Category Archives: Alpha Antagonists

Prazosin: Cut the Corset!

Ladies, and some Gentlemen, you know what I mean:  Although corsets and bustiers are incredibly sexy, very little can compare to the feeling of utter freedom when they are finally taken off.  Corsets constrict your poor expanding rib cage*, giving you a teensy tiny waist, much like alpha-1 constricts the heck out of your blood vessels!

Well, as you can tell by the title, prazosin (Minipress) cuts the constriction.  It is our prototype for the very carefully-prescribed alpha blockers.  You might remember from an earlier post that blocking alpha results in vasorelaxation, dropping the blood pressure by reducing resistance of the arterial walls.  This is very useful when your blood pressure is way too high.  Unfortunately, because it directly affects the blood vessels (instead of the heart, like beta blockers), it has the serious side effect of rebound hypotension and rebound tachycardia.

But wait, there’s more!

There are also alpha-1 receptors near your bladder.  These work in conjunction with muscarinic receptors to control the flow of urine and prevent urinary retention.

Some disease processes interfere with these systems, however, and one of the more common in men over 50 is Benign Prostatic Hyperplasia, or BPH.

Deutsch: Harnverhalt mit riesiger Blase in der...
Deutsch: Harnverhalt mit riesiger Blase in der Computertomographie. (Photo credit: Wikipedia)

Alpha-1 receptors line the internal urethral sphincter–a smooth muscle that tenses to prevent urine outflow.  In BPH, patients suffer urinary retention as a result of the swollen prostate.  Some other alpha blockers, like doxazosin, help relax the sphincter and restore some urine flow.  Save the kidneys!

See that HUGE grey blob in the picture?  That is a BLADDER.  A hugely distended, probably very uncomfortable, urine-filled bladder.  OUCH.  Thank you, alpha-1 blockers, thank you.

To summarize, alpha-1 blockers:

1) Stop vasoconstriction and relax the arterial walls

2) Relax the internal urethral sphincter

3) Can cause rebound hypotension

4) Can cause rebound tachycardia, because now the heart has to make up for the drop in resistance!

*I know there are many people out there who LOVE corsets, so by all means, do not let me dissuade you!  I don’t want any nerdy (because you are reading this post, which implicates you by association) hate mail (because you love corsets and are feeling militant).  Please.  🙂