The stimulatory effect of alloxan-diabetes on the gluconeogenesis from alanine and glutamine in rabbit hepatocytes

Effect of glucagon on alanine 2-oxoglutarate aminotransferase

Alanine-2-oxoglutarate aminotransferase activity in mouse liver is stimulated by the intravenous injection of glucagon. The stimulation is abolished by pretreatment with actinomycin D indicating that the increased activity is probably due to new enzyme formation. Administration of dibutyryl cyclic AMP, isoproterenol, an activator of adenyl cyclase and theophylline, an inhibitor of phosphodiesterase also increases the enzyme activity suggesting the involvement of cyclic AMP in glucagon-mediated increase of enzyme activity.

The influences of glucagon, epinephrine and adrenergic agents on glycogen phosphorylase a and pyruvate kinase activities in hepatocytes from juvenile and adult rabbits

1. Glucagon, epinephrine, norepinephrine, isoproterenol and phenylephrine each increases significantly glucose appearance and glycogen disappearance from hepatocytes of both juvenile and adult fed rabbits. Such increases caused by catecholamines and adrenergic agonists are suppressed significantly by the beta-adrenergic antagonist propranolol but are unchanged by the alpha-antagonist phentolamine. 2. Glucagon, epinephrine, norepinephrine, isoproterenol and phenylephrine each increases significantly glycogen phosphorylase a activity and decreases significantly the pyruvate kinase activity ratio (assayed with 0.8 mM phosphoenolpyruvate +/- 200 microM fructose 1,6-bisphosphate) in hepatocytes from both juvenile and adult rabbits. Changes induced by catecholamines and adrenergic agonists in the activities of both enzymes are significantly diminished by propranolol but unaltered by phentolamine. 3. These observations suggest that regulation of glycogenolysis and gluconeogenesis in rabbits by glucagon and catecholamines is at least partially due to activation of glycogen phosphorylase and inhibition of pyruvate kinase. Contrary to the age-related changes observed in the adrenergic nature of catecholamines' regulation of these two processes in rats, such regulation of both processes by catecholamines is beta-adrenergic in rabbits regardless of age.