A 28-year-old man who recently received an injection of epinephrine following a bee sting now has hyperglycemia. The most likely cause is an increase in which of the following processes?

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Epinephrine stimulates hepatic glycogenolysis, which increases blood glucose levels, leading to hyperglycemia. Epinephrine can bind and activate both α-adrenergic and β-adrenergic receptors. When epinephrine binds α₁-adrenergic receptors, there is an activation of the membrane-associated enzyme PLC- β. PLC-β hydrolyzes membrane PIP₂ into DAG and IP₃. The IP₃ then binds to receptors present in membranes of the endoplasmic reticulum (ER) resulting in release of stored calcium ion. The released calcium binds to the calmodulin subunit of glycogen synthasephosphorylase kinase, resulting in activation of this regulatory enzyme. The net effect is enhanced activity of phosphorylase and inhibited activity of glycogen synthase. When epinephrine binds β-adrenergic receptors, there is activation of adenylate cyclase resulting in increased cAMP with consequent activation of PKA. PKA phosphorylates and activates glycogen synthasephosphorylase kinase with the results being the same as for α-adrenergic receptor activation.

A 28-Year-Old Man Who Recently Received an Injection of Epinephrine