Muscle Plasticity andβ2-Adrenergic Receptors: Adaptive Responses ofβ2-Adrenergic Receptor Expression to Muscle Hypertrophy and Atrophy

Abstract

We discuss the functional roles ofβ2-adrenergic receptors in skeletal muscle hypertrophy and atrophy as well as the adaptive responses ofβ2-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 increasingβ2-adrenergic receptor density in exercise-recruited slow-twitch muscles. However, excessive stimulation ofβ2-adrenergic receptors negates their beneficial effects. Although the preventive effects ofβ2-adrenergic receptor stimulation on atrophy induced by muscle disuse and catabolic hormones or drugs are observed, these catabolic conditions decreaseβ2-adrenergic receptor expression in slow-twitch muscles. These findings present evidence against the use ofβ2-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.