Mode of action of glucocorticoids: II. Early effects of triamcinolone on amino acid incorporation into various tissues in vivo

Abstract

1. 1. Acute effects of the glucocorticoid triamcinolone (350 μg per 100 g body weight, 2 to 4 h) on labeled amino acid incorporation into protein of subcellar components in various tissues have been investigated in fed rats. 2. 2. The incorporation of uniformely labeled L-[ 14C]valine and DL-[3- 14C]phenylalanine into proteins of nuclei, mitochondria, microsomes and supernatant fractions of hepatic cells was not modified by the administration of triamcinolone, whereas the incorporation of these amino acids into proteins of each of these fractions of the thymus was reduced by triamcinolone given either 2 or 4 h previously. 3. 3. The administration of triamcinolone increased liver glycogen, but did not significantly affect the concentration of blood sugar and muscle glycogen in fed animals. The incorporation of 14C from uniformely labeled L-[ 14C]valine as well as DL-[3 14]phenylalanine into liver glycogen and blood glucose were s by triamcinolone administration, indicating increased gluconeogenesis from the carbon of phenylalanine as well as from that of valine. 4. 4. The size of the pool of free amino acids and the specific activities of free amino nitrogen in the blood and thymus, were not significantly modified by triamcinolone, but the size of the pool and the radioactivities of free amino acids in hepatic cells were increased. 5. 5. These findings suggest that triamcinolone inhibits protein synthesis in the thymus even in very short-term experiments and that this inhibiting effect is due neither to the effect of hormone on cell membrane transport of amino acids nor to the catabolism of amino acids in the liver for gluconeogenesis with resultant shortage of amino acids for protein synthesis in peripheral tissue.