title: Muscle plasticity and β₂-adrenergic receptors: adaptive responses of β₂-adrenergic receptor expression to muscle hypertrophy and atrophy.
abstract: We discuss the functional roles of β₂-adrenergic receptors in skeletal muscle hypertrophy and atrophy as well as the adaptive responses of β₂-adrenergic receptor expression to anabolic and catabolic conditions. β₂-Adrenergic receptor stimulation using anabolic drugs increases muscle mass by promoting muscle protein synthesis and/or attenuating protein degradation. These effects are prevented by the downregulation of the receptor. Endurance training improves oxidative performance partly by increasing β₂-adrenergic receptor density in exercise-recruited slow-twitch muscles. However, excessive stimulation of β₂-adrenergic receptors negates their beneficial effects. Although the preventive effects of β₂-adrenergic receptor stimulation on atrophy induced by muscle disuse and catabolic hormones or drugs are observed, these catabolic conditions decrease β₂-adrenergic receptor expression in slow-twitch muscles. These findings present evidence against the use of β₂-adrenergic agonists in therapy for muscle wasting and weakness. Thus, β₂-adrenergic receptors in the skeletal muscles play an important physiological role in the regulation of protein and energy balance.
authors.affiliation: Laboratory of Physiological Sciences, Faculty of Human Sciences, Waseda University, 2-579-15 Mikajima, Tokorozawa, Saitama 359-1192, Japan.
authors.forename: Shogo
authors.initials: S
authors.lastname: Sato
authors.forename: Ken
authors.initials: K
authors.lastname: Shirato
authors.forename: Kaoru
authors.initials: K
authors.lastname: Tachiyashiki
authors.forename: Kazuhiko
authors.initials: K
authors.lastname: Imaizumi
mesh_terms: D045930:Anabolic Agents / Q000627:therapeutic use; D000818:Animals; D004734:Energy Metabolism; D005786:Gene Expression Regulation; D006801:Humans; D018657:Muscle Fibers, Slow-Twitch / Q000378:metabolism* / Q000473:pathology; D009124:Muscle Proteins / Q000378:metabolism*; D009133:Muscular Atrophy / Q000188:drug therapy / Q000378:metabolism* / Q000473:pathology; D059748:Proteolysis / Q000187:drug effects; D018343:Receptors, Adrenergic, beta-2 / Q000096:biosynthesis*
chemical_list: D045930:Anabolic Agents; D009124:Muscle Proteins; D018343:Receptors, Adrenergic, beta-2