Role of thyroid hormones in the regulation of hepatic glucokinase and phosphoenolpyruvate-carboxykinase gene expression during the starvation-refeeding transition.

Thyroid hormones act at the transcriptional level in the induction of the important hepatic glucoregulatory enzyme PEP-carboxykinase and glucokinase (Fig. 1 and Fig. 2). They have no significant effect on the degradation of both enzymes, nor on the degradation of the specific mRNAs. A T3-receptor interaction is essential for their effect. Suggestions have been made for a thyroid hormone regulatory element in the promotor region of T3-dependent genes (for a review see [18]). Thyroid hormones probably do not determine the direction of the metabolic flux; however, they significantly enhance in a permissive way the transition from one state, e.g. starvation, to another, e.g. refeeding. And by enhancing significantly the activity of important regulatory enzymes, they enhance the flux of metabolites under different metabolic conditions, such as in starvation or after refeeding.