with the anticipated peripheral vasoconstriction via ETA receptors.

Inotropic response of rabbit ventricular myocytes to endothelin-1: difference from isolated papillary muscles

Endothelin-1 (ET-1) increased cell shortening and Ca2+ transients over the concentration of 3 x 10(-11) M to 10(-9) M with EC50 of 8.3 x 10(-11) M in rabbit single ventricular myocytes. Thus ET-1 was approximately 60 times more potent in single myocytes than in papillary muscles (EC50 = 5.1 x 10(-9) M) of the same species. In single myocytes, ET-1 at 10(-8) M elicited an inhibitory response that counteracted the facilitatory response: the concentration-response curve (CRC) for ET-1 was bell shaped. The ET(A)-receptor antagonist BQ-485 shifted CRC for ET-1 to the right in parallel; however, the facilitatory response to 10(-8) M ET-1 was markedly enhanced by BQ-485 and also by the ET(B) antagonist BQ-788. The ET(A)/ET(B) antagonist TAK-044 abolished the ET-1-induced response. These findings indicate that the response to ET-1 of single myocytes is different from that of papillary muscles in concentration dependence, characteristics of the response, and susceptibility to ET-receptor antagonists. Anomalous pharmacological characteristics of ET-1-induced response in rabbit papillary muscles may be due to integrated regulatory mechanisms that may involve also various types of noncardiac cell in ventricular myocardium.

Investigating the dual nature of endothelin-1: ischemia or direct arrhythmogenic effect?

Endothelin-1 (ET-1) is a potent vasoconstrictor peptide, which may also elicit severe ventricular arrhythmias. The aims of our study were to compare the effects of total left anterior descending coronary artery (LAD) occlusion to intracoronary (ic.) ET-1 administration and to investigate the pathomechanism of ET-1 induced arrhythmias in 3 groups of anesthetized, open-chest mongrel dogs. In group A (n=10) a total LAD occlusion was carried out for 30 min, followed by a 60 min reperfusion period. In groups B and C ET-1 was administered into LAD for 30 min at a rate of 30 pmol/min (n=6) and 60 pmol/min (n=8). Epi- and endocardial monophasic action potential (MAP) recordings were performed to detect electrophysiologic changes and ischemia Blood samples for lactate measurements were collected from the coronary sinus (CS) and from the femoral artery. Infrared imaging was applied to follow epimyocardial heat emission changes. At the end of the ET-1 infusion period coronary blood flow (CBF) was reduced significantly in groups B and C (deltaCBF30MIN B: 21+/-2%, p<0.05; C: 35+/-2%, p<0.05), paralleled by a significant epimyocardial temperature decrease in group C (deltaT30MIN: -0.65+/-0.29 degrees C, p<0.05). Two dogs died of ventricular fibrillation (VF) in the reperfusion period in group A. Ventricular premature contractions and non-sustained ventricular tachycardic episodes appeared in group B, whereas six dogs died of VF in group C. Significant CS lactate level elevation indicating ischemia was observed only in group A from the 30th min occlusion throughout the reperfusion period (control vs. 30 min: 1.3+/-0.29 vs. 2.2+/-0.37 mmol/l, p<0.05). Epi- and endocardial MAP durations (MAPD90) and left ventricular epicardial (LV(EPI)) upstroke velocity decreased significantly in group A in the occlusion period. ET-1 infusion significantly increased LV(EPI) MAPD90 in group B and both MAPD90-s in group C. In conclusion, ischemic MAP and CS lactate changes were observed only in group A. Although ET-1 reduced CBF significantly in groups B and C, neither MAP nor lactate indicated ischemic alterations. ET-1 induced major ventricular arrhythmias appeared before signs of myocardial ischemia developed, though reduced CBF presumably contributed to sustaining the arrhythmias.

Verapamil reduces the arrhythmogenic effect of endothelin

In a previous study we established that endothelin-1 (ET-1) can induce characteristic ventricular tachycardias (VT) with significant prolongation of QT and QTc time. In this investigation we studied the role of CA2+ channels in the pro-arrhythmic effects of ET-1. In 24 anesthetized, open-chest mongrel dogs, ET-1 was administered into the left anterior descending coronary artery at a comparatively low dose (60 pmol/min) for 30 min. Twelve dogs received the Ca(2+)-channel blocker verapamil (0.4 mg/kg) before ET-1 application. The following parameters were recorded continuously over the infusion period: systemic arterial blood pressure, coronary blood flow, surface ECG leads, epicardial atrial and ventricular electrograms, and right and left ventricular endocardial monophasic action potentials (MAP). Electrophysiologic studies were performed by programmed electrical stimulation of the heart. Blockade of myocardial Ca2+ channels attenuated the arrhythmogenic action of ET-1. After verapamil administration to ET-1-treated dogs, sustained VT did not appear and ventricular fibrillation (VF) developed only in two dogs. In the control group serious and sustained VT and VF developed in nine animals. It is noteworthy that verapamil did not prevent ET-1-induced prolongation of QT time. The results appear to prove that myocardial Ca2+ channels are involved in the proarrhythmic effect of ET-1.

Hemodynamic and inotropic effects of the endothelin A antagonist BQ-610 in vivo

The positive inotropy of endothelin-1 (ET-1) described by in vitro studies is not detectable in vivo because this effect is antagonized by cardiodepressive effects due to ET-induced vasoconstriction with subsequent myocardial ischemia. This vasoconstriction is mainly mediated by ETA receptors. In a previous in vivo study with a selective ETB receptor agonist, we showed that ETB receptors play an important role in the ET-induced positive inotropy. The present in vivo study examined whether selective ETA receptor blockade can unmask the ETB receptor-mediated positive inotropy of endogenous ET-1 by preventing its cardiodepressive effects via ETA receptors. In an open-chest rat model, we compared the acute hemodynamic and inotropic effects of the highly selective ETA receptor antagonist BQ-610 (100 micrograms/kg) with NaCl controls during and after a 7-min infusion. In addition to measurements in the intact circulation, the effects on myocardial contractility were studied by isovolumic registrations (peak LVSP, peak dP/dtmax), which are independent of peripheral vascular effects. Acute blockade of the ETA receptors by BQ-610 had no effect on blood pressure and heart rate. BQ-610 caused vasodilatation (total peripheral resistance -7.5% vs. control at the end of infusion; p < 0.01) with a consecutive increase in stroke volume (+15.3%; p < 0.01), cardiac output (+15.4%; p < 0.001), and ejection fraction (+10.4%; p < 0.01). The isovolumic measurements indicated a significant positive inotropic effect of BQ-610 (peak LVSP + 4.2%, p < 0.01; peak dP/dtmax + 5.5%, p < 0.01). Therefore, selective ETA receptor blockade by BQ-610 improves the hemodynamics in the intact circulation by causing a reduction in afterload and an increase in myocardial contractility. The positive inotropic effect of BQ-610 may be mediated by the positive inotropy of endogenous ET-1 via ETB receptors after selective ETA receptor blockade.

Differential effects of endothelin-1 on basal and isoprenaline-enhanced Ca2+ current in guinea-pig ventricular myocytes

1. We examined the effect of endothelin-1 (ET-1) on basal and isoprenaline-enhanced L-type Ca2+ current (ICa,L) in guinea-pig ventricular myocytes under nystatin-perforated patch configuration. 2. ET-1 at concentrations of 1, 5 and 10 nM had little effect on basal ICa,L. However, ICa,L enhanced by isoprenaline (500 nM) was significantly attenuated by 5 nM ET-1 by more than 50%. This effect was reversed upon washout. ICa,L enhanced by forskolin was also decreased by ET-1. 3. The inhibitory effect of ET-1 against isoprenaline was completely blocked by the ETA receptor antagonist BQ-123 (1 microM). In myocytes incubated with pertussis toxin (PTX, 2 micrograms ml-1) for 5 h, ET-1 did not inhibit isoprenaline-enhanced ICa,L. 4. Although ET-1 has been shown to activate specific protein kinase C (PKC) isoforms, a significant inhibitory effect of ET-1 was maintained in the presence of the PKC inhibitor bisindolylmaleimide (20 nM). The nitric oxide (NO) donor SIN-1 (10 microM) attenuated but failed to prevent the ET-1 effect. 5. In summary, our results demonstrate that ET-1 is devoid of any significant effects on basal ICa,L. However, it exerts a potent inhibitory effect against isoprenaline-enhanced ICa,L. This effect is mediated through ETA receptors coupled to PTX-sensitive G-proteins and occurs in the presence of PKC inhibition and NO generation.

Does nitric oxide contribute to the negative chronotropic and inotropic effects of endothelin-1 in the heart?

N omega-nitro-L-arginine methyl ester, an inhibitor of nitric oxide synthase, was used to examine whether nitric oxide was involved in the negative chronotropic and inotropic effects of endothelin-1 in the presence of isoprenaline in mammalian heart. In isolated rabbit right atria, endothelin-1 elicited a negative chronotropic effect in the presence of isoprenaline, which was associated with a decrease in the isoprenaline-induced accumulation of cyclic AMP. On the other hand, in the dog ventricular trabeculae, the negative inotropic effect of endothelin-1 was not accompanied by a significant reduction in the isoprenaline-induced accumulation of cyclic AMP. N omega-nitro-L-arginine methyl ester affected neither the negative chronotropic effect nor the negative inotropic effect of endothelin-1. The effects of endothelin-1 on the isoprenaline-induced cyclic AMP accumulation were not influenced by N omega-nitro-L-arginine methyl ester either. These results indicate that the negative chronotropic and inotropic effects of endothelin-1 in the presence of isoprenaline in mammalian cardiac muscle do not involve the nitric oxide-mediated signaling pathway.

Cardiovascular and renal actions of the endothelin(B) receptor in pigs

Previously we showed that blocking the endothelin (ET)A receptor subtype with BQ-153 inhibited the vasoconstrictor effects of intravenously administered ET-1. In the presence of the ET(A) antagonist, ET-1 produced marked reductions in myocardial contractility and renal blood flow. We postulated that either the ET(B) receptor, or some other, as yet unidentified, ET-receptor subtype mediated the observed hemodynamic changes. In anesthetized pigs, this hypothesis was tested by using a recently developed selective, high-affinity antagonist to the ET(B) receptor, BQ-788, and sarafotoxin S6c, a selective ET(B) agonist, to determine the contribution of this receptor subtype to cardiovascular function. Endothelin-1 (0.4 nmol/kg, i.v.) produced the characteristic biphasic hemodynamic responses, consisting of an initial transient reduction in mean arterial pressure (MAP; 83 +/- 3 to 72 +/- 4 mm Hg; n = 9) followed by a prolonged increase (112 +/- 4 mm Hg; p < 0.01). As well, cardiac output (-58%; p < 0.05), myocardial contractility (-19%; p < 0.01), and renal blood flow (63%; p < 0.05) decreased. Sarafotoxin S6c produced marked but transient reductions in MAP (p < 0.001), cardiac output (p < 0.01), myocardial contractility (p < 0.001), and renal blood flow (p < 0.05). BQ-788 (1.0 mg/kg, i.v.), administered 3 min before sarafotoxin S6c, inhibited its effects. BQ-788 also inhibited the initial transient reduction in MAP seen after the injection of ET-1, but the subsequent sustained pressor responses were enhanced as reflected in the greater increases in left ventricular pressure (p < 0.02), myocardial contractility (p < 0.05), MAP (p < 0.01), and a larger reduction in cardiac output (p < 0.05). The heart rate was not changed after the initial ET injection, but it increased 54% when the peptide was administered in the presence of BQ-788. The reduction in renal blood flow was still evident, and its magnitude (64%) remained the same (p < 0.01) after treatment with BQ-788. Only the combined administration of both the ET(A) (BQ-123) and ET(B) (BQ-788) receptor antagonists blocked the effects of ET-1 on renal blood flow (p < 0.05). These data confirm that BQ-788 is a selective and effective antagonist of the ET(B) receptor and show that activation of this receptor subtype is involved in the transient vasodilation provoked by ET-1. Additionally, the ET(B) receptor appears to oppose the vasoconstrictor effects of the ET(A) receptor, which clearly mediates vasoconstriction. Combined treatment with BQ-123 and BQ-788 attenuated the reductions in renal blood flow produced by ET-1. Furthermore, some actions of ET-1 were not blocked by these antagonists and cannot be attributed to either the ET(A) or ET(B) receptors. We hypothesize the existence of an additional ET receptor or a subtype of the ET(B) receptor that is insensitive to BQ-788.

Pharmacological characteristics of endothelin receptors in the rabbit ventricular myocardium: the nonselective endothelin receptor antagonist PD 145065 antagonizes the positive inotropic effect of endothelin-3 but not of endothelin-1

Endothelin-3 (ET-3) elicited a concentration-dependent positive inotropic effect on rabbit papillary muscle, the maximal response being approximately 65% of the maximal response to isoproterenol. ET-1 induced a positive inotropic effect over the concentration range below 10(-9) M, at which ET-3 did not produce a positive inotropic effect, but the maximal response to ET-1 was equivalent to or slightly lower than that of ET-3. The nonselective ET receptor antagonist PD 145065 effectively antagonized the positive inotropic effect of ET-3 in a concentration-dependent manner and abolished it at 10(-5) M. PD 145065 decreased the positive inotropic effect induced by ET1 at lower concentrations (< 10(-9) M) but it did not affect the main portion of the concentration-response curve for the positive inotropic effect, i.e., the effect induced by high concentrations (> 10(-9) M) of ET-1. PD 145065 antagonized also the positive inotropic effect of sarafotoxin S6c. PD 145065 inhibited the specific binding of [125I]ET-1 and of [125I]ET-3 with a high- and a low-affinity site for competition. ETB selective ligands, RES-701-1 and sarafotoxin S6c, displaced [125Iuc]ET-3 with high affinity but they scarcely affected the [125I]ET-1 binding. These findings indicate that different subtypes of the ET receptor are responsible for the induction of the positive inotropic effect of ET-3 and ET-1. ET receptors involved in the production of the positive inotropic effect in the rabbit ventricular myocardium have pharmacological characteristics that are different from those of conventional ET receptors originally classified based on the pharmacological findings in noncardiac tissues. The positive inotropic effect of ET-3 in the rabbit ventricular muscle may be mediated predominantly by ETA1 receptors that are susceptible to PD 145065 as well as BQ-123 and FR139317, and partially mediated by ETB receptors that are inhibitable with RES-701-1. ETA2 receptors that are resistant to ETA selective as well as nonselective antagonists may mainly be responsible for the positive inotropic effect of ET-1 in the rabbit ventricular muscle.

Effects of a new endothelin receptor antagonist, TAK-044, on myocardial stunning in dogs

The effects of a new endothelin receptor antagonist, TAK-044, (cyclo[D-alpha-aspartyl-3-[(4-phenylpiperazin-1-yl)carbonyl]L-alan yl-L-alpha aspartyl-D-2-(2-thienyl)glycyl-L-leucyl-D-tryptophyl]disodium salt, on ischemic and post-ischemic myocardial dysfunction (stunned myocardium) were studied in anesthetized open-chest dogs. A short (15 min) occlusion of the left anterior descending coronary artery followed by 5-h reperfusion significantly reduced myocardial segment shortening during and after the ischemic period in the ischemic region. Regional myocardial blood flow was also decreased significantly 10 min after the occlusion, whereas it returned almost completely to its pre-ischemic value 5 h after reperfusion TAK-044 (3 mg/kg,i.v.) administered 10 min before occlusion significantly improved the reduced myocardial segment shortening in the ischemic region during and after occlusion. Cardiovascular hemodynamics and regional myocardial blood flow in a TAK-044-treated group were identical to those in the control group. These results indicate that endogenous endothelin contributes to the cause of ischemic and post-ischemic myocardial dysfunction without changing either hemodynamics or regional myocardial blood flow.

Endothelin-1 inhibits L-type Ca currents enhanced by isoproterenol in guinea-pig ventricular myocytes

To investigate the action of endothelin-1 (ET-1) on L-type Ca currents (ICa,L) in guinea-pig ventricular cells, whole-cell currents were recorded at approximately 36-37 degrees C in enzymatically isolated myocytes. ET-1 (> or =10 nM) suppressed the basal ICa,L to 79+/-8% of control at 20 nM. Bath application of isoproterenol (ISO; 10 nM) enhanced ICa,L to 192+/-28% with about a -10-mV shift of its relationship with membrane potential. ET-1 concentration dependently inhibited this ISO-enhanced ICa,L with a half-maximally inhibitory concentration (IC50) of 168 pM. The inhibitory actions of ET-1 were antagonised by BQ-123 (300 nM), cyclo(D-Asp-L-Pro-D-Val-L-Leu-D-Trp), a specific ETA receptor antagonist. Histamine-enhanced ICa,L was also suppressed by ET-1, but ICa, L potentiated by internal adenosine 3',5'-cyclic monophosphate (cAMP) was unaffected. Preincubation of myocytes with pertussis toxin (PTX, at 5 microgram/ml for >60 min at 36 degrees C) completely occluded the ET-1 action. Thus, stimulation of ETA receptors by subnanomolar ET-1 inhibits ICa,L via PTX-sensitive G-proteins.

Endothelial cell products alter mammalian skeletal muscle function in vitro

We tested the hypothesis that endothelin and nitric oxide (NO) alter the force developed by fast-twitch and slow-twitch mammalian skeletal muscle, using a mouse skeletal muscle preparation trimmed to approximately 50% of the original diameter to decrease diffusion distances. We suspended trimmed soleus (SOL) and extensor digitorum longus (EDL) muscles in Krebs-Henseleit buffer (27 degrees C; pH 7.4) gassed with 95% O2 -5% CO2. Muscles were stimulated once every 90 s for 500 ms at 50 Hz for SOL and 100 Hz for EDL. The force developed by trimmed SOL was 223.8 +/- 9.1 mN/mm2 and by EDL was 247.3 +/- 9.4 mN/mm2. Endothelin 1 (ET-1) had no effect on EDL but significantly accelerated the rate of decrease of developed force of SOL at concentrations of 10(-10) mol/L and higher within 10 contractions. When ET-1 was removed, force returned toward control value. Endothelin 3 (ET-3) had no effect on either muscle. S-Nitroso-N-acetylpenicillamine (SNAP), a source of NO, increased developed force over time in both muscles, with a threshold of 10(-6) mol/L. The effect was evident within 5 contractions in both muscles. Force remained elevated above control values after the removal of SNAP. Thus ET-1 attenuated and NO amplified mammalian skeletal muscle function.

Endothelin and myocardial ischemia

Endothelin is a potent vasoconstrictor with a wide range of effects on the heart. Changes in myocardial and circulating levels of endothelin have been described in various experimental models of myocardial ischemia, and in humans with acute myocardial infarction and different forms of angina pectoris. The role played by endothelin in the different states of myocardial ischemia is unclear. However, myocardial damage has been shown to be reduced in several experimental models of myocardial infarction by administering agents that block the action of endothelin. The aim of this review article is to present the current literature concerning the interaction between endothelin and the various forms of myocardial ischemia, and to explore the significance of such interactions.

Hemodynamic and inotropic effects of endothelin-1 in vivo

Endothelin-1 (ET-1) is known to have strong vasoactive properties. Contradictory results have been reported with regard to its inotropic effects. This study examined the dose-dependent (500, 1000, 2500, 5000 and 10,000 ng ET-1/kg vs. NaCl controls) hemodynamic and inotropic effects of ET-1 in 53 open-chest rats during and after a 7-min infusion. Besides measurements in the intact circulation the myocardial function was examined by isovolumic registrations independent of peripheral vascular effects. A transient ET-1 induced (500, 1000, 2500, 5000 ng ET-1/kg) decrease of the left ventricular systolic pressure (LVSP) and the mean aortic pressure (AoPmean) was followed by a dose-related rise of these pressures (LVSP: -1%, -1%, +8%, +16% vs. preinfusion values; AoPmean: -11%, +9%, +39%, +52%). Heart rate (HR) was not influenced by ET-1. Due to the dose-dependent decrease of the stroke volume (SV) the cardiac output (CO) was reduced (CO: -8%, -23%, -40%, -50%). After an initial vasodilatation ET-1 elevates the total peripheral resistance (TPR: -1%, +49%, +139%, +215%) dose-dependently. 10,000 ng ET-1/kg was a lethal dose resulting in cardiac failure within minutes (low output). Since the maximum of the isovolumic LVSP (peak LVSP) and the corresponding dP/dtmax (peak dP/dtmax) were unchanged under ET-1, the isovolumic measurements do not indicate a positive inotropic effect of ET-1 in vivo in contrast to published results of in vitro experiments. It may be possible that a direct positive inotropic effect of ET-1 observed in in vitro studies is counterbalanced in vivo by an indirect negative inotropic effect due to the coronary-constrictive effect of ET-1.

Role of endothelial cells in cardiovascular function

Since the first description of vascular endothelium-dependent relaxation in response to acetylcholine, the role of endothelial cells in the regulation of cardiovascular function has been increasingly studied. The identification of endothelial releasing factors such as nitric oxide and endothelin has enabled us to better understand the mechanisms involved in autoregulation. It has also been shown that both vascular and endocardial endothelium can modify the contractile characteristics of their adjacent myocardium. In the heart, these modulating effects of endothelial cells are more widespread than previously thought and, can be the result of the direct effects of endocardial and vascular endothelial cells and their indirect effects, via modulation of the myocardial response to inotropic agents.

Effect of dysfunctional vascular endothelium on myocardial performance in isolated papillary muscles

Vascular endothelium has been shown to modify the contractile characteristics of vascular smooth muscle, and endocardial endothelium has been shown to modify the contractile characteristics of adjacent myocardium. In this study, whether vascular endothelium also modifies the contractile characteristics of adjacent myocardium and whether these effects are additive to those of endocardial endothelium were investigated. Rabbit hearts (n = 54) were excised and mounted in a Langendorff preparation. Vascular reactivity was verified by acetylcholine infusion. One group of these hearts had Triton X-100 injected as a bolus into the coronaries to render the vascular endothelium dysfunctional. The other portion served as control hearts. Triton X-100 bolus injection resulted in little or no pathological changes on morphological examination; however, the vasodilatory response to acetylcholine in these hearts was abolished, suggesting vascular endothelial dysfunction. Vascular smooth muscle reactivity was verified in Triton X-100-injected hearts by nitroprusside infusion. In the control Langendorff-perfused hearts, there was little evidence of vascular endothelial dysfunction, with the coronary perfusion rate increasing from 8.9 +/- 0.4 to 11.0 +/- 0.3 ml/g per minute (p < 0.01) in response to acetylcholine. All hearts were then removed, and right ventricular papillary muscles were excised for myocardial mechanical studies. Control Langendorff-perfused hearts had myocardial mechanical characteristics similar to those of muscles from 18 other control hearts without Langendorff perfusion, indicating that the Langendorff perfusion itself had little effect on myocardial mechanics. The muscles from the Triton X-100-injected Langendorff hearts had marked changes: a shortening of twitch duration (363 +/- 16 versus 449 +/- 9 msec, p < 0.01) and decreases in total tension (2.2 +/- 0.2 versus 2.9 +/- 0.2 g/mm2, p < 0.01), dT/dt (9 +/- 1 versus 12 +/- 1 g/mm2 per second, p < 0.05), and maximum velocity of unloaded muscle shortening (Vmax) (0.89 +/- 0.06 versus 1.14 +/- 0.07 length at which maximum developed tension occurred [Lmax]/sec, p < 0.05). Endocardial endothelial removal of the papillary muscles in the two control groups (with and without Langendorff perfusion) by Triton X-100 caused the same changes in twitch characteristics as occurred in muscles from the Langendorff-perfused hearts injected with Triton X-100 but with intact endocardial endothelium, suggesting that vascular endothelial dysfunction had similar effects on contractile characteristics as endocardial endothelial removal.(ABSTRACT TRUNCATED AT 400 WORDS)

Characterization and localization of endothelin receptor subtypes in the human atrioventricular conducting system and myocardium

The characterization and localization of endothelin A (ETA) and endothelin B (ETB) receptors have been determined in tissue sections of the human atrioventricular conducting system, surrounding regions of atrial and ventricular myocardium, and the left ventricular free wall by use of radioligand binding, polymerase chain reaction, and in situ hybridization. Selective ETA (BQ123) and ETB (BQ3020) compounds in conjunction with [125I]endothelin-1 revealed the presence of ETA and ETB receptors in the left ventricular free wall (BQ123: 57 +/- 5% ETA, 43 +/- 2% ETB, n = 3; BQ3020: 67 +/- 3% ETA, 33 +/- 3% ETB, n = 3). Autoradiography using [125I]endothelin-1 in the absence or presence of BQ3020, BQ123, or endothelin-1 showed ETA and ETB receptors localized to atrial and ventricular myocardium, the atrioventricular conducting system, and endocardial cells. There was a higher proportion of ETB receptors in the atrioventricular node and the penetrating and branching bundles of His than in the surrounding interventricular and interatrial septa (p < 0.0001). There was a lower density of ETB receptors in the interventricular septum compared with the interatrial septum and the atrioventricular conducting system (p = 0.009) and a lower density of ETA receptors in the atrioventricular conducting system compared with interatrial and interventricular septa (p = 0.008). Isolated right atrial myocytes showed a higher proportion of ETA receptors (91 +/- 12%, n = 3). Amplification of left ventricular free wall cDNA by polymerase chain reaction revealed the presence of ETA and ETB receptor mRNA. mRNA for both subtypes was detected in isolated atrial myocytes. In situ hybridization showed ETA and ETB receptor mRNA localization to atrial and ventricular myocardium, the atrioventricular conducting system, and endocardial cells. These studies demonstrate the presence of ETA and ETB receptors in human myocardium and the atrioventricular conducting system.

Regulation of cortical collecting duct function: effect of endothelin

We recently showed that endothelin-1 (ET-1) increases cell Ca2+ in the mouse cortical collecting duct. To clarify the cellular action and target cell of ET-1, electrophysiologic techniques and cell Ca2+ measurement were applied to rabbit cortical collecting ducts perfused in vitro. When 10(-8) mol/L ET-1 was added to the bath, a transient increase followed by a sustained increase in cell Ca2+ was observed. A sustained increase in cell Ca2+ lasted 10 to 20 minutes and was associated with a decrease in lumen-negative transepithelial voltage. To confirm the target cell type of ET-1, confocal laser microscopy was used. An increase in cell Ca2+ was observed in the same cell, which also showed an increase in cell Ca2+ in response to arginine vasopressin (AVP), which indicated that the principal cell has ET-1 receptors in the basolateral membrane. When ET-1 was applied to the bath, total cellular membrane resistance (Ri) decreased initially and then gradually increased because of inhibition of the luminal Na+ channel. An initial decrease in Ri was considered an influx of Ca2+ from the basolateral membrane. To further determine the source of an increase in cell Ca2+, the effect of ET-1 was tested in the absence of external Ca2+ and in the presence of a Ca2+ channel blocker in the bath. Cell Ca2+ did not respond to ET-1 in the absence of external Ca2+, a condition in which an AVP-stimulated increase in cell Ca2+ was preserved.(ABSTRACT TRUNCATED AT 250 WORDS)

Endothelin as a neuropeptide. Cardiovascular effects in the brainstem of normotensive rats

The relevance of endothelin in central cardiovascular function was studied in urethane-anesthetized Sprague-Dawley rats. Blood pressure (BP) was monitored intra-arterially, and cerebrospinal fluid (CSF) was collected through an intracisternal catheter for radioimmunoassay of endothelin-1 (ET-1). Endothelin levels in the CSF were significantly higher (39 +/- 3 pg/ml) than in plasma (10 +/- 3 pg/ml, n = 11). ET-1 in CSF or plasma was not affected by systemic infusion of saline, but its levels significantly decreased when a sustained increase in BP was elicited with phenylephrine (14 +/- 7 pg/ml in the CSF and 6 +/- 4 pg/ml in plasma, n = 5). In sinoaortic-denervated animals, phenylephrine failed to reduce CSF endothelin levels. In different experiments, intracisternal administration of ET-1 (10 pmol) evoked an initial decrease in BP and heart rate (HR), followed by pronounced hypertension, bradycardia, and, in 70% of the animals, death from cardiorespiratory failure. Intracisternal administration of endothelin-3 (ET-3, 80 pmol, n = 11) evoked only a modest hypotensive and bradycardic response without cardiorespiratory impairment. Microinjection of ET-1 (0.5, 1, 2, 4, and 6 pmol/60 nl) into the nucleus of the solitary tract or area postrema produced a decrease in BP and HR. On the other hand, injection of low concentrations of ET-3 into the nucleus of the solitary tract increased BP and HR (at 2 pmol, 17 +/- 3 mm Hg, 14 +/- 6 beats per minute, n = 7), whereas ET-3 in the area postrema produced a prominent dose-related decrease in BP and HR. In the rostroventrolateral medulla, the lowest doses of ET-1 first modestly increased BP and renal sympathetic nerve activity. These effects were followed by hypotension, bradycardia, increase in respiratory frequency, and further enhancement of sympathetic nerve traffic. In 29% of the animals, these effects were followed by cardiorespiratory arrest. The specificity of the cardiovascular response to endothelin was demonstrated by the inhibitory effects of the receptor antagonist BQ-123. These results demonstrate that endothelin has specific cardiovascular effects in the brainstem of the rat and support a role for endothelin in cardiovascular regulation.

Increased plasma concentrations of endothelin in congestive heart failure in humans

Congestive heart failure is characterized by decreased cardiac output and increased peripheral vascular resistance. Endothelin, a peptide found in plasma, is a potent vasoconstrictor. We hypothesized that plasma concentrations of endothelin are increased in humans with congestive heart failure. Plasma samples were obtained from 71 healthy control subjects and 56 patients with congestive heart failure. The mean plasma concentration of endothelin, measured by radioimmunoassay, was 7.1 +/- 0.1 pg/ml in the 71 normal control subjects but 12.6 +/- 0.6 pg/ml in the 56 patients with heart failure (P = 0.001). To evaluate the relationship between circulating endothelin and clinical stage of congestive heart failure, we categorized patients into two groups--those with mild heart failure (New York Heart Association class I or II) and those with severe heart failure (class III or IV). Circulating endothelin in the 24 patients with mild disease was 11.1 +/- 0.7 pg/ml, significantly higher than in normal subjects (P < 0.001). Endothelin in the 32 patients with severe heart failure was 13.8 +/- 0.9 pg/ml, a level significantly higher than that in the group with mild disease (P = 0.029). In the 56 patients with congestive heart failure, a negative correlation was found between plasma concentration of endothelin and left ventricular ejection fraction (r = -0.279; P = 0.037). These data demonstrate that the plasma concentration of endothelin is increased in humans with congestive heart failure and that the level correlates with the severity of disease. Endothelin may have a role in the increased vascular resistance in patients with chronic congestive heart failure.

Identification and characterization of Drosophila female germ line transcriptional control elements

The highly organized structure of the Drosophila ovary makes it an ideal system for studying mechanisms of differential gene expression. Here we report the identification of a 171 bp sequence from the 5' end of the hsp26 gene that functions as a female germ-line-specific transcriptional regulator when linked in two copies to a basal promoter. The regulator is active only in nondividing cells of the germ line, i.e., only in nurse cells and oocytes. It is not active in any examined tissue or cell type outside of the female germ line. Copper nuclease footprinting studies show that the germ line regulator contains two binding sites for each of two different ovarian nuclear factors. Point mutations in the DNA target sites of either nuclear factor abolish in vitro binding and in vivo transcriptional activity, indicating that each factor is a positive activator of nurse cell/oocyte transcription. The two factors may represent different classes of activator proteins, since an increase in the copy number of one factor's DNA target site cannot compensate for a decrease in the copy number of the other factor's target site.

Endothelin activates voltage-dependent Ca2+ current by a G protein-dependent mechanism in rabbit cardiac myocytes

1. Endothelin is a vasoactive peptide released from vascular endothelial cells which has potent cardiac inotropic effects. We examined the effect of endothelin on the verapamil-sensitive Ca2+ current (ICa) in enzymatically dispersed rabbit ventricular myocytes. 2. Using the whole-cell voltage clamp technique with a standard dialysing pipette solution, the application of extracellular endothelin (20 nM) did not increase the peak ICa, but in fact caused a small reversible decline (903 +/- 109 pA without endothelin, 727 +/- 95 pA with endothelin (means +/- S.E.M., n = 14, P less than 0.05)). 3. If GTP (100 microM) was added to the pipette solution, the extracellular application of endothelin (0.2 or 20 nM) caused a large, reproducible increase in peak ICa (871 +/- 85 pA without endothelin, 1230 +/- 110 pA with 20 nM-endothelin (n = 10, P less than 0.05). The endothelin enhancement of ICa occurred after a delay of approximately 3-4 min at room temperature. 4. The GTP requirement for the endothelin effect on ICa suggests that its effect may be mediated through a G protein-dependent pathway. To investigate this further, experiments were performed with pipette solutions containing guanosine-5'-O-(2-thiodiphosphate) (GDP beta S), a GDP analogue which inhibits G protein cycling. With the addition of GDP beta S (0.5-5.0 mM) to the pipette solution (along with 100 microM-GTP), the effect of endothelin on peak ICa was blocked (1062 +/- 86 pA without endothelin, 1170 +/- 134 pA with endothelin (n = 11, P greater than 0.05)). 5. Incubation of myocytes with pertussis toxin (500 ng/ml) prevented the partial ACh-induced reversal of the isoprenolol enhancement of ICa. However, this identical treatment failed to block the endothelin enhancement of the voltage-dependent Ca2+ current (n = 4). 6. Taken together, these results confirm that while the effect of endothelin in rabbit cardiac ventricular myocytes is mediated through a G protein-dependent pathway, the G protein involved is pertussis toxin-insensitive.

Endothelins. Myocardial actions of a new class of cytokines

There is growing evidence to support the existence of a dynamic interaction in vivo between cardiac myocytes and adjacent microvascular endothelial cells in the regulation of both cardiac myocyte and possibly endothelial cell phenotype and function. Endothelins may be only one of several endogenous cytokines or autocoids that are released by the cardiac microvascular and/or endocardial endothelium and transported vectorially to adjacent myocytes that could modify cardiac contractile state, perhaps in response to changes in microvascular blood flow. Similarly, cardiac myocytes themselves could release cytokines that could directly affect endothelial cell proliferation or angiogenesis and indirectly elicit or modify the release of endothelium-derived cytokines and autocoids. Thus, in addition to modifying function, endothelial cell-cardiac myocyte interactions may also be of importance in the dynamic events that lead to myocardial wall remodeling and angiogenesis during hypertrophic growth and in the response to cardiac injury.

Effects of endothelin-1 on epicardial coronary tone, coronary blood flow, ECG-ST change and regional wall motion in anesthetized dogs

The effects of intracoronary-administrated endothelin-1 on coronary hemodynamics and regional myocardial function were studied in anesthetized open-chest dogs. Epicardial coronary diameter (CoD) and coronary blood flow (CBF) were measured by a sonomicrometer of 10 MHz piezoelectric crystals and an electro-magnetic flow probe on the left circumflex coronary artery (LCX). Regional wall motion was sonomicrometrically measured at regions supplied by the LCX and left anterior descending artery (LAD) and electrocardiograms were recorded. Endothelin-1, administered as a bolus injections into the LCX via an intracoronary cannula, in a dose-dependent manner reduced COD and CBF. The extent of the reduction of COD and CBF at a dose-dependent manner reduced COD and CBF. The extent of the reduction of COD and CBF at a dose of 300 pmol was 12.3 +/- 1.5% (P less than 0.01) and 86 +/- 5% (P less than 0.01), respectively, of the control. The extent of CBF reduction and deterioration of systolic wall motion were linearly related with the dosage of endothelin-1. ST-elevation (lead II) and fatal ECG abnormalities, including complete atrioventricular block or ventricular fibrillation, were observed with doses above 60 and 100 pmol, respectively. Coronary angiography revealed that filling defects of dye were propagated from the third or distal branches to those of more proximal arteries when the doses of endothelin-1 were cumulatively infused into the LCX. Accordingly, lethal myocardial ischemia induced by endothelin-1 is produced by critical obstruction of rather small coronary vessels.

Myocardial contractile actions of endothelin-1 in rat and rabbit papillary muscles. Role of endocardial endothelium

The actions of endothelin on the contractile and twitch configuration characteristics of rat and rabbit papillary muscles were evaluated before and after endocardial endothelium removal. In rabbit papillary muscles, endothelin produced a dose-dependent (10(-11) to 10(-7) M) increase in tension (T) (from 2.7 +/- 0.2 to 8.9 +/- 0.7 g/mm2, p less than 0.01), dT/dt, and Vmax (from 1.14 +/- 0.03 to 3.0 +/- 0.13 Lmax/sec, p less than 0.01), a decrease in time to peak tension (from 251 +/- 9 to 216 +/- 7 msec, p less than 0.05), and an increase in time to half relaxation (from 168 +/- 9 to 293 +/- 14 msec, p less than 0.01). Increasing calcium concentration in the bath from 1.25 to 15 mM greatly attenuated these changes. In the presence of propranolol (10(-5) M), endothelin increased all indexes of contractility but to a lesser extent (T = 2.6 +/- 0.3 to 6.5 +/- 0.2 g/mm2, p less than 0.01; Vmax = 1.16 +/- 0.10 to 2.06 +/- 0.10 Lmax/sec, p less than 0.01). Myocardial catecholamine depletion with reserpine had effects similar to those of propranolol. The myocardial contractile and twitch configuration characteristics of endothelin were similar to those of phenylephrine (10(-4) M), a strong stimulator of the phosphatidylinositol pathway and a moderate beta-adrenergic stimulator. The effects of phenylephrine and endothelin were modified in a similar manner by propranolol (10(-5) M). The presence of nicardipine (3 X 10(-7) M) decreased the absolute increase in contractility caused by endothelin but did not alter the percent change or shift the dose-response curve of endothelin. The actions of endothelin in rat papillary muscles studied at physiological calcium concentrations (Ca2+ = 1.25 mM) were less marked than those of rabbit studied at physiological calcium (Ca2+ = 1.25 mM) but similar to those of rabbit studied at high calcium concentrations (Ca2+ = 15 mM). Removing the endocardial endothelial layer of rabbit papillary muscles did not alter the absolute changes in contractility caused by endothelin but shifted the dose-response curve to the left and markedly altered the effects of endothelin on twitch configuration characteristics. Thus, it would appear that endothelin increases contractility and modifies twitch configuration. It does so more at lower rather than higher extracellular calcium concentrations and in a species, such as rabbit, that responds more to interventions that increase intracellular calcium.(ABSTRACT TRUNCATED AT 400 WORDS)

Contribution of endogenous endothelin to the extension of myocardial infarct size in rats

Pathophysiological roles of endogenous endothelin have been studied from the viewpoint of its contribution to the extension of myocardial infarct size. A monoclonal antibody against endothelin 1 (AwETN40) suppressed changes induced by endothelin 1 and endothelin 2 but did not modify those by endothelin 3 in vivo or in vitro. Effects of AwETN40 on myocardial infarct size were investigated. Coronary ligation (1 hour) and reperfusion (24 hours) in rats caused infarction in 35% of the left ventricle. Repetitive or single administration of AwETN40 reduced the infarct size; an intravenous injection of 22.5 mg/kg of the antibody 5 minutes after coronary occlusion or 5 minutes before reperfusion reduced the size by 38% or 31% of the control, respectively. Plasma and tissue endothelin 1 and plasma big endothelin 1 in rats were measured at various stages after occlusion. Plasma endothelin 1 showed a fourfold increase 10 minutes after reperfusion (from 1.02 to 3.96 pg/ml) and had returned to the control value after 8 hours. Plasma big endothelin 1 showed changes similar to those of plasma endothelin 1. No significant changes in plasma endothelin 2 and endothelin 3 were observed. Cardiac tissue contained seven times as much endothelin 1 as the control value 1 hour after reperfusion (4.59 versus 33.1 pg/g tissue), and a high concentration (13.2 pg/g tissue) was maintained even after 48 hours. We concluded that an increase in endogenous endothelin 1 plays an important role in the extension of myocardial infarct size.

Effects of endothelin-1 on arterial pressure and myocardial contractility in the conscious normotensive rabbit

1. We studied the effects of an intravenous bolus of endothelin-1 on arterial pressure and myocardial contractility in the conscious rabbit. 2. Endothelin produced an initial fall in arterial pressure accompanied by an increase in heart rate. This was followed by a dose-dependent increase in arterial pressure, peaking about 7 min after injection, accompanied by a reciprocal fall in heart rate. 3. Left ventricular rate of change of pressure (LV dP dt) increased with endothelin except at higher doses (0.8 and 1.6 nmol/kg), where in some animals it decreased.

Interactions between endothelin-1 and other chronotropic agents in rat isolated atria

In isolated spontaneously beating right and left atria and in electrically driven left atrium from rat, endothelin-1 increased the rate and force of contraction, but significantly decreased the positive chronotropic and inotropic responses to sympathetic nerve stimulation. The decrease may be partly dependent on the positive cronotropic and inotropic effects of endothelin-1, since other agents with chronotropic activity (noradrenaline, isoprenaline, serotonin and Bay k 8644) also decreased stimulation-induced chronotropic responses. Endothelin-1 caused a significant rightward shift of the linear portion of the log concentration-response curve for the chronotropic actions of noradrenaline and isoprenaline. The changes in the log concentration-response curve were not a consequence of the direct chronotropic effect of endothelin-1, since they were still evident when the chronotropic action of endothelin-1 was offset by carbachol. Furthermore, the chronotropic agent, Bay k 8644, did not shift the linear portion of the log concentration-response curves for noradrenaline and isoprenaline. The mechanism of the effects of endothelin-1 in rat atria is not known, but they were not changed by blockade of alpha-adrenoceptors or of L-type voltage-sensitive Ca2+ channels.

Endothelin-1-induced vasoconstriction in humans. Reversal by calcium channel blockade but not by nitrovasodilators or endothelium-derived relaxing factor

The vascular effects of endothelin-1 (ET) in humans were investigated by brachial artery infusions of ET into 25 healthy volunteers. Forearm blood flow increased from a mean +/- SD value of 2.3 +/- 1.5 to 2.5 +/- 1.5 ml/min/100 ml forearm tissue (n = 25, p less than 0.05) in response to low dose (0.5 ng/min/100 ml forearm tissue) ET infusion and decreased to 1.78 +/- 1.3 and 1.1 +/- 0.9 ml/min/100 ml forearm tissue (p less than 0.001) during higher dosages (25 and 50 ng/min/100 ml forearm tissue). Sodium nitroprusside (0.6 micrograms/min/100 ml forearm tissue, n = 6), acetylcholine (16 micrograms/min/100 ml forearm tissue, n = 7), nifedipine (6 micrograms/min/100 ml forearm tissue, n = 6), and verapamil (80 micrograms/min/100 ml forearm tissue, n = 6) were infused alone and in combination with ET to evaluate the interactions between ET-induced vasoconstriction and stimulation of vascular muscle cyclic GMP levels by sodium nitroprusside, release of endothelium-derived relaxing factor by acetylcholine, and blockade of voltage-operated calcium channels by nifedipine and verapamil. Neither the vasodilator nor the vasoconstrictor response to ET was influenced by sodium nitroprusside or acetylcholine. In contrast, both calcium antagonists converted ET-induced vasoconstriction (e.g., delta forearm vascular resistance to ET 50 ng/min/100 ml forearm tissue, 151 +/- 100% and 164 +/- 92% in verapamil and nifedipine groups, respectively) to vasodilation (-35 +/- 12% and -21 +/- 16%, p less than 0.05). Our results demonstrate both ET-induced vasodilation (at low dosages) and vasoconstriction (at high dosages) in resistance vessels of normal humans. Blockade of voltage-operated calcium channels prevented ET-induced vasoconstriction and unmasked the vasodilator effect of high ET dosages. In human resistance vessels, blockade of voltage-operated Ca2+ channels but not cyclic GMP-dependent vasodilation may be an effective tool to inhibit ET-induced vasoconstriction.

Comparison of the effects of endothelin and Bay k 8644 on cardiohemodynamics in anesthetized pigs

The effects of endothelin on cardiohemodynamics in anesthetized open-chest pigs were compared with those of the Ca2+ channel agonist Bay k 8644. I.v. administration of endothelin (0.1-1 microgram/kg) dose relatedly decreased coronary blood flow velocity (CFV), cardiac output, the maximal rate of rise in left ventricular pressure (LV dP/dtmax) and heart rate, and increased systolic and diastolic blood pressure and systemic vascular resistance. Bay k 8644 (0.1-30 micrograms/kg) showed similar effects on cardiohemodynamics, except that it caused a substantial increase in LV dP/dtmax and did not change stroke volume. I.c. administration of endothelin (0.1-1 microgram) into the left circumflex coronary artery (LCX) produced a dose-dependent and sustained decrease in CFV followed by a marked increase in the ST segment of epicardial electrocardiograms and a depression in myocardial shortening in the region supplied by LCX. An increase in left ventricular end-diastolic pressure and a reduction in LV dP/dtmax were also observed after endothelin. In contrast, Bay k 8644 caused a transient decrease in CFV and an increase in LV dP/dtmax, without causing any changes indicative of myocardial ischemia. Although the reduction in CFV after i.c. endothelin was not affected by i.v. infusion of nicardipine (1 microgram/kg per min), the reduction in CFV observed after i.c. Bay k 8644 was significantly suppressed (P less than 0.05). We conclude that endothelin is a more potent coronary vasoconstrictor than Bay k 8644 and provokes marked myocardial ischemia.

Effect of endothelin on total and regional coronary resistance and on myocardial contractility

Endothelin is a 21-amino acid peptide produced by the endothelium and has a potent vasoconstrictor effect. Because of the importance of the endothelium on vasomotor regulation, we studied the effect of endothelin on total and regional coronary vascular resistance and on myocardial contractility in the intact heart of anesthetized dogs. Intracoronary administration of 2 to 80 pmol/kg of endothelin produced a dose-dependent increase in coronary resistance, ischaemic decrease in myocardial contractility and atrium-ventricular blockade. The increase in resistance was greater towards the outer layer of the left ventricular wall. When the coronaries were perfused at a constant rate and vasoconstriction was prevented with adenosine or nitroglycerine, endothelin did not produce inotropic changes. These results show that endothelin is a potent vasoconstrictor of the resistance coronary vessels, producing a redistribution of transmural blood flow and a decrease in myocardial contractility secondary to ischaemia.

Cerebrospinal fluid endothelin-1 and endothelin-3 levels in normal and neurosurgical patients: a clinical study and literature review

Endothelins are a family of structurally related, potent, long-lasting vasoconstrictor peptides. There are no established normal human levels of endothelin-1 or endothelin-3 in the cerebrospinal fluid. We measured cerebrospinal fluid endothelin-1 and endothelin-3 levels in five groups of patients: normal controls, patients with subarachnoid hemorrhage and cerebral vasospasm, patients with severe head injuries, patients undergoing temporal lobectomy for intractable epilepsy, and a patient with a gunshot injury to the thoracic spine. Endothelin-3 levels were significantly elevated in patients with subarachnoid hemorrhage and may participate in cerebral vasospasm and subsequent neurologic deterioration.

Endothelin-1-induced constriction in the coronary resistance vessels and abdominal aorta of the guinea pig

The purpose of this study was to examine contractile properties of endothelin-1, a newly discovered vasoactive peptide, in guinea pig coronary resistance vessels and abdominal aorta. Changes in perfusion pressure after injections of endothelin-1 were measured using a constant-flow modified Langendorff preparation. The ED10 values of coronary perfusion pressure were about 100-fold less for endothelin-1 than for prostaglandin F2 alpha. After the endothelium was damaged by exposure to free radicals, maximal coronary constriction in response to endothelin-1 (10(-9) moles) was not altered, whereas dilator responses to low doses of endothelin-1 were converted to constrictor responses. Removal of the endothelium from aortic rings significantly increased responsiveness to endothelin-1 and the maximal response to the peptide. In calcium-free medium, endothelin-1 induced small increases both in perfusion pressure in coronary vessels and in tension in the aorta. Reintroduction of calcium in the coronary and aortic preparations produced a rapid increase in perfusion pressure and tension, respectively. Further, endothelin-1-induced coronary constriction was inhibited 59% +/- 7% by nifedipine (10(-7) moles). We conclude that endothelin-1 is a more potent constrictor than prostaglandin F2 alpha in the coronary vasculature. Endothelin-1-induced constriction in the coronary vasculature of the guinea pig is not mediated through an endogenous constricting factor released from the endothelium or a constrictor prostaglandin. Further, endothelin-1-induced dilation in the coronary vasculature and attenuation of endothelin-1-induced contraction in the abdominal aorta of the guinea pig are mediated through the release of a factor from the endothelium.(ABSTRACT TRUNCATED AT 250 WORDS)

Endothelin: a new cardiovascular regulatory peptide

Endothelin, a recently discovered peptide produced by endothelial cells, contracts vascular strips in vitro with greater potency than any previously known vasoconstrictor. Infusions of pharmacologic doses of endothelin in vivo result in a prolonged pressor response and a preferential impairment of renal hemodynamic and excretory functions. Endothelin also directly stimulates the release of aldosterone from the adrenal gland and inhibits renin release in vitro. A highly sensitive and specific radioimmunoassay has confirmed that endothelin circulates in human plasma, and increased plasma endothelin levels have been associated with various cardiovascular disease states. This review summarizes the current knowledge about the molecular biologic features and physiologic actions of endothelin and also explores the role of endothelin, through its local and systemic function, as a regulator of vascular tone in normal and pathophysiologic states.

Endothelin enhances the contractile responsiveness of adult rat ventricular myocytes to calcium by a pertussis toxin-sensitive pathway

It has long been assumed that the primary influences regulating cardiac contractility are the extent of mechanical loading of muscle fibers and the activity of the autonomic nervous system. However, the vasoactive peptide endothelin, initially found in vascular endothelium, is among the most potent positively inotropic agents yet described in mammalian myocardium. In isolated adult rat ventricular cells, endothelin's action was slow in onset but very long lasting with an EC50 of 50 pM that approximates the reported KD of the peptide for its receptor in rat heart. When the calcium activity of the buffer superfusing isolated single fura-2-loaded myocytes paced at 1.5 Hz was varied from 0.1 to 0.9 mM [Ca2+]o, 100 pM endothelin increased contractile amplitude with no significant change in diastolic or systolic [Ca2+]i, thus appearing to sensitize the myofilaments to intracellular calcium. Pertussis toxin, or prior exposure to a beta-adrenergic agonist, reduced or abolished the increase in myocyte contractility induced by endothelin. This novel and potent pharmacologic action of endothelin points to the potential importance of local, paracrine factors, perhaps derived from microvascular endothelium or endocardium, in the control of the contractile function of the heart.

Nickel inhibits endothelin-induced contractions of vascular smooth muscle

Endothelin (ET)-induced contractions of vascular smooth muscle (VSM) are dependent on extracellular Ca2+ yet display only partial sensitivity to L-type Ca2+ antagonists. The purpose of this study was to evaluate the effect of nickel (Ni2+), a Ca2+ channel antagonist with clearly documented differential potency toward L- vs. T-type Ca2+ currents on ET-mediated contractions in VSM. Treatment of rings of left anterior descending porcine coronary artery (LAD) with Ni2+ produced a profound dose-dependent inhibition of isometric force development in response to porcine ET (ET-1). At a concentration of 360 microM, Ni2+ exerted a significant inhibitory effect on contracture in response to doses of ET-1 ranging from 3 to 100 nM. In contrast, the same concentration of Ni2+ failed to significantly affect peak force development in response to KCl depolarization (5-77 mM) or to phenylephrine (0.3-30 mM). In addition, 360 microM Ni2+ significantly inhibited the contractile response of rat aorta to 10 nM ET-1. We conclude that ET-1 activates a Ni2(+)-sensitive process in VSM which may signal an additional Ca2+ influx pathway that appears to be functionally distinct from the L-type Ca2+ channel.