Adrenergic Receptors Within the Cardiovascular System

THE CONCEPT that drugs react with specific receptors in living tissues to produce pharmacologic effects is believed to have originated with Langley in 19051 although Ehrlich and others had certainly conceived of specific drug-cellular interactions. Today receptors have achieved such status amnong pharmacologists to be almost commonplace in spite of the fact that their identity has not been established. In undertaking a discussion of adrenergic receptors in the cardiovascular system consideration should be given to what is meant by " receptor." The definitions which follow are intended to be operational and heuristic: operational in the sense of providing a conceptual framework on which both the experimentalist and the physician can establish a common basis for understanding and classifying sympathomimetic drugs; heuristic in the sense that this framework may provide a basis for further investigation into mechanisms of action of drugs and to the design of more nearly "perfect" drugs. Until more refined technics lead to precise description of the molecular dynamics of drug-receptor interactions, the definition of receptors must remain general. Let us first consider a schematic representation of a sympathetic nerve ending and the adjacent effector cell (fig. 1). The chemical transmitter-here labeled "sympathin" (probably norepinephrine*) -is synthesized and bound in the nerve cell. In response to impulses it is released to diffuse to the effector cell and react with a receptor. The trans-