Effect of repeated administration of glucocorticoid on the glycogen level of mouse muscle

Abstract

Glycogen content and glycogen synthetase activity in mouse skeletal muscle (M. gastrocnemius) after single or repeated administrations of glucocorticoid were investigated and compared with those in liver, in a series of experiments to elucidate the biochemical mechanism of steroid myopathy. Results obtained were as follows. After a single administration of triamcinolone acetonide (TA, 5 mg/kg i.p.), glycogen content in muscle increased maximally at about 12 hr and returned to control level at about 24 hr. The I form activity of glycogen synthetase in muscle was increased only 6 hr after a single administration, while the total activity of the enzyme was not significantly changed. Similar results were obtained with the liver. After repeated administrations of TA for one week, the glycogen accumulation in the muscle was lowered markedly as compared with that after a single administration. No increase in synthetase I activity was observed, or rather, the enzyme activity was decreased as compared with that from control. Similar results were obtained with the liver. After single or repeated administrations, blood glucose level decreased slightly, glucose level of muscle was not affected and G-6-P level of muscle increased markedly. These results suggest that the lower accumulation of glycogen in the muscle after repeated administrations of glucocorticoid may be primarily due to an abnormality in the glycogen synthetase system.