β-Adrenoceptors

β-Adrenoceptors regulate many aspects of lung function and β-adrenergic agonists have become the most widely used bronchodilators for the treatment of obstructive airway diseases. There have been important advances in our understanding of the molecular structure and regulation of β-adrenoceptors, which have implications for elucidating β-adrenoceptor function in airway disease and the mechanisms of action of β-agonists [1, 2]. At least three β-adrenoceptors are now recognized (Table 1). β1-Receptors, which are preferentially activated by noradrenaline, are physiologically regulated by sympathetic nerves; β2-receptors are preferentially regulated by circulating adrenaline; β3-receptors or "atypical" β-receptors are involved in lipolysis but are increasingly recognized in other functions. β2-Receptors predominate in lungs and mediate most of the effects of β-agonist on airway function.