BETA(3)-ADRENOCEPTORS AND AIRWAYS

beta(3)-adrenoceptors have been identified in a variety of tissues fro m humans and animals: adipose tissue, gastrointestinal smooth muscle, rat skeletal muscle, bovine skeletal muscle, and human and canine hear t. In the airways, the investigation of the beta(3)-adrenoceptors came from studies with a series of novel selective agonists. Stimulation o f the ''atypical'' beta-adrenoceptor increases the active transport of albumin across the ferret tracheal epithelium and the ciliary beat fr equency of canine bronchial epithelium. Furthermore, it has been demon strated that beta(3)-adrenoceptors agonists selectively inhibited nona drenergic noncholinergic contractions of guinea-pig bronchi induced by electrical field stimulation or capsaicin. The presence of functional beta(3)-adrenoceptors in the bronchial smooth muscle is disputed and seems to be species-related. In isolated canine bronchi, selective ago nists induced a relaxation whereas they had no or slight effect in iso lated human, guinea-pig and sheep bronchi. Likewise in man, a fall in airway resistance measured by plethysmography, was mediated by beta(2) -adrenoceptors, but nor beta(3)-adrenoceptors. To conclude, an ''atypi cal'' or beta(3)-adrenoceptor-mediated modulation of bronchomotricity exists, nevertheless strong species specific differences have been rep orted.