The Insulin Concentration in the Pancreatic Veins Is Measured After

The insulin concentration in the pancreatic veins is measured after various agents are administered in a series of animal experiments. Insulin levels are reduced when epinephrine is administered. However, following pretreatment with Drug A, epinephrine injection results in an unexpected increase in insulin concentration. Which of the following receptors does Drug A most likely block?

A) Alpha-2 adrenergic receptors
B) Beta-2 adrenergic receptors
C) Glucagon-like peptide-1 receptors
D) Histamine H2 receptors
E) Muscarinic M3 receptors