Involvement of superoxide in ozone-induced airway hyperresponsiveness in anesthetized cats

To determine whether oxygen radical scavengers inhibit ozone-induced airway hyperresponsiveness, we examined the protective effect of polyethylene glycol-superoxide dismutase (PEG-SOD) and PEG-catalase (PEG-CAT) on ozone-induced airway hyperresponsiveness in cat airways. Twenty-five cats divided into five groups were anesthetized and mechanically ventilated. There was no difference between the groups in baseline airway responsiveness to inhaled acetylcholine (ACh). In the control group, AChPC, the concentration required to produce a doubling increase in baseline pulmonary resistance, was significantly reduced by ozone exposure (2.0 ppm for 2 h); the ratios of AChPC before ozone exposure to after ozone exposure (AChPC ratio) were 14.8 +/- 5.7 (p < 0.001) and 4.80 +/- 1.6 (p < 0.01) 30 and 120 min after exposure, respectively. Local administration of PEG-SOD (2,000 U/kg) into airways partially but significantly prevented ozone-induced airway hyperresponsiveness. The AChPC ratios were 6.2 +/- 1.4 and 1.5 +/- 0.2 30 and 120 min after exposure, respectively, which were significantly different from those of the control group (p < 0.05), whereas PEG-CAT pretreatment (6,000 U/kg) was without effect. Combined pretreatment with PEG-SOD and PEG-CAT had no additional protective effect compared with PEG-SOD alone. PEG-SOD had no direct effect on airway responsiveness to ACh. These results suggest that superoxide may be involved in ozone-induced airway hyperresponsiveness.

Bradykinin causes airway hyperresponsiveness and enhances maximal airway narrowing. Role of microvascular leakage and airway edema

The relationship between bronchial edema and airway responsiveness was studied in cats in situ. Five cats were exsanguinated, and the bronchial arteries were perfused. We monitored pulmonary resistance (RL), and the provocative dose of acetylcholine (ACh) required to produce a 300% increase in RL (PD300) was determined. Bronchial vascular permeability was measured by quantifying extravasation of Evans blue (EB) dye. Bradykinin (BK) and ACh were administered via the bronchial arteries to increase leakage and bronchoconstriction, respectively. BK preperfusion (for 30 min) significantly increased bronchial vascular permeability to four times the control values (p < 0.05). BK preperfusion did not alter baseline RL but caused hyperresponsiveness to ACh, with log [PD300 (mole)] of -6.53 +/- 0.42 (mean +/- SD) and -6.90 +/- 0.30, before and after BK, respectively (p < 0.01). Furthermore, the maximal airway narrowing after BK was 58% higher than before BK (p < 0.01). Histologic study showed peribronchial edema after BK. The enhancement of maximal airway narrowing was significantly correlated with the degree of EB dye extravasation. These results suggest that BK causes airway hyperresponsiveness to ACh and increases maximal airway narrowing, possibly because of airway edema.

Dysfunction of nonadrenergic noncholinergic inhibitory system after antigen inhalation in actively sensitized cat airways

We have investigated whether proteases released during antigen inhalation cause dysfunction of the nonadrenergic noncholinergic inhibitory nervous system (NANCIS). Frequency-response (F-R) studies of NANCIS were performed before and after Ascaris antigen (ASC) inhalation using actively sensitized cats. NANC dilatatory effects were obtained by stimulating bilateral cervical vagi under cholinergic and beta-adrenergic blockade and serotonin-induced bronchoconstriction, and assessed by maximal percent relaxation (rmax) and the frequency causing 50% of maximal relaxation (EF50). ASC inhalation caused a transient increase in pulmonary resistance in all animals. One hour after ASC inhalation, pulmonary resistance returned to the baseline value, but ASC inhalation significantly attenuated NANC inhibitory activities: rmax decreased from 82.2 +/- 4.7 (mean +/- SE) to 64.3 +/- 11.2% (p less than 0.05), and the geometric mean of EF50 increased from 1.7 to 4.3 Hz (p less than 0.05). Dilatatory effects of infused VIP, a possible neurotransmitter of NANCIS, was also attenuated after ASC inhalation. Pretreatment with leupeptin (3 mg/kg) abolished ASC-induced impairment of NANC inhibitory activities. By contrast, dilatatory effects of adrenergic nerve stimulation were not affected by ASC inhalation. These results suggest that NANC inhibitory activities can be impaired after ASC inhalation, and that this impairment of NANCIS may be due to effects of proteases released during allergic reaction.

Bradykinin-induced cough reflex markedly increases in patients with cough associated with captopril and enalapril

We studied the effects of angiotensin converting enzyme (ACE) inhibitors on cough responses to bradykinin (BK), substance P (SP) and citric acid in a double blind, random study on 10 hypertensive patients receiving ACE inhibitors. Of these patients, five had reported cough with ACE inhibitors. Cough responses to citric acid were similar between patients with and without cough, and SP up to 10(-5) M did not cause cough in any of the subjects. BK caused cough at 13.4 +/- 1.2 (-log M) in 5 patients with cough associated with ACE inhibitors, but it did not cause cough at concentrations up to 10(-5) M in other 5 patients. One month after the withdrawal of ACE inhibitors, 5 patients were free from cough symptoms, and BK did not cause cough up to 10(-5) M in these patients, except for one who coughed at 10(-9) M, without changes in responses to citric acid. BK caused cough at 14.3 +/- 0.7 (-log M) although BK1-7, a major metabolite of BK by ACE, caused cough at 5.7 +/- 0.7 (-log M) in another 3 patients with cough associated with ACE inhibitor. These results suggest that impaired metabolism of BK induced by ACE inhibitors may relate to the manifestation of cough in hypertensive patients receiving ACE inhibitors.

[Abnormalities in cough reflex]

Enzymes degrading peptides may participate in the regulation of the cough reflex. Thus, decreases in enzyme activities may enhance cough reflex and a decrease in cough reflex may lead to aspiration pneumonia. Down- and up-regulation of cough reflex is important for the understanding of cough reflex.

Oxygen radicals produce airway constriction and hyperresponsiveness in anesthetized cats

Using 30 anesthetized cats, we examined whether oxygen radicals produce airway constriction or hyperresponsiveness. In one group, we administered aerosolized xanthine (0.1%) for 3 min followed by aerosolized xanthine oxidase (XO) (1 U/ml) for 5 min in order to generate oxygen radicals enzymatically in the airways. Pulmonary resistance (RL) instantaneously increased from 14.8 +/- 0.9 to 30.8 +/- 1.4 cm H2O/L/s (p less than 0.01). The increase in RL was significantly depressed by prior administration of polyethylene glycol-superoxide dismutase (PEG-SOD) or polyethylene glycolcatalase (PEG-CAT). In a second group, in order to examine changes in airway responsiveness, we studied acetylcholine (ACh) challenge before and 30, 60, and 120 min after inhalations of xanthine and XO. After xanthine-XO, the airways were hyperresponsive to ACh at 30 and at 60 min (p less than 0.05) but not at 120 min. The geometric means of ACh provocative concentrations that caused an increase in RL of 10 cm H2O/L/s above the baseline value before and 30, 60, and 120 min after xanthine-XO were 0.25, 0.045, 0.073, and 0.15%, respectively. The increase in responsiveness to ACh was significantly correlated with the increase in RL after xanthine-XO inhalation (r = 0.88, p less than 0.05). These data support the concept that oxygen radicals generated by xanthine-XO inhalation may induce bronchoconstriction and airway hyperresponsiveness.

Effect of nonadrenergic noncholinergic inhibitory nerve stimulation on the allergic reaction in cat airways

To examine the effect of nonadrenergic noncholinergic (NANC) inhibitory nerve stimulation on the antigen inhalation with allergic animals, changes in pulmonary resistance (RL) and arterial plasma histamine concentration ([H]) caused by inhalation of Ascaris suum antigen were studied in five control (Group A) and five nerve-stimulated (Group B) cats, which were anesthetized and mechanically ventilated. All animals were actively sensitized with Ascaris antigen before the experiment. After cholinergic and beta-adrenergic blockade with intravenously administered atropine (3 mg/kg) and propranolol (2 mg/kg), inhalation of the antigen (1:100 dilution) was performed for 3 min. For Group B, bilateral cervical vagi were stimulated electrically for 1 min before the antigen inhalation and successively every 30 s until 5 min had passed from the onset of inhalation. RL and [H] were determined before, during, and after antigen inhalation in both groups. Baseline RL and [H] did not differ significantly between groups (16.3 +/- 2.2 (mean +/- SE) cm H2O/L/s and 14.0 +/- 0.7 ng/ml, respectively, for Group A; 14.4 +/- 1.3 and 15.6 +/- 2.7, respectively, for Group B). Increases in RL and [H] of Group B after the antigen inhalation were significantly depressed, compared with Group A (p less than 0.01 and p less than 0.05, respectively, two-way ANOVA). The increase in RL 5 min after antigen inhalation was 113 +/- 19% for Group A and 28 +/- 8% for Group B, and the increase in [H] at the same point was 36.3 +/- 9.1 ng/ml for Group A and 4.4 +/- 1.4 ng/ml for Group B.(ABSTRACT TRUNCATED AT 250 WORDS)

Increase in luminal mast cell and epithelial damage may account for increased airway responsiveness after viral infection in dogs

To elucidate the mechanisms of airway hyperresponsiveness induced by viral infection, we examined histologically and analyzed bronchoalveolar lavage (BAL) fluid using dogs infected with influenza C and noninfected control dogs. Airway responsiveness was assessed as inhaled acetylcholine concentration required to increase pulmonary resistance by 5 cm H2O/L/s (ACh PC). Airway responsiveness was determined before and 2 wk after virus or vehicle inoculation in infected and control dogs, and BAL and histologic studies were performed after the final challenge. Differential cell numbers and histamine concentration were determined in the BAL fluids of both groups. The ACh PC of control dogs did not change with the vehicle inoculation. However, that of infected dogs decreased two to five times as much as their initial value with viral infection. Histologic studies revealed diffuse epithelial damage in the central airways of infected dogs, but infiltrated cell counts within the airway tissue of both groups were not significantly different. From BAL analysis, mast cell number and the histamine concentration of infected dogs increased significantly compared with those of control dogs (3.1 +/- 0.4 x 10(5) versus 0.9 +/- 0.3 x 10(5) cells/ml and 7.3 +/- 1.7 versus 1.9 +/- 0.5 ng/ml, respectively). Luminal mast cell number and epithelial damage score in each dog was correlated with the increase in airway responsiveness. These findings indicate that airway inflammation in virus-induced hyperreactive dogs is characterized by epithelial damage and luminal increase in mast cells and related mediators, and these changes may be related to the appearance of virus-induced airway hyperreactivity.

Direct write-out of particle size distribution of inhaled aerosol deposition using a laser scattering method

We developed a device to measure inhaled aerosol deposition in the lung from the difference in particle size distribution of the aerosol during inspiration and expiration. To measure quantity and size distribution of nebulized aerosol particles directly at the subject's mouth we used a He-Ne gas laser scattering technique. To test the reliability of the instrument, we measured particle size distributions of saline aerosols generated by four kinds of nebulizer and compared the results with those from a Malvern 2600D particle sizer as a standard of comparison. Measured mass median diameters (MMDs) were almost identical by both methods. Aerosol deposition in five normal subjects showed that the deposition fraction of the particles increased the larger the particle sizes inhaled. The data suggest that the newly developed aerosol spectrometer can directly analyze aerosol particle size distribution at the mouth during tidal breathing, and that the instrument is useful for quantitative analysis of aerosol inhaled and of inhaled aerosol deposition.

Neurokinin A-induced bronchial hyperresponsiveness to methacholine in Japanese monkeys

The present study was designed to investigate whether neurokinin A (NKA) and substance P (SP) increase bronchial responsiveness to methacholine (MCh). Before and 1, 2, 3 and 4 weeks after three Japanese monkeys had inhaled 10(-8) M NKA and 10(-8) M SP for 2 min, bronchial responsiveness to inhaled MCh was evaluated. Pulmonary flow resistance (R1) and dynamic lung compliance (Cdyn) were used as pulmonary function tests. Dose-response curves of R1 to inhaled MCh were shifted to the left 1 to 4 weeks after NKA treatment, compared with that obtained before treatment. However, SP treatment did not change the R1 dose-response curve. Thus, bronchial responsiveness to MCh was increased by inhalation of 10(-8) M NKA in Japanese monkeys.

Inhibitory actions of procaterol, a beta-2 stimulant, on substance P-induced cough in normal subjects during upper respiratory tract infection

We studied substance P (SP)-induced cough in normal subjects without and with colds, and the effects of orally administered procaterol on SP-induced cough in normal subjects with colds. SP aerosols caused cough at a concentration of approximately 10(-15) M in subjects with colds whereas it did not cause cough at a concentration of up to 10(-5) M in subjects without colds. Procaterol (50 micrograms) completely inhibited SP-induced cough in normal subjects with colds. These results suggest that cough response to SP remarkably increases during colds and that beta-2 stimulant may be a useful tool for treatment of cough during colds in normal subjects.

Sensory receptors and reflex pathways of nonadrenergic inhibitory nervous system in feline airways

The sensory receptors and reflex pathways of the nonadrenergic inhibitory nervous system (NAINS) were examined, using separately ventilated left and right lungs in cats. During bronchoconstriction induced by 5-hydroxytryptamine (5-HT) (50 to 250 micrograms/kg/min, i.v.) infusion after atropine (3 mg/kg, i.v.) and propranolol (2 mg/kg, i.v.), one lung was challenged with (1) citric acid aerosol or (2) capsaicin aerosol or (3) lung volume change (lung inflation). Citric acid or capsaicin inhalation to one lung produced significant bronchodilatation in not only the stimulated lung (SL) but also in the opposite lung (OL). The 5-HT-induced change in pulmonary resistance (RL) was reduced 66.5 +/- 3.3% (mean +/- 1 SE) (SL) and 53.0 +/- 8.1% (OL) by citric acid (20%) and 40.5 +/- 8.9% (SL) and 44.0 +/- 9.9% (OL) by capsaicin (0.1%) inhalation, respectively. These bronchodilatations were abolished by bilateral vagotomy. Inflation of one side of the lung did not reduce the 5-HT-induced change in RL in the OL. These findings indicate that (1) C-fiber and irritant receptors are the possible sensory receptors of the NAINS reflex pathway, and (2) afferent nerve stimulation of NAINS in one lung can produce reflex bronchodilatation in both lungs.