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. Stimulation of the β2-adrenergic receptor 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 preventive effects of β2- adrenergic receptor stimulation on atrophy induced by muscle disuse and catabolic hormones or drugs were observed, these catabolic conditions decreased 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.
- Skeletal muscle atrophy
- Skeletal muscles
- Sports doping
- β<inf>2</inf>-adrenergic receptors
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