August 02, 2010

MRCP 2 Question 18

A comparison of norepinephrine and phenylephrine shows that, when given at therapeutic doses both can:

a) Decrease skin blood flow
b) Stimulate liver gluconeogenesis
c) Cause reflex tachycardia
d) Relax pregnant uterus
e) Increase A-V conduction

The correct answer is A


Norepinephrine works on alpha-1 and 2 and beta-1 receptors. Phenylephrine works on alpha-1 only.

Stimulation of liver gluconeogenesis is activated by Beta-2. Reflex tachycardia is elicited by blocking alpha-1. Relaxation of pregnant uterus is achieved by activation of Beta-2. Increase of A-V conduction is accomplished by activation of Beta-1.

As we notice these are functions that are not in common to both drugs.

On the other hand decrease in skin blood flow is an alpha-1 function. This is an action that is done by both drugs.

This makes choice A the correct answer

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