Effects of Glucagon on Carbohydrate Synthesis and Enzyme Activity in Rat Liver

The present investigation was conducted to study the influence of glucagon on hepatic gluconeogenesis and to learn if hormone effects on glucose synthesis are mediated through changes in enzyme activity. Subcutaneous administration of a single dose of glucagon caused phosphoenolpyruvate (PEPCK) activity to rise and liver glycogen to decline within 3 hr. Four subcutaneous doses of glucagon given over 2 days led to reduced PEPCK levels and increased hepatic glycogen. Other enzymes were not affected by the doses of glucagon used. Dexamethasone injection (4 doses in 2 days) induced increased activities of all enzymes assayed except pyruvate carboxylase (PC); however, those enzymes which demonstrated the greatest responses were glutamic pyruvic transaminase (GPT), glutamic oxaloacetic transaminase (GOT) and PEPCK. Dexamethasone caused a large rise of liver glycogen. In fed adrenalectomized rats, GPT activity declined markedly and there was a small reduction of glucose-6-phosphatase (G6Pase) but activities of o...