Bronchial Contraction Research Articles

KF19514, a phosphodieterase 4 and 1 inhibitor, inhibits PAF-induced lung inflammatory responses by inhaled administration in guinea pigs.

Phosphodiesterase (PDE) 4 inhibitors are well known for their inhibitory effect on bronchoconstriction and inflammation and may be promising anti-asthma drugs. Platelet-activating factor (PAF) has been proposed as an inflammatory mediator to be relevant to asthma. It causes bronchoconstriction, airway microvascular leakage, inflammatory cell accumulation in the lung and hyperresponsiveness. In this study, we therefore have investigated the anti-asthmatic effects of the inhaled KF19514 [5-phenyl-3'-(3-pyridyl)methyl-3H-imidazo(4,5-c)(1,8) naphthyridin-4(5H)-one], a PDE 4 and 1 inhibitor, on PAF-induced lung inflammatory responses in guinea pigs. The inhaled KF19514 (0.0001-0.01%) significantly inhibited PAF-induced eosinophil and neutrophil accumulation into the airway and hyperresponsiveness in guinea pigs. The IC50 value of KF19514 against eosinophil accumulation was 14.8 microM (0.00063%). Moreover, the effect of KF19514 on the electrical field stimulation-induced bronchial contraction was examined using the main bronchi of guinea pigs in vitro. KF19514 inhibited both cholinergic and tachykininergic contraction and, in particular, produced a potent inhibitory effect on tachykininergic contraction (IC50 = 0.49 microM). The mechanism by which KF19514 inhibited the PAF-induced hyperresponsiveness may in part be the suppression of the tachykinin release. Based on these results, it was demonstrated that the inhaled KF19514 might have a significant potential effect on the inflammatory cell accumulation and hyperresponsiveness induced by PAF.

Evidence that allergen-induced contraction of guinea pig bronchi is mediated in part by the release of tachykinins.

To study the role of tachykinins in allergic responses in the airways of guinea pigs sensitized to ovalbumin (OVA), we examined the bronchial contractile response to allergen in the presence or absence of the tachykinin antagonist FK224 in vitro. Because neutral endopeptidase (NEP) effectively cleaves tachykinins, we incubated bronchial tissues with the NEP inhibitor phosphoramidon (10(-5) M) to maintain the activity of endogenously released tachykinins. Then we added 10(-5)% (10 microns/ml) OVA in the presence or absence of FK224 (10(-5) M). FK224 significantly inhibited OVA-induced contraction plateaued and began to relax, we added 10(-5) M phosphoramidon. In the tissue without FK224, phosphoramidon blocked the relaxation and enhanced the contraction. In contrast, in the tissues treated with FK224, phosphoramidon did not enhance the OVA-induced contraction. The enhancement of the contraction induced by phosphoramidon was not inhibited by the sodium channel blocker tetrodotoxin. These results suggest that (1) allergic response causes release of tachykinin-like substances to induce bronchial contraction in part, (2) these responses are blocked by tachykinin antagonist FK224 and (3) nerve conduction is not necessary for the release of tachykinin-like substances induced by allergic response in the guinea pig bronchus.

Incubation with IgE increases cholinergic neurotransmission in human airways in vitro.

Airway cholinergic hyperresponsiveness is frequently observed in asthmatic patients. Recent reports suggest the possible involvement of IgE in hyperresponsiveness, although the exact mechanism is still uncertain. In this study, we examined whether incubation with IgE could facilitate the cholinergic function in human airways. Bronchi were obtained from 20 patients undergoing lung resection. Cholinergic contractile responses were induced by electrical field stimulation (EFS) or exogenous acetylcholine (ACh), and they were assessed by isometric tension measurement. EFS-induced ACh release from cholinergic nerves was also measured by high performance liquid chromatography. Incubation with IgE significantly enhanced EFS-induced bronchial contraction and ACh release as compared with the values of the bronchi incubated with heat inactivated IgE (control) (p < 0.05, respectively), but it did not alter the contractile responses induced by exogenous ACh. Pretreatment with the muscarinic M2-receptor agonist pilocarpine reduced the EFS-induced ACh release in the control tissues (p < 0.05), but not in the tissues incubated with IgE. The M2-receptor antagonist methoctramine significantly enhanced the EFS-induced contraction in control bronchi (p < 0.05), but this augmentation was not observed in the tissues incubated with IgE. These results suggest that IgE itself can enhance cholinergic bronchial contraction via facilitation of ACh release from cholinergic nerves and that this augmentation is related to autoreceptor M2 dysfunction at nerve endings.

Canine bronchial sustained contraction in Ca2+-free medium: role of intracellular Ca2+

We evaluated whether cartilage was a source of Ca2+ and the possible role of Ca2+ recycling in the sustained bronchial contraction (SBC) induced by carbachol (Cch) in Ca2+-free medium. Canine first-order bronchi were studied with cartilage and epithelium (+CAR + EPI) and without these structures individually (-CAR + EPI and +CAR - EPI) or together (-CAR - EPI). After cartilage removal (-CAR - EPI or -CAR + EPI) Cch produced a transient contraction in Ca2+-free medium. Removal of the epithelium alone had minor effects on the magnitude of the SBC but increased the effect of removal of cartilage to diminish the SBC. Bronchial strips with cartilage were able to respond to Cch with lower Ca2+ concentrations (10-100 microM) than could dissected preparations. Preincubation with BAY K 8644 (30-1000 nM) or 60 mM KCl or -CAR - EPI tissues converted the transient contractions to Cch in Ca2+-free medium to sustained contractions. In microelectrode studies, 50 nM Cch induced membrane oscillations in solutions with 2.5 mM Ca2+ in bronchial preparations, plus or minus cartilage, and in undissected tissues in Ca2+-free medium but not in -CAR - EPI tissues. Preincubation with 1 microM BAY K 8644 in Ca(2+)-free medium restored these oscillations in -CAR - EPI tissues. The release of 45Ca2+ from cartilage was too rapid to provide a reservoir of Ca2+ to support multiple SBCs in Ca2+-free medium. Moreover, in the Ca2+-free medium (with 10 nM Ca2+ after tissue +CAR + EPI incubation) excitatory junction potentials rapidly disappeared. Addition of 1 microM nifedipine or 1 mM EGTA during the SBC of +CAR + EPI tissues produced complete relaxation. A transient contraction to Cch occurred with prior addition of nifedipine. Inhibition of the sarcoplasmic reticulum Ca2+ pump by tissue incubation with cyclopiazonic acid (CPA; 10 microM), or briefly with 1 mM EGTA significantly diminished the SBC induced by Cch in Ca2+-free medium. CPA and EGTA together abolished the Cch-induced SBC. Thus, cartilage plays a more complex role than as a Ca2+ reservoir to support the SBC induced by Cch in Ca2+-free solution; its removal affects the process supporting SBCs involving intracellular Ca2+ storage and Ca2+ entrance through voltage-dependent channels.

Repeated allergen exposure enhances excitatory nonadrenergic noncholinergic nerve-mediated bronchoconstriction in sensitized guinea-pigs.

The effect of repeated allergen inhalation challenge on the airway excitatory nonadrenergic noncholinergic (e-NANC) nerve-mediated bronchoconstrictor response was studied in ovalbumin (OA) sensitized guinea-pigs. Three weeks after sensitization, OA inhalation, 0.03% for 3 min (challenged group), or saline inhalation (control group) was repeated every day for 4 weeks. The e-NANC nerve function was examined in vitro by means of isometric tension measurement of main bronchi. After pretreatment with atropine (10(-6) M) and propranolol (10(-6) M), we performed electrical field stimulation (EFS) or exogenous neurokinin A (NKA) administration. In the challenged group, EFS-induced main bronchial contraction was significantly greater than that of the control group (p < 0.05 or p < 0.01), but exogenous NKA-mediated responses were almost the same in both groups. The e-NANC-induced main bronchial contractions after EFS were enhanced by pretreatment with the neutral endopeptidase inhibitor, phosphoramidon, to the same degree in the control and challenged groups, indicating that the peptide degradation mechanisms were not impaired even in the challenged group. Substance P immunoreactivities in the lung of the challenged group were significantly higher than those of the control group. These results suggest that chronic airway inflammation after repeated allergen challenge increases excitatory nonadrenergic noncholinergic nerve function, possibly by enhancing sensory neuropeptide production and/or release.

Canine bronchial sustained contraction in Ca&lt;SUP&gt;2+&lt;/SUP&gt;-free medium: role of intracellular Ca&lt;SUP&gt;2+&lt;/SUP&gt;

Canine bronchial sustained contraction in Ca&lt;SUP&gt;2+&lt;/SUP&gt;-free medium: role of intracellular Ca&lt;SUP&gt;2+&lt;/SUP&gt;

Evidence that PGF2 alpha-induced contraction of isolated guinea pig bronchi is mediated in part by release of tachykinins

To investigate whether prostaglandin F2 alpha (PGF2 alpha) stimulates the release of tachykinins and whether the tachykinins play a role in the PGF2 alpha-induced bronchial contraction, we examined the contractile response to PGF2 alpha in the presence or absence of a neutral endopeptidase (NEP) inhibitor phosphoramidon in the guinea pig main bronchus in vitro. Because NEP effectively cleaves tachykinins, we hypothesized that the inhibition of NEP would enhance a PGF2 alpha-induced bronchial contraction if PGF2 alpha stimulates the release of tachykinins. Phosphoramidon significantly enhanced the concentration-response curve to PGF2 alpha. And it also significantly enhanced 10(-5) M PGF2 alpha-induced contraction. The enhancement was significantly attenuated in tissues where the tachykinins had been depleted by treatment with capsaicin. Furthermore, the enhancement of contraction was also significantly attenuated in the presence of tachykinin antagonist FK-224 (10(-5) M). Tetrodotoxin, a sodium-channel blocker that blocks nerve conduction, did not affect the enhancement. From these results we conclude that 1) PGF2 alpha causes the release of tachykinin-like substances, 2) these substances play a role in bronchial contraction in tissues where NEP activity is inhibited, and 3) nerve conduction is not necessary for the release of these substances in the guinea pig bronchus.

5-HT2-mediated bronchial responses after syngeneic lung transplantation in the rat.

1. The effect of lung transplantation was assessed on the subsequent bronchial responses to 5-hydroxytryptamine (5-HT) in the rat in vitro. 2. Bronchial ring segments from syngeneic lung transplant recipients, from sham-operated and from non-operated control animals were studied in organ baths one month after unilateral left lung transplantation. 3. Responses of the bronchial smooth muscle to 5-HT (10(-8) to 10(-4) M) significantly increased after lung transplantation (80.6 +/- 7.6% of the maximal contractile response to acetylcholine) compared with the responses of all other controls (ca. 40% of the maximal contractile response to acetylcholine, P < 0.01). pD2 values were similar for the left transplanted (5.70 +/- 0.11) and all other control bronchi (ranging from 5.53 to 5.82). 4. Contraction to 5-HT was blocked by the selective 5-HT2 antagonist, ketanserin. Responses to the selective 5-HT2 agonist, alpha-methyl-5-HT, were similar to those to 5-HT; pD2 values were similar in all groups (ranging from 5.41 to 5.74). 5. The selective 5-HT3 agonist, 1-m-chlorophenyl biguanide, had no contractile effect on rat bronchus, whether transplanted or not. 6. Atropine, a muscarinic cholinoceptor blocking agent, had no effect on 5-HT-induced bronchial contraction. Hence, acetylcholine released from nerve terminals does not play any role in the observed bronchial hyperresponsiveness to 5-HT. 7. These results show bronchial hyperresponsiveness to 5-HT in vitro one month after lung transplantation in the rat, mediated through 5-HT2 receptor activation. This might be caused by upregulation of 5-HT2 receptors in the lung after transplantation.

P3-264 - Pharmacological evaluation of inhibitoryaction of KW-4679 on tachykinin-mediated bronchial contraction

P3-264 - Pharmacological evaluation of inhibitoryaction of KW-4679 on tachykinin-mediated bronchial contraction

Arachidonic acid induces [Ca 2+] i oscillations in smooth muscle cells from human airways

The role of phospholipase A 2 (PLA 2) in mediating agonist-stimulation of bronchial contraction has not yet been studied at a cellular level. The aim of the present work was to examine the Ca 2+ signal elicited in human bronchial smooth muscle cells by exogenous arachidonic acid (AA), a first product of PLA 2 activity. To study the effect of AA (2–20 μM) on [Ca 2+] i, a single cell video imaging technique was used. AA induced various patterns of [Ca 2+] i increase; most frequently, [Ca 2+] i oscillations were observed. The amplitude of [Ca 2+] i repetitive peaks, but not the frequency, was dependent on AA concentration. In the absence of external Ca 2+, AA evoked a slower and reduced transient increase in [Ca 2+] i. It is concluded that AA or some of its metabolites release Ca 2+ from intracellular stores and that a contribution of extracellular Ca 2+ is essential for [Ca 2+] i oscillations.

Epithelium acts as a modulator and a diffusion barrier in the responses of canine airway smooth muscle.

The present study was designed to determine the role of the respiratory epithelium as a diffusion barrier and a modulator of the responsiveness of airway smooth muscle to bronchoactive agents. Segments of canine bronchi, with or without epithelium, were suspended in organ chambers and perfused intraluminally. The isometric tension was recorded. Acetylcholine, given intraluminally, induced significantly smaller contractions in bronchi with than in bronchi without epithelium. When this agonist was given extraluminally, no difference in contractions was noted between the tissues. In the presence of acetylcholine and phentolamine, norepinephrine, given either intra- or extraluminally, induced significantly larger relaxations in bronchi with than in bronchi without epithelium. High potassium given intraluminally induced contractions only in bronchi without epithelium; however, in the presence of ouabain, both tissues contracted similarly. When high potassium was given extraluminally, no difference in contraction between tissues with and without epithelium was noted. When [3H]acetylcholine and [3H]norepinephrine were perfused intraluminally, the accumulation of 3H radioactivity in the extraluminal solutions was significantly less in bronchi with than in bronchi without epithelium. These observations suggest that the epithelium acts as both a diffusion barrier and a modulator of the responses of canine airways to bronchoactive agents.

Evidence that nitric oxide partially mediates capsaicin-induced relaxation in the rat gastric fundus

Summary: Isbufylline (1,3-dimethyl-7-isobutylxanthine) is a new xanthine derivative claimed to possess remarkable antibronchospastic properties coupled to reduced pro-convulsive side-effects. In guinea-pig bronchial preparations, isbufylline showed a differential and more pronounced, as compared to theophylline, relaxant activity on tonic bronchial contractions evoked by exogenous administration of equieffective concentrations of capsaicin (0.3 μM), neurokinin A (0.1 μM) and carbachol (0.3 μM) (in the presence of indomethacin 5 μM and thiorphan 10 μM). Isbufylline gave an IC50 of 21 (19-25, 95% confidence limits) μM on capsaicin-evoked contractile effects, and 36 (30-43) μM on carbachol-produced contractile effects, whilst it was almost ineffective in inhibiting neurokinin A-induced bronchospasm (IC50 not evaluable, > 100 μM). 'In vitro' studies were also performed using electrical field stimulation (EFS) to produce non-adrenergic non-cholinergic (NANC)- or cholinergic nerves-mediated contractions in guinea-pig isolated bronchi or trachea. Isbufylline (10-90 μM) produced a concentration-dependent inhibition of the NANC response (EFS: 20 Hz, supramaximal voltage, 0.5 ms pulse, width for 10 s) of bronchi (IC50=47 μM) without affecting the cholinergic contractile response in tracheal smooth muscle (EFS: 0.5 up to 32 Hz, supramaximal voltage, 0.5 ms pulse, for 15 s every min). The activity of isbufylline was also confirmed in anaesthetized guinea-pig showing a greater antibronchospastic activity towards capsaicin (8 nmol/kg iv) or vagal non-cholinergic (10 V, 1 ms, 20 Hz for 20 s) stimulation as compared to the inhibition exerted against acetylcholine (50 nmol/kg iv) or neurokinin A (1 nmol/kg iv). These results indicate that isbufylline may inhibit the bronchomotor action of capsaicin-sensitive sensory nerves in the guinea-pig at concentrations lower than those necessary to relax cholinergic- or NKA-precontracted bronchial preparations.

Isbufylline, a Xanthine Derivative, Inhibits Bronchoconstrictor Responses Produced by Stimulation of Capsaicin-sensitive Sensory Nerves in Guinea-pig: 'In Vitro' and 'In Vivo' Evidence

Summary: Isbufylline (1,3-dimethyl-7-isobutylxanthine) is a new xanthine derivative claimed to possess remarkable antibronchospastic properties coupled to reduced pro-convulsive side-effects. In guinea-pig bronchial preparations, isbufylline showed a differential and more pronounced, as compared to theophylline, relaxant activity on tonic bronchial contractions evoked by exogenous administration of equieffective concentrations of capsaicin (0.3 μM), neurokinin A (0.1 μM) and carbachol (0.3 μM) (in the presence of indomethacin 5 μM and thiorphan 10 μM). Isbufylline gave an IC50 of 21 (19-25, 95% confidence limits) μM on capsaicin-evoked contractile effects, and 36 (30-43) μM on carbachol-produced contractile effects, whilst it was almost ineffective in inhibiting neurokinin A-induced bronchospasm (IC50 not evaluable, > 100 μM). 'In vitro' studies were also performed using electrical field stimulation (EFS) to produce non-adrenergic non-cholinergic (NANC)- or cholinergic nerves-mediated contractions in guinea-pig isolated bronchi or trachea. Isbufylline (10-90 μM) produced a concentration-dependent inhibition of the NANC response (EFS: 20 Hz, supramaximal voltage, 0.5 ms pulse, width for 10 s) of bronchi (IC50=47 μM) without affecting the cholinergic contractile response in tracheal smooth muscle (EFS: 0.5 up to 32 Hz, supramaximal voltage, 0.5 ms pulse, for 15 s every min). The activity of isbufylline was also confirmed in anaesthetized guinea-pig showing a greater antibronchospastic activity towards capsaicin (8 nmol/kg iv) or vagal non-cholinergic (10 V, 1 ms, 20 Hz for 20 s) stimulation as compared to the inhibition exerted against acetylcholine (50 nmol/kg iv) or neurokinin A (1 nmol/kg iv). These results indicate that isbufylline may inhibit the bronchomotor action of capsaicin-sensitive sensory nerves in the guinea-pig at concentrations lower than those necessary to relax cholinergic- or NKA-precontracted bronchial preparations.

Bronchial contractions in transplanted lungs: Influence of denervation, acute rejection, and the bronchial epithelium

The effects of pulmonary denervation and rejection on contractions of bronchial smooth muscle and epithelial modulation of these contractions were studied in dogs after denervation in right lung autotransplantation (n = 6) and acute rejection after right lung allotransplantation (n = 8). Immunosuppression was withdrawn from the latter group after 5 days; rejection developed after 3 additional days. A significant (p < 0.05) increase in mean peak airway pressure occurred with rejection of allotransplanted lungs. Rings cut from third-order bronchi of transplanted and contralateral unoperated (native) lungs in each animal were suspended in organ chambers for the measurement of isometric force. In some rings, the epithelium was removed mechanically. Acetylcholine (cholinergic neurotransmitter), serotonin (platelet-product), histamine (mast cell product), and endothelin-1 (endothelium-derived contracting factor) caused concentration-dependent contractions in all rings. In bronchi from native lungs, rings with epithelium contracted less than those without epithelium. This difference was lost after autotransplantation. The smooth muscle and epithelium were affected differently by autotransplantation. Contractions of rings without epithelium decreased in response to acetylcholine and endothelin-1, whereas contractions of rings with epithelium increased in response to histamine and 5-hydroxytryptamine (p < 0.05). During acute rejection, contractions were the same as those after autotransplantation. Bronchial content of endothelin increased fourfold with rejection. Relaxations to isoproterenol and prostaglandin E2 were similar in both groups. In conclusion, denervation reduced the ability of the smooth muscle to contract. The degree of acute pulmonary rejection seen in this study did not further affect bronchial contractions. Modulation of contractions by the bronchial epithelium was lost with both denervation and rejection.

Effect of thiazide diuretics against neurally mediated contraction of guinea pig airways. Contribution of carbonic anhydrase.

The effect of thiazide diuretics on neurally and agonist-induced contractile responses of guinea pig airways in vitro were investigated. Tracheal or bronchial strips were suspended in organ baths and isometric tension recorded. Chlorothiazide (CTZ, 10(-4) to 3 x 10(-3) M), hydrochlorothiazide (HCTZ, 10(-3) M), and dichlorphenamide (DCPM, 10(-3) M) significantly potentiated contraction of tracheal strips induced by electrical field stimulation (EFS). They also increased acetylcholine (ACh)- but not carbachol-induced tracheal contraction. In the presence of atropine and propranolol, on the other hand, CTZ and DCPM but not HCTZ significantly inhibited EFS-induced contraction in bronchial strips. We determined whether carbonic anhydrase inhibition could mimic the effects of CTZ and DCPM. Acetazolamide (ATZ), an inhibitor of carbonic anhydrase, had no effect on either EFS- or ACh-induced contraction in tracheal strips but significantly inhibited nonadrenergic, noncholinergic (NANC) contractile responses induced by EFS in bronchial strips. CTZ, DCPM, and ATZ did not affect substance P-induced contractile responses in the bronchi. We conclude that CTZ, DCPM, and ATZ attenuate NANC neurally mediated bronchial contraction by preventing the release of contractile neuropeptides from sensory nerve endings. This effect may occur through inhibition of carbonic anhydrase activity. In addition, thiazide diuretics potentiate contractile responses to ACh in the trachea, probably through inhibition of acetylcholinesterase activity.

Effect of ozone exposure in vivo on response of bronchial rings in vitro: role of intracellular Ca2+.

In this study we investigated the role of intracellular Ca2+ in ozone- (O3) induced airway hyperresponsiveness. Acetylcholine-induced airway responses were measured before and after inhalation of O3 (3 ppm, 30 min) or dry air. In vitro experiments were performed with intact ring segments of third- to fifth-order bronchi. Bronchial responses to carbachol (CCh) were evaluated in Krebs solution (2.5 mM Ca2+) and in Ca(2+)-free [0.1 mM ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA)] Krebs solution with or without indomethacin (IDM, 10(-5) M) and were expressed as percentage of the maximal KCl response (60 mM). Inhalation of O3, but not dry air, caused airway hyperresponsiveness to acetylcholine in vivo. Responses to 50% effective concentrations of CCh were similar in bronchial preparations from O3 and control animals (with or without IDM) in normal Krebs solution. In Ca(2+)-free solution, CCh induced a sustained (20-min) bronchial contraction. These contractions relaxed immediately when nifedipine or a high EGTA concentration was added to the organ bath. The sustained contraction was abolished when the tissues had been incubated with cyclopiazonic acid (10(-5) M), a novel inhibitor of the sarcoplasmic reticulum Ca2+ pump. After O3 exposure, responses of the bronchial smooth muscle (in Ca(2+)-free medium without IDM) were increased (P < 0.05) compared with controls during the first and second CCh stimulations. This O3-induced increase in response to CCh in Ca(2+)-free solution was abolished when the tissues were incubated with IDM.(ABSTRACT TRUNCATED AT 250 WORDS)

Postjunctional inhibitory effect of the NK2 receptor antagonist, SR 48968, on sensory NANC bronchoconstriction in the guinea-pig.

1 The effects of a selective NK2 receptor antagonist, SR 48968, on non-adrenergic non-cholinergic (NANC) bronchoconstriction in the guinea-pig were investigated in both in vitro and in vivo studies. 2 In isolated bronchus, the electrical field stimulation (EFS, 1 Hz for 1 min)-induced NANC bronchoconstriction was inhibited by 83% after preincubation with SR 48968 (10(-7) M) for 1 h. The selective NK1 receptor antagonist, CP 96,345 (10(-6) M), together with SR 48968 completely abolished the remaining EFS-evoked NANC bronchial contraction. ST 48968 (10(-7) M) totally blocked the bronchial contraction caused by neurokinin A (NKA), but reduced only slightly the bronchoconstriction caused by high concentrations of substance P (SP) and did not influence the response to acetylcholine (ACh). 3 In the guinea-pig isolated perfused lung, SR 48968 (5 x 10(-7) M) perfusion for 30 min markedly reduced, by 95% and 68% respectively, the increase in lung resistance (RL) and the decrease in dynamic compliance (CDyn) evoked by vagal stimulation (1 Hz for 1 min). Capsaicin (10(-8) M)-evoked bronchoconstriction was also significantly inhibited by SR 48968 (5 x 10(-7) M). However, the same concentration of SR 48968 did not affect the release of neuropeptide calcitonin gene-related peptide (CGRP)-like immunoreactivity (LI) evoked by either vagal stimulation or capsaicin in the isolated perfused lung, suggesting no prejunctional action. SR 48968 (5 x 10-7 M) caused a parallel shift of the concentration response curve to the right by a factor of 10 for the bronchoconstriction evoked by NKA(l0-9-3 x 10-7 M) in the isolated lung, while it abolished the contraction induced by the selective NK2 receptor agonist, Nle10 NKA(4-10) (10-9-3 x 10- 7 M).4. In in vivo studies, ST 48968 (0.3 mg kg-1, i.v.) also greatly inhibited the increase in insufflation pressure evoked by either capsaicin (10 microg kg-'1 i.v.) or NKA (1 microg kg-1, i.v.), without any measurable effect on the accompanying hypotensive responses.5. The results suggest: (i) ST 48968 is a selective and potent NK2 postjunctional receptor antagonist both in vitro and in vivo in the guinea-pig, and (ii) the NANC bronchoconstriction evoked by sensory nerve activation either by antidromic nerve stimulation or by capsaicin is mediated mainly via NK2 receptors and only to a minor extent via NK, receptors.

Respiratory epithelium modulates the responses of canine bronchi to cooling.

The present study was designed to investigate the effect of cooling on the modulatory role of the respiratory epithelium on the underlying smooth muscle. Canine bronchial rings and segments (with or without epithelium) were suspended in organ chambers and perfused with modified Krebs-Ringer bicarbonate solution, respectively. Isometric force was recorded. Cooling did not affect the resting tension of the bronchi. During contractions to carbachol, cooling evoked contractions in bronchi with epithelium but relaxations in those without epithelium. In the presence of indomethacin, cooling induced contractions in both preparations with and without epithelium. The contractions in bronchi with epithelium were significantly larger than those in bronchi without epithelium. After treatment with indomethacin, exogenous arachidonic acid potentiated the cooling-induced contractions in preparations with epithelium but not in those without epithelium. This potentiation was not affected by nordihydroguaiaretic acid. SKF 525-A and metyrapone, inhibitors of cytochrome P-450 monooxygenases, converted the cooling-induced contractions of preparations with epithelium to relaxations and had no significant effects on the responses of preparations without epithelium. These observations suggest that cooling induces from the epithelium the release of a cytochrome P-450-derived eicosanoid that potentiates contractions of the underlying airway smooth muscle to carbachol.

Endothelium-derived factors modulate contraction of bronchial smooth muscle.

Experiments were designed to determine how changes in the ratio of specific vascular endothelium-derived factors might affect reactivity of bronchial smooth muscle. The epithelium was mechanically removed from rings of third-order canine bronchi, and the rings were suspended in organ chambers for measurement of isometric force. Rings of pulmonary artery were cut; in some the endothelium was mechanically removed. The arterial rings were everted and pairs, with and without endothelium, were incubated with control solution, NG-monomethyl-L-arginine (L-NMMA), indomethacin, or both L-NMMA and indomethacin for 90 min. They were then inserted into the lumen of the bronchial rings. Cumulative concentration-response curves to acetylcholine and 5-hydroxytryptamine were obtained. There was no significant difference in response between bronchi containing arteries with or without endothelium incubated with control solution. Contractions of bronchi containing arteries without endothelium, incubated in either L-NMMA or indomethacin, increased from control. However, in rings containing arteries with endothelium, incubation with either inhibitor decreased bronchial contractions. Incubation with both inhibitors eliminated the difference. These results suggest that the vascular endothelium produces factors that can both contract and relax bronchial smooth muscle. With inhibition of production of either nitric oxide with L-NMMA or prostanoids with indomethacin, release of other endothelium-derived factors occurs that attenuates contractions of bronchial smooth muscle. Therefore, an imbalance in the ratio of production of endothelium-derived factors may contribute to bronchospastic disorders.

Effect of a new leukotriene receptor antagonist, ONO-1078, on human bronchial smooth muscle in vitro

Peptide leukotrienes (LT) have been postulated to play a major role in the etiology of bronchial asthma. The present study investigated the effect of a new peptide LT receptor antagonist, ONO-1078, on isolated human bronchial smooth muscle in vitro. Helical strips of bronchi were suspended in the organ baths filled with 37°C Krebs solution and mechanical responses were recorded isometrically. ONO-1078 produced dose-dependent relaxations, which suggested that the spontaneous basal tone was in part mediated by LT. ONO-1078 caused dose-dependent relaxations of the tissues which were precontracted with LTC 4 or LTD 4 (3 × 10 −8 M). Pretreatment of bronchi with ONO-1078 (10 −8 M, 10 −7 M) significantly inhibited dose-dependent contractions induced by LTC 4 and LTD 4. ONO-1078 (10 −6 M) also significantly reduced the antigen-induced contractions in bronchi passively sensitized with atopic serum from mite-allergic patients. Moreover the combination of an H 1-receptor antagonist, diphenhydramine (10 −5 M), and ONO-1078 (10 −6 M) completely abolished the antigen-induced contractions. The present findings demonstrate that ONO-1078 is a potent antagonist of exogenous and endogenous LT in the human airway. The selective LT antagonist such as ONO-1078 may be valuable in the therapy of allergic asthma.