Role of tachykinins in airway narrowing induced by cigarette smoke in guinea pigs

To investigate the mechanism of the airway narrowing induced by cigarette smoke, anaesthetized guinea pigs were exposed to 200 puffs of smoke for 10 min. Airway narrowing was assessed by monitoring the total pulmonary resistance (R_L). Plasma extravasation was determined by measuring the amount of Evans blue dye extravasated into the trachea and main bronchi. Exposure to cigarette smoke caused a marked airway narrowing and plasma extravasation. Pretreatment with the dual NK₁ and NK₂ receptor antagonist, FK224, abolished such airway narrowing and significantly inhibited the extravasation. While the NK₁ receptor antagonist, FK888, inhibited the extravasation, it had no effect on airway narrowing. Atropine partially inhibited airway narrowing without affecting extravasation. Results suggest that the airway narrowing induced by cigarette smoke is caused by tachykinins, and that a cholinergic pathway is involved. Thickening of the airway walls induced by NK₁ receptor-mediated extravasation may not be involved in such airway narrowing.     

Involvement of hydroxyl radicals in neurogenic airway plasma exudation and bronchoconstriction in guinea-pigs in vivo.

1. Cigarette smoke induces plasma exudation in the airways of rodents by activation of capsaicin-sensitive 'sensory-efferent' nerves. The response is mediated predominantly by substance P (SP) and the magnitude of exudation is regulated by neutral endopeptidase (NEP). The component(s) of the smoke responsible for the activation of the nerves may be reactive oxygen radicals. We investigated the effect of the hydroxyl radical scavenger dimethylthiourea (DMTU), a regulator of superoxide anion, superoxide dismutase (SOD), and a regulator of hydrogen peroxide, catalase, on plasma exudation (measured using Evans blue dye) induced by cigarette smoke in guinea-pig main bronchi in vivo. The effect of DMTU on plasma exudation and non-cholinergic bronchoconstriction (measured as pulmonary insufflation pressure, PIP) induced by electrical stimulation of the vagus nerves was also assessed. Interaction between hydroxyl radicals and NEP was assessed with the NEP inhibitor phosphoramidon. 2. In each of the experiments, cigarette smoke increased plasma exudation by approximately 200% above air-exposed controls. Acute administration of DMTU (1.5 g kg-1, i.v. for 20 min) significantly reduced cigarette smoke-induced plasma exudation by 69%. In contrast, neither SOD (240,000 u kg-1, i.v.) nor catalase (400,000 u kg-1, i.v.) significantly affected the exudative response. 3. Chronic pretreatment with DMTU (1.25 g kg-1 over 4 days) significantly reduced bronchial plasma exudation induced by cigarette smoke by 72%. Phosphoramidon (1.5 mg kg-1, i.v.) completely reversed the inhibition by DMTU of cigarette smoke-induced plasma exudation. 4. Vagal stimulation increased plasma exudation by approximately 200% and PIP by approximately 250%. Acute treatment with DMTU had no significant inhibitory effect on these responses, whereas chronic pretreatment inhibited them by approximately 80%. Phosphoramidon reversed the inhibition by chronic DMTU. 5. SP (1 nmol kg-1) increased plasma exudation by approximately 250%, a response which was not inhibited by either acute or chronic DMTU. 6. We conclude that hydroxyl radicals, rather than superoxide anion or hydrogen peroxide, are involved in the induction of neurogenic plasma exudation and bronchoconstriction induced by cigarette smoke or by electrical stimulation of the vagus nerves. These radicals also affect the activity of NEP. Acute DMTU may affect directly the neural actions of hydroxyl radicals contained in the cigarette smoke. Chronic pretreatment with DMTU may inhibit the neurogenic airway responses by effects on tachykinin biosynthesis and/or axonal transport.     

Alleviation of wood smoke-induced lung injury by tachykinin receptor antagonist and hydroxyl radical scavenger in guinea pigs

We recently reported that wood smoke inhalation initially (within 5 min) causes airway injury and subsequently produces both airway and parenchymal injury after a delay (within 2 h). In this study, we investigated the mediator mechanisms of this delayed smoke-induced lung injury in 126 anesthetized and artificially ventilated guinea pigs who received challenges of either air or 40 tidal breaths of wood smoke. Two hours after inhalation, wood smoke produced various injurious responses, including increases in alveolar-capillary permeability, microvascular permeabilities, and histological injury scores, in airway and parenchymal tissues. Pre-treatment given before smoke challenge with CP-96,345 [a tachykinin NK1 receptor antagonist; (2S,3S)-cis-2-(diphenylmethyl)-N-((2-methoxyphenyl)-methyl)-1-aza bicyclo(2.2.2.)-octan-3-amine], dimethylthiourea (a hydroxyl radical scavenger), or a combination of these two drugs largely alleviated both the airway and parenchymal responses, whereas pre-treatment with SR-48,968 [a tachykinin NK2 receptor antagonist; (S)-N-methyl-N(4-(4-acetylamino-4-phenylpiperidino)-2-(3,4-dichlorophenyl)-butyl)benzamide] or a combination of CP-96,344 and SR-48,965 (inactive enantiomers) failed to do so. Post-treatment given at 5 min after smoke challenge with CP-96,345 or dimethylthiourea significantly alleviated the parenchymal responses, while having no effect on the airway responses. Pre-treatment with dimethylthiourea prevented the smoke-induced reduction in airway neutral endopeptidase activity (an enzyme for tachykinin degradation). We concluded that (1) tachykinins and hydroxyl radical play important roles in producing smoke-induced delayed lung injury in guinea pigs, and both may be involved in the spread of injury from the airways to the pulmonary parenchyma, and (2) the contribution of tachykinins is mediated via the activation of tachykinin NK1 receptors, and is associated with the hydroxyl radical-induced inactivation of airway neutral endopeptidase.     

Tryptase-induced airway microvascular leakage in guinea pigs: involvement of tachykinins and leukotrienes.

Tryptase, a serine protease synthesized by and stored in mast cells, is implicated as an important mediator in the pathogenesis of airway inflammation. In this study, tryptase was evaluated for its ability to induce microvascular leakage into the airways of guinea pigs. Dose- and time-dependent increases in airway microvascular leakage were produced by intratracheal tryptase (0.3-3 microg). Intratracheal tryptase (3-30 microg) had no effect on airway tone as measured by pulmonary insufflation pressure. Tryptase-induced airway microvascular leakage was partially blocked by the tachykinin NK1 receptor antagonist CP 99994 [(+)-(2S,3S)-3-(2-methoxybenzylamino)-2-phenylpiperidine] and an inhibitor of leukotriene formation SCH 37224 (1-(1,2-dihydro-4-hydroxy-2-oxo-1-phenyl-1,8-naphthyridin-2-yl)pyrrolidinium, hydroxide inner salt). Neither CP 99994 nor SCH 37224 inhibited tryptase proteolytic activity in-vitro. Pretreatment of guinea pigs with histamine H1 receptor antagonists or a tachykinin NK2 receptor antagonist had no affect on the airway microvascular leakage induced by tryptase. It is speculated that tryptase may be important in the pathogenesis of airway inflammation, particularly in disorders that involve increased airway microvascular leakage such as asthma.     

Lack of a role for bradykinin in inhaled sodium metabisulphite-induced airway microvascular leakage in guinea pigs

We have investigated the role of bradykinin in airway microvascular leakage and bronchoconstriction induced by inhaled sodium metabisulphite (MBS) in guinea pigs. A selective bradykinin B2 receptor antagonist, HOE 140 (D-Arg[Hyp³, Thi⁵, D-Tic⁷, Oic⁸]-bradykinin), was used because this drug has been shown to abolish the airway responses induced by bradykinin. Lung resistance (R_L) was measured for 6 min after challenge with MBS, followed by measurement of extravasation of Evans Blue dye into airway tissues, used as an index of plasma exudation. Aerosolized MBS (40 and 80 mmol/L, 30 breaths) induced a significant increase in R_L and leakage of dye in the trachea, main bronchi and intrapulmonary airways, whereas 20 mmol/L MBS caused these responses except for the dye leakage in the trachea and main bronchi. HOE 140 (100 nmol/kg iv) had no effect against these airway responses. We conclude that bradykinin-mediated mechanisms do not play a significant role in the acute airway effects induced by inhaled MBS.     

Effects of inhaled aminophylline on airway constriction and inflammation in ovalbumin-sensitized guinea pigs

Abstract

Background: The systemic administration of theophylline is useful for asthma treatment. However its narrow therapeutic range makes it difficult to use. Little is known about its potential in inhalation therapy, particularly repeated inhalation.

Objective: The purpose of this study is to investigate the therapeutic usefulness of inhaled aminophylline in an asthma model.

Methods: The effects of pretreatment with inhaled aminophylline (25?mg/mL for 30?min/dose) on airway response and inflammation after an ovalbumin (OVA) challenge and airway hypersensitivity to acetylcholine (Ach) were evaluated using guinea pigs sensitized with OVA.

Results: Aminophylline relaxed the ACh-induced contraction of tracheal smooth muscle in vitro in a concentration-dependent manner. Pretreatment with single-dose aminophylline inhalation suppressed OVA-induced airway constriction to the same extent as the intraperitoneal pretreatment with high-dose aminophylline (10–20?mg/kg). However, pretreatment with single-dose aminophylline inhalation did not suppress eosinophil infiltration into airways (neither bronchoalveolar lavage [BAL] fluid nor lung tissue) and did not suppress airway hyperreactivity to ACh, 24?h after OVA challenge. Repeated inhalation of aminophylline (twice daily for 7 days) suppressed the infiltration of eosinophils and suppressed airway hypersensitivity to ACh. In addition, high concentrations of aminophylline inhibited production of oxygen radicals by BAL cells.

Conclusion: Single-dose inhalation treatment with aminophylline has transient but relatively strong bronchodilating effects due to delivery of high doses into local airways. Repeated inhalation treatment suppressed airway inflammation and hypersensitivity induced by allergens. Therefore, inhaled aminophylline may be useful for asthma treatment.     

Evaluation of the pulmonary effects of wood smoke in guinea pigs by repeated CO2 challenges

Male, English smooth haired guinea pigs were exposed to thermal decomposition products, i.e., smoke, generated by heating Douglas fir in an open system. Various amounts of Douglas fir were placed in a furnace, at room temperature, and heated at a rate of 11 degrees C/min until completely decomposed. Major decomposition occurred between 160 and 490 degrees C, and the animals were exposed during this time for a period of 30 min. Immediately before exposure and at various times after exposure, each animal was evaluated by whole-body plethysmography to measure tidal volume and respiratory frequency during air breathing as well as during challenge with 10% CO2. Exposure to smoke from Douglas fir resulted in a diminished ventilatory response to 10% CO2. Comparing the effect of wood smoke to the effect of smoke from polyvinylchloride from previous experiments wood smoke was found to be 10 times less potent than smoke from polyvinylchloride and animals recovered much more rapidly than with smoke from polyvinylchloride.     

血小板活化因子诱发豚鼠气道高反应性及阿魏酸钠对其的影响

正常豚鼠吸入血小板活化因子（ＰＡＦ）２４ｈ后气道对组胺引起的收缩反应性明显增高，支气管肺泡灌洗液中的嗜酸性白细胞计数明显增多。用兔抗豚鼠血小板血清选择性耗竭血小板，向气道内注入肝素，或用阿魏酸钠２５，５０和１００ｍｇ·ｋｇ－１，ｉｖ均可不同程度抑制ＰＡＦ诱发的气道高反应性和嗜酸性白细胞向肺内募集。     

Catecholamines in hyperpnoea‐induced airway constriction of guinea pigs

1 We found previously that propranolol augments hyperpnoea‐induced bronchoconstriction (HIB). This study was performed to investigate the underlying mechanism of this aug‐ menting action of propranolol. 2 In the first series, 45 young Hartley guinea‐pigs were divided into five groups: control; propranolol; adrenalectomy; metoprolol and reserpine. Each animal underwent three periods: baseline, hyperpnoea, and recovery. For each animal 1 ml of arterial blood was sampled during the baseline and recovery periods. 3 Treatments of propranolol, metoprolol, and reserpine caused significant decreases in both dynamic respiratory compliance (C_rs) and forced expiratory volume in 0.1 s (FEV_0.1) during the baseline period. Hyperpnoea caused slight but not significant decreases in C_rs, FEV_0.1, and maximal expiratory flow at 50% total lung capacity (TLC) (V˙_max50) during the recovery period in the control group. Propranolol, but not other treatments, significantly augmented these decreases (indicating HIB). Plasma noradrenaline and adrenaline levels in the reserpine group were not detectable. The above treatments or hyperpnoea did not induce any significant effect on the plasma noradrenaline level. Plasma adrenaline level of the control group was higher than that of either adrenalectomy or reserpine group during the baseline and the recovery periods. 4 In the second series, we avoided repeated blood samplings. Forty‐eight animals were evenly divided into two groups: control and propranolol. Each group was again evenly divided into three subgroups: baseline; hyperpnoea, and recovery. Five minutes into the recovery period, we demonstrated HIB in the control group. In terms of V˙_max50, this HIB was significantly augmented by propranolol. Plasma noradrenaline and adrenaline levels, however, were not significantly altered by either hyperpnoea or propranolol. 5 Taken together, these data suggest that propranolol‐augmented HIB has no direct relationship with decreased catecholamine activity.     

Effects of inhaled low molecular weight heparin on airway allergic inflammation in aerosol-ovalbumin-sensitized guinea pigs

Low molecular weigh, heparin (LMWH) possesses multiple nonanticoagulant properties. In the present study, we observed its anti-airway allergic inflammatory effects by bronchoalveolar lavage in guinea pigs. Guinea pigs were sensitized by repeatedly inhaling aerosolized ovalbumin. LMWH (400 u/l, 800 u/l), dexamethasone (1.2 mg/1) or vehicle (normal saline) was inhaled for 7 days. Then the animals were sacrificed under anesthesia and then lavaged with ice-cold Hank's buffer immediately; bronchoalveolar lavage fluid (BALF) was prepared 24 h after the animals were challenged by antigen exposure. The effects of LMWH on total cell counts, absolute eosinophil counts and cell catalogues in BALF were studied; effects on the activity of eosinophil peroxidase (EPO) and the contents of histamine and eosinophil cationic protein (ECP) in BALF supernatant were detected. Our results showed that compared with the vehicle group, LMWH at 400 u/l and 800 u/1 could significantly reduce total cell counts, absolute eosinophil counts and percentage of eosinophils in BALF (P<0.05 and P<0.01, respectively); LMWH at 800 u/l markedly inhibited the activity of EPO in BALF supernatant (P<0.05); LMWH at 400 u/l and 800 u/l remarkably reduced the content of histamine in BALF supernatant (P<0.05 and P<0.01, respectively), LMWH at 800 u/l decreased the content of ECP (P<0.05) significantly. It suggested that LMWH exerted anti-airway allergic inflammatory action by inhibiting infiltration of inflammatory cells and reducing release of inflammatory mediators, as well as antagonizing their activities, and that LMWH could be developed as a potential anti-bronchial asthmatic drug.     

Bronchopulmonary inflammation and airway smooth muscle hyperresponsiveness induced by nitrogen dioxide in guinea pigs.

We investigated whether acute exposure to nitrogen dioxide (NO2) causes major inflammatory responses (inflammatory cell recruitment, oedema and smooth muscle hyperresponsiveness) in guinea pig airways. Anaesthetised guinea pigs were exposed to 18 ppm NO2 or air for 4 h through a tracheal cannula. Bronchoalveolar lavage was performed and airway microvascular permeability and in vitro bronchial smooth muscle responsiveness were measured. Exposure to NO2 induced a significant increase in eosinophils and neutrophils in bronchoalveolar lavage fluid, microvascular leakage in the trachea and main bronchi (but not in peripheral airways), and a significant in vitro hyperresponsiveness to acetylcholine, electrical field stimulation, and neurokinin A, but not to histamine. Thus, this study shows that in vivo exposure to high concentrations of NO2 induces major inflammatory responses in guinea pig airways that mimic acute bronchitis induced by exposure to irritant gases in man.     

Acute hypersensitivity to aerosolized histamine induced by aerosolized ovalbumin in guinea pigs.

Acute airway hyperresponsiveness can be induced after exposure to aerosolized ovalbumin in sensitized guinea pigs. The purpose of the present studies was to determine if "pro-inflammatory agents" would potentiate and prolong antigen-induced pulmonary hyperresponsiveness to histamine in guinea pigs. Guinea pigs were sensitized to aerosolized ovalbumin by exposing them to a 3 min aerosol, generated ultrasonically from a 10% ovalbumin solution on day 0 and day 7. On day 13 the guinea pigs were exposed to a 3 min aerosol of deionized water or a pro-inflammatory agent (1 microgram/ml PAF, 1 mg/ml LPS, or 4% B. pertussis vaccine). Twenty-four hours later, on day 14, the conscious guinea pigs were challenged with a 3 min aerosolized ovalbumin exposure (under isoproterenol cover) and the individual guinea pig responsiveness to aerosolized histamine was determined 2 and 24 h later in an anesthetized modified Konzett-Rossler preparation. Under these experimental conditions, ovalbumin challenge to sensitized guinea pigs produced only an acute hyperresponsiveness (about a 3-10-fold shift) to aerosolized histamine, which lasted less than 24 h. The pro-inflammatory agents neither potentiated nor prolonged the duration of the hyperresponsiveness.     

Effect of dimethylthiourea, a hydroxyl radical scavenger, on cigarette smoke-induced bronchoconstriction in guinea pigs

Cigarette smoke exposure causes bronchoconstriction in guinea pigs by stimulating cholinergic and excitatory nonadrenergic, noncholinergic (eNANC)-nerves in vagus system. The aim of this study is to elucidate the role of hydroxyl radical (OH(-)), contained in cigarette smoke, in bronchoconstriction. Anaesthetized animals were exposed to 80 puffs of smoke for 4 min. Pretreatment with dimethylthiourea, a OH(-) scavenger, significantly inhibited cigarette smoke-induced bronchoconstriction. To investigate its site of action, effects of dimethylthiourea were examined on vagally mediated bronchcoconstriction by electrical stimulation and on the bronchoconstriction by intravenous acetylcholine and neurokinin-A. Dimethylthiourea did not inhibit bronchoconstriction evoked by vagal stimulation, acetylcholine or neurokinin-A. These results suggest that dimethylthiourea inhibits cigarette smoke-induced bronchoconstriction by scavenging the smoke-derived OH(-), but not by inhibiting airway nerve function.     

Naringin attenuates enhanced cough, airway hyperresponsiveness and airway inflammation in a guinea pig model of chronic bronchitis induced by cigarette smoke

Naringin is a flavanone with various bioactivities including expectorant effect, antitussive effect and inhibitory effects on asthma and acute lung injury. In present study we examined the effects of naringin on enhanced cough, airway hyperresponsiveness (AHR) and airway inflammation in chronic cigarette smoke (CS) exposure-induced chronic bronchitis in guinea pigs. To achieve this, guinea pigs were exposed to CS for 8weeks (10cigarettes/day, 6days/week). Oral administration of naringin (9.2, 18.4 and 36.8mg/kg) significantly attenuated the enhanced cough and AHR in smoke-exposed guinea pigs, reduced the concentrations of interleukin-8 (IL-8), leukotriene B4 (LTB4) and tumor necrosis factor-α (TNF-α) in bronchoalveolar lavage fluid (BALF) and decreased the myeloperoxidase (MPO) activity in both BALF and lung tissue, but did not significantly decrease the leukocytes in BALF. Naringin also improved superoxidase dismutase (SOD) activity in lung tissue and increased the content of lipoxin A4 (LXA4) in BALF in this guinea pig model of chronic bronchitis. These results suggested that naringin exhibited antitussive, anti-AHR and anti-inflammation effects on chronic CS exposure-induced chronic bronchitis in guinea pigs, and may possess novel therapeutic potential in the treatment of chronic bronchitis.     

Acute toxic effects of inhaled dichlorvos vapor on respiratory mechanics and blood cholinesterase activity in guinea pigs

Using a modified noninvasive volume-displacement plethysmography system, we investigated the effects of inhaled dichlorvos (2,2-dimethyl-dichlorovinyl phosphate, or DDVP) vapor on the respiratory mechanics and blood cholinesterase activity of guinea pigs. Data revealed significant dose-dependent changes in several pulmonary parameters. Animals exposed to a DDVP concentration of 35 mg/m(3) did not show any significant changes in frequency, tidal volume, or minute ventilation. However, animals exposed to 55 mg/m(3) DDVP showed significantly decreased respiratory frequency and significantly increased tidal volume with no significant changes in minute ventilation. Similarly, animals exposed to 75 mg/m(3) DDVP showed significantly decreased respiratory frequency along with significantly increased tidal volume. The decreased respiratory frequency was large enough in the high exposure group to offset the increased tidal volume. This effect resulted in significantly decreased minute ventilation by the end of exposure, which remained attenuated 10 min after exposure. An analysis of whole-blood cholinesterase activity revealed significantly decreased activity for both acetylcholinesterase (AChE) and butyl-cholinesterase (BChE). Peak inhibition occurred for both enzymes at the end of exposure for all three concentrations and rapidly recovered within several minutes of exposure. Analysis of blood samples using gas chromatography-mass spectroscopy (GC-MS) revealed that minute ventilation may only play a minimal role in the dosimetry of inhaled DDVP vapor.     

Effects of actinomycin D on airway constriction induced by tachykinins and capsaicin in guinea-pigs.

The effects of actinomycin D on airway constriction induced by tachykinins was studied in guinea-pigs in vitro and in vivo. Actinomycin D significantly inhibited the constriction of isolated guinea-pig trachea induced by neurokinin A (NKA) and eledoisin. Conversely, substance P (SP)- and physalaemine-induced constrictions were not affected by actinomycin D. The same selectivity in the inhibitory action of actinomycin D against tachykinins was also observed in in vivo. Actinomycin D given i.v. specifically inhibited the increase in airway resistance induced by NKA. I.v. injection of NKA caused not only airway constriction but also transient systemic hypotension. Interestingly, actinomycin D injected i.v. inhibited only airway constriction and the systemic hypotension induced by NKA was not affected. These results clearly suggest that actinomycin D specifically inhibits NKA-induced airway constriction in guinea-pigs. Actinomycin D also had an inhibitory action on the airway constriction induced by capsaicin. In the case of capsaicin-induced constriction, actinomycin D was more effective on the later phase of constriction than on the acute phase. The airway constriction induced by capsaicin is thought to be mediated by the release of SP and NKA from sensory nerve endings, and the persistent increase in airway resistance induced by capsaicin is thought to be due mainly to NKA.     

Delayed manifestation of ultra violet radiation induced erythema in guinea pigs by sodium pyruvate--a free radical scavenger

Sodium pyruvate, a free radical scavenger was evaluated for anti-inflammatory activity using UV radiation induced dermal erythema on guinea pig and compared with that of standard naproxen. Oral as well as topical pyruvate exhibited significant activity against UV induced dermal erythema model and the activity was comparable to that of naproxen. In the other pharmacodynamic studies, such as the studies on rat blood pressure, isolated guinea pig ileum and rat uterus, it showed no effect on any of these. In conclusion, sodium pyruvate showed a significant protection in the UV induced dermal erythema in guinea pigs. It also showed good absorption in UV-B range and this property can be utilised to develop the sodium pyruvate as a sunscreening agent.     

Effect of NZ-107 on late-phase airway responses and airway hyperreactivity in guinea pigs

The effect of NZ-107 (4-bromo-5-(3-ethoxy-4-methoxybenzylamino)-3(2H)-pyridazinone) on late-phase airway responses and airway hyperreactivity was investigated in the guinea pig. Challenge with inhaled ovalbumin in conscious guinea pigs actively sensitized with inhaled ovalbumin caused triphasic bronchial obstruction, which peaked at 5-30 min, 6-8 h and 24 h. In this model, airway hyperreactivity to acetylcholine was observed 48 h after antigen challenge. Orally administered NZ-107, given 2 h before ovalbumin challenge significantly inhibited airway responses at 5-30 min (10 mg/kg), 6-8 h (30 mg/kg), 24 h (10 mg/kg) and airway hyperreactivity (30 mg/kg). When NZ-107 (10 mg/kg) was orally administered to the guinea pigs 3 h after ovalbumin challenge, it also inhibited airway responses at 6-8 h and 24 h and airway hyperreactivity. In anaesthetized guinea pigs, intravenous administration of NZ-107 (0.03-1.0 mg/kg) inhibited platelet-activating factor (PAF)- and propranolol-induced airway hyperreactivity to histamine. These results suggest that NZ-107 may be a useful drug for the treatment of bronchial asthma by reducing late-phase airway responses and airway hyperreactivity.     

Prevention of ozone-induced airway hyperresponsiveness and epithelial injury by phosphodiesterase inhibitors in guinea pigs

We investigated the effects of phosphodiesterase (PDE) inhibitors on ozone-induced airway hyperresponsiveness (AHR) in guinea pigs. Theophylline (10-100 mg/kg), rolipram (1-100 mg/kg) and T-440 (1-100 mg/kg) were orally administered 30 min before ozone exposure (3 ppm, for 30 min). Ozone exposure caused an increase in airway responsiveness to methacholine aerosol, and log PC(10) (log-transformed methacholine concentration causing a 10 cm H(2)O increase in pulmonary inflation pressure) in the control and ozone-exposed group was 4.43±0.05 (n=6) and 3.26±0.15 (n=12), respectively. Theophylline at 100 mg/kg, 10 mg/kg rolipram and 10 mg/kg T-440 significantly inhibited AHR with log PC(10) value of 4.73±0.16 (n=7), 3.74±0.11 (n=7), 3.82±0.15 (n=6), respectively. On histological examination, epithelial damage in the trachea and peripheral airways was recognized after ozone exposure. At 100 mg/kg, rolipram, T-440 and theophylline caused complete inhibition of AHR, and prevented epithelial damage of the trachea and peripheral airways. These results indicate that PDE inhibitors prevent not only ozone-induced AHR but also airway epithelial injury by ozone.