Antigen-induced Histamine Release Research Articles

Blocking of passive sensitization of human mast cells and basophil granulocytes with IgE antibodies by a recombinant human epsilon-chain fragment of 76 amino acids.

The recombinant peptide corresponding to residues 301-376 at the junction of constant regions 2 and 3 of the human IgE epsilon chain blocked the in vivo passive sensitization of human skin mast cells and in vitro sensitization of human basophil granulocytes with human IgE antibodies. An injection of the recombinant peptide or E myeloma protein into normal skin sites 1 hr before sensitization with an allergic serum blocked passive sensitization. In this system, approximately 10-fold higher molar concentration of the recombinant peptide than E myeloma protein was required for 50% inhibition of Prausnitz-Küstner reactions. When the mononuclear cells of two normal individuals were preincubated with the recombinant peptide or E myeloma protein for 15 min before passive sensitization with the same allergic serum and the cells were challenged with an optimal concentration of an antigen, approximately 11- to 13-fold higher concentration of the recombinant peptide than E myeloma protein was required for 50% inhibition of antigen-induced histamine release. Further studies with several recombinant peptides indicated that amino acid resides 363-376 in the Fc epsilon-chain fragment are not essential for binding of the peptide to Fc epsilon-chain receptor I.

Role of adenosine in hypoxic alterations of anaphylaxis of isolated guinea pig hearts.

Previous studies suggest that high levels of adenosine may enhance histamine release and contribute to atrioventricular (AV) nodal conduction arrhythmias during anaphylaxis of isolated guinea pig hearts. To determine whether elevations in endogenous adenosine evoked by hypoxic conditions have similar effects, isolated hearts of guinea pigs passively sensitized by intracardiac injection were perfused with solutions equilibrated with 95% O2 (normoxia) or 30% O2 (hypoxia). When compared with normoxia, hypoxia before antigen challenge increased adenosine release, decreased vascular resistance, and prolonged P-R intervals, whereas hypoxia during anaphylaxis potentiated the increase in adenosine release, attenuated the increases in vascular resistance and atrial rate, and increased the occurrence of conduction arrhythmias without altering the antigen-induced release of either histamine or thromboxane. Addition of the adenosine receptor antagonist 8-(4-sulfophenyl)theophylline (SP-T) to the hypoxic perfusate significantly decreased antigen-induced release of histamine and thromboxane. These data indicate that 1) hypoxia-induced depression of antigen-induced mediator release may be counteracted by the stimulatory effect of the increased adenosine induced by hypoxia, and 2) under hypoxic conditions, adenosine's negative dromotropic, chronotropic, and vasodilatory effects may influence the anaphylactic reaction.

Relevance of basophil histamine release changes during venom immunotherapy

We investigated the effect of rush and long-term venom immunotherapy on histamine release parameters in bee venom allergic patients. Ten patients received rush venom immunotherapy, and histamine release data were obtained immediately before and after treatment. 17 patients were assessed by histamine release 24 to 63 months after termination of long-term venom immunotherapy. A control group of 10 non-allergic subjects was included in this study. Histamine released from whole blood was determined in a sensitive radio-enzymatic assay using a single isotope technique. Bee venom phospholipase A-induced histamine release from whole blood proved to be a test procedure of high specificity and sensitivity. Eight of 10 untreated patients and no control subject showed significant antigen-induced histamine release. Results obtained from patients immediately after successful rush venom immunotherapy showed an important decrease (mean 45.9%) of total histamine content of basophil leukocytes in all patients. Antigen-induced maximum histamine release was found to be increased in one, decreased in two and unchanged in seven patients. In patients who received long-term immunotherapy cell sensitivity to phospholipase A was significantly lower than in a group of untreated patients (P less than or equal to 0.002). These results suggest that even years after discontinuation of immunotherapy, histamine release parameters reflect patients' protection from systemic sting reactions as assessed by sting challenges. Histamine depletion of basophils induced by rush immunotherapy may play an important role in patients' protection immediately after termination of the rush regimen.

HIV antigen stimulates basophil leukocytes from AIDS patients to release histamine due to type I allergy

HIV antigen-induced histamine release was examined in leukocyte suspensions from 12 patients with AIDS and 10 healthy controls. Nine of the twelve patients released histamine, while no release was obtained in cells from the control group. The mechanism was examined by removal of immunoglobulins (Ig) from the patient cells before stimulation with HIV antigen, which resulted in an abolition of the histamine release. Transfer of the Ig to cells from normal individuals rendered these cells able to respond to HIV. The removal and fixation of Ig were followed by disappearance and reappearance of the response to anti-IgE. These findings indicate that the histamine release by HIV is caused by a type I (IgE-mediated) reaction.

Anti-asthmatic activity of newly synthesized calcium antagonists: 2-n-butyl-1 (N-methyl-n-[2-(N',N'-dimethylamino)ethyl]amino) -5,6-methylenedioxy-indene and -indane.

The anti-asthmatic activity of the newly synthesized methylenedioxyindene (MDI) derivatives, 2-n-butyl-1 (N-methyl-N-[2-(N', N' -dimethylamino)ethyl]amino)-5, 6-methylenedioxy-indene (MDI-C) and -indane (MDI-D), were investigated in vitro and in vivo in guinea pigs. The in vitro pharmacological activity of both derivatives was compared to that of 8-(diethylamino)octyl-3,4, 5-trimethyoxybezoate hydrochloride. All three agents caused a concentration-dependent inhibition of the antigen-induced contraction of sensitized guinea pig tracheal smooth muscle. In histamine and leukotriene D4-induced contractions of guinea pig tracheal smooth muscle, each agent showed clear antagonistic actions. Additionally, all three agents demonstrated potent calcium antagonistic actions via inhibition of guinea pig tracheal smooth muscle contractions caused by CaCl2 in a high potassium and Ca-free medium and by compound 48/80 in a solution of ethylene glycol bis(beta-aminoethylether)-N,N,N',N'-tetraacetic acid in a contained Ca-free medium. MDI-C and MDI-D inhibited the antigen-induced release of histamine and slow reacting substance of anaphylaxis from sensitized guinea pig lung tissue. Lastly, both MDI is clearly inhibited asthmatic respiratory disorders without affecting blood pressure in guinea pigs.

Biochemical and pharmacological characterization of ICI 198,615: a peptide leukotriene receptor antagonist

ICI 198,615 is one representative of a new chemical class of peptide leukotriene receptor antagonists that are the most potent and selective described to date. ICI 198,615 antagonized LTC 4-, LTD 4- and LTE 4-induced increases in cutaneous vascular permeability in the guinea pig, with i.v. ED 50 values of 0.083, 0.11 and 0.067 μmol/kg, respectively. Against LTD 4, ICI 198,615 was 615 and 415 times more potent than LY 171883 and FPL 55712, respectively. L-Serine borate, an inhibitor of the metabolism of LTC 4 to LTD 4, did not influence the antagonism by ICI 198,615 of LTC 4-induced increases in cutaneous vascular permeability. The compound both inhibited and reversed aerosol ovalbumin antigen-induced increases in pulmonary resistance in passively sensitized guinea pigs, but demonstrated little ability to inhibit or reverse ovalbumin antigen-induced decreases in dynamic lung compliance. At concentrations ranging from 10 −8 to 10 −5 M, ICI 198,615 had no significant effect on either the spontaneous or ovalbumin antigen-induced release of histamine, peptide leukotrienes, thromboxane B 2 or 6-keto-prostaglandin F 1α from chopped guinea pig lung. At 10 μM, the compound did not inhibit 5-, 12- or 15-lipoxygenase. Finally, ICI 198,615 antagonized LTD 4-induced increases in TxB 2 release from chopped guinea-pig lung.

Immunopharmacological studies on TBX, a new antiallergic drug. (3). Inhibitory effects on histamine release from lung fragments and bronchoconstriction in guinea pigs.

The effects of 9-methyl-3-(1H-tetrazol-5-yl)-4H-pyrido[1,2-a]pyrimidin-4-one potassium salt (TBX), a new antiallergic drug, on histamine release from lung fragments, experimental asthma and isolated tracheal muscle were investigated in guinea pigs. TBX (10(-7) to 10(-4) g/ml) dose-dependently inhibited antigen-induced histamine release from lung fragments of guinea pigs passively sensitized with homologous IgE serum. Antigen inhalation-induced experimental asthma in passively sensitized animals was inhibited in a dose-dependent fashion by i.v. (1 to 5 mg/kg) and p.o. (10 to 100 mg/kg) administrations of TBX. In vivo bronchoconstriction by platelet-activating factor (PAF, i.v.) was also inhibited by TBX (0.3 to 10 mg/kg, i.v.). However, high concentrations of TBX (more than 3 x 10(-4) g/ml) were needed to inhibit PAF-induced platelet aggregation in vitro. With regard to the effect on isolated tracheal muscle, TBX itself at concentrations higher than 10(-5) g/ml induced dose-dependent reduction in the resting tonus, which was not affected by pretreatment with propranolol. Neither the leukotriene D4-induced contraction nor the prostaglandin F2 alpha-induced one was specifically antagonized by TBX. The results obtained indicate that TBX is an antiasthmatic agent effective in inhibiting both IgE- and PAF-induced bronchoconstriction, possibly by interfering with mediator release.

Effect of 8-hexyloxy-3-(1H-tetrazol-5-yl)-2H-chromen-2-one (KP-136) on experimental asthma: A comparison with disodium cromoglycate.

The pharmacological properties of 8-hexyloxy-3-(1H-tetrazol-5-yl)-2H-chromen-2-one, KP-136 were compared with those of an antiallergic medicament, disodium cromoglycate (DSCG) in experimental asthma models. KP-136 (0.125-1 mg/kg i.v., 0.5-2 mg/kg p.o.) produced a dose-dependent inhibition to allergic asthma of rats and was more potent than DSCG (1-5 mg/kg i.v.). KP-136 (1 mg/kg, i.v.) was also effective on allergic asthma of guinea pigs, although DSCG was ineffective even at a high dose of 50 mg/kg (i.v.). In rats, both KP-136 and DSCG significantly blocked the reduction of histamine content of the trachea after allergic asthma and inhibited the antigen-induced histamine release from lung fragments (KP-136 0.5 micrograms/ml, DSCG 50 micrograms/ml) and peritoneal exudate cells (KP-136 0.1 micrograms/ml, DSCG 10 micrograms/ml). KP-136 also showed relaxation activity for isolated guinea pig trachea at high doses of 2 and 5 micrograms/ml. The major mechanism of the potent antiasthmatic activity of KP-136 is postulated to be the blocking of bronchoactive mediator release. The relaxation of smooth muscle is also suggested to be an additive mechanism.

Immunopharmacological Studies on TBX, a New Antiallergic Drug (3) Inhibitory Effects on Histamine Release from Lung Fragments and Bronchoconstriction in Guinea Pigs

The effects of 9-methyl-3-(1 H-tetrazol-5-yl)-4H-pyrido[1,2-a]pyrimidm-4-one potassium salt (TBX), a new antiallergic drug, on histamine release from lung fragments, experimental asthma and isolated tracheal muscle were investigated in guinea pigs. TBX (10-7 to 10-4 g/ml) dose-dependently inhibited antigen-induced histamine release from lung fragments of guinea pigs passively sensitized with homologous IgE serum Antigen inhalation-induced experimental asthma in passively sensitized animals was inhibited in a dose-dependent fashion by i.v. (1 to 5 mg/kg) and p.o. (10 to 100 mg/kg) administrations of TBX. In vivo bronchoconstriction by platelet-activating factor (PAF. i.v.) was also inhibited by TBX (0.3 to 10 mg/kg, i.v). However, high concentrations of TBX (more than 3×10-4 g/ml) were needed to inhibit PAF-induced platelet aggregation in vitro. With regard to the effect on isolated tracheal muscle, TBX itself at concentrations higher than 10-5 g/ml induced dose-dependent reduction in the resting tonus, which was not affected by pretreatment with propranolol. Neither the leukotriene D4-induced contraction nor the prostaglandin F2α-induced one was specifically antagonized by TBX. The results obtained indicate that TBX is an antiasthmatic agent effective in inhibiting both IgE- and PAF-induced bronchoconstriction. possibly by interfering with mediator release.

Identification of a histamine release inhibitory factor (HRIF) and an inhibitor of histamine releasing factor synthesis (IHS) produced by guinea pig lymphoid cells

Guinea pig spleen cells, thymocytes, and blood mononuclear cells have been shown to produce a histamine releasing factor (HRF) spontaneously or after stimulation with PHA or specific antigens. In this study we have shown that antigenic stimulation of spleen cells obtained from animals immunized with high doses of antigen suppresses the spontaneous HRF production. Likewise, stimulation with Con A of spleen cells also inhibits the spontaneous HRF production. When the supernatants from Con A- and antigen-stimulated cultures were added to fresh thymocyte cultures, a significant inhibition of HRF production was observed. These supernatants also inhibited HRF-induced histamine release from mast cells. We have identified an inhibitor of HRF synthesis (IHS) and also a histamine release inhibitory factor (HRIF) by gel chromatography. Virtually all mitogen- and antigen-stimulated culture supernatants elaborated the activities of HRF, IHS, and HRIF in various quantities depending on the dose of antigen and the kind of adjuvant used for immunization. IHS has a MW of 22K-35K and 10K. This cytokine also inhibits DNA synthesis by thymocytes. HRIF has a MW of 15K–20K. and 10K. It inhibits both HRF- and antigen-induced histamine release from lung mast cells. These results suggest that lymphocytes produce a variety of factors which function to regulate histamine release from mast Cells.

Inhibitory effect of anti-allergic agent NCO-650 on histamine release induced by various secretagogues

Histamine release from rat peritoneal mast cells induced by antigen and anti-IgE was essentially complete within 2 min and 3 min, respectively, but that due to Concanavalin A (Con A) was complete only within 9 min. An anti-allergic agent NCO-650 [trans-4-Guanidinomethylcyclohexanecarboxylic acid p-tert-butylphenyl ester hydrochloride], which is a strong inhibitor of trypsin, dose-dependently inhibited anti-IgE-induced histamine release from rat peritoneal mast cells. Moreover, the rate and extent of histamine release from rat peritoneal mast cells induced by various histamine liberators such as antigen, concanavalin A, ionophore A 23187 and compound 48/80 are significantly diminished in samples incubated with NCO-650. The IC50 values of NCO-650 on histamine release induced by antigen, anti-IgE, Concanavalin A, A23187 and compound 48/80 were in the order of micromolar range, i.e. 1.9, 3.6, 4.6, 2.9 and 6.1 microM, respectively. On a molecular basis, NCO-650 is 1000-fold more potent than DSCG, an anti-allergic drug, in inhibiting the antigen-induced histamine release. The present results suggest that the effect of NCO-650 might be due to the inhibition of a common process underlying the release of histamine by various histamine liberators.

Inhibitory effect of oral cetirizine on in vivo antigen-induced histamine and PAF-acether release and eosinophil recruitment in human skin

The use of a noninvasive skin chamber technique in vivo in pollen-sensitive patients allowed us to quantify the time-course release of histamine and the recruitment of inflammatory cells (i.e., neutrophils, monocytes, and eosinophils) in skin sites challenged with pollen, histamine, and compound 48 80 . The new H I-receptor antagonist, cetirizine 2 HCl, orally administered with 10 mg once a day to pollen-sensitive patients in a double-blind, crossover study versus placebo, induced a significant decrease in the wheal-and-flare cutaneous reaction induced by intradermal injection of pollen, histamine, and compound 48 80 . It also significantly inhibited the immediate histamine release occurring in skin chambers after pollen introduction, whereas it did not significantly inhibit the late release. In patients receiving placebo, we detected platelet-activating factor—acether in media collected at the sixth hour from chambers filled with pollen. With cetirizine 2 HCl treatment, platelet-activating factor—acether was not detected in chamber media. Interestingly, cetirizine 2 HCl significantly reduced the eosinophil recruitment observed on the superficial dermis 24 hours after pollen challenge.

The influence of tetradecanoyl-phorbol-acetate (TPA) on histamine release from isolated rat mast cells

A detailed investigation of the influence of tetradecanoyl-phorbol-acetate (TPA) on isolated rat mast cells was undertaken in order to explore the possible involvement of protein kinase C in histamine release. TPA alone could induce histamine release in a medium without calcium, whereas 1 mM CaCl2 suppressed the release. TPA in combination with a low concentration of the ionophore A23187 induced a considerable histamine release. Preincubation with TPA followed by incubation with the ionophore induced a similar release at low concentrations of TPA (less than or equal to 2.5 nM) whereas the response was reduced at higher concentrations of TPA. The inhibition after preincubation with TPA was almost at a maximum within 2 min and was due to a decreased rate of release. TPA could also increase antigen-induced histamine release. After preincubation the potency of low concentrations of TPA increased, whereas higher concentrations (50 nM) became inhibitory. The effects of preincubation were almost fully expressed after 2 min and were not due to altered kinetics of the release. The interaction of oleoylacetylglycerol (OAG) with the ionophore A23187 and with antigen resembled that of TPA, but OAG was considerably less potent. Preincubation with TPA was inhibitory to the histamine release induced by compound 48/80, particularly in the absence of calcium. The release induced by TPA and the ionophore or antigen was calcium-dependent and energy-requiring, and the effects of TPA persisted after washing the cells before exposure to antigen or the ionophore. Preincubation with the protein kinase C inhibitor isoquinolinesulfonyl-methylpiperazine (H7) slightly enhanced the histamine release induced by the combination of TPA and the ionophore.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of TMB-8 on calcium transport in mast cells in relation to histamine secretion

We have previously reported an inhibition of histamine release by TMB-8 both in the presence and absence of calcium and with glucose in the medium. In the present investigation we have studied the effect of TMB-8 on calcium transport. The observations show that TMB-8 inhibits calcium uptake and enhances calcium efflux in mast cells. As antigen-induced histamine release from sensitized mast cells is primarily dependent on extracellular calcium, the inhibition of anaphylactic histamine release by TMB-8 is probably mainly due to an inhibition of calcium influx into the mast cells. We have shown an increased calcium efflux during histamine release from mast cells induced by compound 48/80 in the absence of calcium in the medium, suggesting the release of intracellular calcium stores. The increased calcium efflux was not inhibited by TMB-8. On the contrary, the enhanced calcium efflux caused by compound 48/80, was added to that by TMB-8. TMB-8 thus had no effect on the calcium release from intracellular stores by compound 48/80 but the enhanced calcium efflux by TMB-8 would tend to inhibit histamine release.

Effect of cholera toxin on histamine release from bone marrow-derived mouse mast cells.

Bone marrow-derived mouse mast cells were sensitized with monoclonal mouse IgE antibody and treated with cholera toxin (CT), which ADP-ribosylated the alpha-subunit of the stimulatory guanine nucleotide-binding regulatory protein Gs, prior to challenge with either antigen or thrombin. The CT treatment increased intracellular cAMP levels, but neither enhanced nor inhibited antigen-induced histamine release or arachidonate release. The same treatment of the sensitized bone marrow-derived mouse mast cells with CT markedly enhanced thrombin-induced histamine release without affecting arachidonate release. The CT treatment failed to affect antigen-induced and thrombin-induced generation of inositol trisphosphate and of diacylglycerol or mobilization of intracellular Ca2+. The results indicate that Gs in bone marrow-derived mouse mast cells is not involved in the transduction of the antigen-induced or thrombin-induced triggering signal to phospholipase C, which initiates the enhancement of phosphatidylinositol turnover. The enhancement of thrombin-induced histamine release by CT treatment with the observations that thrombin-induced histamine release was inhibited by pretreatment of the cells with pertussis toxin suggest that the involvement of a guanine nucleotide-binding regulatory protein in thrombin-induced biochemical events is an event distal to Ca2+ mobilization.

Study of the Mechanism of Inhibitory Action of Tranilast on Chemical Mediator Release

We investigated the mechanism of inhibitory action of tranilast on chemical mediator release by antigen-antibody reactions. Tranilast (10-5–10-3 M) inhibited antigen (DNP-Ascaris)-induced histamine release from sensitized purified rat mast cells (PMC), but did not show an obvious influence on intracellular cyclic AMP. 45Ca uptake into PMC induced by antigen (300 μg/ml) was obviously suppressed by tranilast (10-6–10-3 M). Tranilast (10-4 M) inhibited antigen-induced histamine release from and 45Ca uptake into PMC independently of the presence or absence of glucose in the medium. On the other hand, 2-deoxyglucose (10-2 M) markedly inhibited both responses in the absence but not in the presence of glucose. Tranilast slightly inhibited Ca-induced contraction of guinea pig taenia coli, but had no influence on aggregation of rabbit platelets. Verapamil (10-6–10-4 M) had no effect on antigen-induced histamine release, but it markedly suppressed Ca-induced contraction and platelet aggregation. From these results, we suggest that the mechanism of inhibitory action of tranilast on the release of antigen-induced chemical mediator from mast cells involves the suppression of Ca uptake, but that its mode of action is apparently different from those of 2-deoxyglucose and verapamil.

Study of the mechanism of inhibitory action of tranilast on chemical mediator release.

We investigated the mechanism of inhibitory action of tranilast on chemical mediator release by antigen-antibody reactions. Tranilast (10(-5)-10(-3) M) inhibited antigen (DNP-Ascaris)-induced histamine release from sensitized purified rat mast cells (PMC), but did not show an obvious influence on intracellular cyclic AMP. 45Ca uptake into PMC induced by antigen (300 micrograms/ml) was obviously suppressed by tranilast (10(-6)-10(-3) M). Tranilast (10(-4) M) inhibited antigen-induced histamine release from and 45Ca uptake into PMC independently of the presence or absence of glucose in the medium. On the other hand, 2-deoxyglucose (10(-2) M) markedly inhibited both responses in the absence but not in the presence of glucose. Tranilast slightly inhibited Ca-induced contraction of guinea pig taenia coli, but had no influence on aggregation of rabbit platelets. Verapamil (10(-6)-10(-4) M) had no effect on antigen-induced histamine release, but it markedly suppressed Ca-induced contraction and platelet aggregation. From these results, we suggest that the mechanism of inhibitory action of tranilast on the release of antigen-induced chemical mediator from mast cells involves the suppression of Ca uptake, but that its mode of action is apparently different from those of 2-deoxyglucose and verapamil.

Modulation of humoral immune responses by endogenous opioids

The effects of opioid agonists and antagonists were investigated on humoral immune mechanisms in mice and rats. Opioid agonists like morphine, Leu-enkephalin, and Met-enkephalin, enhanced antigen-induced histamine release from mixed peritoneal cells of rats in vitro; this enhancement was effectively antagonized by naloxone, an opioid antagonist. Naloxone, per se, decreased anaphylactic mortality in doses of 10 mg/kg, while it increased mortality in a dose of 1 mg/kg. Reduced IgE antibody titer, measured by passive cutaneous anaphylaxis, decreased hemagglutination titer to sheep red blood cells, blocked histamine release from mixed peritoneal cells of rats in vitro induced by antigen, but had no significant effect when histamine release was induced by compound 48/80. Thus, it appears that endogenous opioids are involved in humoral immune responses.

Immunopharmacological Studies on TBX, a New Antiallergic Drug (2) Inhibitory Effects on Histamine Release from Peritoneal Mast Cells and Lung Fragments of Rats

The ability of 9-methyl-3-(1H-tetrazol-5-yl)-4H-pyrido[1,2-a]pyrimidin-4-one potassium salt (TBX) to inhibit histamine release from both peritoneal exudate cells (PEC) containing mast cells and lung fragments of rats was investigated in vitro. Low concentrations of TBX dose-dependently inhibited IgE-mediated histamine release from PEC of passively sensitized animals; its IC50 was 5.1 × 10−9 g/ml. When TBX was added simultaneously with the antigen challenge, the highest inhibition was obtained. In contrast, extension of preincubation time with the agent resulted in a marked decrease in the inhibition of histamine release. The potent inhibition of histamine release by TBX was observed equally in glucose-free as well as complete Tyrode’s solution, whereas TBX reduced its inhibitory action in Ca2+free or D2 O-supplemented medium. In addition, TBX inhibited compound 48/80- but not calcium ionophore A23187-induced histamine release from normal PEC. With regard to the intracellular cyclic AMP level in normal PEC, it was significantly enhanced by a high concentration of TBX (10−3 g/ml). TBX also inhibited antigen-induced histamine release from lung fragments of actively immunized animals. Interestingly, TBX displayed non-competitive inhibition of cyclic AMP-dependent phosphodiesterase derived from lung homogenates; its K1 value was 8.70 × 10−4 M.

Effect of OKY-046, a new thromboxane A 2 synthetase inhibitor, on experimental asthma in guinea pigs

The effect of OKY-046, a newly synthetized thromboxane A 2 (TxA 2) synthetase inhibitor, on IgE mediated experimental asthma in guinea pigs was investigated. Indomethacin, a cyclooxygenase inhibitor, and tranilast (N-5′), a potent anti-allergic agent, were used as comparative drugs. OKY-046 clearly improved asthmatic respiratory disorders in guinea pigs. Whereas indomethacin had no effect on the changes of asthmatic respiration, tranilast significantly inhibited the changes. OKY-046 inhibited the in vitro antigen-induced contraction of sensitized guinea pig lung parenchyma. This antigen-induced contraction was also inhibited by tranilast, but not by indomethacin. OKY-046 inhibited the contractions of lung parenchyma caused by leukotriene C 4, D 4 and E 4 (LTC 4, LTD 4 and LTE 4), but not by histamine. Indomethacin showed a biphasic action on the contractile responses caused by histamine and LTD 4 Consequently, contractions due to either agonist at low concentrations were inhibited by indomethacin, but those at high concentrations were enhanced. Tranilast inhibited the contraction of lung parenchyma induced by a low concentration of LTD 4 but not that produced by histamine. Moreover, OKY-046 inhibited an elevation of concentration of thromboxane B 2 (TxB 2) in guinea pig lung perfusate after infusion of LTC 4 but did not affect the elevation of 6-keto-PGF 1α. OKY-046 had no effect on the antigen-induced release of histamine but it inhibited the release of the slow reacting substance of anaphylaxis (SRS-A) from sensitized chopped lung tissues. Indomethacin at a high concentration inhibited the release of histamine but did not affect the release of SRS-A. Tranilast clearly inhibited the release of both mediators. These results suggest that OKY-046 inhibits IgE mediated experimental asthma in guinea pigs and that its main mechanism is related to the inhibition of LT induced contraction of airway smooth muscle and the release of SRS-A from lung tissues.