Airway Responsiveness In Rats Research Articles

DM-induced Hypermethylation of IR and IGF1R attenuates mast cell activation and airway responsiveness in rats.

Diabetes has been reported to modulate the airway smooth muscle reactivity and lead to attenuation of allergic inflammatory response in the lungs. In this study, we aimed to study the effect of insulin on cell activation and airway responsiveness in patients with diabetes mellitus (DM). The airway contraction in rat model groups including a non‐DM group, a non‐DM+INDUCTION group, a DM+INDUCTION group and a DM+INDUCTION+INSULIN group was measured to observe the effect of insulin on airway responsiveness. Radioenzymatic assay was conducted to measure the levels of histamine, and ELISA assay was conducted to measure bronchial levels of interleukin (IL)‐1b, tumour necrosis factor (TNF)‐a, cytokine‐induced neutrophil chemoattractant (CINC)‐1, P‐selectin and β‐hexosaminidase. The tension in the main and intrapulmonary bronchi of DM+INDUCTION rats was lower than that of the non‐DM+INDUCTION rats, whereas the treatment of insulin partly restored the normal airway responsiveness to OA in DM rats. The release of histamine was remarkably suppressed in DM+INDUCTION rats but was recovered by the insulin treatment. Also, OA significantly increased the levels of IL‐1b, TNF‐a, CINC‐1 and P‐selectin in non‐DM rats, whereas insulin treatment in DM+INDUCTION rats partly restored the normal levels of IL‐1b, TNF‐a, CINC‐1 and P‐selectin in DM rats. Moreover, the expression of IR and IGF1R was evidently suppressed in DM rats, with the methylation of both IR and IGF1R promoters was aggravated in DM rats. Therefore, we demonstrated that DM‐induced hypermethylation inhibited mast cell activation and airway responsiveness, which could be reversed by insulin treatment.

Effects of chronic exposure to Aspergillus fumigatus on epidermal growth factor receptor expression in the airway epithelial cells of asthmatic rats

ABSTRACTEpidemiologic studies suggest that increased concentrations of airborne spores of Aspergillus fumigatus closely relate to asthma aggravation. Chronic exposure to A. fumigatus aggravates airway inflammation, remodeling, and airway hyperresponsiveness in asthmatic rats. The effects of chronic exposure to A. fumigatus on epidermal growth factor receptor (EGFR) expression in the airway epithelial cells of asthmatic rats remain unclear. This study aimed to investigate the effects of chronic exposure to A. fumigatus on injury and shedding of airway epithelium, goblet cell metaplasia, and EGFR expression in the airway epithelial cells of asthmatic rats. A rat model of chronic asthma was established using ovalbumin (OVA) sensitization and challenge. Rats with chronic asthma were then exposed to long-term inhalation of spores of A. fumigatus, and the dynamic changes in injury and shedding of airway epithelium, goblet cell metaplasia, and EGFR expression were observed and analyzed. Chronic exposure to A. fumigatus could aggravate airway epithelial cell damage, upregulate the expression of EGFR and its ligands EGF and TGF-α, promote goblet cell metaplasia, and increase airway responsiveness in rats with asthma. Chronic exposure to A. fumigatus upregulates the expression of EGFR and its ligands in asthmatic rats. The EGFR pathway may play a role in asthma aggravation induced by exposure to A. fumigatus.

Comparison of non‐invasive measures of cholinergic and allergic airway responsiveness in rats

Non-invasive analysis of tidal expiratory flow parameters such as Tme/TE (time needed to reach peak expiratory flow divided by total expiratory time) or midexpiratory tidal flow (EF50) has been shown useful for phenotypic characterization of lung function in humans and animal models. In this study, we aimed to compare the utility of two non-invasive measures, EF50 and Tme/TE, to monitor bronchoconstriction to inhaled cholinergic and allergic challenges in Brown-Norway rats. Non-invasive measurements of Tme/TE and EF50 were paralleled by invasive recordings of Tme/TE, EF50 and pulmonary conductance (GL). First, dose-response studies with acetylcholine were performed in naive rats, showing that EF50 better than Tme/TE reflected the dose-related changes as observed with the classical invasive outcome parameter GL. The subsequent determination of allergen-specific early airway responsiveness (EAR) showed that ovalbumin-sensitized and -challenged rats exhibited airway inflammation and allergen-specific EAR. Again, EF50 was more sensitive than Tme/TE in detecting the allergen-specific EAR recorded with invasive and non-invasive lung function methods and agreed well with classical GL measurements. We conclude that non-invasive assessment of EF50 is significantly superior to Tme/TE and serves as a suitable and valid tool for phenotypic screening of cholinergic and allergic airway responsiveness in rats.

Enhanced Allergic Inflammation and Airway Responsiveness in Rats with ChronicCryptococcus neoformansInfection: Potential Role for Fungal Pulmonary Infection in the Pathogenesis of Asthma

Although Cryptococcus neoformans is recognized for its ability to cause meningoencephalitis and pneumonia among immunocompromised persons, subclinical pulmonary infection is also common among immunocompetent persons. The significance of this infection is unknown. Using a rat model, we explored the potential for pulmonary cryptococcosis to modify allergic responses and airway reactivity. Our findings indicate that localized pulmonary cryptococcal infection (but not disseminated infection) can exacerbate allergic responses to respiratory challenge with ovalbumin, as measured by total immunoglobulin E levels, ovalbumin-specific immunoglobulin E titers, and eosinophil content of bronchoalveolar lavage fluid. Infection-associated enhancement of allergic responses was not dependent on cryptococcal encapsulation and was partially ameliorated by the administration of fluconazole. Increases in both the number of goblet cells and airway responsiveness, which are also features of reactive airway disease, were also present with pulmonary infection. An examination of lung cytokine levels in the context of active pulmonary infection revealed increased expression of interleukin (IL)-10, tumor necrosis factor- alpha , and IL-13, but not IL-12 or interferon- gamma . In contrast, systemic infection was associated with higher levels of interferon- gamma but lower levels of IL-13. Our studies highlight the potential for localized pulmonary C. neoformans infection to potentiate allergic responses and airway reactivity and suggest a potential role for subclinical pulmonary cryptococcosis in the pathogenesis of asthma.

Airway hyperresponsiveness induced by cationic proteins in vivo: site of action

Major basic protein and other native cationic proteins increase airway hyperresponsiveness when administered to the luminal surface of the airways in vitro. To determine whether the same applies in vivo, we assessed airway responsiveness in rats challenged with both aerosolized and intravenously infused methacholine. We partitioned total lung resistance into its airway and tissue components using the alveolar capsule technique. Neither poly-l-lysine nor major basic protein altered baseline mechanics or its dependence on positive end-expiratory pressures ranging from 1 to 13 cmH(2)O. When methacholine was administered to the lungs as an aerosol, both cationic proteins increased responsiveness as measured by airway resistance, tissue resistance, and tissue elastance. However, responsiveness of all three parameters was unchanged when the methacholine was infused. Together, these findings suggest that cationic proteins alter airway responsiveness in vivo by an effect that is apparently limited to the bronchial epithelium.

Robust two-stage approach to repeated measurements analysis of chronic ozone exposure in rats

A robust two-stage approach is used to reanalyze the repeated measurements from an experiment of airway responsiveness in rats randomized to long-term exposure at four ozone doses. The concentration-response data generated for each rat may be represented as a hierarchical nonlinear model encompasing the sources of variation within and between individual profile for each rat, the conditional modeling approach can assess the adequacy of an assumed mean model, a fundamental advantage not intrinsic to marginal techniques. The two-stage population inference is based on the estimated individual parameters, thus maintaining an intuitive appeal to the toxicologists who traditionally have fitted a separate curve for each animal and then applied ANOVA to the summary statistics. However, we formally adjust the standard errors for the extra variability due to the initial estimation of the individual parameters and also allow for their within-rat correlation. The robust two-stage method appropriately down weights the a berrant responses arising sporadically within individualsand, more importantly, the rats which may be outlying relative to the usual population variation. The true effect of chronic ozone exposure, including a significant gender interaction, may be masked by a few rats which exert undue influence on the population estimates in a nonrobust analysis.

Chronic exposure to hypoxia attenuates contractile responses in rat airways in vitro: a possible role for nitric oxide

We investigated the effect of chronic hypoxia (10% O 2 for 14 days) on airway responsiveness in rats. Chronic hypoxia significantly ( P<0.05, P<0.01, P<0.01, respectively) attenuated contractions evoked by methacholine (10 −9–3×10 −4 M), endothelin-1 (10 −10–3×10 −7 M) and potassium chloride (10 −3–7×10 −2 M) in rat isolated trachea. To investigate this attenuation, we studied the effect of epithelial removal, indomethacin (3×10 −6 M), and l-nitro arginine methyl ester ( l-NAME, 10 −4 M), on contractile responses in control and chronically hypoxic rat trachea. Indomethacin did not alter contractions evoked by methacholine or endothelin-1 in control or hypoxic rats. In contrast, epithelial removal and l-NAME both significantly potentiated responses to methacholine and endothelin-1 in trachea from control and chronically hypoxic rats. In separate experiments, tracheal rings were first contracted with methacholine (10 −6 M) and then relaxed, either by the nitric oxide donor sodium nitroprusside or by the β 2-adrenoceptor agonist, salbutamol. Sodium nitroprusside was significantly ( P<0.001) more effective at reversing induced tone in tracheal rings from chronically hypoxic than control rats. Salbutamol, however, was equally effective in chronically hypoxic and control rats. These results suggest that, in trachea from both control and chronically hypoxic rats, contractile responses to methacholine and endothelin-1 are inhibited by nitric oxide, probably released from the epithelium. The attenuation of contractile responses in airways from chronically hypoxic rats may be due to an enhanced guanylyl cyclase activity and hence, an increased response to nitric oxide.

IL-2 enhances allergic airway responses in rats by increased inflammation but not through increased synthesis of cysteinyl leukotrienes

Background: IL-2 has been shown to increase allergic airway responses in rats. Objective: The purpose of this study was to investigate whether induction of inflammation and enhancement of cysteinyl-leukotriene (cys-LT) synthesis were involved in the augmentation of airway responses caused by IL-2. Methods: Brown Norway rats received human recombinant IL-2 or saline subcutaneously twice a day from day 9 to day 14 after sensitization to ovalbumin (OVA). On day 14, rats underwent either lung lavage or were challenged with an aerosol spray of OVA, the airway responses and biliary excretion of cys-LTs were measured for a period of 8 hours after challenge, and the lung leukocyte numbers were determined after enzymatic digestion of lung tissues. Results: The early response after OVA increased from 184.2% ± 13.5% in the animals receiving saline (n = 10) to 309% ± 51% (baseline lung resistance) in IL-2–pretreated animals (n = 17; P < .05). The late response also increased from 19.6 ± 4.5 (area under the curve of baseline lung resistance vs time) in the animals receiving saline to 37 ± 5.4 after administration of IL-2 ( P < .05). However, IL-2–treated animals had lower levels of biliary cys-LTs during the late response than saline-treated animals but similar levels during the early response. This difference could not be attributed to an increase in LT metabolism, which we assessed by the recovery of 3 H-LTC 4 instilled intratracheally in challenged or unchallenged rats. When compared with control animals, pretreatment with IL-2 increased all cell types retrieved from lung lavage fluid before OVA challenge ( P < .05). After OVA challenge, the total cell yield from lung lavage fluid was also increased, mostly because of an increase in neutrophils ( P < .05). Eosinophils and lymphocytes were greater in the lungs of IL-2–treated than vehicle-treated and OVA-challenged rats ( P < .01), and IL-2–treated rats had a lower CD4 + /CD8 + ratio in the blood after challenge ( P < .001). Conclusion: In conclusion, IL-2 increases early and late responses in rats, and it induces lung inflammation. Altered airway responses are not attributable to an increase in cys-LT production. (J Allergy Clin Immunol 1999;104:145-52.)

Long term cigarette smoke exposure does not increase airway responsiveness in rats.

To ascertain whether chronic cigarette smoke exposure induces increased airway responsiveness, we performed methacholine response tests in Sprague-Dawley rats by calculating pulmonary resistance after nebulization of saline followed by an increasing concentration of methacholine. We also calculated the concentration of methacholine which doubled the baseline resistance (R200). Tests were performed at baseline and after 2, 4, 8, and 12 months of exposure to the smoke of seven cigarettes per day, 5 days each week; control animals were exposed to room air. At the completion of the study, there were 13 rats in the smoke-exposed group and 7 rats remaining in the control group. Airway morphology was assessed using a point counting technique. We found that (1) chronic exposure to cigarette smoke did not alter either the baseline resistance or the R200; (2) the saline baseline resistance decreased over time in the control animals; and (3) at the 12-month time point, smokers with increased baseline airway resistance had greater amounts of airway smooth muscle compared with the smoke-exposed animals without increased resistance. We conclude that in this animal model, long term exposure to cigarette smoke did not alter the response to methacholine but did increase airway smooth muscle and baseline resistance in some but not all animals.

The effect of a nitric oxide synthase inhibitor on the modulation of airway responsiveness in rats.

The possible role of nitric oxide (NO) in the regulation of airway tone remains to be fully explored. In the present study we examined the effect of NG-nitro-L-arginine methyl ester (L-NAME), an inhibitor of NO synthase, on airway responsiveness in rats. The effect of L-NAME on endotoxin (lipopolysaccharide; LPS)-induced changes in airway responsiveness was also evaluated. L-NAME (1 mg/kg given intravenously) caused a 33.3 +/- 6.9% increase in blood pressure, but did not influence baseline airway tone or the provocative dose of carbachol causing a 50% increase in pulmonary resistance (RL)(PD50RL). Exposure of F344 rats to LPS induced a transient increase in airway responsiveness at 90 min after exposure, followed by a significant hyporesponsiveness between 9 and 12 h after exposure. L-NAME (1 mg/kg intravenously) did not influence the increase in responsiveness but inhibited the LPS-induced hyporesponsiveness; in LPS-exposed, L-NAME-treated animals, the PD50RL for carbachol was 3.0 +/- 0.1, versus 4.8 +/- 0.3 micrograms/kg in the LPS-exposed, placebo-pretreated group (p < 0.05). The effect of L-NAME was abolished by pretreatment with L-arginine but not with D-arginine. L-NAME did not influence the LPS-induced increase of neutrophils in bronchoalveolar lavage fluid (BALF). These results suggest that in rats, consitutive NO synthesis does not contribute either to basal airway tone or to the basal degree of airway responsiveness, but that inducible NO synthesis mediates endotoxin-induced hyporesponsiveness.

The Effect of a Nitric Oxide Synthase Inhibitor on the Modulation of Airway Responsiveness in Rats

The Effect of a Nitric Oxide Synthase Inhibitor on the Modulation of Airway Responsiveness in Rats

Allergen-induced airway responses in rats pretreated with Sephadex.

Even though the eosinophil is potentially an important contributor to airway narrowing during the late allergic airway response, direct evidence of its participation is lacking. Therefore, we examined the effects of eosinophilia induced by Sephadex on the magnitude of the late airway response of sensitized rats following allergen challenge. Brown Norway rats were actively sensitized to ovalbumin (OA). At the same time and 14 days later, a test group was administered Sephadex G200 (0.5 mg intravenously). The animals were challenged with an aerosol of OA and pulmonary resistance (RL) was measured over 6 h. The early response to OA reached a peak more rapidly and the magnitude of the late response, measured as the area under the curve of RL against time, was significantly greater in the Sephadex-treated group (48.3; geometric mean) compared to the control animals (18.9; p < 0.02). The percentage of eosinophils was increased in the bronchoalveolar lavage of Sephadex-treated animals (4%) compared to the controls (0.9%; p < 0.02) following OA challenge. These results demonstrate that Sephadex induces eosinophilia in Brown Norway rats and is associated with an increase in the late allergic airway response. This is consistent with the hypothesis that the eosinophil is an important determinant of the late response.

Acute Effects of Interleukin-2 on Lung Mechanics and Airway Responsiveness in Rats

We studied the acute effects of interleukin-2 (IL-2), the principal lymphokine responsible for lymphocyte proliferation, on lung mechanics and airway responsiveness to methacholine (MCh) in rats. Lewis (n = 12) and Fisher 344 (n = 13) rats were anesthetized and intubated, and intravenous and intra-arterial lines were inserted. IL-2 (750,000 U/kg) was infused intravenously over 2 to 4 min into seven Lewis and seven Fisher rats, and vehicle alone was administered to five Lewis and six Fisher rats. Blood pressure, heart rate, respiratory frequency (f), tidal volume (VT), minute ventilation (VE), and lung resistance (RL) were measured before and every 5 min for 45 min after the infusion of IL-2. Lung compliance was measured before and 30 min after IL-2. Bronchial provocation testing with MCh was performed 45 min after the infusion of IL-2. Subsequently, the animals were exsanguinated, and the lungs were removed for histologic examination. Infused IL-2 did not alter heart rate or blood pressure, VT, f, VE, and RL increased significantly by 15 min (p less than 0.05), but they returned to baseline by 45 min. Lung compliance decreased significantly in both rat strains. IL-2 increased airway responsiveness only in Lewis rats; the concentration of MCh that caused a doubling of RL (EC200RL) was 0.6 mg/ml and 4.3 mg/ml (p = 0.003) in IL-2-treated and control rats, respectively. The airway responsiveness did not change significantly in Fisher rats; EC200RL was 0.13 and 0.35 mg/ml for IL-2-treated and control rats, respectively (p = 0.09).(ABSTRACT TRUNCATED AT 250 WORDS)

Persistent airway hyperresponsiveness after neonatal viral bronchiolitis in rats

Viral bronchiolitis in human infants has been associated with permanent changes in small airways and gas exchange and an increased incidence of hyperresponsive airways later in life. Respiratory infection by Sendai virus in neonatal rats also has been reported to cause permanent changes in lung morphology and increased numbers of bronchiolar mast cells and eosinophils. We evaluated pulmonary mechanics, gas exchange, and airway responsiveness in rats at 7 and 13-16 wk after neonatal Sendai virus infection. Rats from the virus group had lower arterial PO2 and increased total lung resistance compared with controls. There were no significant differences between groups for arterial PCO2, dynamic lung compliance, quasi-static respiratory system compliance, or vital capacity. Rats from the infected group were significantly more sensitive to aerosolized methacholine than were controls, although both virus and control groups became less sensitive with age. We conclude that neonatal Sendai virus infection in rats results in persistent alterations in lung function and airway responsiveness. This phenomenon may be valuable for the study of the relationships among airway inflammation, lung morphology, and airway hyperresponsiveness, and it may be relevant to human airway disease.

In vivo exposure to hyperoxia increases airway responsiveness in rats. Demonstration in vivo and in vitro.

Studies regarding O2-induced lung injury have concentrated on damage to alveolar structures and pulmonary vasculature without consideration of alterations that may be occurring in airways. This study was undertaken to determine the effects of in vivo hyperoxic exposure on airway responses to excitatory stimuli in intact, anesthetized rats and in intrapulmonary bronchi isolated from hyperoxia-exposed rats. Using lung conductance (G1) as an index of bronchoconstriction, intravenously administered 5-hydroxytryptamine (5HT) elicited greater bronchoconstrictor responses in anesthetized, mechanically ventilated rats that had been exposed to 85% O2 for 7 days rather than to air. Further, airways of hyperoxia-exposed rats were more sensitive to the effects of intravenously administered 5HT as evidenced by the lower log dose of 5HT required to decrease G1 30%. Cylindrical segments of intrapulmonary bronchi isolated from hyperoxia-exposed rats were more responsive to the contractile effects of 5HT and electrical field stimulation. However, no differences in responsiveness to bethanechol or KCl were observed between the two groups. The log concentration of 5HT and the log frequency of electrical field stimulation that elicited half-maximal responses were smaller in bronchi isolated from hyperoxia-exposed animals, indicating an increase in sensitivity of the airways to these stimuli. These results suggest that prolonged exposure to greater than ambient levels of O2 can alter airway function; however, the mechanism responsible for these changes remains to be determined.