Mechanism of epinephrine's glycogenolytic effect in isolated canine hepatocytes

Epinephrine (10 −7 mol/L) addition to isolated canine hepatocytes activates glycogen phosphorylase from 12.3 ± 0.4 to 28.6 ± 2.6 U/g and glucose output from 42 ± 3 to 170 ± 24 nmol/mg/h. Preincubation of hepatocytes with propranolol (2 × 10 −5 mol/L) caused a 73% inhibition of phosphorylase activation and a 77% inhibition of the stimulation of glucose output by epinephrine. Phentolamine (2 × 10 −5 mol/L) on the other hand, caused a 16% inhibition of phosphorylase activation and a 27% inhibition of the stimulation of glucose output by epinephrine. These results were unaffected by the sex of the animal. In the dog the glycogenolytic effects of epinephrine appear to be mediated primarily by a β-adrenergic mechanism.