Activity of a novel thienodiazepine derivative as a platelet-activating factor antagonist in guinea pig lungs. Effects on platelet-activating factor and allergen induced eosinophil accumulation.

Platelet-activating factor (PAF) inhalation in guinea pigs caused a significant increase in the number of eosinophils recovered from bronchoalveolar lavage fluid (BALF). Oral administration of (S)-(+)-6-(2-chlorophenyl)-3-cyclopropanecarbonyl-8,11- dimethyl-2,3,4,5-tetrahydro-8H-pyrido[4',3':4,5]thieno[3,2-f] [1,2,4]triazolo[4,3-a][1,4]diazepine (E-6123), a novel PAF antagonist, at the dose of 100 micrograms/kg completely inhibited the PAF-induced eosinophil accumulation. Antigen inhalation in passively sensitized guinea pigs caused a significant increase in lung contents of PAF at 5 min, and accumulation of eosinophils in the bronchi 1 and 2 days thereafter, E-6123 inhibited the antigen-induced eosinophil accumulation and the maximum inhibition was approximately 65%. On the other hand, methylprednisolone completely inhibited the antigen-induced eosinophil accumulation. The results suggest that PAF is a potent attractant of eosinophils and is involved in antigen-induced eosinophil infiltration into bronchi. The results also suggest that E-6123 may be of therapeutic value in the treatment of asthma exhibiting eosinophil recruitment in airways.