Incorporation of C¹⁴-amino acids into protein of isolated diaphragms: role of the adrenal steroids

The incorporation of C 14 -amino acids into a protein fraction of diaphragms incubated in vitro was measured. Adrenalectomy led to an increase in amino acid incorporation into protein. Cortisone (0.3 mg/day) administered to adrenalectomized rats tended to restore incorporation to normal; desoxycorticosterone (0.06 mg/day) was without effect. Larger doses of cortisone (1 or 2 mg/day) produced a marked reduction in amino acid incorporation into diaphragms from both normal and adrenalectomized rats. Fasting reduced histidine incorporation into muscle protein whether the donor rat was normal or adrenalectomized. Phenylalanine-3-C 14 incorporation into diaphragm protein was measured at several phenylalanine concentrations. Despite large (100-fold) changes in the phenylalanine pool size the percentage increase in C 14 incorporation after adrenalectomy was similar.