Histamine and leukotrienes mediate pulmonary hypersensitivity to antigen in guinea pigs

and slow-reacting substance of anaphylasis (SRS-A) in me-diating airway responses following antigen challenge, mediator antagonists were administered to guinea pigs sensitized with ovalbumin 10 days before the study. Twenty-three animals were divided into the following five treatment groups: I) saline only (control 1, n = 5); 2) antigen challenged (n = 5); 3) antigen + methapyrilene (antihistamine, n = 5); 4) FPL 55712 only (SRS-A antagonist, control 2; n = 4), and 5) antigen + FPL 55712 (n = 4). Control groups were not sensitized. Experimental values were compared with those of controL I at equal times after injections. Pulmonary resistance ( RL), dynamic compli-ance (Cdyn), breathing frequency (f), tidal volume, minute ventilation (VIZ) and systemic arterial pressure were measured for 15-20 min just before (base line) and for up to 30 min after saline or antigen administration. Antigen challenge alone in