Inhibition of antigen-induced airway hyperresponsiveness in rats: effects of ozagrel (a thromboxane A2 synthase inhibitor) and of CV-3988 (a platelet activating factor antagonist).

The effects of ozagrel, a thromboxane A2 (TXA2) synthase inhibitor, and CV-3988, a platelet activating factor (PAF) antagonist, was investigated on the repeatedly antigenic challenge-induced airway hyperresponsiveness (AHR) in rats. Rats were actively sensitized with DNP-Ascaris antigen and received 3 inhalations of antigen (challenges) or saline (sensitized control) every 48 hr. These animals were also pretreated with ozagrel (100 mg/kg, p.o., 30 min before), CV-3988 (3 mg/kg, i.v., 5 min before) or respective vehicle (water and saline, respectively) before each inhalation of antigen or saline. The in vivo airway responsiveness to cumulatively inhaled acetylcholine (ACh; 0.001-0.03%, each for 3 min) was measured 24 hr after the last inhalation of antigen or saline under anesthesia. A marked AHR was observed after repeated antigenic challenge when compared with the sensitized control group (5.5-9.5 times in order). This AHR was significantly, but partly, attenuated by pretreatment with ozagrel although this treatment alone had no effect on the airway responsiveness to inhaled ACh in sensitized control animals. On the other hand, CV-3988 had no inhibitory effect on this AHR. These findings suggest that TXA2, but not PAF, is one of the most important mediators participating in the pathogenesis of the antigen-induced AHR in rats.