Time course of bronchoconstriction induced by dry gas hyperpnea in guinea pigs

We examined the effects of hyperpnea duration and abrupt changes in inspired gas heat and water content on the magnitude and time course of hyperpnea-induced bronchoconstriction (HIB) in anesthetized mechanically ventilated male Hartley guinea pigs. In 12 animals subjected to 5, 10, and 15 min (random order) of dry gas isocapnic hyperpnea [tidal volume (VT) 4-6 ml, 150 breaths/min) followed by quiet breathing of humidified air (VT 2-3 ml, 60 breaths/min), severe bronchoconstriction developed only after the cessation of hyperpnea; the magnitude of respiratory system resistance (Rrs) increased with the duration of dry gas hyperpnea [peak Rrs 1.0 +/- 0.2, 1.8 +/- 0.3, and 2.3 +/- 0.3 (SE) cmH2O.ml-1.s, respectively]. Seven other guinea pigs received, in random order, 10 min of warm humidified gas hyperpnea, 10 min of room temperature dry gas hyperpnea, and 5 min of dry gas hyperpnea immediately followed by 5 min of warm humidified gas hyperpnea. After each hyperpnea period, the animal was returned to quiet breathing of humidified gas. Rrs rose appreciably after the 10 min of dry and 5 min of dry-5 min of humidified hyperpnea challenges (peak Rrs 1.3 +/- 0.2 and 0.7 +/- 0.2 cmH2O.ml-1.s, respectively) but not after 10 min of humidified hyperpnea (0.2 +/- 0.04 cmH2O.ml-1.s). An additional five animals received 10 min of room temperature dry gas hyperpnea followed by quiet breathing of warm humidified air and 10 min of room temperature dry gas hyperpnea followed by 30 min of warm humidified gas hyperpnea in random order.(ABSTRACT TRUNCATED AT 250 WORDS)     

Tachykinins mediate hypocapnia-induced bronchoconstriction in guinea pigs

The aim of this study was to determine whether hypocapnia causes bronchoconstriction by releasing tachykinins (TKs) from C-afferent nerves in airways. Hypocapnia-induced bronchoconstriction (HIBC) was induced in anesthetized vagotomized guina pigs by ventilating lungs with a heated humidified hypocapnic gas mixture for 15 min after sudden circulatory arrest. The intensity of bronchoconstriction was assessed by calculating changes in dynamic compliance and by measuring the relaxation lung volume at the completion of experiments. Visualization of the airways by tantalum bronchography showed constriction of segmental bronchi with relative sparing of more proximal airways. Hypocapnia-induced bronchoconstriction was prevented by prior administration of salbutamol aerosol. Three experimental interventions were used to investigate the role of TKs in HIBC: 1) repeated capsaicin injections to deplete airway sensory nerves of TKs, 2) treatment with phosphoramidon, an inhibitor of enkephalinase, the main enzyme responsible for TK inactivation, and 3) topical airway anesthesia. Capsaicin pretreatment markedly attenuated the hypocapnia-induced changes in dynamic compliance (P less than 0.0005) and relaxation lung volume (P less than 0.0002), whereas phosphoramidon augmented these changes (P less than 0.02, P less than 0.03, respectively). Topical anesthesia of airways with lignocaine postponed the onset of bronchoconstriction, whereas the longer-acting, more lipid-soluble local anesthetic, bupivacaine, almost completely prevented HIBC. We conclude that, in the guinea pig lung, HIBC is mediated by TKs that are released after the activation of bronchial axonal reflexes.     

Tachykinins mediate bronchoconstriction elicited by isocapnic hyperpnea in guinea pigs

We tested the hypothesis that tachykinins mediate hyperpnea-induced bronchoconstriction (HIB) in 28 guinea pigs. Stimulus-response curves to increasing minute ventilation with dry gas were generated in animals depleted of tachykinins by capsaicin pretreatment and in animals pretreated with phosphoramidon, a neutral metalloendopeptidase inhibitor. Sixteen anesthetized guinea pigs received capsaicin (50 mg/kg sc) after aminophylline (10 mg/kg ip) and terbutaline (0.1 mg/kg sc). An additional 12 animals received saline (1 ml sc) instead of capsaicin. One week later, all animals were anesthetized, given propranolol (1 mg/kg iv), and mechanically ventilated (6 ml/kg, 60 breaths/min, 50% O2 in air fully water saturated). Phosphoramidon (0.5 mg iv) was administered to five of the noncapsaicin-treated guinea pigs. Eucapnic dry gas (95% O2-5% CO2) hyperpnea "challenges" were performed by increasing the tidal volume (2-6 ml) and frequency (150 breaths/min) for 5 min. Capsaicin-pretreated animals showed marked attenuation in HIB, with a rightward shift of the stimulus-response curve compared with controls; the estimated tidal volume required to elicit a twofold increase in respiratory system resistance (ES200) was 5.0 ml for capsaicin-pretreated animals vs. 3.7 ml for controls (P less than 0.03). Phosphoramidon-treated animals were more reactive to dry gas hyperpnea compared with control (ES200 = 2.6 ml; P less than 0.0001). Methacholine dose-response curves (10(-11) to 10(-7) mol iv) obtained at the conclusion of the experiments were similar among capsaicin, phosphoramidon, and control groups. These findings implicate tachykinin release as an important mechanism of HIB in guinea pigs.     

Met-enkephalin effects on histamine-induced bronchoconstriction in guinea pigs

We investigated the effects of the neuropeptide met-enkephalin on histamine-induced bronhoconstriction in an experimental model of asthma. Classic Konzett and R?ssler's method of whole body plethysmography modified by Gjuris, was applied in the study. This method represents a standard experimental model of bronchoconstriction, suitable for the evaluation of peptide effects on the histamine-induced bronchoconstriction. The results of the measurements implicate a dose-related modulatory effect of met-enkephalin on the bronchoconstrictor action of histamine. Met-enkephalin doses of 1 mg/kg and 10 mg/kg, respectively, caused statistically significant reduction of the histamine-induced bronchoconstriction. Estimated ED50 dose was 0.235 mg/kg. Further studies are needed to define practical and therapeutical use of the presented observations in respiratory pharmacology.     

Cholinergic component of histamine-induced bronchoconstriction in newborn guinea pigs

The magnitude of parasympathetic reflex-mediated bronchoconstriction during histamine infusion was compared in anesthetized paralyzed newborn and adult guinea pigs. The animals were ventilated using a constant-flow ventilator, and the conductance and compliance of the respiratory system were continuously monitored. We found that reactivity to histamine infusion was less in newborns than in adults, because newborns required a larger dose of histamine than adults (300 vs. 125 ng.kg-1.s-1) to produce an equivalent decrease in conductance (42 +/- 13 vs. 42 +/- 15%). Vagal interruption by bilateral cervical vagotomy or muscarinic blockade with atropine (3 mg/kg) significantly reduced the bronchoconstrictor response to histamine in adults. By contrast, neither vagotomy nor atropine significantly changed this response in the newborns. These results indicate the lack of a vagal component in the bronchoconstriction that histamine induced in the newborns. Their relative unresponsiveness to histamine might partly be related to the fact that, in the newborn, histamine mainly acts directly via its airway receptors.     

Influence of body temperature on histamine-induced bronchoconstriction in guinea pigs

The effects of body temperature on histamine-induced bronchoconstriction were investigated in anesthetized, paralyzed, and mechanically ventilated guinea pigs. Four groups of guinea pigs were studied with constant body temperatures of 40, 38, 35, and 32 degrees C, respectively. Histamine was infused for 5 min at a rate of 50 ng.kg-1.s-1. Body cooling from 40 to 32 degrees C augmented the bronchomotor responses to histamine, which eventually rose almost fourfold. The enhancement of histamine-induced bronchoconstriction induced by body cooling was not suppressed by pretreating guinea pigs with 5 mg/kg hexamethonium or 5 mg/kg hexamethonium plus 3 mg/kg atropine; neither was the enhancement of histamine-induced bronchoconstriction suppressed in pithed guinea pigs, demonstrating that the autonomic nervous system is not involved in potentiating bronchoconstriction at low body temperatures. These results suggest that, at low body temperatures, increased airway responsiveness to histamine may be because of some direct effect of temperature on bronchial airway smooth muscle.     

Phosphoramidon potentiates the endothelin-1-induced bronchopulmonary response in guinea-pigs

We investigated the effect of the endopeptidase-inhibitor, phosphoramidon, on the bronchopulmonary response induced by endothelin-1 in vivo or in isolated perfused lungs. In vivo aerosol administration of 1 or 3 μg/ml endothelin-1 for 2 min provoked no significant bronchopulmonary response. When awake animals were pretreated by an aerosol of phosphoramidon (0.1 mM, for 15 min), the bronchopulmonary response induced by 1 and 3 μg/ml endothelin-1 was markedly enhanced. In isolated guinea-pig lungs, aerosol administration of endothelin-1 (3 μg/ml, for 2 min) evoked a low increase in pulmonary inflation pressure. Treatment of awake animals with an aerosol of phosphoramidon before lung recollection led to a significant potentiation of the endothelin-1-induced increase in pulmonary inflation pressure. These results demonstrate that phosphoramidon potentiates the in vivo and in vitro bronchopulmonary response evoked by low doses of endothelin-1 and suggest that endopeptidase-like enzymes present in the airway tissue modulate the effect of the peptide.     

Influence of tidal volume on histamine-induced bronchoconstriction in guinea pigs

The effects of tidal volume amplitude on bronchopulmonary reactivity were investigated in three groups of 14 anesthetized paralyzed mechanically ventilated guinea pigs. Animals of group 1 served as control; in animals of group 2, both the sympathetic and parasympathetic nervous systems were blocked; in animals of group 3, only the parasympathetic system was blocked. In each group, the animals were randomly divided into two subgroups characterized by their ventilatory pattern: rate of 60/min with a 6-ml/kg tidal volume or rate of 40/min with a 9-ml/kg tidal volume. Bronchopulmonary reactivity to infused histamine was assessed by the respiratory compliance and conductance values measured during bronchoconstriction and expressed as a percentage of the corresponding basal values. In group 1 the animals ventilated with a 9-ml/kg tidal volume were found significantly less reactive than those ventilated with a 6-ml/kg tidal volume. This difference was abolished in groups 2 and 3. These results demonstrate that the effects of increased tidal volume on bronchopulmonary reactivity are vagally mediated and suggest that the decrease observed in histamine-induced bronchoconstriction is mainly due to reflex effects evoked by stretch receptor stimulation.     

Distribution of airway narrowing during hyperpnea-induced bronchoconstriction in guinea pigs

Increasing minute ventilation of dry gas shifts the principal burden of respiratory heat and water losses from more proximal airway to airways farther into the lung. If these local thermal transfers determine the local stimulus for bronchoconstriction, then increasing minute ventilation of dry gas might also extend the zone of airway narrowing farther into the lung during hyperpnea-induced bronchoconstriction (HIB). We tested this hypothesis by comparing tantalum bronchograms in tracheostomized guinea pigs before and during bronchoconstriction induced by dry gas hyperpnea, intravenous methacholine, and intravenous capsaicin. In eight animals subjected to 5 min of dry gas isocapnic hyperpnea [tidal volume (VT) = 2-5 ml, 150 breaths/min], there was little change in the diameter of the trachea or the main stem bronchi up to 0.75 cm past the main carina (zone 1). In contrast, bronchi from 0.75 to 1.50 cm past the main carina (zone 2) narrowed progressively at all minute ventilations greater than or equal to 300 ml/min (VT = 2 ml). More distal bronchi (1.50-3.10 cm past the main carina; zone 3) did not narrow significantly until minute ventilation was raised to 450 ml/min (VT = 3 ml). The estimated VT during hyperpnea needed to elicit a 50% reduction in airway diameter was significantly higher in zone 3 bronchi [4.3 +/- 0.8 (SD) ml] than in zone 2 bronchi (3.5 +/- 1.1 ml, P less than 0.012).(ABSTRACT TRUNCATED AT 250 WORDS)     

Lack of adrenomedullin on antigen-induced bronchoconstriction in guinea pigs in vivo

Antigen challenge can provoke acute bronchoconstriction, recognized as immediate asthmatic response (IAR), but the evolving events in this reaction are not well defined. Recently, a novel peptide, designated adrenomedullin, was isolated from human pheochromocytoma, and has been shown to have potent systemic and pulmonary vasodilator activity.The purpose of this study was to elucidate the influence of adrenomedullin in the development of IAR. Passively sensitized guinea pigs were anesthetized and treated with diphenhydramine hydrochloride, and then artificially ventilated. Ovalbumin was inhaled after an intravenous administration of adrenomedullin. Other studies were performed in naive guinea pigs to investigate the airway responses to inhaled methacholine or histamine after an intravenous administration of adrenomedullin. Antigen challenge caused bronchoconstriction in sensitized guinea pigs. Adrenomedullin did not inhibit the antigen-induced bronchoconstriction in sensitized guinea pigs or the dose-dependent responses to inhaled methacholine or histamine in naive animals in spite of its vasodilating effect. We conclude that an intravenous administration of adrenomedullin does not influence antigen-induced bronchoconstriction or bronchial responsiveness to inhaled methacholine or histamine in vivo.     

Cigarette smoke exposure potentiates bleomycin-induced lung fibrosis in guinea pigs

The role of tobacco smoking in the development and outcome of pulmonary fibrosis is uncertain. To approach the effects of cigarette smoke on bleomycin-induced lung fibrosis, we studied five groups of guinea pigs: 1) controls, 2) instilled with bleomycin (B), 3) exposed to tobacco smoke for 6 wk (TS), 4) bleomycin instillation plus tobacco smoke exposure for 6 wk (B+TS), and 5) tobacco smoke exposure for 6 wk and bleomycin after smoking (TS/B). Guinea pigs receiving bleomycin and tobacco smoke exposure exhibited higher fibrotic lesions including a significant increase in the number of positive alpha-smooth muscle actin cells compared with bleomycin alone (B+TS, 3.4 +/- 1.2%; TS/B, 3.7 +/- 1.5%; B, 2.3 +/- 1.5%; P < 0.01). However, only the TS/B group reached a significant increase in lung collagen compared with the bleomycin group (TS/B, 3.5 +/- 0.7; B +/- TS, 2.9 +/- 0.4; B, 2.4 +/- 0.2 mg hydroxyproline/lung; P < 0.01). Bronchoalveolar lavage (BAL) from TS/B showed an increased number of eosinophils and higher levels of IL-4 and tissue inhibitor of metalloproteinase-2 (P < 0.01 for all comparisons) and induced a significant increase in fibroblast proliferation (P < 0.05). Importantly, smoke exposure alone induced an increase in BAL neutrophils, matrix metalloproteinase-9, and fibroblast proliferation compared with controls, suggesting that tobacco smoke creates a profibrotic milieu that may contribute to the increased bleomycin-induced fibrosis.     

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.