Allergen tachyphylaxis of guinea pigs in vivo; a prostaglandin E mediated phenomenon?

Ovalbumin (OA) sensitized guinea pigs were repeatedly challenged with 1% OA in saline nebulized ultrasonically at the 0, 10, 20, 60 and 70th min. The intensity of bronchial obstruction was measured by body plethysmography. The first three challenges (0. 10, 20 min) caused strong asthmatic reactions in all animals, the last two (60, 70 min) only mild one in 10 out of 15 animals. The development of this "tachyphylaxis" was markedly reduced by pretreatment of the animals with cyclooxygenase inhibitors (indomethacin 10 mg/kg intraperitoneally resp, acetylsalicylic acid 10 mg/kg orally 2 h before tests). The effect of both inhibitors (i.e. inhibition of tachyphylaxis) was abolished by supplementing prostaglandin E2 as aerosol simultaneously to the allergen (100-200 ng per inhalation). The results suggest that allergen tachyphylaxis we have observed in vivo might be due to synthesis of cyclooxygenase products, e.g. prostaglandin E.