Epinephrine is used to treat cardiac arrest and status asthmaticus because of which of the following actions?
A. Increased speed of conduction and gluconeogenesis.
B. Bronchodilation and increased heart rate, contractility, and conduction.
C. Increased vasodilation and enhanced myocardial contractility.
D. Bronchoconstriction and increased heart rate.
Correct Answer: B. Bronchodilation and increased heart rate, contractility, and conduction.
Bronchodilation results from stimulated beta receptors, and cardiac effects result from the stimulation of ß1 receptors. Epinephrine is a sympathomimetic catecholamine that exerts its pharmacologic effects on both alpha and beta-adrenergic receptors using a G protein-linked second messenger system. It has a greater affinity for beta receptors in small doses.
Option A: This does not address respiratory effects of medication. However, large doses produce selective action on alpha receptors. Through its action on alpha-1 receptors, epinephrine induces increased vascular smooth muscle contraction, pupillary dilator muscle contraction, and intestinal sphincter muscle contraction.
Option C: A-stimulating drugs cause vasoconstriction. Other significant effects include increased heart rate, myocardial contractility, and renin release via beta-1 receptors.
Option D: Bronchodilation, not bronchoconstriction, results from ß2 activity. Beta-2 effects produce bronchodilation, which may be useful as an adjunct treatment of asthma exacerbations as well as vasodilation, tocolysis, and increased aqueous humor production.