We studied the magnitude and the time course of changes in pulmonary resistance (RL) after aerosol challenge with chicken ovalbumin (OA) of 15 sensitized, highly inbred Brown-Norway (BN) rats. Animals were actively sensitized and 2 wk later were challenged through the airways. Airway responses of sensitized animals were compared to those of 6 control animals challenged with sufficient methacholine (MCh) to at least double RL and to 4 unsensitized control rats challenged with OA. Ten of 15 rats in the experimental group displayed an early response (ER), defined as an increase in RL of at least 50% within 1 h of challenge. A late response (LR) was considered to have occurred when the value of RL exceeded the mean plus 2 standard deviations of all the measurements taken from 1 h after challenge to the end of the experiment. Two rats died less than 240 min after OA challenge with RL greater than 200% baseline. The remaining 13 were studied for a total duration that ranged from 390 to 720 min and of these animals 10 demonstrated LRs. Maximal RL during the LR after OA was 287 +/- 49% (SE) baseline (range, 129 to 760) versus 115 +/- 15% (75 to 176) for control animals after MCh (p less than 0.01) and 52 +/- 3% (51 to 142; p less than 0.01) for unsensitized control animals after OA. There was no correlation between the magnitude of ER and LR; 3 LRs occurred in the absence of detectable ERs. The median time to the peak of the LR was 450 min; median duration of LRs was 90 min (range, 30 to 135 min).(ABSTRACT TRUNCATED AT 250 WORDS)