Hyperresponsiveness In Guinea Pigs Research Articles

Airway Exposure to 1,3-Beta-d-Glucan Induces Airway Hyperresponsiveness in Guinea Pigs.

1,3-Beta-d-glucan (β-glucan) is a component of mold cell walls and is frequently found in fungi and house dust mites. The studies of β-glucan are inconsistent, although it has been implicated in airway adverse responses. This study was carried out to determine whether airway hyperresponsiveness was seen 24 h after airway exposure to β-glucan in guinea pigs. Two matching guinea pigs were exposed intratracheally to either β-glucan or its vehicle. Twenty-four hours after intratracheal instillation, there was no difference between these two groups in the baseline of the total pulmonary resistance (R L), dynamic lung compliance (C dyn), arterial blood pressure, and heart rate. In contrast, the responses of R L to capsaicin injection were significantly increased in β-glucan animals; capsaicin at the same dose of 3.2 μg/kg increased R L by 184% in vehicle animals and by 400% in β-glucan animals. The effective dose 200% to capsaicin injection was lower in the β-glucan animals. Furthermore, the increases in R L were partially reduced after transient lung hyperinflation to recruit the occluding airways; however, the R L induced by capsaicin injection after lung hyperinflation was significantly larger than the baseline in β-glucan animals; also, the lung wet-to-dry ratio in capsaicin-injected animals was augmented in the β-glucan group. Moreover, the airway hyperresponsiveness was accompanied by increases in neutrophils in the bronchoalveolar lavage fluid in the β-glucan animals. Furthermore, the levels of substance P and the calcitonin gene-related peptide in the bronchoalveolar lavage fluid collected after capsaicin injection were increased in β-glucan animals. We provide definitive evidence that β-glucan can induce airway hyperresponsiveness in guinea pigs, and the neuropeptide releases play an important role in this airway hyperresponsiveness.

Small airway hyperresponsiveness in COPD: relationship between structure and function in lung slices.

The direct relationship between pulmonary structural changes and airway hyperresponsiveness (AHR) in chronic obstructive pulmonary disease (COPD) is unclear. We investigated AHR in relation to airway and parenchymal structural changes in a guinea pig model of COPD and in COPD patients. Precision-cut lung slices (PCLS) were prepared from guinea pigs challenged with lipopolysaccharide or saline two times weekly for 12 wk. Peripheral PCLS were obtained from patients with mild to moderate COPD and non-COPD controls. AHR to methacholine was measured in large and small airways using video-assisted microscopy. Airway smooth muscle mass and alveolar airspace size were determined in the same slices. A mathematical model was used to identify potential changes in biomechanical properties underlying AHR. In guinea pigs, lipopolysaccharide increased the sensitivity of large (>150 μm) airways toward methacholine by 4.4-fold and the maximal constriction of small airways (<150 μm) by 1.5-fold. Similarly increased small airway responsiveness was found in COPD patients. In both lipopolysaccharide-challenged guinea pigs and patients, airway smooth muscle mass was unaltered, whereas increased alveolar airspace correlated with small airway hyperresponsiveness in guinea pigs. Fitting the parameters of the model indicated that COPD weakens matrix mechanical properties and enhances stiffness differences between the airway and the parenchyma, in both species. In conclusion, this study demonstrates small airway hyperresponsiveness in PCLS from COPD patients. These changes may be related to reduced parenchymal retraction forces and biomechanical changes in the airway wall. PCLS from lipopolysaccharide-exposed guinea pigs may be useful to study mechanisms of small airway hyperresponsiveness in COPD.

Dose dependent effects of tadalafil and roflumilast on ovalbumin-induced airway hyperresponsiveness in guinea pigs

ABSTRACT Introduction: Chronic obstructive diseases of airways associated with cough and/or airway smooth muscle hyperresponsiveness are usually treated with bronchodilating and anti-inflammatory drugs. Recently, selective phosphodiesterase (PDE) 4 inhibitors have been introduced into the therapy of chronic obstructive pulmonary disease. Several studies have demonstrated their ability to influence the airway reactivity and eosinophilic inflammation by increasing the intracellular cAMP concentrations also in bronchial asthma. Furthermore, the expression of PDE5 in several immune cells suggests perspectives of PDE5 inhibitors in the therapy of inflammation, as well. Purpose: The aim of this study was to assess the dose-dependent effects of PDE4 and PDE5 inhibitors in allergic inflammation. Therefore, the effects of 7-days administration of PDE4 inhibitor roflumilast and PDE5 inhibitor tadalafil at two different doses in experimentally-induced allergic inflammation were evaluated. Materials and Methods: In the study, male adult guinea pigs were used. Control group was non-sensitized. Other animals were sensitized with ovalbumin over two weeks and thereafter treated intraperitoneally for 7 days with roflumilast or tadalafil (daily dose 0.5 mg/kg or 1.0 mg/kg b.w.), or with vehicle. Results: Both roflumilast and tadalafil reduced specific airway resistance after nebulization of histamine (marker of in vivo airway reactivity) at both doses used. The in vitro airway reactivity to cumulative doses of acetylcholine was significantly reduced for roflumilast at higher dose, predominantly in the lung tissue strips. Histamine-induced contractile responses were significantly influenced in both lung and tracheal tissue strips, predominantly at the higher doses. Tadalafil led to a decrease in contractile responses induced by both acetylcholine and histamine, with more significant effects in the lung tissue strips. These changes were associated with decreased numbers of circulating leukocytes and eosinophils and concentrations of interleukin (IL)-4, IL-5 and TNF-α in the lung homogenate. Conclusions: The selective PDE4 and PDE5 inhibitors alleviated allergic airway inflammation, with more significant effects at the higher doses.

Inhibition of antigen-induced airway inflammation and hyperresponsiveness in guinea pigs by a selective antagonist of “chemoattractant receptor homologous molecule expressed on Th2 cells” (CRTH2)

Chemoattractant receptor homologous molecule expressed on T helper type 2 cells (CRTH2) is a PGD2 receptor found on eosinophils, basophils, and Th2 type T cells which exhibits chemotaxis and functions in activation cascades. However, while a number of CRTH2 antagonists, including ramatroban, are known to exert activity in certain animal models, activity in a guinea pig model of EA-induced airway hyperresponsiveness has not been demonstrated. The newly developed CRTH2 antagonist ASP5642 has shown antagonistic activity against human and guinea pig CRTH2 in previous studies and has also been found effective in treating guinea pig models of airway inflammation and airway hyperresponsiveness. While previous studies have used animals such as rats and mice to evaluate CRTH2 antagonist effects, ours is the first attempt to evaluate CRTH2 function in a guinea pig asthma model, which may prove useful in evaluating the compound’s effects in humans, given the comparable airway function between the two species taken together, these data from the present study strongly suggest the utility of ASP5642 in investigating the role of CRTH2 in inflammatory responses and as a drug treatment for human asthma.

Intratracheal Sensitization/Challenge-Induced Biphasic Asthmatic Response and Airway Hyperresponsiveness in Guinea Pigs

In most experimental model of asthma using guinea pigs, the animals are made to inhale an aerosolized antigen which passes through the nasal cavity. In the present study, we attempted to create an animal model of asthma showing a biphasic asthmatic response and airway hyperresponsiveness, in which the allergic responses are restricted to the lung. Guinea pigs were sensitized by the intratracheal instillation of ovalbumin (OVA)+Al(OH)₃ once a day for 7 d, and then intratracheally challenged with OVA 12 d after the last sensitization. The change in specific airway resistance (sRaw) and airway responsiveness to histamine were measured. Pranlukast (100 mg/kg), theophylline (50 mg/kg), and dexamethasone (10 mg/kg) were orally administered 18 and 2 h before the antigen challenge. The challenge caused a marked biphasic elevation of sRaw with peaks at 5 min and 4 h. At 24 h, airway hyperresponsiveness to histamine was observed. Pranlukast, theophylline, and dexamethasone suppressed the late asthmatic response and airway hyperresponsiveness. The early asthmatic response was inhibited by theophylline and dexamethasone. In conclusion, the intratracheal sensitization and challenge caused a biphasic asthmatic response and airway hyperresponsiveness in guinea pigs. This model may be useful for the evaluation of anti-asthma drugs.

Effects of Nω-nitro-L-arginine methyl ester and aminoguanidine on lipopolysaccharide-induced airway hyperresponsiveness in guinea pigs

The down-regulation of constitutive nitric oxide synthase (cNOS) and up-regulation of inducible nitric oxide synthase (iNOS) are associated with the allergen-provocated airway hyperresponsiveness (AHR). This study aimed to determine whether their alteration also plays an important role in the AHR induced by lipopolysaccharide (LPS). Hartley male guinea pigs, weighing between 250 g and 350 g, were injected with LPS at a dose of 1 mg/kg every 24 hours for three days. A non-selective NOS inhibitor, N(omega)-nitro-L-arginine methyl ester (L-NAME), or a selective inducible NOS inhibitor, aminoguanidine (AG), were used thirty minutes before each injection of LPS. Airway reactions, nitric oxide (NO) production and inflammatory changes were detected 24 hours after the last dose of LPS. AG significantly decreased the NO production in the bronchoalveolar lavage fluid (BALF) and sharply reduced the intensity of bronchoconstriction to histamine challenge. L-NAME also significantly decreased the NO production in the BALF, but had no effect on airway reactions or, perhaps, a tendency to enhance the intensity of AHR. The data suggest that inducible NOS contributes to the AHR induced by repetitive intraperitoneal LPS, and constitutive NOS was also involved.

Contribution of prostaglandin D 2 via prostanoid DP receptor to nasal hyperresponsiveness in guinea pigs repeatedly exposed to antigen

We examined the role of prostanoid DP receptor in nasal blockage in an experimental allergic rhinitis model in guinea pigs. Local inhalation of prostaglandin D 2 (PGD 2) to the nasal cavity resulted in an increase in intranasal pressure in guinea pigs actively sensitized by repeated antigen exposure but not in non-sensitized guinea pigs. Nasal hyperresponsiveness was observed when the guinea pigs were exposed to histamine and U-46619 (11α, 9α-epoxymethano-PGH 2; a thromboxane (TX) A 2 mimetic) after repeated antigen exposure. S-5751 ((Z)-7-[(1R,2R,3S,5S)-2-(5-hydroxybenzo[b]thiophen-3-ylcarbonylamino)-10-norpinan-3-yl]hept-5-enoic acid), a prostanoid DP receptor antagonist, inhibited not only PGD 2-induced nasal blockage but also nasal hyperresponsiveness to histamine and U-46619 in sensitized guinea pigs. Combined exposure of the nasal cavity of guinea pigs to an aerosol of PGD 2 with histamine or U-46619 at sub-threshold concentrations synergistically caused a marked increase in intranasal pressure. These responses were significantly suppressed by S-5751. These results suggest that PGD 2 plays a critical role in the increase in intranasal pressure via prostanoid DP receptor, probably through synergistically enhancing the nasal response with other chemical mediators released from mast cells and other inflammatory cells activated by allergens.

Kinins are involved in the development of allergic nasal hyperresponsiveness in guinea pigs

We evaluated roles of kinins in allergen-induced nasal blockage and sneezing, and development of nasal hyperresponsiveness to leukotriene D 4 in a Japanese cedar pollen-induced allergic rhinitis model of guinea pigs. Sensitised guinea pigs were repeatedly challenged by pollen inhalation once every week. Neither a bradykinin B 1 receptor antagonist, des-Arg 9-[Leu 8]bradykinin nor a bradykinin B 2 receptor antagonist, icatibant suppressed allergen-induced sneezing and nasal blockage. However, development of nasal hyperresponsiveness to leukotriene D 4 was significantly suppressed by them. The amount of bradykinin in nasal cavity lavage fluid was immediately increased after the challenge. In non-sensitised animals, hyperresponsiveness to leukotriene D 4 was developed by a bradykinin B 2 receptor agonist, bradykinin, but not by a bradykinin B 1 receptor agonist, des-Arg 10-kallidin, while in the sensitised-challenged animal, both agonists developed hyperresponsiveness. In conclusion, the nasal hyperresponsiveness appeared to be induced by kinins produced in response to the antigen challenge through activation of not only bradykinin B 2 but also B 1 receptors.

Role of Rho-Associated Protein Kinase and Histamine in Lysophosphatidic Acid-Induced Airway Hyperresponsiveness in Guinea Pigs

Inhalation of oleoyl lysophosphatidic acid (LPA) induced airway hyperresponsiveness to acetylcholine (ACh). In contrast, palmitoyl and stearoyl LPA exerted minimal effects. Airway hyperresponsiveness was inhibited by inhalation of Y-27632, an inhibitor of Rho-associated protein kinase (ROCK). Mepyramine, an H1 histamine receptor antagonist and ketotifen, an inhibitor of histamine release and H1 histamine receptor antagonist, also inhibited airway hyperresponsiveness induced by LPA; however, aspirin failed to attenuate this response. The incubation of lung fragments with LPA gave rise to releases in histamine. On the other hand, LPA produced no significant changes on the smooth muscle contraction evoked by ACh. These findings suggest that LPA-induced airway hyperresponsiveness is attributable to activation of the Rho/ROCK-mediated pathway via endothelial cell differentiation gene (EDG) receptors, probably EDG 7. Moreover, histamine release may be involved.

Modification of eosinophil function by suplatast tosilate (IPD), a novel anti-allergic drug

Suplatast tosilate (IPD), a new dimethylsulfonium agent, is used therapeutically in allergic diseases. Suplatast has been reported to attenuate airway hyperresponsiveness in guinea pigs, human IgE synthesis, and murine peritoneal eosinophilia. However, the effect of suplatast on human eosinophils is not known. In this study, we examined the effects of suplatast in human eosinophils on platelet activating factor (PAF, 1 μM)-induced chemotaxis by the blind well chamber technique, eosinophil adhesion to TNF-α (10 ng/ml) or IL-4 (10 ng/ml)-stimulated human umbilical vein endothelial cells (HUVECs), and expression of very late antigen-4 (VLA-4) on eosinophils and vascular cell adhesion molecule-1 (VCAM-1) on HUVECs by flow cytometry. Suplatast suppressed IL-4-induced eosinophil adhesion to HUVECs in a dose-dependent manner. Eosinophils from the normal subjects did not express VLA-4. However, there was a significant increase ( P<0.01) in the basal expression of VLA-4 in allergic patients. PAF or IL-4 did not enhance VLA-4 expression on eosinophils, and there was no significant effect of suplatast on VLA-4 expression in allergic patients. Suplatast did not affect TNF-α-induced VCAM-1 expression. Interestingly, suplatast significantly suppressed IL-4 induced VCAM-1 expression on HUVECs and PAF-induced eosinophil chemotaxis. These data suggest that suplatast may modify eosinophil participation in airway inflammation by attenuating inflammatory mediators-induced chemotaxis and adhesion to endothelial cells, and thus might be useful in the treatment of bronchial asthma.

Decreased pulmonary and tracheal smooth muscle expression and activity of type 1 nitric oxide synthase (nNOS) after ovalbumin immunization and multiple aerosol challenge in guinea pigs.

Pharmacological evidence supports a role of a transient decreased endogenous nitric oxide (NO) synthesis in ovalbumin (OVA)-induced early airway hyperresponsiveness in guinea pigs. However, no data are available regarding the expression and activity of the constitutive NO synthases (cNOS; NOS1 and NOS3, nNOS and eNOS, respectively) in this model. Therefore, we evaluated cNOS activity (conversion of L-[3H]arginine to L-[3H]citrulline in the presence of Ca2+ and calmodulin), nitrate and nitrite (NOx) concentration (modified Griess method), and NOS1 and NOS3 protein expression (Western blot) in lung homogenates and in the tracheal smooth muscle from OVA-immunized and multiple aerosol-challenged guinea pigs (six challenges, once daily). The expression and activity of the inducible NOS isoform (NOS2), the levels of exhaled NO, and the in vivo airway reactivity were also determined. Constitutive NOS activity and NO(x) concentration were significantly lower 6 h after the last OVA challenge as compared with saline exposure, being similar at 24 h. Expression of NOS1 paralleled cNOS activity, which was reduced 6, but not 24 h after OVA challenge. The decrease in NOS1 expression was accompanied by a significant decrease in the amounts of exhaled NO and by a maximal airway hyperresponsiveness to histamine. The levels of NOS3 were not modified at the two time points evaluated, and no NOS2 expression and activity were found at any time point. Similar modifications were observed in the tracheal smooth muscle. We conclude that OVA stimulation in immunized guinea pigs induced a transient reduction in NOS1 protein expression and activity in the respiratory system, which probably participates in airway hyperresponsiveness.

Effect of a cysteinyl leukotriene antagonist, pranlukast hydrate, on acetaldehyde-induced bronchoconstriction in asthmatic patients

Acetaldehyde is a main factor of alcohol-induced asthma. We previously reported that the cysteinyl leukotriene (cys-LT) receptor antagonist, pranlukast hydrate, inhibits acetaldehyde-induced airway hyperresponsiveness in guinea pigs. The purpose of this study was to evaluate the involvement of cys-LT on bronchial responsiveness to acetaldehyde in asthmatic patients. We investigated the bronchial response to inhalation of acetaldehyde in 10 asthmatic patients, who were treated with placebo or pranlukast hydrate (225.5 mg), a cys-LT receptor antagonist, twice a day for 1 wk using a double-blind, randomized, placebo-controlled, cross-over design. Although a remarkable improvement of acetaldehyde bronchoconstriction was observed in 3 out of 10 subjects, PC20-AcCHO values were identical between placebo [12.0 (GSEM, 1.192) mg/ml] and pranlukast [14.7 (GSEM, 1.245) mg/ml] groups. The changes in bronchial responsiveness to acetaldehyde were similar in the six patients who had never experienced alcohol-induced asthma and the four who had. In conclusion, cys-LTs are not involved in acetaldehyde-induced bronchoconstriction.

IMPROVEMENT OF INTERSTITIAL CYSTITIS SYMPTOMS AND PROBLEMS THAT DEVELOPED DURING TREATMENT WITH ORAL IPD-1151T

We examined the efficacy of Suplatast Tosilatedouble dagger (IPD-1151T), a new immunoregulator that suppresses helper T cell mediated allergic responses, including IgE production and eosinophilic inflammation for treating patients with interstitial cystitis. A total of 14 women (average age 43.7 years) with interstitial cystitis, which was nonulcerative in 13 and ulcerative in 1, were treated with 300 mg. IPD-1151T orally daily for 12 months. All patients received laboratory assessments, including hematology (eosinophils and CD20 positive cells) and serum chemistry (IgE, and interleukin-4 (IL-4) and 5, and immunohistochemical analyses of urine leukocytes (CD45RO positive cells as a T cell marker) before treatment. These parameters were also measured 4 and 12 months after continuous treatment. The voiding chart, and interstitial cystitis symptom and problem indexes were evaluated before and after IPD-1151T treatment. IPD-1151T treatment for 1 year resulted in a significantly increased bladder capacity and decreased symptoms, such as urinary urgency, frequency and lower abdominal pain, in patients with nonulcerative interstitial cystitis. These effects also correlated with a reduction in blood eosinophils, CD20 positive cells and IgE, and urine CD45RO positive memory T cells. No major side effects were observed. Our study suggests that immunological responses are involved in the development of interstitial cystitis symptoms. IPD-1151T could be a new oral agent for treatment of voiding symptoms and bladder pain in patients with interstitial cystitis.

Effect of eotaxin and platelet-activating factor on airway inflammation and hyperresponsiveness in guinea pigs in vivo.

Although eotaxin causes selective infiltration of eosinophils into the lung, its role in airway hyperresponsiveness remains unclear. We studied the effects of local administration of eotaxin on airway inflammation and hyperresponsiveness in guinea pigs in vivo. Airway responsiveness to inhaled histamine and differential cell counts in bronchoalveolar lavage fluid (BALF) were evaluated 12 h, 24 h, 3 d, and 7 d after intratracheal instillation of eotaxin. Significant eosinophilia in BALF was observed between 6 h and 7 d after eotaxin administration. Histologically, eosinophil accumulation was observed in the airways but not in the alveoli. In contrast, eotaxin did not affect airway responsiveness between 12 h and 7 d after its administration. We then studied the effects on airway responsiveness of subthreshold doses of interleukin 5, leukotriene D(4) (LTD(4)), and platelet-activating factor (PAF) combined with eotaxin. Neither interleukin 5 nor LTD(4) affected airway responsiveness. After eotaxin treatment, PAF significantly enhanced airway responsiveness without further increases in eosinophil counts. Eotaxin plus PAF significantly increased in eosinophil peroxidase activity in BALF compared with control and with eotaxin alone. These data indicate that eotaxin alone causes eosinophil accumulation in the airways but not hyperresponsiveness, and that additional factors such as PAF are needed to activate eosinophils for the development of airway hyperresponsiveness.

Virus- and bradykinin-induced airway hyperresponsiveness in guinea pigs.

The involvement of bradykinin in virus-induced airway hyperresponsiveness (AHR) in guinea pig airways in vivo was determined with the B(2)-receptor antagonist Hoe 140. The efficacy of Hoe 140 treatment was assessed through its effect on the bradykinin-induced (up to 2.5 microgram/100 g B.W. administered intravenously) decrease in blood pressure (BP). Hoe 140 (0.1 micromol/kg), administered subcutaneously twice a day for 5 d almost completely blocked bradykinin-induced changes in BP. Four days after parainfluenza-3 (PI-3) virus infection, guinea pigs showed AHR; excessive airway contraction was found with histamine-receptor stimulation. This hyperresponsiveness was completely inhibited by pretreatment with Hoe 140 (0.1 micromol/kg) administered subcutaneously twice a day for five consecutive days, starting 1 d before virus inoculation. Interestingly, nebulized delivery of bradykinin itself to captopril-treated animals induced an AHR comparable to that observed in virus-treated guinea pigs. Viral infection also caused influx of bronchoalveolar cells into the lungs. Both histologic examinations and lung lavage experiments showed that this cell influx could not be inhibited by pretreatment with Hoe 140. In summary, the results of the study show that bradykinin is involved in a cascade of events leading to AHR after a viral infection in guinea pigs, without affecting bronchoalveolar cell influx.

Neurokinin B‐ and specific tachykinin NK3 receptor agonists‐induced airway hyperresponsiveness in the guinea‐pig

1. The aim of this study was to determine whether neurokinin B (NKB) or specific agonists of tachykinin NK(3) receptors, [MePhe(7)]NKB and senktide, were able to induce airway hyperresponsiveness in guinea-pigs. The effects of these compounds were compared to those of substance P (SP), neurokinin A (NKA) and the preferential tachykinin NK(1) ([Sar(9), Met(0(2))(11)]SP) or NK(2) ([betaAla(8)]NKA (4-10)) receptor agonists. 2. In guinea-pigs pretreated with phosphoramidon (10(-4) M aerosol for 10 min) and salbutamol (8.7x10(-3) M for 10 min), all tachykinins administrated by aerosol (3x10(-7) to 10(-4) M) induced airway hyperresponsiveness 24 h later, displayed by an exaggerated response to the bronchoconstrictor effect of acetylcholine (i.v.). The rank order of potency was: [betaAla(8)]NKA (4-10)>NKA=NKB=senktide=[MePhe(7)]NKB=[Sar(9),Met(0(2))(11)]SP>SP. 3. Airway hyperresponsiveness induced by [MePhe(7)]NKB was prevented by the tachykinin NK(3) (SR 142801) and NK(2) (SR 48968) receptor antagonists. 4. Bronchoconstriction induced by tachykinins administered by aerosol was also determined. SP, NKA, NKB and the tachykinin NK(1) and NK(2) receptor agonist induced bronchoconstriction. The rank order of potency was: NKA=[betaAla(8)]NKA (4-10)>NKB=SP=[Sar(9), Met(0(2))(11)]SP. Under similar conditions, and for concentrations which induce airway hyperresponsiveness, senktide and [MePhe(7)]NKB failed to induce bronchoconstriction. 5. It is concluded that tachykinin NK(3)-receptor stimulation can induce airway hyperresponsiveness and that this effect is not related to the ability of tachykinins to induce bronchoconstriction.

Effect of YM158, a Dual Lipid Mediator Antagonist, on Immediate and Late Asthmatic Responses, and on Airway Hyper-responsiveness in Guinea Pigs

The effects of lipid mediator antagonists: the LTD4-receptor antagonist pranlukast, the TXA2-receptor antagonist seratrodast, and the novel dual LTD4- and TXA2-receptor antagonist YM158 (3-[(4-tert-butylthiazol-2-yl)methoxy]-5'-[3-(4-chlorobenzenesulfonyl) propyl]-2'-(1H-tetrazol-5-ylmethoxy)benzanilide monosodium salt monohydrate) were investigated in animals exhibiting immediate asthmatic response (IAR), late asthmatic response (LAR) and airway hyper-responsiveness (AHR). Antigen-induced LAR and AHR are inhibited by orally administered pranlukast (30, 100 mg/kg) and seratrodast (3, 10 mg/kg). YM158 (30 mg/kg), orally administered before or after IAR induction, also inhibited both LAR and AHR. However, while the inhibitory effects of pranlukast and seratrodast on IAR were marginal, the effects of YM158 (3, 10, 30 mg/kg) were dose-dependent, probably due to its multiple sites of action. Additionally, orally administered YM158 (30 mg/kg) inhibited ozone-induced AHR in guinea pigs. Thus, an antagonist that inhibits several lipid mediators might exhibit greater efficacy in treating asthmatic responses than antagonists with a single site of action. Therefore, YM158 shows great promise as a drug that will be able to treat bronchial asthma and related disorders more potently than currently used single-pathway inhibitors.

Betamethasone prevents virus‐induced airway inflammation but not airway hyperresponsiveness in guinea pigs

In this study the effect of betamethasone was investigated in guinea pigs that demonstrate airway inflammation and airway hyperresponsiveness after a viral respiratory tract infection with parainfluenza-3 (PI3) virus. Guinea pigs were pretreated with saline or betamethasone 8 mg/kg intraperitoneally twice a day for five consecutive days, starting on day 0 and ending on day 4. On day 1, the guinea pigs were inoculated with either control solution (medium) or PI3 virus. On day 5, airway responsiveness was measured. Furthermore, a blood sample was taken, lungs were lavaged, blood leucocytes were counted, and bronchoalveolar lavage (BAL) cells were counted and differentiated. Accordingly, the activity of the bronchoalveolar cells was measured by lucigenin-amplified chemiluminescence. In virus-infected guinea pigs the total bronchoalveolar cell number was increased by 44% compared with medium-treated guinea pigs. This was mainly due to the increase in macrophages (70%, P < 0.05) and eosinophils (344%, P < 0.001). The increase in both total and differential (macrophages and eosinophils) cell numbers in virus-infected guinea pigs was completely abolished in animals treated with betamethasone. Moreover, betamethasone prevented the decrease in number of blood leucocytes in virus-infected guinea pigs. In contrast, betamethasone did not prevent the increase in airway responsiveness to both histamine (>200%) and methacholine (>100%) after the virus infection. In conclusion, betamethasone treatment prevents virus-induced airway inflammation but not airway hyperresponsiveness in guinea pigs.

Nerve growth factor induces a neurokinin-1 receptor- mediated airway hyperresponsiveness in guinea pigs.

Because asthmatic patients show increased nerve growth factor (NGF) serum levels, we examined the effect of NGF on airway function. Intravenously administered NGF potentiates the histamine- induced bronchoconstriction with a maximum of over 200% in anesthetized spontaneously breathing guinea pigs. Doses of 8 ng and 80 ng NGF/kg body weight induce a significant hyperresponsiveness to histamine. NGF itself does not affect airway reactivity. Airway hyperresponsiveness is observed 30 min and 3 h after NGF administration, and has disappeared after 24 h. The neurokinin-1 receptor antagonist SR 140333 completely blocks the NGF-induced hyperresponsiveness, pointing to a role for tachykinins. This is the first report showing a direct relation between peripherally administered NGF and airway hyperresponsiveness. Taking into consideration that plasma NGF levels have been shown to be elevated in asthmatic patients, our result points to an important role for NGF in the pathogenesis of asthma.

The Role of Sensory Nerves in Propranolol-Induced Bronchial Hyperresponsiveness in the Guinea-pig

The racemic mixture propranolol (RS-(±)-, and theS-(−)- andR-(+)-) isomers of propranolol have been shown to induce bronchial hyperresponsiveness in the guinea-pig unrelated toβ-adrenoreceptor occupancy, that is attentuated by vagal section and mediated via the generation of 5-lipoxygenase metabolites of arachidonic acid. We have investigated the role of sensory nerves in propranolol-induced bronchial hyperresponsiveness in guinea-pigs. Airways responsiveness to acetylcholine, bradykinin and bombesin was determined before and 10 min after intravenous infusion withRS-(±)-,S-(−)- andR-(+)-propranolol (1 mg/kg) in vehicle and capsaicin-treated guinea-pigs. Propranolol (1 mg/kg, iv) significantly augmented the bronchoconstrictor response to acetylcholine, bradykinin and bombesin (P<0.001), an effect that was observed forRS-(±)-,S-(−)- andR-(+)-propranolol. In capsaicin-treated animals, the increased airways responsiveness to acetylcholine following intravenous infusion ofS-(−)-propranolol was significantly inhibited. Capsaicin treatment tended to reduce the increase in airways responsiveness to bradykinin following infusion withR-(+)-propranolol, but was only significant for the highest dose used. Similarly, capsaicin treatment had no effect on the ability ofRS-(±)-,S-(−)- andR-(+)-propranolol to enhance the bronchoconstrictor response to bombesin. Our results suggest that propranolol-induced bronchial hyperresponsiveness to certain spasmogens is in part mediated by the action of capsaicin-sensitive nerves.