CONTRACTILE RESPONSES TO ALLERGEN AND CHOLINERGIC STIMULATION IN BRONCHUS AND TRACHEA OF COCKROACH ALLERGEN-SENSITIZED GUINEA-PIGS

Airway hyperreactivity is a hallmark of asthma. Yet, the role of aller gic sensitization in the hyperreactivity remains controversial. This s tudy examined the effects of airborne cockroach allergen (CRa) sensiti zation on the contractility of bronchial (BSM) and tracheal (TSM) smoo th muscle rings to cholinergic stimulations, and to specific antigen, in vitro. Guinea pigs were actively immunized with CRa, 5 mg (high dos e, HD), 0.5 mg (low dose, LD), or saline aerosols (2 x/day, 5 days/wee k, for 4 weeks) and challenged by CRa inhalation 5 days after last exp osure. Twenty-four hours postchallenge, the contractions of the TSM an d BSM to electrical field stimulation (EFS), acetylcholine (ACh), and to CRa were measured in vitro. In addition, the contraction to these s timuli were also examined in the passively sensitized TSM with the ser a of CRa-immunized guinea pigs. The contractile responses of actively immunized and passively sensitized tissues to EFS and ACh were very si milar to those of control tissues. CRa induced dose-dependent contract ions in both actively immunized and passively sensitized, but not in c ontrol, tissues. The CRa-induced contraction was stronger in the HD gr oup than in the LD group (p < 0.0001). Leukotriene C4/D4 receptor anta gonist LY-171883 inhibited the CRa-induced contraction by 86% in activ ely immunized TSM, and by 9% in the passively sensitized TSM. Pyrilami ne inhibited the contraction by 57% in actively immunized TSM and 70% in passively sensitized TSM. The results indicate that CRa sensitizati on does not cause increased airway smooth muscle contractility to chol inergic stimulations, but induces antigen-specific contractions in vit ro. Leukotrienes appear to play a significant role in the CRa-specific contractions, more in the actively immunized than those in the passiv ely sensitized tissues, while histamine exerts a moderate effect on th e CRa-induced contractions.