Effect of glycogenolytic agents on phosphorylase activity of perfused rat liver

The effect of glycogenolytic agents on phosphorylase activity has been studied in the isolated perfused rat liver. Evidence is presented showing that endoportal administration of 10 –6 m glucagon, 10 –5 m epinephrine, and 10 –3 M cyclic 3',5'-adenosine monophosphate (3',5'-AMP) induced glycogenolysis, hyperglycemia, and increase in liver phosphorylase activity, usually within 1 hr after the onset of infusion. ATP, 10 –3 m, also caused glycogenolysis, but the onset was slower than with the cyclic nucleotide, and phosphorylase activation was inconstant Hyperglycemic effects of these two adenine nucleotides were also demonstrated in intact rats. Anoxia and hypoxia caused substantial glycogenolysis but did not stimulate phosphorylase activity, implying that some other mechanism accounts for the glycogen breakdown induced by reduced oxygen tension. Glycogenolysis and phosphorylase activation were not produced by administration of 10 –2 M 5'-AMP, 10 –4 M isoproterenol, adrenocorticotrophic hormone, or insulin.