Adenosine-induced bronchoconstriction in conscious hyperresponsive and sensitized guinea pigs.

Inhaled adenosine induces bronchoconstriction in asthmatic and allergic subjects but not in nonasthmatics. This study examined the responses of conscious guinea pigs in which antigen sensitization is induced by ovalbumin pretreatment and airway hyperresponsiveness to carbachol is induced by exposure to ozone and platelet-activating factor-acether (PAF). Airway responses to aerosol challenge with carbachol or adenosine were determined as the change in specific airway conductance (SGaw) measured by whole-body plethysmography. In untreated animals, carbachol (20 micrograms/ml, 60 s) induced a rapid fall in SGaw (peak, 18 +/- 5% at 5 min) indicative of bronchoconstriction, whereas adenosine (1 mg/ml, 60 s) caused an increase in SGaw (34 +/- 8% at 15 min). Animals pretreated with ovalbumin displayed similar responses to carbachol (14 +/- 5% at 5 min) as control animals and were therefore sensitized but not hyperresponsive. However, adenosine (1 mg/ml) caused a rapid bronchoconstriction, peaking at 20 min (25 +/- 5%). Exposure of animals to nebulized PAF-acether (10 micrograms/ml) for 60 s produced a bronchoconstriction, which peaked at 10 min (18 +/- 7%) and returned to basal levels by 60 min. Similarly, exposure to ozone (1.4 ppm) for 60 min caused bronchoconstriction (peak at 20 min, 19 +/- 6%), with recovery after 1 h. Both PAF- and ozone-exposed animals displayed significant hyperresponsiveness to carbachol administered 1 h from the end of the exposure period. The peak bronchoconstrictor responses before and after PAF exposure were 10 +/- 9 and 28 +/- 4%, and responses before and after ozone exposure were 22 +/- 5 and 61 +/- 9%.(ABSTRACT TRUNCATED AT 250 WORDS)