DEXAMETHASONE-INDUCED CATABOLISM AND INSULIN RESISTANCE IN L6 MYOBLASTS ARE REVERSED BY THE REMOVAL OF SERUM

1. One hundred nanomolar dexamethasone reduced protein synthesis by 16% and also decreased the accretion of protein and RNA in L6 myoblasts when foetal calf serum was present; these effects were reversed when serum was omitted from the medium. 2. Insulin (100-mu-U/ml) increased protein synthesis, protein accretion and RNA accretion both in the presence and the absence of serum. 3. Dexamethasone inhibited the effects of 100-mu-U insulin/ml in the presence of serum and induced insulin resistance; in the presence of 25 or 100 nM dexamethasone insulin was ineffective at concentrations below 250-mu-U and 1 mU/ml respectively.