Bronchoconstrictor Activity Research Articles

Airway Smooth Muscles Contractions in Metabolic Syndrome.

We studied contractile responses of isolated airway smooth muscle segments from rats with metabolic syndrome. Metabolic syndrome was induced in rats by high-fat and high-carbohydrate diet. It was shown that metabolic syndrome was associated with an increase of bronchoconstrictor action of cholinergic receptor activator carbacholine (0.1-100 μM) and a decrease of the dilatory effect of β2-adrenoreceptor activator salbutamol (0.1-100 μM). The observed effects of agonists are epithelium-dependent. Disorders in contractile activity in the airway smooth muscles were accompanied by bronchial epithelium destruction, immune inflammation in the bronchial wall, muscular and peribronchial adipose tissue hypertrophy.

Heightened respiratory-parasympathetic coupling to airways in the spontaneously hypertensive rat.

Carotid body (CB) chemoreceptors are hyperactive in hypertension, and their acute activation produces bronchoconstriction. We show that the respiratory-modulated bronchiolar tone, pulmonary parasympathetic efferent activity, and the firing frequency and synaptic excitation of bronchoconstrictor motoneurones in the nucleus ambiguus were all enhanced in spontaneous hypertensive (SH) rats. In SH rats, CB denervation reduced the respiratory-related parasympathetic-mediated bronchoconstrictor tone to levels seen in normotensive rats. Chemoreflex evoked bronchoconstrictor tone was heightened in SH versus normotensive rats. The intrinsic electrophysiological properties and morphology of bronchoconstrictor motoneurones were similar across rat strains. The heightened respiratory modulation of parasympathetic-mediated bronchoconstrictor tone to the airways in SH rats is caused by afferent drive from the CBs. Much research has described heightened sympathetic activity in hypertension and diminished parasympathetic tone, especially to the heart. The carotid body (CB) chemoreceptors exhibit hyperreflexia and are hyperactive, providing excitatory drive to sympathetic networks in hypertension. Given that acute CB activation produces reflex evoked bronchoconstriction via activation of parasympathetic vagal efferents, we hypothesised that the parasympathetic bronchoconstrictor activity is enhanced in spontaneously hypertensive (SH) rats and that this is dependent on CB inputs. In situ preparations of Wistar and SH rats were used in which bronchiolar tone, the pulmonary branch of the vagus (pVN) and phrenic nerves were recorded simultaneously; whole cell patch clamp recordings of bronchoconstrictor vagal motoneurones were also made from the nucleus ambiguus. Bronchiolar tone, pVN and bronchoconstrictor motoneurones were respiratory modulated and this modulation was enhanced in SH rats. These differences were all eliminated after CB denervation. Stimulation of the CBs increased the phrenic frequency that caused a summation of the respiratory-related increases in pVN, resulting in the development of bronchoconstrictor tone. This tone was exaggerated in SH rats. The enhanced respiratory-parasympathetic coupling to airways in SH rats was not due to differences in the intrinsic electrophysiological properties of bronchoconstrictor motoneurones but reflected heightened pre-inspiratory- and inspiratory-related synaptic drive. In summary, in SH rats the phasic respiratory modulation of parasympathetic tone to the airways is elevated and the greater development of this bronchoconstrictor tone is caused by the heightened afferent drive originating from the CBs. Thus, targeting the CBs may prove effective for increasing lower airway patency.

Leukotrienes: One step in our understanding of asthma.

The steps leading to the discovery of leukotrienes and the researchers that played a major part in this long process are presented. The pharmacology of these exquisitely potent compounds shows that they express bronchoconstrictor activity and numerous cellular effects via very specific receptors. Experimental evidence strongly suggests that these mediators play a significant role in asthma physiopathology. Numerous approaches were taken to block their effects on the lungs and this led to the discovery of selected drugs used for asthma treatment. The complexity of this disease and its treatment is emphasized.

PKC-dependent regulation of Kv7.5 channels by the bronchoconstrictor histamine in human airway smooth muscle cells.

Kv7 potassium channels have recently been found to be expressed and functionally important for relaxation of airway smooth muscle. Previous research suggests that native Kv7 currents are inhibited following treatment of freshly isolated airway smooth muscle cells with bronchoconstrictor agonists, and in intact airways inhibition of Kv7 channels is sufficient to induce bronchiolar constriction. However, the mechanism by which Kv7 currents are inhibited by bronchoconstrictor agonists has yet to be elucidated. In the present study, native Kv7 currents in cultured human trachealis smooth muscle cells (HTSMCs) were observed to be inhibited upon treatment with histamine; inhibition of Kv7 currents was associated with membrane depolarization and an increase in cytosolic Ca2+ ([Ca2+]cyt). The latter response was inhibited by verapamil, a blocker of L-type voltage-sensitive Ca2+ channels (VSCCs). Protein kinase C (PKC) has been implicated as a mediator of bronchoconstrictor actions, although the targets of PKC are not clearly established. We found that histamine treatment significantly and dose-dependently suppressed currents through overexpressed wild-type human Kv7.5 (hKv7.5) channels in cultured HTSMCs, and this effect was inhibited by the PKC inhibitor Ro-31-8220 (3 µM). The PKC-dependent suppression of hKv7.5 currents corresponded with a PKC-dependent increase in hKv7.5 channel phosphorylation. Knocking down or inhibiting PKCα, or mutating hKv7.5 serine 441 to alanine, abolished the inhibitory effects of histamine on hKv7.5 currents. These findings provide the first evidence linking PKC activation to suppression of Kv7 currents, membrane depolarization, and Ca2+ influx via L-type VSCCs as a mechanism for histamine-induced bronchoconstriction.

Stereoselective activity of 2-(4-amino-3-chloro-5- trifluomethyl-phenyl)-2-tert-butylamino-ethanol hydrochloride to improve the pulmonary function in asthma

Asthma is a chronic airway disease that is characterized by significantly exacerbated bronchospasms and marked inflammation of the airways. Although the etiology of asthma remains to be determined, genetic predisposition is one of the factors involved. β2-agonists compounds may serve as options for the treatment of bronchial asthma. The aim of the present study was to investigate the effects of 2-(4-amino-3-chloro-5-trifluomethyl-phenyl)-2-tert-butylamino-ethanol hydrochloride (SPFF) and its enantiomers with regard to improving asthmatic pulmonary function and selective binding to β2-adrenergic receptor. The bronchoconstrictor action of histamine in guinea pigs was conducted and the results demonstrated that (-)SPFF and (±)SPFF could significantly inhibit the increase of bronchoconstriction induced by histamine, while (+)SPFF did not show an effect. Inflammatory mediator release from allergic lung tissues was determined and it was found that (±)SPFF showed the highest activity among all the tested compounds, while the efficacy of (-)SPFF was similar to that of (+)SPFF. SPFF and its enantiomers stimulated cyclic adenosine monophosphate (cAMP) production in the asthmatic lung tissues examined, showing that asthmatic lung tissues had a significant cAMP enhancement in response to (-)SPFF and (±)SPFF compared with (+)SPFF. Cardiac contractility of the right atria was assessed in the guinea pigs to establish the receptor selectivity of the compounds. The results indicated that all the compounds had high affinities to the β2 receptor. In conclusion, with regards to asthmatic pulmonary function improvement, (-)SPFF was more efficient as compared to (+)SPFF, while no significant difference was observed for the receptor selectivity of (-)SPFF and (+)SPFF.

Cysteinyl leukotriene receptor-1 antagonists as modulators of innate immune cell function.

Cysteinyl leukotrienes (cysLTs) are produced predominantly by cells of the innate immune system, especially basophils, eosinophils, mast cells, and monocytes/macrophages. Notwithstanding potent bronchoconstrictor activity, cysLTs are also proinflammatory consequent to their autocrine and paracrine interactions with G-protein-coupled receptors expressed not only on the aforementioned cell types, but also on Th2 lymphocytes, as well as structural cells, and to a lesser extent neutrophils and CD8+ cells. Recognition of the involvement of cysLTs in the immunopathogenesis of various types of acute and chronic inflammatory disorders, especially bronchial asthma, prompted the development of selective cysLT receptor-1 (cysLTR1) antagonists, specifically montelukast, pranlukast, and zafirlukast. More recently these agents have also been reported to possess secondary anti-inflammatory activities, distinct from cysLTR1 antagonism, which appear to be particularly effective in targeting neutrophils and monocytes/macrophages. Underlying mechanisms include interference with cyclic nucleotide phosphodiesterases, 5′-lipoxygenase, and the proinflammatory transcription factor, nuclear factor kappa B. These and other secondary anti-inflammatory mechanisms of the commonly used cysLTR1 antagonists are the major focus of the current review, which also includes a comparison of the anti-inflammatory effects of montelukast, pranlukast, and zafirlukast on human neutrophils in vitro, as well as an overview of both the current clinical applications of these agents and potential future applications based on preclinical and early clinical studies.

Antileukotriene Agents for the Treatment of Lung Disease

Leukotrienes (LTs) C4, D4, and E4, collectively termed cysteinyl LTs (cysLTs), are lipid mediators formed by the 5-lipoxygenase (5-LO) pathway of arachidonic acid metabolism. Originally recognized for their potent bronchoconstrictor actions, they were subsequently determined also to promote inflammation, microvascular permeability, and mucus secretion. These actions that are so central to asthma pathophysiology are mediated to a significant extent by ligation of the cysLT receptor 1 (CysLT1). Antagonism of CysLT1 and inhibition of 5-LO have both been shown to have clinical use in the management of asthma, but substantial interindividual heterogeneity is observed in the response to these agents. In this article, we review the biologic actions of LTs, their biosynthetic pathways and cognate receptors, the pharmacology of available anti-LT agents, and the clinical evidence for the use of anti-LT agents as monotherapy and combination therapy in asthma. We also consider heterogeneity of response, the possible roles of cysLT receptors other than CysLT1, the role of another class of LT, LTB4, and the potential role of LTs in lung diseases other than asthma.

High production of endothelin after foam sclerotherapy: a new pathogenetic hypothesis for neurological and visual disturbances after sclerotherapy

Visual and neurological disturbances have always been reported following liquid sclerotherapy (LS) for venous insufficiency. In 1993 Cabrera introduced foam sclerotherapy (FS) using a detergent sclerosant as Lauromacrogol 400 or sodium tetradecyl sulphate. Several authors have reported with FS an increased incidence of such transient visual disturbances and neurological complications. This has been associated with gas or air used to generate the sclerosing foam. The frequent association of the presence of a patent foramen ovale, a common condition in normal population, and such complications has led several authors to consider neurological and visual disturbances as paradoxical gas embolism. We are introducing a new pathogenetic hypothesis for sclerotherapy complications. Medical literature shows evidence of a clear relationship among cerebral and retinal vasospasm, migraine and intimal irritation. We think that the irritating sclerosant agent may stimulate a significant release of vasoactive substances from the venous wall, specifically endothelin 1 (ET-1), the most powerful vasoconstricting agent. We have studied systemic ET-1 levels after LS and FS with Lauromacrogol 400 in a group of 13 rats at one and five minutes after injection. While ET-1 levels did not change significantly in control and in the LS group, a significant increase was detected after FS at one and five minutes. We conclude that should the same results be found in patients treated using sclerosing foam (SF), ET-1 levels may closely correlate to the onset of visual or cerebral complications. Due to the bronchoconstrictor activity of ET-1, a relationship with post-treatment cough can be also postulated.

Bronchodilatory effects of the aqueous extract of Gynostemma pentaphyllum and gypenosides III and VIII in anaesthetized guinea-pigs

The bronchodilatory activity of the aqueous extract of Gynostemma pentaphyllum Makino leaves was investigated in anaesthetized guinea-pigs and compared with two of its isolated gypenosides (III and VIII). The results showed that the intravenous administration of the decoction of G. pentaphyllum (2.5, 5 or 10 mg kg(-1)) decreased bronchial resistance in basal conditions and significantly (P < 0.01) reduced (68% inhibition) the bronchoconstrictor action of histamine. Furthermore, the extract antagonized (80% inhibition) the bronchoconstrictor response induced by the antigen in sensitized guinea-pigs. Gypenosides III (0.7 mg kg(-1), i.v.) and VIII (0.3 mg kg(-1), i.v.) caused a similar protective effect in both experimental models used; however, the duration and the intensity of the action was less than that of the extract containing corresponding quantities of gypenosides III and VIII. This study confirmed the validity of the traditional use of this plant in the treatment of asthma and other respiratory disorders.

Pharmacologic Effects of Tobacco Dust Extract on Isolated Guinea Pig Trachea

To determine the effects of tobacco dust extract (TDE) on isolated guinea pig tracheal smooth muscle. A controlled, in vitro smooth-muscle study of the effect of pharmacologic agents on TDE. The effect of TDE on isolated guinea pig tracheal smooth muscle was tested using water-soluble extracts of dust obtained from machines in a cigarette manufacturing plant. Dose-related contractions of nonsensitized guinea pig trachea were demonstrated using these extracts. The dust extracts contained significant quantities of bacterial components (eg, endotoxin). Pharmacologic studies were performed by pretreating guinea pig tracheal tissue with drugs known to modulate smooth-muscle contraction: atropine, indomethacin, pyrilamine, nordihydroguaretic acid, acivicin, bromophenacyl bromide, 3,4,5-trimethoxybenzoic acid-8-(diethylamino)octyl ester, captopril, and capsaicin. Atropine strikingly reduced the contractile effects of these extracts. Inhibition of contraction by blocking other mediators was less complete. There was no inhibition of contraction by hexamethonium (10(-4) mol/L, 10(-5) mol/L, 10(-6) mol/L), suggesting that nicotine was not the major contractile mediator of TDE. A separate analysis using different molecular weight fractions of TDE indicated that the constrictor activity appears to be primarily in the fraction with a molecular weight < 10 kd. Additionally, the constrictor effect resided entirely in the nonlipid fraction of the extract. We suggest that TDE causes dose-related airway smooth-muscle constriction by nonimmunologic mechanisms involving a variety of airway mediators and possibly cholinergic receptors. The bronchoconstrictor activity of TDE resides primarily in its low molecular weight, nonlipid fraction, and hexamethonium studies suggest that this agent is not nicotine.

Mechanisms underlying tissue selectivity of anandamide and other vanilloid receptor agonists.

Anandamide acts as a full vanilloid receptor agonist in many bioassay systems, but it is a weak activator of primary afferents in the airways. To address this discrepancy, we compared the effect of different vanilloid receptor agonists in isolated airways and mesenteric arteries of guinea pig using preparations containing different phenotypes of the capsaicin-sensitive sensory nerve. We found that anandamide is a powerful vasodilator of mesenteric arteries but a weak constrictor of main bronchi. These effects of anandamide are mediated by vanilloid receptors on primary afferents and do not involve cannabinoid receptors. Anandamide also contracts isolated lung strips, an effect caused by the hydrolysis of anandamide and subsequent formation of cyclooxygenase products. Although capsaicin is equally potent in bronchi and mesenteric arteries, anandamide, resiniferatoxin, and particularly olvanil are significantly less potent in bronchi. Competition experiments with the vanilloid receptor antagonist capsazepine did not provide evidence of vanilloid receptor heterogeneity. Arachidonoyl-5-methoxytryptamine (VDM13), an inhibitor of the anandamide membrane transporter, attenuates responses to olvanil and anandamide, but not capsaicin and resiniferatoxin, in mesenteric arteries. VDM13 did not affect responses to these agonists in bronchi, suggesting that the anandamide membrane transporter is absent in this phenotype of the sensory nerve. Computer simulations using an operational model of agonism were consistent, with differences in intrinsic efficacy and receptor content being responsible for the remaining differences in agonist potency between the tissues. This study describes differences between vanilloid receptor agonists regarding tissue selectivity and provides a conceptual framework for developing tissue-selective vanilloid receptor agonists devoid of bronchoconstrictor activity.

Regulation of leukotrienes in the management of asthma: biology and clinical therapy.

Leukotrienes (LTs) are the ultimate synthetic product resulting from the intracellular hydrolysis of membrane phospholipid at the nuclear envelope in inflammatory cells. Activated cytosolic phospholipase (cPLA2) catalyzes the production of arachidonic acid, which is converted by cyclooxygenases into leukotriene A4 (LTA4) and subsequently into the chemotaxin LTB4, which has no direct bronchoconstrictor activity. In certain inflammatory cells, LTA4 is converted into the cysteinyl leukotriene (cysLT) LTC4, which is converted into LTD4 and finally to LTE4 after extracellular transport. All cysLTs occupy the same receptors and are extremely potent bronchoconstricting agents that are pathogenetic in both asthma and allergy. With the identification of the structure of the cysLT receptor, antileukotriene therapies have been developed that either (a) inhibit synthesis of leukotriene (through 5-lipoxygenase inhibition) or (b) block the cysLT receptor. Preliminary investigations indicate that corticosteroids also may partially block the synthesis of cysLT and that cysLTs may be chemotactic for other inflammatory cells, e.g. eosinophils, by a mechanism that has not yet been defined. Currently, anti-LT therapies are approved by the US Food and Drug Administration (FDA) only for patients with asthma. These drugs generally are moderately efficacious agents, although they are highly efficacious in aspirin-induced asthma (AIA). In other forms of asthma, inhaled corticosteroid (ICS) therapy has been more effective than anti-LT therapy in improving air flow obstruction. However, anti-LT agents are additive to beta-adrenoceptor and ICS in their effects. Accordingly, anti-LT therapies are used frequently as supplemental treatments in asthmatic patients whose asthma is not optimally controlled by a combination of other drugs, including long-acting beta-adrenoceptor drugs and ICS agents. The growth of leukotriene receptor antagonists (LTRAs) has been extraordinary in the United States. The exceptional safety of these agents and their ease of administration as tablets taken once or twice daily has spurred this growth. In the past year, the high-affinity cysLT receptor has been cloned. This holds forth the promise of a second generation of LTRA agents of even greater efficacy and possibly greater duration of action.

Eosinophils in asthma and other allergic diseases

A hallmark of allergic disease is infiltration of the tissues with increased numbers of eosinophils. This is the result of the co-ordinated action of cytokines, particularly IL-5, CCR3 binding chemokines and the adhesion molecules P-selectin and VCAM-1, acting in concert to cause selective trafficking of eosinophils into allergic tissue. This process is orchestrated by the Th-2 allergen specific lymphocyte. While there is little data to support the view that eosinophils ameliorate the allergic process, although they could have an important role in the disordered repair that leads to permanently impaired function in some allergic diseases, the evidence that they cause many of the pathophysiological features of allergic disease, while strong, remains circumstantial. Much of the data could be interpreted just as easily to suggest that eosinophils are bystander cells; markers of a certain type of pathological process, but not impinging upon it. The most direct evidence for a pathological role rests on the toxicity of the eosinophil granule proteins for bronchial epithelium and the bronchoconstrictor actions of the sulphidopeptide leukotrienes. The actions of LT antagonists in asthma which are certainly beneficial, but in most cases are not as effective as glucocorticoids, could be interpreted both for and against the eosinophil. In this paper we have focused on the studies that ask most directly the question of whether eosinophils are important effector cells in the pathogenesis of allergic disease. We conclude with a qualified affirmative. Even if they are only bystander cells they remain clinically important as diagnostic markers and a guide to the management of allergic disease.

Effect of Infused Angiotensin II on the Bronchoconstrictor Activity of Inhaled Endothelin-1 in Asthma

Endothelin (ET)-1 is a potent bronchoconstrictor, and asthmatics demonstrate bronchial hyperresponsiveness to ET-1 given by inhalation. Angiotensin II (Ang II) is increased in plasma in acute severe asthma, causes bronchoconstriction in asthmatics, and potentiates contractions induced by ET-1 in bovine bronchial smooth muscle in vitro, and contractions induced by methacholine both in vitro and in vivo. We wished to examine any potentiation of the bronchoconstrictor activity of inhaled ET-1 by infused Ang II at subbronchoconstrictor doses. Double-blind randomized placebo-controlled study. Asthma research unit in university hospital. Eight asthmatic subjects with baseline FEV1 88% predicted, bronchial hyperreactivity (geometric mean, concentration of methacholine producing 20% fall, methacholine PC20 2.5 mg/mL), and mean age 37.1 years. We examined the effect of subbronchoconstrictor doses of infused Ang II (1 ng/kg/min and 2 ng/kg/min) or placebo on bronchoconstrictor responses to inhaled ET-1 (dose range, 0.96 to 15.36 nmol). Oxygen saturation, noninvasive BP, and spirometric measurements were made throughout the study visits. Blood was sampled for plasma Ang II levels at baseline and before and after ET-1 inhalation. Ang II infusion did not produce bronchoconstriction per se at either dose prior to ET-1 challenge. Bronchial challenge with inhaled ET-1 produced dose-dependent bronchoconstriction, but there was no difference in bronchial responsiveness to ET-1 comparing infusion of placebo with Ang II at 1 ng/kg/min or 2 ng/kg/min (geometric mean, concentration of ET-1 producing 15% fall, 5.34 nmol, 4.95 nmol, and 4.96 nmol, respectively) (analysis of variance, p > 0.05). There was an increase in systolic and diastolic BP at the higher dose of Ang II compared to placebo (mean 136/86 vs 117/75 mm Hg, respectively). Plasma Ang II was elevated following infusion of both doses of Ang II compared to placebo. In contrast to the potentiating effect on methacholine-induced bronchoconstriction, Ang II at subbronchoconstrictor doses does not potentiate ET-1-induced bronchoconstriction in asthma.

Prostanoids counterbalance the bronchoconstrictor activity of endothelin-1 in pigs

In 12 anaesthetized spontaneously breathing pigs divided into two groups of six animals we evaluated the respiratory and haemodynamic responses to endothelin-1 (ET-1) administered by aerosol (200 pmol.kg −1 in 1 ml of saline solution). In the first group (control group), the responses to ET-1 were evaluated before and after the blocking of endogenous nitric oxide (NO) by N G-nitro-L-arginine methyl ester (L-NAME 5 mg.kg −1, i.v.). In the second group (indomethacin-pretreated group), the experimental protocol was similar to that of the control group, but the responses were evaluated after the blocking of endogenous prostanoids by indomethacin (3 mg.kg −1, i.v.). Results show that in the control group ET-1 administered before and after L-NAME did not change compliance (Crs) or resistances (Rrs) of the respiratory system. In indomethacin-pretreated pigs, ET-1 significantly increased Rrs and decreased Crs. This constrictor effect appearing only during the block of arachidonic acid metabolites showed that ET-1 activity can be counterbalanced by a release of dilator prostanoids. In this group after L-NAME pretreatment ET-1 did not alter the mechanical properties of the respiratory system, suggesting an involvement of other bronchodilator mechanisms. In the control group, aerosol administered ET-1 increased mean systemic (MAP) and pulmonary (MPAP) arterial pressures, while when ET-1 was administered after L-NAME pretreatment, MPAP decreased. In the indomethacin-pretreated group, the peptide did not modify MAP, but caused an early decrease in MPAP when administered after L-NAME. Therefore, our results show that ET-1 caused a bronchoconstrictor effect only in indomethacin-pretreated pigs and suggest that the intrinsic constrictor activity of the peptide can be modulated especially by the release of dilator prostanoids.

Bronchodilatory and cardiovascular effects of an ethanol extract of Bacopa monniera in anaesthetized rats

The bronchodilatory effect of the ethanol extract of Bacopa monniera on anaesthetized rats was studied. The extract antagonized the bronchoconstrictor action of carbachol. The bronchodilatory property shown by the plant extract (50 mg/kg) is reflected by a reduction in expiratory pressure which resembled more a salbutamol induced effect as compared with isoprenaline. The bronchodilatory action of the plant extract is probably mediated jointly by β-adrenoceptor dependent and independent mechanisms. Thus providing a rationale for its traditional use in the treatment of asthma.

Effects of FR173657, a non‐peptide B2 antagonist, on kinin‐induced hypotension, visceral and peripheral oedema formation and bronchoconstriction

1. Kinins are believed to play a key role in many inflammatory conditions. Therefore, bradykinin antagonists are being developed for potential therapeutic applications. In the present investigation we describe the pharmacology, in vivo, of (E)-3-(6-acetamido-3-pyridyl)-N-[N-[2,4-dichloro-3-[2-methyl-8-quinoliny l) oxymethyl]phenyl]-N-methylaminocarbonylmethyl]acrylamide (FR173657), a novel, non-peptide bradykinin antagonist. 2. The hypotensive effects of i.v. injections of bradykinin (50 pmol) in captopril-pre-treated anaesthetized rats were significantly inhibited by 100 nmol kg-1 FR173657 s.c., and completely abolished by 300 nmol kg-1. The full inhibitory effect developed within 60 min and remained unchanged for at least 4 h. However, the effect was reversible, since 24 h after an injection of 300 nmol kg-1 FR173657 no inhibitory effect could be observed. 3. The plasma protein extravasation into the pancreas and duodenum induced by an i.v. infusion of bradykinin (11 nmol kg-1 within 20 min) in captopril-treated anaesthetized rats was completely abolished by FR173657 at doses of 30 nmol kg-1 s.c. and above, given 60 min before bradykinin. FR173657 3 nmol kg-1 was ineffective, while a dose of 10 nmol kg-1 produced an intermediate effect. 4. The paw oedema induced by the subplantar injection of bradykinin (30 nmol) in anaesthetized rats was inhibited slightly by s.c. injection of FR173657 0.3 mumol kg-1, whereas 1 and 3 mumol kg-1 produced significant inhibition of the bradykinin-induced oedema. The maximum inhibition amounted to about 50% and could not be increased even when the dose of FR173657 was increased to 30 mumol kg-1. FR173657 did not effect the oedema caused by histamine or 5-hydroxytryptamine. 5. Bradykinin (20 nmol kg-1, i.v.) caused increases in pulmonary inflation pressure by 300-600 Pa in anaesthetized, respirated guinea-pigs. The effect was reduced to 58 +/- 9% of the initial value 60 min after the s.c. injection of FR173657 1 mumol kg-1, whereas only 9 +/- 7% remained after 10 mumol kg-1. The bronchoconstrictor actions of histamine remained unaffected by FR173657. 6. In summary, FR173657 is a highly potent and selective bradykinin antagonist. The inhibitory action in vivo lasts for longer than 4 h but is fully reversible. FR173657, or similar compounds, will be a useful tool for the pharmacological investigation of pathophysiological states and may possess a therapeutic potential in diseases involving the endogenous release of kinins.

BAY u3405, a Thromboxane A2 Antagonist, Reduces Bronchial Hyperresponsiveness in Asthmatics

Thromboxane A2 (TXA2) is reported to induce bronchial hyperresponsiveness along with the well-documented bronchoconstrictor action on smooth muscles. We examined the effect of the TXA2 antagonist, BAY u3405, on bronchial hyperresponsiveness to methacholine (MCh) in asthmatics. Twelve adult asthmatics were studied in a randomized, double-blind, placebo-controlled, crossover fashion. Following a 2-week run-in period, the subjects were administered 75 mg of BAY u3405 or placebo orally, twice a day for 2 weeks each in a crossover design, interposing a 2-week washout period. Bronchial hyperresponsiveness was measured by the astograph method. Briefly, the respiratory resistance (Rrs) was measured by the forced oscillation method during continuous inhalation of MCh in stepwise incremental concentrations, until Rrs reached twice the baseline value. Bronchial hyperresponsiveness was evaluated as the minimum cumulative dose (Dmin) of MCh that induced an increase in Rrs. Dmin was calculated so that 1 U of Dmin equals to 1 min of inhalation of aerosol solution at 1.0 mg/mL during quiet breathing. Three subjects were withdrawn from the evaluation because they had asthmatic attacks or wheezing during the study. The Dmin value of 0.533 U (GSEM 1.675) after the BAY u3405 treatment was significantly greater than that of 0.135 U (GSEM 1.969) after the placebo treatment (p = 0.0139). There were no safety concerns in either treatment group. We conclude that BAY u3405 may be a useful drug for attenuating bronchial hyperresponsiveness in bronchial asthma.

Bronchodilatory effects of ipratropium bromide in patients with tetraplegia

Airway hyperresponsiveness was recently described in patients with chronic cervical spinal cord injury (tetraplegia). The response was attributed to unopposed cholinergic broncho-constrictor activity due to loss of sympathetic innervation of the airway. To determine if the administration of a cholinergic antagonist alters resting airway tone in these patients, ipratropium bromide (72 micrograms) was administered by aerosol to 25 tetraplegic patients. We found that 12 of 25 patients (48%) had significant improvement (defined as > or = 12%) in forced expired volume in 1 s (FEV1) and/or forced vital capacity (FVC). A significant correlation between airway responsiveness and complaints of dyspnea at rest, completeness of injury (sensory), or smoking history was not found. These findings of improved airflow after the use of an anticholinergic bronchodilator agent provides further evidence that transection of the cervical cord results in unopposed parasympathetic activity and a resultant increase in resting airway tone.

Substance P induces histamine release from human pulmonary mast cells

Substance P elicits histamine release from human skin and rodent mast cells. Since neuropeptide-mediated reflexes may be important in asthma, we examined the ability of substance P to stimulate human mast cells obtained at bronchoalveolar lavage (BAL). BAL samples were obtained at routine bronchoscopy from 35 non-preselected patients. Histamine release experiments were performed in a standard manner using substance P and the calcium ionophore A23187. Both substance P (50 microM) and A23187 caused histamine release (median 26.7% range 6.2-62.8% and 32.1%, 7.7-56.8% respectively) which was significantly greater (P < 0.0001) than the spontaneous release (median 15.6%, range 4.1-33.4%), i.e. that in the absence of any stimulus. Substance P induced histamine release was via an energy dependent process and was blocked by preincubation with antimycin A. A significant correlation was observed between substance P induced release and spontaneous release but was not observed with A23187 induced release. Mast cell counts correlated significantly with substance P induced release but not with spontaneous or A23187 induced release. The substance P induced histamine secretion was elicited at similar concentrations to those used with rodent and human skin mast cells. Asthma is associated with increased numbers of mast cells which have both increased spontaneous and stimulated secretory responses. Thus, in vivo, the bronchoconstrictor action of substance P may in part result from activation of mast cells in the bronchial lumen.