H. Aizawa

A possible role of airway epithelium in modulating hyperresponsiveness

1 In order to examine the role of airway epithelium in the responsiveness of smooth muscle in man, we measured the contractile responses to acetylcholine (ACh), histamine, and prostaglandin F2α (PGF2α) and the relaxation response to isoprenaline (Isop), in 48 bronchi obtained from 10 patients who received surgery. Responses were measured in the presence and absence of the epithelium. 2 Removal of epithelium (by rubbing the mucosa gently with forceps) significantly increased the contractile responses evoked by ACh, histamine and PGF2α. 3 In contrast, removal of epithelium did not alter the relaxation response to Isop. 4 To clarify the mechanism underlying this epithelial inhibitory effect on smooth muscle contraction, we measured the contractile responses of dog trachea with the epithelium removed to increasing concentrations of ACh. After measuring the control response, we added about 0.1 g of the chopped epithelium in the organ chamber, and measured the response again. 5 After adding airway epithelium and incubating with tracheal strips, the contractile response of tracheal strips decreased significantly as compared to the control response. 6 These results show that airway epithelium possesses the ability to decrease the smooth muscle contraction to ACh, histamine and PGF2α in man and dogs. 7 The mechanism of this inhibitory effect of the airway epithelium is not explained by a change in mechanical property of the airway nor the change in diffusion of these drugs to the smooth muscle across the epithelium. Thus, these results suggest that airway epithelium may have an important role in modulating smooth muscle tone, possibly by inactivation of these mediators, or by releasing an epithelium‐derived relaxing factor.

Eosinophilic airway inflammation induced by repeated exposure to cigarette smoke

Acute exposure to cigarette smoke causes airway hyperresponsiveness (AHR) in guinea-pigs, which resolves within a few hours. Repeated exposure may have a different effect on the airways. To address this question, guinea-pigs were repeatedly exposed to cigarette smoke (six cigarettes for 1 h x day(-1)) for 14 consecutive days. Airway responsiveness to inhaled histamine and differential cell counts in bronchoalveolar lavage fluid (BALF) were evaluated 1 day after the last exposure. Significant neutrophilia in BALF was observed after 3 days of smoke exposure. Significant eosinophilia in BALF and AHR were observed after 14 days of smoke exposure, but not after 3 or 7 days of smoke exposure. These changes persisted until 3 days after the last exposure and resolved 7 days afterwards. Histologically, the recruited eosinophils were observed predominantly in the airways, but not in the alveoli. Treatment with E-6123, a specific platelet-activating factor receptor antagonist (1 mg x kg(-1) x day(-1) p.o. during smoke exposure) significantly inhibited the eosinophil influx and AHR. Repeated exposure to cigarette smoke may induce prolonged airway inflammation and airway hyperresponsiveness in guinea-pigs. Platelet-activating factor or platelet-activating factor-like lipids may play a key role in airway hyperresponsiveness, presumably by the induction of eosinophilic airway inflammation.

Effect of inhaled glucocorticoid on the cellular profile and cytokine levels in induced sputum from asthmatic patients

Abstract. Cytokines are considered to play a role in the airway inflammation of bronchial asthma. We examined the cellular profile and cytokine levels in induced sputum samples obtained before and after treatment with beclomethasone dipropionate (BDP, 800 μg/day, for 4 weeks) in 12 mild to moderate asthmatic subjects who had not previously received inhaled glucocorticosteroids. Sputum was induced with a 20-min inhalation of 3% saline by an ultrasonic nebulizer. The freshly expectorated sputum separated from the saliva was analyzed for cell counts, for the concentration of interleukin-8 (IL-8), and for the concentration of granulocyte-macrophage colony-stimulating factor (GM-CSF). The mean percentage of eosinophils in the sputum samples decreased significantly after BDP treatment, but no significant change in the percentage of neutrophils was observed. The mean IL-8 and GM-CSF levels also decreased significantly after treatment. The BDP treatment was associated with an increase in the mean peak expiratory flow (PEF) and with a decrease in the diurnal variation of PEF. These results suggest that inhaled steroids improve airway inflammation and lung function in asthmatics, presumably in part by inhibiting the synthesis of inflammatory cytokines such as IL-8 and GM-CSF.

The spontaneous electrical and mechanical activity of human bronchial smooth muscle: its modulation by drugs.

1 Tissue taken at operation was used to study the electrical and mechanical properties of human bronchial smooth muscle with intracellular microelectrodes and isometric recording of tension changes. 2 Over 90% of the muscle strips exhibited spontaneous tone and 70% produced spontaneous phasic contractions. The resting membrane potential of the smooth muscle cells ranged between −40 to −50 mV with a mean value of −44.9 ± 5.2 mV (n = 92 ± s.d.). Spontaneous oscillations of the membrane potential (slow waves) were observed in 90% of the cells examined. 3 The electrical slow waves, phasic contractions and spontaneous tone were greatly reduced by FPL 55712 (10−6−10−5m). Indomethacin (1–5 × 10−5m), atropine (10−6m) or a 5‐lipoxygenase inhibitor, AA 861 (5 × 10−6m) each reduced spontaneous mechanical tone. Indomethacin and atropine each caused minor reduction in the amplitude of electrical slow waves. 4 Leukotriene C4 (10−8m), physostigmine (10−6m) and K+‐rich physiological salt‐solution (containing atropine 10−6m) each caused tone development in tissue treated with AA 861 (5 × 10−6m). In the case of leukotriene C4 and physostigmine, phasic contractions were superimposed on the developed tone. 5 Electrical field stimulation evoked an excitatory junction potential (e.j.p.) followed by a small group of slow waves. Repetitive field stimulation (2–20 stimuli at 20 Hz) markedly enhanced the amplitude of oscillatory slow waves. FPL 55712 (1.9 × 10−6m) abolished the oscillatory slow waves following the e.j.p., and physostigmine (10−6m) enhanced the amplitude of the e.j.p. and slow waves. 6 These results indicate that, under in vitro conditions, the electrical activity of human bronchial smooth muscle comprises slow wave discharge which may be related to the spontaneous contractions and generation of basal tone.

Pre-junctional inhibitory action of prostaglandin E2 on excitatory neuro-effector transmission in the human bronchus

The effects of prostaglandin E2 (PGE2) and indomethacin on excitatory neuro-effector transmission in the human bronchus were investigated by tension recording and microelectrode methods. PGE2 (10(-10)-10(-9)M) suppressed the amplitude of twitch contractions and excitatory junction potentials (e.j.ps) evoked by field stimulation at a steady level of basal tension obtained by the combined application of indomethacin (10(-5) M) and FPL55712 (10(-6) M). In doses over 10(-8)M, PGE2 reduced the muscle tone and dose-dependently suppressed the amplitude of twitch contractions. Indomethacin (10(-5) or 5 x 10(-5) M) reduced the muscle tone and enhanced the amplitude of twitch contractions and e.j.ps evoked by field stimulation in the presence of FPL55712. PGE2 (10(-9) M) had no effect on the post-junctional response of smooth muscle cells to exogenously applied acetylcholine (ACh) (4 x 10(-7) M). However, indomethacin (10(-5) M) significantly enhanced the ACh-induced contraction of the human bronchus. These results indicate that PGE2 in low concentrations has a pre-junctional action to inhibit excitatory neuro-effector transmission in addition to a post-junctional action, presumably by suppressing transmitter release from the vagus nerve terminals in the human bronchial tissues.

A possible role of a nonadrenergic inhibitory nervous system in airway hyperreactivity

To investigate a possible role of a nonadrenergic inhibitory nervous system in airway hyperreactivity, we measured changes in RL and CL caused by electrical stimulation of cervical vagus nerve during the infusion of 5-HT, after treatment with atropine and propranolol in 18 cats. RL decreased to 56 +/- 3% (mean +/- SE) and CL increased to 186 +/- 13% of the prestimulated values, respectively, after stimulation. Hexamethonium diminished these responses significantly. Airway reactivity to 5-HT was reduced by continuous electrical stimulation of cervical vagus nerve in cats pretreated with atropine and propranolol. Hexamethonium potentiated airway reactivity to 5-HT. These results suggest that a nonadrenergic inhibitory nervous system could play an important role in the control of the bronchomotor tone and contribute to airway hyperreactivity.

Once–Daily Theophylline Reduces Serum Eosinophil Cationic Protein and Eosinophil Levels in Induced Sputum of Asthmatics

Background: Because eosinophilic airway inflammation is a characteristic feature of bronchial asthma, the treatment of airway inflammation is important in the management of asthma. Theophylline has been reported to reduce airway inflammation, in addition to its well–known bronchodilating effect. Objective: In order to evaluate the effects of theophylline on airway inflammation, we investigated 48 subjects with mild and moderate asthma. Methods: The patients were randomly divided into two groups, with or without theophylline treatment (control n = 24; theophylline, n = 24). We examined the level of serum eosinophil cationic protein (ECP), induced sputum samples, and peak expiratory flow (PEF) and obtained spirograms before and after 4 weeks of treatment with once–daily theophylline (200–600 mg/day) of subjects with mild or moderate asthma. Results: Theophylline significantly increased morning and evening PEF and significantly decreased the diurnal variation of PEF. After treatment with theophylline, both serum ECP and the percentage of eosinophils in induced sputum were significantly decreased. In contrast, peripheral blood eosinophil count was unchanged after treatment with theophylline. Conclusions: These findings suggest that theophylline reduces airway inflammation and the severity of asthma, presumably via suppression of both eosinophil activity and subsequent eosinophil infiltration of the airways.

Effects of thromboxane A2 antagonist on airway hyperresponsiveness, exhaled nitric oxide, and induced sputum eosinophils in asthmatics

We examined effects of a thromboxane A2 (TXA2) antagonist seratrodast on airway hyperresponsiveness, exhaled nitric oxide (NO), and eosinophils in induced sputum in 14 asthmatics. Subjects were administered 80 mg of seratrodast once a day for 4 weeks. Respiratory conductance (Grs) was measured by the forced oscillation method and airway responsiveness was evaluated as the inhaled dose of methacholine, which induced 35% decrease in Grs. Subjects breathed into a Teflon bag, and NO concentration in the bag was measured by a chemiluminescence analyzer. Induced sputum comprised the entire expectorate produced during a 20 min inhalation of 3% saline, and was analyzed for total and differential cell counts. Airway hyperresponsiveness was significantly decreased by seratrodast. By contrast, no differences in either exhaled NO or percentage of eosinophils in sputum were observed before or after seratrodast. We conclude that seratrodast may attenuate airway hyperresponsiveness, presumably by antagonizing TXA2 released from the inflamed airways.

Effect of Endogenous Tachykinins on Neuro-Effector Transmission of Vagal Nerve in Guinea-Pig Tracheal Tissue

To elucidate the effect of endogenous tachykinins on neuro-effector transmission of vagal nerves, we performed in vitro experiments using guinea-pig tracheal smooth muscle. The subthreshold dose (the highest dose which did not induce any smooth muscle contraction) of capsaicin (10(-8) to 10(-7) M) increased the amplitudes of contractions evoked by electrical field stimulation (EFS) significantly, but not those by acetylcholine (ACh). The inhibitor of neutral endopeptidase, phosphoramidon (10(-7) to 10(-6) M), increased the contractions evoked by EFS significantly. The inhibitor of cholinesterase, physostigmine (10(-6) to 10(-5) M), induced smooth muscle contractions, but such contractions were inhibited by atropine, suggesting the spontaneous release of ACh from the vagal nerve terminals. The subthreshold dose of substance P or capsaicin increased the contractions evoked by physostigmine. These results indicated that endogenous tachykinins increase the spontaneous ACh release as well as the ACh release in response to vagal stimulation from the nerve terminals. Furthermore, it is suggested that the excitatory effects of the tachykinins on the vagal neuro-effector transmission may be modulated by neutral endopeptidase in the guinea pig.

Pituitary adenylate cyclase activating peptide regulates neurally mediated airway responses

To clarify the protective effects of pituitary adenylate cyclase activating peptide (PACAP) on airway narrowing, we examined the effects of PACAP on smooth muscle contraction and plasma extravasation in guinea-pig airways. Smooth muscle contraction evoked by electrical field stimulation (EFS) or exogenously applied acetylcholine (ACh) or substance P (SP) was measured before and after PACAP in vitro. The effect of PACAP on airway plasma extravasation was also measured in vivo. In trachea, PACAP (10(-9) - 10(-7) M) significantly suppressed smooth muscle contraction evoked by EFS without affecting ACh sensitivity, suggesting that PACAP inhibits cholinergic neuroeffector transmission. In the main bronchi, PACAP (10(-9) - 10(-8) M) significantly suppressed the contraction evoked by EFS without affecting SP sensitivity in the presence of atropine, suggesting that PACAP inhibits SP release from excitatory nonadrenergic noncholinergic (eNANC) nerves. In animals treated with atropine and propranolol, PACAP attenuated the increase in plasma extravasation induced by electrical vagus stimulation or by SP. These results suggest that pituitary adenylate cyclase activating peptide may play a role in modulation of airway responses through inhibition of cholinergic and noncholinergic mechanisms.