Enhancement by carbon tetrachloride treatment of hepatic tyrosine amino-transferase induction in the presence of net polyribosome breakdown in the rat

Abstract

Carbon tetrachloride treatment inhibited the glucocorticoid induction of hepatic tryptophan oxygenase (TPO) while simultaneously enhancing the induction of hepatic tyrosine aminotransferase (TAT) in intact or adrenalectomized rats. In addition, treatment with CCl 4 alone increased the activity of hepatic TAT, but the extent of the CCl 4-induced stimulation of TAT was decreased by adrenalectomy or by hypophysectomy. The CCl 4-induced stimulation of TAT was prevented by high doses of actinomycin D but was enhanced further by 5-fluorouracil. CCl 4 also enhanced the labeling of hepatic polyribosomes with [ 14C]orotic acid while simultaneously producing breakdown of heavy polysomes. These findings suggest that CCl 4 treatment may enhance the synthesis of certain hepatic enzymes, possibly via synthesis of new polysomes, while simultaneously inhibiting the induction of other enzymes such as TPO.