Bronchoconstriction In Dogs Research Articles

Pharmacological preclinical characterization of LAS190792, a novel inhaled bifunctional muscarinic receptor antagonist /β2-adrenoceptor agonist (MABA) molecule

LAS190792 is a novel muscarinic antagonist and β2-adrenoceptor agonist in development for chronic respiratory diseases. This study investigated the pharmacological profile of LAS190792 in comparison to batefenterol, tiotropium, indacaterol and olodaterol. LAS190792 is potent at the human M3 receptor (pIC50: 8.8 in binding assays). It is selective for the β2-adrenoceptor over the β1-and β3-adrenoceptor, and shows a functional potency in a similar range to batefenterol and LABA compounds (pEC50 in spontaneous tone isolated trachea: 9.6). The relaxant potency of LAS190792 in electrically stimulated tissue is similar to batefenterol, with an antimuscarinic activity in presence of propranolol slightly higher than batefenterol (pIC50 of 8.3 versus 7.9 in human tissue). LAS190792 exhibits a sustained duration of action in isolated tissue longer than that of batefenterol. Nebulized LAS190792 inhibits acetylcholine-induced bronchoconstriction in dog with minimal cardiac effects and sustained bronchodilation (t1/2: 13.3 h). In conclusion, these studies suggest that LAS190792 is a dual-acting muscarinic antagonist β2-adrenoceptor agonist that has the potential to be a next generation bronchodilator with long-lasting effects and wide safety margin in humans.

Evaluation of variables to describe the shape of volumetric capnography curves during bronchoconstriction in dogs

The aim of the study was to investigate changes in volumetric capnography (VC) variables during bronchoconstriction in dogs and compare it with total respiratory resistance (RL) measured with a Fleisch pneumotachograph. Six dogs were challenged with increasing concentrations of carbachol until obvious signs of bronchoconstriction were seen. All VC parameters were obtained before, directly after, 10 and 20min after maximal bronchoconstriction. The slope of phase III (SIII) and airway and alveolar dead space parameters were significantly different from baseline directly after the challenge. The VC curve obtained a typical shape at the time of maximal bronchoconstriction and a trend to return to baseline shape was seen over time. A significant correlation was found for all aforementioned parameters with RL. We conclude that the shape of the VC curve in combination with dead space calculation can be used to verify bronchoconstriction on a breath-to-breath basis.

Respiratory safety pharmacology: Positive control drug responses in Sprague–Dawley rats, Beagle dogs and cynomolgus monkeys

Rats are most frequently used to fulfill ICH S7A requirements for respiratory safety pharmacology. We hypothesized that the models used to assess respiratory safety pharmacology present different ventilatory responses to bronchoconstriction, bronchodilation and respiratory depression. Respiratory monitoring was performed with head-out plethysmographs for rats, masks for dogs and bias airflow helmets for monkeys. Respiratory rate (RR), tidal volume (TV) and minute volume (MV) were recorded. Forty rats, 18 dogs and 8 monkeys were acclimated to the respiratory monitoring equipment. Animals received saline (IV), albuterol (inhalation), methacholine (IV) and remifentanil (IV). Albuterol increased TV in all species. Methacholine decreased TV and MV in monkeys. In dogs, methacholine increased TV, RR and MV. In rats, methacholine increased TV and decreased RR. Remifentanil induced central respiratory depression in all species with decreased MV, except in rats. Dogs presented a biphasic response to remifentanil with hypoventilation followed by delayed hyperventilation. The monkeys presented similar responses to humans which may be due to biologic similarities. Dogs and rats presented clinically significant ventilatory alterations following positive control drugs. Although, the response to bronchoconstriction in dogs and rats was different from humans, the two species presented ventilatory changes that highlight the potential adverse effect of test articles.

Effects of the alpha2-adrenoceptor agonist dexmedetomidine on bronchoconstriction in dogs.

Tracheal intubation can elicit reflex bronchoconstriction in patients with asthma or chronic obstructive pulmonary disease, complicating mechanical ventilation and weaning from mechanical support. In vitro studies of human and animal bronchial tissue indicate that alpha2-adrenoceptor stimulation can lead to smooth muscle relaxation and prevention of bronchoconstriction. Dexmedetomidine is a selective alpha2-adrenoceptor agonist approved for sedation in the intensive care unit. Whether dexmedetomidine can affect reflex bronchoconstriction is unknown. After the approval of the institutional animal care and use committee, five mongrel dogs were anesthetized with thiopental, endotracheally intubated, and ventilated, and their airways were challenged with histamine. High-resolution computed tomography was used to measure airway luminal areas at baseline and after nebulized histamine. After recovery to baseline, on separate days, dexmedetomidine (0.5 microg/kg) was administered either intravenously or as an aerosol, and the histamine challenge was repeated. At baseline, histamine constricted the airways to 66 +/- 27% (mean +/- SD) (P < 0.0001) and 59 +/- 30% (P < 0.0001) of maximum on the days dexmedetomidine was administered by intravenous and inhalational means, respectively. After recovery, intravenous administration of dexmedetomidine blocked the histamine-induced bronchoconstriction (87 +/- 30.4% of maximum, compared with histamine alone (P < 0.0001), whereas dexmedetomidine administered by inhalation showed no protective effect (45 +/- 30% of maximum; P < 0.0001 compared with histamine alone). alpha2-Adrenoceptor stimulation with intravenous dexmedetomidine completely blocked histamine-induced bronchoconstriction in dogs. Therefore, dexmedetomidine might be beneficial to decrease airway reactivity in patients with chronic obstructive pulmonary disease or asthma, particularly during weaning from mechanical ventilation, when neurally mediated airway reflexes may be elicited.

Differential effects of thiopental on methacholine- and serotonin-induced bronchoconstriction in dogs

Thiopental sometimes causes bronchospasm during induction of anaesthesia. In addition, we have reported previously that thiopental produced transient bronchospasm, which was blocked by atropine pretreatment, and worsened histamine-induced bronchoconstriction in dogs. Previous in vitro reports suggest that synthesis of contractile cyclooxygenase products, such as thromboxane A(2), may be involved in the mechanism of bronchospasm. However, the in vivo spastic effects have not been defined comprehensively. Twenty-seven mongrel dogs were anaesthetized with pentobarbital. Bronchoconstriction was elicited with methacholine (0.5 microg kg(-1)+5.0 microg kg(-1) min(-1); Mch group, n=7) or serotonin (10 microg kg(-1)+1 mg kg(-1) h(-1); 5HT group, n=20), and assessed as percentage changes in bronchial cross-sectional area (BCA, basal=100%) using a bronchoscope. In the 5HT group, dogs were subdivided into four groups of five each: S-5HT, I-5HT, 5HT-S and 5HT-A. In the S-5HT and I-5HT groups, 30 min before serotonin infusion dogs were given saline and indomethacin respectively at 5 mg kg(-1) i.v. In all groups, 30 min after bronchoconstrictor infusion started, dogs were given thiopental at doses between 0 (saline) and 20 mg kg(-1). In the 5HT-S and 5HT-A groups, dogs were given saline or atropine 0.2 mg kg(-1) i.v. 5 min after thiopental 20 mg kg(-1). Methacholine and serotonin reduced BCA by about 50 and 40% respectively. Thiopental 20 mg kg(-1) increased and decreased BCA by about 20 and 10% in the Mch and 5HT groups respectively. Indomethacin and atropine did not attenuate the potentiation of serotonin bronchoconstriction produced by thiopental. The present study indicates that thiopental may attenuate or worsen bronchoconstriction induced by muscarinic or serotonin receptor stimulation, respectively. The synthesis of contractile cyclooxygenase products and cholinergic stimulation may not be involved in the contractile effect of thiopental on serotonin bronchoconstriction.

Spasmolytic effects of colforsin daropate on serotonin-induced pulmonary hypertension and bronchoconstriction in dogs.

We have previously found that agents increasing intracellular cAMP levels of smooth muscles, such as PDE3 inhibitors, aminophylline and prostaglandin E1, produce both bronchodilation and pulmonary vasodilation in serotonin-induced pulmonary hypertension and bronchoconstriction models. In the present study we have simultaneously evaluated the spasmolytic effects of colforsin daropate, a novel forskolin derivative, on serotonin-induced pulmonary hypertension and bronchoconstriction. Ten mongrel dogs were anesthetized with pentobarbital. The pulmonary hypertension and bronchoconstriction were elicited with serotonin (10 microg/kg + 1 mg x kg(-1) x h(-1)) and assessed as percentage changes in pulmonary vascular resistance (PVR) and bronchial cross-sectional area (BCA) (basal = 100%). Initially, the relaxant effects of colforsin daropate (0-300 microg/kg) were determined. The PVR and BCA were assessed before and 30 min after serotonin infusion began and 5 min after each dose of colforsin daropate. To determine whether colforsin daropate-induced relaxation is independent of plasma catecholamine, propranolol 0.4 mg/kg was given following colforsin daropate 300 microg/kg i.v. Colforsin daropate reversed both pulmonary hypertension and bronchoconstriction dose-dependently: -logED50 (95% confidence intervals, mean ED50) for pulmonary hypertension and bronchoconstriction 5.44 (5.08-5.80, 3.6 microg/kg) and 4.90 (4.06-5.20, 12.5 microg/kg), respectively. However, colforsin daropate (>or= 30 microg/kg) produced a more pronounced systemic than pulmonary vasodilation. Although colforsin daropate (>or= 30 microg/kg) significantly increased plasma catecholamines, propranolol did not reverse the relaxant effects. Colforsin daropate may attenuate bronchoconstriction and pulmonary hypertension. In addition, as beta-blockade did not change the attenuation, the relaxant effects may be independent of plasma catecholamines.

Spasmolytic effect of magnesium sulfate on serotonin-induced pulmonary hypertension and bronchoconstriction in dogs.

Magnesium (Mg2+) has relaxant effects on histamine-induced bronchoconstriction. In addition, Mg2+ has been reported to reduce vascular smooth muscle tone and be clinically useful for treatment of persistent pulmonary hypertension of the newborn. In this study, we evaluated the relaxant effect of Mg2+ on serotonin (5HT)-induced bronchoconstriction and pulmonary hypertension. Seven mongrel dogs were anesthetized with pentobarbital (30 mg x kg(-1) + 2 mg x kg(-1) x h(-1)) and paralyzed by pancuronium (0.2 mg x kg(-1) x h(-1)). Bronchoconstriction and pulmonary hypertension were elicited with 5HT (10 microg x kg(-1) + 1 mg x kg(-1) x h(-1)). Airway caliber was evaluated by changes in bronchial cross-sectional area (BCA) of the 3rd bronchial bifurcation measured by a fiberoptic bronchoscope method as previously reported. Pulmonary hypertension was assessed by changes in pulmonary vascular resistance (PVR). The BCA and PVR were expressed as per cent of the basal level. Thirty minutes after start of 5HT infusion, magnesium sulfate (MgSO4): 0 (saline), 1, 10, 100 and 1000 micromol x kg(-1) was given i.v.. Arterial blood was also collected to measure plasma level of Mg2+ and catecholamines. 5HT increased %PVR to 163+/-25% and decreased % BCA by 39.2+/-4.5%. Plasma level of Mg2+ following MgSO4 1000 micromol x kg(-1) i.v. exceeded its toxic level. The ED50s of MgSO4 (dose producing 50% relaxation of maximal constriction) was 47.8 micromol x kg(-1) and 1.09 mmol x kg(-1) for pulmonary hypertension and bronchoconstriction, respectively. The ratio of %PVR to %SVR was about 1.0 after MgSO4 0-100 micromol x kg(-1) i.v., although the ratio significantly increased after 1000 micromol x kg(-1) i.v.. In dogs, 5HT-induced pulmonary hypertension but not bronchoconstriction was significantly reduced by an iv bolus of MgSO4, resulting in a plasma concentration within the assumed therapeutic level.

Comparison of relaxant effects of propofol on methacholine-induced bronchoconstriction in dogs with and without vagotomy

Propofol has been suggested to have in vivo airway relaxant effects, although the mechanism is still unclear. In this study, we determined whether propofol could antagonize methacholine-induced bronchoconstriction and determined whether vagotomy modifies this relaxant effect. Fourteen mongrel dogs anaesthetized with pentobarbital and pancuronium were assigned to a control group (n=7) and a vagotomy group (n=7). The trachea was intubated with a special endotracheal tube that had a second lumen for insertion of the bronchoscope. Bronchial cross-sectional area, which was monitored continuously through the bronchoscope, was measured with image analysis software. Bronchoconstriction was elicited with methacholine (0.5 microg kg(-1) + 5.0 microg kg(-1) min(-1)) until the end of the experiment. Thirty minutes after the start of methacholine infusion, propofol 0, 0.2, 2.0 and 20 mg kg(-1) was administered. Changes in bronchial cross-sectional area were expressed as percentages of the basal area. Plasma concentrations of propofol and catecholamine were measured by high-performance liquid chromatography. Maximal inhibition (bronchoconstriction = 0%, baseline = 100%) and IC50 (concentration producing 50% inhibition of maximal effect) produced by propofol was obtained from each concentration-response curve using a curve-fitting program. Methacholine decreased bronchial cross-sectional area to 49.3% (95% confidence interval 38.5-60.1%) and 45.3% (34.8-55.7%) of the baseline value. Propofol 20 mg kg(-1) significantly reversed this effect: bronchial cross-sectional area was reduced to 77.8% (66.2-89.6%) and 75.9% (64.0-87.9) in the control and vagotomy groups respectively. The two groups did not differ significantly in the maximal inhibitory effect of propofol [control group, 61.1% (46.3-75.9%), vagotomy group, 64.2% (40.1-88.3%)] or pIC50 [control group 5.03 (4.55-5.51), vagotomy group 4.86 (4.49-5.24)]. Therefore, the relaxant effects of propofol on methacholine-induced bronchoconstriction may not be mediated centrally. Propofol may relax airway smooth muscles directly or through the peripheral vagal pathway.

A potent, long-acting, orally active (2R)-2-[(1R)-3, 3-difluorocyclopentyl]-2-hydroxy-2-phenylacetamide: novel muscarinic M(3) receptor antagonist with high selectivity for M(3) over M(2) receptors.

A novel series of (2R)-2-[(1R)-3, 3-difluorocyclopentyl]-2-hydroxy-2-phenylacetamides was designed and synthesized based on the structure and biological profiles of an active metabolite 2 of our prototype muscarinic M(3) receptor selective antagonist 1, to develop a potent, long-acting, orally active M(3) antagonist for the treatment of urinary tract disorders, irritable bowel syndrome, and respiratory disorders. Investigation of (2R)-2-[(1R)-3, 3-difluorocyclopentyl]-2-hydroxy-2-phenylacetamides containing a phenyl or heterocyclic ring as the piperidinyl side chain in place of the 4-methyl-3-pentenyl moiety of 15a revealed that this acid moiety was a versatile template for improving the selectivity for M(3) over M(2) receptors in comparison with the corresponding cyclopentylphenylacetic acid group. However, since the in vitro metabolic stability of these analogues was insufficient compared with that of 2, further derivatization was performed by introducing an appropriate hydrophilic group into the phenyl or 2-pyridyl ring. Thus, the 1-(6-aminopyridin-2-ylmethyl)piperidine analogue 15y exhibiting 190-fold selectivity for M(3) receptors (K(i) = 2.8 nM) over M(2) receptors (K(i) = 530 nM) in a human binding assay and good in vitro metabolic stability in dog and human hepatic microsomes was identified. This compound has excellent oral activity at 4 h after oral dosing (1 mg/kg), inhibiting methacholine-induced bronchoconstriction in dogs, and may be useful in clinical situations in which M(3) over M(2) selectivity is desirable.

Room G, 10/17/2000 2: 00 PM - 4: 00 PM (PS) Propofol Antagonizes Methacholine-Induced Bronchoconstriction in Dogs with and without Wagotomy

<b>Room G, 10/17/2000 2: 00 PM - 4: 00 PM (PS) Propofol Antagonizes Methacholine-Induced Bronchoconstriction in Dogs with and without Wagotomy</b>

Heparin inhibits eicosanoid metabolism and hyperventilation-induced bronchoconstriction in dogs.

Inhalation of heparin, an anticoagulant, attenuates exercise- induced asthma (EIA) in human subjects. The purpose of this study was to determine if heparin inhibits hyperventilation-induced bronchoconstriction (HIB) in a canine model of EIA, and if its mode of action involves the inhibition of eicosanoid mediator production and release. We used a wedged bronchoscope technique to measure baseline peripheral airway resistance (Rp). We then performed either a 2-min or 5-min dry air challenge (DAC) by temporarily increasing from 200 to 2,000 ml/min the flow of 5% CO(2) in air used to ventilate a wedged sublobar segment. We compared HIB before and 60 min after aerosol treatment with either bacteriostatic water (BW) or heparin. We found that (1) heparin had no effect on baseline Rp, (2) BW did not alter the response to DAC, and (3) heparin reduced HIB by approximately 50-60%. On the basis of bronchoalveolar lavage fluid (BALF) cell analysis, heparin and BW caused acute infiltration of macrophages and eosinophils, and heparin increased the number of erythrocytes recovered immediately after DAC. Despite these acute inflammatory effects initiated prior to DAC, BALF mediator analyses revealed that pretreatment with heparin either attenuated or abolished hyperventilation-induced leukotriene, prostaglandin, and thromboxane release. Thus, our data provide direct evidence that inhaled heparin inhibits eicosanoid mediator production and release caused by hyperventilation with dry air, and significantly attenuates HIB.

Milrinone attenuates serotonin-induced pulmonary hypertension and bronchoconstriction in dogs.

We determined whether milrinone, a phosphodiesterase III inhibitor, attenuates serotonin-induced (5-hydroxytryptamine [5HT]) pulmonary hypertension (PH) and bronchoconstriction. Dogs were anesthetized with pentobarbital (30 mg/kg + 2 mg. kg(-1). h(-1)). Bronchoconstriction and PH were elicited by 5HT (10 microg/kg + 1.0 mg. kg(-1). h(-1)). Pulmonary vascular resistance was used to assess PH. Bronchoconstriction was also assessed by changes in bronchial cross-sectional area obtained from our bronchoscopic method. At 30 min after 5HT infusion started, seven dogs were given milrinone: 0 (saline), 5, 50, 500, and 5000 microg/kg at 10-min intervals. The other 12 dogs were given milrinone 5000 microg/kg 30 min after 5HT infusion, and 5 min later were given propranolol 0.2 mg/kg (n = 6) or saline (n = 6) IV. The 5HT significantly increased percentage of pulmonary vascular resistance to 208% +/- 27% and decreased percentage of bronchial cross-sectional area to 52% +/- 5% of the basal. Milrinone significantly attenuated both PH and bronchoconstriction in a dose-dependent manner. However, -log 50% effective concentration (mean ED(50) in microg/kg) of milrinone for bronchoconstriction: 4.32 +/- 0.13 (47.6) was significantly smaller than that for PH: 3.84 +/- 0.29 (144.9) (P < 0.01). In addition, the spasmolytic effects of milrinone (5000 microg/kg) were not antagonized by propranolol, although this dose significantly increased plasma catecholamines. In conclusion, milrinone attenuates 5HT-induced PH and bronchoconstriction; however, this drug may be more sensitive to phosphodiesterase III in the airway smooth muscle than in pulmonary vascular smooth muscle. In addition, the relaxant effects could not be caused by beta-adrenoceptor activation because beta-blocker did not antagonize. We studied the effects of milrinone on serotonin-induced pulmonary hypertension and bronchoconstriction in dogs. Milrinone produces pulmonary vasodilation and bronchodilation, whose effects may not be caused by beta-adrenoceptor activation. In addition, this drug may be more sensitive to phosphodiesterase III in the airway smooth muscle than that in pulmonary vascular smooth muscle.

Milrinone Attenuates Serotonin-Induced Pulmonary Hypertension and Bronchoconstriction in Dogs

We determined whether milrinone, a phosphodiesterase III inhibitor, attenuates serotonin-induced (5-hydroxytryptamine [5HT]) pulmonary hypertension (PH) and bronchoconstriction. Dogs were anesthetized with pentobarbital (30 mg/kg + 2 mg · kg−1 · h−1). Bronchoconstriction and PH were elicited by 5HT (10 μg/kg + 1.0 mg · kg−1 · h−1). Pulmonary vascular resistance was used to assess PH. Bronchoconstriction was also assessed by changes in bronchial cross-sectional area obtained from our bronchoscopic method. At 30 min after 5HT infusion started, seven dogs were given milrinone: 0 (saline), 5, 50, 500, and 5000 μg/kg at 10-min intervals. The other 12 dogs were given milrinone 5000 μg/kg 30 min after 5HT infusion, and 5 min later were given propranolol 0.2 mg/kg (n = 6) or saline (n = 6) IV. The 5HT significantly increased percentage of pulmonary vascular resistance to 208% ± 27% and decreased percentage of bronchial cross-sectional area to 52% ± 5% of the basal. Milrinone significantly attenuated both PH and bronchoconstriction in a dose-dependent manner. However, −log 50% effective concentration (mean ED50 in μg/kg) of milrinone for bronchoconstriction: 4.32 ± 0.13 (47.6) was significantly smaller than that for PH: 3.84 ± 0.29 (144.9) (P < 0.01). In addition, the spasmolytic effects of milrinone (5000 μg/kg) were not antagonized by propranolol, although this dose significantly increased plasma catecholamines. In conclusion, milrinone attenuates 5HT-induced PH and bronchoconstriction; however, this drug may be more sensitive to phosphodiesterase III in the airway smooth muscle than in pulmonary vascular smooth muscle. In addition, the relaxant effects could not be caused by β-adrenoceptor activation because β-blocker did not antagonize. Implications: We studied the effects of milrinone on serotonin-induced pulmonary hypertension and bronchoconstriction in dogs. Milrinone produces pulmonary vasodilation and bronchodilation, whose effects may not be caused by β-adrenoceptor activation. In addition, this drug may be more sensitive to phosphodiesterase III in the airway smooth muscle than that in pulmonary vascular smooth muscle.

I.V. Lidocaine Worsens Histamine-Induced Bronchoconstriction in Dogs

HIROTA, K.; HASHIMOTO, Y.; SATO, T.; YOSHIOKA, H.; KUDO, T.; ISHIHARA, H.; MATSUKI, A. Author Information

Prostaglandin E1 produces spasmolytic effects on histamine-induced bronchoconstriction in dogs.

In this study, we evaluated the spasmolytic effect of intravenous prostaglandin (PG) E1 on histamine-induced bronchoconstriction with a direct visualization method using a superfine fiberoptic bronchoscope. A university research laboratory. Mongrel dogs. The bronchial cross-sectional area (BCA) of mongrel dogs was measured by a direct visualization method using a superfine fiberoptic bronchoscope. Bronchoconstriction was elicited with histamine (H) infusion: 10 microg/kg iv bolus + 500 microg/kg/h continuous iv. The first protocol (n = 7) was designed to determine the effects of intravenous bolus of PGE1: 0 (saline), 0.01, 0.1, 1.0 and 10 microg/kg on H-induced bronchoconstriction. BCA was assessed before and 30 min after starting the H infusion and 5 min after each dose of intravenous PGE1. The second protocol was designed to determine whether continuous intravenous infusion of PGE1 reverses H-induced bronchoconstriction. In the PG group (n = 6), PGE1 was continuously infused at 0.1 microg/kg/min (20 mL/hr). In the control group (n = 6), saline was administered at a rate of 20 mL/hr iv. BCA was assessed before and 30 min after starting the H-infusion and at 5, 10, 30 and 60 min after commencing the PGE1 or saline infusion. Arterial blood was obtained simultaneously for measurement of plasma concentrations of epinephrine and norepinephrine by gas chromatography mass spectrometry. In the first protocol, PGE1 produced a dose-dependent increase in the percentage of BCA and 10 microg/kg of PGE1 almost fully reversed the H-induced bronchoconstriction. Plasma catecholamines did not change significantly. In the second protocol, continuous infusion of PGE1 produced a time-dependent reversal of H-induced bronchoconstriction (percentage of BCA increased to 80.0+/-9.0% 60 min after the start of PGE1 infusion), whereas saline infusion did not reverse the bronchoconstriction. Plasma catecholamines did not change significantly in either group. Both intravenous bolus and continuous intravenous infusion of PGE1 reversed the H-induced bronchoconstriction. PGE1 may be used safely for patients with the hyperreactive airway and might be useful as a therapeutic agent for these patients.

Tidal volume amplitude affects the degree of induced bronchoconstriction in dogs.

When isolated constricted airway smooth muscle is oscillated, muscle tone decreases. We investigated whether changing tidal volume (VT) would affect induced bronchoconstriction in an in vivo canine model. Open-chest dogs were intubated with a double-lumen endotracheal tube, which isolated each main bronchus, and mechanically ventilated with a dual-cylinder ventilator. Bronchial pressure (Pbr) and flow were measured separately in each lung. Resistance and elastance were calculated by fitting the changes in Pbr, flow, and volume to the equation of motion. After baseline measurements at the same VT (150 ml), the two lungs were ventilated with different VT (50 vs. 250 ml) at a constant positive end-expiratory pressure. A continuous infusion of methacholine was begun, and measurements were repeated. The two lungs were then ventilated with the same VT (250 ml), and measurements were again repeated. A similar protocol was performed in a second group of dogs in which mean Pbr was kept constant. Bronchoconstriction was more severe in the lung ventilated with lower VT in both protocols. When VT was reset to the same amplitude in the two lungs, the difference in bronchoconstriction was abrogated. These results demonstrate that large VT inhibits airway smooth muscle contraction, regardless of mean Pbr.

Relaxant effect of magnesium and zinc on histamine-induced bronchoconstriction in dogs.

Magnesium sulfate (MgSO4) has been reported to produce bronchodilation in asthmatic patients. In vitro studies have suggested that divalent cations inhibit L-type voltage-sensitive calcium ion (Ca2+) channels in cardiac and smooth muscles. In this study, we evaluated the in vitro and in vivo effects of magnesium ion (Mg2+) and zinc ion (Zn2+) on the airway contracted by histamine. A university research laboratory. Tracheal smooth muscle from guinea pigs. Mongrel dogs. The tension of isolated guinea pig tracheal strips was measured isometrically with a force displacement transducer. The specimen was contracted with histamine (10 microM). Then, MgSO4 (n = 6), zinc sulfate (ZnSO4, n = 6), or sodium sulfate (Na2SO4, n = 6) was cumulatively added to the organ bath. The bronchial cross-sectional area of mongrel dogs was measured by a direct visualization method demonstrated previously. The dogs were randomly assigned to three groups: group Mg (n = 7), group Zn (n = 7), and group Na (n = 7). Bronchoconstriction was elicited with histamine (10 microg/kg plus 500 microg/kg/hr iv). Thirty minutes after the start of histamine infusion, 0 (saline), 1, 10, and 100 micromol/kg ZnSO4 or 1, 10, 100, and 1000 micromol/kg MgSO4 or Na2SO4 were administered intravenously in group Zn, Mg, or Na, respectively. The bronchial cross-sectional area was assessed before (basal) and 30 mins after the start of histamine infusion and 5 mins after each dose of ZnSO4, MgSO4, or Na2SO4. Arterial blood was also obtained to measure plasma levels of epinephrine and norepinephrine by gas chromatography-mass spectrometry. All data are expressed as mean +/- SEM. The doses of the divalent cations that reversed histamine-induced contraction by 50% were calculated by GraphPad Prism. MgSO4 and ZnSO4 (9.38+/-0.28 and 1.84+/-0.30 mM, respectively) relaxed histamine-contracted tracheal strip in a concentration-dependent manner, whereas Na2SO4 did not. Similarly, the in vivo study showed that MgSO4 and ZnSO4 dose-dependently reversed histamine-induced bronchoconstriction (potency, ZnSO4 > MgSO4), whereas Na2SO4 did not. In groups Mg and Zn, the plasma catecholamine levels also dose-dependently increased except when 1000 micromol/kg MgSO4 was administered. Because the divalent cations tested produced a spasmolytic effect on the contracted airway, infusion of divalent cations might be effective against asthmatic attack. However, high concentrations of these cations produce significant toxicity, so dosage will be an important concern in development of these agents.

Larynx vs. esophagus as reflexogenic sites for acid-induced bronchoconstriction in dogs.

Bronchoconstriction in asthmatic patients is frequently associated with gastroesophageal reflux. However, it is still unclear whether bronchoconstriction originates from the esophagus or from aspiration of the refluxate into the larynx and larger airway. We compared the effect of repeated esophageal and laryngeal instillations of HCl-pepsin (pH 1.0) on tracheal smooth muscle activity in eight anesthetized and artificially ventilated dogs. Saline was used as control. We used pressure in the cuff of an endotracheal tube (Pcuff) as a direct index of smooth muscle activity at the level of the larger airways controlled by vagal efferents. The Pcuff values of the first 60 s after instillations were averaged, and the difference from the baseline values was evaluated. Changes in Pcuff were significantly greater with laryngeal than with esophageal instillations (P = 0.0166). HCl-pepsin instillation into the larynx evoked greater responses than did saline (P = 0.00543), whereas no differences were detected with esophageal instillations. Repeated laryngeal exposure enhanced the responsiveness significantly (P < 0. 001). Our data indicate that the larynx is more important than the esophagus as a reflexogenic site for the elicitation of reflex bronchoconstriction in response to acidic solutions.

I.v. lidocaine worsens histamine-induced bronchoconstriction in dogs

We have assessed the effect of lidocaine (lignocaine) on histamine-induced bronchoconstriction by direct visualization with a superfine fibreoptic bronchoscope. Seven mongrel dogs were anaesthetized with pentobarbital (pentobarbitone) 30 mg kg-1 followed by 2 mg kg-1 h-1 and pancuronium 200 micrograms kg-1 h-1. The trachea was intubated with a tracheal tube containing a second lumen for insertion of a 2.2-mm fibreoptic bronchoscope. This allowed estimation of the bronchial cross-sectional area (BCA) of the third bronchial bifurcation of the right lung. We used NIH image, a public domain image processing and analysis program. Bronchoconstriction was produced with a bolus dose of histamine 10 micrograms kg-1 i.v. followed by continuous infusion of 500 micrograms kg-1 h-1. After 30 min the following i.v. doses of lidocaine were given: lidocaine 0 (saline), 0.01, 0.1, 1.0 and 10 mg kg-1 at 10-min intervals. BCA was assessed 90 s after each dose. Arterial blood sampling was performed for measurement of plasma catecholamines. Lidocaine 1.0 and 10 mg kg-1 significantly reduced histamine-decreased BCA from 69.7 (SEM 4.1)% to 59.8 (7.3)% and 34.3 (6.8)%, respectively. Plasma concentrations of catecholamines decreased significantly after lidocaine 10 mg kg-1 i.v. In addition, there was a significant correlation between percentage decreases in plasma concentrations of epinephrine (adrenaline) and norepinephrine (noradrenaline) and reduction in %BCA (epinephrine-BCA, P < 0.01, r = 0.674; norepinephrine-BCA, P < 0.01, r = 0.510). This study suggests that i.v. lidocaine may exacerbate histamine-induced bronchoconstriction by a sympatholytic effect. This may have therapeutic implications for patients with acute asthma or anaphylactic shock who may become dependent on circulating catecholamines.

Effect of phenylephrine on histamine-induced bronchoconstriction in dogs.

Although an α-adrenoceptor has been suggested to be involved in the mechanism of asthma, the effect of α1-agonist on the airway is still unclear. In this study we evaluated the effect of phenylephrine on the airway with a direct visualization method using a superfine fiberoptic bronchoscope (SFB). Seven mongrel dogs were anesthetized with pentobarbital (30 mg·kg-1 IV) and paralyzed by pancuronium (0.2mg·kg-1·h-1). The trachea was intubated with an endotracheal tube (ID 7 mm) that has a second lumen for insertion of a SFB (OD 2.2 mm) to monitor the bronchial cross-sectional area (BCA) continuously. The tip of a SFB was placed at the level between the second and third bronchial bifurcation. To assess hemodynamics, the direct arterial blood pressure (ABP) and pulmonary arterial pressure (PAP) were monitored via a femoral arterial catheter and Swan-Granz catheter. Bronchoconstriction was elicited by histamine (10 μg·kg-1+ 500 μg·kg-1·h-1_. At 30 min after the histamine was started, saline or phenylephrine (1, 10, and 100μg·kg-1) was given intravenously. The BCA and hemodynamic variables were assessed before (basal) and 30 min after the histamine was started and 5 min after saline and each phenylephrine dose. Histamine reduced BCA by 40.3±6.3%. Phenylephrine at 10 and 100 μg·kg-1 significantly increased the ABP and PAP; and it significantly decreased the BCA, by 6.5±6.9% and 14.2±7.9%, respectively. Plasma epinephrine and norepinephrine were also significantly reduced following phenylephrine 100 μg·kg-1 IV. The dose of phenylephrine that produced vasopressive actions worsened the histamine-induced bronchoconstriction slightly but significantly. Therefore, phenylephrine should be used with caution in asthmatic patients.