RESUMEN
OBJECTIVE: To determine the content of bradykinin (BK) and markers of cartilage degradation and inflammation in the synovial fluid (SF) of patients with knee osteoarthritis (OA), and to evaluate correlations with biomarkers or clinical parameters. METHODS: SFs were obtained from 30 patients with knee OA. Levels of basal and generated BK, cartilage oligomeric matrix protein (COMP), interleukin (IL) 1, IL-6, IL-8 and matrix metalloprotease (MMP) 1, MMP-3, MMP-13 and sulfated glycosaminoglycans (GAGs) were measured by enzyme-linked immunosorbent assay (ELISA) or colorimetric assays. RESULTS: The mean concentration of basal BK (in the presence of peptidase and protease inhibitors to avoid degradation and de novo formation of BK) was 422 pg/ml (95% confidence interval, CI, 281-563) whereas that of in vitro generated BK (in the presence of peptidase inhibitors SFs were incubated 60 min at 37°C to measure the potential capability to generate BK) was 3427 pg/ml (2591-4264). The content of MMP-13, IL-1α, and IL-1ß was under assay sensitivity. Basal BK levels positively correlated (Spearman's rank correlation) with GAGs (40 µg/ml, 26-54, r = 0.4834, P = 0.0308) and IL-6 (553 pg/ml, 171-935, r = 0.3946, P = 0.0377) similarly to the generated BK (GAGs, r = 0.4563, P = 0.0431; IL-6, r = 0.5605, P = 0.0019). Statistical analysis of basal BK and biomarkers was significant (P = 0.0483). When applying a stepwise logistic regression analysis considering biomarkers together with clinical parameters, results indicated that K/L radiographic OA grade and COMP improved the model (P = 0.0032). CONCLUSION: The presence of BK in the knee OA SF and its correlations with cartilage degradation and inflammation markers of OA support its participation in OA pathology.
Asunto(s)
Bradiquinina/metabolismo , Osteoartritis de la Rodilla/metabolismo , Líquido Sinovial/metabolismo , Anciano , Anciano de 80 o más Años , Biomarcadores/metabolismo , Femenino , Humanos , Interleucina-6/metabolismo , Masculino , Persona de Mediana Edad , Osteoartritis de la Rodilla/complicaciones , Osteoartritis de la Rodilla/diagnóstico por imagen , Dolor/etiología , Dimensión del Dolor/métodos , Radiografía , Índice de Severidad de la EnfermedadRESUMEN
This study investigates the effect of the selective and potent B(2) receptor antagonist fasitibant (MEN16132) on the proinflammatory effect of bradykinin (BK) and its interaction with interleukin 1ß (IL-1ß) in human synoviocytes. PGE(2) content was detected in the surnatants and COX-2 and COX-1 gene and protein expression determined in the cells. Radioligand binding ([(3) H]BK) and BK-induced inositolphosphate experiments were performed. Incubation of synoviocytes with BK induced a sustained production of PGE(2) and transient COX-2 gene expression that were prevented by pretreatment with fasitibant (1 µM, 30 min preincubation). IL-1ß increased PGE(2) release and COX-2 expression more than BK alone. The combined treatment of cells with BK and IL-1ß induced an even increase of released PGE(2) and COX-2 gene and protein expression indicating a synergistic rather than an additive effect, not related to an increase of B(2) receptors density or its coupling. These potentiating effects of BK on PGE(2) production and increased COX-2 expression produced by IL-1ß were B(2)-receptor-mediated as fasitibant could prevent them. None of the treatments induced changes in the COX-1 expression. The synergistic PGE(2) production was abolished by the specific NF-kappaB inhibitor (BAY-117085), whereas specific inhibitors for the p38 (SB203580), JNK (SP600125), and ERK1/2 (PD98059) mitogen-activated protein kinases could prevent the prostanoid release. BK can potentiate the COX-2 gene expression and consequent prostanoid production induced by IL-1ß. The prevention of this synergism by fasitibant indicates BK B(2) receptor blockade as an alternative symptomatic therapy for osteoarthritis.
Asunto(s)
Antagonistas del Receptor de Bradiquinina B2 , Bradiquinina/antagonistas & inhibidores , Ciclooxigenasa 2/biosíntesis , Dinoprostona/metabolismo , Fibroblastos/metabolismo , Interleucina-1beta/antagonistas & inhibidores , Ornitina/análogos & derivados , Sulfonamidas/farmacología , Líquido Sinovial/metabolismo , Western Blotting , Bradiquinina/farmacología , ADN Complementario/biosíntesis , ADN Complementario/genética , Inhibidores Enzimáticos/farmacología , Fibroblastos/efectos de los fármacos , Gliceraldehído-3-Fosfato Deshidrogenasas/metabolismo , Humanos , Interleucina-1beta/farmacología , Ornitina/farmacología , ARN/biosíntesis , ARN/aislamiento & purificación , Ensayo de Unión Radioligante , Reacción en Cadena en Tiempo Real de la Polimerasa , Líquido Sinovial/citología , Líquido Sinovial/efectos de los fármacosRESUMEN
BACKGROUND AND PURPOSE: Icatibant is a well-known kinin B2 receptor antagonist currently used for angiooedema attacks. MEN16132 is a non-peptide B2 receptor antagonist, more potent and long lasting than icatibant in different models. Here we studied the reasons for these differences between the two antagonists. EXPERIMENTAL APPROACH: Rate of reversibility (over about 3 h) of the functional receptor blockade exerted by the antagonists was compared (inositol phosphates accumulation assay) in CHO cells expressing the human B2 receptor and in human synovial cells. Antagonist pretreated cells were washed with medium and the time taken to restore bradykinin (BK) response measured. Antagonist affinity was measured by radioligand binding to wild type and mutated B2 receptors. KEY RESULTS: Recovery of BK-induced responses was slower in cells pretreated with MEN16132 than in those treated with icatibant. The affinity of icatibant (for the [³H]-BK or the B2 receptor antagonist [³H]-MEN11270 binding site) was compared to that of MEN16132 using a panel of point-mutated receptors with mutations located at the transmembrane regions of the B2 receptor, previously shown to decrease MEN16132 high affinity interaction. No consistent decrease of icatibant affinity was observed. From the different affinity of MEN16132 derivatives at wild type and W86A (transmembrane 2 region) receptors, and by evaluating its antagonist profile at the D266A/D284A double mutant receptor, a model of the MEN16132-B2 receptor complex is proposed. CONCLUSIONS AND IMPLICATIONS: MEN16132 dissociated from the B2 receptor compartment more slowly than icatibant and interacted at a deeper level in transmembrane regions of the receptor.
Asunto(s)
Antagonistas del Receptor de Bradiquinina B2 , Bradiquinina/análogos & derivados , Ornitina/análogos & derivados , Sulfonamidas/farmacología , Sustitución de Aminoácidos , Animales , Sitios de Unión , Bradiquinina/metabolismo , Bradiquinina/farmacología , Células CHO , Cricetinae , Cricetulus , Humanos , Técnicas In Vitro , Cinética , Modelos Moleculares , Mutagénesis Sitio-Dirigida , Proteínas Mutantes/antagonistas & inhibidores , Proteínas Mutantes/química , Proteínas Mutantes/genética , Proteínas Mutantes/metabolismo , Oligopéptidos/metabolismo , Oligopéptidos/farmacología , Ornitina/química , Ornitina/metabolismo , Ornitina/farmacología , Péptidos Cíclicos/metabolismo , Péptidos Cíclicos/farmacología , Receptor de Bradiquinina B2/química , Receptor de Bradiquinina B2/genética , Receptor de Bradiquinina B2/metabolismo , Proteínas Recombinantes/antagonistas & inhibidores , Proteínas Recombinantes/química , Proteínas Recombinantes/genética , Proteínas Recombinantes/metabolismo , Sulfonamidas/química , Sulfonamidas/metabolismoRESUMEN
BACKGROUND AND PURPOSE: In osteoarthritis (OA), bradykinin (BK) is known to contribute to pain and synovitis, but not to cartilage degradation. Here, we investigated effects of BK and its antagonists on chondrocytes, cells involved in cartilage homeostasis. EXPERIMENTAL APPROACH: BK receptor density and affinities of BK, its analogues and antagonists were measured in cultured human and rat chondrocytes by radioligand binding. Effects of BK were assessed by accumulation of inositol phosphates (IP) and release of interleukin (IL)-6 and IL-8. KEY RESULTS: Density of [³H]-BK binding sites was higher (13-30-fold) and BK evoked a greater (48-fold) IP production, in human than in rat chondrocytes. The BK B2 receptor antagonists MEN16132 and icatibant displayed similar binding affinity. MEN16132 was 40-fold more potent than icatibant in the IP assay. In human chondrocytes, BK increased release (over 24 h) of IL-6 and IL-8, effects blocked by MEN16132 but not by the B1 receptor antagonist Lys-[Leu8][desArg9]BK. BK-induced release of IL-6, but not of IL-8, was partially inhibited by indomethacin (10 µM) and nordihydroguaiaretic acid (10 µM). Antagonists for the prostanoid EP receptors (AH6809 10 µM; L-798,196, 200 nM; L-161,982, 1 µM) were ineffective. Dexamethasone (100 nM) partially inhibited release of both IL-6 and IL-8. Inhibitors of intracellular downstream signalling pathways (SB203580 10 µM; PD98059, 30 µM; SP600125, 30 µM; BAY-117085, 5 µM) indicated the involvement of p38 MAPK and the activation of NF-κB. CONCLUSION AND IMPLICATIONS: BK mediated inflammatory changes and cartilage degradation and B2 receptor blockade would, therefore, be a potential treatment for OA.
Asunto(s)
Antagonistas del Receptor de Bradiquinina B2 , Bradiquinina/metabolismo , Bradiquinina/farmacología , Cartílago Articular/efectos de los fármacos , Condrocitos/efectos de los fármacos , Animales , Bradiquinina/análogos & derivados , Cartílago Articular/citología , Cartílago Articular/metabolismo , Células Cultivadas , Condrocitos/metabolismo , Humanos , Fosfatos de Inositol/análisis , Fosfatos de Inositol/metabolismo , Interleucina-6/metabolismo , Interleucina-8/metabolismo , Rodilla , Ornitina/análogos & derivados , Ornitina/metabolismo , Ornitina/farmacología , Ensayo de Unión Radioligante , Ratas , Ratas Sprague-Dawley , Receptor de Bradiquinina B2/metabolismo , Sulfonamidas/metabolismo , Sulfonamidas/farmacologíaRESUMEN
BACKGROUND AND PURPOSE: Bradykinin (BK) and B2 receptors have been implicated in the pathophysiology of osteoarthritis (OA), and synovitis is one of its hallmarks. Here, the selective B2 receptor antagonists MEN16132 and icatibant have been pharmacologically characterized in human synovial cells. EXPERIMENTAL APPROACH: Radioligand and functional studies (inositol phosphate (IP) accumulation, interleukin (IL)-6 and IL-8 release) were performed in cultured synoviocytes. KEY RESULTS: [3H]-BK saturation studies indicated receptor density (Bmax) and K(d) values of 121,550 sites per cell and 1.14 nM respectively. In synoviocytes, MEN16132 (pK(I) 8.9) was threefold more potent than icatibant (pK(I) 8.4). Both antagonists showed competitive antagonism in the BK-induced IP assay (control EC50 0.45 nM), with pK(B) values of 9.9 (MEN16132) and 8.1 (icatibant). 24h incubation with BK induced IL-6 (EC50 216 nM) and IL-8 (EC50 53 nM) release. Both MEN16132 (IL-6: pIC50 8.1; IL-8: pIC50 8.4) and icatibant (IL-6: pIC50 6.6; IL-8: pIC50 6.7) completely prevented this BK-induced release. Indomethacin did not affect the basal or the IL-6/IL-8 release induced by BK, whereas nordihydroguaiaretic acid decreased the basal release, although BK still increased IL-6 and IL-8 production. BK-induced IL-8 release was attenuated by inhibitors of phospholipase C (U73122), p38 (SB203580), JNK (SP600125), ERK 1/2 (PD98059) MAPKs, phosphoinositide 3-kinase (LY294002), NF-kappaB (BAY-117085) and by the glucocorticoid dexamethasone. CONCLUSIONS AND IMPLICATIONS: Bradykinin via B2 receptors can participate in inflammatory events in synovitis. MEN16132 is a highly potent B2 receptor antagonist capable of blocking pro-inflammatory responses to BK evoked in human synoviocytes.
Asunto(s)
Antagonistas del Receptor de Bradiquinina B2 , Bradiquinina/metabolismo , Ornitina/análogos & derivados , Sulfonamidas/farmacología , Bradiquinina/administración & dosificación , Bradiquinina/análogos & derivados , Bradiquinina/farmacología , Células Cultivadas , Fibroblastos/efectos de los fármacos , Fibroblastos/metabolismo , Humanos , Concentración 50 Inhibidora , Fosfatos de Inositol/metabolismo , Interleucina-6/metabolismo , Interleucina-8/metabolismo , Ornitina/administración & dosificación , Ornitina/farmacología , Ensayo de Unión Radioligante , Receptor de Bradiquinina B2/metabolismo , Sulfonamidas/administración & dosificación , Membrana Sinovial/citología , Membrana Sinovial/efectos de los fármacos , Membrana Sinovial/metabolismo , Sinovitis/tratamiento farmacológico , Sinovitis/fisiopatologíaRESUMEN
High affinity peptide ligands for the bradykinin (BK) B(2) subtype receptor have been shown to adopt a beta-turn conformation of the C-terminal tetrapeptide (H-Arg(1)-Pro(2)-Pro(3)-Gly(4)-Phe(5)-Ser(6)-Pro(7)-Phe(8)-Arg(9)-OH). We investigated the replacement of the Pro(7)-Phe(8) dipeptide moiety in BK or the D-Tic(7)-Oic(8) subunit in HOE140 (H-D-Arg(0)-Arg(1)-Pro(2)-Hyp(3)-Gly(4)-Thi(5)-Ser(6)-D-Tic(7)-Oic(8)-Arg(9)-OH) by 4-amino-1,2,4,5-tetrahydro-2-benzazepin-3-one templates (Aba). Binding studies to the human B(2) receptor showed a correlation between the affinities of the BK analogs and the propensity of the templates to adopt a beta-turn conformation. The L-spiro-Aba-Gly containing HOE140 analog BK10 has the best affinity, which correlates with the known turn-inducing property of this template. All the compounds did not modify basal inositolphosphate (IP) output in B(2)-expressing CHO cells up to 10 microM concentration. The antagonist properties were confirmed by the guinea pig ileum smooth muscle contractility assay. The new amino-benzazepinone (Aba) substituted BK analogs were found to be surmountable antagonists.
Asunto(s)
Benzazepinas/química , Bradiquinina/análogos & derivados , Músculo Liso/fisiología , Receptor de Bradiquinina B2/metabolismo , Secuencia de Aminoácidos , Animales , Benzazepinas/síntesis química , Benzazepinas/farmacología , Bradiquinina/síntesis química , Bradiquinina/metabolismo , Bradiquinina/farmacología , Células CHO , Cricetinae , Cricetulus , Cobayas , Humanos , Contracción Muscular/efectos de los fármacos , Músculo Liso/efectos de los fármacos , Conformación ProteicaRESUMEN
BACKGROUND AND PURPOSE: The aim was to characterize the recently discovered non-peptide antagonist MEN16132 at the mouse B2 receptor, relative to other antagonists. EXPERIMENTAL APPROACH: [3H]-BK binding experiments used mouse lung and ileum tissue membranes and antagonist potency was measured in the isolated ileum contractility assay. KEY RESULTS: Two BK binding sites resulted from saturation and homologous competition experiments. A role for the B1 receptor was excluded because of the poor affinity of B1 receptor ligands (pIC50<5). MEN16132, and the other reference antagonists, inhibited only one portion of BK specific binding, and the rank order of potency was (pIC50): Icatibant (lung 10.7; ileum 10.2)=MEN11270 (lung 10.4; ileum 9.9)=MEN16132 (lung 10.5; ileum 9.9).>LF16-0687 (lung 8.9; ileum 8.8)>FR173657 (lung 8.6; ileum 8.2). BK homologous curves performed with lung membranes after treatment with the antagonist MEN16132 or Icatibant (10 nM) displayed only the low affinity site. The functional antagonism by MEN16132 (pA2 9.4) and Icatibant (pA2 9.1), towards BK (control EC50 6.1 nM) induced ileum contractions, was concentration-dependent and surmountable, but the Schild plot slope was less than unity. CONCLUSIONS AND IMPLICATIONS: In mouse tissue, radiolabelled BK recognizes two binding sites and B2 receptor antagonists can compete only for the higher affinity one. The pharmacological profile of the novel non-peptide antagonist MEN16132 indicates that it exhibits subnanomolar affinity and potency for the mouse B2 receptor and is suitable for further characterization in in vivo pathophysiological models.
Asunto(s)
Antagonistas Adrenérgicos beta/farmacología , Contracción Muscular/efectos de los fármacos , Músculo Liso/efectos de los fármacos , Ornitina/análogos & derivados , Receptor de Bradiquinina B2/efectos de los fármacos , Sulfonamidas/farmacología , Animales , Íleon/efectos de los fármacos , Técnicas In Vitro , Pulmón/efectos de los fármacos , Masculino , Ratones , Ornitina/administración & dosificación , Ornitina/farmacología , Ensayo de Unión Radioligante , Sulfonamidas/administración & dosificaciónRESUMEN
BACKGROUND AND PURPOSE: Kinins have an important role in inflammatory cystitis and in animal pathophysiological models, by acting on epithelium, fibroblasts, sensory innervation and smooth muscle. The aim of this study was to characterize the receptors responsible for direct motor responses induced by kinins on human detrusor. EXPERIMENTAL APPROACH: Human detrusor cells from biopsies were isolated and maintained in culture. B(1) and B(2) kinin receptors were characterized by means of radioligand and functional experiments (PI accumulation and PGE(2) release). KEY RESULTS: [(3)H]-[desArg(9)]-Lys-BK and [(3)H]-BK saturation studies indicated receptor density (B(max)) and K (d) values of 19 or 113 fmol mg(-1), and 0.16 or 0.11 nM for the B(1) or B(2) receptors, respectively. Inhibition binding studies indicated the selectivity of the B(1) receptor antagonist [desArg(9)Leu(8)]-Lys-BK and of the B(2) receptor antagonists Icatibant and MEN16132. [DesArg(9)]-Lys-BK and BK induced PI accumulation with an EC(50) of 1.6 and 1.4 nM and different maximal responses (E(max) of [desArg(9)]-Lys-BK was 10% of BK). BK also induced prostaglandin E(2) release (EC(50) 2.3 nM), whereas no response was detected with the B(1) receptor agonist. The incubation of detrusor smooth muscle cells with interleukin 1beta (IL-1beta) or tumour necrosis factor-alpha (TNF-alpha) (10 ng ml(-1)) induced a time-dependent increase in radioligand-specific binding, which was greater for the B(1) than for the B(2) receptor. CONCLUSIONS AND IMPLICATIONS: Human detrusor smooth muscle cells in culture retain kinin receptors, and represent a suitable model to investigate the mechanisms and changes that occur under chronic inflammatory conditions.
Asunto(s)
Músculo Liso/metabolismo , Receptor de Bradiquinina B1/fisiología , Vejiga Urinaria/metabolismo , Bradiquinina/análogos & derivados , Bradiquinina/farmacología , Antagonistas del Receptor de Bradiquinina B1 , Células Cultivadas , Dinoprostona/biosíntesis , Humanos , Fosfatos de Inositol/biosíntesis , Interleucina-1beta/farmacología , Calidina/análogos & derivados , Calidina/farmacología , Masculino , Persona de Mediana Edad , Músculo Liso/citología , Ornitina/análogos & derivados , Ornitina/farmacología , Ensayo de Unión Radioligante , Receptor de Bradiquinina B1/agonistas , Receptor de Bradiquinina B1/metabolismo , Sulfonamidas/farmacología , Factor de Crecimiento Transformador alfa/farmacología , Vejiga Urinaria/citologíaRESUMEN
A series of 14 mutants on nine selected residues of the human tachykinin NK(2) receptor was produced and stably transfected into CHO cells to investigate the binding of the peptide MEN 11420 and the nonpeptide SR 48968 antagonists. The main interactions found for MEN 11420 were with Thr171, Tyr206, Tyr266 and Phe270. In the case of SR 48968 crucial residues were Tyr266 and Tyr289. While some overlapping of the binding sites exists, the binding modes suggested by this study appear not to allow structural correlation, and therefore general SAR, between these two antagonists.
Asunto(s)
Receptores de Neuroquinina-2/antagonistas & inhibidores , Receptores de Neuroquinina-2/genética , Secuencia de Aminoácidos , Sustitución de Aminoácidos , Animales , Benzamidas/metabolismo , Benzamidas/farmacología , Sitios de Unión/genética , Células CHO , Cricetinae , Humanos , Datos de Secuencia Molecular , Mutagénesis Sitio-Dirigida , Neuroquinina A/metabolismo , Péptidos Cíclicos/metabolismo , Péptidos Cíclicos/farmacología , Piperidinas/metabolismo , Piperidinas/farmacología , Mutación Puntual , Unión Proteica , Ensayo de Unión Radioligante , Receptores de Neuroquinina-2/metabolismoRESUMEN
We used membranes from Chinese hamster ovary cells stably transfected with the human tachykinin NK(2) receptor, either wild-type or mutated, at four aromatic residues (His(198), Tyr(266), Phe(270), Tyr(289)) located in transmembrane segments V to VII, to assess the role of these residues in the binding of natural tachykinins and peptide and nonpeptide antagonists. Three radioligands, the agonist [(125)I]neurokinin A (NKA), the peptide antagonist [(3)H]MEN 11420, and the nonpeptide antagonist [(3)H]SR 48968 bound to the wild-type receptor with high affinity (K(d) = 2.4 nM, 0.3 nM, and 4.0 nM, respectively). Four of the six mutant receptors tested retained high affinity for at least one of the radioligands. H(198)A mutation abrogated the binding of NKA but not that of MEN 11420 or SR 48968 (K(d) = 4.8 and 11.5 nM, respectively); Y(266)F mutation abrogated the binding of MEN 11420 but not that of NKA or SR 48968 (K(d) = 2.8 nM and 1.2 nM, respectively); F(270)A mutation abrogated the binding of both NKA and MEN 11420 but not that of SR 48968 (K(d) = 1.6 nM); Y(289)F mutation abrogated the binding of SR 48968 but not that of NKA and MEN 11420 (K(d) = 2.0 and 2.9 nM, respectively). Y(266)A and Y(289)A mutations abrogated the binding of all radioligands. Among the unlabeled antagonists, the affinity of the nonpeptide GR 159897, at variance with SR 48968, resulted heavily compromised by H(198)A and Y(266)F mutations; the peptide antagonists R396 and MEN 10376 essentially followed the binding profile of NKA, but R396 showed markedly increased affinity for the Y(289)F mutant receptor. Taken together, these results indicate that different, partially overlapping sets of sites may be involved in the binding of agonists and diverse antagonists to the human tachykinin NK(2) receptor.
Asunto(s)
Péptidos/metabolismo , Receptores de Neuroquinina-2/antagonistas & inhibidores , Receptores de Neuroquinina-2/química , Animales , Benzamidas/química , Benzamidas/metabolismo , Benzamidas/farmacología , Unión Competitiva , Células CHO , Cricetinae , ADN Complementario/efectos de los fármacos , ADN Complementario/genética , Humanos , Indoles/química , Indoles/metabolismo , Indoles/farmacología , Mutagénesis Sitio-Dirigida , Mutación , Neuroquinina A/química , Neuroquinina A/metabolismo , Neuroquinina A/farmacología , Péptidos/química , Péptidos Cíclicos/química , Péptidos Cíclicos/metabolismo , Péptidos Cíclicos/farmacología , Piperidinas/química , Piperidinas/metabolismo , Piperidinas/farmacología , Conformación Proteica , Receptores de Neuroquinina-2/genética , Receptores de Neuroquinina-2/metabolismoRESUMEN
We investigated the pharmacological profile of MEN 11270, or H-D-Arg-Arg-Pro-Hyp-Gly-Thi-c(Dab-DTic-Oic-Arg)c(7gamma-10 alpha), a conformationally constrained derivative of the B2 kinin receptor antagonist Icatibant. MEN 11270 bound with high-affinity to the B2 kinin receptor constitutively expressed by WI38 human fibroblasts, inhibiting 3H-bradykinin (BK) with a pKi value of 10.3 +/- 0.08 (n = 5). The rank order of affinity of several peptide and nonpeptide antagonists was also assessed: Icatibant (pKi = 10.6) approximately MEN 11270 (pKi = 10.3) approximately B9430 (pKi = 10.0) > B9858 (pKi = 8.0) > FR173657 (pKi = 7.6) > WIN64338 (pKi = 7.2) > Lys-[des-Arg9, Leu8]-BK (pKi < 6) > [des-Arg9,Leu8]-BK (pKi < 5). MEN 11270 showed a low affinity in inhibiting 3H-Lys-[des-Arg9]-BK binding at the human B1 kinin receptor constitutively expressed by the same cells (pKi 6.0 +/- 0.33; n = 3). MEN 11270 showed no binding affinity (pIC50 < 5.5) at 29 different receptors and ion channels. In the human umbilical vein contraction assay, MEN 11270, shifted the concentration-response curve to BK to the right in a concentration-dependent manner (pA2 8.14 +/- 0.22, n = 7). The Schild plot was linear (slope 0.95 +/- 0.11), consistent with a competitive antagonism. In the same bioassay, MEN 11270 (10 microM) did not affect the concentration-response curve to the B1 agonist Lys-[des-Arg9]-BK nor the contractile responses elicited by noradrenaline or serotonin. These findings indicate MEN 11270 as an antagonist at the human B2 kinin receptor, with potency and selectivity comparable to those of the linear peptide antagonist, supporting the hypothesis that a constrained C-terminal beta-turn conformation preserves a high affinity for the interaction of Icatibant with the B2 kinin receptor.
Asunto(s)
Bradiquinina/metabolismo , Músculo Liso Vascular/fisiología , Oligopéptidos/farmacología , Péptidos Cíclicos/farmacología , Receptores de Bradiquinina/metabolismo , Adulto , Antiinflamatorios no Esteroideos/farmacología , Unión Competitiva , Bioensayo , Bradiquinina/análogos & derivados , Bradiquinina/farmacología , Antagonistas de los Receptores de Bradiquinina , Línea Celular , Membrana Celular/metabolismo , Femenino , Humanos , Técnicas In Vitro , Cinética , Contracción Muscular/efectos de los fármacos , Músculo Liso Vascular/efectos de los fármacos , Norepinefrina/farmacología , Oligopéptidos/farmacocinética , Péptidos Cíclicos/farmacocinética , Embarazo , Quinolinas/farmacología , Receptor de Bradiquinina B2 , Serotonina/farmacología , Relación Estructura-Actividad , Venas UmbilicalesRESUMEN
A point mutation was made at position 289 in the transmembrane segment 7 of the human tachykinin NK2 receptor to yield a tyrosine/phenylalanine (Tyr/Phe) substitution. Chinese hamster ovary cells stably transfected with the wild-type or Tyr289Phe mutant NK2 receptor both bound neurokinin A (NKA) and the synthetic NK2 receptor-selective agonists, GR 64349 and [betaAla8]NKA(4-10), with high and even affinities. Neurokinin B (NKB) and substance P (SP) also displayed sizeable binding affinities, albeit with lower affinity as compared to NKA. In a functional assay (production of inositol-1,4,5-trisphosphate, IP3), NKA, GR 64349, and [betaAla8]INKA(4-10) stimulated IP3 accumulation via the wild-type and mutant receptors with similar potencies. On the other hand, NKB and SP exhibited a dramatic reduction in their agonist efficacies at the mutant receptor, NKB acting as a partial agonist (maximum effect = 50% of the response to NKA) and SP being totally inactive. The results obtained with phenoxybenzamine inactivation experiments indicated that a large and similar receptor reserve existed for both the wild-type and the mutant receptor. SP, which displayed sizeable binding affinity for the mutant receptor but did not stimulate IP3 accumulation, antagonized the agonist effect of NKA. The antagonist action of SP at the mutant NK2 receptor cannot be ascribed to receptor internalization. The Tyr/Phe replacement at position 289 markedly reduced the binding affinity and antagonist potency of the non-peptide ligand, SR 48968, without affecting the binding affinity and antagonist potency of the bicyclic peptide antagonist MEN 11420. The results indicate that the hydroxyl radical function of Tyr289 in transmembrane segment 7 of the human NK2 receptor is, directly or indirectly, involved in stimulus transduction when the NK2 receptor is occupied by NKB or SP, but not when using NKA or NK2 receptor-selective agonists.
Asunto(s)
Fenilalanina/fisiología , Receptores de Neuroquinina-2/fisiología , Transducción de Señal , Taquicininas/metabolismo , Tirosina/fisiología , Animales , Unión Competitiva , Células CHO , Cricetinae , Guanosina Trifosfato/metabolismo , Humanos , Inositol 1,4,5-Trifosfato/metabolismo , Neuroquinina A/antagonistas & inhibidores , Neuroquinina A/metabolismo , Fenoxibenzamina/farmacología , Fenilalanina/genética , Mutación Puntual , Receptores de Neuroquinina-2/genética , Sustancia P/farmacología , Transfección , Tirosina/genéticaRESUMEN
The human tachykinin NK2 receptor stably expressed in Chinese hamster ovary cells (CHO-hNK2R cells) was characterized by studying the effect of neurokinin A (NKA), the preferred natural ligand, and that of other agonists and antagonists in both binding experiments and functional assays. Competition experiments using [125I]NKA showed that CHO-hNK2R cells express binding sites which have high affinity for NKA (Ki=3.4+/-0.9 nM), GR 64349 (Ki=12+/-3 nM) and [betaAla8]NKA(4-10) (Ki=21+/-8 nM) and for the antagonists MEN 10627 (Ki=0.55+/-0.2 nM), and MEN 11420 (Ki=2.4+/-0.8 nM). In contrast, the tachykinin NK1 and NK3 receptor agonists [Sar9,Met(O2)11]SP and senktide, respectively, were recognized with low affinity (Ki>10 microM). NKA (EC50=68+/-18 nM) induced a rapid and concentration-dependent increase in the intracellular level of inositoltrisphosphate (IP3). The concentration-response curve to GR 64349 (EC50=155+/-14 nM) was close to that of NKA, whereas [betaAla8]NKA(4-10) (EC50=445+/-78 nM) and SP (EC50=3197+/-669 nM) were 7- and 50-fold less potent, respectively. In addition, NKA stimulated the release of arachidonic acid and the production of prostaglandin E2 (PGE2) in a concentration-dependent manner. Also in this assay, NKA was found to be more potent than the other agonists tested (the EC50 values were 3+/-0.3, 9+/-3, 7.8+/-0.9 and 217+/-37 nM for NKA, GR 64349, [betaAla8]NKA(4-10) and SP, respectively). MEN 10627 and MEN 11420 were potent and competitive antagonists in blocking NKA-induced IP3 formation and PGE2 release: MEN 10627 and MEN 11420 displayed comparable potencies in blocking the two functional responses initiated by occupancy of the NK2 receptor by NKA. Pretreatment of the cells with pertussis toxin (500 ng/ml for 18 h) did not significantly modify the basal or stimulated phosphatidylinositol turnover but reduced the basal and NKA-induced PGE2 release by about 35%. The phospholipase C inhibitor U-73122 (10 microM) prevented the NKA-induced formation of IP3 but did not affect PGE2 release. Conversely, the phospholipase A2 inhibitor quinacrine (100 microM) blocked the release of arachidonic acid and PGE2 without affecting the NKA-stimulated formation of IP3. Chelation of extracellular calcium with 3 mM EGTA inhibited the NKA-induced PGE2 release by 81% but was without effect on basal and NKA-stimulated IP3 production. The calcium channel blockers verapamil (10 microM) and omega-conotoxin GVIA (0.1 microM) did not modify the basal PGE2 production and had no significant effect on the response to tachykinins while the blocker of non-selective cation channels, SKF-96365 (10 microM), inhibited the response to NKA by about 74%. SKF-96365 did not affect the basal or the NKA-induced IP3 formation. In conclusion, our data demonstrate that the human tachykinin NK2 receptor expressed in CHO cells displays binding affinity and functional properties which are those of a native NK2 receptor. No pharmacological evidence for heterogeneity of the human NK2 receptor was obtained in this study. Our findings indicate that the human tachykinin NK2 receptor is independently coupled to both PLC and PLA2 signaling pathways. Activation of the PLA2 pathway may be linked to the opening of a voltage-independent cation channel which activates a Ca2+-dependent PLA2.
Asunto(s)
Fosfolipasas A/fisiología , Receptores de Neuroquinina-2/fisiología , Fosfolipasas de Tipo C/fisiología , Animales , Ácido Araquidónico/metabolismo , Sitios de Unión , Células CHO , Calcio/metabolismo , Bloqueadores de los Canales de Calcio/farmacología , Cricetinae , Dinoprostona/metabolismo , Humanos , Inositol 1,4,5-Trifosfato/biosíntesis , Toxina del Pertussis , Fosfolipasas A2 , Transfección , Factores de Virulencia de Bordetella/farmacologíaRESUMEN
The contractile responses elicited by the selective kinin B1 and B2 receptor agonists [desArg9]-bradykinin ([desArg9]-BK) and [Hyp3, Tyr(Me)8]-bradykinin ([Hyp3, Tyr(Me)8]-BK) (1 nM-10 microM), respectively, were evaluated in control vs. inflamed (cyclophosphamide 150 mg kg-1 i.p., 48 h before the sacrifice) rat isolated urinary bladder strips. The contractile responses to the B2 receptor agonist did not differ in control vs. inflamed bladders, whereas the contractile responses to [desArg9]-BK were potentiated in inflamed bladders. The selective B1 and B2 receptor antagonists B 9858 (H-Lys-Lys-Arg-Pro-Hyp-Gly-Igl-Ser-DIgl-Oic-OH) and Hoe 140 (H-DArg-Arg-Pro-Hyp-Gly-Thi-Ser-DTic-Oic-Arg-OH), both at 1 microM, inhibited the response to the B1 and B2 receptor agonists, respectively, in both control and inflamed bladders. In addition, the concentration-response curve to [Hyp3, Tyr(Me)8]-BK was shifted to the right and depressed by B 9858 in inflamed bladders. The nonselective cyclooxygenase (COX) inhibitors S-(-)-ketoprofen (10 microM) and piroxicam (30 microM) markedly depressed the concentration-response curves to [desArg9]-BK and [Hyp3, Tyr(Me)8]-BK in control bladders, but neither drug affected the B1 or B2 receptor agonist-mediated responses in inflamed bladders. The selective inhibitor of the inducible COX-2 isoenzyme, NS-398 (1 microM), did not inhibit the contractile responses to [desArg9]-BK and [Hyp3, Tyr(Me)8]-BK in either control or inflamed bladders, whereas it significantly potentiated the response to the B1 receptor agonist in inflamed bladders. The exogenous administration of prostaglandin E2 (PGE2) induced S-(-)-ketoprofen-resistant contractile responses that were depressed in inflamed bladders. Pretreatment with S-(-)-ketoprofen restored the PGE2-mediated contractile responses of inflamed bladders to control values. PGE2 assay revealed that the basal production of PGE2 is significantly higher after inflammation than in control conditions. [desArg9]-BK and [Hyp3, Tyr(Me)8]-BK (1 microM each) both stimulated PGE2 production, and their effect was larger in inflamed than in control bladders. Piroxicam (30 microM) prevented the PGE2 production evoked by [desArg9]-BK in both control and inflamed bladders and likewise abolished that produced by [Hyp3, Tyr(Me)8]-BK. NS-398 (1 microM) reduced the PGE2 production elicited by [desArg9]-BK in control and inflamed bladders. When NS-398 was tested on the [Hyp3, Tyr(Me)8]-BK-induced PGE2 production, it inhibited PGE2 production in the inflamed bladders only, without significantly modifying the response obtained in controls. These findings demonstrate that 1) in normal bladders, the activation of B1 and B2 receptors evokes contraction that is largely mediated by COX-1 metabolites, whereas the COX-2 appears to be involved in PGE2 production after the activation of B1 receptor only, without interfering with contraction, and 2) in inflamed bladders, the activation of B1 and B2 receptors still produce PGE2, but the contractile response is not reduced by COX inhibitors, a result that indicates that additional mechanisms play a compensatory role.
Asunto(s)
Bradiquinina/farmacología , Cistitis/fisiopatología , Contracción Muscular/efectos de los fármacos , Prostaglandina-Endoperóxido Sintasas/fisiología , Receptores de Bradiquinina/agonistas , Vejiga Urinaria/efectos de los fármacos , Animales , Dinoprostona/biosíntesis , Dinoprostona/farmacología , Técnicas In Vitro , Cetoprofeno/farmacología , Masculino , Nitrobencenos/farmacología , Piroxicam/farmacología , Ratas , Ratas Wistar , Receptor de Bradiquinina B1 , Receptor de Bradiquinina B2 , Sulfonamidas/farmacología , Vejiga Urinaria/fisiologíaRESUMEN
[3H]MEN 11420, a radiolabeled glycosylated peptide antagonist of the tachykinin NK2 receptor, has been investigated in ligand-receptor binding assays using membranes of CHO cells transfected with the human tachykinin NK2 receptor. [3H]MEN 11420 bound to a single class of high affinity binding sites: its binding was inhibited by natural tachykinins (potency ranking: NKA >> SP > or = NKB), as well as by peptide (MEN 11420 > MEN 10376 >> R 396) and nonpeptide (SR 48968 > GR 159897) selective NK2 receptor antagonists. These data indicate that [3H]MEN 11420 is a potent radioligand for the human tachykinin NK2 receptor that may represent a useful tool for studying ligand-receptor interactions at the molecular level.
Asunto(s)
Péptidos Cíclicos/metabolismo , Receptores de Neuroquinina-2/antagonistas & inhibidores , Animales , Sitios de Unión , Unión Competitiva , Células CHO , Cricetinae , Humanos , Cinética , Ensayo de Unión Radioligante , Receptores de Neuroquinina-2/genética , Receptores de Neuroquinina-2/metabolismo , Taquicininas/metabolismo , Taquicininas/farmacología , TransfecciónRESUMEN
1. The pharmacological profile was studied of MEN 11420, or cyclo[[Asn(beta-D-GlcNAc)-Asp-Trp-Phe-Dap-Leu]cyclo(2beta-5beta )], a glycosylated derivative of the potent, selective, conformationally-constrained tachykinin NK2 receptor antagonist MEN 10627 (cyclo(Met-Asp-Trp-Phe-Dap-Leu)cyclo(2beta-5beta)). 2. MEN 11420 competitively bound with high affinity to the human NK2 receptor stably transfected in CHO cells, displacing radiolabelled [125I]-neurokinin A and [3H]-SR 48968 with Ki values of 2.5+/-0.7 nM (n = 6) and 2.6+/-0.4 nM (n = 3), respectively. 3. MEN 11420 showed negligible binding affinity (pIC50 < 6) at 50 different receptors (including tachykinin NK1 and NK3 receptors) and ion channels. 4. In the rabbit isolated pulmonary artery and rat urinary bladder MEN 11420 potently and competitively antagonized tachykinin NK2 receptor-mediated contractions (pK(B) = 8.6+/-0.07, n = 10, and 9.0+/-0.04, n = 12; Schild plot slope = -1.06 (95% c.l. = -1.3; -0.8) and -1.17 (95% c.l. = -1.3; -1.0), respectively). MEN 11420 produced an insurmountable antagonism at NK2 receptors in the hamster trachea and mouse urinary bladder. However, in both preparations, the effect of MEN 11420 was reverted by washout and an apparent pK(B) of 10.2+/-0.14, n = 9, and 9.8+/-0.15, n = 9, was calculated in the hamster trachea and mouse urinary bladder, respectively. 5. MEN 11420 showed low affinity (pK(B) < 6) at guinea-pig and rat tachykinin NK1 (guinea-pig ileum and rat urinary bladder) and NK3 (guinea-pig ileum and rat portal vein) receptors. On the whole, the affinities (potency and selectivity) showed by MEN 11420 for different tachykinin receptors, measured either in binding or in functional bioassays, were similar to those shown by the parent compound, MEN 10627. 6. The in vivo antagonism of the contractions produced by [betaAla8]neurokinin A(4-10) (1 nmol kg(-1)) was observed after intravenous (dose range: 1-10 nmol kg(-1)), intranasal (3-10 nmol kg(-1)), intrarectal (30-100 nmol kg(-1)) and intraduodenal (100-300 nmol kg(-1)) administration of MEN 11420. MEN 11420 was more potent (about 10 fold) and longer lasting than its parent compound MEN 10627, possibly due to a greater metabolic stability. 7. A dose of MEN 11420 (100 nmol kg(-1), i.v.), that produced potent and long lasting inhibition of the contraction of the rat urinary bladder induced by challenge with the NK2 selective receptor agonist [betaAla8]neurokinin A(4-10) (10-300 nmol kg(-1)), was without effect on the responses produced by the NK1 receptor selective agonist [Sar9]substance P sulphone (1-10 nmol kg(-1)). 8. These findings indicate that MEN 11420 is a potent and selective tachykinin NK2 receptor antagonist. The introduction of a sugar moiety did not produce major changes in the affinity profile of this antagonist as compared to MEN 10627, but markedly improved its in vivo potency and duration of action. With these characteristics, MEN 11420 is a suitable candidate for studying the pathophysiological significance of tachykinin NK2 receptors in humans.
Asunto(s)
Péptidos Cíclicos/farmacología , Receptores de Neuroquinina-2/antagonistas & inhibidores , Animales , Células CHO , Cricetinae , Femenino , Cobayas , Humanos , Técnicas In Vitro , Canales Iónicos/efectos de los fármacos , Canales Iónicos/metabolismo , Masculino , Péptidos Cíclicos/antagonistas & inhibidores , Péptidos Cíclicos/farmacocinética , Conejos , Ensayo de Unión Radioligante , Ratas , Ratas Wistar , Receptores de Neuroquinina-1/metabolismo , Receptores de Neuroquinina-2/metabolismo , Receptores de Neuroquinina-3/metabolismoRESUMEN
Substance P (SP) and neurokinin A (NKA) are synthesized by enteric cholinergic motorneurons that project to the longitudinal and circular muscle of the mammalian intestine. Thus, acetylcholine, SP, and NKA are the excitatory neuromuscular transmitters in the intestine. Tachykinin NK1 and NK2 receptors are expressed by smooth muscle cells in most regions of the intestine: the corelease of SP and NKA from nerves thus realizes paradigms of tachykininergic cotransmission. Examples have been found in which a cooperative model can be applied to account for the action of SP-NKA acting at NK1 and NK2 receptors (e.g., circular muscle of guinea-pig duodenum), as well as examples in which the message produced by activation of the two receptors diverges sharply in producing responses that have a markedly different time course and use different effector systems (e.g., circular muscle of guinea-pig colon). NK3 receptors are expressed on both excitatory and inhibitory motor neurons: indirect contractions (via release of acetylcholine and tachykinins) and relaxations (via release of nitric oxide) can be evoked in the gut by selective stimulation of NK3 receptors. Although a role of NK3 receptors in certain enteric reflexes has been evidenced, the importance of this system in mediating hexamethonium-resistant enteric transmission appears less important than previously speculated.
Asunto(s)
Motilidad Gastrointestinal/fisiología , Receptores de Taquicininas/fisiología , Animales , Cobayas , Humanos , RatasRESUMEN
The aim of the present work was to study how human umbilical vein smooth muscle cells (HUVSMC) can initiate the coagulation process and to investigate the responses of these cells to thrombin. Exposure of HUVSMC to recalcified human plasma led to a time-dependent production of thrombin, measured both as amidolytic activity and as release of fibrinopeptide A. Thrombin activity was dose-dependently reduced by an anti-human tissue factor antibody (76 +/- 3% at 10 micrograms/ml) and by inhibitors like heparin, rec-hirudin, hirulog 1, Napap and hirunorm, a novel hirudin-like thrombin inhibitor (IC50 = 2 +/- 0.4, 8 +/- 1, 130 +/- 22, 199 +/- 29 and 68 +/- 8 nM, respectively). The release of fibrinopeptide A was similarly prevented (IC50 = 14 +/- 1, 132 +/- 25 and 50 +/- 8 nM for rec-hirudin, Napap and hirunorm, respectively). Exogenously added thrombin increased thymidine incorporation into HUVSMC to 240 +/- 30% of basal (EC50 = 0.49 +/- 0.09 nM) and thrombin inhibitors blocked this effect (IC50 = 10 +/- 3, 37 +/- 17, 343 +/- 165 and 1402 +/- 758 nM for rec-hirudin, hirunorm, Napap and hirulog-1, respectively). Also recalcified human plasma was mitogenic for HUVSMC and its effect was mainly due to endogenously generated thrombin, as shown by the use of thrombin inhibitors. In conclusion, HUVSMC are capable of initiating the extrinsic coagulation cascade, leading to the formation of thrombin which promotes clotting and stimulates DNA synthesis. Thrombin inhibitors prevent both coagulative and cellular effects of thrombin.
Asunto(s)
Factores de Coagulación Sanguínea/fisiología , Músculo Liso Vascular/efectos de los fármacos , Inhibidores de Serina Proteinasa/farmacología , Trombina/fisiología , Secuencia de Aminoácidos , Células Cultivadas , ADN/biosíntesis , Estudios de Evaluación como Asunto , Fibrinopéptido A/metabolismo , Humanos , Modelos Logísticos , Modelos Cardiovasculares , Datos de Secuencia Molecular , Músculo Liso Vascular/citología , Músculo Liso Vascular/metabolismo , Péptidos/farmacología , Trombina/antagonistas & inhibidores , Trombina/biosíntesis , Venas Umbilicales/efectos de los fármacos , Venas Umbilicales/metabolismoRESUMEN
1. The pharmacological profile of LR-B/081, (methyl 2-[[4-butyl-2-methyl- 6-oxo-5-[[2'-(1H-tetrazol-5-yl)[1,1'-biphenyl]-4-yl]methyl]-1(6H)- pyrimidinyl]methyl]-3-thiophenecarboxylate), a novel antagonist at the angiotensin II (AII) AT1-receptor, was studied in vitro and in vivo. 2. In rabbit aortic strips incubated with LR-B/081 (1-1,000 nM), the concentration-response curve to AII was displaced to the right in a nonparallel fashion and the maximal contraction was progressively reduced, indicating that the compound is an insurmountable antagonist in this preparation (apparent pKB = 9.50 +/- 0.23). However, the interaction of LR-B/081 with AII receptors was found to be reversible, since the maximal response to AII was restored by coincubation with losartan, a surmountable AII AT1-antagonist. Contractions elicited by KCl or phenylephrine were not affected by 10 microM LR-B/081. 3. In rat isolated perfused kidney, LR-B/081 and losartan antagonized the AII-induced vasoconstriction [IC50 (95% confidence limits) = 17(13-24) and 39(32-54) nM, respectively]. The LR-B/081 antagonism was incompletely reversed by excess AII, while losartan was fully displaced. The IC50 values of LR-B/081 and losartan obtained against vasoconstriction induced by endothelin-1 and noradrenaline were two orders of magnitude higher. 4. In pithed rats, the intravenous administration of LR-B/081 (0.2-2 mumol kg-1) dose-dependently shifted to the right in a nonparallel fashion the dose-pressor response curve to AII. The maximal pressor response to AII was reduced by LR-B/081 in a dose-dependent fashion. The coadministration of losartan induced a progressive recovery of the maximal pressor response to All, indicating that in vivo the interaction of LR-B/081 with All receptors is reversible. LR-B/081 at 6 micromol kg-1, i.v. also did not affect the vasopressor response induced by noradrenaline in the pithed rat.5. In conscious normotensive rats, single oral administration of LR-B/081 at 6 micromol kg-1 markedly inhibited the All-induced pressor response; the inhibition lasted more than 24 h.6. In conscious renal hypertensive rats, intravenous LR-B/081 appeared as potent as losartan (ED40mmHg(95% confidence limits) = 0.50(0.36-0.70) and 0.86(0.57-1.3) micromol kg-1, respectively). A single intravenous(2 micromol kg-1) or oral (6 micromol kg-1) administration of LR-B/081 induced a marked fall in blood pressure which lasted for at least 12 h.7. In conscious spontaneously hypertensive rats, LR-B/081 at 20 micromol kg-1 , p.o., induced a marked and sustained fall in blood pressure. The duration of the antihypertensive effect was longer than 12 h.Heart rate was not modified by LR-B/081 treatment. Repeated oral administration of 17 micromol kg-1LR-B/081 for 16 days did not result in the development of tolerance.8 These results demonstrate that LR-B/081 is a potent, selective and orally active antagonist of All at the AT1-receptor subtype, which markedly lowers the blood-pressure in conscious renal and spontaneously hypertensive rats.
Asunto(s)
Antagonistas de Receptores de Angiotensina , Pirimidinonas/farmacología , Tiofenos/farmacología , Administración Oral , Animales , Aorta/efectos de los fármacos , Presión Sanguínea/efectos de los fármacos , Estado de Descerebración , Técnicas In Vitro , Masculino , Perfusión , Conejos , Ratas , Ratas Endogámicas SHR , Ratas Sprague-Dawley , Vasoconstricción/efectos de los fármacosRESUMEN
We studied the pharmacologic properties of LR-B/057, a novel nonpeptide angiotensin II (AII) receptor antagonist. The compound potently displaced [3H]AII from AT1 but not from AT2 receptors in rat adrenal cortex (Ki 3 nM), but did not modify the dissociation rate of the radioligand from the receptors. Both its affinity and the nature of its interaction with AT1 receptors (saturation studies) were markedly affected by the presence of bovine serum albumin (BSA) in the binding assay. In rabbit aorta, LR-B/057 caused nonparallel shifts to the right of the dose-response curve to AII and decreased the maximal response (pKB 9.6). Oral (p.o.) administration of LR-B/057 to conscious rats dose-dependently antagonized the pressor response to AII. LR-B/057 administered either intravenously (i.v.) or p.o. to conscious renal hypertensive rats produced a powerful dose-dependent antihypertensive effect. These results show that LR-B/057 is a potent and selective antagonist at AT1 receptors and has p.o. bioavailability.