Medications that cause urine retention

[skybmonkey]

Could someone please help me figure this out, bc I searched all over and can't find the physio-mechanics

Why/how do beta blockers (as well as some antihypertensive drugs) cause urine retention?

as far as i am concerned, beta blockers act on the kidneys to decrease the production of renin, thus angiotensinogen is unable to ultimately be converted to angiotensin II. As we know, Angiontensin II acts on the adrenal gland releasing vasopresin, thus increasing H2O/NaCl retention in the kidneys. but if no vasopresin, then why the urine retention?

Thank you.

[pharmacist2040]

It is very unlikely for beta blockers to cause urinary retention. In fact, if you check package insert for various selective and non-selective beta blockers, you will not find urinary retention as an adverse reaction. I did not see any case reports with these drugs where urinary retention has been reported.

The detrusor muscle of the bladder contain high density of cholinergic receptors. There are two types of cholinergic receptors (muscarinic and nicotinic). These receptors have a high response to one of the major neurotransmitters found throughout the central and peripheral nervous systems, achetylcholine. In the bladder, you mainly find muscarinic receptors. Stimulation of muscarinic receptors will result in significant contractions of detrusor muscle, and, therefore, in micturition. Thus, muscarinic receptors are primarily responsible for tonicity of the bladder. The second most common receptors in the bladder, prostate, and urethra are L1 and L2 receptors. B adrenergic receptors are also found in the bladder, however, THEIR DENSITY is much lower when compared to muscarinic and L-adrenergic receptors. Theoretically, you may speculate that when you block B-adrenergic receptors it will result in reduced bladder contractions to some degree. This is true. However, it is very unlikely that blockage of beta adrenergic receptors will result in impaired bladder voiding to cause urinary retention. On the other hand, never forget about anatomic, physiologic, and biochemical differences from one human to another. This is why certain risk factors or chemicals will result in a disease or condition in one person but not in another. Therefore, I am saying it is very UNLIKELY.