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Selectivity in Beta‐Adrenergic Responses: Clinical Implications

THE CONCEPT of drug receptors and of selectivity in drug action is of fundamental importance both to clinicians as they select agents for specific therapeutic problems and for researchers investigating the molecular basis of drug action. Receptors are those cellular structures with which drugs or hormones initially interact. They perform two crucial functions. First, they recognize or discriminate certain biologically active molecules, e.g., adrenergic receptors bind catecholamines, cholinergic receptors bind acetylcholine and related drugs. Second, they transmit a signal which alters certain cellular functions such as enzymes, e.g., adenylate cyclase and ion impermeability of membranes. Thus, receptors determine which drug or drugs will affect a given tissue response-such as cardiac contractility, or rate. The idea of a receptive mechanism for drugs was first clearly described by Langley about 70 years ago.' Adrenergic receptors were first discussed by Dale.2 Our current classification of adrenergic receptors into two basic types, a and /3, was originated by Ahlquist some 25 years ago.3 His