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1 The role of platelet activating factor (PAF) in neutrophil infiltration in air pouch type allergic inflammation in rats was investigated. 2 Neutrophil infiltration into the pouch fluid 8 h after injection of the antigen (azobenzenearsonateconjugated acetyl bovine serum albumin) solution into the air pouch of immunized rats was inhibited dose-dependently by treatment with PAF antagonists 180) in parallel with the decrease in neutrophil chemotactic activity in the pouch fluid. 3 Four hours after injection of the antigen solution into the air pouch of immunized and nonimmunized rats, there was no significant difference between the two groups in the number of total leucocytes, neutrophils, mononuclear cells and eosinophils in the pouch fluid. However, when the infiltrated leucocytes were incubated in medium, chemotactic factor production by leucocytes from immunized rats was greater than that from non-immunized rats. 4 When leucocytes from non-immunized rats were preincubated for various periods in the medium containing 10 or 50 nM of PAF, washed, and further incubated in the medium containing no PAF, chemotactic factor production was not stimulated. 5The increase in the chemotactic activity in the conditioned medium was not suppressed by the 5-lipoxygenase inhibitor, AA861. In addition, the chemotactic activity in the conditioned medium was not inhibited by the PAF antagonists. 6 Incubation of the infiltrated leucocytes in the medium containing the protein synthesis inhibitor, cycloheximide, inhibited chemotactic factor production in a concentration-dependent manner in parallel with the decrease in uptake of [3H]-leucine into the acid-insoluble fraction of leucocytes. 7 Separation of the chemotactic activity in the conditioned medium by isoelectric focusing revealed that the leucocyte infiltrated into the pouch fluid produce two kinds of factors, viz. leucocyte-derived neutrophil chemotactic factor-i (LDNCF-1) and LDNCF-2 of which pI values are 4-5 and above 8, respectively. 8 The results indicate that PAF has no significant role in leucocyte activation to produce chemotactic factors, and that neutrophil chemotactic factors produced by infiltrated leucocytes are not PAF or leukotriene B4 but are produced through a protein synthesis mechanism. 9 The mechanism of action of PAF antagonists on neutrophil infiltration into the inflammatory locus is discussed.

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The antagonistic activity of oral YM158 (3-[(4-tert-butylthiazol-2-yl)methoxy]-5'-[3-(4-chlorobenzenesu lfonyl)propyl]-2'-(1H-tetrazol-5-ylmethoxy)benzanilide monosodium salt monohydrate), a new dual antagonist for leukotriene (LT) D4 and thromboxane (TX) A2 receptors, was investigated. Oral YM158 caused dose-dependent inhibition of LTD4-induced increases in plasma leakage and LTD4- or U46619-induced increases in airway resistance, with ED50 values of 6.6, 8.6 and 14 mg/kg, respectively. The dose-range of YM158's inhibitions was almost the same for both LTD4 and TXA2 receptors, and repeated oral doses did not affect its efficacy. Furthermore, oral YM158 inhibited antigen-induced bronchoconstriction. Although the potency of pranlukast for LTD4 receptor antagonism (ED50 = 0.34 mg/kg) is greater than that of YM158 (ED50 = 8.6 mg/kg), the doses of both pranlukast and YM158 for significant inhibition of the antigen-evoked airway response were the same, indicating that the TXA2 receptor antagonism of YM158 plays an important role in its anti-asthmatic effects. In conclusion, YM158 promises to be a novel agent for treating bronchial asthma.

The effects of lipid mediator antagonists: the LTD4-receptor antagonist pranlukast, the TXA2-receptor antagonist seratrodast, and the novel dual LTD4- and TXA2-receptor antagonist YM158 (3-[(4-tert-butylthiazol-2-yl)methoxy]-5'-[3-(4-chlorobenzenesu lfonyl) propyl]-2'-(1H-tetrazol-5-ylmethoxy)benzanilide monosodium salt monohydrate) were investigated in animals exhibiting immediate asthmatic response (IAR), late asthmatic response (LAR) and airway hyper-responsiveness (AHR). Antigen-induced LAR and AfR are inhibited by orally administered pranlukast (30, 100 mg/kg) and seratrodast (3, 10 mg/kg). YM158 (30 mg/kg), orally administered before or after IAR induction, also inhibited both LAR and AHR. However, while the inhibitory effects of pranlukast and seratrodast on IAR were marginal, the effects of YM158 (3, 10, 30 mg/kg) were dose-dependent, probably due to its multiple sites of action. Additionally, orally administered YM158 (30 mg/kg) inhibited ozone-induced AHR in guinea pigs. Thus, an antagonist that inhibits several lipid mediators might exhibit greater efficacy in treating asthmatic responses than antagonists with a single site of action. Therefore, YM158 shows great promise as a drug that will be able to treat bronchial asthma and related disorders more potently than currently used single-pathway inhibitors.