NBME 23 Stimulation of α-adrenoreceptors (NBME Answers)

NBME 23 Answers

nbme23/Block 2/Question#12 (reveal difficulty score)
A 75-year-old woman has stress urinary ...
Stimulation of α-adrenoreceptors 🔍 / 📺 / 🌳 / 📖
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+6 upvote downvote
submitted by ∗sugaplum(487)

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phenylpropanolamine is an alpha agonist that stimulates urethral smooth muscle contraction. - from uptodate, however, it also says it is not recommended treatment anymore

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ugalaxy α1 stimulation (via α1 agonist) constricts the bladder sphincter thereby, preventing sudden bouts of micturition during coughing/sneezing (abdominal stress). +10

sammyj98 I thought that B3 stimulation stopped urination +9

adong @sammyj98 B3 would facilitate bladder relaxation +

hvancampen @sammyj98- were you thinking of oxybutynin? (thats what I thought of!) According to FA, its used for urge incontinence not stress. +2

drzed Nah he/she's talking about Beta-3 receptors which are Gs coupled. Gs increases cAMP thus it would cause smooth muscle relaxation -> bladder relaxation! +1

donttrustmyanswers From Mayo: "There are no approved medications to specifically treat stress incontinence in the United States. The antidepressant duloxetine (Cymbalta) is used for the treatment of stress incontinence in Europe, however." +1

nreid4 @hvancampen oxybutynin is an M3 muscarinic antagonist, not B3. +

alienfever I thought about B3 agonist as well and got this wrong. I think maybe B3 agonist can be used for bladder (URGENCY incontinence) where the main issue is detrusor over reactivity. In STRESS incontinence however the problem has nothing to do with detrusor, so we use α1 agonist to constrict the sphincter. +2

fatboyslim (FA 2020 242) Mirabegron is a B3 agonist. B3 stimulation causes detrusor muscle relaxation, hence it is used for URGE incontinence, not STRESS incontinence. I think the drug they are referring to is Ephedrine? Also, remember "O"xybutynin (muscarinic antagonist) is for "O"veractive bladder (urge incontinence) +1

handsome what is the educational objective of this question? what is the author trying to ask and want us to learn/know? +

bcher @handsome I would add another line to the table on FA2020 p237: alpha agonists; +alpha-1 receptor which causes bladder sphincter muscle contraction; treats stress urinary incontinence with sphincteric incontinence +

l0ud_minority I thought that females didn't have the internal urethral sphincter only external thus a more appropriate drug for stress urinary incontinence would be something that affects the nicotinic receptors????? Am I missing something??? If this was a male then yes alpha 1 receptors are located on the internal urethral sphincter and stimulation of them would help with symptoms in question. +

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submitted by ugalaxy(15)

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α1 stimulation (via α1 agonist) constricts the bladder sphincter thereby, preventing sudden bouts of micturition during coughing/sneezing (abdominal stress).

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+2 upvote downvote
submitted by ∗veryhungrycaterpillar(30)

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I used reverso logic.

Terazosin is an alpha blocker, helps with urinary retention by relaxing sphincter smooth muscle. What would help constrict the same muscle? Stimulating the same receptor. Ez pz.

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+1 upvote downvote
submitted by ∗lulumomovicky(4)

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The key point was ''sphincteric incompetence''. Stimulation of B3 adrenoreceptors will work if it was overreactive bladder, where detrusor muscle is over activated. This patient's main problem was sphincteric incompetence, so relaxing the bladder wouldn't solve the problem. I think of it as if you should try to close the door, so there are two doors, internal (sympathetic) and external (somatic, pudendal). In stress incontinence, the external door is not working, probably due to pudendal nerve injury after vaginal delivery or obesity. So you should try to close the remaining door, the internal sphincter which contracts with Alpha 1 adrenergic stimulation.

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blue4415 wow ！ exactly what I think ～ nice metaphor +

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