Glucocorticoid-mediated induction of glutamine synthetase in skeletal muscle.

We studied the effect of glucocorticoids on glutamine synthetase in rat skeletal muscle in culture and in vivo. Dexamethasone, a synthetic glucocorticoid, caused striking, receptor-mediated increases in both glutamine synthetase activity and the steady-state glutamine synthetase mRNA level. This effect was observed in rat skeletal muscle cells in culture, as well as in rat muscles in vivo. Glucocorticoid-mediated induction of glutamine synthetase was blocked by androgenic/anabolic steroids at high doses, suggesting that anabolic steroids might have an anticatabolic mode of action in enhancing skeletal muscle mass in athletes. Further studies of the control of glutamine synthetase expression may shed light on mechanisms of muscle atrophy and hypertrophy.