Effects of insulin on protein synthesis in muscles from normal and dystrophic mice.

Protein synthesis in soleus and extensor digitorum longus (EDL) muscles was measured in vitro to test the hypothesis that the lack of muscle protein accumulation in dystrophic conditions could be caused by a reduced sensitivity to insulin. We demonstrate that physiological insulin concentrations stimulate protein synthesis in soleus muscles from normal mice but not from muscles obtained from dystrophic (dy) animals. The difference is lost at very high insulin concentrations (1 microM) and could not be shown at any concentration with EDL muscles. These results, together with the reported reduced inhibitory effect of insulin on protein synthesis in dystrophic hamsters and on protein breakdown in dystrophic mice, suggest that protein metabolism in certain muscles from dystrophic animals may be less responsive to the anabolic effects of insulin.