G protein-coupled receptors respond to many neuro- and autocrine transmitters. Among these receptors, adrenergic receptors are particularly important in the regulation of cardiovascular function. The primary physiological agonists for these receptors are epinephrine and norepinephrine, which have been used to differentiate α- and s-receptor families [1]. Pharmacological properties can distinguish the subtypes α1-, α2-, s1- and s2-receptors [2,3]. Further subdivisions have been made possible by radioligand binding techniques (e.g. α2A-, α2B-, α2C-receptors). Additional subtypes have been characterized by molecular biology techniques, which have also revealed common features in quite different G protein-coupled receptors, suggesting that these receptors might be members of a large receptor superfamily.