Which agent is virtually devoid of beta 2 adrenergic activity?

Norepinephrine is considered virtually devoid of beta 2 adrenergic activity because its primary action is on alpha-1 and beta-1 adrenergic receptors. It primarily facilitates vasoconstriction (through alpha-1 activity) and increases heart rate and contractility (via beta-1 activity). Although norepinephrine can have some effect on beta-2 receptors, this effect is minimal compared to its strong affinity for alpha-1 and beta-1 receptors.

This makes it significantly different from the other agents listed. Isoproterenol, for instance, is a non-selective beta agonist that activates both beta-1 and beta-2 receptors, leading to increased heart rate and bronchodilation. Terbutaline primarily targets beta-2 receptors and is used for its bronchodilator effects, particularly in asthma and other pulmonary conditions. Epinephrine also interacts with both alpha and beta adrenergic receptors, but has a notable effect on beta-2 receptors, contributing to its role in bronchodilation.

Thus, the absence of significant beta-2 activity in norepinephrine is what distinguishes it as the correct choice in this context.