Production of early and late pulmonary responses with inhaled leukotriene D4 in allergic sheep

Some allergic sheep respond to inhalation of Ascaris suum antigen with both immediate and late increases in airflow resistance (late response). The mechanism of the late response is unknown but recent evidence suggests that the initial generation of slow-reacting substance of anaphylaxis (SRS-A) immediately after antigen challenge is a necessary pre-requisite for the physiologic expression of this late response. Based on this evidence we hypothesized that airway challenge with leukotriene D4 (LTD4), an active component of SRS-A would produce acute and late airway responses in allergic sheep similar to those observed with antigen. In five allergic sheep with documented early and late pulmonary responses to Ascaris suum antigen, inhalation of leukotriene D4 aerosol (delivered dose (mean +/- SE) 0.55 +/- 0.08 ug) resulted in significant early and late increases in specific lung resistance (SRL). In three allergic sheep which only demonstrated acute responses to antigen, LTD4 aerosol (delivered dose 0.59 +/- 0.09 ug) only produced an acute increase in SRL. In the late responders pretreatment with aerosol cromolyn sodium (1 mg/kg) did not affect the acute response but blunted the late increase in SRL. Pretreatment with aerosol FPL-57231 (1% w/v solution) completely blocked both the acute and late responses. These data support the hypothesis that initial release of LTD4 in the airways of sensitive animals is important for the physiologic expression of the late response.     

The effect of an orally active leukotriene D4/E4 antagonist, LY171883, on antigen-induced airway responses in allergic sheep

Leukotriene (LT) D4 is a putative mediator of allergic asthma: inhaled LTD4 produces early and late increases in specific lung resistance (SRL) and slows tracheal mucus velocity (TMV) similar to inhaled antigen. In this study we examined the effects of an orally active LTD4/LTE4 antagonist, LY171883 [1-less than 2-Hydroxy-3-propyl-4-less than 4-(1H-Tetrazol-5-yl) Butoxy greater than Phenyl greater than Ethanone], on early and late changes in SRL and TMV following airway challenge with Ascaris suum antigen in conscious allergic sheep. SRL and TMV were measured before and up to 8 h and 24 h after antigen challenge after either LY171883 (30 mg/kg, p.o. 2 h before challenge) or placebo pretreatment. After placebo pretreatment antigen challenge resulted in significant early (483% over baseline) and late (221% over baseline) increases in SRL (n = 9). LY171883 pretreatment, however, significantly reduced the early increase in SRL (163% over baseline) and blocked the late response. LY171883 did not prevent the antigen-induced fall in TMV from 5-8 h post challenge (n = 6), but TMV recovered more rapidly in the drug trial returning to baseline values by 24 h. These results suggest that the generation of LTD4, and its metabolite LTE4, during airway anaphylaxis contributes to the early increase in SRL and is important for eliciting the late increase in SRL as well as contributing to the fall in TMV.     

The effect of an orally active leukotriene (LT) antagonist YM-16638 on antigen-induced early and late airway responses in allergic sheep

In this study we examined the effects of an orally active leukotriene (LT) antagonist YM-16638 [[5-[[3-(4-acetyl-3-hydroxy-2-propyl-phenoxy)propyl]thio]-1,3,4- thiadiazol-2-yl]thio] acetic acid on antigen-induced early and late responses in allergic sheep. For all studies YM-16638 was administered via intragastric tube 1 h before airway challenge with Ascaris suum antigen. Six allergic sheep were challenged on four occasions (2 control and 2 drug trials) each greater than or equal to 14 days apart and the tests were conducted in the following order: control-1; YM-16638 30 mg/kg; control-2; YM-16638 10 mg/kg. Specific lung resistance (SRL) was used as an index of the airway response to antigen and was measured before and serially after antigen challenge. In both control trials antigen challenge resulted in significant early and late airway responses (i.e. increases in SRL); however, there was a significant difference between the peak late increases of SRL in control-1 (206%) and control-2 (115%) suggesting a carry-over effect of the 30 mg/kg dose of YM-16638. At both doses, YM-16638 reduced the early response and blocked the late response when compared to either control trial. These results suggest that sulfidopeptide LTs contribute to both antigen-induced early and late airway responses in allergic sheep.     

Differences in airway responsiveness to leukotriene D4 in allergic sheep with and without late bronchial responses

Allergic sheep respond to inhaled Ascaris suum antigen with either acute and late bronchial obstructions (dual responders) or only acute bronchoconstriction (acute responders). In this study we tested the hypothesis that one factor which may distinguish between these two populations is the difference in sensitivity to a specific mediator of airway anaphylaxis, leukotriene (LT) D4 (a major component of slow reacting substance of anaphylaxis). We postulated that if the hypothesis was correct then dual responders should demonstrate increased airway responses to inhaled LTD4 and that this increased responsiveness should also be reflected by a more severe response to inhaled antigen. To test this we used animals from both groups with the same degree of non-specific airway responsiveness to carbachol and determined their airway responses to controlled inhalation challenges with synthetic LTD4 and Ascaris suum antigen. Airway responsiveness to carbachol was determined by measuring the change in specific lung resistance (SRL) to increasing concentrations of carbachol aerosol, and then identifying, by linear interpolation, the provocative carbachol concentration which produced a 150% increase (PC150) in SRL. Airway responses to LTD4, and antigen were determined by measuring the percentage change in SRL after a controlled inhalation challenge with either aerosol. Airway responsiveness to carbachol was not different between the two groups. There was, however, a difference (p less than 0.05) in the airway response to the same dose of LTD4 in the two groups. Dual responders showed a 297 +/- 72% increase in SRL as compared to a 90 +/- 13% increase in SRL in the acute responders. Dual responders also showed a greater immediate and more prolonged response to antigen than did acute responders. These results suggest that increased responsiveness to LTD4 may be one factor which may distinguish dual responders from acute responders.     

Wy-48,252 (1,1,1-trifluoro-N-[3-(2-quinolinylmethoxy)phenyl]methane sulfonamide) an orally active leukotriene D4 antagonist: pharmacological characterization in vitro and in vivo in the guinea pig

The following communicates the pharmacology of Wy-48,252 (1,1,1-trifluoro-N-[3-(2-quinolinylmethoxy)phenyl]methanesulfonamide) a chemically novel and orally potent leukotriene (LT) D4 receptor antagonist. In the isolated guinea-pig trachea pretreated with indomethacin (5 microM) and L-cysteine (10 mM), Wy-48,252 antagonized TD4-induced contraction with a pKB = 7.6. Against LTC4 on tissues pretreated with IND and glutathione (10 mM), Wy-48,252 had a pKB greater than 5. Wy-48,252 (10 microM) did not antagonize pilocarpine-, histamine- or PGF2 alpha-induced tracheal contraction. Further, in the presence of indomethacin and chlorpheniramine (1 microM), Wy-48,252 dose-dependently inhibited the antigen-induced contraction of guinea-pig trachea in a manner consistent with antagonism at the LTD4 receptor and inhibition of LT synthesis. In the Konzett-Rossler model of i.v. LTD4-induced bronchoconstriction in indomethacin treated guinea pigs, intragastric Wy-48,252 (2 hr) had an ID50 of 100 micrograms/kg and a functional half-life of 5 hr. Against i.v. antigen-induced bronchoconstriction in guinea pigs treated with indomethacin and chlorpheniramine, intragastric Wy-48,252 (2 hr) had an ID50 of 0.6 mg/kg and a 5 hr half life. Intragastric Wy-48,252 also selectively blocked the cutaneous wheal reaction to intradermal LTD4 but not histamine. We conclude that Wy-48,252 is distinguished from other selective LTD4 receptor antagonists by its oral potency and should be useful in ascertaining the role of LTD4 mediated processes in asthma, allergy and animal models.     

Effects of leukotriene D4 on mucociliary and respiratory function in allergic and nonallergic sheep

We determined the effect of aerosol challenge with leukotriene D4 (LTD4) on specific lung resistance (sRL) and tracheal mucous velocity (TMV) in conscious sheep with (allergic) and without (nonallergic) Ascaris suum hypersensitivity. In allergic sheep LTD4 in concentrations of 50, 100, and 150 micrograms/ml produced dose-dependent increases in mean sRL by 44 (P = NS), 154 (P less than 0.05), and 233% (P less than 0.05), respectively. The increase in sRL produced by 150 micrograms/ml LTD4 was prevented by FPL 55712, an antagonist of slow-reacting substance of anaphylaxis. In nonallergic sheep 150 micrograms/ml LTD4 failed to elicit a significant change in sRL. In contrast to the changes in airway mechanics, concentrations of LTD4 as low as 25 micrograms/ml produced significant decreases in TMV in allergic sheep. The maximum decrease in TMV at this dose occurred 2 h after challenge; with larger doses of LTD4 (100 and 150 micrograms/ml) the maximum effect was observed 3 h after challenge. Furthermore, 150 micrograms/ml LTD4 reduced TMV in nonallergic sheep (mean decrease 43%, P less than 0.05). FPL 55712 only had a minor effect on the LTD4-induced decreases in TMV. We conclude that allergic sheep exhibit greater airway responsiveness to inhaled LTD4 than nonallergic sheep but that this difference is not evident for the concomitant changes in mucociliary transport. This suggests that the allergic state is associated with an increased responsiveness to LTD4 in tissues controlling airway caliber but not in those contributing to mucociliary function.     

Increased leukotriene E4 excretion during antigen-induced bronchoconstriction in allergic sheep

The metabolism of leukotrienes (LT) in the sheep was investigated to define markers of 5-lipoxygenase involvement in allergic responses, obtainable by noninvasive techniques. Intravenous administration of 14, 15-[3H]LTC4 (0.5 microCi/kg) revealed a rapid clearance from the circulation (half time = 90 s). Circulatory metabolism was apparent, with early formation (within 1 min) of LTD4 and LTE4 shown by reverse-phase high-pressure liquid chromatography (RP-HPLC). Urinary 3H excretion comprised 10% of the original dose. [3H]LTE4 (characterized by coelution with authentic standards during RP-HPLC analysis) was observed in early urine samples. By use of a sensitive and specific RP-HPLC radioimmunoassay analysis, immunoreactive material coeluting with LTE4 was detected in urine from allergic sheep. Excretion of this material was significantly increased during antigen-induced acute bronchoconstriction in eight conscious allergic sheep [preantigen, 65.70 +/- 24.27 (SE) pg; 0-1 h postantigen, 208.00 +/- 71.10 pg, P less than 0.05], but not during late responses. However, total postantigen LTE4 excretion (37.8 - 956.1 pg/8 h) was highly correlated (r = 0.976, P less than 0.001) with the severity of bronchoconstriction (445.3 - 2,409.1% specific pulmonary resistance per hour) assessed by measurement of the area under the curve of pulmonary function plotted against time. These findings represent an important demonstration of in vivo allergen-induced peptide LT generation in a physiologically characterized animal model of prolonged allergic bronchoconstriction and further substantiate an important role for LT in this model of allergic asthma.     

A possible role for PAF in allergen-induced late responses: modification by a selective antagonist

We determined whether platelet-activating factor (PAF) plays a role in allergen-induced airway responses by studying the effects of a selective PAF antagonist WEB-2086 on antigen-induced early and late airway responses in allergic sheep. In seven sheep, inhaled Ascaris suum produced significant early (282%) and late (176%) increases in specific lung resistance (sRL). WEB-2086 (1 mg/kg iv) given 20 min before antigen challenge did not affect the early response, but the peak late increase in sRL was only 37% over base line (P less than 0.05 vs. control). To study the mechanism by which PAF contributes to antigen-induced responses, we evaluated the effects of pharmacological probes on PAF-induced bronchoconstriction. Inhaled PAF (dose range 75-700 micrograms) caused reproducible (r = 0.781, P less than 0.05) increases in sRL in eight sheep. The PAF-induced bronchoconstriction was blocked by WEB-2086 (1 mg/kg iv) and by the leukotriene antagonist FPL-55712 (30 mg by aerosol); however, neither the cyclooxygenase blocker indomethacin (2 mg/kg iv) nor the histamine H1-antagonist chlorpheniramine (2 mg/kg iv) blocked the PAF response. WEB-2086, however, did not block bronchoconstriction induced by aerosol leukotriene D4, indicating that PAF acts indirectly through leukotrienes. Finally, we determined whether PAF could induce late airway responses. Inhaled PAF produced an immediate increase in sRL in all seven sheep tested, but late airway responses were observed in only three of the seven sheep.(ABSTRACT TRUNCATED AT 250 WORDS)     

Nedocromil sodium in allergen-induced bronchial responses and airway hyperresponsiveness in allergic sheep

We examined the effects of nedocromil sodium, a new drug developed for the treatment of reversible obstructive airway disease, on allergen-induced early and late bronchial responses and the development of airway hyperresponsiveness 24 h after challenge in nine allergic sheep. On occasions greater than 2 wk apart the sheep were treated with 1) placebo aerosol (buffered saline) before and 3 h after antigen challenge, 2) an aerosol of nedocromil sodium (1 mg/kg in 3 ml buffered saline) before antigen challenge and placebo 3 h after challenge, and 3) placebo aerosol before and nedocromil sodium aerosol 3 h after challenge. Early and late bronchial responses were determined by measuring specific lung resistance (sRL) before and periodically after challenge. Airway responsiveness was assessed by determining from dose-response curves the carbachol concentration (in % wt/vol) that increased sRL to 5 cmH2O/s. In the placebo trial, antigen challenge resulted in early and late increases in sRL over a base line of 353 +/- 32 and 131 +/- 17% (SE), respectively. Both early and late increases in sRL were blocked (P less than 0.05) when the sheep were pretreated with nedocromil sodium. When nedocromil was given after the early response, the late response was reduced significantly. Eight of nine sheep developed airway hyperresponsiveness 24 h after antigen challenge. In these eight sheep, carbachol concentration before antigen challenge was 2.6 +/- 0.3%, 24 h later carbachol concentration was significantly lower (1.8 +/- 0.3%). Both nedocromil sodium treatments blocked (P less than 0.05) this antigen-induced airway hyperresponsiveness.(ABSTRACT TRUNCATED AT 250 WORDS)     

The effect of an orally active leukotriene D4/E4 antagonist, LY171883, on antigen-induced airway responses in allergic sheep

Leukotriene (LT) D₄ is a putative mediator of allergic asthma: inhaled LTD₄ produces early and late increases in specific lung resistance (SR_L) and slows tracheal mucus velocity (TMV) similat to inhaled antigen. In this study we examined the effects of an orally active LTD₄/LTE₄ antagonist, LY171883 [1-<2-Hydroxy-3-propyl-4-<4-(1H-Tetra-zol-5-yl) Butoxy>Phenyl>Ethanonel], on early and late changes in SR_L and TMV following airway challenge with antigen in conscious allergic sheep. SR_L and TMV were measured before and up to 8 h and 24 h after antigen challenge after either LY171883 (30 mg/kg, p.o. 2 h before challenge) or placebo pretreatment. After placebo pretreatment antigen challenge resulted in significant early (483% over baseline) and late (221% over baseline) increases in SR_L (n=9). LY171883 pretreatment, however, significantly reduced the early increase in SR_L (163% over baseline) and blocked the late response. LY171883 did not prevent the antigen-induced fall in TMV from 5–8 h post challenge (n=6), but TMV recovered more rapidly in the drug trial returning to baseline values by 24 h. These results suggest that the generation of LTD₄, and its metabolite LTE₄, during airway anaphylaxis contributes to the early increase in SR_L and is important for eliciting the late increase in SR_L as well as contributing to the fall in TMV.     

Separation of late bronchial responses from airway hyperresponsiveness in allergic sheep

Allergic sheep with antigen-induced early and late responses were used to determine whether airway hyperresponsiveness (AHR) to carbachol is present during the late response and whether blocking the late response with the leukotriene D4 (LTD4) antagonist MK-571 also blocks this AHR. To do this, we first showed that MK-571 blocked the antigen-induced late response, and then, in a separate study, we determined the effect of MK-571 treatment on airway responsiveness 6 h after antigen challenge (at the start of the late response). MK-571 (5 mg, by metered dose inhaler) given 30 min before and 4 h after Ascaris suum challenge had no effect on the acute response to antigen but blocked (P less than 0.05) the late response compared with placebo (n = 7). In the second study (n = 6), the antigen-induced acute increases in mean specific lung resistance (sRL) were also similar in the placebo (249%) and drug trials (247%). By 6 h postchallenge, however, mean sRL in the placebo trial began to increase (54%, P less than 0.05), whereas in the drug trial mean sRL was baseline. Nevertheless, AHR was apparent in both trials as indicated by a mean twofold leftward shift in the dose-response curves to inhaled carbachol (P less than 0.05 vs. prechallenge). Bronchoalveolar lavage at 6 h showed that MK-571 did not prevent the inflammatory cell influx into the lung. These observations suggest that although LTD4 may be a mediator of the late response in sheep, it is not a primary mediator affecting cholinergic AHR during this period.     

Production of early and late pulmonary responses with inhaled leukotriene D4 in allergic sheep

Some allergic sheep respond to inhalation of antigen with both immediate and late increases in airflow resistance (late response). The mechanism of the late response is unknown but recent evidence suggests that the initial generation of slow-reacting substance of anaphylaxis (SRS-A) immediately after antigen challenge is a necessary pre-requisite for the physiologic expression of this late response. Based on this evidence we hypothesized that airway challenge with leukotriene D₄ (LTD₄), an active component of SRS-A would produce acute and late airway responses in allergenic sheep similar to those observed with antigen. In five allergic sheep with documented early and late pulmonary responses to antigen, inhalation of leukotriene D₄ aerosol (delivered dose {mean ±SE} 0.55±0.08 ug) resulted in significant early and late increases in specific lung resistance (SR_L). In three allergic sheep which only demonstrated acute responses to antigen, LTD₄ aerosol (delivered dose 0.59±0.09ug) only produced an acute increase in SR_L. In the late responders pretreatment with aerosol cromolyn sodium (1 mg/kg) did not affect the acute response but blunted the late increase in SR_L. Pretreatment with aerosol FPL-57231 (1% w/v solution) completely blocked both the acute and late responses. These data support the hypothesis that initial release of LTD₄ in the airways of sensitive animals is important for the physiologic expression of the late response.     

Late-phase bronchial vascular responses in allergic sheep

Sheep were classified on the basis of their airway response to Ascaris suum antigen aerosols as allergic or nonsensitive. Allergic sheep were classed as acute or dual responders. Acute responders had only an immediate increase in mean airflow resistance after antigen, whereas dual responders had an immediate and late-phase (6-8 h after antigen challenge) increase in mean airflow resistance; nonsensitive sheep had minimal airway responses to antigen (less than 30% increase from base line). The sheep were anesthetized 2 wk later and, after a left thoracotomy, were challenged with antigen to determine bronchial vascular responses; bronchial artery blood flow was measured with an electromagnetic flow probe. Airway responses to antigen aerosol challenge were similar in the anesthetized and conscious animals. The mean fall in bronchial vascular resistance (BVR) immediately after antigen challenge was similar in acute and dual responders (41 +/- 7 and 47 +/- 9% of base line, respectively). In dual responders, late-phase airway responses were preceded by a significant increase from base line in Qbr and a fall in bronchovascular resistance (BVR). The mean fall in BVR 6-8 h after antigen challenge in documented dual responders was significantly different from bronchial vascular responses in acute responders (59 +/- 3 vs. 89 +/- 10%, respectively). Sheep without airway responses to A. suum had no significant changes in bronchial hemodynamics or airways mechanics. Late-phase-associated changes in BVR are a specific response to antigen challenge and may be a sensitive index of mediators being released.(ABSTRACT TRUNCATED AT 250 WORDS)     

Ciliary responsiveness in allergic and nonallergic airways

Allergic asthma is associated with airway (smooth muscle) hyperresponsiveness to several chemical mediators of anaphylaxis; however, it is not known whether this is accompanied by mucociliary hyperresponsiveness. The purpose of this study was therefore to determine if airway ciliary activity, a component function of mucociliary clearance, exhibits exaggerated responses to prostaglandin E1 (PGE1), prostaglandin E2 (PGE2), and leukotriene D4 (LTD4) in allergic sheep when compared with nonallergic sheep, and the effects of LTD4 are direct or involve the generation of cyclooxygenase products of arachidonate metabolism. Ciliary beat frequency (CBF) was measured in a perfusion chamber with a microscopic technique using tracheal epithelial cells obtained from brushing of "allergic" (positive cutaneous reaction and previous bronchospastic response to inhaled specific antigen) and "nonallergic" (negative cutaneous reaction, no previous inhalation challenge with antigen) sheep. Mean base-line CBF was not different among the groups; PGE1, PGE2, and LTD4 induced dose-dependent increases in CBF, and these increases were not different in allergic and nonallergic sheep. At the highest agonist concentration the mean increase in CBF from base line varied between 13 and 16% (P less than 0.05). The ciliostimulatory effect of LTD4 was significantly blunted by both the sulfidopeptide leukotriene antagonist FPL-55712 and the cyclooxygenase inhibitor indomethacin. These results suggest that allergic sheep fail to exhibit ciliary hyperresponsiveness to selected chemical mediators of anaphylaxis and the ciliostimulatory effect of LTD4 depends on the activation of cyclooxygenase and possibly the generation of prostaglandins.     

Pharmacology of aerosol leukotriene C4- and D4-induced alteration of pulmonary mechanics in anesthetized cynomolgus monkeys

Aerosol administration of solutions of 900 micrograms/ml of leukotriene C4 (LT) or D4 to cynomolgus monkeys produced dose-dependent, equipotent increases in pulmonary resistance (Rp) and decreases in dynamic lung compliance (Cdyn). Time to peak response was, in part, related to dose and ranged from 4 to 20 min. Both LTC4 and LTD4 were less potent than histamine. Aerosol pretreatment with the cyclooxygenase inhibitor indomethacin had no significant effect on either LTC4 or LTD4 dose-response curves; however, at the highest doses of these agonists a notable, nonsignificant inhibition of effects on both Rp and Cdyn was seen. Intravenous dl-propranolol had no effect on responses to LTD4. Aerosol pretreatment with FPL 55712 significantly (P less than 0.05) inhibited airway responses to both LTC4 and D4. In contrast, an intravenous infusion of FPL 55712 failed to block the bronchospastic activity of LTD4. In conclusion, cynomolgus monkeys are responsive to aerosol administration of LTC4 and LTD4, and the pharmacology of their responses appears to resemble that of man.     

Inhibition of allergic late airway responses by inhaled heparin-derived oligosaccharides.

Inhaled heparin has been shown to inhibit allergic bronchoconstriction in sheep that develop only acute responses to antigen (acute responders) but was ineffective in sheep that develop both acute and late airway responses (LAR) (dual responders). Because the antiallergic activity of heparin is molecular-weight dependent, we hypothesized that heparin-derived oligosaccharides (<2, 500) with potential anti-inflammatory activity may attenuate the LAR in the dual-responder sheep. Specific lung resistance was measured in 24 dual-responder sheep before and serially for 8 h after challenge with Ascaris suum antigen for demonstration of early airway response (EAR) and LAR, without and after treatment with inhaled medium-, low-, and ultralow-molecular-weight (ULMW) heparins and "non-anticoagulant" fractions (NAF) of heparin. Airway responsiveness was estimated before and 24 h postantigen as the cumulative provocating dose of carbachol that increased specific lung resistance by 400%. Only ULMW heparins caused a dose-dependent inhibition of antigen-induced EAR and LAR and postantigen airway hyperresponsiveness (AHR), whereas low- and medium-molecular-weight heparins were ineffective. The effects of ULMW heparin and ULMW NAF-heparin were comparable and inhibited the LAR and AHR even when administered "after" the antigen challenge. The ULMW NAF-heparin failed to inhibit the bronchoconstrictor response to histamine, carbachol, and leukotriene D(4), excluding a direct effect on airway smooth muscle. In six sheep, segmental antigen challenge caused a marked increase in bronchoalveolar lavage histamine, which was not prevented by inhaled ULMW NAF-heparin. The results of this study in the dual-responder sheep demonstrate that 1) the antiallergic activity of inhaled "fractionated" heparins is molecular-weight dependent, 2) only ULMW heparins inhibit the antigen-induced EAR and LAR and postantigen AHR, and 3) the antiallergic activity is mediated by nonanticoagulant fractions and resides in the ULMW chains of <2,500.     

Pharmacological characterization using selected antagonists of the leukotriene receptors mediating contraction of guinea-pig trachea

The effects of six leukotriene (LT) antagonists on LTC4-, D4- and E4-induced contraction of isolated guinea-pig tracheal spirals were examined. Concentration-response effects of the leukotrienes were determined by cumulative addition in the presence of indomethacin (5 microM) alone for LTE4, or with 10 mM of either glutathione or L-cysteine to inhibit metabolism of LTC4 or LTD4, respectively. Concentration-response curves to the LTs were obtained in the absence and presence of Wy-45,911, Wy-44,329, FPL-55,712, Ly-171,883, Wy-48,252 and ICI-198,615 representing three structurally different chemical groups of LT antagonists. At 30 microM, the antagonists produced little or no antagonism of LTC4-induced contractions. Analysis of the Schild plots for antagonism of LTD4 and E4 suggested two receptors for the agonist effects of LTD4 and a single receptor for the agonist effects of LTE4. Comparison of pA2 values for Wy-45,911, FPL-55,712, LY-171,883 and Wy-48,252 provided evidence that LTE4 is acting at the antagonist high affinity LTD4 receptor to produce contractile effects. From the data, we conclude that there are three LT receptors (one for LTC4 and two LTD4 subtypes) through which exogenously applied LTs evoke contraction of the isolated guinea-pig trachea.     

Bronchodilator drugs and their combinations antagonize the dose-related leukotriene D4-induced airway obstruction in guinea pigs

The effects of theophylline (THEO), terbutaline (TER), and ipratropium bromide (IPRA), given i.v. alone or in combination, were studied on leukotriene D4 (LTD4)-induced airway obstruction in anaesthetized guinea pigs. LTD4 (0.1-1.6 microgram/kg i.v.) obstructed small airways more than large ones as assessed in terms of relative changes of lung resistance (RL) and dynamic lung compliance (CDyn). A slight tachyphylaxis to LTD4 was observed after repeated administration, especially in the responses of large bronchi. The airway effects of LTD4 were almost totally abolished by prior administration of indomethacin (5 mg/kg i.v.) suggesting a central role of secondarily released cyclo-oxygenase products in this model. THEO (1 to 20 mg/kg) and TER (10 to 400 micrograms/kg) antagonized dose-dependently the LTD4 (0.4 microgram/kg i.v.) induced rise in RL and decrease in CDyn, whereas IPRA (10 to 400 micrograms/kg) failed to show comparably activity. THEO 5 and 20 mg/kg proved highly efficient also on the dose-related airway challenge by LTD4 (0.6 and 1.5 microgram/kg i.v.). Combined treatment with THEO 5 mg/kg + Ter 80 micrograms/kg resulted in an additive effect on RL and CDyn. The combination to THEO 20 mg/kg + TER 80 micrograms/kg was about as effective as THEO 20 mg/kg alone suggesting a nearly maximal effect by the latter treatment. It is concluded that THEO is considerably more efficient on the LTD4-induced airway obstruction than previously observed on the cholinergic model in guinea pigs. Combined treatment with THEO and beta 2-adrenoceptor agonist may antagonize in an additive manner the LTD4 effects on large and small airways.     

Effects of a newly synthesized leukotriene antagonist, NZ-107, on immediate-type hypersensitivity reaction in rats and guinea-pigs.

The effects of 4-bromo-5-(3-ethoxy-4-methoxybenzylamino)-3(2H)-pyridazinone (NZ-107) on immediate type hypersensitivity reactions in rats and guinea-pigs were studied. 1. When NZ-107, at a dose of 50 mg/kg (i.p.) or 100 mg/kg (orally), was administered to rats, 48-h homologous passive cutaneous anaphylaxis (PCA) reaction and histamine-, leukotriene C4 (LTC4)- and leukotriene D4 (LTD4)-induced skin reactions were suppressed by the agent. 2. NZ-107 (10(-6) g/ml) inhibited both LTC4- and LTD4-induced contractions of isolated rat stomach smooth muscle. 3. NZ-107 inhibited antigen-induced histamine release from rat peritoneal mast cells by 26% at a concentration of 10(-4) g/ml. 4. NZ-107, at doses of 25 and 50 mg/kg (orally), significantly inhibited guinea-pig 3-h heterologous PCA reaction. 5. NZ-107 inhibited antigen-induced histamine release from guinea-pig lung tissue by 17% and 48% at concentrations of 5 x 10(-5) and 10(-4) g/ml, respectively. 6. NZ-107, at doses of 25 and 50 mg/kg (i.p.), inhibited antigen-induced bronchoconstriction and eosinophil accumulation in the bronchoalveolar lavage fluid (BALF) of guinea-pigs. These results suggest that NZ-107 has anti-allergic action including inhibition of eosinophil accumulation in an antigen-challenged airway lesion in rats and guinea-pigs. The anti-allergic action of this agent is thought to be due to its action as a histamine and LT antagonist and its consequent inhibition of antigen-induced histamine release.     

Immediate hypersensitivity reactions in the guinea-pig conjunctiva: studies with a second-generation leukotriene D4 receptor antagonist, MK-571

The role of leukotriene D4 (LTD4) as a mediator of immediate hypersensitivity reactions in the guinea-pig conjunctiva was examined using a potent, second-generation LTD4 receptor antagonist, MK-571 (also known as L-660,711). The microvascular permeability changes in the guinea-pig conjunctiva following challenge with either LTD4 or antigen were measured through accumulation of intravenously administered 99mtechnetium-labeled albumin. Topical application of MK-571 (up to 2 h pretreatment) significantly inhibited the conjunctival responses to LTD4 (ED50 of 18-60 ng/eye) but not to histamine. The responses to a single topical antigen challenge in ovalbumin-sensitized guinea pigs were significantly inhibited (44%) by topical treatment with MK-571, in contrast to the lack of effect previously observed with prototypic antagonists. The inhibitory effects of MK-571 did not involve an action on conversion of [3H]LTC4 to LTD4 and LTE4. Following a second antigen challenge (24 h after the first), MK-571 inhibited the resultant permeability changes by 78%. Specific histamine H1 and H2 antagonists similarly inhibited the responses to the first and second challenges (63 and 74%, respectively). The present study suggests that LTD4 is involved in conjunctival hypersensitivity reactions and that potent LTD4 receptor antagonists may be of therapeutic value in the treatment of allergic conjunctivitis.