Response differences in some steroid-sensitive hepatic enzymes in the fasting rat.

Abstract

The activities of the glucocorticoid-inducible enzymes, tryptophan pyrrolase, tryptophan and tyrosine α-ketoglutarate transaminases, and phenylalanine and tryptophan hydroxylases, were measured during fasting and realimentation. Of these, only tryptophan pyrrolase activity increased during the fasting period, despite sustained elevations in adrenocortical activity as evidenced by increased levels of corticosteroids. The increase appeared to reflect increased synthesis and resembled substrate induction. Total liver transaminase activity was unaltered by fasting whereas hydroxylase activity decreased. The results demonstrate the non-equivalence of exogenous glucocorticoid administration and the endogenous adrenal activation accompanying this stress in eliciting enzyme induction.