Hyperoxic exposure enhances airway reactivity of newborn guinea pigs

To determine whether altered airway smooth muscle contractility contributes to airway hyperreactivity resulting from hyperoxic exposure, in vitro contractile responses of airways to two physiological constrictors, acetylcholine (10(-9) to 10(-4) M) and histamine (10(-8) to 10(-4) M), were examined. Extrathoracic trachea, intrathoracic trachea, and bronchus from 1- to 2-day-old (newborn) guinea pigs exposed to 85% oxygen for 84 h were compared with tissues obtained from newborns reared in room air. Responses in the presence and absence of aspirin (ASA; 10(-3) M) were compared. Hyperoxic exposure did not affect the histology of the airway epithelia. Contractile responses to acetylcholine and histamine were similar. Without ASA, maximal tensions generated were higher in both extrathoracic and intrathoracic trachea obtained from hyperoxia-exposed neonates than in trachea from newborns reared in room air. ASA caused maximal tensions of trachea from newborns reared in room air to increase but did not affect the already increased contractility of trachea from hyperoxia-exposed animals; the tensions achieved in hyperoxic tissues with and without ASA were similar to the hyperactive responses induced by ASA in tissues from animals reared in room air. Bronchi showed responses similar to those seen in tracheal segments. Thus, despite no apparent histological effect on the airway epithelium, hyperoxic exposure seems to increase airway smooth muscle contractility, is nonspecific for different constricting agents, and shows no regional differences in airway reactivity.