Neuromuscular blocking agents inhibit receptor-mediated increases in the potassium permeability of intestinal smooth muscle.

The neuromuscular blocking agents tubocurarine, atracurium and pancuronium have been tested for their ability to inhibit receptor-mediated increases in the K+ permeability of intestinal smooth muscle. All three agents, as well as the bee venom peptide apamin, reduced both the resting efflux of 86Rb and the increase in efflux caused by the application of either bradykinin (1 microM) or an alpha 1-adrenoceptor agonist, amidephrine (20 microM), to depolarized strips of guinea-pig taenia caeci. This suggested that like apamin, the neuromuscular blocking agents inhibit the Ca2+-dependent K+ permeability (PK(Ca] mechanism which in this tissue is activated by a variety of membrane receptors. The concentrations (IC50S) of atracurium, pancuronium and (+)-tubocurarine which reduced the effect of amidephrine on 86Rb efflux by 50% were 12, 37 and 67 microM respectively. Also in keeping with an ability to block PK(Ca), the neuromuscular blockers and apamin reduced the inhibition by amidephrine and bradykinin of physalaemin-mediated contractions of the taenia caeci. The IC50 values were 15, 31 and 120 microM for atracurium, tubocurarine and pancuronium respectively, and 2.3 nM for apamin. Each of the neuromuscular blockers, and apamin, increased the spontaneous contractions of the rabbit duodenum and blocked the inhibitory effect of amidephrine thereon. It is concluded that the PK(Ca) mechanism in the longitudinal smooth muscle of the intestine It is concluded that the PK(Ca) mechanism in the longitudinal smooth muscle of the intestine resembles that of hepatocytes and sympathetic ganglion cells in its susceptibility to inhibition by neuromuscular blocking agents, as well as by apamin.

Relative activities of substance P-related peptides in the guinea-pig ileum and rat parotid gland, in vitro.

The relative potencies of a series of substance P analogues have been determined for spasmogenic activity in the guinea-pig ileum in vitro and for the release of 86Rb and alpha-amylase activity from rat parotid gland slices in vitro. Equipotent molar ratios (EMR), relative to substance P, were determined for all the compounds. In the rat parotid gland, EC50 values for amylase release were, on average, 35.5 times greater than those for 86Rb release. Analysis of Hill plots suggests that spare receptors exist for 86Rb release but not for amylase release and it is suggested that the stimulus-response coupling for amylase release may be less efficient than that for 86Rb release. In the parotid gland, the octapeptide and [less than Glu6]-hexapeptide C-terminal fragments of substance P were less active than substance P itself, whereas in the ileum, the octapeptide was as active as substance P. Substitutions at the Phe7 or Phe8 positions in general reduced activity relative to substance P. This effect was particularly apparent in C-terminal hexapeptide analogues. Substitutions at the Phe7 and Phe8 positions in C-terminal hexapeptide analogues produced a greater reduction in activity in the parotid gland than in the ileum. The most marked difference was observed with eledoisin-related peptide for which the ratio of EMRs for ileum and 86Rb release was 18.1. The unsubstituted C-terminal octapeptide fragment similarly showed a discrepancy between the two assay systems (EMR ratio, ileum: 86Rb release = 7.75). It is suggested that the results may indicate the presence of sub-populations of 'substance P receptors' which are represented at least in different proportions in the two tissues studied, although alternative explanations such as differences in metabolism of agonists are possible.

Effects of Ro 47-0203 on endothelin-1 and sarafotoxin S6c-induced contractions of human bronchus and guinea-pig trachea.

Endothelin exerts a variety of biological effects in the lung which indicate that this peptide may have a role in the pathophysiology of a number of pulmonary diseases. In this study, the endothelin receptors on the human bronchus were compared with those on the guinea-pig trachea using the novel, non-peptide antagonist Ro 47-0203 (4-tert-butyl-N-[6-(2-hydroxy-ethoxy)-5-(2-methoxy-phenoxy)-2,2' -bipyrimidin-4-yl]-benzenesulphonamide, non-selective for endothelin ETA over endothelin ETB receptor) and the peptide antagonist BQ123 (cyclo(-D-Val-Leu-D-Trp-D-Asp-Pro), endothelin ETA receptor selective). On the human bronchus and guinea-pig trachea, the concentration-effect curve for endothelin-1 was shifted to the right by Ro 47-0203 (100 microM) with concentration ratios of 28.2 +/- 6.8 and 39.5 +/- 13.9, respectively but lower concentrations of the antagonist had no effect. Although the concentration-effect curve for sarafotoxin S6c on the human bronchus was shifted to the right by Ro 47-0203 (30 and 100 microM, concentration ratio: 6.88 +/- 1.72 and 69.7 +/- 17.2, respectively), equivalent degrees of inhibition could be obtained on guinea-pig trachea with lower concentrations of antagonist (10 and 30 microM, concentration ratio: 6.90 +/- 1.58 and 75.8 +/- 14.1 respectively). The lack of effect of BQ123 (10 microM) and the high concentrations of Ro 47-0203 needed to show antagonism indicate that endothelin receptors on both tissues are probably the endothelin ETB subtype. Although the antagonism by Ro 47-0203 is not classically competitive, the greater effect of Ro 47-0203 against sarafotoxin S6c on the guinea-pig trachea may reflect a difference between the endothelin ETB receptors on these tissues.

The inhibitory effects of Ro 31-6930 and BRL 38227 on cholinergically-mediated bronchoconstriction in the guinea-pig.

This study compares the effects of two K(+0-channel openers, Ro 31-6930 and BRL 38227, on cholinergically-evoked contraction of guinea-pig airways to examine whether either compound acts through prejunctional inhibition of the release of acetylcholine. In the isolated trachea, Ro 31-6930 and BRL 38227 evoked concentration-dependent inhibition of tone generated by electrical field stimulation with pD2 values of 7.03 (6.77-7.29) and 6.26 (5.91-6.61) respectively and of that elicited by acetylcholine with pD2 values of 7.38 (6.52-8.24) and 6.65 (6.16-7.13). Neither compound was more potent against responses to electrical field stimulation than against acetylcholine. In the anaesthetised guinea-pig, Ro 31-6930 inhibited the bronchoconstriction evoked by bilateral vagus nerve stimulation and intravenous acetylcholine with ID50 values of 12.9 +/- 3.9 and 3.6 +/- 1.3 micrograms/kg i.v. respectively. The corresponding values for BRL 38227 were 356 +/- 157 and 37.9 +/- 13.4 micrograms/kg i.v. respectively. Thus, in vivo, both compounds were more potent against acetylcholine than against vagal stimulation. These results provide indirect evidence that K(+)-channel openers do not inhibit the release of acetylcholine from parasympathetic nerves in guinea-pig airway smooth muscle.

Ro 45-2081, a TNF receptor fusion protein, prevents inflammatory responses in the airways.

The TNF receptor fusion protein, Ro 45-2081, inhibited allergic and non-allergic inflammatory responses in the airways. Treatment of sensitized guinea-pigs with Ro 45-2081 reduced allergen-induced influx of inflammatory cells into the lungs, abolished edema formation and inhibited hyperreactivity to substance P. Administration of Ro 45-2081 after allergen challenge reversed the influx of inflammatory cells into the lungs. Sephadex-induced neutrophil influx into the lungs of rats was also blocked by Ro 45-2081. The effects of Ro 45-2081 suggest that inhibitors of TNF may have potential as therapeutics for inflammatory diseases in the lung.

Airway inflammation driven by antigen-specific resident lung CD4(+) T cells in alphabeta-T cell receptor transgenic mice.

CD4(+) T cells are thought to play a major role in the initiation and perpetuation of T helper cell, type 2 (Th2)-like allergic airway inflammation. However, it is not clear whether activation of resident antigen-specific CD4(+) T cells is in itself sufficient to induce such a phenotype. Using ovalbumin (OVA)-specific alphabeta-T cell receptor transgenic Balb/c DO11.10 mice, we were able to test this hypothesis. Nonsensitized DO11.10 mice but not wild-type mice responded to a primary OVA aerosol with a rapid and impressive bronchoalveolar lavage (BAL) neutrophilia followed by a smaller but significant eosinophilia. Responses in DO11.10 mice were mediated by OVA-specific activation of CD4(+) T cells because in vivo depletion of CD4(+) but not CD8(+) T cells abrogated inflammatory cell influx. Cytokines measured in BAL fluid (BALF) after OVA aerosol exposure of DO11.10 mice were indicative of a T helper cell, type 1 (Th1)-like immune response. Further, neutralization of interferon gamma (IFN-gamma) with antibody enhanced eosinophil influx, suggesting that IFN-gamma production was limiting the development of a Th2 response. Despite this, an increased prevalence of cells staining for mucus was seen in the bronchial epithelium, a feature more commonly associated with a Th2-immune response. Unlike what was seen in OVA-sensitized wild-type mice, multiple OVA aerosol exposures of DO11.10 mice failed to induce airway hyperresponsiveness (AHR) to inhaled methacholine. In conclusion, in vivo stimulation of resident lung CD4(+) T cells with antigen caused lung inflammation with characteristics of both a Th1- and Th2-immune response but was insufficient to directly induce AHR.

A study of the muscarinic receptor subtype mediating mucus secretion in the cat trachea in vitro.

Mucus secretion from the cat trachea simulated by muscarinic receptor agonists has been studied by monitoring both the weight and acid glycoconjugate content of samples taken from an in vitro preparation. The nature of the receptor has been probed using a number of competitive muscarinic receptor antagonists by estimating their affinities from the degree to which the response could be blocked. Antagonist affinities have also been compared with those obtained in tracheal smooth muscle and atria from the guinea-pig. Atropine had similar affinities for all receptors investigated. 4DAMP and AF-DX116 had relatively high (pA2 = 9) and low (pA2 = 6) affinities respectively for the secretory receptor. The pA2 value of 7.5 calculated for pirenzepine suggested that the receptor was not of the M1 subtype. However, the value was higher than that for pirenzepine in both guinea-pig tissues indicating that the receptor may be an 'intermediate' between M1 and M2 subtypes. The lack of antagonists with absolute selectivity for a particular subtype of the muscarinic receptor prohibits a definitive classification.

Inhibition of Sephadex-induced lung injury in the rat by Ro 45-2081, a tumor necrosis factor receptor fusion protein.

Tumor necrosis factor (TNF) is an inflammatory cytokine produced by many cell types which may contribute to the pathophysiology of a variety of lung diseases. In this study we have used Ro 45-2081 (a soluble receptor composed of the human p55 TNF receptor and human heavy-chain immunoglobulin G) to explore the role of TNF in the acute inflammatory response in the rat lung to intravenous injection of Sephadex beads. The effects of Ro 45-2081 have also been compared with those of dexamethasone. At 24 and 72 h after Sephadex, there was a significant increase in the total number of leukocytes in bronchoalveolar lavage fluid (BALF). At 24 h, the number of neutrophils comprised around 50% of the total leukocyte number, decreasing to around 10% of total by 72 h. The eosinophil count was maintained at around 10% of the total leukocyte number. Pretreatment with either Ro 45-2081 [1 and 3 mg kg-1, intraperitoneally (i.p.)] or dexamethasone (0.1 and 0.3 mg kg-1, i.p.) inhibited the neutrophilia at 24 h after Sephadex, although Ro 45-2081 had no significant effect on total cell number. At 72 h after Sephadex, Ro 45-2081 (1 and 3 mg kg-1, i.p., daily) significantly reduced the neutrophil influx into BALF but had no inhibitory effect on eosinophil number. In contrast, dexamethasone (0.1 and 0.3 mg kg-1, i.p., daily) virtually abolished the infiltration of neutrophils and eosinophils into BALF. The lack of effect of Ro 45-2081 on eosinophil infiltration into the rat lung and the inhibition caused by dexamethasone suggest that factors other than TNF are involved in this part of the inflammatory response induced by Sephadex. However, the inhibitory effects of Ro 45-2081 show that TNF may play an important role in the recruitment of neutrophils into the lungs of Sephadex-treated rats.

Rapid up-regulation of CXC chemokines in the airways after Ag-specific CD4+ T cell activation.

Ag-specific activation of CD4(+) T cells is known to be causative for the cytokine production associated with lung allergy. Chemokine-induced leukocyte recruitment potentially represents a critical early event in Ag-induced lung inflammation. Whether Ag-specific, lung CD4(+) T cell activation is important in lung chemokine production is currently not clear. Using alphabeta-TCR transgenic BALB/c DO11.10 mice, we investigated the ability of Ag-specific CD4(+) T cell activation to induce lung chemokine production and leukocyte recruitment. Within 1 h of exposure of DO11. 10 mice to OVA aerosol, lung mRNA and protein for the neutrophil chemokines KC and macrophage inflammatory protein (MIP)-2 were greatly increased. Accordingly, neutrophils in the airways increased by >50-fold, and KC and MIP-2 proved to be functional because their neutralization significantly reduced airway neutrophilia. CD4(+) T cell activation was critical because CD4(+) but not CD8(+) T cell depletion reduced KC production, which correlated well with the previously observed inhibition of neutrophil influx after CD4(+) T cell depletion. In vitro studies confirmed that OVA-induced KC and MIP-2 production was conditional upon the interaction of CD4(+) T cells with APCs. A likely secondary mediator was TNF-alpha, and a probable source of these chemokines in the lung was alveolar macrophages. Thus, Ag-specific CD4(+) T cell activation in the lung leads to rapid up-regulation of neutrophil chemokines and the recruitment of neutrophils to the site of Ag exposure. This may be a key early event in the pathogenesis of Ag-induced lung inflammation.

Some studies of the action of betahistine at H1 and H2 receptors for histamine.

Betahistine produced a concentration-dependent contraction of the guinea-pig ileum and was about 27 times less active than histamine in this respect. Betahistine induced desensitization of contractile responses to histamine in the guinea-pig ileum. The H1 histamine receptor antagonist mepyramine was a competitive antagonist of the action of betahistine on the guinea-pig ileum. Betahistine caused relaxation of the rat uterus contracted by acetylcholine, and this action of betahistine was blocked by the H2 receptor antagonist cimetidine. Betahistine had a concentration-dependent positive chronotropic action on isolated guinea-pig atria, and in this respect was tenfold less potent than histamine. The action of betahistine on the atria was blocked by the H2 receptor antagonist YM11170. Betahistine caused a concentration-related contraction of the isolated lung parenchymal strip of the guinea-pig, and YM11170 potentiated this effect. Betahistine failed to release histamine from rat peritoneal mast cells at concentrations up to 100 microM and it did not prevent histamine release induced by either substance P or anti-IgE. Betahistine produced a dose-related flare and wheal reaction when injected intradermally into human skin. It is concluded that betahistine has agonist activity at both H1 and H2 receptors for histamine.

Inhibition by Ro 31-6930 of agonist and allergen induced bronchoconstriction in anaesthetised guinea-pigs and cats.

Ro 31-6930, a potent smooth muscle relaxant from the novel class of potassium channel openers, has been compared with BRL 38227, salmeterol and theophylline in a range of models of airway function. Ro 31-6930 relaxed isolated tracheal muscle from sensitised guinea-pigs which had been contracted by ovalbumin and was equipotent with salmeterol in inhibiting antigen-induced bronchospasm in anaesthetised, sensitised guinea-pigs. In both anaesthetised guinea-pig and cat, Ro 31-6930, BRL 38227 and theophylline were more potent against 5-HT evoked increases in lung resistance than they were on falls in dynamic compliance. Although salmeterol had equivalent activity on both parameters it is unlikely that the small difference seen with the other compounds reflect a preferential effect on large airways. In addition, Ro 31-6930 was an effective bronchodilator when given by inhalation to the anaesthetised guinea-pig. In view of the protective activity of Ro 31-6930 against antigen challenge in the sensitised guinea-pig and its potency in relation to other bronchodilators, it is considered that compounds which relax airway smooth muscle by the opening of plasmalemmal potassium channels may have a role in the treatment of asthma.

Pharmacological evidence for tumor necrosis factor as a mediator of allergic inflammation in the airways.

Tumor necrosis factor (TNF) has been implicated in the pathophysiology of a number of inflammatory diseases of the lung. Using the TNF receptor fusion protein, Ro 45-2081, our study investigated the involvement of TNF in allergic inflammatory responses in the airways of sensitized guinea pigs and Brown-Norway rats. Sensitized guinea pigs exhibited an enhanced airway reactivity to substance P (1-10 micrograms/kg, i.v.) at 6 hr after antigen challenge which was inhibited (P < .05) by Ro 45-2081 (3 mg/kg, i.p.). Treatment with Ro 45-2081 (1-3 mg/kg, i.p.) dose-dependently inhibited (P < .05) the accumulation of neutrophils and total cells in bronchoalveolar lavage fluid in sensitized guinea pigs examined at 6 and 24 hr postchallenge. Ro 45-2081 (3 mg/kg, i.p.) also significantly (P < .05) reduced the number of eosinophils in bronchoalveolar lavage at both time points whereas a lower dose (1 mg/kg, i.p.) had no effect. Ro 45-2081 (1 or 3 mg/kg, i.p.) abolished antigen-induced microvascular leakage (quantified by tissue content of Evans blue dye) in the trachea and main bronchi in sensitized guinea pigs. In the Brown-Norway rat, Ro 45-2081 (1-3 mg/kg, i.p.) caused a dose-dependent inhibition of neutrophil and eosinophil infiltration into bronchoalveolar lavage fluid at 24 hr after antigen challenge. In both guinea pig and Brown-Norway rat models, treatment with dexamethasone (30 mg/kg, i.p., for guinea pig and 0.3 mg/kg, i.p., for Brown-Norway rat) produced virtually identical results to those obtained with Ro 45-2081. The ability of Ro 45-2081 to inhibit antigen-induced responses in sensitized animals suggests that TNF is a mediator of allergic inflammation in the lung.