Regulation of phosphoenolpyruvate carboxykinase (GTP) in adipose tissue in vivo by glucocorticoids and insulin

Abstract

The regulation of the synthesis of phosphoenolpyruvate carboxykinase (GTP) (EC 4.1.1.32) in epididymal adipose tissue, liver and kidney in vivo was studied immunochemically. Phosphoenolypyruvate carboxykinase (GTP) synthesis in adipose tissue is increased by starvation, diabetes and noradrenaline, and decreased by re-feeding and insulin. These changes were also seen in adrenalectomized rats and are qualitatively similar to those observed for the liver enzyme. This indicates the involvement of cyclic AMP as an inducer and insulin as a de-inducer in the regulation of phosphoenolypyruvate carboxykinase (GTP) in both tissues. (Induction and de-induction are defined as selective increase and decrease respectively in the rate of enzyme synthesis, regardless of the mechanism involved.) Adrenalectomy had little effect on phosphoenolpyruvate carboxykinase (GTP) synthesis in liver and kidney, but increased the synthesis rate of the adipose tissue enzyme. Starvation and adrenalectomy had additive effects in increasing the synthesis rate of adipose-tissue phosphoenolpyruvate carboxykinase (GTP). In adrenalectomized diabetic rats glucocorticoids increased phosphoenolpyruvate carboxykinase (GTP) synthesis in liver and kidney while decreasing enzyme synthesis in adipose tissue. De-induction of adipose tissue phosphoenolpyruvate carboxykinase (GTP) is therefore regulated independently by glucocorticoids and insulin. Although liver, kidney and adipose tissue phosphoenolpyruvate carboxykinases (GTP) are seemingly identical, there is an apparent tissue-specific differentiation in regulatory systems for the enzyme.