Hyperpnea-induced Bronchoconstriction Research Articles

A Prebiotic Galactooligosaccharide Mixture (B-GOS) Reduces Severity of Hyperpnea-Induced Bronchoconstriction and Airway Inflammation

PURPOSE: Emerging evidence suggests that the gut microbiota could be a therapeutic target for asthma via the common mucosal system. The aim of the current study was to investigate the effects of prebiotic Bimuno-galactooligosaccharide (B-GOS) supplementation on hyperpnea-induced bronchoconstriction (HIB), a surrogate for exercise-induced bronchoconstriction (EIB), and airway inflammation in adults with asthma. METHODS: In a double blind cross over trial, 10 participants with asthma and HIB (27 ± 7 years; height: 173 ± 8 cm; body mass: 70 ± 9 kg), and 8 control participants without asthma (age: 26 ± 4 years; height: 174 ± 10 cm; body mass: 72 ± 12 kg) were randomized to receive 5.5 gd-1 of either prebiotic B-GOS or placebo (maltodextrin) for 3 weeks separated by a 2 week washout. HIB severity was based on the peak fall in forced expiratory volume in 1 s (FEV1) following a eucapnic voluntary hyperpnea (EVH) challenge. Markers of airway inflammation included serum concentrations of chemokines (CCL11 and CCL17), tumor necrosis factor alpha (TNF-α), c-reactive protein (CRP), and immunoglobulin E (IgE), and fraction of exhaled nitric oxide (FENO). RESULTS: In the HIB group, the peak fall in FEV1 after EVH was unchanged following placebo (day 0; -880 ± 480 mL, vs day 21; -840 ± 430 mL). Following B-GOS the peak fall in FEV1 after EVH was attenuated by 40% (day 0; -940 ± 460 mL, vs. day 21; -570 ± 310 mL, P = 0.004). No changes in pulmonary function in the control group were evident. In the HIB group B-GOS resulted in baseline reductions in CCL17 (day 0; 399.3 ± 139.6 pg·mL-1, vs. day 21 323.0 ± 133.9 pg·mL-1, P = 0.005) and TNF-α (day 0; 2.68 ± 0.98 pg·mL-1, vs. day 21 2.18 ± 0.59 pg·mL-1, P = 0.004) and the TNF-α increase after EVH was abolished. Baseline CRP was reduced following B-GOS in both the HIB and control groups (P < 0.05). No changes in FENO and CCL11 were evident following either intervention. CONCLUSIONS: B-GOS supplementation attenuated HIB severity in adults with asthma. The associated reduction in markers of airway inflammation suggests that B-GOS may target the underlying immunopathologic features of asthma, thereby attenuating the airway hyperresponsiveness associated with HIB/EIB.

A standard, single dose of inhaled terbutaline attenuates hyperpnea-induced bronchoconstriction and mast cell activation in athletes.

Release of bronchoactive mediators from mast cells during exercise hyperpnea is a key factor in the pathophysiology of exercise-induced bronchoconstriction (EIB). Our aim was to investigate the effect of a standard, single dose of an inhaled β2-adrenoceptor agonist on mast cell activation in response to dry air hyperpnea in athletes with EIB. Twenty-seven athletes with EIB completed a randomized, double-blind, placebo-controlled, crossover study. Terbutaline (0.5 mg) or placebo was inhaled 15 min prior to 8 min of eucapnic voluntary hyperpnea (EVH) with dry air. Pre- and postbronchial challenge, urine samples were analyzed by enzyme immunoassay for 11β-prostaglandin F2α (11β-PGF2α). The maximum fall in forced expiratory volume in 1 s of 14 (12-20)% (median and interquartile range) following placebo was attenuated to 7 (5-9)% with the administration of terbutaline (P < 0.001). EVH caused a significant increase in 11β-PGF2α from 41 (27-57) ng/mmol creatinine at baseline to 58 (43-72) ng/mmol creatinine at its peak post-EVH following placebo (P = 0.002). The rise in 11β-PGF2α was inhibited with administration of terbutaline: 39 (28-44) ng/mmol creatinine at baseline vs. 40 (33-58) ng/mmol creatinine at its peak post-EVH (P = 0.118). These data provide novel in vivo evidence of mast cell stabilization following inhalation of a standard dose of terbutaline prior to bronchial provocation with EVH in athletes with EIB.

Self-reported Symptoms after Induced and Inhibited Bronchoconstriction in Athletes.

ABSTRACTPurposeA change in the perception of respiratory symptoms after treatment with inhaled beta2 agonists is often used to aid diagnosis of exercise-induced bronchoconstriction (EIB). Our aim was to test the association between subjective ratings of respiratory symptoms and changes in airway caliber after induced and inhibited bronchoconstriction in athletes with EIB.MethodsEighty-five athletes with diagnosed or suspected EIB performed a eucapnic voluntary hyperpnea (EVH) challenge with dry air. Of the 45 athletes with hyperpnea-induced bronchoconstriction [i.e., post-EVH fall in forced expiratory volume in 1 s (FEV1) ≥10%, EVH−], 36 were randomized in a double-blind, placebo-controlled, crossover study. Terbutaline (0.5 mg) or placebo was administered by inhalation 15 min before EVH. Spirometry (for FEV1) was performed before and after EVH, and respiratory symptoms were recorded 15 min after EVH on visual analog scales.ResultsTerbutaline inhibited bronchoconstriction (i.e., maximal fall in FEV1 <10% after EVH) in 83% of the EVH-positive athletes, with an average degree of bronchoprotection of 53% (95% confidence interval [CI], 45% to 62%). Terbutaline reduced group mean symptom scores (P < 0.01), but the degree of bronchoprotection did not correlate with individual differences in symptom scores between terbutaline and placebo. Of the 29 athletes who had less than 10% FEV1 fall after EVH in the terbutaline condition, almost half (48%) rated at least one respiratory symptom higher under terbutaline, and more than one quarter (28%) had a higher total symptom score under terbutaline.ConclusionSelf-reports of respiratory symptoms in conditions of induced and inhibited bronchoconstriction do not correlate with changes in airway caliber in athletes with EIB. Therefore, subjective ratings of respiratory symptoms after treatment with inhaled beta2 agonists should not be used as the sole diagnostic tool for EIB in athletes.

The Effect of Combining Fish Oil and Vitamin C on Airway Inflammation and Hyperpnea-Induced Bronchoconstriction in Asthma

Purpose: To compare the effects of two mono-therapies (fish oil and vitamin C) alone and in combination, on airway inflammation and the bronchoconstrictor response to eucapnic voluntary hyperpnea (EVH) in asthmatics. Methods: Sixteen asthmatic subjects with hyperpnea-induced bronchoconstriction (HIB) entered the study on their usual diet (pre-treatment, n=16) and then randomly assigned to receive either active vitamin C tablets (1.5 g) and placebo fish oil capsules (n=8) or active fish oil capsules (3.2 g EPA/2.0 g DHA) and placebo vitamin C tablets (n=8) taken for 3 weeks. Thereafter, all subjects (combination treatment; n=16) underwent a further 3-week treatment period consisting of active vitamin C tablets and active fish oil capsules taken daily (NT01057615). Results: HIB was significantly inhibited (p<0.017) by fish oil, vitamin C and combination treatment compared to pre-treatment (usual diet); percent fall in post-EVH forced expiratory volume in 1-sec was 18.8 + 5.7%, 9.7 + 5.4%, 10.5 ± 10.2% and 10.7 ± 9.3% on the usual diet, fish oil, vitamin C and combination treatment respectively. All three treatments, compared to the usual diet, were associated with a significant reduction (p<0.017) in the fraction of exhaled nitric oxide and bronchodilator use, and improvement in asthma symptom scores and exhaled breath condensate pH. There was no significant difference between treatment groups for any dependent variables. Conclusion: While fish oil and vitamin C supplementation are both effective in attenuating airway inflammation and HIB, combining these two nutrients does not confer a greater anti-inflammatory effect or suppression of HIB than either intervention alone.

Marine lipid fraction PCSO-524™ (lyprinol®/omega XL®) of the New Zealand green lipped mussel attenuates hyperpnea-induced bronchoconstriction in asthma

Evaluate the effect of the marine lipid fraction of the New Zealand green-lipped mussel (Perna canaliculus) PCSO-524 (Lyprinol/Omega XL), rich in omega-3 fatty acids, on airway inflammation and the bronchoconstrictor response to eucapnic voluntary hyperpnea (EVH) in asthmatics. Twenty asthmatic subjects, with documented HIB, participated in a placebo controlled double-blind randomized crossover trial. Subjects entered the study on their usual diet and were then placed on 3 weeks of PCSO-524 or placebo supplementation, followed by a 2 week washout period, before crossing over to the alternative diet. Pre- and post-eucapnic voluntary hyperpnea (EVH) pulmonary function, fraction of exhaled nitric oxide (FENO), asthma symptom scores, medication use, exhaled breath condensate (EBC) pH, cysteinyl leukotrienes (cyst-LT), 8-isoprostane and urinary 9α, 11β-prostaglandin (PG)F2 and Clara (CC16) protein concentrations were assessed at the beginning of the trial and at the end of each treatment period. The PCSO-524 diet significantly reduced (p < 0.05) the maximum fall in post-EVH FEV1 (-8.4 ± 3.2%) compared to usual (-19.3 ± 5.4%) and placebo diet (-22.5 ± 13.7%). Pre- and post- EVH EBC cyst-LT and 8-isoprostane, and urinary 9α, 11β-PGF2 and CC16 concentrations were significantly reduced (p < 0.05) on the PCSO-524 diet compared to the usual and placebo diet. EBC pH and asthma symptom scores were significantly improved (p < 0.05) and rescue medication use significantly reduced (p < 0.05) on the PCSO-524 diet compared to the usual and placebo diet. PCSO-524 (Lyprinol)/Omega XL) may have beneficial effects in HIB and asthma by serving as a pro-resolving agonist and/or inflammatory antagonist.

Hyperpnea-Induced Bronchoconstriction and Urinary CC16 Levels in Athletes

Exercise-induced bronchoconstriction (EIB) is a common condition in both individuals with asthma and otherwise healthy elite athletes. Although excessive water loss by peripheral airways during hyperpnea is regarded as the initial trigger for EIB, the cascade of events that follows remains unclear. Our goal was to establish whether transient disruption of the airway epithelial barrier occurs after a short period of hyperpnea of dry air in athletes with EIB. Urinary concentration of the pneumoprotein Clara cell (CC16) was used as an assumed biomarker of lung epithelial cell damage or dysfunction. Samples were collected at baseline and for 90 min after an 8-min eucapnic voluntary hyperpnea (EVH) test in 50 female individuals (28 athletes and 22 untrained). Nineteen subjects (10 athletes) demonstrated a sustained bronchoconstriction after EVH (mean±SE forced expiratory volume in the first second (FEV1) fall from baseline=23.4%±2.6%). The remaining subjects had a negative challenge result with an FEV1 fall of 5.9%±0.6%. An increase (P<0.001) in urinary CC16 concentration was noticed after EVH in all but one subject, with no group difference (median CC16 increase before to after challenge: athletes EVH 0.083 ng·μmol, athletes EVH 0.223 ng·μmol, untrained EVH 0.074 ng·μmol, untrained EVH 0.571 ng·μmol; P>0.05). Urinary levels of CC16 are increased after EVH in all individuals (trained and untrained, with and without EIB) suggestive of dehydration-induced perturbation of the distal respiratory epithelium during episodes of hyperventilation.

Conjugated Linoleic Acid’s Lack of Attenuation of Hyperpnea-Induced Bronchoconstriction in Asthmatic Individuals in the Short Term

Conjugated linoleic acid (CLA) has been reported to modify the inflammatory response associated with allergic airway disease, primarily in animal models. To extend these observations to humans, the effect of short-term CLA supplementation on the severity of exercise-induced bronchoconstriction (EIB) was investigated in asthmatics. Six subjects with physician-diagnosed asthma and EIB began the study on their usual diet, to which was added 4.8 g CLA/d for 8 wk. Pulmonary-function tests were administered before and after eucapnic voluntary hyperventilation (EVH) challenge at the commencement (Week 0) and conclusion of the treatment period (Week 8). Pre- and 90 min post-EVH challenge, urine was assayed for the presence of cysteinyl leukotrienes (LT) C4-E4 and 9α, 11β-prostaglandin (PG) F2. Pre- to post-EVH forced expiratory volume in 1 s (FEV1) did not significantly differ (p > .05) from Week 8 to Week 0. The pre- to post-EVH decline in FEV1 at Week 8 (-29.6% ± 6.6%) was not significantly different (p > .05) from that at Week 0 (-32.0% ± 5.5%). Area under the curve of FEV1 plotted against time from zero to 60 min (AUC0-60) was unaltered at Week 8 (-931% ± 350% change per minute) compared with Week 0 (-1,090% ± 270% change per minute). CLA supplementation did not alter forced midexpiratory flow, forced vital capacity (FVC), or FEV1/FVC. In addition, post-EVH urinary LTC4-E4 and 9α, 11β-PGF2 were unchanged after CLA supplementation. Daily supplementation of 4.8 g CLA for 8 wk does not attenuate airway inflammation or hyperpnea-induced bronchoconstriction in asthmatic individuals.

Randomized Controlled Trial of Fish Oil and Montelukast and Their Combination on Airway Inflammation and Hyperpnea-Induced Bronchoconstriction

BackgroundBoth fish oil and montelukast have been shown to reduce the severity of exercise-induced bronchoconstriction (EIB). The purpose of this study was to compare the effects of fish oil and montelukast, alone and in combination, on airway inflammation and bronchoconstriction induced by eucapnic voluntary hyperpnea (EVH) in asthmatics.MethodsIn this model of EIB, twenty asthmatic subjects with documented hyperpnea-induced bronchoconstriction (HIB) entered a randomized double-blind trial. All subjects entered on their usual diet (pre-treatment, n = 20) and then were randomly assigned to receive either one active 10 mg montelukast tablet and 10 placebo fish oil capsules (n = 10) or one placebo montelukast tablet and 10 active fish oil capsules totaling 3.2 g EPA and 2.0 g DHA (n = 10) taken daily for 3-wk. Thereafter, all subjects (combination treatment; n = 20) underwent another 3-wk treatment period consisting of a 10 mg active montelukast tablet or 10 active fish oil capsules taken daily.ResultsWhile HIB was significantly inhibited (p<0.05) by montelukast, fish oil and combination treatment compared to pre-treatment, there was no significant difference (p>0.017) between treatment groups; percent fall in forced expiratory volume in 1-sec was −18.4±2.1%, −9.3±2.8%, −11.6±2.8% and −10.8±1.7% on usual diet (pre-treatment), fish oil, montelukast and combination treatment respectively. All three treatments were associated with a significant reduction (p<0.05) in FENO, exhaled breathe condensate pH and cysteinyl-leukotrienes, while the fish oil and combination treatment significantly reduced (p<0.05) urinary 9α, 11β-prostaglandin F2 after EVH compared to the usual diet; however, there was no significant difference (p>0.017) in these biomarkers between treatments.ConclusionWhile fish oil and montelukast are both effective in attenuating airway inflammation and HIB, combining fish oil with montelukast did not confer a greater protective effect than either intervention alone. Fish oil supplementation should be considered as an alternative treatment for EIB.Trial RegistrationClinicalTrials.gov NCT00676468

Role of nitric oxide in hyperpnea-induced bronchoconstriction and airway microvascular permeability in guinea pigs

ABSTRACTThe present study aimed to evaluate the role of nitric oxide (NO) on hyperpnea-induced bronchoconstriction (HIB) and airway microvascular hyperpermeability (AMP). Sixty-four guinea pigs were anesthetized, tracheotomized, cannulated, and connected to animal ventilator to obtain pulmonary baseline respiratory system resistance (Rrs). Animals were then submitted to 5 minutes hyperpnea and Rrs was evaluated during 15 minutes after hyperpnea. AMP was evaluated by Evans blue dye (25 mg/kg) extravasation in airway tissues. Constitutive and inductible NO was evaluated by pretreating animals with NG-nitro-l-arginine methyl ester (l-NAME) (50 mg/kg), aminoguadinine (AG) (50 mg/kg), and l-arginine (100 mg/kg) and exhaled NO (NOex) was evaluated before and after drug administration and hyperpnea. The results show that l-NAME potentiated (57%%) HIB and this effect was totally reversed by l-arginine pretreatment, whereas AG did not have effect on HIB. l-NAME decreased basal AMP (48%%), but neither l-NAME nor AG had any effect on hyperpnea-induced AMP. NOex levels were decreased by 50%% with l-NAME, effect that was reversed by l-arginine treatment. These results suggest that constitutive but not inducible NO could have a bronchoprotective effect on HIB in guinea pigs. The authors also observed that neither constitutive nor inducible NO seems to have any effect on hyperpnea-induced AMP.

Acute Effects of Beclomethasone on Hyperpnea-Induced Bronchoconstriction

The aim of this study was to assess whether a single high dose of beclomethasone dipropionate (BDP) could blunt mast cell activation and bronchoconstriction after eucapnic voluntary hyperpnea (EVH). In this model of exercise-induced bronchoconstriction (EIB), seven athletes with EIB and eight untrained subjects with mild asthma performed two EVH tests 5.5 h apart on the same day; the first challenge after inhalation of a placebo aerosol and the second 4 h after inhalation of BDP (1500 microg). Prechallenge and postchallenge pulmonary function and urinary excretion of the mast cell mediator 9alpha, 11beta-prostaglandin (PG) F2 were followed, as well as urinary excretion of the bronchoconstrictor leukotriene (LT) E4. The EVH-induced bronchoconstriction was inhibited by BDP in both groups (P < 0.001): in athletes, mean +/- SEM percent fall in forced expiratory volume in 1 s was 22% +/- 4% after placebo versus 13% +/- 3% after BDP; in subjects with asthma, 23% +/- 4% after placebo versus 14 +/- 3% after BDP. This inhibition of airway response was associated with a significant reduction in the urinary excretion of 9alpha,11beta-PGF2 (P = 0.039) and LTE4 (P = 0.003) in both groups. Significant correlations were found between the percent fall in forced expiratory volume in 1 s and the increase in urinary excretion of both mediators 9alpha,11beta-PGF2 (r = 0.544, P = 0.002) and LTE4 (r = 0.380, P = 0.038) after EVH. We conclude that a single dose of BDP has an acute protective effect on the bronchial response to hyperpnea in both untrained subjects with asthma and athletes with EIB. This effect was associated with decreased excretion of urinary mediators, suggesting that BDP blunted the mast cell activation.

Airway function after cyclooxygenase inhibition during hyperpnea-induced bronchoconstriction in guinea pigs.

Airway function deteriorates significantly on cessation of exercise or isocapnic hyperventilation challenges but is largely preserved during the challenge in humans and guinea pigs. PGE(2), an endogenous bronchodilator, might be responsible for the preservation of lung function during hyperventilation (HV). We hypothesized that PGE(2) might have a protective effect during HV, partially explaining the minimal changes in respiratory system resistance (Rrs) usually seen during HV in humans and guinea pigs. Therefore, changes in Rrs were measured during and after HV in anesthetized, mechanically ventilated guinea pigs treated with flurbiprofen (FBN) or placebo. With HV, there was an initial bronchodilation that was unaffected by FBN. Rrs then increased with time during HV, an effect that was blocked by FBN. After HV, Rrs increased further in all groups, but the increase in Rrs was less in the FBN-treated groups. FBN treatment reduced the PGE(2) concentration slightly in lung lavage fluid compared with placebo. We found no enhancement or refractoriness of the Rrs response to repeat bouts of HV and no effect of FBN treatment on the response of Rrs to repeat HV. These results suggest that a constrictor PG is released during and possibly after HV and that the post-HV increase in Rrs is the sum of effects of the PG released during HV and a second constrictor mechanism operating after HV. We found no evidence for bronchodilator PG during or after HV in the guinea pig.

Bradykinin-induced Airway Constriction in Guinea-pigs: Role of Leukotriene D4

Tachykinins (TK) have been implicated in both bradykinin-(BK) and hyperpnea-induced broncho-constriction (HIB) in the guinea-pig. However, TKs appear to have an indirect effect in HIB by releasing leukotriene (LT)D4. We postulated that BK may cause bronchoconstriction through a cascade involving TK and LTD4. We examined the role of TK and LTD4in BK-induced bronchoconstriction in ventilated Hartley guinea-pigs. Respiratory resistance (Rrs) was monitored for 2 h following insufflation of BK (150 nM). Animals were pretreated with propranolol, then with either neurokinin (NK)1 (CP-99,994)+NK2 (SR-48,968) receptor antagonists or pranlukast (90 μ g or 900 μ g), an LTD4antagonist. Control animals received no pretreatment. BK-induced bronchoconstriction was significantly lower in NK1/NK2 (128%±6% baseline RrsSEM) and pranlukast (90 μ g; 205±22, 900μ g; 169±20) animals compared to controls (284±22), P<0.0001 ANOVA. Bile from control and saline challenged animals was analysed for LTD4by HPLC and radio-immunoassay. However, LTD4excretion rate showed no significant difference over a 2-h collection period following insufflation of either BK or saline, respectively; baseline =2.5 pmol/h±0.6 SEM vs. 2.3±0.2, 0–1 h=2.8±0.7 vs. 2.0±0.6, 1–2 h=2.3±0.6 vs. 1.7±0.7. We conclude that BK-induced bronchoconstriction is mediated in part through the release of both TK and LTD4, but the latter is released in insufficient quantities to be detectable by biliary analysis.

Mediators in hyperpnea-induced bronchoconstriction of guinea pigs.

Both tachykinins and leukotrienes (LTs) have been demonstrated to be the mediators for hyperpnea-induced bronchoconstriction (HIB) of guinea pigs. We tested the hypothesis that leukotrienes modulate HIB indirectly by triggering tachykinin release. Ninety nine young guinea pigs were divided into four groups: control; LTC4; FPL 55712 (a LT receptor antagonist); and MK-886 (an inhibitor of LT synthesis). Each animal was anesthetized, cannulated, paralyzed, and artificially ventilated. The protocol included the baseline, hyperpnea, and recovery periods. Thus, animals in each group were further divided into three subgroups: baseline; recovery-3 min; and recovery-8 min. We measured dynamic respiratory compliance (Crs), forced expiratory volume in 0.1 s (FEV0.1) and maximal expiratory flow at 30% total lung capacity (Vmax30), as well as determined substance P (SP) and LT levels in plasma and bronchoalveolar lavage (BAL) during either the baseline or the recovery (3 or 8 min) period. Hyperpnea caused decreases in Crs, FEV0.1 and Vmax30, indicating HIB, in the control group at 3 min and 8 min of the recovery period. Both FPL 55712 and MK-886 significantly attenuated HIB. In the control group, hyperpnea caused significant increases in SP and LT levels in both plasma and BAL. These increases in SP levels were significantly suppressed, however, by FPL 55712 and MK-886. Compared to the control group, infusion of LTC4 did not significantly alter either HIB, SP or LT levels in most cases. An additional group of 24 animals treated with neurokinin-2 receptor antagonist, SR 48968, demonstrated that SR 48968 significantly suppressed hyperpnea-induced increases in plasma, but not in BAL, LT levels. Since FPL 55712 and MK-886 first suppress LT activities, these results suggest that suppressed LT activities attenuate HIB indirectly via reducing tachykinin release.

The β2-agonist Salbutamol Inhibits Bronchoconstriction and Leukotriene D4Synthesis After Dry Gas Hyperpnea in the Guinea-pig

Isocapnic dry gas hyperpnea-induced bronchoconstriction (HIB) in the guinea-pig is mediated by both tachykinin release from airway sensory nerve C-type fiber terminals and secondary synthesis of cysteinyl-leukotrienes, in particular LTD4. Beta (β)2-agonists are potent bronchodilators but potentially could also inhibit the airway response to hyperpnea challenge via effects on the release of LTD4from airway cells in vivo. The purpose of this study was to test the hypothesis that β2agonists attenuate HIB in guinea-pigs, in part, by reduction in LTD4release in vivo. Twenty-six guinea-pigs (400–550 g) were anesthetized with xylazine (7 mg/kg) and pentobarbital (65 mg/kg), tracheotomized and mechanically ventilated with a small animal ventilator using a tidal volume of 3 ml and a breathing frequency of 60 breaths/min. Dry gas (95%O2/5%CO2) with a 4 ml tidal volume and a breathing frequency of 150/min was used for hyperpnea challenge. Challenge with isocapnic dry gas triggered a significant increase in pulmonary resistance (0.3 ± 0.02 vs. 0.57 ± 0.06 cmH2O/ml per s; P=0.017; n=13) and excretion of LTD4in the bile (baseline: 2.43 vs. HIB: 4.66 pmol/h; P=0.04). Salbutamol pretreatment completely blocked the airway response to the challenge (0.3±0.02 vs. 0.3±0.05 cmH2O/ml per s; n=13) and reduced the biliary excretion of LTD4(baseline: 2.42 pmol/h; vs. HIB: 2.40 pmol/h). We conclude that salbutamol inhibited the airway responses to dry gas hyperpnea challenge and LTD4synthesis by the airway cells.

Elastase in hyperpnea-induced guinea pig airway constriction

Aerosolized elastase has been shown to produce airway constriction in guinea pigs. In this study, we examined whether endogenous elastase plays a role in isocapnic hyperpnea-induced airway constriction using an elastase inhibitor, eglin-c. The study was divided into three experiments. In the first experiment, we used an elastase inhibitor, eglin-c, to suppress hyperpnea-induced bronchoconstriction. Twenty-two young male Hartley guinea pigs were divided into three groups: control (n=8), eglin-c(1) (a lower dose of eglin-c, n=7), and eglin-c(2) (a higher dose of eglin-c, n=7). In the second experiment, we tested whether eglin-c affects pulmonary function following 15 min of normal air ventilation in two groups of animals: control (n=8) and eglin-c (n=8). In the third experiment, animals were divided into two groups: control (n=7) and compound 48/80 (a mast cell degranulating agent, n=7). Airway function was examined in the anesthetized–paralyzed animal. In the first and third experiments, 15 min of isocapnic hyperpnea caused marked decreases in dynamic respiratory compliance, forced expiratory flow at 0.1 s and maximal expiratory flow at 50% total lung capacity, demonstrating hyperpnea-induced airway constriction. This bronchoconstriction was significantly attenuated by eglin-c and by pretreatment with compound 48/80. In the second experiment, eglin-c did not significantly affect bronchial function following normal air ventilation. These data suggest that elastase released from mast cells directly or indirectly induces hyperpnea-induced bronchoconstriction.

Hyperpnea-induced bronchoconstriction is dependent on tachykinin-induced cysteinyl leukotriene synthesis.

The purpose of the study was to test the hypothesis that tachykinins mediate hyperpnea-induced induced bronchoconstriction indirectly by triggering cysteinyl leukotriene (LT) synthesis in the airways. Guinea pigs (350-600 g) were anesthetized with xylazine and pentobarbital sodium and received hyperpnea challenge (tidal volume 3.5-4.0 ml, frequency 150 breaths/min) with either humidified isocapnic gas (n = 6) or dry gas (n = 7). Dry gas challenge was performed on animals that received MK-571 (LTD4 antagonist; 2 mg/kg i.v.; n = 5), capsaicin (n = 4), neurokinin (NK) antagonists [NK1 (CP-99994) + NK2 (SR-48968) (1 mg/kg i.v.); n = 6], or the H1 antihistamine pyrilamine (2 mg/kg i.v.; n = 5). We measured the tracheal pressure and collected bile for 1 h before and 2 h after hyperpnea challenge. We examined the biliary excretion of cysteinyl LTs; the recovery of radioactivity in bile after instillation of 1 microCi [3H]LTC4 intratracheally averaged 24% within 4 h (n = 2). The major cysteinyl LT identified was LTD4 (32% recovery of radioactivity). Cysteinyl LTs were purified from bile of animals undergoing hyperpnea challenge by using reverse-phase high-pressure liquid chromatography and quantified by radioimmunoassay. There was a significant increase in the peak value of tracheal pressure after challenge, indicating bronchoconstriction in dry gas-challenged animals but not after humidified gas challenge. MK-571, capsaicin, and NK antagonists prevented the bronchoconstriction; pyrilamine did not. Cysteinyl LT levels in the bile after challenge were significantly increased from baseline in dry gas-challenged animals (P < 0.05) and were higher than in the animals challenged with humidified gas or dry gas-challenged animals treated with capsaicin or NK antagonists (P < 0.01). The results indicate that isocapnic dry gas hyperpnea-induced bronchoconstriction is LT mediated and the role of tachykinins in the response is indirect through release of LTs. Endogenous histamine does not contribute to the response.

Roles of calcitonin gene-related peptide (CGRP) in hyperpnea-induced constriction in guinea pigs.

It has been reported that hyperpnea-induced bronchoconstriction in guinea pigs is a potential model for exercise-induced asthma in humans. We hypothesized that calcitonin gene-related peptide (CGRP) could modulate leukotriene D4 (LTD4)-induced responses and be involved in the pathophysiology in this asthma model. We measured tracheal (Ptr) and alveolar pressure (PA) using alveolar capsules in open-chested, mechanically ventilated (f = 1 Hz, VT = 9 ml/kg, PEEP = 4 cm H2O) guinea pigs. Animals were intravenously pretreated with saline (SAL), CGRP(8-37) (CGRP receptor antagonist), CGRP, MK-571 (LTD4 receptor antagonist), MK-886 (5-lipoxygenase inhibitor), or CGRP(8-37) + MK-571, and then underwent dry gas hyperpnea challenge (HC, 95% 02-5% CO2, 150 breaths/min, 7 min). We calculated resistance of lung (RL), tissue (Rti), and airway (Raw). HC increased RL, Rti, and Raw in SAL controls (322 +/- 27, 430 +/- 59, 299 +/- 23% baseline, respectively). MK-571, MK-886, and CGRP significantly reduced the responses to HC, while CGRP(8-37) enhanced HC-induced responses. Pretreatment with CGRP(8-37) and MK-571 in combination attenuated HC-induced constriction. In addition, pretreatment with CGRP reduced responses induced by intravenous administration of LTD4. These observations suggest that CGRP might be involved in the pathophysiology of hyperpnea-induced constriction in guinea pigs via modulation of LTD4-elicited responses.

Eicosanoids modulate hyperpnea-induced bronchoconstriction in canine peripheral airways.

We examined the role of leukotrienes (LTs) in the development of dry air-induced bronchoconstriction (AIB) in canine peripheral airways. Airway reactivity to exogenous LTs was first tested by using an LTD4 aerosol challenge: peripheral airway resistance increased approximately 130 +/- 51% (n = 4) above baseline when compared with its vehicle control. AIB was then assessed by measuring peripheral airway resistance after, and airway wall temperature during, a dry air challenge (DAC). Treatment with a peptidoleukotriene biosynthesis inhibitor (MK-0591) attenuated AIB by approximately 65% without altering airway wall temperature. The fact that MK-0591 did not alter airway reactivity to aerosolized acetylcholine and completely inhibited Ca2+ ionophore-induced LTB4 generation in canine whole blood attests to the specificity of the drug. Treatment with MK-0591 did not affect the increased number of epithelial cells recovered in bronchoalveolar lavage fluid 5 min after DAC. Concentrations of LTs and other eicosanoids in bronchoalveolar lavage fluid from vehicle-treated DAC airways were increased above baseline values; only LTs were reduced by MK-0591. Before MK-0591, AIB was significantly correlated with the dry air-induced generation of LTC4, LTD4, and LTE4. After treatment with MK-0591, AIB was correlated with thromboxane B2, prostaglandin (PG) F2 alpha, and PGE2. We conclude that hyperpnea with dry air stimulates local production and release of LTs in canine bronchi and, alone with the generation of bronchoconstricting and bronchodilating PGs, plays a central role in the modulation of AIB.

Tachykinin NK2 receptors further characterized in the lung with nonpeptide receptor antagonists.

Two nonpeptide tackykinin NK2 receptor antagonists have now been described, SR 48968 and GR 159897. These drugs are highly specific and very potent antagonists with affinity (binding and in vitro study) for NK2 receptors in the subnanomolar range (pKi = 9-10), without intrinsic activity. They act preferentially on the human NK2A receptor subtype. These drugs exert potent and long-acting antagonism by both i.v. and oral administration. Their use has first confirmed the preponderant role of NK2 receptors in airway smooth muscle contraction, especially in human bronchi. A role for NK2 receptor stimulation has also been clearly demonstrated in bronchoconstriction induced by various agents known to induce the release of tachykinins (capsaicin, resiniferatoxin, citric acid, sodium metabisulfite diethyl ether, serotonin, and bradykinin), in allergen-induced airway constriction in the guinea pig sensitized to ovalbumin, and in hyperpnea-induced bronchoconstriction. Inhibition of neurokinin A mediated or capsaicin-mediated dyspnea by SR 48968 has also been demonstrated in the guinea pig. SR 48968 also is very efficient in inhibiting cough induced by citric acid or capsaicin. Finally, SR 48968 is able to abolish in guinea pigs in vivo the bronchial hyperreactivity induced after 24 or 48 h by a citric acid challenge or an ovalbumin challenge, respectively. Thus, nonpeptide, long-acting NK2 receptor antagonists can be regarded as suitable tools for investigations in humans. They may shortly allow a precise determination of the role of tachykinins in asthmatic patients.

Dry air-induced mucosal cell injury and bronchovascular leakage in canine peripheral airways.

The purpose of this study was to examine the relationship between hyperpnea-induced mucosal injury, bronchovascular hyperpermeability, and airway reactivity. Hyperpnea-induced bronchoconstriction was assessed by measuring peripheral airway resistance (Rp) in anesthetized mechanically ventilated male mongrel dogs. Either colloidal carbon or monastral blue was used to localize bronchovascular leakage after a 5-min exposure to either a 1000 ml/min dry, 2000 ml/min wet, or 2000 ml/min dry air challenge. Morphometric analyses of cross-sectioned bronchi revealed that hyperpnea with dry air stimulated goblet cell degranulation, damaged the bronchial mucosa, and increased bronchovascular permeability. Exposure to only a 2000 ml/min dry air challenge produced marked mucosal injury when compared with control. Regardless of treatment, bronchial vessels lying below normal mucosa characterized by goblet/ciliated cell (G/C) ratios > or = 0.3 did not leak. A G/C transition zone between 0 and 0.3 separated normal from damaged mucosa. Within this zone, vascular permeability was inversely correlated with G/C ratio. In addition, airflow-induced changes in Rp were inversely related to G/C ratio and positively correlated with bronchovascular leakage. Although these correlations are consistent with the speculation that bronchovascular leakage and edema formation are responsible for the dry air-induced changes in Rp, it is equally plausible that bronchovascular leakage is not the cause of but occurs in concert with airway narrowing to protect cells in the bronchial mucosa from excessive losses of heat and water.