Alpha-adrenergic blockers – how do they work?

Alpha-adrenergic blockers or alpha-adrenergic antagonists affect the alpha receptors of the sympathetic nervous system. There are two kinds of alpha-adrenergic receptors: alpha-1 and alpha-2. Alpha-1 adrenergic receptors are present in vascular smooth muscle akin to the skin, gastrointestinal sphincters, kidneys, and brain, and cause vasoconstriction when activated by catecholamines (Nachawati and Patel, 2021). Alpha-2 adrenergic receptors are positioned in peripheral nerve endings and, when activated, inhibit the discharge of norepinephrine. Nonselective alpha-adrenergic antagonists cause vasodilation by blocking each alpha-1 and alpha-2 receptors.

By occupying the sites of alpha receptors, alpha-adrenergic blocking drugs cause the partitions of blood vessels to calm down. This results in dilation of blood vessels and a discount in peripheral vascular resistance (the pressure that the blood flowing through the vessel must overcome). This effect may end in orthostatic hypotension, i.e. a drop in blood pressure that happens when changing the position from lying right down to standing. Redistribution of blood into the dilated blood vessels of the legs causes hypotension.

• Phenoxybenzamine (dibenzyline): Treats sweating and hypertension (HTN) related to pheochromocytoma.
• Phentolamine: Treats hypertensive episodes in patients with pheochromocytoma during preoperative preparation and surgical excision.

it causes blood vessels to dilate, which causes a drop in blood pressure, which is why it’s used to treat hypertension. Alpha-1 blockers also calm down prostate smooth muscle and are used to treat benign prostatic hyperplasia (BPH).

are currently under investigation and haven’t received approval from the Federal Medicines Agency (FDA).

Facts and Comparisons (2022). Alpha-1 adrenergic blockers. . Retrieved January 11, 2022 from https://online.factsandcomparisons.com/lco/action/doc/retrieve/docid/fc_dfc/5546106?cesid=4Z6bkQiTceV&

Nachawati, D. and Patel, J. (2021, July 6). Alpha blockers. . Downloaded from https://www.ncbi.nlm.nih.gov/books/NBK556066/