Biomedical subjects

H Meurs

Publications and source records attributed to H Meurs.

At least 19 recordsLinked to original sources

PubMed2006

Insulin induces airway smooth muscle contraction.

BACKGROUND AND PURPOSE: Recently, the use of inhaled insulin formulations for the treatment of type I and type II diabetes has been approved in Europe and in the United States. For regular use, it is critical that airway function remains unimpaired in response to insulin exposure. EXPERIMENTAL APPROACH: We investigated the effects of insulin on airway smooth muscle (ASM) contraction and contractile prostaglandin (PG) production, using guinea-pig open-ring tracheal smooth muscle preparations. KEY RESULTS: It was found that insulin (1 nM-1 microM) induced a concentration-dependent contraction that was insensitive to epithelium removal. These sustained contractions were susceptible to inhibitors of cyclooxygenase (indomethacin, 3 microM), Rho-kinase (Y-27632, 1 microM) and p42/44 MAP kinase (PD-98059, 30 microM and U-0126, 3 microM), but not of PI-3-kinase (LY-294002,10 microM). In addition, insulin significantly increased PGF(2alpha)-production which was inhibited by indomethacin, but not Y-27632. Moreover, the FP-receptor antagonist AL-8810 (10 microM) and the EP(1)-receptor antagonist AH-6809 (10 microM) strongly reduced insulin-induced contractions, supporting a pivotal role for contractile prostaglandins. CONCLUSIONS AND IMPLICATIONS: Collectively, the results show that insulin induces guinea-pig ASM contraction presumably through the production of contractile prostaglandins, which in turn are dependent on Rho-kinase for their contractile effects. The data suggest that administration of insulin as an aerosol could result in some acute adverse effects on ASM function.

Animals↗

PubMed2005

Effects of salbutamol and enantiomers on allergen-induced asthmatic reactions and airway hyperreactivity.

Salbutamol consists of a racemic mixture of R- and S-salbutamol. R-salbutamol (levalbuterol) is the active bronchodilating enantiomer, whereas S-salbutamol is thought to be pharmacologically inactive or to exert adverse effects. This study evaluated the bronchoprotective effects of inhalation of therapeutically relevant doses of the racemate and individual enantiomers in guinea pigs. It was found that basal airway reactivity to histamine was similarly reduced 30 min after inhalation of equivalent doses of RS- and R-salbutamol; this protective effect disappeared within 3 h. Inhalation of RS- and R-salbutamol 30 min before and 5.5 h after allergen challenge suppressed allergen-induced airway hyperreactivity to histamine after the early and late asthmatic reaction, completely inhibiting the early asthmatic reaction and tending to reduce the development of the late asthmatic reaction. At 5 h after allergen challenge, the inhibition of airway hyperreactivity was more pronounced in animals treated with R-salbutamol compared to racemate-treated animals. Both basal airway reactivity and allergen-induced hyperreactivity were not affected by S-salbutamol. Inflammatory cell infiltration was not affected by the racemate or the individual enantiomers. In conclusion, inhalation of therapeutically relevant doses of R- and RS-salbutamol effectively suppress allergen-induced airway reactivity after the early and late asthmatic reactions, the R-enantiomer being slightly more potent with respect to early airway reactivity than the racemate. No adverse effects were observed for the S-enantiomer.

Albuterol↗

PubMed2002

Beta2 adrenoceptor promoter polymorphisms: extended haplotypes and functional effects in peripheral blood mononuclear cells.

BACKGROUND: The beta2 adrenoceptor and its 5' untranslated region contain a number of genetic variants. The aim of this study was to investigate the potential for genetic variation at this locus to influence the expression of beta2 adrenoceptors on circulating peripheral blood mononuclear cells (PBMCs). METHODS: Genotype was determined in 96 individuals with asthma for four polymorphisms at the beta2 adrenoceptor locus. Beta2 adrenoceptor binding and cyclic AMP responses to isoprenaline in PBMCs were determined and the relationship between genotype/haplotype and beta2 adrenoceptor expression and response to isoprenaline examined. RESULTS: Beta2 adrenoceptor promoter polymorphisms were found to be common in white subjects. Strong linkage disequilibrium exists across this locus, resulting in the occurrence of several common haplotypes. No single polymorphism or haplotype was correlated with the level of beta2 adrenoceptor expression or cyclic AMP responses to isoprenaline in vitro. CONCLUSION: Beta2 adrenoceptor polymorphisms, when considered in isolation or by extended haplotypes, do not determine the basal level of expression or coupling of beta2 adrenoceptors in PBMCs from asthmatic subjects.

Adolescent↗

PubMed2001

Effect of fenoterol-induced constitutive beta(2)-adrenoceptor activity on contractile receptor function in airway smooth muscle.

In the present study, we investigated the effect of fenoterol-induced constitutive beta(2)-adrenoceptor activity on muscarinic receptor agonist- and histamine-induced bovine tracheal smooth muscle contractions. Bovine tracheal smooth muscle strips were incubated with 10 microM fenoterol or vehicle for various periods of time (5, 30 min, 18 h) at 37 degrees C. After extensive washout (3 h, 37 degrees C), isometric contractions were measured to the full muscarinic receptor agonist methacholine, the partial muscarinic receptor agonist 4-(m-chlorophenyl-carbamoyloxy)-2-butynyltrimethylammonium (McN-A-343) and histamine. Fenoterol treatment significantly reduced the sensitivity (pEC(50)) to methacholine in a time-dependent manner, without affecting maximal contraction (E(max)). Fenoterol treatment similarly reduced the pEC(50) of McN-A-343 and histamine; however, E(max) values were also reduced, to approximately 70% of control after 18-h treatment. The inverse agonist timolol, having no effect on control preparations, consistently restored the reduced pEC(50) and E(max) values of the contractile agonists. Remarkably, in the presence of timolol the pEC(50) values of McN-A-343 and histamine in fenoterol-treated airways were significantly enhanced compared to controls. In conclusion, fenoterol-induced constitutive beta(2)-adrenoceptor activity reduces muscarinic receptor agonist- and histamine-induced contractions of bovine tracheal smooth muscle, which can be reversed by the inverse agonist timolol. Moreover, after beta(2)-adrenoceptor agonist treatment, inverse agonism by beta-adrenoceptor antagonists may cause enhanced airway reactivity to contractile mediators.

Adrenergic beta-2 Receptor Agonists↗

PubMed2001

Effects of fenoterol on beta-adrenoceptor and muscarinic M2 receptor function in bovine tracheal smooth muscle.

Prolonged (18 h) incubation of isolated bovine tracheal smooth muscle with the beta2-adrenoceptor agonist fenoterol (10 microM) induced desensitization of isoprenaline-induced adenylyl cyclase activity in bovine tracheal smooth muscle membranes, characterized by a 25% decrease in maximal effect (Emax) (P < 0.05), while the sensitivity to the agonist (pEC50) was unchanged. The Emax value of isoprenaline-induced smooth muscle relaxation of submaximal methacholine-induced contractile tones was similarly reduced by about 25% (P < 0.001), while the pEC50 value was diminished by 1.0 log unit (P < 0.001). As determined by 30 microM gallamine-induced muscarinic M2 receptor antagonism and pertussis toxin-induced inactivation of G(i alpha), muscarinic M2 receptor-mediated functional antagonism did not play a role in isoprenaline-induced relaxation of bovine tracheal smooth muscle contracted by methacholine, both in control and in 18-h fenoterol-treated tissue. In line with these observations, we found no enhanced muscarinic M2 receptor-mediated inhibition of 1 microM forskolin-stimulated adenylyl cyclase activity after 18-h fenoterol treatment. These data indicate that 18-h fenoterol treatment of bovine tracheal smooth muscle induces beta2-adrenoceptor desensitization and reduced functional antagonism of methacholine-induced contraction by beta-adrenoceptor agonists, without a change of muscarinic M2 receptor function.

Adenylate Cyclase Toxin↗

PubMed2001

Role of nitric oxide and superoxide in allergen-induced airway hyperreactivity after the late asthmatic reaction in guinea-pigs.

1. In the present study, the roles of nitric oxide (NO) and superoxide anions (O2(-)) in allergen-induced airway hyperreactivity (AHR) after the late asthmatic reaction (LAR) were investigated ex vivo, by examining the effects of the NO synthase inhibitor N(omega)-nitro-L-arginine methyl ester (L-NAME) and superoxide dismutase (SOD) on the responsiveness to methacholine of isolated perfused guinea-pig tracheae from unchallenged (control) animals and from animals 24 h after ovalbumin challenge. 2. At 24 h after allergen challenge, the animals developed AHR in vivo, as indicated by a mean 2.63 +/- 0.54 fold (P < 0.05) increase in sensitivity to histamine inhalation. 3. Compared to unchallenged controls, tracheal preparations from the ovalbumin-challenged guinea-pigs displayed a significant 1.8 fold (P < 0.01) increase in the maximal response (E(max)) to methacholine, both after intraluminal (IL) and extraluminal (EL) administration of the agonist. No changes were observed in the sensitivity (pEC(50)) to the agonist. Consequently, the DeltapEC(50) (EL-IL), as a measure of epithelial integrity, was unchanged. 4. In the presence of L-NAME (100 microM, IL), tracheae from control guinea-pigs showed a 1.6 fold (P < 0.05) increase in the E(max) of IL methacholine. By contrast, the E(max) of IL methacholine was significantly decreased in the presence of 100 u ml(-1) EL SOD (54% of control, P < 0.01). 5. Remarkably, the increased responsiveness to IL methacholine at 24 h after allergen challenge was reversed by L-NAME to control (P < 0.01), and a similar effect was observed with SOD (P < 0.01). 6. The results indicate that both NO and O2(-) are involved in the tracheal hyperreactivity to methacholine after the LAR, possibly by promoting airway smooth muscle contraction through the formation of peroxynitrite.

Allergens↗

PubMed2001

Inflammatory cell distribution in guinea pig airways and its relationship to airway reactivity.

Although airway inflammation and airway hyperreactivity are observed after allergen inhalation both in allergic humans and animals, little is known about the mechanisms by which inflammatory cells can contribute to allergen-induced airway hyperreactivity. To understand how inflammatory cell infiltration can contribute to airway hyperreactivity, the location of these cells within the airways may be crucial Using a guinea pig model of acute allergic asthma, we investigated the inflammatory cell infiltration in different airway compartments at 6 and 24 h (i.e. after the early and the late asthmatic reaction, respectively) after allergen or saline challenge in relation to changes in airway reactivity (AR) to histamine. At 6 h after allergen challenge, a threefold (p < 0.01) increase in the AR to histamine was observed. At 24 h after challenge, the AR to histamine was lower, but still significantly enhanced (1.6-fold, p < 0.05). Adventitial eosinophil and neutrophil numbers in both bronchi and bronchioli were significantly increased at 6 h post-allergen provocation as compared with saline (p < 0.01 for all), while there was a strong tendency to enhanced eosinophils in the bronchial submucosa at this time point (p = 0.08). At 24h after allergen challenge, the eosinophilic and neutrophilic cell infiltration was reduced. CD3+ T lymphocytes were increased in the adventitial compartment of the large airways (p < 0.05) and in the parenchyma (p < 0.05) at 24h post-allergen, while numbers of CD8+ cells did not differ from saline treatment at any time point post-provocation. The results indicate that, after allergen provocation, inflammatory cell numbers in the airways are mainly elevated in the adventitial compartment. The adventitial inflammation could be important for the development of allergen-induced airway hyperreactivity.

Animals↗

PubMed2000

Modulation of cholinergic airway reactivity and nitric oxide production by endogenous arginase activity.

Cholinergic airway constriction is functionally antagonized by agonist-induced constitutive nitric oxide synthase (cNOS)-derived nitric oxide (NO). Since cNOS and arginase, which hydrolyzes L-arginine to L-ornithine and urea, use L-arginine as a common substrate, competition between both enzymes for the substrate could be involved in the regulation of cholinergic airway reactivity. Using a perfused guinea-pig tracheal tube preparation, we investigated the modulation of methacholine-induced airway constriction by the recently developed, potent and specific arginase inhibitor N(Omega)-hydroxy-nor-L-arginine (nor-NOHA). Intraluminal (IL) administration of nor-NOHA caused a concentration-dependent inhibition of the maximal effect (E(max)) in response to IL methacholine, which was maximal in the presence of 5 microM nor-NOHA (E(max)=31.2+/-1.6% of extraluminal (EL) 40 mM KCl-induced constriction versus 51.6+/-2.1% in controls, P<0.001). In addition, the pEC(50) (-log(10) EC(50)) was slightly but significantly reduced in the presence of 5 microM nor-NOHA. The inhibition of E(max) by 5 microM nor-NOHA was concentration-dependently reversed by the NOS inhibitor N(Omega)-nitro-L-arginine methyl ester (L-NAME), reaching an E(max) of 89.4+/-7.7% in the presence of 0.5 mM L-NAME (P<0.01). A similar E(max) in the presence of 0.5 mM L-NAME was obtained in control preparations (85.2+/-9.7%, n.s.). In the presence of excess of exogenously applied L-arginine (5 mM), 5 microM nor-NOHA was ineffective (E(max)=33.1+/-5.8 versus 31.1+/-7.5% in controls, n.s.). The results indicate that endogenous arginase activity potentiates methacholine-induced airway constriction by inhibition of NO production, presumably by competition with cNOS for the common substrate, L-arginine. This finding may represent an important novel regulation mechanism of airway reactivity.

Animals↗

PubMed2000

Beta-agonist-induced constitutive beta(2)-adrenergic receptor activity in bovine tracheal smooth muscle.

According to the two state receptor model, the beta(2)-adrenergic receptor (beta(2)-AR) isomerizes between an inactive state and a constitutively active state, which couples to the stimulatory G-protein in the absence of agonist. In bovine tracheal smooth muscle (BTSM), we investigated the effect of short and long term beta(2)-AR activation by fenoterol on constitutive receptor activity. Preincubation of the BTSM strips for 5 min, 30 min and 18 h with 10 microM fenoterol, followed by extensive washout (3 h, 37 degrees C), caused a rapid and time-dependent inhibition of KCl-induced contraction, reaching 68+/-10, 51+/-6 and 46+/-4% of control, respectively, at 40 mM KCl (P:<0.05 all). At all time points, the EC(50) values to KCl were significantly reduced as well. Preincubation of BTSM with 0.1, 1.0 and 10 microM fenoterol during 18 h caused a concentration-dependent decrease of the 40 mM KCl response to 70+/-5, 47+/-12 and 43+/-9% of control, respectively (P:<0.05 all). The reduced KCl contractions were reversed in the presence of 1 microM timolol. Moreover, the sensitivity to KCl in the presence of timolol was enhanced after fenoterol incubation. Inverse agonism was also found for other beta-blockers, with a rank order of efficacy of pindolol >/=timolol=propranolol>alprenolol>/=sotalol>labetalol. At 25 mM KCl-induced tone, the contraction induced by cumulative timolol administration was competitively antagonized by the less efficacious inverse agonist labetalol, indicating that the fenoterol-induced effects cannot be explained by residual beta-agonist binding. In conclusion, fenoterol treatment of BTSM causes a time- and concentration-dependent development of constitutive beta(2)-AR activity, which can be reversed by various inverse agonists. The beta-agonist-induced changes could represent a novel regulation mechanism of beta(2)-AR activity.

Adrenergic beta-Agonists↗

PubMed1999

Deficiency of nitric oxide in polycation-induced airway hyperreactivity.

Using a perfused guinea-pig tracheal tube preparation, we investigated the role of endogenous nitric oxide (NO) in polycation-induced airway hyperreactivity (AHR) to methacholine. Intraluminal (IL) administration of the NO synthase inhibitor Nomega-nitro-L-arginine methyl ester (L-NAME; 100 microM) caused a 1.8 fold increase in the maximal contractile response (Emax) to IL methacholine compared to control, without an effect on the pEC50 (-log10 EC50). The polycation poly-L-arginine (100 microg ml(-1), IL) similarly enhanced the Emax for methacholine; however, the pEC50 value was also increased, by one log10 unit. L-NAME had no effect on the enhanced methacholine response of poly-L-arginine-treated airways, while the enhanced agonist response was completely normalized by the polyanion heparin (25 u ml(-1), IL). In addition, the effect of L-NAME was fully restored in the poly-L-arginine plus heparin treated airways. The results indicate that, in addition to enhanced epithelial permeability, a deficiency of endogenous NO contributes to polycation-induced AHR. The latter finding may represent a novel mechanism of AHR induced by eosinophil-derived cationic proteins in allergic asthma.

Animals↗

PubMed1999

Role of tachykinin NK2-receptor activation in the allergen-induced late asthmatic reaction, airway hyperreactivity and airway inflammatory cell influx in conscious, unrestrained guinea-pigs.

1. In a guinea-pig model of allergic asthma, we investigated the involvement of the tachykinin NK2 receptors in allergen-induced early (EAR) and late (LAR) asthmatic reactions, airway hyperreactivity (AHR) after these reactions and inflammatory cell influx in the airways, using the selective non-peptide NK2 receptor antagonist SR48968. 2. On two different occasions, separated by a 1 week interval, ovalbumin (OA)-sensitized guinea-pigs inhaled either vehicle (3 min) or SR48968 (100 nM, 3 min) at 30 min before as well as at 5.5 h after OA provocation (between the EAR and LAR) in a random crossover design. 3. SR48968 had no significant effect on the EAR, but significantly attenuated the LAR by 44.2+/-16.4% (P<0.05) compared to saline control. 4. The NK2 receptor antagonist did not affect the OA-induced AHR to histamine after the EAR at 5 h after OA challenge (3.59+/-0.59 fold increase in histamine reactivity vs 3.79+/-0.61 fold increase in the controls, NS), but significantly reduced the AHR after the LAR at 23 h after OA challenge (1.59+/-0.24 fold increase vs 1.93+/-0.15 fold increase, respectively, P<0.05). 5. Bronchoalveolar lavage studies performed at 25 h after the second OA provocation showed that SR48968 significantly inhibited the allergen-induced infiltration of neutrophils (P<0.05) and lymphocytes (P<0.01) in the airways. 6. These results indicate that NK2 receptor activation is importantly involved in the development of the allergen-induced late (but not early) asthmatic reaction and late (but not early) AHR to histamine, and that NK2 receptor-mediated infiltration of neutrophils and lymphocytes in the airways may contribute to these effects.

Allergens↗

PubMed1999

Role of L-arginine in the deficiency of nitric oxide and airway hyperreactivity after the allergen-induced early asthmatic reaction in guinea-pigs.

1. Using a guinea-pig model of allergic asthma, we investigated the role of L-arginine limitation in the allergen-induced deficiency of nitric oxide (NO) and airway hyperreactivity (AHR) after the early asthmatic reaction, by examining the effects of various concentrations of the NO synthase (NOS) substrate on the responsiveness to methacholine of isolated perfused tracheae from unchallenged (control) animals and from animals 6 h after ovalbumin challenge. 2. Preparations from ovalbumin-challenged guinea-pigs showed a 1.9 fold increase in the maximal response (Emax) to intraluminal (IL) administration of methacholine compared to controls (P<0.001). A similar 2.0 fold (P<0.05) increase in Emax to methacholine was observed in control airways incubated with the NOS inhibitor Nomega-nitro-L-arginine methyl ester (L-NAME; 0.1 mM, IL), while L-NAME had no further effect on the airways from ovalbumin-challenged animals. 3. In control airways, extraluminal (EL) administration of 0.3, 1.0 and 5.0 mM L-arginine all suppressed the Emax for methacholine by approximately 40% (P<0.01 all), whereas 5.0 mM D-arginine (EL) had no effect. 4. L-Arginine dose-dependently reduced the AHR to methacholine in tracheae from ovalbumin-challenged guinea-pigs, the responsiveness being normalized in the presence of 5.0 mM L-arginine. As in controls, 5.0 mM D-arginine was without effect. 5. The results demonstrate that deficiency of endogenous NO contributes to the allergen-induced AHR to methacholine after the early asthmatic reaction, which is reversed by exogenous administration of L-arginine. This indicates that limitation of substrate may underly the reduced cNOS activity and subsequent AHR after the acute asthmatic response.

Allergens↗

PubMed1999

Role of tachykinin NK1 and NK2 receptors in allergen-induced early and late asthmatic reactions, airway hyperresponsiveness, and airway inflammation in conscious, unrestrained guinea pigs.

Using a guinea pig model of allergic asthma, we investigated the effects of the inhaled, highly selective nonpeptide tachykinin NK1 and NK2 receptor antagonists SR 140333 and SR 48968, respectively, on allergen-induced early (EAR) and late (LAR) asthmatic reactions, airway hyperreactivity (AHR) after these reactions, and infiltration of inflammatory cells in the airways. Both SR 140333 (100 nM, 3 min) and SR 48968 (100 nM, 3 min) had no effect on the severity of the EAR, while the NK2 receptor antagonist SR 48968, but not the NK1 receptor antagonist SR 140333, caused significant inhibition of the LAR. SR 140333 significantly reduced the allergen-induced AHR to histamine, both after the EAR and the LAR. By contrast, SR 48968 did not affect the AHR after the EAR, but significantly attenuated the AHR after the LAR. Bronchoalveolar lavage studies performed after the LAR indicated that SR 140333 caused significant inhibition of allergen-induced infiltration of eosinophils, neutrophils and lymphocytes, while SR 48968 attenuated the infiltration of neutrophils and lymphocytes, but not of eosinophils. Both NK receptor antagonists tended to reduce the accumulation of ciliated epithelial cells in the airways. These results indicate that NK1 and NK2 receptors are importantly, but differentially, involved in the development of allergen-induced airways obstruction, AHR and infiltration of inflammatory cells in the airways. Therefore, both NK1 and NK2 receptor antagonists, or dual NK1 and NK2 antagonists, could be useful in the treatment of allergic asthma.

Allergens↗

PubMed1999

Involvement of tachykinin NK1 receptor in the development of allergen-induced airway hyperreactivity and airway inflammation in conscious, unrestrained guinea pigs.

It has been suggested that tachykinin NK1 receptor-mediated neurogenic inflammation, characterized by microvascular leakage, mucus secretion, and infiltration and activation of inflammatory cells in the airways, may be involved in allergic asthma. Therefore, in a guinea pig model of allergic asthma, we investigated the involvement of the NK1 receptor in allergen-induced early (EAR) and late (LAR) asthmatic reactions, airway hyperreactivity (AHR) after these reactions and airway inflammation, using the selective nonpeptide NK1 receptor antagonist SR140333. On two different occasions, separated by 1 wk interval, OA-sensitized guinea pigs inhaled either saline (3 min) or SR140333 (100 nM, 3 min) at 30 min before as well as at 5.5 h after OA provocation (between the EAR and LAR) in a random crossover design. A control group, receiving saline inhalations before and at 5.5 h after the two OA provocations, was included as well. SR140333 had no significant effect on either the EAR or the LAR compared with saline control inhalations. However, the NK1 receptor antagonist significantly reduced the OA-induced AHR to histamine, both after the EAR at 5 h after OA challenge (1.77 +/- 0.13-fold increase in histamine reactivity versus 2.50 +/- 0.25-fold increase in the control animals, p < 0.01) and after the LAR at 23 h after OA challenge (1.15 +/- 0.12-fold increase versus 1.98 +/- 0. 34-fold increase, respectively, p < 0.05). Moreover, bronchoalveolar lavage studies performed at 25 h after the second OA provocation indicated that SR140333 significantly inhibited the allergen-induced infiltration of eosinophils, neutrophils, and lymphocytes in the airways (p < 0.05 for all observations), whereas a tendency to reduced accumulation of ciliated epithelial cells in the airway lumen was observed (p = 0.10). These results indicate that the NK1 receptor is involved in the development of allergen-induced AHR to histamine, and that NK1 receptor-mediated infiltration of inflammatory cells in the airways may contribute to this AHR.

Allergens↗

PubMed1998

Role of nitric oxide in the development and partial reversal of allergen-induced airway hyperreactivity in conscious, unrestrained guinea-pigs.

1. Using a conscious, unrestrained guinea-pig model of allergic asthma, we investigated the role of endogenous nitric oxide (NO) in the regulation of airway (hyper)reactivity to histamine before and after the allergen-induced early and late asthmatic reactions, by examining the effect of inhalation of the NO synthase inhibitor N(omega)-nitro-L-arginine methyl ester (L-NAME, 12 mM, 15 min) on the histamine-induced airway obstruction of ovalbumin-sensitized guinea-pigs before, and at 5.5 h and 23.5 h after allergen challenge. 2. Before allergen challenge, inhaled L-NAME caused a significant 2.02+/-0.25 fold increase (P<0.01) in airway reactivity to histamine; this effect was reversed within 2.5 to 6 h after administration. 3. After the allergen-induced early asthmatic reaction at 5 h after ovalbumin provocation, a significant 3.73+/-0.67 fold increase (P<0.01) of the airway reactivity to histamine was observed; subsequent inhalation of L-NAME at 5.5 h had no effect on the airway hyperreactivity, reassessed at 6 h. 4. After the late asthmatic reaction, at 23 h after ovalbumin provocation, a reduced, but still significant airway hyperreactivity to histamine (2.18+/-0.40 fold; P<0.05) was observed. Subsequent inhalation of L-NAME now significantly potentiated the partially reduced airway hyperreactivity 1.57+/-0.19 fold (P<0.05) to the level observed after the early asthmatic reaction. 5. When administered 30 min before allergen exposure, L-NAME significantly enhanced the allergen-induced early asthmatic reaction. However, when administered at 5.5 h after allergen provocation, L-NAME did not affect the subsequent late asthmatic reaction. 6. These results indicate that endogenous NO is involved the regulation of histamine- and allergen-induced bronchoconstriction and that a deficiency of cNOS-derived NO contributes to the allergen-induced airway hyperreactivity to histamine after the early asthmatic reaction, while a recovery of NO deficiency may account for the partial reversal of the allergen-induced airway hyperreactivity after the late asthmatic reaction.

Allergens↗

PubMed1998

Dual action of iNOS-derived nitric oxide in allergen-induced airway hyperreactivity in conscious, unrestrained guinea pigs.

Using a guinea pig model of acute allergic asthma, we recently established that a deficiency of nitric oxide (NO) contributes to airway hyperreactivity (AHR) after the early asthmatic reaction (EAR) and that restoration of NO activity may contribute to the (partial) reversal of AHR after the late asthmatic reaction (LAR). In the present study, we investigated the role of iNOS-derived NO in the regulation of AHR to histamine after the LAR. Inhalation of a selective dose of the specific iNOS inhibitor aminoguanidine (0.1 mM, 3 min) had no effect on basal airway reactivity to histamine in unchallenged, ovalbumin-sensitized animals and did not affect the allergen-induced AHR after the EAR. By contrast, this dose of aminoguanidine significantly potentiated the partially reduced AHR after the LAR to the level of AHR observed after the EAR, indicating that induction of iNOS during the LAR contributes to the reversal of AHR. Inhalation of a higher aminoguanidine concentration (2.5 mM) shortly before the onset of the LAR diminished the AHR after the LAR and reduced the number of neutrophils, lymphocytes, and ciliated epithelial cells in the bronchoalveolar lavage at this time point. The results indicate that iNOS-derived NO may have both beneficial and detrimental effects on allergen-induced AHR to histamine after the LAR by functional antagonism of histamine-induced bronchoconstriction, and by promoting airway inflammation and epithelial damage on the other hand, respectively.

Acute Disease↗

PubMed1998

Effects of endogenous superoxide anion and nitric oxide on cholinergic constriction of normal and hyperreactive guinea pig airways.

In a guinea pig model of allergic asthma, we have recently established that a deficiency of nitric oxide (NO) contributes to the increased ex vivo responsiveness of isolated perfused tracheae to methacholine after the early asthmatic reaction at 6 h after inhalational challenge of the animals with ovalbumin aerosol. Because this deficiency could be caused by a reaction of NO with enhanced levels of inflammation-induced superoxide anion (O-2), we examined the effect of endogenous O-2 on the regulation of methacholine-induced constriction by NO of intact perfused tracheal tube preparations from unchallenged (control) guinea pigs and from animals 6 h after ovalbumin challenge. In the presence of the NO synthase (NOS) inhibitor N omega-nitro-L-arginine methyl ester (L-NAME; 100 microM), tracheae obtained from unchallenged guinea pigs showed a 1.7-fold increase in the maximal response to intraluminally applied methacholine (p < 0.05). By contrast, the maximal airway response to methacholine was significantly decreased in the presence of the O-2 scavenger superoxide dismutase (SOD; 100 U/ml), by approximately 45% (p < 0.01). The SOD-induced decrease in responsiveness to methacholine was reversed by L-NAME. Tracheal preparations obtained at 6 h after allergen challenge showed a 1. 8-fold increased responsiveness to intraluminally applied methacholine compared with controls (p < 0.001), which was not further enhanced in the presence of L-NAME. SOD had neither an effect on the increased responsiveness nor did it restore the potentiating effect of L-NAME. These results indicate that (1) in normoreactive tracheal preparations, the regulatory role of NO is partially counteracted by endogenous O-2, and ( 2) the deficiency of NO in hyperreactive tracheae obtained at 6 h after ovalbumin challenge is not caused by its reaction with O-2, but rather to decreased cNOS activity. De Boer J, Pouw FMH, Zaagsma J, Meurs H. Effects of endogenous superoxide anion and nitric oxide on cholinergic constriction of normal and hyperreactive guinea pig airways.

Administration, Inhalation↗

PubMed1997

Muscarinic control of airway function.

Muscarinic M1, M2, and M3 receptor subtypes have been shown to be involved in the pre- and postjunctional control of airway diameter of various species, including man. In a guinea pig model of allergic asthma, the prejunctional M2 receptor was shown to become dysfunctional already during the early allergic reaction, thereby contributing to exaggerated vagal reflex activity and airway hyperreactivity. Moreover, a deficiency of endogenous nitric oxide was observed after allergen provocation, which may also contribute to an enhanced postjunctional M3 receptor-mediated cholinergic response. Both in human and in animal airway preparations it was shown that enhanced cholinergic contractions are relatively resistent to beta-adrenoceptor-mediated relaxation. The reduced beta-adrenoceptor function may primarily be due to transductional cross-talk between PI metabolism and adenylyl cyclase, including protein kinase C-induced uncoupling of the beta-adrenoceptor from the effector system. Cross-talk between postjunctional M2 receptor-mediated inhibition and beta-adrenoceptor-induced activation of adenylyl cyclase appears to be of minor functional importance, but could be enhanced in allergic asthma due to increased expression of the inhibitory G protein as induced by cytokines.

Animals↗