Biomedical subjects

J G Filep

Publications and source records attributed to J G Filep.

At least 37 records · Page 2Linked to original sources

PubMed1998

Analysis of effects of bosentan (Ro 47-0203), a nonpeptide endothelin ETA/ETB receptor antagonist, in the hind-limb vascular bed of the cat.

The effects of bosentan (Ro 47-0203), an endothelin A and B receptor antagonist, on responses to endothelin-1, sarafotoxin 6c, angiotensin II, and arginine vasopressin were investigated in the hind-limb vascular bed of the cat. Under constant-flow conditions, intraarterial injections of endothelin-1 and sarafotoxin 6c induced biphasic changes in hind-limb perfusion pressure characterized by an initial decrease followed by a secondary increase in perfusion pressure. The vasodilator and vasoconstrictor components of the biphasic responses to endothelin-1 and sarafotoxin 6c were reduced by bosentan, and the endothelin receptor antagonist reduced baseline systemic arterial and hind-limb perfusion pressures. Bosentan decreased vasoconstrictor responses to lower doses of angiotensin II, whereas responses to higher doses of angiotensin II and responses to vasopressin, U46619, BAY K8644, norepinephrine, acetylcholine, bradykinin, levcromakalim, PGE1, adrenomedullin, and calcitonin gene-related peptide were not altered. Vasoconstrictor responses to ET-1 were not altered by the angiotensin AT1 receptor antagonist DuP 532 or the AT2 receptor antagonist PD123,319. The results of the present study show that bosentan attenuates vasodilator and vasoconstrictor responses to endothelin-1 and sarafotoxin 6c and vasoconstrictor responses to lower doses of angiotensin II in the hind-limb vascular bed of the cat. These results suggest that endothelin may be involved in mediating responses to lower doses of angiotensin II and in the maintenance of baseline tone in the systemic vascular bed of the cat.

Angiotensin II↗

PubMed1997

Prevention of In vitro neutrophil adhesion to endothelial cells through shedding of L-selectin by C-reactive protein and peptides derived from C-reactive protein.

C-Reactive protein (CRP), the classic acute-phase reactant in humans, diminishes accumulation of neutrophils at inflammatory sites. To evaluate the underlying mechanisms, we have studied whether CRP and peptides derived from CRP could affect the first step of neutrophil extravasation, the L-selectin-mediated interaction of neutrophils with endothelial cells. CRP markedly attenuated attachment of human neutrophils to cultured LPS-activated human coronary artery and pulmonary microvascular endothelial cells with apparent IC50 values of 20 and 22 microg/ml, respectively. At similar concentrations, CRP rapidly downregulated the expression of L-selectin on the neutrophil surface, whereas it failed to affect expression of CD11b and CD45 or to induce granule enzyme release. The loss of L-selectin was due to cleavage and shedding of the molecule from the cell surface, as quantitated by the soluble form of L-selectin in cell-free supernatants. The effects of CRP could be prevented by an anti-CRP antiserum and by KD-IX-73-4, which inhibits shedding of L-selectin. Inhibition of adhesion with CRP was additive with function-blocking anti-E-selectin and anti-CD18 antibodies, but was not additive with anti-L-selectin antibody. Neutrophil attachment and L-selectin expression were also diminished by CRP peptides 174-185 and 201-206, but not peptide 77-82, albeit these peptides showed a weaker inhibitory effect than the parent protein. These studies indicate a specific activation-independent action of CRP and CRP peptides 174-185 and 201-206 on expression of L-selectin, and suggest that by attenuating neutrophil adhesion to the endothelium and consequently neutrophil traffic into tissues, native CRP and peptides 174-185 and 201-206 may be major mechanisms to attenuate or limit the inflammatory response.

C-Reactive Protein↗

PubMed1997

Glucocorticoid receptor regulates expression of L-selectin and CD11/CD18 on human neutrophils.

BACKGROUND: Recent studies have raised the hypothesis that glucocorticoids could diminish the ability of endothelial cells to direct leukocyte traffic into inflamed tissues by inhibiting expression of the adhesion molecules endothelial-leukocyte adhesion molecule-1 and intercellular adhesion molecule-1. The aim of the present study was to investigate whether glucocorticoids also regulate the expression of L-selectin and CD11/CD18 integrins on human neutrophil granulocytes. METHODS AND RESULTS: Incubation of human whole blood with platelet-activating factor (PAF, 1 mumol/L) evoked downregulation of L-selectin and upregulation of CD11/CD18 adhesion receptors on neutrophils as measured by flow cytometry. While dexamethasone (0.1 nmol/L to 100 mumol/L) did not affect expression of adhesion molecules on resting neutrophils, it attenuated the PAF-induced changes in L-selectin and CD18 expression in a time- and concentration-dependent fashion with IC50 values of 31 and 13 nmol/L, respectively. These effects of dexamethasone were completely aborted by RU-486 (10 mumol/L), which blocks transcriptional activation of the glucocorticoid receptor, and by the protein synthesis inhibitor cycloheximide (35.5 mumol/L). Dexamethasone, up to a concentration of 1 mumol/L, neither affected significantly the release of granule enzymes nor interfered with PAF binding to its membrane receptors. CONCLUSIONS: Our results show that glucocorticoids at clinically relevant concentrations exert specific actions on expression of adhesion molecules on activated neutrophils, which are mediated through ligation of glucocorticoid receptors and induction of protein synthesis, and suggest a novel mechanism by which anti-inflammatory corticosteroids may inhibit leukocyte accumulation.

CD11 Antigens↗

PubMed1997

Nitric oxide co-operates with hydrogen peroxide in inducing DNA fragmentation and cell lysis in murine lymphoma cells.

We examined whether NO and H2O2 could interact in inducing DNA fragmentation and cell death. H2O2 and the NO-releasing compounds sodium nitroprusside (SNP) and S-nitroso-N-acetyl-D,L-penicillamine (SNAP) by themselves elicited lysis of YAC-1 murine lymphoma cells in a concentration-dependent manner. Exposure of the cells to a combination of sublytic concentrations of SNP (0.78 mM) plus H2O2 (7.8 microM) or SNAP (0.18 mM) plus H2O2 (7.8 microM) resulted in cell death which is mediated, in part, through apoptosis. Evidence for this direction is provided by fluorescence microscopic evaluation of the cells, which revealed the presence of changes in nuclear morphology characteristic of apoptosis in 30-40% of lymphoma cells and by the specific pattern of internucleosomal DNA fragmentation detected by gel electrophoresis. The cytotoxic effect of SNP plus H2O2 could be effectively inhibited by either oxyhaemoglobin, which binds NO, or catalase, which eliminates H2O2. Partial protection from SNP-plus-H2O2-induced cell lysis was observed with the poly(ADP-ribose) polymerase inhibitors, nicotinamide and 3-aminobenzamide, parallelling their ability to reverse depletion of cellular NAD+ pools. These results indicate an interaction between NO and H2O2 which leads to a markedly enhanced cytotoxic activity, in part, via induction of apoptosis and suggest that poly(ADP-ribosylation) and subsequent NAD+ depletion mediate, at least in part, this cytotoxic activity.

Animals↗

PubMed1997

On the mechanisms of immunodominance in cytotoxic T lymphocyte responses to minor histocompatibility antigens.

Although there are numerous minor histocompatibility antigens (MiHA), T cell responses leading to graft-versus-host (GVH) and graft-versus-tumor effects involve only a small number of immunodominant MiHA. The goal of the present study was to analyze at the cellular and molecular levels the mechanisms responsible for MiHA immunodominance. Cytotoxic T lymphocytes (CTL) generated in eight combinations of H2b strains of mice were tested against syngeneic targets sensitized with HPLC-fractionated peptides eluted from immunizing cells. The number of dominant MiHA was found to range from as little as two up to ten depending on the strain combination used. The nature of dominant MiHA was influenced by both the antigen profile of the antigen-presenting cells (APC) and the repertoire of responding CTL. When C57BL/6 dominant MiHA (B6dom) and H-Y were presented on separate APC, they showed similar immunogenicity. In contrast, when they were presented on the same APC, B6dom MiHA totally dominated H-Y. B6dom MiHA did not suppress anti-H-Y responses by acting as T cell receptor antagonists for anti-H-Y CTL, nor were anti-B6dom CTL precursors more abundant than anti-H-Y CTL precursors. Dominance resulted from competition for the APC surface between anti-B6dom and anti-H-Y CTL; the crucial difference between the dominant and the dominated MiHA appears to depend on the differential avidity of their respective CTL for APC. The only B6dom epitope thus far identified is the nonapeptide AAPDNRETF presented by H2-D(b). We found that compared with other known D(b)-binding peptides, AAPDNRETF is expressed at very high levels on the cell surface, binds to the D(b) molecule with very high affinity, and dissociates very slowly from its presenting class I molecule. These data indicate that one cannot predict which MiHA will be dominant or dominated based simply on their respective immunogenicity when presented on separate APC. Indeed, the avidity of T cell/APC interactions appears to determine which antigen(s) will trigger T cell responses when numerous epitopes are presented by the same APC.

Animals↗

PubMed1997

Endogenous endothelin modulates blood pressure, plasma volume, and albumin escape after systemic nitric oxide blockade.

To assess whether acute nitric oxide (NO) blockade could unmask the vascular actions of endogenous endothelin, we tested the effects of the endothelin type A/type B (ET(A)/ET(B)) receptor antagonist bosentan and the selective ET(A) antagonist FR 139317 on blood pressure, plasma volume, and albumin escape after inhibition of NO synthesis with N(G)-nitro-L-arginine methyl ester (L-NAME). Conscious, chronically catheterized rats received L-NAME in the absence and presence of 17.4 micromol/kg (10 mg/kg) bosentan or 3.8 micromol/kg (2.5 mg/kg I.V., 10 minutes before L-NAME) FR 139317. Red blood cell volume and plasma volume were determined with chromium-51-tagged erythrocytes and iodine-125-labeled albumin, respectively. L-NAME (0.46 to 7.42 micromol/kg [0.125 to 2 mg/kg]) induced a dose-dependent increase in blood pressure, which was attenuated by 60% and 48% with bosentan and FR 139317, respectively (P<.01). L-NAME (7.42 micromol/kg) also increased hematocrit. This effect was associated with an increase in total-body albumin escape, which is reflected by a 14% reduction in plasma volume. Red blood cell volume remained unchanged. L-NAME promoted albumin escape primarily in the lung, heart, liver, kidney, and gastrointestinal tract. Both bosentan and FR 139317 markedly reduced these effects of L-NAME. Furthermore, L-NAME increased plasma levels of immunoreactive endothelin-1 from 8.6+/-0.4 (n=10) to 14.7+/-1.4 pg/mL (n=9, P<.01). These results demonstrate that the pressor response, losses in plasma volume, and increase in albumin escape observed after inhibition of NO synthesis are in part the consequence of unmasking the actions of endogenous endothelin, which are mediated predominantly via ET(A) receptors. These findings suggest a role for endogenous endothelin in the regulation of vascular functions in conditions when NO formation by endothelial cells is impaired.

Analysis of Variance↗

PubMed1997

Dual role for nitric oxide in the regulation of plasma volume and albumin escape during endotoxin shock in conscious rats.

To assess the role of nitric oxide (NO) produced by the constitutive (cNOS) and inducible NO synthase (iNOS) in the regulation of vascular functions, we compared the effects of aminoguanidine, a relatively selective inhibitor of iNOS, and NG-nitro-L-arginine methyl ester (L-NAME), a nonselective NOS inhibitor on blood pressure, plasma volume, and albumin escape during the early and delayed phases of endotoxin shock in conscious, chronically catheterized rats. Red blood cell volume and plasma volume were determined by using chromium-51-tagged erythrocytes and iodine-125-labeled albumin, respectively. Injection of lipopolysaccharide (LPS) 10 mg/kg i.v. resulted in a fall in blood pressure, hemoconcentration, and increased total-body albumin escape, which is reflected by a 25% reduction in plasma volume. When LPS was injected into animals pretreated with L-NAME (7.4 mumol/kg i.v. 15 minutes before LPS), losses in plasma volume and albumin escape were significantly greater than in rats that received LPS alone, despite that L-NAME attenuated the hypotensive action of LPS. Aminoguanidine pretreatment (162 mumol/kg) had no effect on the early responses to LPS, whereas it was as potent as L-NAME in reversing hypotension when injected 70 minutes after LPS. Aminoguanidine treatment also prevented further losses in plasma volume and markedly attenuated total-body and organ albumin escape rates elicited by LPS. L-NAME produced only a slight attenuation of LPS-induced losses in plasma volume and albumin escape in most organs studied, whereas it potentiated albumin extravasation in the lung. These results demonstrate that inhibition of cNOS potentiates, whereas inhibition of iNOS markedly attenuates, losses in plasma volume and albumin escape elicited by LPS, and suggest that selective inhibitors of iNOS may be more effective than nonselective inhibitors of all forms of NOS in the therapy of septic shock.

Animals↗

PubMed1996

Identification of an immunodominant mouse minor histocompatibility antigen (MiHA). T cell response to a single dominant MiHA causes graft-versus-host disease.

T cell responses to non-MHC antigens are targeted to a restricted number of immunodominant minor histocompatibility antigens whose identity remains elusive. Here we report isolation and sequencing of a novel immunodominant minor histocompatibility antigen presented by H-2Db on the surface of C57BL/6 mouse cells. This nonapeptide (AAPDNRETF) shows strong biologic activity in cytotoxic T lymphocyte sensitization assays at concentrations as low as 10 pM. C3H.SW mice primed with AAPDNRETF in incomplete Freund's adjuvant generated a potent anti-C57BL/6 T cell-mediated cytotoxic activity, and T lymphocytes from AAPDNRETF-primed mice caused graft-versus-host disease when transplanted in irradiated C57BL/6 recipients. These results (a) provide molecular characterization of a mouse dominant minor histocompatibility antigen, (b) identify this peptide as a potential target of graft-versus-host disease and, (c) more importantly, demonstrate that a single dominant minor antigen can cause graft-versus-host disease. These findings open new avenues for the prevention of graft-versus-host disease and should further our understanding of the mechanisms of immunodominance in T cell responses to minor histocompatibility antigens.

Amino Acid Sequence↗

PubMed1996

Involvement of nitric oxide in target-cell lysis and DNA fragmentation induced by murine natural killer cells.

Although it has been recognized for sometime that target cells destroyed by natural killer (NK) cells die largely by apoptosis, the underlying mechanisms are not fully understood. The aim of the present study was to examine the role of nitric oxide (NO) in mediating murine NK-cell-induced killing of YAC-1 lymphoma cells. NK calls induced extensive release of 125I-DNA and 51Cr from YAC-1 cells. The target killing ability of NK cells was associated with an increased production of NO as measured by concentrations of nitrite in the culture medium. That YAC-1 killing resulted, in part, from the production of NO was confirmed by the significant protection of cell lysis in L-arginine-depleted medium and by approximately 30 % attenuation of cell lysis and DNA fragmentation by an inhibitor of NO synthase, NG-nitro-L-arginine methyl ester (L-NAME) in a culture medium containing 1 mmol/L L-arginine. Fluorescence microscopic examination of YAC-1 cells showed the presence of changes in nuclear morphology characteristic for apoptosis. The percentage of apoptotic cells was markedly decreased by L-NAME. Further evidence for apoptosis is provided by the specific pattern of internucleosomal DNA fragmentation both in the absence and presence of L-NAME. During target-cell killing, an increased oxidation of intracellularly trapped dichlorofluorescein was observed in cells labeled with an antimouse NK-cell monoclonal antibody, as measured by flow cytometry. These increases were effectively prevented by L-NAME, but not W-13, an inhibitor of calmodulin. The ability of NO to induce cell lysis and DNA fragmentation in YAC-1 cells was further demonstrated by exposing tumor cells to chemically generated NO. Taken together, these observations suggest a role for NO as one of the mediators of NK-cell-mediated DNA fragmentation and cell lysis.

Animals↗

PubMed1996

Effects of calcium antagonists on endothelin-1-induced myocardial ischaemia and oedema in the rat.

1. The effects of the calcium channel blockers, verapamil and nifedipine on myocardial ischaemia and oedema evoked by endothelin-1 (ET-1) or IRL 1620, an ETB receptor-selective agonist were studied in anaesthetized and conscious rats. 2. Bolus injection of ET-1 (1 nmol kg-1, i.v.) or IRL 1620 (1 nmol kg-1, i.v.) to conscious chronically catheterized rats evoked a transient depressor response followed by a prolonged pressor effect. Corresponding to changes in blood pressure, a transient tachycardia and a sustained bradycardia were observed. Pretreatment of the animals with verapamil (1 mg kg-1, i.v.) or nifedipine (200 micrograms kg-1, i.v.) produced on average 5 mmHg decrease in mean arterial blood pressure. Both verapamil and nifedipine inhibited by 63 and 44% the pressor actions of ET-1 or IRL 1620 (1 nmol kg-1), respectively, and the accompanying bradycardia. Both verapamil and nifedipine potentiated the magnitude of the depressor action of ET-1 and IRL 1620 without affecting the accompanying tachycardia. Decreasing mean arterial blood pressure with hydralazine (0.2 - 0.3 micromol kg-1, i.v.) to levels comparable to those observed after verapamil or nifedipine had no significant effects on the haemodynamic responses to ET-1 or IRL-1620. 3. Intravenous bolus injection of ET-1 or IRL 1620 (0.1-2 nmol kg-1) into anaesthetized rats produced dose-dependent ST segment elevation of the electrocardiogram without causing arrhythmias. ST segment elevation developed within 30-50s and persisted for at least 10-20 min following injection of the peptides. 4. Pretreatment of the animals with verapamil (1 mg kg-1, i.v.) or nifedipine (200 micrograms kg-1, i.v.) inhibited on average by 79 and 76% the ST segment elevation elicited by ET-1 (1 nmol kg-1), respectively. Verapamil and nifedipine also attenuated IRL 1620 (1 nmol kg-1)-induced ST segment elevation on average by 71 and 74%, respectively. In contrast, no significant inhibition was observed with hydralazine (0.2-0.3 mumol kg-1). 5. Both ET-1 and, to a lesser extent, IRL 1620 (0.1-2 nmol kg-1) evoked albumin accumulation in cardiac tissues in a dose-dependent fashion as measured by the local extravascular accumulation of Evans blue dye in conscious rats. ET-1 and IRL 1620 (1 nmol kg-1) enhanced albumin extravasation by 109 and 82%, and 34 and 44% in the left ventricle and right atrium, respectively. ET-1 or IRL 1620-induced albumin extravasation was completely prevented by verapamil (1 mg kg-1) or nifedipine (200 micrograms kg-1) in these vascular beds. In contrast, hydralazine (0.2-0.3 mumol kg-1) failed to modify the effects of ET-1 or IRL 1620 on albumin extravasation. 6. These results show that verapamil and nifedipine are highly effective in protecting the myocardium against the pro-ischaemic and microvascular permeability enhancing effects of ET-1 and suggest that ETA and constrictor ETB (tentatively termed ETB2) receptors mediating these actions of ET-1 are coupled to calcium influx through dihydropyridine-sensitive calcium channels.

Albumins↗

PubMed1995

Plasma endothelin correlates with antiendothelial antibodies in patients with mixed connective tissue disease.

BACKGROUND: Elevated circulating levels of the vasoactive peptide endothelin-1 have been reported in various cardiovascular disorders. Because these conditions are frequently associated with endothelial dysfunction and damage and the vasoconstrictor effect of endothelin-1 is believed to be produced at the local vascular level, it is uncertain whether circulating endothelin-1 is a causal factor in enhanced vascular tone or instead a marker of endothelial injury. METHODS AND RESULTS: We tested whether elevated immunoreactive endothelin-1 could be detected by radioimmunoassay in plasma and whether endothelin-1 levels correlated with antiendothelial autoantibodies in patients with mixed connective tissue disease. Venous blood samples were collected from 21 patients in the morning after an overnight fast and before medication. The plasma immunoreactive endothelin-1 level was 2.7 +/- 0.5 pg/mL (range, 1.1 to 5.2 pg/ml; n = 9) and 7.3 +/- 1.5 pg/mL (range, 2.8 to 20.7 pg/mL; n = 12) in patients who had no antiendothelial antibodies and in patients with antiendothelial antibodies, respectively. These latter values were significantly (P < .001) increased compared with 10 age-matched healthy volunteers (2.0 +/- 0.3 pg/mL; range, 0.5 to 3.0 pg/mL). Plasma endothelin-1 level strongly correlated with antiendothelial antibodies (rs = .836, n = 21, P < .001), whereas there was no correlation between age, systolic and diastolic blood pressures, antinuclear antibodies, and duration of the disease and endothelin-1 values. The incidence of Raynaud's phenomenon and angina did not differ significantly in patients with low and high endothelin-1 levels. CONCLUSIONS: This study showed that mixed connective tissue disease is associated with elevated plasma immunoreactive endothelin-1 and that endothelin-1 levels significantly correlate with antiendothelial autoantibodies. These findings suggest that increases in plasma endothelin-1 concentration may be secondary to vascular injury and do not necessarily represent enhanced susceptibility to vasoconstriction.

Adult↗

PubMed1995

Acute pro-inflammatory actions of endothelin-1 in the guinea-pig lung: involvement of ETA and ETB receptors.

1. Although recent observations suggest that endothelin-1 (ET-1) may play a role in the pathogenesis of asthma, to date little is known about the effects of ET-1 on parameters other than bronchoconstriction. The objectives of the present experiments were to study whether intravenously administered ET-1 could exert pro-inflammatory actions in the guinea-pig lung and to assess the involvement of endothelin ETA and ETB receptors in these events by using the ETA receptor-selective antagonist, FR 139317, the novel ETA/ETB receptor antagonist, bosentan and the ETB receptor-selective agonist, IRL 1620. 2. Bolus i.v. injection of ET-1 (0.1-1 nmol kg-1) to anaesthetized guinea-pigs evoked dose-dependent increases in mean arterial blood pressure which lasted for 6-12 min. This was accompanied by a dose-dependent haemoconcentration (8-15% plasma volume losses) and increases (up to 546%) in albumin extravasation in the trachea, upper and lower bronchi, but not in the pulmonary parenchyma. Qualitatively similar changes were observed following i.v. injection of the ETB receptor agonist, IRL 1620 (0.3 and 1 nmol kg-1), although IRL 1620 appeared to be about 3 times less potent than ET-1. The ETA receptor-selective antagonist, FR 139317 (2.5 mg kg-1) inhibited the ET-1 (1 nmol kg-1)-induced pressor response, haemoconcentration and albumin extravasation by 75, 77 and 60-70%, respectively, whereas it did not attenuate IRL 1620 (1 nmol kg-1)-induced changes. The ETA/ETB receptor antagonist, bosentan (10 mg kg-1) almost completely inhibited the pressor, haemoconcentration and permeability effects of both ET-1 and IRL 1620. 3. ET-1, but not IRL 1620 (0.1-1 nmol kg-1), produced a dose-dependent neutropenia with relative lymphocytosis and monocytosis, but did not induce influx of neutrophil granulocytes into pulmonary tissues or the bronchoalveolar space. ET-1 (1 nmol kg-1)-induced neutropenia was prevented by pretreatment of the animals with FR 139317 (2.5 mg kg-1), bosentan (10 mg kg-1) or adrenaline (90 nmol kg-1), indicating that ET-1 caused intravascular sequestration of neutrophil granulocytes. 4. ET-1 or IRL 1620 (10(-10)-10(-6) M) alone did not activate alveolar macrophages in vitro, whereas at a concentration of 10(-8) M, ET-1, but not IRL 1620, markedly potentiated superoxide production in response to f-Met-Leu-Phe (10(-9)-10(-7) M) and platelet-activating factor (PAF, 10(-9)-10(-7) M), but not to phorbol 12-myristate 13-acetate (10(-9) M). ET-1 did not affect f-Met-Leu-Phe- or PAF-induced increases in intracellular free calcium concentration. This potentiating effect of ET-1 was abolished by FR 139317(1.5 X 10-7 M).5. We conclude that, in addition to evoking airway contractions, ET-1 exerts pro-inflammatory actions via activation of the ETA and to a lesser extent the ETB receptors, and therefore, might contribute to the airway inflammation present in asthma. These findings also suggest the therapeutic potential of ETA/ETB receptor and perhaps ETA receptor-selective antagonists in this disease.

Animals↗

PubMed1995

Effects of the ETA/ETB receptor antagonist, bosentan on endothelin-1-induced myocardial ischaemia and oedema in the rat.

1. The purpose of this study were to assess the role of ETB receptors in mediating endothelin-1 (ET-1)-induced myocardial ischaemia and oedema in rats and to study the inhibitory action of the novel nonpeptide ETA/ETB receptor antagonist, bosentan on these actions of ET-1. 2. Intravenous bolus injection of ET-1 (1 nmol kg-1) into anaesthetized rats produced marked ST segment elevation of the electrocardiogram without causing arrhythmias. ST segment elevation developed within 30-50 s and persisted for at least 30 min following injection of the peptide. 3. Pretreatment of the animals with bosentan (10 mg kg-1, i.v.) inhibited on average by 96% the ST segment elevation elicited by ET-1 (1 nmol kg-1) compared to the 82% inhibition observed with the ETA receptor-selective antagonist, FR 139317 (2.5 mg kg-1, i.v.). 4. Bolus injection of ET-1 (1 nmol kg-1, i.v.) to conscious chronically catheterized rats evoked a transient depressor response followed by a prolonged pressor effect. Corresponding to changes in blood pressure, a transient tachycardia and a sustained bradycardia were observed. ET-1 (1 nmol kg-1) enhanced albumin extravasation by 119 and 93% in the left ventricle and right atrium, respectively, as measured by the local extravascular accumulation of Evans blue dye. 5. Pretreatment of the animals with bosentan (10 mg kg-1) inhibited by 71 and 90% the depressor and pressor actions of ET-1 (1 nmol kg-1) and the accompanying tachycardia and bradycardia, respectively. FR 139317 (2.5 mg kg-1) attenuated the pressor response to ET-1 and accompanying bradycardia by 75%, without affecting the depressor action and accompanying tachycardia. ET-1-induced albumin extravasation was completely inhibited by bosentan (10 mg kg-1) both in the left ventricle and right atrium, compared to the 86% inhibition observed with FR 139317 (2.5 mg kg-1).6. Like ET-1, the ETB receptor-selective agonist, IRL 1620 (0.3 and 1 nmol kg-1, i.v.) also produced dose-dependent ST segment elevation in anaesthetized rats and enhanced albumin extravasation (up to141% of control) in the left ventricle and right atrium, respectively, in conscious rats. These effects ofIRL 1620 were completely prevented by bosentan (10 mg kg-1).7. These results indicate that ETB receptors, albeit to a lesser extent than ETA receptors, are also involved in mediating ET-1-induced myocardial ischaemia and oedema in the rat, and suggest the therapeutic potential for bosentan in the treatment of ischaemic myocardial diseases.

Animals↗

PubMed1994

Pulmonary surfactant lipids inhibit prostanoid production of guinea pig alveolar macrophages.

Changes in the amount and composition of pulmonary surfactant are important features of the adult respiratory distress syndrome. The goal of the present study was to investigate the effects of natural surfactant material and several of its lipid components on prostanoid production and superoxide generation by guinea pig alveolar macrophages. Natural surfactant (10-500 micrograms/ml) inhibited (up to 65%) prostaglandin E2 (PGE2) and thromboxane B2 (TxB2) production elicited by platelet-activating factor (PAF, 10(-6) M) and arachidonic acid (5 x 10(-6) M) but not fMet-Leu-Phe (10(-7) M). Dioleyl-phosphatidylglycerol (diOPG, 1-100 micrograms/ml) and dioleyl-phosphatidylcholine (diOPC, 1-100 micrograms/ml) prevented fMet-Leu-Phe- and PAF-stimulated prostanoid release in a concentration-dependent fashion with a maximal inhibition of 94%. DiOPC (100 microgram/ml) also inhibited arachidonic acid induced PGE2 production by 67%. Phosphatidylcholine (100 micrograms/ml) and sphingomyelin (10-100 micrograms/ml) significantly attenuated TxB2 production elicited by arachidonic acid. Neither PAF- nor fMet-Leu-Phe-stimulated superoxide production was affected significantly by natural surfactant and its lipid components with the exception of phosphatidylcholine. At a concentration of 100 micrograms/ml, phosphatidylcholine decreased superoxide production by about 57% in response to PAF. These results show that diOPC and diOPG are capable of inhibiting prostanoid production of guinea pig alveolar macrophages in response to inflammatory stimuli and suggest that a decrease in the diOPG and diOPC content of surfactant would lead to enhanced intrapulmonary formation of prostanoids and consequently to the deterioration of pulmonary function in the adult respiratory distress syndrome.

Animals↗

PubMed1994

Endothelin-1-induced myocardial ischaemia and oedema in the rat: involvement of the ETA receptor, platelet-activating factor and thromboxane A2.

1. The objectives of the present experiments were to assess the role of ETA receptors in mediating endothelin-1 (ET-1)-induced myocardial ischaemia and oedema and to study the involvement of platelet-activating factor (PAF) and thromboxane A2 (TxA2) in these actions of ET-1 in rats. 2. Intravenous bolus injection of ET-1 (0.1-2 nmol kg-1) into anaesthetized rats induced ST segment elevation of the electrocardiogram in a dose-dependent manner without causing arrhythmias. ST segment elevation developed within 20-90 s and persisted for at least 10-20 min following administration of ET-1. 3. Pretreatment of the animals with the selective endothelin ETA receptor antagonist, FR 139317 (2.5 mg kg-1, i.v.) inhibited by 86% the ST segment elevation elicited by ET-1 (1 nmol kg-1). Pretreatment with intravenous administration of BM 13505 (1 mg kg-1), a TxA2 receptor antagonist, OKY-046 (10 mg kg-1), a thromboxane synthase inhibitor or the specific PAF receptor antagonist, WEB 2086 (1 mg kg-1) or BN 52021 (10 mg kg-1) markedly suppressed ST segment elevation in response to ET-1. Infusion of indomethacin (3 mg kg-1 bolus plus 2 mg kg-1 h-1) did not significantly affect ET-1-induced ST segment elevation. 4. Bolus injection of ET-1 (1 nmol kg-1, i.v.) to conscious rats resulted in a prolonged pressor effect preceded by a transient depressor response. Corresponding to changes in blood pressure, a small transient tachycardia was followed by a sustained bradycardia. ET-l enhanced albumin leakage by 87 and 120% in the left ventricle and right atrium, respectively, as measured by the extravasation of Evans blue dye.5. The selective ETA receptor antagonist, FR 139317 (2.5 mg kg-1) significantly blunted the pressor action of ET-1 and the accompanying bradycardia without affecting the depressor response. Furthermore,FR 139317 almost completely abolished the permeability effect of ET-l in both vascular beds studied.6. Pretreatment of the animals with BM 13505 (1 mg kg-1), OKY-046 (10mg kg-1), WEB 2086(1 mg kg-1) or BN 52021 (10mg kg-1) significantly reduced ET-1 (1 nmol kg-1)-induced albumin extravasation both in the left ventricle and right atrium. The PAF receptor antagonists, WEB 2086 and BN 52021 were equally potent inhibitors in the left ventricle, whereas BN 52021 appeared to be a more potent inhibitor than WEB 2086 in the right atrium. Pretreatment with indomethacin (3 mg kg-1 plus 2 mg kg-1 h-1) did not modify the permeability response to ET-1. None of these compounds affected significantly ET-l-induced changes in mean arterial blood pressure and heart rate.7. These results indicate that intravenous administration of ET-1 provokes ST segment elevation and myocardial oedema and suggest that these events are mediated, in part, through release of secondary mediators, such as PAF and TxA2 via the activation of ETA receptors.

Anesthesia↗

PubMed1994

Characterization of receptors mediating vascular responses to endothelin-1 in the conscious rat.

1. The present study has determined the receptors mediating the vascular responses (pressor and depressor actions and vascular permeability effect) to endothelin-1 (ET-1) in the conscious rat by using the novel non-peptide ETA/ETB receptor antagonist, bosentan (Ro 47-0203, 4-tert-butyl-N-[6-(2 hydroxyethoxy)-5-(2-methoxy-phenoxy)-2,2'-bipyrimidine- 4-yl]benzene-sulphonamide), the ETA receptor-selective antagonist, FR 139317 and the ETB receptor-selective peptide agonist, IRL 1620. 2. Bolus injection of ET-1 (1 nmol kg-1, i.v.) resulted in a prolonged pressor effect (maximum increase in mean arterial blood pressure (MABP) was 47 +/- 3 mmHg, n = 6) preceded by a transient depressor response (maximum decrease in MABP was 17 +/- 1 mmHg). Both these responses were inhibited by bosentan (1-20 mg kg-1, i.v. bolus) in a dose-dependent manner. The maximum inhibition of ET-induced depressor and pressor responses did not exceed 53 and 87%, respectively. FR 139317 (2.5 mg kg-1, i.v.) attenuated the pressor response to ET-1 by 75% without affecting the depressor response. Furthermore, FR 139317, but not bosentan, prolonged the depressor action of ET-1. Corresponding to changes in blood pressure, a small transient tachycardia (delta heart rate 15 +/- 5 beats min-1) followed by a sustained bradycardia (delta heart rate -48 +/- 10 beats min-1, n = 6) was observed following injection of 1 nmol kg-1 ET-1. FR 139317 and bosentan (10 mg kg-1) inhibited ET-1-induced bradycardia by 79% and 71%, respectively.ET-l-induced tachycardia was significantly attenuated by bosentan,but not FR 139317.3. The ETB receptor agonist, IRL 1620 (0.1-2 micro molkg-1, i.v.) produced biphasic dose-dependent changes in MABP with an initial transient fall followed by a prolonged pressor action. The maximum decrease and increase in MABP were 11 +/- 2 and 19 +/- 3 mmHg, respectively (n = 5). These changes in MABP were accompanied by a transient tachycardia (Delta heart rate 9+/- 3 beats min-1) and prolonged bradycardia (Delta heart rate -17+/-11 beats min-1), respectively. Pretreatment of the animals with FR139317 (2.5 mg kg-1, i.v.) did not affect IRL 1620 (1 nmol kg-1)-induced changes in MABP and heart rate, whereas both the depressor and pressor actions of IRL 1620 and the accompanying tachycardia and bradycardia were almost completely inhibited by bosentan (10mgkg-1).4. ET-1 (1 nmol kg-1) enhanced albumin extravasation in the upper and lower bronchi, spleen, kidney,stomach and duodenum (up to 246%) as measured by the extravasation of Evans blue dye. FR 139317(2.5mgkg-1) completely inhibited ET-l-induced protein extravasation in the stomach and duodenum,whereas 40-75% inhibition was observed in the other vascular beds studied. The permeability effect of ET-l was almost completely inhibited by bosentan (10mgkg-1) in all vascular beds studied.5. IRL 1620 (0.4 or 1 nmol kg-1, i.v.) enhanced albumin extravasation (up to 219%) in the upper and lower bronchi, spleen and kidney in a dose-dependent manner. Unlike ET-1, IRL 1620 failed to increase albumin extravasation in the stomach and duodenum.6. The present study demonstrates in the conscious rat that ETA and ETB receptors are responsible for mediating the majority of the pressor response to ET-l and suggest that a small component of the ET-l pressor response might be mediated via a non-ETA, non-ETB receptor, whereas ETB and perhaps a non-ETA, non-ETB receptor may mediate the depressor action of ET-1. Furthermore, the ET-1 induced albumin extravasation is mediated solely via ETA receptors in the stomach and duodenum, whereas both ETA and ETB receptors are involved in the permeability effect of ET-l in the bronchial, splenic and renal vascular beds.

Animals↗

PubMed1993

Relaxation by dexamethasone of isolated guinea-pig airways precontracted with endothelin-1.

Dexamethasone (1-100 microM) produced concentration-dependent relaxations of isolated guinea-pig tracheal and bronchial strips precontracted with endothelin-1 (100 nM), which were not affected by the removal of the epithelium. Dexamethasone neither induced relaxation of tissues precontracted with carbachol (0.1 microM) or KCl (25 mM) nor inhibition of endothelin-1 (1-100 nM)-induced peak contractions after 10-min preincubation of the tissues with dexamethasone. These findings indicate that acute corticosteroid treatment can reverse the bronchoconstrictor action of endothelin-1.

Animals↗

PubMed1993

Increased plasma levels of endothelin during anaphylactic shock in the guinea-pig.

Intravenous injection of ovalbumin into actively and passively sensitized guinea-pig resulted in acute circulatory collapse. The plasma level of immunoreactive endothelin rose from 22 +/- 2 to 40 +/- 7 fmol/ml (n = 12, P < 0.01) and 29 +/- 5 fmol/ml (n = 12, P < 0.01) in actively and passively sensitized animals, respectively, within 5 min of antigen challenge, and it remained significantly higher in actively sensitized animals that survived for 15 min. The plasma immunoreactive endothelin level was inversely correlated with arterial blood pO2, but not with pH or pCO2, both in actively (rs = -0.585, n = 20, P < 0.05) and passively sensitized animals (rs = -0.558, n = 20, P < 0.05). When non-sensitized animals were bled (5 and 20 ml/kg body weight), the plasma immunoreactive endothelin level remained unchanged. These results suggest that the elevated plasma level of immunoreactive endothelin during anaphylactic shock is independent of hypotension, hypovolemia and respiratory insufficiency.

Anaphylaxis↗