Airway hyperreactivity, an introduction.

Asthma is characterized by the presence of airway inflammation and an increased responsiveness to many different stimuli. The hyperresponsiveness to indirect stimuli such as adenosine, bradykinin, neuropeptides, sulphur dioxide suggest that the hyperresponsiveness in asthma results from the complex interaction between inflammatory cells, neurons and smooth muscle cells. Several mechanisms may be involved in the influence of airway inflammation on airway responsiveness: increased mucosa permeability: enhanced exposure of irritant receptors, modulation of airway smooth muscle behavior by inflammatory mediators, mucosal edema, enhanced release of neurotransmitters, increased local reflex activity, decreased breakdown of neurotransmitters, etc. We have investigated the interaction between airway inflammation and responsiveness in two animal models: acute exposure to endotoxin and chronic exposure to aerosolized antigen. Both models demonstrate the complexity of interaction between inflammatory processes and demonstrate positive controlling mechanisms that inhibit the increase in airway responsiveness due to airway inflammation. The lack of such controlling mechanisms may be involved in the development of the asthmatic airway hyperresponsiveness.