Blockade of Glucocorticoid Receptor Binding and Inhibition of Dexamethasone-Induced Muscle Atrophy in the Rat by RU38486, a Potent Glucocorticoid Antagonist*

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Abstract
Glucocorticoid hormones caused marked muscular atrophy, the mechanism of which is unknown. We employed a potent glucocorticoid antagonist, RU38486 [11.beta.-(4-dimethylaminophenyl)17.beta.-hydroxy-17.alpha.-(prop-1-ynyl)estra-4,9-dien-3-one], to determine whether intracellular glucocorticoid receptors are involved. RU38486 was shown to be an effective blocker of glucocorticoid receptor binding in vivo and in vitro. Furthermore, this compound significantly blocked the loss of body and muscle weight caused by injection of dexamethasone. These data indicate that intracellular glucocorticoid receptors are important in the etiology of steroid myopathy. Studies with glucocorticoid antagonists may lead to the design of specific therapeutic modalities for the treatment of both endogenously and exogenously produced steroid myopathies.