Late Airway Responses to Antigen Challenge in Sensitized Inbred Rats

Abstract

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 > 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 < 0.01) and 52 .+-. 3% (51 to 142; p < 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). We conclude that LRs may be observed in sensitized inbred BN rats after antigen challenge and that these LRs may occur even in the absence of early responses to antigen.