Evidence of direct connection of corticobulbar fibers to orofacial muscles in man: electromyographic study of individual motor unit responses

Endothelins (ETs) are a family of peptide mediators that have a number of biological properties, including the ability to act as potent bronchoconstrictors of isolated human airways. Moreover, elevated concentrations of ET-1 in the bronchoalveolar lavage fluid from patients with symptomatic asthma have also been detected. We investigated the possible contribution of ET-1 in the development of bronchial hyperresponsiveness and the role of inflammatory cell accumulation in rabbit lungs. Our data show that ET-1 challenge to rabbits does not modify basal lung function but results in an increased airway responsiveness to inhaled histamine. Endothelin-treated rabbits were 3-fold (P<0.01) more responsive to inhaled histamine when compared with vehicle-treated rabbits. This hyperresponsiveness was not associated with an alteration in either total or differential inflammatory cell numbers as assessed by bronchoalveolar lavage (BAL). Pre-treatment with capsaicin (80 mg/kg s.c.) did not alter basal lung function or basal responsiveness to inhaled histamine. While capsaicin had no significant effect on the acute bronchoconstriction induced by endothelin-1, this dose was sufficient to significantly inhibit the increase in airway responsiveness to inhaled histamine, achieved 24 h following endothelin-1 challenge. These results indicate that ET-1 may play a role in the development of bronchial hyperresponsiveness to inhaled histamine and that the maintenance of this state is unrelated to a detectable alteration in cellular infiltration within the airway lumen, but probably via the involvement of capsaicin-sensitive nerves.