Claes-Göran Löfdahl

Inhaled formoterol inhibits histamine-induced airflow obstruction and airway microvascular leakage

We studied the effects of inhaled formoterol (0.75 mg/ml, 60 breaths = 26 micrograms), a long-acting beta 2-adrenoceptor agonist, or of the more short-acting drug, salbutamol (25 mg/ml, 60 breaths = 875 micrograms), on acute airflow obstruction and airway microvascular leakage (MVL) induced by inhaled histamine in anesthetized guinea pigs. Lung resistance (RL) and its recovery following hyperinflation (recovery RL) were measured for 6 min after histamine (1 or 2 mg/ml, 30 breaths) in animals pretreated with either inhaled beta 2-adrenoceptor agonist or inhaled saline (0.9%, 60 breaths). MVL was measured by determining the amount of extravasated Evans blue dye at various airway levels. Histamine increased RL dose dependently with a mean peak RL (+/- S.E.M.) of 13.1 +/- 2.41 cmH2O/ml per s after 2 mg/ml of histamine. Both formoterol and salbutamol significantly inhibited both peak and recovery RL and MVL to a similar degree. There was a significant correlation between the degree of extravasated dye and both peak and recovery RL, suggesting that MVL partly contributes to histamine-induced airflow obstruction. Formoterol is approximately 35 times more potent than salbutamol to inhibit both MVL and airflow obstruction induced by histamine aerosol.

Leukotriene D4- and prostaglandin F2 alpha-induced airflow obstruction and airway plasma exudation in guinea-pig: role of thromboxane and its receptor.

1 We studied the effects of a thromboxane A2 receptor (TP receptor) antagonist, ICI‐192,605 (0.5 mg kg−1, i.v.) and a selective thromboxane (Tx) synthetase inhibitor, OKY‐046 (30 mg kg−1, i.v.), on airway responses induced by leukotriene D4 (LTD4; 0.2 nmol) or prostaglandin F2α (PGF2α; 20 nmol) instilled via the airways route to anaesthetized guinea‐pigs. For a comparison, airway responses to a TxA2‐mimetic, U‐46619 (0.02 nmol) were also studied. We measured both lung resistance (RL) to monitor airflow obstruction, and extravasation of Evans Blue dye to quantify airway plasma exudation. 2 Instilled LTD4 into the tracheal lumen induced an immediate peak and subsequently persistent increase in RL and produced a large amount of extravasation of Evans Blue dye at all airway levels. Both ICI‐192,605 and OKY‐046 significantly attenuated the persistent increase in RL following the immediate response and reduced LTD4‐induced extravasation of Evans Blue dye in the trachea and proximal intrapulmonary airway. Instilled LTD4 produced significant increases in immunoreactive TxB2 in bronchoalveolar lavage fluid obtained 1.5 min after instillation of LTD4. 3 Instilled PGF2α into the tracheal lumen induced an immediate increase in RL which peaked at approximately 15 s. We also observed a delayed sustained increase in RL, reaching a second peak at approximately 4 min. PGF2α produced small but significant increases in the amount of Evans Blue dye at all airway levels. As with PGF2α, instillation of U‐46619 produced a biphasic increase in RL and extravasation of Evans Blue dye. The potency of PGF2α in inducing these airway responses was about 1000 times less than U‐46619. ICI‐192,605 abolished both the immediate and the delayed increase in RL after PGF2α, and also blocked PGF2α‐induced extravasation of Evans Blue dye. However, OKY‐046 had no inhibitory effects on these responses. 4 We conclude that airflow obstruction and airway plasma exudation induced by instilled LTD4 is, in part, mediated via TxA2 generation and subsequent activation of TP‐receptors. On the other hand, instilled PGF2α, while inducing similar responses, does so primarily by direct activation of TP receptors, rather than via TxA2 generation.

Pharmacological basis for duration of effect: formoterol and salmeterol versus short-acting beta 2-adrenoceptor agonists.

The mechanisms behind the long duration of bronchodilating action of the β2-adrenoceptor agonists formoterol and salmeterol are only partially understood. This review compares pharmacological characteristics of long-acting versus short-acting β2-adrenoceptor agonists in human and animal airways. Based upon the reviewed evidence, it is concluded that for β2-adrenoceptor agonists, long duration of action may depend upon several factors. Both formoterol and salmeterol display a higher lipophilicity and have a higher affinity, selectivity, and potency than most short-acting agonists at the β2-adrenoceptor. Of these factors, lipophilicity may prove to be one of the most important ones by determining the amount of drug entering into the cell membrane in the vicinity of the β2-adrenoceptor. However, the receptor affinity, maximal relaxant effect (efficacy or intrinsic activity), potency, and receptor selectivity may also be of importance in determining how much β2-adrenoceptor agonist must remain at the receptor for sustained action.

Bradykinin-induced airway responses in guinea pig: effects of inhibition of cyclooxygenase and thromboxane synthetase

We studied the effects of indomethacin (10 mg/kg i.v.), a cyclooxygenase inhibitor, and OKY-046 (1, 10 and 30 mg/kg i.v.), a selective thromboxane synthetase inhibitor, on airflow obstruction and airway plasma exudation induced by bradykinin (150 nmol) instilled by the airway route to anesthetized guinea pigs. To do this, we studied changes in lung resistance (RL) and extravasation of Evans Blue dye respectively. Instilled bradykinin produced an immediate and marked increase in RL which peaked at approximately 30 s. We also observed a delayed increase in RL, reaching a second peak at approximately 3 min. Bradykinin produced airway plasma exudation at all airway levels, measured as extravasation of Evans Blue dye. Indomethacin significantly inhibited both the immediate and the delayed increase in RL after bradykinin. OKY-046 had a similar significant and dose-dependent inhibitory effect on these responses. In addition, both drugs inhibited bradykinin-induced Evans blue dye extravasation in intrapulmonary airways. Bradykinin instilled by the airway route significantly decreased systemic blood pressure but this effect was not altered in animals pretreated with either indomethacin or OKY-046. We conclude that the bronchoconstrictor response and airway plasma exudation induced by instilled-bradykinin may be mediated in part via thromboxane A2 generation.

Basic pharmacology of new long-acting sympathomimetics

A clinically important prolongation of effects have been achieved with two compounds, salmeterol and formoterol, who seem to have an increased binding to the cellular membrane, a binding that not exclusively is related to theβ-receptor.

Non-adrenergic, non-cholinergic regulation of guinea-pig airway smooth muscle-indomethacin-induced changes and segmental differences.

Several lines of evidence suggest a regulatory role for the non-adrenergic, non-cholinergic (NANC) nervous system in the airways of the guinea-pig and man. We examined NANC frequency-response characteristics (0.2-90 Hz) with respect to segmental differences and effects of cyclooxygenase-inhibition (indomethacin 10 microM). Furthermore, the neurogenic contribution to the contractile and the relaxatory NANC response was quantified with tetrodotoxin (1-10 microM). Frontally opened guinea-pig airway rings (n = 3-7) were used. NANC responses were obtained by electrical field stimulation (0.5 ms; 1200 mA; 240 s). A relaxatory NANC response was demonstrated in the proximal and the distal trachea. A contractile NANC response was demonstrated in the distal trachea and the main bronchus. Indomethacin lowered the baseline tension, decreased the relaxatory and increased the contractile NANC response (p less than 0.05; at 0.8 Hz; n = 4). A relationship between the baseline tension and the NANC response is suggested. The relaxatory NANC response was tetrodotoxin-sensitive at 3 Hz stimulation frequency (p less than 0.05; n = 3). At this frequency, the contractile NANC response was also mainly tetrodotoxin-sensitive (p less than 0.05; n = 6) whereas at 60 Hz a dominant, tetrodotoxin-resistant contraction was demonstrated. The pronounced frequency-response relationship as well as the tetrodotoxin sensitivity at very low frequencies (0.2-1.6 Hz) indicates that tetrodotoxin-sensitive NANC nerves are stimulated optimally at low impulse frequencies.

Effect of maturation on airway plasma exudation induced by eicosanoids in guinea pig

Airway reactivity to bronchoconstrictor mediators changes with age. We studied the effects of maturational change on airway responses induced by a thromboxane A2 mimetic, U-46619 (2, 6 and 20 nmol/kg; i.v.), leukotriene D4 (0.6 and 2 nmol/kg; i.v.) or vehicle (0.9% NaCl; i.v.) in immature (196 +/- 3 g: 2 weeks) and adult guinea pigs (512 +/- 5 g: 11 weeks). In the same animals, we measured both lung resistance (RL) to monitor airflow obstruction and extravasation of Evans Blue dye (20 mg/kg) to quantify airway plasma exudation. For a comparison, changes in RL in response to acetylcholine (5, 15 and 50 nmol/kg; i.v.) were also examined in both age groups. The order of potency to induce an increase in RL did not change with age (leukotriene D4 > U-46619 > acetylcholine). In immature animals, the peak RL after U-46619 (2, 6 and 20 nmol/kg; P < 0.05, P < 0.005 and P < 0.01, respectively) and leukotriene D4 (2 nmol/kg; P < 0.01) was significantly higher than in adult animals. U-46619 and leukotriene D4 produced significant extravasation of Evans Blue dye in both immature and adult animals. The order of potency to induce extravasated dye also did not change with age (leukotriene D4 > U-46619). The amount of extravasation of Evans Blue dye after U-46619 (6 and 20 nmol/kg) and leukotriene D4 (0.6 and 2 nmol/kg) was significantly smaller in immature animals than adults at all airway levels.(ABSTRACT TRUNCATED AT 250 WORDS)

Different effects of salmeterol, formoterol and salbutamol on cholinergic responses in the ferret trachea

1 In the present study, the inhibitory effects of the selective β2‐adrenoceptor agonists, salmeterol, formoterol and salbutamol, have been investigated on contractions of ferret trachea induced both by endogenous and exogenous acetylcholine. The aim of the study was to evaluate quantitative and/or qualitative differences in response which may indicate both pre‐and post‐junctional sites of action. The non‐selective β‐antagonist, sotalol, was used to estimate β‐adrenoceptor involvement.

Bradykinin-induced release of thromboxane B2 into bronchoalveolar lavage fluid of guinea pigs: relationship to airflow obstruction.

The aim of this study was to evaluate the role of thromboxane A2 in bradykinin-induced airflow obstruction in guinea pig in vivo. Airway insufflation pressure (Pi) was measured to assess airflow obstruction and the thromboxane B2 (a stable metabolite of thromboxane A2) concentration in bronchoalveolar lavage fluid was determined by radioimmunoassay. The animals were pretreated with propranolol (1 mg/kg i.v.) and suxamethonium (5 mg i.v.) prior to bradykinin administration. Bradykinin instillation into the trachea (300 nmol) induced a Pi increase (47.5 +/- 8.3 cm H2O versus 23.8 +/- 1.5 in sham) and significant thromboxane B2 release into bronchoalveolar lavage fluid (79 +/- 19 pg/ml versus 19 +/- 6 in sham). A thromboxane synthase inhibitor (OKY-046, 30 mg/kg i.v.; ((E-E)-3-[p(1H-imidazole-1-yl-methyl) phenyl]-2-propenoic acid hydrochloride mono-hydrate)) or a thromboxane A2 receptor antagonist (ICI192,605, 0.5 mg/kg i.v.; (4-(Z)-6-(2-o-chloro-phenyl-4-o-hydroxyphenyl-1,3-dioxan-cis-5-yl) hexenoic acid)) reduced the Pi increase evoked by bradykinin (38.7 +/- 3.8 and 40.6 +/- 3.8 cm H2O, respectively). OKY-046 abolished the thromboxane B2 release. A platelet-activating factor receptor antagonist, WEB2086 (1 mg/kg i.v.; (3-[4-(chlorophenyl)-9-methyl-6H-thienol [3,2-f][1,2,4]trizolo-[4,3-a][1,4] diazepin-2-yl]1-4-(4-morpholinyl)-1-propanon) did not significantly affect any measured parameter. We conclude that, in guinea pigs, bradykinin-induced airway effects are associated with a local thromboxane A2 release.

Effect of nedocromil sodium on non-adrenergic, non-cholinergic neural responses in guinea pig bronchi in vitro

OBJECTIVE Nedocromil sodium (nedocromil) improves the clinical condition of asthmatic subjects but its mechanism of action is not fully understood. This study aimed to determine whether nedocromil alters the ability of contractile and relaxant non-adrenergic, non-cholinergic neural (NANC) responses to stabilise tone by inhibiting or potentiating these responses in bronchial smooth muscle and, if so, whether the action is on a pre- or postjunctional level. RESULTS Nedocromil attenuated contractile but not relaxant NANC responses (elicited by electric field stimulation) significantly (P < 0.05) in guinea pig main bronchi in vitro. However, the ability of NANC responses to stabilise tone (convergence effect) was not significantly impaired by nedocromil. Furthermore, nedocromil did not significantly shift the concentration response curve (-log EC50) to neurokinin A (NKA), the dominating contractile NANC transmitter, or alter the maximum response to NKA (P > 0.05). Submaximum or maximum contractile responses to histamine were not markedly affected by nedocromil (P > 0.05). CONCLUSIONS Nedocromil exerts selective neural inhibition of the contractile but not of the relaxant NANC responses on a pre-junctional level in bronchial smooth muscle. Nedocromil does not, however, markedly impair the ability of NANC response to stabilise bronchial smooth muscle tone.