Dose dependent reversal by i.v. glucose administration of the stimulation of rat liver glycogen phosphorylase by epinephrine infusion.
Infusion of 0.5 ml kg-1 min-1 20% glucose i.v. failed to suppress the stimulatory effect of 0.25 microgram kg-1 min-1 epinephrine dissolved in and infused together with the above glucose solution on the activity of liver glycogen phosphorylase in adult male rats. However, 40% glucose solution administered in the same way abolished the effect of the epinephrine infusion completely. An i.v. pulse of 1 g kg-1 glucose in the form of a 40% solution immediately before the infusion of the same dose of epinephrine in saline had only a temporary inhibitory effect on epinephrine induced increase of phosphorylase activity. Finally, i.p. administration of 10 mg kg-1 phentolamine 60 min before epinephrine infusion in saline completely blocked the increasing effect of the latter on both liver phosphorylase and serum glucose, while that of 4 mg propranolol 30 min before the hormone failed to exert any influence. This reconfirmed the well known mediation of the glycogenolytic effect of catecholamines in adult male rats by alpha type adrenergic receptors.