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Biomedical subjects

P J Barnes

Publications and source records attributed to P J Barnes.

At least 19 recordsLinked to original sources
PubMed1992

Tolerance to the nonbronchodilator effects of inhaled beta 2-agonists in asthma.

BACKGROUND: Tolerance to the direct bronchodilator effects of beta 2-agonists does not appear to occur in asthma. However, it is not known whether this is true for the nonbronchodilator effects of these agents, which protect the airways against bronchoconstrictive stimuli. METHODS: We investigated whether tolerance develops to the protective effect of inhaled terbutaline on airway responsiveness to the bronchoconstrictors methacholine (which acts directly on airway smooth muscle) and AMP (which acts indirectly by stimulating the release of mediators from mast cells) during sustained treatment with terbutaline. In a randomized, double-blind, crossover study, 12 patients with mild asthma each inhaled a single dose of terbutaline (500 micrograms) or placebo before a challenge with a series of doubling doses of inhaled methacholine or AMP, before and after treatment for seven days with 500 micrograms of terbutaline four times daily or placebo. RESULTS: Before the seven days of treatment with terbutaline, a single dose of terbutaline reduced airway responsiveness to methacholine by 2.7 doubling doses (95 percent confidence interval, 1.9 to 3.5), but it had an even greater protective effect against AMP, reducing airway responsiveness by 3.8 doubling doses (95 percent confidence interval, 2.7 to 4.9; P less than 0.001). After seven days of treatment with terbutaline, the protective effect of terbutaline against methacholine decreased to 2.2 doubling doses (95 percent confidence interval, 1.3 to 3.0; P = 0.04), and that against AMP decreased even more, to 1.7 doubling doses (95 percent confidence interval, 1.1 to 2.4; P less than 0.001). By contrast, the bronchodilator response to terbutaline was unchanged during seven days of treatment with this agent. CONCLUSIONS: We observed tolerance to the nonbronchodilator actions of the inhaled beta 2-agonist terbutaline in patients with mild asthma, an effect that may be more pronounced in mast cells than in bronchial smooth muscle. This property of beta-agonists may constitute a drawback to their regular use in patients with asthma.

Adenosine Monophosphate↗
PubMed1992

The effect of endogenous nitric oxide on neurogenic plasma exudation in guinea-pig airways.

We studied the effect of endogenous nitric oxide (NO) on vagally induced plasma exudation into guinea-pig trachea and main bronchi using 125I-albumin as a plasma marker. NG-Nitro-L-arginine methyl ester (L-NAME, 1-10 mg/kg) dose dependently inhibited neurogenic plasma exudation. Intravenous phenylephrine which simulated the vasopressor effect as L-NAME (10 mg/kg) was without effect. The effect of L-NAME (5 mg/kg) was reversed by L-arginine (50 mg/kg). These results suggest that endogenous NO may contribute to neurogenic inflammation in the airways.

Animals↗
PubMed1992

The effect of anion transport inhibitors and extracellular Cl- concentration on eosinophil respiratory burst activity.

Furosemide has been shown recently to protect asthmatic patients against certain bronchoconstrictor challenges. We investigated the effect of furosemide on eosinophil function. Since furosemide may be exerting its inhibitory effect on the eosinophil by inhibiting anion transport, we also assessed the effects of the anion transport inhibitors 5-nitro-2-(3-phenylpropylamino)-benzoic acid (NPPB) and 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid (DIDS). Furosemide, NPPB and DIDS inhibited the eosinophil respiratory burst in response to leukotriene B4 (LTB4) and, to a smaller extent, inhibited the response to opsonized zymosan (OZ). To assess whether the anion transport inhibitors were achieving their inhibitory effect by inhibiting an influx of Cl- ions into the eosinophil, the effect of removing extracellular Cl- on eosinophil function was determined. OZ-induced H2O2 production was inhibited by removing extracellular Cl- whereas the LTB4 response was not affected by the concentration of extracellular Cl-.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1992

K+ channel activator inhibition of neurogenic goblet cell secretion in guinea pig trachea.

A potassium (K+) channel activator, BRL 38227, inhibited goblet cell secretion in guinea-pig trachea induced by either electrical stimulation of the vagus nerves or acute inhalation of cigarette smoke, two stimuli which activate both cholinergic nerves and capsaicin-sensitive sensory nerves. BRL 38227 failed to inhibit methacholine- or substance P-induced goblet cell secretion which suggests that K+ channel activators inhibit neurogenic goblet cell secretion via a prejunctional effect on cholinergic and sensory nerves.

Animals↗
PubMed1992

Capsazepine as a selective antagonist of capsaicin-induced activation of C-fibres in guinea-pig bronchi.

We investigated the action of capsazepine, an antagonist of the actions of capsaicin on sensory neurones, on the contractile responses evoked by capsaicin or by electrical field stimulation (EFS) in guinea-pig bronchi. Capsazepine (10(-5) M) selectively inhibited responses to capsaicin, producing a significant change in EC50 values but not the Hill coefficient (nH), suggesting that capsazepine acts as a competitive antagonist (apparent pKB = 5.12) whereas ruthenium red is a non-competitive antagonist. Capsazepine and ruthenium red were without effect on EFS-induced responses.

Animals↗
PubMed1992

Effect of maturation on histamine-induced airflow obstruction and airway microvascular leakage in guinea pig airways.

To study the effect of maturation on histamine-induced airflow obstruction and airway microvascular leakage, we measured concomitant changes in lung resistance (RL) and in extravasation of Evans Blue dye in the airways of anesthetized immature (aged 14 +/- 2 days) and adult guinea pigs (aged 60 +/- 12 days). RL was measured for 6 min after iv. histamine (0, 5, 15, 30 and 50 micrograms/kg). For comparison, responses after 1 microgram/kg substance P were also examined. After measurement of RL, microvascular leakage in trachea, main bronchi, and proximal and distal intrapulmonary airways was also examined in the same animal. Immature animals required a larger dose of histamine than adults to achieve a similar degree of maximal bronchoconstriction after histamine. In contrast, equal doses of histamine (15 and 30 micrograms/kg) induced a significantly greater extravasation of dye in immature airways in both proximal and distal intrapulmonary airways, although not in trachea or main bronchi. Substance P did not cause any age-related differences in dye extravasation at any airway level. These results suggest that i.v. histamine specifically causes a greater degree of airway microvascular leakage in peripheral airways but induces less smooth muscle contraction in the airways of immature guinea pigs than in the airways of adult animals.

Aging↗
PubMed1992

Effect of Hoe 140, a new bradykinin receptor antagonist, on bradykinin- and platelet-activating factor-induced bronchoconstriction and airway microvascular leakage in guinea pig.

We have investigated the effect of a new bradykinin receptor antagonist, Hoe 140 (D-Arg- Hyp3,Thi5,D-Tic7,Oic8]-bradykinin), on bradykinin- and platelet-activating factor (PAF)-induced bronchoconstriction and airway microvascular leakage in anesthetized guinea pigs. Extravasation of Evans blue dye and lung resistance were measured simultaneously. Both i.v. (15 nmol/kg) and inhaled bradykinin (1 mM, 45 breaths) caused a significant increase in lung resistance and leakage of dye at all airway levels. Hoe 140 (100 nmol/kg i.v.) almost completely inhibited these airway responses induced by bradykinin except for dye extravasation in trachea induced by inhaled bradykinin. Inhaled PAF (3 mM, 30 breaths) significantly increased lung resistance and leakage of due at all airway levels, but Hoe 140 had no effect on these responses. Bradykinin-induced bronchoconstriction and airway microvascular leakage are predominantly mediated by activation of B2 receptor, since Hoe 140 is a B2 receptor antagonist. Bradykinin receptor-mediated mechanisms do not play an important role on inhaled PAF-induced bronchoconstriction and microvascular leakage.

Administration, Inhalation↗
PubMed1992

Calcium-activated potassium channels mediate prejunctional inhibition of peripheral sensory nerves.

Activation of several receptors, including mu-opioid, alpha 2-adrenergic, and neuropeptide Y receptors, inhibits excitatory nonadrenergic noncholinergic (NANC) neural responses in airways, which were mediated by the release of peptides from capsaicin-sensitive sensory nerves. This raises the possibility of a common inhibitory mechanism, which may be related to an increase in K+ conductance in sensory nerves. To examine this hypothesis, we have studied whether K(+)-channel blockers inhibit the effects of neuromodulators of sensory nerves in guinea pig bronchi by using selective K(+)-channel blockers. Charybdotoxin (ChTX; 10 nM), which blocks large conductance Ca(2+)-activated K(+)-channel function, completely blocked and reversed the inhibitory effects of a mu-opioid agonist, neuropeptide Y, and an alpha 2-adrenoceptor agonist on excitatory NANC responses. Neither inhibitors of ATP-sensitive K+ channels (BRL 31660 or glibenclamide, both at 10 microM) nor an inhibitor of small conductance Ca(2+)-activated K+ channels (apamin; 0.1 microM) were effective. This suggests that ChTX-sensitive K(+)-channel activation may be a common mechanism for the prejunctional modulation of sensory nerves in airways. This may have important implications for the control of neurogenic inflammation.

Adenosine Triphosphatases↗
PubMed1992

Nitric oxide is the endogenous neurotransmitter of bronchodilator nerves in humans.

In human airways, there is a prominent neural bronchodilator mechanism which is non-adrenergic. In human tracheal segments, we have demonstrated that this response is mediated entirely by nitric oxide (NO), since an inhibitor of NO synthesis, L-NG-nitroarginine methyl ester (L-NAME) (10(-4) M) abolishes this neural response. Identification of the neurotransmitter of this bronchodilator pathway may now make it possible to study its role in physiological control of airway calibre and in airway disease.

Adolescent↗
PubMed1992

Effect of neutral endopeptidase inhibitor on airway function and bronchial responsiveness in asthmatic subjects.

We determined the effect of an inhibitor of neutral endopeptidase, acetorphan, on the skin responses to substance P and on the bronchostrictor effects of sodium metabisulphite aerosol in asthmatic subjects. One hour following ingestion of acetorphan (200 mg) or placebo tablets, cutaneous responses to substance P were performed in four subjects. In seven subjects, bronchial challenge with increasing concentrations of sodium metabisulphite solutions was performed and the concentration required to cause a 20% fall in baseline FEV1 determined (PC20). On the acetorphan day, there was a significant increase in the wheal and flare responses to substance P and to the diluent (0.9% NaCl) alone. However, there was no significant effect of acetorphan on the PC20 metabisulphite. We conclude that metabisulphite airway challenge in vivo may not invoke the release of endogenous neuropeptides. However, the degree of inhibition of neuropeptide breakdown by the oral dose of acetorphan used may not have been optimal.

Adult↗
PubMed1992

Modulation of neurally mediated airway microvascular leakage in guinea-pig airways by beta 2-adrenoceptor agonists.

The effect of two beta 2-adrenoceptor agonists, salbutamol (100 micrograms/kg i.v.) and broxaterol (100 micrograms/kg i.v.), on airway microvascular leakage induced by vagal stimulation was studied in anaesthetised guinea pigs. Airway microvascular leakage was measured by Evans blue extravasation. Broxaterol, but not salbutamol, inhibited Evans blue dye extravasation at all airway levels, an effect prevented by pretreatment with propranolol (1 mg/kg). Neither of the beta 2-agonists had any effect on substance P-induced Evans blue dye extravasation. Broxaterol inhibits the prejunctional release of tachykinins from airway sensory nerves by stimulation of beta-receptors. The mechanism by which beta-adrenoceptor agonists prevent airway microvascular leakage deserves further study.

Adrenergic beta-Agonists↗
PubMed1992

Ibuprofen augments bradykinin-induced glycoconjugate secretion by human nasal mucosa in vivo.

Bradykinin (BK) stimulates vascular permeability and glycoconjugate secretion in human nasal mucosa. Since some of the effects of BK may be mediated by autocrine generation of arachidonic acid metabolites, the influence of ibuprofen, a cyclooxygenase inhibitor, on BK-induced nasal secretion was studied. Six normal male subjects had nasal provocations with 0, 10, 100, and 1000 nmol of BK before and after treatment with 400 mg of ibuprofen. Secretions were collected by nasal lavage. Total protein (marker of protein secretion), glycoconjugate (mucous cell marker), lysozyme (serous cell marker), and albumin (marker of vascular permeability) were measured. Basal glycoconjugate secretion was higher after ibuprofen (219 +/- 32 micrograms/ml) than before (81 +/- 56 micrograms/ml; p less than 0.05 by analysis of variance). BK stimulated significant, dose-dependent albumin, total protein, and glycoconjugate secretion. Lysozyme secretion was not stimulated. BK (1000 nmol) significantly increased total protein secretion, tenfold to twentyfold, and albumin secretion by 40-fold to 60-fold. Ibuprofen did not alter BK-induced total protein or albumin secretion. Glycoconjugate secretion after ibuprofen treatment was significantly higher than normal at 10 nmol (p less than 0.05), 100 nmol (p less than 0.02), and 1000 nmol of BK (519 micrograms/ml +/- 74 versus 213 +/- 15 micrograms/ml; p less than 0.05). Therefore, BK induces vascular permeability and exocytosis from glycoconjugate-containing cells but does not stimulate serous cells. Ibuprofen increases baseline secretion of glycoconjugate and enhances BK-induced glycoconjugate secretion. Ibuprofen does not alter BK-induced vascular permeability.

Adult↗
PubMed1992

Questions about inhaled beta 2-adrenoceptor agonists in asthma.

The safety of the most widely prescribed antiasthma drugs, beta 2-adrenoceptor agonists, has recently been questioned. Issues such as their suitability for long-term and regular prophylactic use are addressed in this Comment article by Peter Barnes and Fan Chung, who examine the possibility that the beta 2-agonists themselves contribute to worsening symptoms in asthma patients, thus setting up a vicious circle with greater use of the drugs. They conclude that it would be prudent to restrict the use of beta 2-agonists in asthma to on-demand immediate symptom control.

Administration, Inhalation↗
PubMed1992

Bleomycin-induced lung injury in rats selectively abolishes hypoxic pulmonary vasoconstriction: evidence against a role for platelet-activating factor.

1. The role of platelet-activating factor in the attenuated hypoxic pulmonary vasoconstriction associated with lung injury was evaluated using specific platelet-activating factor antagonists and an isolated perfused lung preparation. 2. Intratracheal bleomycin was administered to rats to produce acute lung injury. Animals received intratracheal saline (control), intratracheal bleomycin or the platelet-activating factor antagonists BN 52021, WEB 2170 or WEB 2086 before and after bleomycin treatment. Forty-eight hours after intratracheal administration of bleomycin or saline the animals were killed. 3. The increases in pulmonary artery pressure during two periods of hypoxic ventilation and in response to 0.2 microgram of angiotensin II were measured. Acetylcholine-induced vasodilatation after pre-constriction with prostaglandin F2 alpha was also measured. To quantify lung injury, the wet/dry ratio of lung weight was determined. 4. Bleomycin treatment attenuated the first and second hypoxic pressor responses by 93% and 77%, respectively, but not the pressor response to angiotensin II nor the vasodilator response to acetylcholine. BN 52021 plus bleomycin augmented the first hypoxic pressor response compared with bleomycin treatment alone, but the structurally unrelated platelet-activating factor antagonists WEB 2170 and WEB 2086 had no significant effect on the bleomycin-induced attenuation of hypoxic pulmonary vasoconstriction. None of the platelet-activating factor antagonists blocked the increase in the wet/dry lung weight ratio induced by bleomycin. 5. Bleomycin-induced lung injury selectively attenuates hypoxic pulmonary vasoconstriction, an effect that does not appear to be mediated by platelet-activating factor. The mechanism remains to be elucidated, but may involve destruction of the hypoxic 'sensor' within the respiratory tract.

Acetylcholine↗
PubMed1992

Role of inflammatory mediators in asthma.

Release of inflammatory mediators such as histamine and products of arachidonic acid metabolism has been demonstrated in bronchoalveolar lavage fluid of patients with asthma. Their precise cellular source is not clear but many cells types such as eosinophils, macrophages and mast cells may contribute to the generation of a wide variety of chemical mediators. These can mimic many of the features associated with asthma including bronchoconstriction, bronchial hyperresponsiveness and airway microvascular leakage. Development of specific mediator receptor antagonists or inhibitors of mediator synthesis may clarify the role of particular inflammatory mediators such as the sulphidopeptide leukotrienes or platelet-activating factor in asthma. It seems unlikely that only one particular mediator is responsible for all the manifestations of asthma.

Asthma↗