Glucorticoids and the regulation of phosphoenolpyruvate carboxykinase (guanosine triphosphate) in the rat

The effect of glucocorticoids on the synthesis and degradation of phosphoenolpyruvate carboxykinase (GTP) (EC 4.1.1.32) in rat liver and kidney in vivo was studied immunochemically. The glucocorticoid analogue triamcinolone (9α fluoro 11β,21 dihydroxy 16α,17α isopropylidenedioxypregna 1,4 diene 3,20 dione) increased the synthesis rate of the kidney enzyme in fed rats, but did not further increase the high synthesis rate of this enzyme in starved animals. Both triamcinolone and cortisol decreased the synthesis rate of hepatic phosphoenolpyruvate carboxykinase (GTP) in fed and starved rats, but were without effect on the degradation rate of the enzyme. This effect of triamcinolone in liver was reversed by injection of dibutyryl cyclic AMP. However, in diabetic animals glucocorticoids increased the synthesis rate of hepatic phosphoenolpyruvate carboxykinase (GTP). Triamcinolone administration to starved rats in vivo is shown to cause an increase in the portal blood concentrations of insulin and glucose. Since the physiological de-inducer of liver phosphoenolypyruvate carboxykinase (GTP) is insulin, this is the probable cause of the decrease in the synthesis rate of the hepatic enzyme noted when glucocorticoids are administered to non diabetic animals.