Pharmacological modulation of bronchial anaphylaxis induced by aerosol challenge in anaesthetized guinea-pigs.

Anaphylactic bronchoconstriction provoked by aerosol challenge, and its pharmacological modulation, has been investigated in anaesthetized pump-ventilated guinea-pigs actively sensitized to ovalbumin (OA). Aerosol challenge (OA 0.03-10 mg ml-1) provoked immediate bronchoconstriction, the degree of which, and its rate of development, was directly related to antigen concentration. Concomitant changes in heart rate and systemic arterial blood pressure following aerosol challenge were reduced compared with systemic (OA, 1 mg kg-1 i.v.) challenge. Unlike systemic challenge, aerosol challenge did not cause a concomitant fall in either circulating leukocyte or platelet count. When a submaximal (microshock) aerosol challenge stimulus (OA, 0.3 mg ml-1, 5 s) was employed, bronchoconstriction was markedly reduced by mepyramine (2 mg kg-1 i.v.). The residual component of bronchoconstriction was enhanced by indomethacin (10 mg kg-1 i.v.), an effect which was reversed by either BW755C (30 mg kg-1 i.v.) or FPL55712 (10 mg kg-1 i.v.). When a supramaximal (macroshock) aerosol challenge stimulus (OA, 10 mg ml-1, 5 s) was employed, bronchoconstriction was also markedly reduced by mepyramine. Residual bronchoconstriction was not altered by indomethacin, slowed but not reduced by indomethacin plus BW755C, and substantially reduced by indomethacin plus FPL55712. The successive incremental antagonism of anaphylactic bronchoconstriction by mepyramine and mepyramine plus indomethacin and FPL55712 indicates that the predominant mediators involved are histamine and leukotrienes, respectively. The failure of indomethacin plus BW755C to inhibit the mepyramine-resistant bronchoconstriction provoked by OA macroshock may reflect the increased generation of leukotrienes via a 5-lipoxygenase isoenzyme resistant to inhibition by BW755C.(ABSTRACT TRUNCATED AT 250 WORDS)     

The role of prostanoid TP- and DP-receptors in the bronchoconstrictor effect of inhaled PGD2 in anaesthetized guinea-pigs: effect of the DP-antagonist BW A868C.

1. In anaesthetized, pump-ventilated guinea-pigs, bolus intravenous injection of prostaglandin D2 (PGD2 5-160 micrograms kg-1) caused a dose-dependent rise in both heart rate and systemic mean arterial blood pressure with only a small monophasic rise in pulmonary inflation pressure (PIP). 2. In contrast, inhaled PGD2 (0.1-1 mg ml-1, 30s) provoked a substantial concentration-dependent biphasic rise in PIP. The bronchoconstrictor action of inhaled PGD2 was accompanied by minimal cardiovascular effects. 3. The 3-benzyl substituted hydantoin BW A868C (0.1-1 mg kg-1 i.v.) a novel prostanoid DP-receptor antagonist, had no significant effect on the cardiovascular or bronchoconstrictor effects of intravenously administered or inhaled PGD2. 4. However, BW A868C (0.1-1 mg kg-1 i.v.) did inhibit the hypotensive actions of the DP-receptor agonist, BW 245C (1-3 micrograms kg-1 i.v.). 5. The prostanoid TP-receptor antagonist BM 13.177 (2.5 mg kg-1 i.v.) strongly inhibited the bronchoconstrictor effect of inhaled PGD2, abolishing the first phase of this response and reducing the peak increase in PIP provoked by PGD2 (0.1 or 1 mg ml-1 for 30 s), by 67 +/- 16% and 44 +/- 5% respectively. 6. A combination of BW A868C (0.1 or 1 mg kg-1 i.v.) with BM 13.177 (2.5 mg kg-1 i.v.) produced no greater inhibition of the bronchoconstrictor effect of inhaled PGD2 than that seen with BM 13.177 (2.5 mg kg-1 i.v.) alone. 7. Neither bilateral vagotomy, nor selective inhibition of arachidonate cyclo-oxygenase with indomethacin or 5-lipoxygenase with the novel acetohydroxamic acid BW A4C, significantly reduced the bronchoconstrictor effect of inhaled PGD2.(ABSTRACT TRUNCATED AT 250 WORDS)     

Failure of the inhibition of rat gastric mucosal 5-lipoxygenase by novel acetohydroxamic acids to prevent ethanol-induced damage.

1. The role of leukotriene B4 (LTB4) and LTC4 as mediators of gastric mucosal damage following ethanol challenge in vivo has been investigated using two selective 5-lipoxygenase inhibitors, BW A4C and BW A137C. 2. Oral administration of ethanol to rats in vivo, induced macroscopic damage to the gastric mucosa and markedly increased the formation of the 5-lipoxygenase products, LTB4 and LTC4, from the mucosa ex vivo. 3. Pretreatment with the acetohydroxamic acids BW A4C and BW A137C (5-50 mg kg-1 p.o.) dose-dependently reduced ethanol-stimulated LTB4 and LTC4 formation by the gastric mucosa, with an ID50 of approximately 5 mg kg-1 p.o. 4. A single oral dose of BW A4C (20 mg kg-1) induced near-maximal inhibition of mucosal LTB4 formation within 30 min, which was well maintained for 5 h, whereas BW A137C (20 mg kg-1 p.o.) induced maximal inhibition between 30 and 60 min after administration, which then diminished over the subsequent 5 h. 5. The mucosal formation of the cyclo-oxygenase product, 6-keto-prostaglandin F1 alpha, which was unaltered following ethanol challenge, was not inhibited by the acetohydroxamic acids. Likewise, the small increase in mucosal thromboxane B2 formation following challenge was not inhibited by BW A4C. 6. Neither BW A4C nor BW A137C, at doses that almost completely inhibited the mucosal synthesis of LTB4 or LTC4, reduced the macroscopic gastric mucosal damage induced by ethanol. 7. Pretreatment with the lipoxygenase inhibitor BW 755C (5-50 mg kg-1 p.o.) did reduce mucosal damage, but there was a dissociation between the degree of protection and the inhibition of leukotriene biosynthesis.(ABSTRACT TRUNCATED AT 250 WORDS)     

Selective inhibition of arachidonate 5-lipoxygenase by novel acetohydroxamic acids: biochemical assessment in vitro and ex vivo

1. The chemically novel acetohydroxamic acids, BW A4C, BW A137C and BW A797C, are potent inhibitors of the synthesis of leukotriene B4 (LTB4) from arachidonic acid by human leucocyte homogenates: the concentrations required for 50% inhibition (IC50) were 0.1 microM, 0.8 microM and 0.5 microM respectively. Inhibition was less at higher concentrations of arachidonic acid. 2. These compounds also inhibited the synthesis of [14C]-5-HETE from [14C]-arachidonic acid and the calcium-dependent synthesis of LTB4 from 5-HPETE. This, therefore, suggests that they inhibit 5-lipoxygenase and LTA4 synthase. 3. Concentrations of acetohydroxamic acids required to inhibit metabolism of arachidonic acid by cyclo-oxygenase, 12-lipoxygenase and 15-lipoxygenase were 10 to 100 times higher than those required to inhibit 5-lipoxygenase. 4. The compounds were potent inhibitors of LTB4 synthesis induced by the ionophore, A23187, in human intact leucocytes. This inhibition was reversed by washing the cells. They were also potent, selective inhibitors of LTB4 synthesis induced by A23187 in whole rat blood: binding to rat plasma proteins did not greatly reduce the effectiveness of the compounds. 5. The effects of the acetohydroxamic acids, administered either intravenously or orally to rats, on the synthesis of LTB4, and thromboxane B2 (TXB2) in A23187-stimulated blood ex vivo was studied. The three compounds caused dose-dependent inhibition of the synthesis of LTB4 but not TXB2. Inhibition of LTB4 synthesis persisted for up to 6 h after a single oral dose of 50 mg kg-1. 6. The plasma concentrations of unchanged compound determined by h.p.l.c. correlated with the inhibition of LTB4 synthesis ex vivo.     

The booster injection of antigen during active sensitization of guinea-pig modifies the anti-anaphylactic activity of the PAF antagonist WEB 2086.

1. Serum IgG levels of sensitized guinea-pigs bled at various times after the booster injection were evaluated and its capacity to sensitize passively lung strips from normal guinea-pigs assessed. Following the booster injection, both serum IgG and the ability to sensitize passively lung strips increased during the first week and decreased slowly thereafter. 2. The PAF antagonist WEB 2086 (3 mg kg-1, i.v.) blocked the anaphylactic bronchoconstriction induced by intravenous administration of ovalbumin (1 mg kg-1) when guinea-pigs were challenged 2 and 4 days after the booster injection, but became ineffective when tested in guinea-pigs challenged 7, 28 and 56 days after the booster injection. 3. The ability of WEB 2086 to reduce anaphylactic bronchoconstriction of guinea-pigs challenged 2 and 4 days after the booster injection was unrelated to either the selective involvement of one type of immunoglobulin, low IgG titres in sera or a reduced sensitizing capacity. 4. The booster injection, which accounts for the loss of efficacy of WEB 2086 from the fourth day thereafter, probably operates as a PAF-independent inflammatory challenge. 5. The protocol for immunisation and the day of experiment after the booster injection determines the sensitivity of the anaphylactic bronchoconstriction to inhibition of PAF antagonists.     

Modulation of substance P-induced bronchoconstriction by lipoxygenase metabolites

In anaesthetized, mechanically ventilated guinea-pigs, substance P induces a bronchoconstrictor response comprising increases in airway resistance and decreases in dynamic compliance. Eicosatetraynoic acid (ETYA, 20 mg kg-1 i.v.) or BW755c (20 mg kg-1 i.v.) potentiated the substance P-induced bronchoconstriction. Neither indomethacin (1 or 5 mg kg-1 i.v.) nor aspirin (20 mg kg-1 i.v.) significantly altered the potency of substance P on bronchomotor responses. These observations are consistent with the existence of a bronchodilator lipoxygenase metabolite(s).     

Airway hyperreactivity follows anaphylactic microshock in anaesthetized guinea-pigs

Actively sensitized guinea-pigs were challenged with a dose of ovalbumin aerosol (300 micrograms ml-1, 5 s) that caused submaximal bronchoconstriction (anaphylactic microshock). Airway reactivity to i.v. 5-hydroxytryptamine (5-HT), i.v. acetylcholine (ACh) and aerosolised 5-HT was assessed subsequently. In addition, histological studies were carried out to investigate possible pulmonary recruitment of inflammatory cells following anaphylactic microshock. Following antigen challenge, there was a significant (P less than 0.05) increase in airway reactivity. This phenomenon was temporally separated (60-120 min) from the initial anaphylactic bronchoconstriction, but occurred in the absence of detectable lung pathology other than minor epithelial necrosis. Whilst histamine aerosol (100 micrograms ml-1, 5 s) did not induce airway hyperreactivity, pretreatment with the histamine H1 receptor antagonist mepyramine (2 mg kg-1 i.v.) prevented that occurring following antigen challenge. These observations suggest that in the pathogenesis of airway hyperreactivity, mediator release from resident leukocytes is initially more important than pulmonary infiltration of circulating cells. Depletion of a putative epithelium-derived relaxant factor may also play a contributory role. The anaphylactic release of histamine may modulate the release of secondary mediators of airway hyperreactivity.     

Capsaicin-induced bronchoconstriction in the guinea-pig: contribution of vagal cholinergic reflexes, local axon reflexes and their modulation by BW443C81.

1 The objective of the study was to investigate the central vagal and local axon reflex components of bronchoconstrictor responses evoked by inhalation of capsaicin aerosol in anaesthetized guinea-pigs. This was accomplished by comparing the effects of bilateral vagotomy, atropine and the peripherally-acting polar enkephalin analogue, BW443C81, on bronchoconstrictor responses evoked by capsaicin. The effects of codeine were also determined. 2 Aerosols of capsaicin were generated from a 0.9 microgram ml-1 solution. Inhalation of capsaicin aerosol in 5, 10 and 15 breaths evoked dose-related bronchoconstrictor responses. The responses were immediate in onset and of extended duration. 3 Capsaicin-induced bronchoconstrictor responses were significantly inhibited following bilateral vagotomy or atropine (0.3 mg kg-1, i.v.) pretreatment by 46% +/- 14% (P less than 0.05) and 59% +/- 13% (P less than 0.01), respectively. 4 Administration of BW443C81 by intravenous infusion (3, 30 and 100 micrograms kg-1 min-1) caused a significant inhibition of capsaicin-induced bronchoconstrictor responses which achieved a greater maximum than either bilateral vagotomy or atropine. Codeine (100 micrograms kg-1 min-1, i.v.) did not significantly inhibit the bronchoconstrictor responses. 5 Inhibition of capsaicin-induced bronchoconstrictor responses by BW443C81 (30 micrograms kg-1 min-1, i.v.) was significantly (P less than 0.05) reduced by the peripherally-acting opioid antagonist N-methyl nalorphine (100 micrograms kg-1 min-1, i.v.). 6 These results show that capsaicin-induced bronchoconstrictor responses are mediated by at least two mechanisms, a vagal and/or cholinergic reflex pathway and a non-cholinergic pathway.(ABSTRACT TRUNCATED AT 250 WORDS)     

Selective inhibition of arachidonate 5-lipoxygenase by novel acetohydroxamic acids: effects on acute inflammatory responses.

1. Two selective inhibitors of arachidonate 5-lipoxygenase, BW A4C and BW A797C, have been studied for their effects on acute inflammatory responses following oral administration to rats and mice. 2. The concentrations of the lipoxygenase product leukotriene B4 (LTB4) in 6 h inflammatory exudates, induced in rats by the subcutaneous implantation of carrageenin-soaked polyester sponges, were reduced dose-dependently by BW A4C (ED50 = 2.6 mg kg-1) or BW A797C (ED50 = 14.3 mg kg-1). 3. BW A4C and BW A797C had little or no effect on prostaglandin E2 (PGE2) concentrations in inflammatory exudates (ED50s greater than 100 mg kg-1). 4. Doses of up to 200 mg kg-1 of either BW A4C or BW A797C had no effect on carrageenin-induced oedema in rat paws. 5. BW A4C and BW A797C had little or no effect on carrageenin-induced hyperalgesia in rats or phenyl-benzoquinone-induced writhing in mice. 6. Yeast-induced pyrexia in rats was reduced by both BW A4C (ED50 = 32 mg kg-1) and BW A797C (ED50 = 23 mg kg-1). 7. The accumulation of leucocytes in sponge exudates was reduced dose-dependently by BW A4C (ED50 = 54 mg kg-1) and BW A797C (ED50 = 16.7 mg kg-1). 8. The selective lipoxygenase inhibitors BW A4C and BW A797C do not suppress inflammatory oedema or pain although they are anti-pyretic and they do inhibit leucocyte migration. There is not, however, a close agreement between these in vivo activities and their potencies as lipoxygenase inhibitors.     

Airway hyper- or hyporeactivity to inhaled spasmogens 24 h after ovalbumin challenge of sensitized guinea-pigs.

1. The aim of this study was to determine whether an inhalation of ovalbumin (OA, 10 or 20 mg ml-1) by conscious OA-sensitized guinea-pigs leads to airway hyperreactivity to spasmogens 24 h later. In contrast to most previous studies, the spasmogens (5-HT, methacholine (MCh), U-46619 and adenosine) were administered by inhalation and airway function was measured in conscious guinea-pigs. 2. Guinea-pigs were sensitized by i.p. injection of 10 micrograms OA and 100 mg aluminium hydroxide in 1 ml normal saline; 14-21 days later they were exposed to an inhalation of 5-HT, MCh, U-46619 or adenosine. Specific airway conductance (sGaw) was measured in conscious animals by whole body plethysmography. The spasmogens caused bronchoconstriction, measured as a reduction in sGaw from the pre-inhalation basal values. Dose-related bronchoconstrictions were observed with 5-HT, MCh and U-46619. 3. The effect of an ovalbumin macroshock challenge upon the responses to each spasmogen were examined by giving an inhalation of aerosolized OA at 24 h (or 7 days in the cause of adenosine) after an initial spasmogen challenge. Eighteen to twenty-four hours after the OA macroshock, the same guinea-pigs were exposed to a repeated inhalation of 5-HT, MCh, U-46619 or adenosine. 4. U-46619 was the only spasmogen to demonstrate hyperresponsiveness, the peak change in sGaw being increased from -12.3 +/- 9.9 to -38.8 +/- 5.0% by 10 mg ml-1 OA challenge. In contrast, the ovalbumin challenge (20 mg ml-1) inhibited the bronchoconstrictions to 5-HT (50 micrograms ml-1) and MCh (100 micrograms ml-1). Adenosine demonstrated bronchoconstriction in sensitized guinea-pigs but no significant change in the response was observed after an OA challenge. 5. All results were compared with a control group of sensitized guinea-pigs receiving a NaCl challenge. The bronchoconstrictor responses to 5-HT, MCh, U-46619 or adenosine did not differ significantly before and after the saline challenge, indicating reproducibility of the responses. 6. In further experiments, guinea-pigs were exposed to inhalation of 5-HT (50 micrograms ml-1) or MCh (300 micrograms ml-1) 24 h before atropine (10 micrograms, 100 micrograms or 1 mg ml-1) and again at 0.5 to 1.5 h afterwards. Atropine, antagonized the 5-HT- and MCh-induced bronchoconstrictions over the same antagonist dose-range. This suggests that the bronchoconstriction induced in the conscious guinea-pig by 5-HT is mediated primarily via muscarinic receptors, possibly by a vagal reflex. The inhibition of the responses to 5-HT and MCh by OA challenge would therefore appear to be related to interference with a common cholinergic pathway for these spasmogens. 7. In summary, airway hyperresponsiveness was evident at 24 h after OA challenge as measured by an enhanced bronchoconstrictor response to inhaled U-46619. When 5-HT or MCh were used as the spasmogens, an opposing decrease in responsiveness was observed. This was presumed to be due to an inhibition of cholinergic pathways by the OA challenge. Adenosine caused a bronchoconstriction in the sensitized animals but this was not enhanced by the OA challenge.     

CHARACTERIZATION OF SUBSTANCE P-INDUCED BRONCHOCONSTRICTION IN THE GUINEA-PIG: A COMPARISON WITH ACETYLCHOLINE

Substance P (0.5-8.0 micrograms/kg, i.v.) induced bronchoconstriction in anaesthetized, mechanically-ventilated guinea-pigs, comprising increases in airways resistance and decreases in dynamic compliance. These bronchoconstrictor responses were unaffected by bilateral vagotomy, pretreatment with pheniramine (2 mg/kg, i.v.) or by pretreatment with atropine (100 micrograms/kg, i.v.). Acetylcholine-induced (4-32 micrograms/kg, i.v.) bronchoconstriction was prevented by atropine pretreatment, whereas bilateral vagotomy inhibited responses to acetylcholine. Ganglionic blockade using hexamethonium (20 mg/kg, i.v.) potentiated both substance P and acetylcholine on airways resistance and dynamic compliance. Indomethacin (1 or 5 mg/kg, i.v.) did not affect substance P-induced bronchoconstriction, whereas the higher dose enhanced acetylcholine-induced increases in airways resistance. In addition, aspirin pretreatment (20 mg/kg, i.v.) did not alter the bronchoconstrictor potency for either substance P or acetylcholine. On the other hand, the combined cyclo-oxygenase/lipoxygenase inhibitors eicosatetraynoic acid (ETYA, 20 mg/kg, i.v.) and BW755C (20 mg/kg, i.v.) potentiated both acetylcholine and substance P on airways resistance and dynamic compliance. The results suggest that substance P-induced bronchoconstriction may be modulated by the sympathetic nervous system and does not appear to be influenced by vagal or histaminergic mechanisms. The failure of indomethacin or aspirin to affect substance P-induced bronchoconstriction, together with the enhancing effects of ETYA and BW755C pretreatments, provide evidence consistent with the existence of a bronchodilator mechanism which may be inhibited by compounds inhibiting lipoxygenase enzymes.     

A comparative study of the cardiovascular and biochemical actions of the imidazo [4,5b] pyridine sulmazole and an imidazo [4,5c] pyridine analogue, BW A746C.

1. BW A746C is a chemical analogue of the imidazo [4,5b] pyridine, sulmazole (AR-L115 BS). Like sulmazole, BW A746C possesses positive inotropic and vasodilator activity in vivo. 2. In anaesthetized guinea-pigs, dogs and primates, a bolus i.v. injection of BW A746C, (0.001-1.0 mg kg-1) caused a significant, dose-related increase in ventricular dP/dt, and reduction in diastolic blood pressure, with small increases in heart rate. In these species, a significantly higher dose of BW A746C was required to lower blood pressure by 30% from basal, than was needed to raise ventricular dP/dt by 50% over basal. 3. In anaesthetized guinea-pigs and dogs, bolus i.v. injections of sulmazole (0.1-10.0 mg kg-1) caused similar effects to those observed with BW A746C. In these species, however, there was no significant difference between the dose of sulmazole required to lower blood pressure by 30% from basal and that required to raise ventricular dP/dt by 50%. 4. In conscious dogs, i.v. infusion of BW A746C (to a total dose of 0.3 mg kg-1) caused a significant increase in ventricular dP/dt, but no significant change in either diastolic blood pressure or heart rate. 5. In cell-free biochemical assays, there were no clear differences between the observed activities of BW A746C and sulmazole. Both compounds are cyclic nucleotide phosphodiesterase inhibitors with similar potencies and selectivities for the Type III enzyme (IC50 BW A746C = 3.0 +/- 0.5 X 10(-5) M, sulmazole 5.0 +/- 1.9 X 10(-5) M). The compounds had little or no effects on sarcolemmal Na+/K+-ATPase, Ca2+ ATPase or Na+/Ca2+ exchange, and sulmazole, but not BW A746C, had a small, stimulatory effect on myofibrillar ATPase. 6. In anaesthetized guinea-pigs and dogs, BW A746C was significantly more potent as a positive inotrope than sulmazole. In contrast with sulmazole, BW A746C produced its inotropic effects at significantly lower doses than those required to reduce diastolic blood pressure. This was also apparent from the results obtained in the anaesthetised primates and the conscious dogs. It was therefore concluded that the inotropic/vasodilator profile of BW A746C favours its positive inotrope activity. This profile cannot be explained on the basis of any biochemical differences from sulmazole.     

Contribution of thromboxane A2 to the antigen-induced immediate asthmatic response mediated by IgG1 antibody by augmentation of bronchial responsiveness in guinea-pigs.

1. IgG1-mediated anaphylactic bronchoconstriction was elicited by intravenous administration of antigen to guinea-pig 2 days after passive sensitization with IgG1-rich serum, and this response was not affected by heating the serum (at 56 degrees C, for 4 h). IgE-mediated bronchoconstriction, provoked 14 days after passive sensitization with IgE-rich serum, was completely abolished by the heating of the serum. 2. S-1452 (10 mg kg-1, p.o.), a selective thromboxane (Tx) A2 antagonist, significantly but incompletely suppressed the IgG1-mediated bronchoconstriction, but did not affect the IgE-mediated one, while diphenhydramine (5 mg kg-1, i.v.), a histamine antagonist, almost completely inhibited both IgG1- and IgE-mediated bronchoconstriction. 3. Pretreatment with propranolol (1 mg kg-1, i.v.), a beta-adrenergic blocker, in addition to diphenhydramine, caused a long-lasting bronchoconstriction following antigen challenge in both animal models. This histamine-independent bronchoconstriction was markedly suppressed by S-1452 at a low dose of 0.1 mg kg-1. 4. A significant increase in bronchial responsiveness to i.v. acetylcholine (ACh), compared to the prechallenge value, occurred as early as 3 min and persisted for 24 h after antigen challenge in the IgG1 model, but was not observed in the IgE model. S-1452 (10 mg kg-1, p.o.) inhibited the IgG1-mediated bronchial hyperresponsiveness, as assessed 60 min after antigen challenge. 5. A marked elevation of TxB2 levels was observed in bronchoalveolar lavage fluid (BALF) 3 min after antigen challenge in the IgG1 model, while levels were not changed in the IgE model.(ABSTRACT TRUNCATED AT 250 WORDS)     

The induction of a biphasic bronchospasm by the ETB agonist, IRL 1620, due to thromboxane A2 generation and endothelin-1 release in guinea-pigs.

1. IRL 1620 (0.01-0.1 mg kg-1, i.v.), a selective endothelin B (ETB) receptor agonist, induced a dose-dependent biphasic increase in total lung resistance and a decrease in dynamic compliance in anaesthetized and artificially ventilated guinea-pigs. After intravenous injection of IRL 1620 (0.03 mg kg-1), the first phase was observed within 2 min whereas the second phase started between 5 and 10 min after injection and was long lasting. 2. In order to characterize which endothelin receptors are involved in both phases of bronchoconstriction, we studied the effect of ETA and ETB receptor antagonists (BQ 123 and BQ 788, respectively). BQ 788 (0.1-1 mg kg-1, i.v.) inhibited, in a dose-dependent manner, both phases of bronchoconstriction. BQ 123 (3 mg kg-1, i.v.) markedly inhibited (by 76%) the second phase of bronchoconstriction but had no effect on the early component of the response. 3. The effect of atropine, neurokinin-I (NK1) and neurokinin-2 (NK2) receptor antagonists (SR140333 and SR48968, respectively) were tested to investigate the possible involvement of cholinergic and sensory nerve activation, respectively, in the response to IRL 1620. Likewise, the role of arachidonic acid metabolites (leukotriene D4 antagonist, ONO-1078 and thromboxane A2 (TXA2) inhibitor, OKY-046) in this response was also investigated. OKY-046 (1 mg kg-1, i.v.) and atropine (1 mg kg-1, i.v.) partially inhibited the first phase (by 80% and 20%, respectively) without affecting the late phase of bronchoconstriction. Neither ONO-1078 (1 mg kg-1, i.v.) nor the combination of SR140333 (0.2 mg kg-1, i.v.) and SR 48968 (0.2 mg kg-1, i.v.) modified IRL 1620-induced bronchoconstriction. 4. A low dose of IRL 1620 (0.005 mg kg-1, i.v.) induced a monophasic bronchoconstriction. Pretreatment by phosphoramidon (100 mumol kg-1, i.v.) restored the second phase of bronchoconstriction. In this condition, BQ 123 (3 mg kg-1, i.v.) was able to inhibit partially the second phase of bronchoconstriction. 5. These results suggest that both phases of bronchoconstriction induced by IRL 1620 were mediated primarily by ETB receptor activation, the first phase being a consequence of TXA2 and acetylcholine release. The inhibition by an ETA receptor antagonist and the restoration by a neutral endopeptidase (NEP) inhibitor of the second phase of bronchoconstriction suggests that primary activation of ETB receptors leads to autocrine/paracrine endothelin-1 (ET-1) release that would subsequently cause profound bronchoconstriction through both ETA and ETB receptor activation.     

Inhibitory effect of HSR-6071, a new anti-allergic agent, on experimental asthma in rats and guinea-pigs

The experimental asthma caused by IgE antibody in rats was inhibited by HSR-6071 (6-(1-pyrrolidinyl)-N-(1H-tetrazol-5-yl)-2-pyrazinecarboxamide) (0.01-0.1 mg kg-1 i.v.) in a dose-dependent manner. The inhibitory activity of HSR-6071 was more potent than those of disodium cromoglycate and ketotifen, and equipotent with amlexanox. The bronchoconstriction mediated by IgE or IgG antibody in guinea-pigs was also prevented by HSR-6071 (0.3, 1 and 3 mg kg-1 i.v.), amlexanox (3, 10 and 30 mg kg-1 i.v.) and ketotifen (0.1 mg kg-1 i.v.) but not by disodium cromoglycate (10 mg kg-1 i.v.). HSR-6071 was more potent than amlexanox, but less potent than ketotifen. HSR-6071 suppressed antigen-induced histamine and SRS-A release from minced lung tissues of guinea-pigs sensitized passively with rabbit anti-EA serum and was a more potent inhibitor of the release of SRS-A than of histamine. On the other hand, histamine- or acetylcholine-induced bronchoconstriction in guinea-pigs was scarcely affected by HSR-6071 at doses sufficient to inhibit the experimental asthma, but LTD4-induced bronchoconstriction was dramatically inhibited. These results indicate that the inhibitory action on experimental allergic asthma of HSR-6071 may be due to suppression of antigen-induced histamine and SRS-A release from lung tissues and to antagonism of SRS-A action. In addition, HSR-6071 inhibited cyclic AMP phosphodiesterase activity and produced relaxation of the guinea-pig isolated trachea. These pharmacological actions may contribute to the production of the anti-allergic action of HSR-6071.     

Evidence against leukotriene-mediation of propranolol-induced airway hyperreactivity to acetylcholine

In unanaesthetized guinea-pigs, propranolol treatment (0.1 mg kg-1 i.v.) substantially increased reactivity to intravenous acetylcholine infusion or aerosolized histamine to a comparable degree. Neither BW755c (5 mg kg-1 i.v.), FPL 55712 (1 mg kg-1 i.v.), nor piriprost (5 mg kg-1 i.v.) pretreatment influenced propranolol's effect on muscarinic reactivity although BW755c abolished histaminic hyperreactivity. This suggests that propranolol-induced muscarinic hyperreactivity in the guinea-pig is not mediated by leukotrienes whereas histaminic hyperreactivity may be.     

Pulmonary effects of type V cyclic GMP specific phosphodiesterase inhibition in the anaesthetized guinea-pig.

1. We have investigated the bronchodilator potential of type V phosphodiesterase (PDE V) inhibitors in anaesthetized ventilated guinea-pigs using the potent and selective PDE V inhibitor, SK&F 96231. We have compared its activity to that of salbutamol, the PDE III inhibitors, siguazodan and SK&F 95654 and to the PDE IV inhibitor rolipram. 2. Administered as an i.v. infusion SK&F 96231 (0.6 and 1 mg kg-1 min-1, i.v.) caused a slowly developing inhibition of histamine (100 nmol kg-1, i.v.)-induced bronchoconstriction and elevated tracheal cyclic GMP levels in the anaesthetized guinea-pig. SK&F 96231 (0.1 and 0.3 mg kg-1 min-1, i.v.) was without effect on histamine-induced bronchoconstriction. In the presence of a sub-threshold infusion of SNP (0.1 mumol kg-1 min-1, i.v.) there was a marked enhancement of SK&F 96231-induced inhibition of histamine responses such that at infusion rates that were ineffective alone, SK&F 96231 caused a > 50% inhibition of histamine responses. The stimulation of tracheal cyclic GMP accumulation by SK&F 96231 was also potentiated. 3. Administered directly into the airway, SK&F 96231 (300 micrograms in 5 mg lactose carrier) was largely without effect on histamine-induced bronchoconstriction (4.9 +/- 1.9% inhibition). In the presence of SNP (0.1 mumol kg-1 min-1, i.v.) or isosorbide dinitrate (200 micrograms administered by insufflation into the trachea) there was a marked potentiation of the inhibitory activity of SK&F 96231 (40 +/- 4% and 62 +/- 1.8% respectively).(ABSTRACT TRUNCATED AT 250 WORDS)     

Role of oxygen radicals and arachidonic acid metabolites in the reverse passive Arthus reaction and carrageenin paw oedema in the rat.

1. The role of arachidonic acid metabolites and oxygen radicals in carrageenin-induced rat paw oedema and dermal reverse passive Arthus reaction (RPA) have been investigated. 2. Indomethacin (10 mg kg-1, p.o.) inhibited carrageenin paw oedema when administered 30 min before, but not 2 h after carrageenin. BWB70C (10 mg kg-1, p.o.), a selective inhibitor of 5-lipoxygenase, had no effect whether administered before or after carrageenin. Administration of both indomethacin and BWB70C had no greater anti-inflammatory effect than indomethacin alone. 3. BW755C (20 mg kg-1, p.o.), which inhibits the cyclo-oxygenase and lipoxygenase pathways of arachidonic acid metabolism, or superoxide dismutase-polyethylene glycol conjugate (SOD-PEG, 3000 u, i.v.) inhibited carrageenin paw oedema whether administered either 30 min before, or 2 h after carrageenin. 4. Pretreatment with dexamethasone (0.1 mg kg-1) or colchicine (2 mg kg-1), likewise suppressed carrageenin paw oedema. 5. BW755C (25-100 mg kg-1, p.o.) dose-dependently reduced plasma leakage in the RPA, whereas indomethacin (5 mg kg-1, p.o.) or BWB70C either alone or in combination, did not. 6. SOD-PEG (300-3000 u, i.v.) dose-dependently inhibited plasma leakage in the RPA. In addition, the iron chelator and peroxyl radical scavenger, desferrioxamine (200 mg kg-1, s.c.) also inhibited plasma leakage. 7. Pretreatment with dexamethasone (0.1 mg kg-1) or colchicine (1 mg kg-1) reduced the plasma leakage in RPA, whereas MK-886 (10 mg kg-1) had no effect.(ABSTRACT TRUNCATED AT 250 WORDS)     

Involvement of NK2 receptors rather than NK1 receptors in bronchial hyperresponsiveness induced by allergic reaction in guinea-pigs.

1. In this study, the role of neuropeptides in antigen-induced bronchoconstriction and bronchial responsiveness in guinea-pigs was evaluated by use of phosphoramidon, the inhibitor of neutral endopeptidases (NEP), the NK1 receptor antagonist, FK888, and the dual NK1/NK2 receptor antagonist, FK224. The role of endogenous tachykinins in bronchial hyperresponsiveness induced by inhaled capsaicin was also observed with FK888 and FK224. 2. Allergic bronchoconstriction and bronchial responsiveness was evoked by inhalation of ovalbumin (OA), and increasing doses of methacholine were inhaled at 5-min intervals for 30 min after OA challenge in passively sensitized and artificially ventilated guinea-pigs. Animals were treated with a 30 s inhalation of phosphoramidon (10(-3)M) or saline 10 min before the OA challenge. FK888 (1.0 or 10 mg kg-1) or FK224 (1.0 or 10 mg kg-1) was administered intravenously 5 min before the OA challenge. 3. Treatment with phosphoramidon did not alter the increase in the lateral pressure at the tracheal tube (Pao) caused by OA inhalation or the increase in bronchial response to methacholine following the allergic reaction. Pretreatment with FK224 did not inhibit the increase in Pao after antigen provocation but did significantly inhibit antigen-induced bronchial hyperresponsiveness in a dose-dependent manner, while FK888 did not affect either allergic bronchoconstriction or post-allergic bronchial hyperresponsiveness. 4. Histamine, 25, 50, 100 or 200 micrograms ml-1 was inhaled for 20 s at 5-min intervals in non-sensitized guinea-pigs which were pretreated with inhalation of subthreshold dose of capsaicin (10(-7) M). FK888 or FK224, each at a dose of 0.1 or 1.0 mg kg-1, or vehicle was given to guinea-pigs intravenously 3 min before inhalation of capsaicin. The capsaicin inhalation significantly potentiated bronchial responsiveness to histamine, compared with control. The capsaicin-induced bronchial hyperresponsiveness was completely blocked by FK224 in a dose-dependent manner but not by FK888. 5. These results suggest that NK2 receptors rather than NK1 receptors may play an important role in bronchial hyperresponsiveness induced by antigen challenge as well as capsaicin while tachykinins do not play a primary role in the acute bronchospasm elicited by antigen challenge in passively sensitized guinea-pigs.     

速激肽受体拮抗剂抗豚鼠过敏性哮喘的作用

实验目的是研究速激肽与哮喘的关系,评价速激肽受体拮抗剂对哮喘的治疗作用。结果表明,ip速激肽NK-1受体拮抗剂CP-96345,NK- 2受体拮抗剂SR-48968或两药合用,均可有效减少清醒致敏豚鼠吸入抗原引起的喘息反应,降低过敏性休克死亡率。SR-48968减轻麻醉豚鼠抗原引起的气道收缩,并浓度依赖性降低抗原引起的气管和支气管平滑肌收缩幅度。CP-96345可抑制抗原诱导的支气管和肺叶伊文思蓝渗出,仅对支气管平滑肌收缩有部分抑制作用。结果提示,速激肽参与哮喘发病,速激肽受体拮抗剂可抑制抗原诱导的气道平滑肌收缩(NK-2受体)和微血管渗漏(NK-1受体)而减轻哮喘反应。