Effects of glucocorticoids on myoblast proliferation and differentiation were determined in cell culture. Dexamethasone (1 × 10−7 M) decreased myoblast doubling time by 7 h and increased cell densities as much as 800% after 8 days of exposure of the cells to dexamethasone. Stimulation of myoblast proliferation by glucocorticoids was dose dependent, with halfmaximal activity exhibited at concentrations of 3 × 10−9 M dexamethasone or 2.3 × 10−8 M corticosterone. In differentiating cultures, the rate of accumulation and final levels of DNA and creatine phosphokinase were highly stimulated by dexamethasone. However, normalization of creatine phosphokinase levels (a marker for myoblast differentiation) per μg DNA demonstrated a small (30%) decrease in differentiation in cultures exposed to glucocorticoids. These results indicate that glucocorticoids stimulate early myogenesis by increasing the number of myoblasts but do not stimulate the differentiation of these cells.
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