Review Question - QID 100562

Epinephrine has alpha-1 & -2 and beta-1 and -2 activity, however in the presence of a non-selective beta blocker such as propranolol, only the alpha effects will manifest, resulting in vasoconstriction, increased blood pressure and ensuing reflex decrease in heart rate.

Epinephrine's adrenergic agonist effects can be summarized as follows: alpha-1 results in vasoconstriction (increased systolic BP), beta-1 leads to increased HR and cardiac contractility, and beta-2 results in vasodilation (decreased diastolic BP). At low doses of epinephrine, the beta-2 effect on the peripheral vasculature results in vasodilation and decreased diastolic BP; however, at high doses of epinephrine, the alpha-1 effects overpower those of beta-2, resulting in an increased diastolic BP. Coadministration of epinephrine and a nonselective beta blocker has the potential to lead to either a hypertensive crisis (unopposed alpha-adrenergic action) or, if the patient is in anaphylaxis, blunted response or resistance to the therapeutic effect of epinephrine administration.

Incorrect Answers:
Answer 1: The addition of the beta-2 agonist action of epinephrine opposes the beta-2 antagonist action of propranolol, leading to increased smooth muscle relaxation in the bronchioles and thus increased bronchodilation.
Answer 2: The addition of the beta-2 agonist action of epinephrine opposes the beta-2 antagonist action of propranolol, leading to increased smooth muscle relaxation in the GI tract, which results in decreased motility.
Answer 4: The unopposed alpha-agonist action that occurs with coadministration of propranolol and epinephrine results in increased blood pressure.
Answer 5: The increased blood pressure discussed above leads to reflex bradycardia, a decreased heart rate.