Antiadrenergic agents, peripherally acting 

Alpha adrenoreceptor antagonists prevent the stimulation of alpha-adrenergic receptors at the nerve endings of the sympathetic nervous system. There are two types of alpha-adrenergic receptors, alpha 1 (on the vascular smooth muscle) and alpha 2 (on the vascular smooth muscle and sympathetic nerve terminals).

Alpha-adrenoreceptor antagonists are classed either as non-selective alpha adrenoreceptor antagonists, alpha1-selective antagonists, alpha2-selective antagonists and ergot derivatives.

The medicines used as cardiovascular agents are alpha1-selective antagonists. Alpha1-selective antagonists block the alpha adrenoreceptors on the vascular smooth muscle and widen the arteries, causing vasodilatation and a drop in blood pressure. These agents are used to treat hypertension.

Alpha1-receptor antagonists also cause relaxation of the smooth muscle of the bladder neck and prostate capsule. The longer acting alpha1 antagonists are used to treat urinary retention related to benign prostate hypertrophy.

Peripheral presynaptic anti-adrenergics are a class of medication that’s not very commonly used these days. Their mechanism of action is to target the presynaptic adrenergic neurons in the peripheral nervous system, and prevent them from effectively releasing the catecholamines, norepinephrine, and epinephrine.