Abstract
The effect of airway sensitization to Ova on the response of vagal pulmonary rapidly adapting receptors (RARs) to capsaicin was investigated in Brown-Norway rats. Two groups of young rats (sensitized and control) were exposed to aerosolized Ova and vehicle, respectively, 3 days a week for 3 weeks. Differential cell count of the bronchoalveolar lavage indicated a distinct increase in the numbers of eosinophils and neutrophils in the Ova-sensitized rats. Single-unit fiber activities (FA) of RARs were recorded in anesthetized, artificially ventilated rats, and identified by their firing behaviors and adaptation index of >70%. Our results showed that right atrial injection of capsaicin (0.5 and 1.0 μg/kg) evoked either negligible or no response in RARs of control rats (ΔFA = 2.3 ± 0.8 imp/sec; n=5), which was consistent with that previously reported in the rat (Ho et al., Respir. Physiol. 127: 113–124, 2001). However, in striking contrast, the same dose of capsaicin evoked an immediate stimulatory effect on RARs of Ova-sensitized rats (ΔFA = 6.7 ± 4.2 imp/sec; n=6), with distinct and intense responses in two of these receptors. These pilot data seem to suggest that Ova-sensitization in the airways induced an expression of capsaicin sensitivity in RARs, probably resulting from the chronic airway sensitization and inflammation in sensitized animals. (Supported in part by NIH HL 67379)
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