(1/1796) Inhibition of in vitro enteric neuronal development by endothelin-3: mediation by endothelin B receptors.
The terminal colon is aganglionic in mice lacking endothelin-3 or its receptor, endothelin B. To analyze the effects of endothelin-3/endothelin B on the differentiation of enteric neurons, E11-13 mouse gut was dissociated, and positive and negative immunoselection with antibodies to p75(NTR )were used to isolate neural crest- and non-crest-derived cells. mRNA encoding endothelin B was present in both the crest-and non-crest-derived cells, but that encoding preproendothelin-3 was detected only in the non-crest-derived population. The crest- and non-crest-derived cells were exposed in vitro to endothelin-3, IRL 1620 (an endothelin B agonist), and/or BQ 788 (an endothelin B antagonist). Neurons and glia developed only in cultures of crest-derived cells, and did so even when endothelin-3 was absent and BQ 788 was present. Endothelin-3 inhibited neuronal development, an effect that was mimicked by IRL 1620 and blocked by BQ 788. Endothelin-3 failed to stimulate the incorporation of [3H]thymidine or bromodeoxyuridine. Smooth muscle development in non-crest-derived cell cultures was promoted by endothelin-3 and inhibited by BQ 788. In contrast, transcription of laminin alpha1, a smooth muscle-derived promoter of neuronal development, was inhibited by endothelin-3, but promoted by BQ 788. Neurons did not develop in explants of the terminal bowel of E12 ls/ls (endothelin-3-deficient) mice, but could be induced to do so by endothelin-3 if a source of neural precursors was present. We suggest that endothelin-3/endothelin B normally prevents the premature differentiation of crest-derived precursors migrating to and within the fetal bowel, enabling the precursor population to persist long enough to finish colonizing the bowel. (+info)
(2/1796) Endogenous plasma endothelin concentrations and coronary circulation in patients with mild dilated cardiomyopathy.
OBJECTIVE: To determine whether increased plasma concentrations of endothelin-1 (ET-1) and big endothelin (BET) play a role in the regulation of coronary circulation in patients with idiopathic dilated cardiomyopathy (IDCM). SETTING: Tertiary referral centre for cardiac diseases. PATIENTS: Fourteen patients (eight male/six female; mean (SD) age 59 (9) years) with IDCM (ejection fraction 36 (9)%) and five normotensive subjects (two male/three female; age 52 (7) years) serving as controls were studied. METHODS: Functional status was classified according to New York Heart Association (NYHA) class. Endogenous ET-1 and BET plasma concentrations from the aorta and the coronary sinus were determined by radioimmunoassay. Coronary blood flow, using the inert chromatographic argon method, myocardial oxygen consumption, and coronary sinus oxygen content under basal conditions were determined. RESULTS: In the aorta, mean (SD) concentrations of ET-1 (IDCM 0.76 (0.25) v controls 0.31 (0.06) fmol/ml; p = 0.002) and BET (IDCM 3.58 (1.06) v controls 2.11 (0.58) fmol/ml; p = 0.014) were increased in patients with IDCM. Aortic ET-1 concentrations correlated positively with NYHA class (r = 0. 731; p < 0.001), myocardial oxygen consumption (r = 0.749; p < 0. 001), and coronary blood flow (r = 0.645; p = 0.003), but inversely with coronary sinus oxygen content (r = -0.633; p = 0.004), which was significantly decreased in IDCM patients (IDCM 4.68 (1.05) v controls 6.70 (1.06) vol%; p = 0.003). CONCLUSIONS: The coronary circulation in patients with IDCM is exposed to an increased endothelin load. ET-1 concentrations correlate with functional deterioration. A decrease of the coronary sinus content of oxygen suggests a mismatch between coronary blood flow and metabolic demand. Thus, ET-1 might be a marker of a disequilibrium between myocardial oxygen demand and coronary blood flow in IDCM. (+info)
(3/1796) Endothelin up-regulation and localization following renal ischemia and reperfusion.
BACKGROUND: Endothelin (ET), a potent vasoconstrictor, is known to play a role in ischemic acute renal failure. Although preproET-1 (ppET-1) mRNA is known to be up-regulated following ischemia/reperfusion injury, it has not been determined which component of the injury (ischemia or reperfusion) leads to initial gene up-regulation. Likewise, although ET-1 peptide expression has been localized in the normal kidney, its expression pattern in the ischemic kidney has not been determined. Therefore, the purpose of this study was twofold: (a) to determine whether ischemia alone or ischemia plus reperfusion is required for the up-regulation of ppET-1 mRNA to occur, and (b) to localize ET-1 peptide expression following ischemia in the rat kidney to clarify better the role of ET in the pathophysiology of ischemia-induced acute renal failure. METHODS: Male Lewis rats underwent clamping of the right renal vascular pedicle for either 30 minutes of ischemia (group 1), 60 minutes of ischemia (group 2), 30 minutes of ischemia followed by 30 minutes of reperfusion (group 3), or 60 minutes of ischemia followed by three hours of reperfusion (group 4). The contralateral kidney acted as a control. ppET-1 mRNA up-regulation and ET-1 peptide expression were examined using the reverse transcription-polymerase chain reaction and immunohistochemistry, respectively. RESULTS: Reverse transcription-polymerase chain reaction yielded a control (nonischemic) value of 0.6 +/- 0.2 densitometric units (DU) of ppET-1 mRNA in the kidney. Group 1 levels (30 min of ischemia alone) were 1.8 +/- 0.4 DU, a threefold increase (P < 0.05). Group 2 levels (60 min of ischemia alone) increased almost six times above baseline, 3.5 +/- 0.2 DU (P < 0.01), whereas both group 3 and group 4 (ischemia plus reperfusion) did not experience any further significant increases in mRNA levels (1.9 +/- 0.4 DU and 2.8 +/- 0.6 DU, respectively) beyond levels in group 1 or 2 animals subjected to similar ischemic periods. ET-1 peptide expression in the ischemic kidneys was significantly increased over controls and was clearly localized to the endothelium of the peritubular capillary network of the kidney. CONCLUSIONS: Initial ET-1 gene up-regulation in the kidney occurs secondary to ischemia, but reperfusion most likely contributes to sustaining this up-regulation. The marked increase of ET-1 in the peritubular capillary network suggests that ET-induced vasoconstriction may have a pathophysiological role in ischemic acute tubular necrosis. (+info)
(4/1796) Nitric oxide limits the eicosanoid-dependent bronchoconstriction and hypotension induced by endothelin-1 in the guinea-pig.
1. This study attempts to investigate if endogenous nitric oxide (NO) can modulate the eicosanoid-releasing properties of intravenously administered endothelin-1 (ET-1) in the pulmonary and circulatory systems in the guinea-pig. 2. The nitric oxide synthase blocker N(omega)-nitro-L-arginine methyl ester (L-NAME; 300 microM; 30 min infusion) potentiated, in an L-arginine sensitive fashion, the release of thromboxane A2 (TxA2) stimulated by ET-1, the selective ET(B) receptor agonist IRL 1620 (Suc-[Glu9,Ala11,15]-ET-1(8-21)) or bradykinin (BK) (5, 50 and 50 nM, respectively, 3 min infusion) in guinea-pig isolated and perfused lungs. 3. In anaesthetized and ventilated guinea-pigs intravenous injection of ET-1 (0.1-1.0 nmol kg(-1)), IRL 1620 (0.2-1.6 nmol kg(-1)), BK (1.0-10.0 nmol kg(-1)) or U 46619 (0.2-5.7 nmol kg(-1)) each induced dose-dependent increases in pulmonary insufflation pressure (PIP). Pretreatment with L-NAME (5 mg kg(-1)) did not change basal PIP, but increased, in L-arginine sensitive manner, the magnitude of the PIP increases (in both amplitude and duration) triggered by each of the peptides (at 0.25, 0.4 and 1.0 nmol kg(-1), respectively), without modifying bronchoconstriction caused by U 46619 (0.57 nmol kg(-1)). 4. The increases in PIP induced by ET-1, IRL 1620 (0.25 and 0.4 nmol kg(-1), respectively) or U 46619 (0.57 nmol kg(-1)) were accompanied by rapid and transient increases of mean arterial blood pressure (MAP). Pretreatment with L-NAME (5 mg kg(-1); i.v. raised basal MAP persistently and, under this condition, subsequent administration of ET-1 or IRL 1620, but not of U-46619, induced hypotensive responses which were prevented by pretreatment with the cyclo-oxygenase inhibitor indomethacin. 5. Thus, endogenous NO appears to modulate ET-1-induced bronchoconstriction and pressor effects in the guinea-pig by limiting the peptide's ability to induce, possibly via ET(B) receptors, the release of TxA2 in the lungs and of vasodilatory prostanoids in the systemic circulation. Furthermore, it would seem that these eicosanoid-dependent actions of ET-1 in the pulmonary system and on systemic arterial resistance in this species are physiologically dissociated. (+info)
(5/1796) Blockade and reversal of endothelin-induced constriction in pial arteries from human brain.
BACKGROUND AND PURPOSE: Substantial evidence now implicates endothelin (ET) in the pathophysiology of cerebrovascular disorders such as the delayed vasospasm associated with subarachnoid hemorrhage and ischemic stroke. We investigated the ET receptor subtypes mediating vasoconstriction in human pial arteries. METHODS: ET receptors on human pial and intracerebral arteries were visualized with the use of autoradiography, and the subtypes mediating vasoconstriction were identified by means of wire myography. RESULTS: ET-1 was more potent than ET-3 as a vasoconstrictor, indicating an ETA-mediated effect. Similarly, the selective ETB agonist sarafotoxin S6c had no effect on contractile action at concentrations up to 30 nmol/L. The nonpeptide ETA receptor antagonist PD156707 (3 to 30 nmol/L) caused a parallel rightward shift of the ET-1-induced response, yielding a pA2 of 9.2. Consistent with these results, PD156707 (30 nmol/L) fully reversed an established constriction in pial arteries induced by 1 nmol/L ET-1, while the selective ETB receptor antagonist BQ788 (1 micromol/L) had little effect. The calcium channel blocker nimodipine (0.3 to 3 micromol/L) significantly attenuated the maximum response to ET-1 in a concentration-dependent manner without changing potency. In agreement with the functional data, specific binding of [125I]PD151242 to ETA receptors was localized to the smooth muscle layer of pial and intracerebral blood vessels. In contrast, little or no [125I]BQ3020 binding to ETB receptors was detected. CONCLUSIONS: These data indicate an important role for ETA receptors in ET-1-induced constriction of human pial arteries and suggest that ETA receptor antagonists may provide additional dilatory benefit in cerebrovascular disorders associated with raised ET levels. (+info)
(6/1796) Endothelin-1 and its mRNA in the wall layers of human arteries ex vivo.
BACKGROUND: The participation of endothelin-1 (ET-1) in the control of vascular tone in humans has been questioned, on the basis of the finding of subthreshold immunoreactive (ir) ET-1 plasma levels. However, because most ET-1 is secreted abluminally, it might attain a higher concentration in the tunica media than in plasma. Furthermore, evidence indicates that vascular smooth muscle cells (VSMCs) can synthesize ET-1 on stimulation in vitro. We therefore looked for irET-1 in the different layers of the wall of human arteries, including renal, gastric, and internal thoracic artery wall, obtained ex vivo from consenting patients with coronary artery disease and/or high blood pressure undergoing surgery, as well as from young organ donors. METHODS AND RESULTS: We performed immunohistochemistry with specific anti-ET-1 and anti-vWF antibodies followed by detection with an avidin-biotin complex ultrasensitive kit. The presence of preproET-1 and human endothelin-converting enzyme-1 (hECE-1) mRNA was also investigated by reverse transcription-polymerase chain reaction in homogenates of vessel wall, including preparations deprived of both endothelium and adventitia, and in isolated VSMCs. We detected irET-1 in the endothelium of all arteries and in the tunica media of internal thoracic artery from most patients with coronary artery disease. PreproET-1 and hECE-1 mRNA was also detected in VSMCs isolated from these vessels. irET-1 and irvWF staining in endothelium and tunica media was measured by use of microscope-coupled computer-assisted technology. Significant correlations between the amount of irET-1 in the tunica media and mean blood pressure (P<0.05), total serum cholesterol (P<0.05), and number of atherosclerotic sites (P<0.001) were found. Thus, in organ donors, irET-1 was detectable almost exclusively in endothelial cells, whereas in patients with coronary artery disease and/or arterial hypertension, sizable amounts of irET-1 were detectable in the tunica media of different types of arteries. In addition, VSMCs isolated from these vessels coexpressed the preproET-1 and hECE-1 genes. CONCLUSIONS: Collectively, these findings are consistent with the contention that endothelial damage occurs in most patients with atherosclerosis and/or hypertension and that ET-1 is synthesized in VSMCs of these patients. (+info)
(7/1796) Effects of hypertension, diabetes mellitus, and hypercholesterolemia on endothelin type B receptor-mediated nitric oxide release from rat kidney.
BACKGROUND: Although endothelin-1 is a potent vasoconstrictor peptide, stimulation of endothelin type B receptor (ETBR) causes bidirectional changes in vascular tone, ie, vasodilation and vasoconstriction. Roles of ETBR in pathological conditions are largely unknown. METHODS AND RESULTS: We studied the effect of BQ-3020, a highly selective ETBR agonist, on renal vascular resistance and nitric oxide (NO) release in the isolated, perfused kidney of rats with hypertension, diabetes mellitus, and hypercholesterolemia. Immunohistochemistry of endothelial NO synthase and ETBR was also examined. Infusion of BQ-3020 at concentrations of =10(-10) mol/L reduced renal perfusion pressure in Dahl salt-resistant (R) rats but increased renal perfusion pressure in Dahl salt-sensitive (S) rats (10(-10) mol/L: -10.3+/-0. 6% versus 11.2+/-1.5%, R versus S; P<0.01). BQ-3020 caused a dose-dependent release of NO in both R and S rats, although the level of NO release in S rats was lower, as detected by chemiluminescence (10(-10) mol/L: 10.7+/-0.7 versus 3.1+/-0.4 fmol/min per gram of kidney, R versus S; P<0.01). Similar effects of BQ-3020 were observed in streptozotocin-induced diabetic rats and diet-induced hypercholesterolemic rats. Expression of endothelial NO synthase decreased in S rats but not in diabetic or hypercholesterolemic rats. In contrast, expression of ETBR in the endothelium was decreased in all 3 disease models compared with that in the vascular smooth muscle cell. CONCLUSIONS: These results suggest that impaired NO release in response to stimulation of ETBR is due, at least in part, to a decrease in endothelial ETBR and may play a role in vascular dysfunction usually associated with arteriosclerosis-related diseases. (+info)
(8/1796) Maintenance of blood pressure in normotensive dogs by endothelin.
The role of endothelin (ET)-1 in blood pressure homeostasis and the interaction with the renin-angiotensin system (RAS) was investigated in normotensive conscious dogs. ETA receptors were blocked by LU-135252 (1-30 mg/kg); trandolapril (2 mg/kg) or losartan (10 mg/kg) was used to inhibit the RAS. LU-135252 in oral doses of 3-30 mg/kg significantly reduced mean arterial pressure (MAP) by approximately 10 mmHg maximally, whereas trandolapril or losartan were without any effect. MAP reduction was more pronounced when LU-135252 was combined with either losartan (-15.5 +/- 3.2 mmHg; 2 h postadministration; P < 0.05) or trandolapril (-30.9 +/- 3.6 mmHg; P < 0.05). When endogenous nitric oxide (NO) generation was blocked but NO concomitantly infused, this synergistic effect on MAP was prevented. The data show that ET-1 contributes to the maintenance of blood pressure via ETA receptors. Furthermore, ET-1 and ANG II play a prominent role in the control of blood pressure by opposing the effects of NO. The pronounced blood pressure fall after combined blockade of ETA receptors and the RAS may be mediated by an enhanced release of NO. (+info)