The effect of fibroblast growth factor (FGF) on the rate of proliferation and fusion of bovine myoblast has been examined. Addition to the cultures of 0.1 mug-1 mug/ml of FGF stimulates the rate of proliferation and delays the fusion of primary cultures of bovine myoblasts cultured in 10% serum. Final cell densities reached in the presence of 0.1 mug/ml of FGF were fivefold higher than in controls; with 1 mug/ml, they were 10-fold higher. Increases in cell density were paralleled by increases in acetylcholine receptor sites as measured by the binding of 125I-alpha-bungarotoxin. Both fusion and the appearance of acetylcholine receptor sites were delayed in the presence of FGF. Growth hormone, insulin and testosterone, which have been reported to be mitogenic for rat and chick embryo myoblasts, did not have significant effects on DNA synthesis in bovine myoblasts when compared to the FGF. Conversely, FGF did not stimulate the proliferation of chick embryo myoblasts, indicating that it is not active in all vertebrate species.

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