What is the ***primary*** mechanism of action of epinephrine in the treatment of anaphylactic shock

Question

A.) increases metabolism

B.) dilation of the bronchioles in the lungs by binding to beta 2 receptors

C.) dilation of the bronchioles in the lungs by binding to beta 2 & alpha 2 receptors

D.) increasing blood pressure

Answer 1

The answer is in the question-treatment of anaphylactic shock. Shock is the clinical syndrome of inadequate blood flow to the organs. Shock in anaphylaxis is due to release of a number of mediators from mast cells and basophils that result in widespread vasodilation which in turn reduces venous return to the heart, reducing in cardiac output and therefore delivery of oxygen to the organs. In addition, low blood pressure reduces perfusion pressure of the organs. Epinephrine reverses these effects due to vasoconstriction.

Bronchoconstriction may reduce the oxygen content of the blood, but without adequate blood flow, it is not going to get to where it needs to be to sustain organ function

Answer 2

B.) dilation of the bronchioles in the lungs by binding to beta 2 receptors

A, C, and D are all things that epinephrine can do, however, the primary reason for using epinephrine in the treatment of anaphylaxis is its effect as a bronchodilator which is mediated by its binding to the beta-2 receptor and increasing cAMP.

Answer 3

This can be a tricky concept! The answer is B. Epinephrine is an alpha- and beta-agonist, meaning it binds to both alpha and beta adrenergic receptors. These receptors are used by catecholamines, which include epinephrine and norepinephrine, and typically stimulate the sympathetic nervous system.

Further explanation:

The beta-2 receptor will cause smooth muscle (bronchial) relaxation, ie dilation. Beta-1 will increase cardiac function, like heart rate and contractility. Since epi is also an alpha agonist, it binds to alpha-1 and alpha-2, which causes vasoconstriction; alpha-1 is the predominant alpha-receptor on vascular smooth tissue and will increase smooth muscle contraction (vasoconstriction) and alpha-2 has a unique role in inhibiting norepinephrine release as a form of negative feedback.

However, epinephrine has a higher affinity for beta-2 over alpha receptors, so the correct answer is B!

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