Ach Challenge Research Articles

Superimposed pressure oscillations: An alternative to treat airway hyperresponsiveness in an acute sensitized airways mouse model

The main driving mechanism during an asthma attack is the hyper-constrictions of airway smooth muscle (ASM), which reduces the airway lumen and makes normal breathing difficult. In spite of some noticeable side effects, bronchodilator drugs such as salbutamol are used to alleviate these symptoms by inducing temporary relaxation of the contracted ASM. In vitro studies have shown that mechanical oscillation can induce relaxation in isolated contracted ASM obtained from healthy subjects but not from asthmatics. To date, little is known about in vivo ASM behaviours, in particular in asthmatic subjects. This in vivo study aims at determining the effect of various superimposed pressure oscillation (SIPO) patterns (different to those occurring during normal breathing) on sensitized airways during an ACh challenge (mimicking an asthmatic attack) and comparing it with the effect of a widely studied broncho-relaxant drug, Isoproterenol (ISO). The study shows that superimposed pressure oscillation in the range of 5-15Hz induces approximately 50% relaxation on pre-constricted sensitized airways in vivo; however, this behaviour was not observed at 20Hz. Our finding suggests that mechanical oscillation, particularly SIPO, may act as a bronchodilator and achieve ASM relaxation.

Stress amplifies lung tissue mechanics, inflammation and oxidative stress induced by chronic inflammation

ABSTRACTBackground: Mechanisms linking behavioral stress and inflammation are poorly understood, mainly in distal lung tissue. Objective: We have investigated whether the forced swim stress (FS) could modulate lung tissue mechanics, iNOS, cytokines, oxidative stress activation, eosinophilic recruitment, and remodeling in guinea pigs (GP) with chronic pulmonary inflammation. Methods: The GP were exposed to ovalbumin or saline aerosols (2×/wk/4wks, OVA, and SAL). Twenty-four hours after the 4th inhalation, the GP were submitted to the FS protocol (5×/wk/2wks, SAL-S, and OVA-S). Seventy-two hours after the 7th inhalation, lung strips were cut and tissue resistance (Rt) and elastance (Et) were obtained (at baseline and after OVA and Ach challenge). Strips were submitted to histopathological evaluation. Results: The adrenals' weight, the serum cortisol, and the catecholamines were measured. There was an increase in IL-2, IL-5, IL-13, IFN-γ, iNOS, 8-iso-PGF2α, and in %Rt and %Et after Ach challenge in the SAL-S group compared to the SAL one. The OVA-S group has had an increase in %Rt and %Et after the OVA challenge, in %Et after the Ach and in IL-4, 8-iso-PGF2α, and actin compared to the OVA. Adrenal weight and cortisol serum were increased in stressed animals compared to nonstressed ones, and the catecholamines were unaltered. Conclusion & clinical relevance: Repeated stress has increased distal lung constriction, which was associated with an increase of actin, IL-4, and 8-iso-PGF2α levels. Stress has also induced an activation of iNOS, cytokines, and oxidative stress pathways.

Evaluating cost-effectiveness using an economic model: analysis from the TAXUS ATLAS long lesion trial

Objective: Drug-eluting stents (DES) are known to impact vascular functions. The impact of the polymers and the drugs used in DES on the pathways regulating vascular reactivity is not well understood. The objective of the present study was to investigate the effect of rapamycin class of DES on vascular reactivity and the genes involved in the vasoregulating nitric oxide pathway. Methods: A porcine model of stent implantation was used. Bare-metal stents (BMS), DES, sirolimus, zotarolimus or other limus stents were placed in two epicardial vessels of each animal with S/A ratio of 1.1:1 and overlapping segment of 1/3 to 1/2 of single stent length. After 28 days, vascular function was determined by acetylcholine (Ach) challenge. Tissue samples from the stented segment of four arteries from each group were collected. RNA and proteins were isolated. Selected genes and proteins regulating the nitric oxide pathway were further analyzed by real-time polymerase chain reaction (PCR) and western blotting. Results and conclusions: As compared to the BMS, the vascular reactivity to Ach challenge was significantly impaired and super oxide generation was significantly increased in vessels implanted with DES. Quantitative reverse transcriptase PCR analysis of genes involved in vascular reactivity and nitric oxide pathway indicated changes in the expression of VEGF, DDAH and Arginase genes. Western blotting showed that the total or phosphorylated forms of eNOS were similar in BMSand DES-implanted vessels. However, the phosphorylated form of the eNOS regulating protein kinase AKT was significantly increased in zotarolimus stent but not in sirolimus stent. The latter results suggest that nitric oxide pathway sites in addition to eNOS gene expression or protein level may play a role in modulating vascular reactivity in response to DES. Our studies suggest that an interplay between multiple vascular genes including AKT may play an important role in the impairment of vascular response by DES. Further studies will delineate the role of various genes in the pathophysiology of DES leading to vascular dysfunction.

Understanding the impact of drug-eluting stent on vascular function and the nitric oxide pathway genes using a pig coronary artery stent implantation model

Objective: Drug-eluting stents (DES) are known to impact vascular functions. The impact of the polymers and the drugs used in DES on the pathways regulating vascular reactivity is not well understood. The objective of the present study was to investigate the effect of rapamycin class of DES on vascular reactivity and the genes involved in the vasoregulating nitric oxide pathway. Methods: A porcine model of stent implantation was used. Bare-metal stents (BMS), DES, sirolimus, zotarolimus or other limus stents were placed in two epicardial vessels of each animal with S/A ratio of 1.1:1 and overlapping segment of 1/3 to 1/2 of single stent length. After 28 days, vascular function was determined by acetylcholine (Ach) challenge. Tissue samples from the stented segment of four arteries from each group were collected. RNA and proteins were isolated. Selected genes and proteins regulating the nitric oxide pathway were further analyzed by real-time polymerase chain reaction (PCR) and western blotting. Results and conclusions: As compared to the BMS, the vascular reactivity to Ach challenge was significantly impaired and super oxide generation was significantly increased in vessels implanted with DES. Quantitative reverse transcriptase PCR analysis of genes involved in vascular reactivity and nitric oxide pathway indicated changes in the expression of VEGF, DDAH and Arginase genes. Western blotting showed that the total or phosphorylated forms of eNOS were similar in BMSand DES-implanted vessels. However, the phosphorylated form of the eNOS regulating protein kinase AKT was significantly increased in zotarolimus stent but not in sirolimus stent. The latter results suggest that nitric oxide pathway sites in addition to eNOS gene expression or protein level may play a role in modulating vascular reactivity in response to DES. Our studies suggest that an interplay between multiple vascular genes including AKT may play an important role in the impairment of vascular response by DES. Further studies will delineate the role of various genes in the pathophysiology of DES leading to vascular dysfunction.

Effect of Age on Relationship Between Exhaled Nitric Oxide and Airway Hyperresponsiveness in Asthmatic Children

Numerous studies have examined the relationship between the fractional concentration of exhaled nitric oxide (Feno) and airway hyperresponsiveness (AHR). Our objective was to determine the effects of age on the relationship between Feno and AHR in asthmatic children. AHR was examined in 267 asthmatic patients (age range, 5 to 20 years). A challenge test was performed using acetylcholine chloride (Ach). We determined the provocative concentration of Ach producing a 20% decrease in FEV(1) from baseline (PC(20)). Feno was examined using the recommended online method before the Ach challenge test. In children < 12 years of age (range, 5 to 11 years), decreasing AHR (PC(20)) was significantly related to higher Feno (r = -0.43; beta = -0.28; p < 0.001). In adolescents >or= 12 years of age (range, 12 to 20 years), decreasing PC(20) was associated with peripheral airway obstruction (FEV(1): r = 0.32; beta = 5.5; p = 0.002; forced expiratory flow at 50% of the FVC: r = 0.24; beta=8.4; p = 0.006; and forced expiratory flow at 25% of FVC: r = 0.28; beta=11.4; p = 0.002). AHR and Feno were weakly related (r = -0.18; beta = -0.14; p = 0.02). In children with asthma, AHR is associated with airway inflammation. AHR in children with asthma may consist of variable components mainly reflecting airway inflammation. In contrast, in adolescents with asthma, AHR is associated with airway structural changes and weakly with airway inflammation. AHR in adolescents with asthma may consist of chronic components mainly reflecting airway remodeling.

Effect of elastase pretreatment on rat lung strip induced constriction

On exposure to contractile agonists, peripheral smooth muscle shortens and induces distortion in lung parenchyma. To assess the influence of elastic integrity on lung tissue constriction, 24 rat lung strips were oscillated in organ bath, at a fixed frequency of 1 Hz, and exposed to acetylcholine (Ach) 10(-1) M, before and after incubation with pancreatic porcine elastase (PPE). Before the post-PPE Ach challenge, 11 samples were re-stretched to recover control elastance value. Tissue elastance (Etis), resistance (Rtis), and minimum stress (sigma(min)) were calculated cycle-by-cycle. PPE exposure significantly decreased Etis by 8.50+/-1.91%, and sigma(min) by 33.2+/-3.6%. PPE digestion affected the dynamic of mechanical changes during constriction in non re-stretched samples, but not in re-stretched ones. We conclude that lung tissue damage induced by PPE impairs the transmission of forces generated by lung tissue constriction, challenging mechanical interdependence. The intrinsic properties of contractile machinery seem unaffected by PPE digestion.

Water-Soluble Cooling Lubricants Induce Airway Hyper- responsiveness in Rabbits

Airway hyperresponsiveness (AHR) to water-soluble cooling lubricants (CL) induced by aerosol administered by tracheal tube was studied in a rabbit model of occupational lung disease. Two commercial CL were examined: the first was of the boric acid amine ester type without biozide (CL-BAE), the second was of the sulfonate type with biozide (CL-SB). 50, 5.0 or 0.5 mg/m³ CL was administered over a period of twice 2 h to six different groups of rabbits. Airway responsiveness (AR) to aerosols of 0.2% and 2.0% acetylcholine solution (ACH) was measured before and after each exposure to CL. A control group A of nine animals not exposed to CL showed no significant respiratory responses following inhalation of 0.2% ACH for 1 min. Conversely, inhalation of 2.0% ACH almost doubled the dynamic elastance (E_dyn) in the ACH challenge test in this animal group. Airway resistance (R_I), E_dyn, slope of inspiratory pressure generation (ΔP_es/t_I), arterial pressure (P_a) and arterial blood gas tensions (P_aO₂, P_aCO₂) were not significantly altered during and after exposures to CL. However, after CL-BAE inhalation of 50 and 5 mg/m³ over 4 h, the amplitude of the ACH-induced airway obstruction indicated by the changes in E_dyn rose significantly to almost five times the control response before exposure (group C, D, p < 0.005). Similar changes in R_I and ΔP_es/t_I were obtained. After inhalation of 0.5 mg/m³ CL-BAE (group D), no significant changes in AR were observed. Similar to CL-BAE inhalation of 50 mg/m³, CL-SB caused enlarged AR in the ACH challenge test (group E), whereas no significant changes were found after exposure to 5.0 and 0.5 mg/m³ in groups F and G. In summary, CL aerosols with and without biozide in the range of 50 and 5 mg/m³ applied via tracheal tubes increased AR to ACH within 4 h of exposure in a time- and concentration-dependent manner. It has to be assumed that this augmented AR indicates an increased risk of developing lubricant-induced obstructive lung diseases.

Modulation of airway responsiveness to acetylcholine by nitric oxide in a rabbit model.

. Nitric oxide (NO) is an important mediator in the regulation of bronchial muscle tone and airway responsiveness. We investigated the influence of exogenous NO on airway responsiveness to acetylcholine aerosols (ACH) in normal and in hyperresponsive rabbits. White New Zealand rabbits were anesthetized, intubated, and breathed room air spontaneously. Responses of respiratory parameters in ACH challenge tests were measured. In group A the influence of NO on ACH infusion-induced airway constriction was measured. Airway responses to aerosols from 0.25 to 8.0% ACH solutions in saline were measured with 150 and 300 ppm NO inhalation (groups B and C) and compared with the same animals' responses without NO. Moreover, we examined the influence of NO synthase inhibition on airway responsiveness (group D) and the modulatory effect of NO in hyperresponsive animals (group E). 300 ppm NO inhalation significantly decreased the bronchoconstrictor response to intravenously administered ACH (group A). However, the baseline value of dynamic elastance (Edyn) was only marginally lower under the influence of 300 ppm NO. During inhalation of 150 or 300 ppm NO, responses to nebulized 2.0% and less ACH solutions remained nearly unaltered. Responses to aerosols of 4.0 and 8.0% diminished significantly (groups B and C). Following 40 min of aerosolized N-nitro-l-arginine-methyl ester (l-NAME) solution (a NO synthase inhibitor, 1.2 mM) inhalation, the response of Edyn to ACH increased significantly in group D. In group E, animals inhaled 500 mg/m3 ammonium persulfate (APS), an oxidant with various industrial applications, after the first ACH challenge test (0.2, 1.0, and 2.0% ACH). After 2 h of APS exposure, the ACH-induced broncho constriction was increased significantly in the challenge test. After another 2 h of APS inhalation, the airway responsiveness to ACH was tested under the influence of 300 ppm NO. NO significantly decreased the response to ACH to almost the same level as before APS exposure. The results indicate that responses to high ACH concentrations as well as an APS-induced increase in ACH responsiveness were effectively reduced by high concentrations of inhaled NO.

Kerosene aerosol induces guinea-pig airway hyperreactivity to acetylcholine.

Kerosene aerosol (32.5 mg/l; 20 min), when administered to guinea pigs 1 h before exposure to acetylcholine (Ach), induced potentiation of cumulative dose-response curve of this agonist on isolated tracheal strips as well as a decrease of the lethal doses of Ach. This enhanced response was absent or greatly reduced when kerosene aerosol was administered to guinea pigs 24 h previously or just before Ach challenge. This airway hyperreactivity was also lacking when carbachol or histamine were used as spasmogens instead of Ach. Possible explanations of these results are discussed.

The role of upper airways and of sensoric receptors on reflex bronchoconstriction

The influence of bilateral transection of the nervi laryngici cranialis, laryngici caudalis and glossopharyngici on ACH and allergen-induced bronchoconstriction was tested in 15 dogs. In three dogs the free preparation of bilateral nervi laryngici cranialis was performed for control measurements. Partial transection of pulmonary left nervus vagus was performed in three dogs and compared to radical transection of the same nerve in three animals. Transection of the nervi laryngici cranialis as well as of the nervi glossopharyngici was followed by the inhibition of the allergen-induced bronchoconstriction. The bronchoconstriction following ACH challenge was not influenced by transection. Bronchoconstriction induced by allergen returned to the same values within three weeks after surgical intervention. Partial unilateral dissection of the vagus nerve on lung hilus shows a small decrease in bronchial constriction induced by allergen and by ACH. Complete unilateral dissection of the vagus nerve on the lung hilus reduced the bronchial constrictoric response to both substances significantly.

Fatigue of airway obstruction during long-term exposure to allergen aerosol.

The response to prolonged antigen exposure and the potentiation of airway resistance increase to ACH challenge, after this exposure, were studied on sixteen boxer dogs. One group of animals presented fatigue to A.E. after 3 hours of exposure. This group developed an increased response to ACH aerosol after fatigue to antigen was present. In a second group of dogs, absence of fatigue during prolonged exposure to allergen was observed. A growing tendency of Edyn (as an index of airway resistance) was observed after 5 hours of exposure. The therapeutical influence of bilateral vagus blockade was tested in these last animals. Blockade of nervus vagus released airway obstruction during prolonged allergen exposure and no bronchoconstriction was observed after ACH challenge during blockade.

The role of unilateral vagotomy on reflex bronchoconstriction.

Unilateral application of histamine in one segmental bronchus potentiated the airway resistance increase caused by ACH challenge of the bronchial tree. Unilateral or contralateral blockade of the N. vagus reduces the severity of the reaction by about 70% of the values before the blockade.