Abstract: β-adrenergic receptors mediate the physiological responses of the catecholamines, epinephrine and norepinephrine and modulate a myriad of physiological functions including relaxation of smooth muscle, chronotropic and inotropic cardiac responses, and lipolysis in adipose tissue. Pharmacologic and functional studies have revealed that β-adrenergic receptors are found in nearly all mammalian tissues and represent a heterogeneous population. β-adrenergic receptors were originally classified into two subtypes, β1- and β2-adrenergic receptors, based on the relative potency of epinephrine and norepinephrine. The β1-adrenergic receptor is equally responsive to these two agonists; the β2-adrenergic receptor is more potently stimulated by epinephrine. More recently, molecular cloning techniques have led to the discovery of an additional receptor subtype, the β3-adrenergic receptor. This subtype is preferentially expressed in adipose tissue and displays a higher sensitivity to norepinephrine and a series of novel β-adrenergic agonists having thermogenic, anti-obesity, and anti-diabetic activities and a lower affinity for classical β-adrenergic blockers as compared to β1- and β2-adrenergic receptors. Molecular biology has proven invaluable as a tool for the elucidation of the gene structure of β-adrenergic receptors and thus, has provided the opportunity to analyze receptor subtypes, receptor structure, ligand binding, and G protein coupling at the molecular level, as well as providing a model system for the study of other G protein-coupled receptors. Some of the new information on β-receptor structure and function derived from the application of molecular biology to receptor studies is summarized in this chapter.
Publication Year: 1996
Publication Date: 1996-01-01
Language: en
Type: book-chapter
Indexed In: ['crossref']
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