Adrenergic receptors (ARs) are expressed in almost all organs and tissues and regulate a large number of diverse physiological processes upon activation by epinephrine and norepinephrine. There are three families of ARs, a1, a2, and b-ARs, with distinct pharmacological properties and functions. Since the first identification of bARs more than three decades ago, research on ARs has led to the establishment of many fundamental concepts in G protein-coupled receptor (GPCR) pharmacology. In addition, appreciation of AR functions in the physiology of various systems and in the pathophysiology of many disease states has established these receptors as viable drug targets and resulted in the identification and development of a number.
