bq-123 and Hypoxia

The pulmonary endothelium modulates vascular tone by the release of endothelium-derived constricting (EDCF) and relaxing (EDRF) factors, among them endothelin-1, nitric oxide, prostacyclin, and putative endothelium-derived hyperpolarizing factors. Abnormalities in EDCF and EDRF generation have been demonstrated in a number of cardiopulmonary disease states, such as primary and secondary pulmonary hypertension, chronic obstructive lung disease, cardiopulmonary bypass, and congestive heart failure. An imbalance between EDCF and EDRF, termed "pulmonary endothelial dysfunction," may contribute to the alteration in vascular tone characteristic of pulmonary disease. The following review summarizes the present knowledge of the role of EDCF and EDRF in such processes with major focus on pulmonary endothelial dysfunction in hypoxia-induced pulmonary hypertension.

Topics: Animals; Antihypertensive Agents; Atrasentan; Bosentan; Controlled Clinical Trials as Topic; Disease Models, Animal; Endothelin Receptor Antagonists; Endothelin-1; Endothelins; Endothelium, Vascular; Epoprostenol; Heart Failure; Humans; Hypertension, Pulmonary; Hypoxia; Lung Diseases, Obstructive; Nitric Oxide; Oligopeptides; Peptides, Cyclic; Piperidines; Pulmonary Circulation; Pyrrolidines; Receptors, Endothelin; RNA, Messenger; Sulfonamides; Time Factors; Vasoconstriction; Vasodilation

Intrarenal tissue hypoxia, secondary to increased oxygen consumption, has been suggested as a unifying mechanism for the development of diabetic nephropathy. Increased endothelin-1 signalling via the endothelin type A receptor (ETA-R) has been shown to contribute to the development of chronic kidney disease, but its role in kidney oxygen homeostasis is presently unknown.. The effects of acute ETA-R inhibition (8 nmol/l BQ-123 for 30-40 min directly into the left renal artery) on kidney function and oxygen metabolism were investigated in normoglycaemic control and insulinopenic male Sprague Dawley rats (55 mg/kg streptozotocin intravenously 2 weeks before the main experiment) used as a model of type 1 diabetes.. Local inhibition of ETA-R in the left kidney did not affect BP in either the control or the diabetic rats. As previously reported, diabetic rats displayed increased kidney oxygen consumption resulting in tissue hypoxia in both the kidney cortex and medulla. The inhibition of ETA-Rs restored normal kidney tissue oxygen availability in the diabetic kidney by increasing renal blood flow, but did not affect oxygen consumption. Furthermore, ETA-R inhibition reduced the diabetes-induced glomerular hyperfiltration and increased the urinary sodium excretion. Kidney function in normoglycaemic control rats was largely unaffected by BQ-123 treatment, although it also increased renal blood flow and urinary sodium excretion in these animals.. Acutely reduced intrarenal ETA-R signalling results in significantly improved oxygen availability in the diabetic kidney secondary to elevated renal perfusion. Thus, the beneficial effects of ETA-R inhibition on kidney function in diabetes may be due to improved intrarenal oxygen homeostasis.

Topics: Animals; Diabetes Mellitus, Experimental; Diabetes Mellitus, Type 1; Diabetic Nephropathies; Disease Models, Animal; Endothelin A Receptor Antagonists; Hypoxia; Kidney; Male; Oxygen Consumption; Peptides, Cyclic; Rats; Rats, Sprague-Dawley; Renal Circulation

Chronic hypoxia in the uteroplacental unit is associated with increased resistance to blood flow in the fetal-placental circulation. These changes can lead to adverse cardiovascular events in adulthood. This study investigates whether L-arginine (substrate for nitric oxide synthase (NOS) or endothelin-A receptor antagonist BQ123 administration reverses hypoxia-induced changes in perfusion pressure in the fetal compartment in dual-perfused placental cotyledons.. Human placental cotyledons (n = 15) from term deliveries (n = 15) were perfused with Krebs solution from maternal and fetal sides. Normal and reduced oxygen tension conditions were sequentially created in the perfused maternal compartment. Fetal perfusion pressure was continuously monitored. 1 mM L-arginine, D-arginine (an enantiomer of L-arginine and not a substrate for NOS), and BQ123 or normal saline were administered to the fetal compartment; L-arginine was also administered to the maternal compartment prior to maternal side hypoxia. Changes in perfusion pressure were compared between groups.. Maternal hypoxia increased (19 ± 6%) perfusion pressure and this was blunted by L-arginine injection (3 ± 5%; p = 0.006) into the fetal compartment. L-arginine in the maternal compartment had no significant effect (22 ± 4% with L-arginine vs.14 ± 3% at control) on perfusion pressure. Similarly, D-arginine (23 ± 11% vs.19 ± 8% at control) or BQ123 (12 ± 3% vs.13 ± 3% at control) in the fetal compartment did not blunt the hypoxia-induced increase in perfusion pressure.. Fetal vasoconstriction induced by maternal hypoxia is blunted by NO synthase substrate L-arginine, but not by D-arginine, in the fetal compartment, suggesting the involvement of NO synthesis in regulating the hypoxia-induced fetal vasoconstriction. Endothelin A receptor-related mechanisms does not appear to play a role in the maternal hypoxia-induced fetal vasoconstriction.

Topics: Arginine; Endothelin Receptor Antagonists; Female; Humans; Hypoxia; In Vitro Techniques; Peptides, Cyclic; Placenta; Pregnancy; Vasoconstriction

Preeclampsia is a life-threatening pregnancy disorder. However, its pathogenesis remains unclear. We tested the hypothesis that gestational hypoxia induces preeclampsia-like symptoms via heightened endothelin-1 (ET-1) signaling. Time-dated pregnant and nonpregnant rats were divided into normoxic and hypoxic (10.5% O2 from the gestational day 6-21) groups. Chronic hypoxia had no significant effect on blood pressure or proteinuria in nonpregnant rats but significantly increased blood pressure on day 12 (systolic blood pressure, 111.7 ± 6.1 versus 138.5 ± 3.5 mm Hg; P=0.004) and day 20 (systolic blood pressure, 103.4 ± 4.6 versus 125.1 ± 6.1 mm Hg; P=0.02) in pregnant rats and urine protein (μg/μL)/creatinine (nmol/μL) ratio on day 20 (0.10 ± 0.01 versus 0.20 ± 0.04; P=0.04), as compared with the normoxic control group. This was accompanied with asymmetrical fetal growth restriction. Hypoxia resulted in impaired trophoblast invasion and uteroplacental vascular remodeling. In addition, plasma ET-1 levels, as well as the abundance of prepro-ET-1 mRNA, ET-1 type A receptor and angiotensin II type 1 receptor protein in the kidney and placenta were significantly increased in the chronic hypoxic group, as compared with the control animals. Treatment with the ET-1 type A receptor antagonist, BQ123, during the course of hypoxia exposure significantly attenuated the hypoxia-induced hypertension and other preeclampsia-like features. The results demonstrate that chronic hypoxia during gestation induces preeclamptic symptoms in pregnant rats via heightened ET-1 and ET-1 type A receptor-mediated signaling, providing a molecular mechanism linking gestational hypoxia and increased risk of preeclampsia.

Topics: Animals; Blood Pressure; Disease Models, Animal; Endothelin A Receptor Antagonists; Endothelin-1; Female; Hypoxia; Hypoxia-Inducible Factor 1, alpha Subunit; Kidney; Peptides, Cyclic; Placenta; Pre-Eclampsia; Pregnancy; Proteinuria; Rats; Rats, Sprague-Dawley; Receptor, Angiotensin, Type 1; Signal Transduction

Obstructive sleep apnea, a condition resulting in chronic intermittent hypoxia (CIH), is an independent risk factor for stroke and dementia, but the mechanisms of the effect are unknown. We tested the hypothesis that CIH increases cerebrovascular risk by altering critical mechanisms regulating cerebral blood flow thereby lowering cerebrovascular reserves. Male C57Bl6/J mice were subjected to CIH (10% O(2) for 90 seconds/room air for 90 seconds; during sleep hours) or sham treatment for 35 days. Somatosensory cortex blood flow was assessed by laser Doppler flowmetry in anesthetized mice equipped with a cranial window. CIH increased mean arterial pressure (from 74±2 to 83±3 mm Hg; P<0.05) and attenuated the blood flow increase produced by neural activity (whisker stimulation; -39±2%; P<0.05) or neocortical application of endothelium-dependent vasodilators (acetylcholine response: -41±3%; P<0.05). The cerebrovascular dysfunction was associated with oxidative stress in cerebral resistance arterioles and was abrogated by free radical scavenging or NADPH oxidase inhibition. Furthermore, cerebrovascular dysfunction and free radical increase were not observed in mice lacking the NOX2 subunit of NADPH oxidase. CIH markedly increased endothelin 1 in cerebral blood vessels, whereas cerebrovascular dysfunction and oxidative stress were abrogated by neocortical application of the endothelin type A receptor antagonist BQ123. These data demonstrate for the first time that CIH alters key regulatory mechanisms of the cerebral circulation through endothelin 1 and NADPH oxidase-derived radicals. The ensuing cerebrovascular dysfunction may increase stroke risk in patients with sleep apnea by reducing cerebrovascular reserves and increasing the brain's susceptibility to cerebral ischemia.

Topics: Acetylcholine; Animals; Antihypertensive Agents; Aspartic Acid Endopeptidases; Blood Pressure; Cerebrovascular Circulation; Chronic Disease; Endothelin Receptor Antagonists; Endothelin-1; Endothelin-Converting Enzymes; Enzyme-Linked Immunosorbent Assay; Hypoxia; Laser-Doppler Flowmetry; Male; Membrane Glycoproteins; Metalloendopeptidases; Mice; Mice, Inbred C57BL; Mice, Knockout; NADPH Oxidase 2; NADPH Oxidases; Peptides, Cyclic; Reactive Oxygen Species; Receptors, Endothelin; Reverse Transcriptase Polymerase Chain Reaction; Somatosensory Cortex; Vasodilator Agents

Ghrelin has cardioprotective properties and, recently, has been shown to improve endothelial function and reduce endothelin-1 (ET-1)-mediated vasoconstriction in peripheral vascular disease. Recently, we reported that ghrelin attenuates pulmonary hypertension (PH) caused by chronic hypoxia (CH), which we hypothesized in this study may be via suppression of the ET-1 pathway. We also aimed to determine whether ghrelin's ability to prevent alterations of the ET-1 pathway also prevented adverse changes in pulmonary blood flow distribution associated with PH. Sprague-Dawley rats were exposed to CH (10% O(2) for 2 weeks) with daily subcutaneous injections of ghrelin (150 μg/kg) or saline. Utilizing synchrotron radiation microangiography, we assessed pulmonary vessel branching structure, which is indicative of blood flow distribution, and dynamic changes in vascular responsiveness to (1) ET-1 (1 nmol/kg), (2) the ET-1(A) receptor antagonist, BQ-123 (1 mg/kg), and (3) ACh (3.0 μg kg⁻¹ min⁻¹). CH impaired blood flow distribution throughout the lung. However, this vessel "rarefaction" was attenuated in ghrelin-treated CH-rats. Moreover, ghrelin (1) reduced the magnitude of endothelial dysfunction, (2) prevented an increase in ET-1-mediated vasoconstriction, and (3) reduced pulmonary vascular remodeling and right ventricular hypertrophy-all adverse consequences associated with CH. These results highlight the beneficial effects of ghrelin for maintaining optimal lung perfusion in the face of a hypoxic insult. Further research is now required to establish whether ghrelin is also an effective therapy for restoring normal pulmonary hemodynamics in patients that already have established PH.

Topics: Acetylcholine; Angiography; Animals; Antihypertensive Agents; Endothelin-1; Ghrelin; Hemodynamics; Hypertension, Pulmonary; Hypoxia; Lung; Male; Peptides, Cyclic; Rats; Rats, Sprague-Dawley; Regional Blood Flow; Synchrotrons; Vasoconstriction; Vasodilator Agents

We have reported that eucapnic intermittent hypoxia (E-IH) causes systemic hypertension, elevates plasma endothelin 1 (ET-1) levels, and augments vascular reactivity to ET-1 and that a nonspecific ET-1 receptor antagonist acutely lowers blood pressure in E-IH-exposed rats. However, the effect of chronic ET-1 receptor inhibition has not been evaluated, and the ET receptor subtype mediating the vascular effects has not been established. We hypothesized that E-IH causes systemic hypertension through the increased ET-1 activation of vascular ET type A (ET(A)) receptors. We found that mean arterial pressure (MAP) increased after 14 days of 7 h/day E-IH exposure (109 +/- 2 to 137 +/- 4 mmHg; P < 0.005) but did not change in sham-exposed rats. The ET(A) receptor antagonist BQ-123 (10 to 1,000 nmol/kg iv) acutely decreased MAP dose dependently in conscious E-IH but not sham rats, and continuous infusion of BQ-123 (100 nmol.kg(-1).day(-1) sc for 14 days) prevented E-IH-induced increases in MAP. ET-1-induced constriction was augmented in small mesenteric arteries from rats exposed 14 days to E-IH compared with those from sham rats. Constriction was blocked by the ET(A) receptor antagonist BQ-123 (10 microM) but not by the ET type B (ET(B)) receptor antagonist BQ-788 (100 microM). ET(A) receptor mRNA content was greater in renal medulla and coronary arteries from E-IH rats. ET(B) receptor mRNA was not different in any tissues examined, whereas ET-1 mRNA was increased in the heart and in the renal medulla. Thus augmented ET-1-dependent vasoconstriction via vascular ET(A) receptors appears to elevate blood pressure in E-IH-exposed rats.

Topics: Animals; Antihypertensive Agents; Blood Pressure; Coronary Vessels; Disease Models, Animal; Dose-Response Relationship, Drug; Endothelin A Receptor Antagonists; Endothelin B Receptor Antagonists; Endothelin-1; Hypertension; Hypoxia; Infusions, Parenteral; Male; Mesenteric Arteries; Oligopeptides; Peptides, Cyclic; Piperidines; Rats; Rats, Sprague-Dawley; Receptor, Endothelin A; Renal Artery; Time Factors; Vasoconstriction

Pulmonary hypertension is a kind of disease associated with a very high rate of mortality. There are not many effective drugs for the treatment of pulmonary hypertension. Treatment with ET-1 receptor antagonists was proved to be effective in the treatment of pulmonary hypertension. Aiming at developing new endothelin A receptor (ET(A)) antagonist for treatment of pulmonary hypertension, 242 peptide compounds were synthesized by structural optimization of a selective ET(A) receptor antagonist BQ-123. Among these, -azabicyclo[3,2,1]octane-1-yl-l-Leucyl-d-tryptophanyl-d-4-Cl-phenylalanine, named ETP-508, was selected for further harmacological characterization.. Radioligand binding assay was performed to study the binding affinity of ETP-508 for ET(A) and ET(B) receptors. The biological activity of ETP-508 was evaluated in isolated rat aortic ring experiment and in systemic arterial pressure experiment. In addition, hypotensive effect of ETP-508 was investigated on hypoxia-induced pulmonary hypertension.. ETP-508 binds to endothelin ET(A) receptor with >10,000-fold higher affinity than to endothelin B receptor in rat lung tissue preparation. ETP-508 inhibited endothelin-1 (ET-1)-induced contraction of isolated rat aortic ring and shifted the cumulative concentration-contraction response curve to ET-1 to right with no change in the maximal response. In vivo, ETP-508 inhibited the increased effect of ET-1 on mean systemic arterial pressure. Pre-treatment with ETP-508 by intravenous infusion significantly inhibited chronic hypoxia-induced pulmonary hypertension and right ventricular hypertrophy. ETP-508 also significantly inhibited the increase in lung ET-1 expression level, hemoglobin, red-cell count and red-cell hematocrit as induced by hypoxia. Furthermore, ETP-508 partially reversed pre-established pulmonary hypertension and right ventricle hypertrophy by chronic hypoxia.. These results indicated that ETP-508 is a novel highly selective ET(A) receptor antagonist and may have a great potential to be developed as a drug of anti-pulmonary hypertension.

Topics: Animals; Aorta, Thoracic; Azabicyclo Compounds; Azepines; Blood Pressure; Chronic Disease; Dose-Response Relationship, Drug; Endothelin A Receptor Antagonists; Endothelin-1; Hypertension, Pulmonary; Hypertrophy, Right Ventricular; Hypoxia; In Vitro Techniques; Lung; Male; Molecular Structure; Oligopeptides; Peptides, Cyclic; Rats; Rats, Wistar; Time Factors; Vasoconstriction

Prolonged exposure to decreased oxygen tension causes contraction and proliferation of pulmonary arterial smooth muscle cells (PASMCs) and pulmonary hypertension. Hypoxia-induced inhibition of voltage-gated K(+) (K(v)) channels may contribute to the development of pulmonary hypertension by increasing intracellular calcium concentration ([Ca(2+)](i)). The peptide endothelin-1 (ET-1) has been implicated in the development of pulmonary hypertension and acutely decreases K(v) channel activity. ET-1 also activates several transcription factors, although whether ET-1 alters K(V) channel expression is unclear. The hypoxic induction of ET-1 is regulated by the transcription factor hypoxia-inducible factor-1 (HIF-1), which we demonstrated to regulate hypoxia-induced decreases in K(V) channel activity. In this study, we tested the hypothesis that HIF-1-dependent increases in ET-1 lead to decreased K(v) channel expression and subsequent elevation in [Ca(2+)](i). Resting [Ca(2+)](i) and K(v) channel expression were measured in cells exposed to control (18% O(2), 5% CO(2)) and hypoxic (4% O(2), 5% CO(2)) conditions. Hypoxia caused a decrease in expression of K(v)1.5 and K(v)2.1 and a significant increase in resting [Ca(2+)](i). The increase in [Ca(2+)](i) was reduced by nifedipine, an inhibitor of voltage-dependent calcium channels, and removal of extracellular calcium. Treatment with BQ-123, an ET-1 receptor inhibitor, prevented the hypoxia-induced decrease in K(v) channel expression and blunted the hypoxia-induced increase in [Ca(2+)](i) in PASMCs, whereas ET-1 mimicked the effects of hypoxia. Both hypoxia and overexpression of HIF-1 under normoxic conditions increased ET-1 expression. These results suggest that the inhibition of K(v) channel expression and rise in [Ca(2+)](i) during chronic hypoxia may be the result of HIF-1-dependent induction of ET-1.

Topics: Animals; Calcium Signaling; Endothelin-1; Gene Expression Regulation; Hypoxia; Hypoxia-Inducible Factor 1, alpha Subunit; Kv1.5 Potassium Channel; Male; Mice; Models, Biological; Myocytes, Smooth Muscle; Oligopeptides; Peptides, Cyclic; Perfusion; Piperidines; Pulmonary Artery; Rats; Rats, Wistar; Shab Potassium Channels

Vascular remodeling, rather than vasoconstriction, is believed to account for high vascular resistance in severe pulmonary arterial hypertension (PAH). We have found previously that acute Rho kinase inhibition nearly normalizes PAH in chronically hypoxic rats that have no occlusive neointimal lesions. Here we examined whether Rho kinase-mediated vasoconstriction was also important in a rat model of severe occlusive PAH. Adult rats were exposed to chronic hypoxia ( approximately 10% O(2)) after subcutaneous injection of the vascular endothelial growth factor receptor inhibitor SUGEN 5416. Hemodynamic measurements were made in anesthetized rats after 2 weeks of hypoxia (early group) and 3 weeks of hypoxia plus 2 weeks of normoxia (late group). Both groups developed PAH, with greater severity in the late group. In the early group, intravenous fasudil was more effective than intravenous bradykinin, inhaled NO, or intravenous iloprost in reducing right ventricular systolic pressure. Despite more occlusive vascular lesions, fasudil also markedly reduced right ventricular systolic pressure in late-stage rats. Blood-perfused lungs from late-stage rats showed spontaneous vasoconstriction, which was reversed partially by the endothelin A receptor blocker BQ123 and completely by fasudil or Y-27632. Phosphorylation of MYPT1, a downstream target of Rho kinase, was increased in lungs from both groups of rats, and fasudil (intravenous) reversed the increased phosphorylation in the late group. Thus, in addition to structural occlusion, Rho kinase-mediated vasoconstriction is an important component of severe PAH in SUGEN 5416/hypoxia-exposed rats, and PAH can be significantly reduced in the setting of a severely remodeled lung circulation if an unconventional vasodilator is used.

Topics: 1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine; Animals; Disease Models, Animal; Disease Progression; Endothelin A Receptor Antagonists; Hypertension, Pulmonary; Hypoxia; Indoles; Intracellular Signaling Peptides and Proteins; Male; Myosin-Light-Chain Phosphatase; Organ Culture Techniques; Peptides, Cyclic; Phosphorylation; Protein Serine-Threonine Kinases; Pulmonary Artery; Pyrroles; Rats; Rats, Sprague-Dawley; rho-Associated Kinases; Vascular Endothelial Growth Factor Receptor-2; Vasoconstriction; Vasodilator Agents

We report in the present study the role of endothelin (ET-1) and ET-1 receptors in the sustained hypoxia-induced systemic hypertension.. Wistar rats were randomly assigned to live continuously in hypobaric hypoxia (CH rats) or normoxia (N rats). At the end of hypoxic stress exposure (5 weeks at 450 mm Hg), measurements of mean systemic arterial pressure were done. The effects of ET-1 in the presence or not of the endothelium and/or of specific ET-A inhibitors (BQ-123) or ET-B inhibitors (BQ-788), have been investigated in an isolated model of rat thoracic aorta. Finally, plasmatic ET-1 concentrations have been determined by assay procedure.. Following five weeks of chronic hypoxic stress, CH rats presented a significant increase of mean systemic arterial pressure (N: 129.1+/-6.8 mm Hg vs CH: 152.5+/-3.4 mm Hg; P<0.05). Despite of this hypoxia-induced hypertension, ET-1 plasmatic concentration was not different between N and CH rats. Finally, CH rats presented a reduce response to ET-1 when compared to N rats. This phenomenon seems to be associated to the ET-A vascular smooth muscle cell receptors, since difference between N and CH rats was still present in endothelium denuded aortic rings in the presence or not of the specific ET-B inhibitors (BQ-788). In addition, in the presence of the specific ET-A inhibitor (BQ-123) response to ET-1 was abolished in N and CH rats to the same extent (N:-98%; CH:-99%).. This work clearly suggests that, following long term exposure to hypoxia, ET-1 and ET-1 receptors are not involved in the persistence of systemic hypertension in a rat model, and that chronic exposure to severe hypoxic stress was associated with a downregulation of the ET-A receptors response to ET-1.

Topics: Animals; Aorta, Thoracic; Endothelin-1; Hypertension; Hypoxia; In Vitro Techniques; Male; Muscle, Smooth, Vascular; Oligopeptides; Peptides, Cyclic; Piperidines; Rats; Rats, Wistar; Receptor, Endothelin A; Receptor, Endothelin B; Vasoconstriction

We have previously reported that vasoconstrictor sensitivity to KCl (a receptor-independent and voltage-gated Ca influx-mediated vasoconstrictor) is augmented in the chronically hypoxic hypertensive rat pulmonary circulation probably through increased Rho kinase-mediated Ca sensitization. However, the upstream mechanism by which the RhoA/Rho kinase signaling pathway is activated is unknown. This study examined if endogenous endothelin-1 (ET-1) and serotonin (5-HT) play roles in the Rho kinase-mediated augmented vasoconstrictor response to KCl and the activation of RhoA in chronically hypoxic hypertensive rat pulmonary arteries. The augmented KCl vasoconstriction in hypertensive lungs was reduced by the ETA receptor antagonist BQ123, while a dual ETA/B antagonist had no further effects. A combination of BQ123 and a 5-HT1B/1D receptor antagonist, GR127935, was more effective than either agent alone. The combined antagonists also reduced augmented contractile sensitivity to KCl in hypertensive intrapulmonary arteries. Membrane-to-cytosol ratio of RhoA expression in hypertensive arteries was greater than that in normotensive arteries and was reduced by BQ123 and GR127935. These results suggest that stimulation of ETA and 5-HT1B/1D receptors by endogenous ET-1 and 5-HT, respectively, is involved in RhoA/Rho kinase-mediated increased Ca sensitization in the chronically hypoxic hypertensive rat pulmonary circulation.

Topics: Amides; Animals; Endothelin A Receptor Antagonists; Endothelin B Receptor Antagonists; Endothelin-1; Enzyme Activation; Hypertension, Pulmonary; Hypoxia; In Vitro Techniques; Lung; Male; Peptides, Cyclic; Perfusion; Potassium Chloride; Pulmonary Artery; Pulmonary Circulation; Pyridines; Rats; Rats, Sprague-Dawley; rho-Associated Kinases; rhoA GTP-Binding Protein; Serotonin; Signal Transduction; Vasoconstriction

The present study investigated whether activation of vasodilatory mechanisms masks the involvement of endothelin in hypoxic pulmonary vasoconstriction. Rat intrapulmonary arteries were mounted in microvascular myographs. In arteries with endothelium and contracted with phenylephrine, hypoxia, evoked by exchanging 5% CO2 in air for CO2 in N2, caused a transient contraction followed by a sustained contraction. Hypoxia evoked relaxation in preparations without endothelium. An inhibitor of ATP-sensitive K+ channels (KATP), glibenclamide (10 microM), blunted hypoxic relaxation in arteries without endothelium and enhanced the sustained hypoxic vasoconstriction in arteries with endothelium. Hypoxic contraction was more pronounced in endothelin compared with phenylephrine-contracted preparations in the absence, but not in the presence of glibenclamide. Antagonism of the endothelin ETA and ETB receptors with SB217242 or the combination of BQ123 and BQ788 inhibited endothelin and hypoxic contraction, but the latter only in the presence of glibenclamide. An inhibitor of nitric oxide (NO) synthase, N-nitro-L-arginine (100 microM), evoked contractions, which were left unaltered by SB217242 in hypoxic conditions. In conclusion, hypoxic contraction is mediated in part by an unknown endothelium-derived contractile factor and incubation with glibenclamide shows endothelin enhances hypoxic contraction in part through inhibition of KATP channels. Moreover, inhibition of NO formation in pulmonary arteries does not change endothelin receptor activation in severe hypoxia.

Topics: Animals; Anti-Arrhythmia Agents; Carboxylic Acids; Dose-Response Relationship, Drug; Endothelin Receptor Antagonists; Endothelins; Endothelium, Vascular; Enzyme Inhibitors; Glyburide; Hypoxia; In Vitro Techniques; Indans; Male; Nitric Oxide Synthase; Nitroarginine; Oligopeptides; Oxyhemoglobins; Peptides, Cyclic; Phenylephrine; Pinacidil; Piperidines; Pulmonary Artery; Rats; Rats, Wistar; Receptors, Endothelin; Vasoconstriction; Vasoconstrictor Agents; Vasodilator Agents

The aim of the present study was to investigate the putative role of endothelin (ET) in mediating ischemia/hypoxia-induced ANP release utilizing exogenous ET-1 or ET receptor antagonists (BQ-123 or Bosentan). Isolated rat hearts with non-distended atria were perfused using a Langendorff apparatus and heart rate maintained constant via atrial pacing. Global ischemia was induced either by direct reduction in perfusion or by infusion of exogenous ET-1 (5 x 10(-10) M) for 30 minutes. Perfusion with the ET receptor antagonists, BQ-123 (10(-6) M) or Bosentan (10(-5) M) was initiated 10 minutes before onset of ischemia. Moderate or severe ischemia was induced by reduction (52-61% and 70-82%, respectively) in perfusate flow. Thirty minutes of ischemia/hypoxia (5% O2) was followed by 30 minutes of reperfusion/re-oxygenation. Both moderate and severe ischemia increased ANP release. BQ-123 and Bosentan did not affect basal or ischemia-induced ANP release. Exogenous ET-1 perfusion induced a late increase in ANP release (P < 0.01) that did not exceed the increase in ANP release associated with equivalent direct flow reduction. Hypoxia induced an 8-fold increase in ANP release rate. The ANP release rate returned toward basal levels after re-oxygenation. Bosentan, but not BQ-123, significantly attenuated (P < 0.01) hypoxia-induced ANP release. In conclusion, in this system, ANP release is stimulated by moderate (or severe) ischemia and severe hypoxia independent of change in atrial distension; endogenous ET does not mediate basal and ischemia-induced ANP release; and hypoxia-induced ANP release is partially modulated via interaction with endogenous ET.

Topics: Animals; Antihypertensive Agents; Atrial Natriuretic Factor; Bosentan; Endothelin Receptor Antagonists; Endothelins; Heart; Hypoxia; Male; Myocardial Ischemia; Peptides, Cyclic; Radioimmunoassay; Rats; Sulfonamides

The aims of this study were to investigate the effects of a selective ETA (BQ-123), a selective ETB (BQ-788), and a specific mixed ETA/ETB receptor antagonist (bosentan) on the pulmonary vasoconstriction induced by hypoxia in the isolated perfused rat lung, and the role of nitric oxide, adenosine triphosphate-sensitive (KATP), large conductance Ca+-activated (BKCa) and 4-aminopyridine-sensitive voltage-gated K channels (K+) in the relaxant effects of the selective ETA receptor antagonist BQ-123 and a protein kinase C inhibitor, bisindolylmaleimide I. K+ channels were inhibited by glibenclamide, charybdotoxin, and 4-aminopyridine and nitric oxide synthase by L-NG-nitroarginine methyl ester (L-NAME). Hypoxic ventilation produced a significant pressure response (+57%, p < 0.001). BQ-123, bosentan, and bisindolylmaleimide I induced a concentration-dependent decrease of the hypoxic pressure response (p < 0.001), whereas BQ-788 did not exhibit any inhibitory effect against hypoxic pressure response. Glibenclamide, charybdotoxin, and 4-aminopyridine partially opposed the inhibitory effects elicited by BQ-123 (p < 0.05), but L-NAME did not modify these effects. The effects of bisindolylmaleimide I on hypoxic pressure response were unaffected by glibenclamide, charybdotoxin, or 4-aminopyridine. The authors conclude that (a) ETA receptors and protein kinase C are involved in the modulation of hypoxic pulmonary vasoconstriction; and (b) the ETA antagonist BQ-123 opposes hypoxic pulmonary vasoconstriction through KATP, KV, and BKCa channels, differing in this from the protein kinase C inhibitor bisindolylmaleimide I. These results suggest that BQ-123 operates through a mechanism independent of bisindolylmaleimide I-inhibited protein kinase C isoforms.

Topics: Animals; Bosentan; Drug Interactions; Endothelin Receptor Antagonists; Hypoxia; Indoles; Lung; Male; Maleimides; Nitric Oxide Synthase; Oligopeptides; Peptides, Cyclic; Piperidines; Potassium Channels; Protein Kinase C; Rats; Rats, Wistar; Sulfonamides; Vasoconstriction

The main aim of this study was to determine the effects of endothelium removal on tension and intracellular Ca(2+) ([Ca(2+)](i)) during hypoxic pulmonary vasoconstriction (HPV) in rat isolated intrapulmonary arteries (IPA). Rat IPA and mesenteric arteries (MA) were mounted on myographs and loaded with the Ca(2+)-sensitive fluorophore fura PE-3. Arteries were precontracted with prostaglandin F(2alpha), and the effects of hypoxia were examined. HPV in isolated IPA consisted of a transient constriction superimposed on a second sustained phase. Only the latter phase was abolished by endothelial denudation. However, removal of the endothelium had no effect on [Ca(2+)](i) at any point during HPV. The endothelin-1 antagonists BQ-123 and BQ-788 did not affect HPV, although constriction induced by 100 nM endothelin-1 was abolished. In MA, hypoxia induced an initial transient rise in tension and [Ca(2+)](i), followed by vasodilatation and a fall in [Ca(2+)](i) to (but not below) prehypoxic levels. These results are consistent with sustained HPV being mediated by an endothelium-derived constrictor factor that is distinct from endothelin-1 and that elicits vasoconstriction via Ca(2+) sensitization.

Topics: Animals; Antihypertensive Agents; Calcium; Endothelin Receptor Antagonists; Endothelium, Vascular; Hypoxia; Male; Oligopeptides; Peptides, Cyclic; Piperidines; Pulmonary Artery; Pulmonary Circulation; Rats; Rats, Wistar; Receptor, Endothelin A; Vasoconstriction

Renal vasoconstriction with resultant tissue hypoxia, especially in the renal medulla, has been suggested to play a role in contrast media (CM)-induced nephropathy. Endothelin (ET) is released into the blood stream following CM injection and has been proposed as a potential mediator through its vasoconstrictive properties.. To investigate the possible protective influence of ET-receptor antagonists against CM-induced reduction in renal function, we studied the effects of injection of iopromide with and without pretreatment with BQ123 (ET-A antagonist) or BQ788 (ET-B antagonist) on renal superficial cortical flow (CBF), outer medullary blood flow (OMBF) and outer medullary oxygen tension (pO2) in normal rats.. Administration of CM (1600 mg I/kg b.w.) did not affect CBF in any of the groups. However, a transient decrease in OMBF occurred, which was unaffected by both BQ123 and BQ788. Also a transient decrease in outer medullary pO2 was induced by CM administration. The pO2 reduction was significantly smaller after pretreatment with BQ123, than after injection of CM alone or together with BQ788, and pO2 returned more rapidly to the control level. Neither receptor antagonist had an effect on CM-mediated increases in electrolyte excretion.. In the normal rat, activation of ET-A receptors is partly involved in the depression of outer medullary pO2 caused by injection of iopromide. However, the decrease in OMBF after iopromide injection is not mediated by ET receptors. The beneficial effects of the ET-A receptor antagonist on CM-induced changes in outer medullary pO2 seem therefore not primarily mediated on the hemodynamic level but may rather involve tubular transport mechanisms.

Topics: Animals; Antihypertensive Agents; Contrast Media; Disease Models, Animal; Endothelin Receptor Antagonists; Hypoxia; Iohexol; Kidney Diseases; Kidney Medulla; Male; Oligopeptides; Peptides, Cyclic; Piperidines; Rats; Rats, Sprague-Dawley; Receptors, Endothelin; Renal Circulation

The contribution of endothelin to resting pulmonary vascular tone and hypoxic pulmonary vasoconstriction in humans is unknown. We studied the hemodynamic effects of BQ-123, an endothelin type A receptor antagonist, on healthy volunteers exposed to normoxia and hypoxia. Hemodynamics were measured at room air and after 15 min of exposure to hypoxia (arterial PO(2) 99.8 +/- 1.8 and 49.4 +/- 0.4 mmHg, respectively). Measurements were then repeated in the presence of BQ-123. BQ-123 decreased pulmonary vascular resistance (PVR) 26% and systemic vascular resistance (SVR) 21%, whereas it increased cardiac output (CO) 22% (all P < 0.05). Hypoxia raised CO 28% and PVR 95%, whereas it reduced SVR 23% (all P < 0.01). During BQ-123 infusion, hypoxia increased CO 29% and PVR 97% and decreased SVR 22% (all P < 0.01). The pulmonary vasoconstrictive response to hypoxia was similar in the absence and presence of BQ-123 [P = not significant (NS)]. In vehicle-treated control subjects, hypoxic pulmonary vasoconstriction did not change with repeated exposure to hypoxia (P = NS). Endothelin contributes to basal pulmonary and systemic vascular tone during normoxia, but does not mediate the additional pulmonary vasoconstriction induced by acute hypoxia.

Topics: Acute Disease; Adult; Endothelin Receptor Antagonists; Endothelins; Female; Hemodynamics; Humans; Hypoxia; Male; Peptides, Cyclic; Pulmonary Circulation; Receptor, Endothelin A; Receptors, Endothelin; Recurrence; Reference Values; Vascular Resistance; Vasomotor System

Endothelins (ETs) are a group of vasoactive peptides (ET-1, ET-2 and ET-3) produced by many cell types that bind to G-protein-linked transmembrane receptors, ET-A receptors (ET-RAs) and ET-B receptors (ET-RBs). These peptides are expressed in several human tumors, including carcinomas of the breast, and have a mitogenic effect in ovarian cancer cell lines. We investigated ET expression in infiltrating ductal carcinomas (IDCs) of the breast and the relationship between ET and hypoxia. ET staining was increased in human grade II IDC samples compared with normal breast tissue. ET-2 and ET-RB mRNA expression were absent in the majority of normal human breast samples (1 of 5 and 0 of 5, respectively) but was present in the majority of IDC tested (13 of 15 and 12 of 15, respectively). In a murine breast cancer model, HTH-K, ET-2, and ET-RB mRNA were detected in tumor but not normal breast tissue, and ET expression colocalized with areas of hypoxia. In vitro, ET-2, ET-RA, and ET-RB mRNA were increased by incubating HTH-K cells in hypoxia (0.1% oxygen) for 24 h. Hypoxia also up-regulated ET-2 mRNA in several human breast tumor cell lines. ET-2 mRNA increased within 3 h in a hypoxia-inducible factor 1-dependent manner. The ET-RB antagonist BQ-788 increased in hypoxia-associated apoptosis of breast tumor cells in vitro. These effects could be reversed by addition of ET-2 peptide. Intratumoral injection of BQ-788 led to an increase in the development and extent of necrosis within the HTH-K tumor and a decrease in the rate of tumor growth. The ET-RA antagonist, BQ-123, also led to a decrease in tumor growth but without a concomitant increase in necrosis. We propose that modulation of ET-2 production via the hypoxia-inducible factor 1 transcription factor and autocrine signaling via ET-RB is a novel mechanism by which tumor cells can withstand hypoxic stress. Treatment of breast carcinomas with ET receptor antagonists may have a therapeutic benefit.

Topics: Antihypertensive Agents; Blotting, Northern; Breast Neoplasms; Cell Survival; DNA-Binding Proteins; Dose-Response Relationship, Drug; Endothelin-2; Female; Humans; Hypoxia; Hypoxia-Inducible Factor 1; Hypoxia-Inducible Factor 1, alpha Subunit; Necrosis; Nuclear Proteins; Oligopeptides; Ovarian Neoplasms; Peptides, Cyclic; Piperidines; Receptor, Endothelin B; Receptors, Endothelin; RNA, Messenger; Time Factors; Transcription Factors; Tumor Cells, Cultured; Up-Regulation

Chronic exposure in a low-PO(2) environment (i.e., chronic hypoxia, CH) elicits an elevated hypoxic ventilatory response and increased hypoxic chemosensitivity in arterial chemoreceptors in the carotid body. In the present study, we examine the hypothesis that changes in chemosensitivity are mediated by endothelin (ET), a 21-amino-acid peptide, and ET(A) receptors, both of which are normally expressed by O(2)-sensitive type I cells. Immunocytochemical staining showed incremental increases in ET and ET(A) expression in type I cells after 3, 7, and 14 days of CH (380 Torr). Peptide and receptor upregulation was confirmed in quantitative RT-PCR assays conducted after 14 days of CH. In vitro recordings of carotid sinus nerve activity after in vivo exposure to CH for 1-16 days demonstrated a time-dependent increase in chemoreceptor activity evoked by acute hypoxia. In normal carotid body, the specific ET(A) antagonist BQ-123 (5 microM) inhibited 11% of the nerve discharge elicited by hypoxia, and after 3 days of CH the drug diminished the hypoxia-evoked discharge by 20% (P < 0.01). This inhibitory effect progressed to 45% at day 9 of CH and to nearly 50% after 12, 14, and 16 days of CH. Furthermore, in the presence of BQ-123, the magnitude of the activity evoked by hypoxia did not differ in normal vs. CH preparations, indicating that the increased activity was the result of endogenous ET acting on an increasing number of ET(A). Collectively, our data suggest that ET and ET(A) autoreceptors on O(2)-sensitive type I cells play a critical role in CH-induced increased chemosensitivity in the rat carotid body.

Topics: Adaptation, Physiological; Animals; Antihypertensive Agents; Carotid Body; Chemoreceptor Cells; Chronic Disease; Electrophysiology; Endothelin Receptor Antagonists; Endothelin-1; Hypoxia; In Vitro Techniques; Male; Peptides, Cyclic; Rats; Rats, Sprague-Dawley; Receptor, Endothelin A; Receptors, Endothelin; RNA, Messenger; Time Factors

The effects on pulmonary artery pressure (PAP) and plasma Endothelin-1 (ET-1) were studied in piglets during severe hypoxemia and reoxygenation for 2 h with selective inhibition of the endothelin receptors. Two groups were subjected to selective ETA (ETA group) or ETB (ETB group) receptor inhibition. During hypoxemia there was an initial increase in PAP to 36.3 and 34.3 mm Hg in the ETA and ETB groups respectively, with a decrease to the end of hypoxemia. During reoxygenation PAP reached a maximum at 5 min with a mean of 29.6 and 38.4 mm Hg in the ETA and ETB groups respectively, and then PAP gradually declined towards baseline. During the 2 h reoxygenation period PAP was higher in the ETB group than in the ETA group (p = 0.02). Plasma ET-1 increased from 1.50 and 1.17 ng/L at baseline to 2.07 and 3.18 ng/L at the end of hypoxemia in the ETA and ETB groups respectively.. ETB receptor inhibition leads to increased pulmonary vasoconstriction during reoxygenation following hypoxemia compared to ETA receptor inhibition. Not only the ETB receptor, but also the ETA receptor plays a role in maintaining plasma ET-1 levels.

Topics: Acid-Base Equilibrium; Animals; Animals, Newborn; Endothelin Receptor Antagonists; Endothelin-1; Hemodynamics; Hypoxia; Lung; Oligopeptides; Peptides, Cyclic; Piperidines; Pulmonary Artery; Receptor, Endothelin A; Receptor, Endothelin B; Swine; Vasoconstriction

This investigation was made to elucidate the role of endothelin (ET) in hypoxic pulmonary hypertension and the preventing effects of BQ-123, an ETA receptor antagonist. Thirty male Wistar rats were divided into three groups and exposed to air, isobaric hypoxia or isobaric hypoxia plus BQ-123 for 3 weeks. The pulmonary artery pressure was measured by right cardiac catheterization. The plasma level of ET-1 was measured by RIA method. Histologic sections of the lungs were examined by a computerized image analyser. In hypoxic rats, the pulmonary artery pressure and the thickness of wall of arteriole were significantly increased, and right ventricular hypertrophy was developed. The plasma level of VEGF in rats treated with hypoxia (192.3 +/- 43.1 pg/ml) was significantly increased as compared with that of normal rats (128.2 +/- 28.1 pg/ml), P < 0.01. Chronic BQ-123 treatment prevented the developments of pulmonary hypertension, thickening of pulmonary arteriole and right ventricular hypertrophy induced by hypoxia. These result indicate that chronic hypoxia can result in hypoxic pulmonary hypertension and increased plasma level of ET-1, and the ETA receptor antagonist can prevent hypoxic pulmonary hypertension.

Topics: Animals; Endothelin Receptor Antagonists; Endothelin-1; Hypertension, Pulmonary; Hypoxia; Male; Peptides, Cyclic; Pulmonary Artery; Rats; Rats, Wistar

There is controversy on the role of endothelin (ET)-1 in the mechanism of hypoxic pulmonary vasoconstriction (HPV). Although HPV is inhibited by ET-1 subtype A (ET(A))-receptor antagonists in animals, it has been reported that ET(A)-receptor blockade does not affect HPV in isolated lungs. Thus we reassessed the role of ET-1 in HPV in both rats and isolated blood- and physiological salt solution (PSS)-perfused rat lungs. In rats, the ET(A)-receptor antagonist BQ-123 and the nonselective ET(A)- and ET(B)-receptor antagonist PD-145065, but not the ET(B)-receptor antagonist BQ-788, inhibited HPV. Similarly, BQ-123, but not BQ-788, attenuated HPV in blood-perfused lungs. In PSS-perfused lungs, either BQ-123, BQ-788, or the combination of both attenuated HPV equally. Inhibition of HPV by combined BQ-123 and BQ-788 in PSS-perfused lungs was prevented by costimulation with angiotensin II. The ATP-sensitive K(+) (K(ATP))-channel blocker glibenclamide also prevented inhibition of HPV by BQ-123 in both lungs and rats. These results suggest that ET-1 contributes to HPV in both isolated lungs and intact animals through ET(A) receptor-mediated suppression of K(ATP)-channel activity.

Topics: Adenosine Triphosphate; Animals; Blood; Endothelin Receptor Antagonists; Glyburide; Hypoxia; In Vitro Techniques; Male; Peptides, Cyclic; Perfusion; Potassium Channel Blockers; Pulmonary Circulation; Rats; Rats, Sprague-Dawley; Receptor, Endothelin A; Receptors, Endothelin; Sodium Chloride; Vasoconstriction

These studies document striking pulmonary vasoconstrictor response to nitric oxide synthase (NOS) inhibition in monocrotaline (MCT) pulmonary hypertension in rats. This constriction is caused by elevated endothelin (ET)-1 production acting on ETA receptors. Isolated, red blood cell plus buffer-perfused lungs from rats were studied 3 wk after MCT (60 mg/kg) or saline injection. MCT-injected rats developed pulmonary hypertension, right ventricular hypertrophy, and heightened pulmonary vasoconstriction to ANG II and the NOS inhibitor NG-monomethyl-L-arginine (L-NMMA). In MCT-injected lungs, the magnitude of the pulmonary pressor response to NOS inhibition correlated strongly with the extent of pulmonary hypertension. Pretreatment of isolated MCT-injected lungs with combined ETA (BQ-123) plus ETB (BQ-788) antagonists or ETA antagonist alone prevented the L-NMMA-induced constriction. Addition of ETA antagonist reversed established L-NMMA-induced constriction; ETB antagonist did not. ET-1 concentrations were elevated in MCT-injected lung perfusate compared with sham-injected lung perfusate, but ET-1 levels did not differ before and after NOS inhibition. NOS inhibition enhanced hypoxic pulmonary vasoconstriction in both sham- and MCT-injected lungs, but the enhancement was greater in MCT-injected lungs. Results suggest that in MCT pulmonary hypertension, elevated endogenous ET-1 production acting through ETA receptors causes pulmonary vasoconstriction that is normally masked by endogenous NO production.

Topics: Angiotensin II; Animals; Drug Combinations; Endothelin-1; Endothelins; Enzyme Inhibitors; Hypertension, Pulmonary; Hypertrophy, Right Ventricular; Hypoxia; In Vitro Techniques; Lung; Male; Monocrotaline; Oligopeptides; omega-N-Methylarginine; Peptides, Cyclic; Piperidines; Rats; Rats, Sprague-Dawley; Vasoconstriction

Endothelin (ET)-1 has been implicated as a critical mediator in the pathogenesis of hypoxic pulmonary hypertension. We questioned whether, during exposure to chronic hypobaric hypoxia, rat pulmonary artery smooth muscle cells (PASMC) became sensitized to ET-1. Two effects of ET-1, inhibition of voltage-gated K(+) (K(v)) channels and release of intracellular Ca(2+), were studied using whole cell patch clamp and single cell indo 1 fluorescence, respectively. In both normotensive and chronically hypoxic-hypertensive PASMC, ET-1 caused concentration-dependent inhibition of voltage-gated K(+) current [I(K(v))], with maximum inhibition of 12-18% seen at a concentration of 0.1-1 nM. Although the chronically hypoxic-hypertensive PASMC was no more susceptible to ET-1-mediated I(K(v)) inhibition, a switch in coupling between ET-1 and I(K(v)) from ET(B) to ET(A) receptors occurred. This switch in receptor coupling, combined with reduced I(K(v)) density and increased ET-1 production in the hypoxic rat lung, may help explain the ability of ET(A)-receptor blockers to attenuate the development of hypoxic pulmonary hypertension in vivo.

Topics: Animals; Antihypertensive Agents; Calcium; Chronic Disease; Electrophysiology; Endothelin Receptor Antagonists; Endothelin-1; Hypertension; Hypoxia; Male; Muscle, Smooth, Vascular; Oligopeptides; Peptides, Cyclic; Piperidines; Potassium Channel Blockers; Potassium Channels; Pulmonary Artery; Rats; Rats, Sprague-Dawley; Receptor, Endothelin A; Receptors, Endothelin

We investigated the effect of systemic hypoxia (Krebs-Henseleit solution gassed with 5% CO2/95% N2) on an isolated, perfused rat lung. Hypoxia resulted in a slowly developing sustained increase in pulmonary perfusion pressure (PPP) accompanied by an increase in lung weight (LW). The endothelin (ET) receptor antagonists BQ123 (3 and 10 microM), BQ788 (3 microM) and bosentan (1.5 and 5 microM) all attenuated the hypoxia-induced increases in LW and PPP. In addition, phosphoramidon (1 microM), an ET-converting enzyme inhibitor, also significantly attenuated the hypoxia-induced increases in PPP and LW. The use of two agents that alter peptide secretion, phalloidin (10 and 50 nM) and colchicine (100 nM), and the peptide synthesis inhibitor cycloheximide (5 microM) all significantly attenuated the hypoxia-induced increases in PPP and LW. The increase in PPP and LW after the onset of hypoxia was accompanied by an increase in perfusate levels of ET-1 compared with normoxic time-matched controls. The results show that in this model, systemic hypoxia is capable of causing a sustained vasoconstriction and increased LW. The fact that these increases can be attenuated by an ET-converting enzyme inhibitor, ET receptor antagonists and agents that block peptide synthesis and secretion, together with the increase in perfusate levels of ET-1, suggests that ET production and release contribute to the changes seen.

Topics: Animals; Colchicine; Cycloheximide; Endothelins; Hypoxia; Lung; Oligopeptides; Peptides, Cyclic; Perfusion; Piperidines; Rats; Rats, Wistar; Vasoconstriction

Our laboratory has recently shown that locally produced endothelin (ET) is involved in the atrial natriuretic peptide (ANP) response to a physical stimulus, stretch. The aim of this study was to determine if factors locally produced in the atria were involved in the ANP response to a chemical stimulus, anoxia. Reduced oxygen tension is a potent stimulus of ANP release, and our results show that, when isolated perfused atria were exposed to anoxic conditions, the ANP secretion rate increased by a maximum of 129 +/- 8% of the baseline. Exposure to anoxia caused neither an elevation in perfusate creatinine phosphokinase, a change in atrial morphology detectable by electron microscopy, nor interfered with the return toward the baseline ANP secretion rate with reoxygenation, suggesting that this response was not due to myocyte damage. When the atria were pretreated with either 3 microM BQ-123, an endothelin receptor inhibitor, or 10 microM indomethacin, a cyclooxygenase inhibitor, the ANP response to anoxia was nearly abolished. To clarify the association between ET and prostaglandins, we showed that the ANP response to 50 nM ET-1 was totally blocked at both high and low pressure by 10 microM indomethacin, but the increased contractility response to ET was unaffected. Therefore, we have concluded that the anoxia-induced ANP response is mediated by locally produced ET, which, in turn, stimulates the production of prostaglandins. Prostaglandins appear to be responsible for the increased ANP secretion rate.

Topics: Animals; Atrial Natriuretic Factor; Cyclooxygenase Inhibitors; Endothelin Receptor Antagonists; Endothelins; Heart; Heart Atria; Hypoxia; In Vitro Techniques; Indomethacin; Microscopy, Electron; Myocardium; Peptides, Cyclic; Rats

The role of endothelin (ET)-1 in pulmonary arterial pressure (Ppa) homeostasis and hypoxia-induced pulmonary hypertension was examined. ET-1 was chronically infused (2 and 4 pmol.kg-1.min-1) into the pulmonary circulation of male Sprague-Dawley rats for 3, 7, and 14 days while they were exposed to normoxia or hypobaric hypoxia (inspired O2 fraction 10%). The role of endogenous ET was examined by infusion of ET antiserum (ET-AS; 0.25 and 0.5 microliter.rat-1.h-1; cross-reacting with ET-1, -2, and -3) or the ETA-receptor blocker BQ-123 (10 pmol.kg-1.min-1). ET-1 (4 pmol) increased Ppa at 3 and 7 days in normoxia and hypoxia and was ineffective at 14 days, probably from ETA-receptor downregulation. BQ-123 blunted the hypoxic Ppa rise at all times, confirming a role for ETA receptors. ET-AS (0.5 microliter) was mostly ineffective but exacerbated hypoxic Ppa at 14 days, in contrast to BQ-123, suggesting that a different ET receptor could be involved. ET-1 infusion (2 pmol) caused right ventricular hypertrophy (RVH) in normoxia and exacerbated RVH in hypoxia, whereas BQ-123 and ET-AS (0.25 microliter) reduced hypoxic RVH. In conclusion, endogenous ET-1 plays a role in hypoxia-induced pulmonary hypertension and RVH by augmenting the level of hypoxic response. ET-1 also affects hematocrit and may reduce blood levels of the vasodilator calcitonin gene-related peptide.

Topics: Animals; Blood Pressure; Calcitonin Gene-Related Peptide; Chronic Disease; Endothelin Receptor Antagonists; Endothelin-1; Hematocrit; Hypoxia; Immune Sera; Longitudinal Studies; Lung; Male; Myocardium; Organ Size; Peptides, Cyclic; Pulmonary Circulation; Rats; Rats, Sprague-Dawley; Reference Values

The selective endothelin-A (ETA)-receptor antagonist BQ-123 has been shown to prevent chronic hypoxia-induced pulmonary hypertension in the rat. Therefore in the current study we utilized BQ-123 to test the hypothesis that blockade of the ETA receptor can reverse as well as prevent the increase in mean pulmonary artery pressure, right ventricle-to-left ventricle plus septum ratio, and percent wall thickness in small (50-100 microns) pulmonary arteries observed in male Sprague-Dawley rats exposed to normobaric hypoxia (10% O2, 2 wk). Infusion of BQ-123 (0.4 mg.0.5 microliter-1.h-1 for 2 wk in 10% O2) begun after 2 wk of hypoxia significantly reversed the established pulmonary hypertension and prevented further progression of right ventricular hypertrophy during the third and fourth week of hypoxia. BQ-123 infusion instituted before exposure to hypoxia completely prevented the hypoxia-induced pulmonary hypertension, right ventricular hypertrophy, and pulmonary vascular remodeling. These findings suggest that, in the lung, hypoxia induced an increase synthesis of endothelin-1, which acts locally on ETA receptors to cause pulmonary hypertension, right heart hypertrophy, and pulmonary vascular remodeling, while ETA-receptor blockade can both prevent and reverse these processes.

Topics: Animals; Cardiomegaly; Chronic Disease; Endothelin Receptor Antagonists; Hypertension, Pulmonary; Hypoxia; Infusions, Intravenous; Male; Peptides, Cyclic; Rats; Rats, Sprague-Dawley

1. Using isolated pulmonary resistance vessels from mature fetal lamb and chronically instrumented lambs (8-17 days old), we have examined whether hypoxic pulmonary vasoconstriction is sustained by activation of a constrictor mechanism or suppression of a dilator mechanism. 2. Hypoxia contracted both arteries and veins in vitro, and the contraction was greater with the former. After removing the endothelium, arteries responded faster to hypoxia, but the magnitude of the response remained unchanged. 3. Hypoxic arteries, unlike normally oxygenated arteries, did not contract with either indomethacin (2.8 microM) or N omega-nitro-L-arginine methyl ester (L-NAME, 100 microM). The same vessels relaxed with sodium nitroprusside (SNP, 0.001-10 microM) but not with bradykinin (0.1-100 nM). 4. Endothelin-1 (ET-1, 0.01-10 nM) contracted isolated arteries and veins under normoxic and hypoxic conditions. In both vessels, the contraction was fast in onset and subsidence, and was inhibited by the ETA receptor antagonist BQ123 (1 microM). The ET-1 precursor, big ET-1 (100 nM), also contracted arteries and veins, but compared with ET-1 its action was slower in development. Big ET-1 contraction, unlike ET-1 contraction, was curtailed by the inhibitor of the ET-1-converting enzyme, phosphoramidon (50 microM). 5. ET-1 (0.1-10 nM) had no effect on isolated arteries precontracted with a thromboxane A2 (TXA2) analogue (ONO-11113) and treated with BQ123 (10 microM). Under the same conditions, ET-1 relaxed the veins. Accordingly, in the absence of BQ123 treatment, the selective ETB receptor agonist IRL-1620 (0.1-100 nM) relaxed the contracted veins but not the arteries. 6. BQ123 (10 microM) inhibited the constriction of isolated arteries and veins to hypoxia. Likewise, in the conscious lamb a bolus of BQ123 (0.4 mg kg-1, injected into the pulmonary artery) curtailed the rise in pulmonary vascular resistance (Rpa) brought about by alveolar hypoxia without changing significantly systemic vascular resistance (Rao). Under normoxia, Rpa was insignificantly affected by BQ123. 7. The results indicate that pulmonary resistance arteries are more susceptible to hypoxia than the veins, and that hypoxic vasoconstriction does not require an intact endothelium to occur. Hypoxic tone is ascribed primarily to intramural generation of ET-1, while removal of the tonic action of a relaxant may only have an accessory role in the response.

Topics: Animals; Arginine; Bradykinin; Endothelins; Endothelium; Female; Hypoxia; Indomethacin; NG-Nitroarginine Methyl Ester; Nitroprusside; Peptide Fragments; Peptides, Cyclic; Pregnancy; Pulmonary Circulation; Sheep; Thromboxane A2; Vasoconstriction

Exposure to hypoxia is associated with increased pulmonary artery pressure and plasma endothelin-1 (ET-1) levels and with selective enhancement in ET-1 peptide and mRNA and endothelin-A (ETA) receptor mRNA levels in rat lung. The current study tested the hypothesis that endogenous ET-1 can account for hypoxia-induced pulmonary hypertension via a paracrine effect on ETA receptors in lung. Intravenous infusion of the ETA receptor antagonist BQ-123 (D-Trp-D-Asp-Pro-D-Val-Leu) (0.4 mg/microliters at 1 microliter/h) into Sprague-Dawley rats beginning 4 h before and for 90 min during normobaric hypoxia (10% O2) markedly attenuated the hypoxic response: mean pulmonary artery pressure increased from 17.2 +/- 0.7 to 29.0 +/- 1.2 mmHg in saline control rats but did not increase from baseline in BQ-123-treated rats. BQ-123 did not alter systemic arterial pressure, heart rate, or plasma endothelin-1 levels. These findings suggest that ET-1 synthesized in lung in response to hypoxia acts locally on ETA receptors to cause pulmonary hypertension.

Topics: Acute Disease; Animals; Blood Pressure; Endothelin Receptor Antagonists; Heart Rate; Hypertension, Pulmonary; Hypoxia; Male; Peptides, Cyclic; Pulmonary Artery; Rats; Rats, Sprague-Dawley; Receptor, Endothelin A

Acute systemic hypoxia induces mesenteric venoconstriction in intact rabbits in part because of an increase in chemoreflex-mediated sympathetic efferent nerve activity. Inhaled anesthetics attenuate this reflex response. The direct effects of hypoxia on mesenteric veins are unknown. The purpose of the current study was to examine the effects of hypoxia on isolated rabbit mesenteric capacitance veins and to determine the effects of halothane, isoflurane, and enflurane on the responses to hypoxia.. Isometric tension was measured before, during, and after 10 min of hypoxia in the rings of either quiescent or norepinephrine contracted veins, with or without endothelium. Effects of various pharmacologic agents and volatile anesthetics on the responses to hypoxia were examined.. Hypoxia augmented contractions to norepinephrine and phenylephrine only in endothelium-intact veins. The hypoxic response was inhibited by phentolamine (alpha-adrenoceptor antagonist) and abolished in the absence of extracellular Ca2+. There were no effects of propranolol (beta-adrenoceptor antagonist), ryanodine (a sarcoplasmic reticulum Ca2+ depleter), indomethacin (cyclooxygenase inhibitor), or nordihydroguaiaretic acid (lipoxygenase inhibitor). L-NAME (an inhibitor of nitric oxide synthase) enhanced basal sensitivity of veins to norepinephrine but had no effect on the response to hypoxia. Nicardipine (a blocker of voltage-gated calcium channels) depressed the hypoxic contraction by 86 +/- 5%, phosphoramidon (an inhibitor of endothelin-converting enzyme) by 82 +/- 8%, and BQ-123 (a specific endothelin-1 receptor antagonist) by 47 +/- 10%. Volatile anesthetics (1.0 MAC) inhibited responses to hypoxia in the absence as well as presence of L-NAME.. These results suggest that in mesenteric capacitance veins of rabbits an intrinsic vascular mechanism contributes to endothelium-dependent hypoxic augmentation of contraction to alpha-adrenergic agonists that involve activation of endothelin-1, an endothelium-derived constricting factor. Inhibition of hypoxic contraction by volatile anesthetics is not mediated by endothelium relaxing factor.

Topics: Acetylcholine; Animals; Arginine; Endothelium, Vascular; Enflurane; Glycopeptides; Halothane; Hypoxia; In Vitro Techniques; Indomethacin; Isoflurane; Male; Masoprocol; NG-Nitroarginine Methyl Ester; Nicardipine; Norepinephrine; Peptides, Cyclic; Rabbits; Ryanodine; Vasoconstriction

A possible role of endothelin (ET)-1 in mediating hypoxic pulmonary vasoconstriction (HPV) was examined by comparing haemodynamic differences between ET-1-induced vasoconstriction and HPV in isolated perfused rat lungs. An ETA receptor antagonist (BQ123) was also employed to assess the effects of ET-1. The pulmonary arterial pressure (Ppa) was significantly increased by alveolar hypoxia (3% O2) and by ET-1 (5 nM). The pulmonary microvascular pressure was not changed by hypoxia, but increased more than two-fold by ET-1 (P < 0.01). Hypoxia significantly increased pulmonary arterial resistance (P < 0.01) while ET-1 significantly increased pulmonary venous resistance (P < 0.01), and slightly increased arterial resistance. Lung weight was increased by ET-1 and decreased by hypoxia, accompanied by similar Ppa responses in both cases. BQ123 (10(-6) M and 10(-5) M) did not influence the changes in Ppa and lung weight induced by hypoxia or angiotensin II (0.3 micrograms). BQ123 did, however, suppress (P < 0.05) the increase in Ppa and lung weight induced by 5 nM ET-1. Thus, it appears unlikely that ET-1 is involved in changes in pulmonary vascular tone during acute HPV.

Topics: Animals; Blood Pressure; Endothelins; Hypoxia; Lung; Male; Organ Size; Peptides, Cyclic; Rats; Rats, Sprague-Dawley; Vascular Resistance; Vasoconstriction

The goal of our studies is to elucidate the role of atrial natrluretic peptide (ANP) and endothelin-1 (ET-1) and their receptor mechanisms in hypoxia-induced pulmonary hypertension and the control of pulmonary artery pressure in patients with pulmonary hypertension. Our experimental model is the male Sprague-Dawley rat subjected to normobaric hypoxia (10% O2, 1 atm) x 4 weeks or less. Our hypothesis is that ET-1 and ANP gene expression are enhanced by exposure to hypoxia and that the ET-1 and ANP so generated have causal and protective, respectively, effects on the development of hypoxia-induced pulmonary hypertension. Results from our studies demonstrated that ANP gene expression and ANP secretion in the heart, and the sensitivity to both endogenous and exogenous ANP in the pulmonary vasculature of hypoxia adapted rats are enhanced during hypoxic exposure. These data defined a role for ANP as a modulator hormone that protects against the development of acute hypoxic pulmonary vasoconstriction and chronic hypoxic pulmonary hypertension. Our studies also demonstrated that ET-1 and endothelin-A receptor (ET-AR) gene expression were selectively enhanced in the pulmonary vasculature by exposure to hypoxia, and that the ET-1 so generated is an important mediator in acute and chronic hypoxia-induced pulmonary hypertension. These results suggest that the intrapulmonary ET-1, acting on ET-AR receptors in the pulmonary vasculature mediates the hypoxia-induced pulmonary vasoconstriction and hypertension. In addition, our recent experiments have demonstrated that administration of BQ-123, a selective ET-AR antagonist, abolished the pulmonary vasoconstrictor response to acute (0-90 min) and chronic (2 weeks) hypoxia, further suggesting that ET-1 plays an important role in the pathogenesis of hypoxia-induced pulmonary hypertension in the rat. Results from our studies also indicate that selective ANP analogs and ET-AR antagonists may be clinically useful for the treatment of pulmonary hypertension.

Topics: Animals; Atrial Natriuretic Factor; Blood Pressure; Cardiac Output; Endothelins; Hypertension, Pulmonary; Hypoxia; Kidney; Liver; Lung; Male; Peptides, Cyclic; Rats; Rats, Sprague-Dawley; Receptors, Atrial Natriuretic Factor; RNA, Messenger; Spleen

To investigate the role of endothelin-1 (ET-1) in the pathogenesis of hypoxic pulmonary hypertension, we studied the effects of a recently described endothelin-receptor antagonist (ETA), BQ123, on the development of this process. Intraperitoneal osmotic pumps were placed into 8-wk-old Sprague-Dawley rats that received either saline or BQ123 (0.15 mg/h). The rats were maintained in room air normoxia or placed in a hypobaric chamber (380 Torr) for 2 wk to induce hypoxic pulmonary hypertension. There were no hemodynamic differences between normoxic rats treated with either saline or BQ123. However, treatment with BQ123 attenuated the hypoxia-induced increase in pulmonary arterial mean pressure and total pulmonary resistance index by 60 and 87% respectively. There was also a reduction in hypoxia-induced right ventricular hypertrophy in the BQ123 group. Histological studies performed using a barium-gelatin fixation technique in hypoxic BQ123-treated animals demonstrated a decrease in medial wall thickness in arteries corresponding to the respiratory and terminal bronchioles, respectively. Similarly, there was a significant reduction in the degree of muscularization of more distal vessels at the level of alveolar ducts in BQ123-treated hypoxic rats. We conclude that the ETA-receptor antagonist BQ123 attenuates the development of hypoxic pulmonary hypertension in rats in vivo, thereby suggesting a possible contributing role for ET-1 and the ETA receptor in the pathogenesis of this process.

Topics: Animals; Blood Vessels; Endothelin Receptor Antagonists; Hemodynamics; Hypertension, Pulmonary; Hypoxia; Male; Peptides, Cyclic; Pulmonary Circulation; Rats; Rats, Sprague-Dawley

Experiments were designed to determine whether or not endogenous endothelin (ET) contributes to endothelium-independent anoxic contractions of canine coronary arteries. Rings without endothelium were suspended for isometric tension recording in conventional organ chambers filled with modified Krebs-Ringer bicarbonate solution. Anoxia (PO2 < or = 1 mm Hg) caused reproducible contractions. The anoxic contractions were augmented by exogenous endothelin-1 (ET-1). At 10(-6) M and 10(-5) M, BQ-123 (a specific endothelin antagonist) inhibited both the facilitatory effect of ET-1 and the anoxic contractions. At these concentrations BQ-123 caused a parallel shift to the right of the concentration-response curve to ET-1 and a small but significant depression of the response to norepinephrine, without affecting the maximal response to the catecholamine. BQ-123 did not significantly affect the concentration-response curve to Ca2+ in depolarizing solution (60 mM KCl). Monoclonal antibodies against ET-1 (70 micrograms/ml) inhibited the response to exogenous ET-1 and abolished the facilitating effect of the peptide, but did not affect the anoxic contractions. These results suggest that ET-1 contributes to anoxic contractions in canine coronary arteries without endothelium. The receptor involved belongs to the ETA-subtype and is not accessible to monoclonal antibodies.

Topics: Animals; Antibodies, Monoclonal; Coronary Vessels; Dogs; Endothelin Receptor Antagonists; Endothelins; Endothelium, Vascular; Female; Hypoxia; In Vitro Techniques; Isometric Contraction; Male; Muscle, Smooth, Vascular; Peptides, Cyclic

The mechanisms by which acute alveolar hypoxia induces pulmonary vasoconstriction remain unclear. Previous studies suggest that hypoxia-induced vasoconstriction is endothelium-dependent and is associated with the release of endothelin-1 (ET-1), a potent vasoactive paracrine hormone produced by vascular endothelial cells. The vasoconstrictive effects of ET-1 are likely to be mediated by ETA receptors located on vascular smooth-muscle cells. BQ-123 is a selective ETA receptor antagonist. To determine the role of ET-1 and ETA receptors on resting tone and hypoxic pulmonary vasoconstriction, we studied the effects of ET-1 and BQ-123 at rest and during hypoxia-induced pulmonary vasoconstriction in 12 intact newborn lambs (< 1 week old). At rest, the intrapulmonary infusion of BQ-123 did not change resting pulmonary arterial pressure but completely blocked the rapid increase in pulmonary artery pressure produced by high doses of ET-1 (2,000 ng/kg) (23.0 +/- 10.8% versus -12.6 +/- 27.5%; p < 0.05). During mechanical ventilation there was no difference in the increase in mean pulmonary arterial pressure and pulmonary vascular resistance induced by alveolar hypoxia before and after BQ-123 (34.0 +/- 8.9% versus 30.5 +/- 10.9% and 25.3 +/- 11.6% versus 35.2 +/- 22.4%). This study suggests that the pulmonary vasoconstrictive effects of ET-1 are mediated by ETA receptors and that ET-1 does not mediate acute hypoxic pulmonary vasoconstriction in intact newborn lambs.

Topics: Acute Disease; Animals; Animals, Newborn; Endothelins; Hypoxia; Muscle Tonus; Peptides, Cyclic; Pulmonary Alveoli; Pulmonary Circulation; Receptors, Endothelin; Sheep; Vascular Resistance; Vasoconstriction

1. The role of endothelin-1 in mediating the phenomenon of hypoxic vasoconstriction was examined in canine, isolated pulmonary, circumflex coronary and femoral arterial rings. 2. In tissues with an intact endothelium, the exogenous application of endothelin-1 (0.1-300 nM) caused concentration-dependent increases in canine, isolated pulmonary artery tone. Endothelin-3 (1-300 nM) was approximately 30 fold less potent than endothelin-1 as a vasoconstrictor in this tissue. In contrast, the selective ETB-receptor agonist, sarafotoxin S6c (0.01-1 microM), failed to elicit vasoconstriction in this tissue. Thus, endothelin isopeptide-induced vasoconstriction of the canine isolated pulmonary artery is mediated exclusively by the ETA-receptor subtype. 3. The concentration-dependent increases in isometric tension induced by endothelin-1 (0.1-300 nM) were antagonized by the ETA-selective antagonist, BQ-123 (10 microM); this concentration of antagonist caused a shift to the right in the concentration-response curve for endothelin-1 of approximately two orders of magnitude. This concentration of BQ-123 did not unmask any ETB-receptor-mediated vasoconstriction since sarafotoxin S6c (0.01-1 microM) still failed to elicit contraction in the presence of this concentration of BQ-123. 4. The hypoxia-induced vasoconstriction of canine, isolated pulmonary, circumflex coronary and femoral arterial rings was unaffected by pretreatment with the endothelin receptor antagonist, BQ-123 (10 microM), a concentration shown previously to antagonize the contractile actions of exogenously applied endothelin-1 in the isolated pulmonary artery. 5. These results are the first to provide direct evidence showing that the endothelium-dependent vasoconstriction observed during acute periods of hypoxia in vitro is not mediated by an endothelin-related isopeptide.

Topics: Amino Acid Sequence; Animals; Blood Vessels; Dogs; Endothelins; Hypoxia; In Vitro Techniques; Male; Molecular Sequence Data; Peptides, Cyclic; Vasoconstriction