Vagal stimulation augments pulmonary anaphylaxis in the guinea pig lung.

The effect of bilateral vagal stimulation on aerosolized antigen-induced responses was examined in the sensitized, perfused guinea pig lung. Vagal stimulation in the sensitized, perfused lung resulted in bronchoconstriction (peak response 160 +/- 18% above baseline) that was unaffected by either atropine (1 microM), a muscarinic receptor antagonist, or CP 96,345 (1 microM), a NK-1 receptor antagonist, but was transiently augmented in the presence of physostigmine (1 microM), a cholinesterase inhibitor, through an atropine-sensitive mechanism. However, SR 48968 (1 microM), a NK-2 receptor antagonist, and SR 48968 + CP 96,345 reduced by approximately 50 and 90%, respectively, vagally mediated increases in intratracheal pressure in the perfused lung. Simultaneous challenge with vagal stimulation and aerosolized antigen in the sensitized perfused lung resulted in a significant (p < 0.01) increase in intratracheal pressure (Pi), pulmonary arterial pressure (Ppa), and lung weight (LW) compared with either vagal stimulation or aerosolized antigen alone. Increases in Pi, Ppa, and LW in response to vagal stimulation + aerosolized antigen were associated with elevated venous effluent concentrations of thromboxane A2 (TXA2), prostacyclin, leukotriene C4, and histamine. Vagally mediated potentiation of aerosolized antigen-induced increases in Pi, Ppa, and LW was unaffected by atropine or CP 96,345 but was inhibited by the NK-2 receptor antagonist, SR 48968. These data suggest that vagally mediated (predominantly NK-2) potentiation of aerosolized antigen-induced increases in Pi, Ppa, and LW is characterized by elevated venous effluent concentrations of eicosanoids and histamine.

Pharmacologic actions of Ro 24-5913, a novel antagonist of leukotriene D4.

Ro 24-5913, (E)-4-[3-[2-(4-cyclobutyl-2- thiazolyl)ethenyl]phenylamino]-2,2-diethyl-4-oxobutanoic acid, has been identified as a chemically unique, potent and selective LTD4 antagonist. In vitro, Ro 24-5913 competes with [3H]LTD4 for its binding site on guinea pig lung membranes with an IC50 of 6.4 +/- 2.2 nM. In isolated guinea pig tracheal smooth muscle, Ro 24-5913 produces concentration-dependent rightward shifts of LTD4-induced contraction curves (pA2 value of 9.6 +/- 0.2). The slope of the Schild plot is not significantly different from 1, indicating that the antagonism is of a competitive nature. In the human bronchus, Ro 24-5913 is an effective antagonist of LTD4-induced contractions (pKB of 9.3 +/- 0.1). In vivo, Ro 24-5913 dose-dependently inhibits LTD4-induced bronchoconstriction in guinea pigs by the i.v. (ID50 0.13 mg/kg), oral (ID50 0.12 mg/kg) and aerosol (IC50 0.008%) routes of administration. This in vivo activity is specific as evidenced by the inability of Ro 24-5913 to inhibit bronchoconstriction induced by LTB4, PAF or histamine. In comparison with other LTD4 antagonists evaluated in this guinea pig model, Ro 24-5913 is markedly superior in terms of oral potency, bioavailability and oral duration of action. Ro 24-5913 also blocks allergic bronchospasm mediated by endogenously generated leukotrienes in guinea pigs; the potency and duration of action is nearly equivalent to that seen as an antagonist of bronchoconstrictions produced by exogenous LTD4. In summary, Ro 24-5913 is representative of a novel chemical class of LTD4 receptor antagonists.(ABSTRACT TRUNCATED AT 250 WORDS)

Pharmacology of a potent platelet-activating factor antagonist: Ro 24-4736.

Ro 24-4736, (5-(3-[4-(2-chlorophenyl)-9-methyl-6H-thieno[3,2-f] [1,2,4]triazolo[4,3-a][1,4]diazepin-2-yl]-2-propynyl)phenanthri din- 6(5H)-one), has been identified as a potent, selective, p.o.-active platelet-activating factor (PAF) antagonist with a long duration of action. In vitro, Ro 24-4736 competes with [3H]PAF for its receptor site on dog platelets with an IC50 of 9.8 +/- 1.0 nM and selectively inhibits PAF-induced aggregation of guinea pig, dog and human platelets with concentration dependence. Ro 24-4736 dose-dependently inhibits in vivo bronchoconstriction (ID50 of 0.006-mg/kg p.o.) and ex vivo platelet aggregation (ID50 of 0.004 mg/kg p.o.) induced by PAF in guinea pigs. Time course studies show complete blockade of PAF-induced platelet aggregation (ex vivo) up to 8 hr after a single p.o. dose of 0.03 mg/kg as well as a long duration of action in vivo (30 hr). The in vivo PAF antagonistic activity is specific because, even at high p.o. doses (up to 10 mg/kg), Ro 24-4736 shows no inhibitory activity toward the bronchoconstrictor effects of leukotriene D4 or histamine. In comparison with other PAF antagonists evaluated in this guinea pig model, Ro 24-4736 is markedly superior in terms of p.o. potency, bioavailability and p.o. duration of action. Studies were also performed with Ro 24-4736 in additional in vivo models. When administered p.o. to sensitized guinea pigs, the drug attenuates inhaled antigen-induced airway hyper-reactivity without effect on bronchoalveolar lavage leukocyte accumulation.(ABSTRACT TRUNCATED AT 250 WORDS)

Differential effects of propranolol on the IgE-dependent, or calcium ionophore-stimulated, phosphoinositide hydrolysis and calcium mobilization in a mast (RBL 2H3) cell line.

Our previous studies demonstrated that propranolol, an inhibitor of phosphatidic acid phosphohydrolase (PAPase) (EC 3.1.3.4) blocks the IgE-dependent mediator release from a rat mast (RBL 2H3) cell line. To continue these studies, we examined the ability of propranolol to inhibit the IgE-dependent or ionomycin-mediated phosphoinositide hydrolysis and calcium mobilization in RBL 2H3 cells. RBL 2H3 cells, sensitized with mouse monoclonal anti-trinitrophenol IgE (anti-TNP IgE), were stimulated to release both histamine and peptidoleukotrienes (LT) in response to a suboptimal concentration of trinitrophenol-ovalbumin conjugate (TNP-OVA) or ionomycin. Preincubation of the cells with d,l-propranolol (300 microM) significantly (P less than 0.05) inhibited the effects of both TNP-OVA and ionomycin on histamine and LT release. There was no difference in potency for the different isomers of propranolol, indicating that these effects were not a consequence of an effect on beta 2-adrenergic receptors. TNP-OVA produced a rapid hydrolysis of phosphoinositides resulting in a time-dependent increase in mono- (IP1), di- (IP2), tri- (IP3), and total inositol phosphate production. Ionomycin also produced a rapid increase in total inositol phosphate production; however, this largely reflected an accumulation of IP1. Both secretagogues produced a rapid elevation in cytosolic free calcium ([Ca2+]i); however, the effect of ionomycin maximized within a much shorter time frame than the effect of TNP-OVA. The effects of TNP-OVA on phosphoinositide hydrolysis and increase in [Ca2+]i were inhibited by propranolol over exactly the same concentration range as the effects of this compound on TNP-OVA-stimulated mediator release. In contrast, propranolol had no effect on the increase in [Ca2+]i and phosphoinositide hydrolysis in response to ionomycin. Taken together, these results suggest that PAPase/phospholipase D (PLD) (EC 3.1.4.4) activation may be a prerequisite for both IgE-dependent and ionomycin-stimulated mediator release from RBL 2H3 cells. Although other explanations are possible, the data further suggest that receptor-mediated, but not ionophore-stimulated, phosphoinositide hydrolysis and [Ca2+]i in RBL 2H3 cells may be regulated by a propranolol-sensitive pathway involving possible activation of PAPase.

Cytosolic calcium ion and arachidonic acid release and metabolism in macrophages.

The aim of the present work was to elucidate the role of cytosolic calcium ions, [Ca2+]i, in the control of arachidonic acid release and metabolism. [Ca2+]i was measured in resident peritoneal rat macrophages loaded with Fura2, and compared with the release of leukotriene B4(LTB4) and prostaglandin l2 (PGL2, assayed through its hydrolysis product 6-keto-PGF1 alpha). The calcium ionophore A 23187 stimulated both an increase in [Ca2+]i and the release of LTB4 and 6-keto-PGF1 alpha. On the contrary, zymosan and opsonized zymosan, while stimulating eicosanoid release to an extent only slightly lower than A 23187, did not affect [Ca2+]i. Lipopolysaccharide stimulated 6-keto-PGF1 alpha, but not LTB4, release, without affecting [Ca2+]i. In parallel experiments, macrophages were prelabelled with [3H]arachidonic acid and the release of total 3H-products was assayed and taken as an index of phospholipase activity. A 23187, zymosan and opsonized zymosan increased the release of 3H-products in the presence of Ca2+. When extracellular Ca2+ was removed, the ionophore-induced 3H-products release was greatly blunted, while the release induced by zymosan was actually augmented. Our data indicate that a generalized [Ca2+]i increase is not necessary for arachidonic acid release and metabolism in rat peritoneal macrophages.

Phospholipase A2-induced pulmonary and hemodynamic responses in the guinea pig. Effects of enzyme inhibitors and mediators antagonists.

The effect of phospholipase A2 (Naja naja) PLA2) on mean arterial blood pressure and intratracheal pressure was examined in anesthetized guinea pigs. Intracheally administered PLA2 (1 to 10 U) produced acute, dose-dependent increases in mean arterial blood pressure and intracheal pressure. However, Intravenously administered PLA2 (doses as large as 1,000 U) did not alter monitored variables. Acute PLA2-induced morphologic alterations were characterized by airway constriction, airway/alveolar cell damage, and pulmonary sequestration of both leukocytes and platelets. PLA2-induced increases in both mean arterial blood pressure and intratracheal pressure were attenuated to varying degrees by pretreating intravenously with indomethacin (10 mg/kg), a cyclooxygenase inhibitor, and WEB 2086 (0.1 mg/kg), a platelet-activating factor antagonist. Both ICI 198,615 (1 mg/kg), a leukotriene D4, receptor antagonist given intravenously, and dexamethasone (50 mg/kg), a steroidal anti-inflammatory agent given intraperitoneally as a 2-day pretreatment, reduced PLA2-induced increases in intratracheal pressure. Pyrilamine (2 mg/kg), a histamine1-receptor antagonist given intravenously, did not modify PLA2-induced pathophysiologic responses. Guinea pigs exposed to aerosolized PLA2 (100 U/ml) exhibited evidence of increased bronchoalveolar lavage macrophage, leukocyte, and lymphocyte accumulation at 24 h post-PLA2. These studies suggest that in vivo PLA2-induced pathophysiologic changes in the guinea pig involve alterations in resident airway cell populations as well as sequestration and infiltration of inflammatory cells. Both eicosanoids and platelet-activating factor appear to contribute to these PLA2-induced pathophysiologic effects.

Propenyl carboxamide derivatives as antagonists of platelet activating factor.

A series of N-[4-(3-pyridinyl)butyl] 3-substituted propenyl carboxamide derivatives bearing an unsaturated bicyclic moiety in the 3-position was prepared and evaluated for PAF (platelet activating factor) antagonist activity. These compounds represent conformationally constrained direct analogues of the corresponding potent 5-aryl-pentadienecarboxamides (5). Most of the new compounds were active in a PAF-binding assay employing whole, washed dog platelets as the receptor source and inhibited PAF-induced bronchoconstriction in guinea pigs after intravenous administration. However, oral activity in the PAF-induced bronchoconstriction model was highly sensitive to the nature and substitution of the bicyclic ring system. The most interesting compounds included [R-(E)]-(1-butyl-6-methoxy-2-naphthyl)-N-[1-methyl-4-(3- pyridinyl)butyl]-2-propenamide (4b), [R-(E)]-(3-butyl-6-methoxy-2- benzo[b]thiophene-yl)-N-[1-methyl-4-(3-pyridinyl)butyl]-2-propenamide (4k), and [R-(E)]-(3-butyl-6-methoxy-1-methyl-2-indoly)-N-[1-ethyl-4- (3-pyridinyl)butyl]-2-propenamide (4l) which inhibited PAF-induced broncho-constriction in guinea pigs with IC50s of 3.0-5.4 mg/kg, when the animals were challenged 2 h after drug treatment. They were also highly effective 6 h after a 50 mg/kg oral dose. This study supports the notion that the key remote aromatic ring present in the 5-arylpentadienecarboxamides (5) is preferentially coplanar with the diene system for good PAF antagonist activity.

The effects of the protein kinase C inhibitors staurosporine and H7 on the IgE dependent mediator release from RBL 2H3 cells.

RBL 2H3 cells, a model for mast cell function, sensitized with rat IgE, released histamine and peptidoleukotrienes (LT) in response to rabbit anti-rat IgE in a concentration-dependent manner. The calcium ionophore, A23187 also stimulated the release of both mediators but to a greater extent. The protein kinase C activator, 12-O-tetradecanoyl phorbol-13-acetate (TPA) failed to influence mediator release when added alone, but when added with either A23187 or anti-IgE, TPA significantly enhanced the release of both histamine and LT. The effects of anti-IgE, TPA and A23187 were completely inhibited by prior addition of the protein kinase C inhibitors staurosporine and 1-(5-isoquinolinesulfonyl)-2-methylpiperazine dihydrochloride (H7) but not by N-(2-guanidinoethyl)-5-isoquinoline-sulfonamide dihydrochloride (HA1004), a compound which has similar potency to H7 as an inhibitor of some protein kinases but is less potent as a protein kinase C inhibitor. Although other explanations are possible, these results support the hypothesis that the release of histamine and leukotrienes from RBL 2H3 cells resulting from the cross bridging of the IgE receptors, is dependent on activation of protein kinase C.

Pertussis toxin pretreatment reveals differential effects of adenosine analogs on IgE-dependent histamine and peptidoleukotriene release from RBL-2H3 cells.

The effects of adenosine (A) and the nonmetabolizable adenosine analogs, N-ethylcarboxamidoadenosine (NECA), L-phenylisopropyladenosine (L-PIA), D-PIA and 2-chloroadenosine (2CHA) were examined on the IgE-dependent mediator release from RBL-2H3 cells, a model for mast-cell function. Adenosine and the adenosine analogs failed to influence mediator release from cells, previously sensitized with monoclonal anti-TNP mouse immunoglobulin E (anti-TNP IgE), when added alone. When added prior to conjugated trinitrophenol-ovalbumin (TNP-OVA), adenosine and the adenosine analogs (10(-8)-10(-4) M) significantly potentiated the release of both histamine (marker for degranulation) and peptidoleukotrienes (LT) (marker for de novo synthesized mediators). The effects were concentration-dependent with the potency order being L-PIA greater than NECA greater than A greater than D-PIA, 2CHA. The stimulatory effect on both histamine and LT release were reversed by prior treatment of the cells with pertussis toxin but not by the purinoceptor antagonists, theophylline and 8-phenyltheophylline, nor adenosine uptake blockers. At higher concentrations (above 10(-5) M), adenosine and adenosine analogs were also inhibitory on LT but not on histamine release. This inhibition was more evident on pertussis-toxin-treated cells in which there was no effect of adenosine or adenosine analogs on histamine release, but a concentration-dependent inhibition of IgE-dependent LT release. These findings demonstrate that adenosine analogs have two distinct mechanisms on mediator release from RBL-2H3 cells; a stimulatory effect on both histamine and LT release, mediated via a pertussis-toxin-sensitive G protein and an inhibitory effect on LT release via a pertussis-toxin-insensitive pathway. An abstract of this work has been published.

Ro 19-3704 directly inhibits immunoglobulin E-dependent mediator release by a mechanism independent of its platelet-activating factor antagonist properties.

Rat basophilic leukemia (RBL 2H3) cells were passively sensitized by exposure to monoclonal anti-trinitrophenol mouse immunoglobulin E (anti-trinitrophenol IgE) (0.5 microgram/ml) and triggered by exposure to a sub-optimal concentration of trinitrophenol ovalbumin conjugate (5 ng/ml). At this concentration, trinitrophenol-ovalbumin increased histamine release from a basal rate of 4.8 +/- 0.5 to 28.5 +/- 4.6% and peptidoleukotrienes from less than 0.1 to 4.2 +/- 1.3 ng/10(6) cells in the activated cells. Ro 19-3704 and Ro 19-1400, platelet activating factor (PAF) antagonists which are structural analogs of PAF, potently inhibited both the IgE-dependent release of histamine (IC50 values of 3.0 and 3.6 microM, respectively) and LT release (IC50 values of 5.0 microM for both compounds) from the cells. These effects appeared to be independent to the ability of the compounds to act as PAF antagonists since PAF on its own had no effect on mediator release, and WEB 2086 and BN 52021, structurally distinct PAF antagonists, were relatively ineffective as inhibitors of mediator release. Ro 19-3704 and Ro 19-1400 were observed to be potent inhibitors of the soluble phospholipase A2 activity in synovial fluid from rheumatoid arthritic patients (IC50 values of 6.5 and 8.4 microM, respectively). In contrast, WEB 2086 and BN 52021 had no effect on this phospholipase A2. Ro 19-3704 significantly inhibited the IgE-dependent formation of inositol phosphates in RBL 2H3 cells (IC50 value of 7.0 microM). These data suggest that the mediator release inhibitory action of these compounds may be related to the ability of these compounds to inhibit phospholipase A2 and/or phospholipase C.

Pulmonary responses to phospholipase A2 in the perfused guinea pig lung.

We examined the effect of phospholipase A2 (PLA2; Naja naja) challenge on pulmonary hemodynamics, airway constriction, and fluid filtration in isolated Ringer-perfused guinea pig lungs. Intratracheal PLA2 (10-100 U) produced dose-dependent increases in pulmonary arterial pressure, intratracheal pressure, and lung weight, although intravenous PLA2 administration had no effect on monitored variables. Morphological features indicative of airway constriction and pulmonary edema were observed by light microscopy. PLA2-induced increases in intratracheal pressure and/or lung weight were attenuated to varying degrees by pretreatment with indomethacin (1 microM, a cyclooxygenase inhibitor), ICI-198,615 (1 microM, a leukotriene D4 receptor antagonist), and WEB 2086 (1 microM, a platelet-activating factor antagonist). PLA2-induced increases in pulmonary arterial pressure and intratracheal pressure were also reduced in lungs removed from animals pretreated with dexamethasone (50 mg/kg ip for 2 days; a steroidal antiinflammatory agent). Pyrilamine (1 microM, a histamine1-receptor antagonist) and Takeda AA861 (1 microM, a delta 5-lipoxygenase inhibitor) did not produce significant inhibitory effects on PLA2-induced pathophysiological changes. Intratracheal instillation of high-dose platelet-activating factor (50 micrograms) or lysophosphatidylcholine (100 micrograms) produced gradual increases in intratracheal pressure and lung weight, but these changes were not as large as those induced by PLA2. Thus these studies suggest that resident cell populations associated with airways may play an important role in PLA2-induced pathophysiological changes in the perfused guinea pig lung. These PLA2-induced effects are most likely partially mediated by generation of eicosanoids and platelet-activating factor.

Biphenylcarboxamide derivatives as antagonists of platelet-activating factor.

A series of N-[4-(3-pyridinyl)butyl]-1,1'-biphenyl-4-carboxamides was prepared, and the compounds were evaluated for platelet-activating factor (PAF) antagonist activity in a binding assay employing washed, whole dog platelets and in vivo for their ability to inhibit PAF-induced bronchoconstriction in the guinea pig. The inclusion of a methyl group in the R configuration on the side-chain carbon adjacent to the carboxamide nitrogen atom of these derivatives resulted in a marked enhancement of potency in the binding assay for compounds unsubstituted in the biphenyl 2-position and, more importantly, in improved oral bioavailability. Previous work with related pyrido[2,1-b]-quinazoline-8-carboxamides suggests that the presence of such an alkyl group improves bioavailability by rendering the resulting compounds resistant to degradation by liver amidases. The most interesting compounds to emerge from this work are (R)-2-bromo-3',4'-dimethoxy-N-[1-methyl-4-(3-pyridinyl)butyl]-1,1'-bi phe nyl- 4-carboxamide (33) and (R)-2-butyl-3',4'-dimethoxy-N-[1-methyl-4-(3-pyridinyl)butyl]- 1,1'-biphenyl-4-carboxamide (40) each of which inhibits PAF-induced bronchoconstriction in the guinea pig by greater than 55%. 6 h after an oral dose of 50 mg/kg.

Anti-inflammatory and immuno-modulatory effects of novel retinoid-like 2,4,6,8-nonatetraenoic acids (NTA) in adjuvant-induced arthritis.

Prophylactic treatment (p.o.) of rats with adjuvant-induced arthritis (AA) with two retinoid-like 2,4,6,8-nonatetraenoic acids (NTA), Ro 23-6457 and Ro 23-2895, significantly reduced hind paw swelling between days 10-23 and the level of plasma fibrinogen (MED approximately 25 mumoles/kg). When given therapeutically (75 mumoles/kg between day 21 and 28) either NTA arrested the progression of the disease (MED, 25-75 mumoles/kg). Unseparated and adherent cell (AC) depleted spleen cells from rats with AA (day 12-15) responded poorly to the T cell mitogen, Con A (2.5 micrograms/ml) and the B cell mitogen, LPS (10 micrograms/ml). The responses were partially restored (approximately 30% of normal responses) in AC-depleted (but not unseparated) spleen cells from Ro 23-6457 treated rats (75 and 250 mumoles/kg/day). These data demonstrate an immunomodulatory effect of Ro 23-6457 in the adjuvant rat which may contribute to its anti-inflammatory activity in AA.

Sodium-calcium exchange in sarcolemmal vesicles from tracheal smooth muscle.

Sarcolemmal vesicles prepared by a new procedure from bovine tracheal smooth muscle were found to have a Na-Ca exchange activity that is significantly higher than that reported for different preparations from other types of smooth muscle. The exchange process system co-purified with 5'-nucleotidase, a plasma membrane marker enzyme, and was significantly enriched (over 100-fold) compared to mitochondria (cytochrome-c oxidase) but only slightly enriched (4-fold) compared to sarcoplasmic reticulum (NADPH-cytochrome-c reductase). The Na+ dependence of Ca2+ transport was demonstrated through both uptake and efflux procedures. The uptake profile with respect to Ca2+ was monotonic with a linear vo VS. vo.S-1 plot. The resultant Km of Ca2+ from the airway sarcolemmal vesicles (20 microM) was similar in magnitude to the Km of cardiac sarcolemmal vesicles (30 microM). Tracheal vesicles demonstrated a Vmax of 0.3-0.5 nmol.mg-1.s-1 which is significantly higher than that reported in preparations from other smooth muscle types. Furthermore, two processes found to stimulate cardiac Na-Ca exchange, pretreatment with either a mixture of dithiothreitol and Fe2+ or with chymotrypsin, were ineffective on the tracheal smooth muscle. Thus, the Na-Ca exchanger identified in tracheal smooth muscle appears to be different from that observed in cardiac muscle, implying that regulation of this activity may also be different.

Comparative study of natural and synthetic retinoids as inhibitors of arachidonic acid release and metabolism in rat peritoneal macrophages.

The effect of several natural and synthetic retinoids on the release and metabolism of arachidonic acid (20:4) in rat peritoneal macrophages (M phi), stimulated in vitro by either Ca2+ ionophore A23187 (A23187), opsonized zymosan (OZ) or 12-O-tetradecanoylphorbol-13-acetate (TPA), was investigated. With the exception of Ro 10-1670, the retinoids containing a free carboxylic acid group [i.e., all-trans-retinoic acid (all-trans-RA), 13-cis-RA, Ro 13-7652, Ro 12-7310 and Ro 13-7410] inhibited 20:4 metabolite formation in A23187- and OZ-stimulated Mø at 1-33 microM. However, only all-trans-RA, Ro 12-7310 and Ro 13-7410 inhibited the formation of 20:4 metabolites in TPA-stimulated Mø. These data suggest that part of the therapeutic effect of retinoids in inflammatory, hyperproliferative dermatologic conditions might be attributed to reduced 20:4 metabolite production.

N-(heterocyclic alkyl)pyrido[2,1-b]quinazoline-8-carboxamides as orally active antiallergy agents.

A series of N-(heterocyclic alkyl)pyrido[2,1-b]quinazoline-8-carboxamides were evaluated for their ability to antagonize slow-reacting substance of anaphylaxis (SRS-A) induced contractions of guinea pig ilea and to inhibit thromboxane synthase in vitro. The results indicated that those pyrido[2,1-b]quinazoline-8-carboxamides bearing a branched-chain alkyl moiety in the 2-position and a four to six atom linear chain between a 3- or 4-substituted pyridine or a 1-substituted imidazole ring and the carboxamide nitrogen atom showed the best combination of potencies in the two assays. Several of these compounds were found to be orally active inhibitors of LTE4-induced bronchoconstriction in the guinea pig and LTE4-induced skin wheal formation in the rat. One of the most potent analogues, 2-(1-methyl-ethyl)-N-(1H-imidazol-1-ylbutyl)-11-oxo-11H-pyrido [2,1-b]quinazoline-8-carboxamide (36), was selected for extensive pharmacological investigation. It was found that this compound was not a specific inhibitor of LTE4-induced symptomatology, but exhibited more general activity by inhibiting bronchospasm in guinea pigs induced by LTC4, LTD4, PAF, and histamine and skin wheal formation in rats and guinea pigs induced by LTC4, LTD4, and PAF. In addition, 36 was orally active in the passive cutaneous anaphylaxis assay, suggesting that it also exhibits mediator release inhibitory activity. On the basis of the overall pharmacological profile of 36 and its closely related analogues, it was concluded that these compounds may be useful for the treatment of asthma.