Hormonal Control of Glycogenolysis in Isolated Chick Embryo Hepatocytes

Hepatocytes were isolated from 15-, 16-, 17-, and 18day-old chick embryos. Glucagon, adrenaline, and dibutyryl cAMP (Bt2cAMP), individually or in combination, activated glycogenolysis in the isolated hepatocytes. The α-adrenergic agonist phenylephrine did not increase glycogen breakdown. The action of adrenaline was abolished upon treatment of hepatocytes with a combination of the hormone and propranolol, a β-adrenergic blocker. The effects of glucagon, adrenaline, and dibutyryl cAMP on glycogenolysis were not additive. Either hormone induced an increase in the concentration of cAMP. The activities of dephosphophosphorylase kinase and phosphorylase a were stimulated by each hormone or Bt2cAMP. It appears likely that glucagon and adrenaline serve as physiological regulators of hepatic glycogen breakdown during embryogenesis in chickens.