<n0:ComplexDefinition xmlns:n0="http://ncicb.nci.nih.gov/xml/owl/EVS/ComplexProperties.xsd#"><n0:def-definition>A highly selective, long-acting beta-2 adrenergic agonist with bronchodilatory activity. Salmeterol's benzene moiety resembles the structure of catecholamines, and occupies the active site of beta-2 adrenergic receptor, while the long, lipophilic side chain of salmeterol, binds to the so called 'exosite' near the beta-2 adrenergic receptors. The binding at the exosite allows the active portion of the molecule to remain at the receptor site and continually engage and disengage with the receptor, therefore providing a long duration of action. This agent stimulates intracellular adenyl cyclase to catalyze the conversion of adenosine triphosphate to cyclic-3',5'-adenosine monophosphate (cAMP). Increased cAMP levels result in relaxation of bronchiolar smooth muscle, bronchodilation and increased bronchial airflow.</n0:def-definition><n0:def-source>NCI</n0:def-source></n0:ComplexDefinition>