Almon R R, Dubois D C
Department of Biological Sciences, State University of New York, Buffalo 14260.
Med Sci Sports Exerc. 1990 Jun;22(3):304-11.
Data are presented which demonstrate that phasic/glycolytic muscles atrophy more than tonic/oxidative muscles in response to exogenously introduced glucocorticoids. Data are also presented demonstrating that immobilization makes a muscle unusually sensitive to glucocorticoid-induced atrophy and that remobilization of a previously immobilized muscle protects a muscle from glucocorticoid-induced atrophy. These observations are discussed within the context of the role of mechanical activity in the acquisition and maintenance of fiber-type characteristics. In addition, the available data on the glucocorticoid receptor population in skeletal muscles of various types and circumstance are reviewed within the context of the recent observations concerning the glucocorticoid induction of the enzyme glutamine synthetase in skeletal muscle. It is proposed here that atrophy is not necessarily the response of skeletal muscle to glucocorticoids. Rather, atrophy is a possible consequence of the glucocorticoid-induced increase in export of amino acid carbon from the muscle. Whether such export causes a muscle to atrophy or perhaps even hypertrophy will depend on the capacity of the muscle to sustain its free amino acid pools. Mechanical activity greatly promotes the uptake of free amino acids in skeletal muscle. Such promotion takes the form of both contraction-induced uptake and increased insulin sensitivity. Within this perspective, it is suggested that tonic muscles and remobilized muscles are protected from atrophy by exogenous glucocorticoids because their high level of mechanical activity allows them to maintain their free amino acid pools.
所呈现的数据表明，对外源性引入的糖皮质激素，相性/糖酵解型肌肉比紧张性/氧化型肌肉萎缩更严重。还呈现的数据表明，固定会使肌肉对糖皮质激素诱导的萎缩异常敏感，而先前固定的肌肉重新活动可保护其免受糖皮质激素诱导的萎缩。在机械活动在纤维类型特征的获得和维持中的作用背景下讨论了这些观察结果。此外，在近期关于糖皮质激素诱导骨骼肌中谷氨酰胺合成酶的观察背景下，回顾了各种类型和情况下骨骼肌中糖皮质激素受体群体的现有数据。这里提出，萎缩不一定是骨骼肌对糖皮质激素的反应。相反，萎缩可能是糖皮质激素诱导的肌肉中氨基酸碳输出增加的结果。这种输出是否导致肌肉萎缩甚至肥大将取决于肌肉维持其游离氨基酸池的能力。机械活动极大地促进了骨骼肌中游离氨基酸的摄取。这种促进表现为收缩诱导的摄取和胰岛素敏感性增加。从这个角度来看，有人认为紧张性肌肉和重新活动的肌肉受到外源性糖皮质激素的保护而不发生萎缩，因为它们高水平的机械活动使它们能够维持其游离氨基酸池。
