Effect of testosterone on whole body amino acid utilization in myotonic dystrophy

Patients with myotonic dystrophy are markedly insulin resistant and have an associated abnormality in the regulation of arterialized amino acid concentrations during euglycemic insulin infusions. We studied the effect of testosterone treatment on whole body amino acid balance in myotonic dystrophy, since it increases muscle mass and muscle protein synthesis rate. Six patients with myotonic dystrophy underwent studies of glucose disposal and amino acid regulation during low dose insulin infusions with maintenance of euglycemia, prior to and after 10 to 13 weeks of testosterone (3 mg/kg/wk). Testosterone increased the insulin-stimulated decline of certain amino acids, but did not improve whole body glucose uptake. The anabolic effect of testosterone is separate from the anabolic effect of insulin.