Autonomic Pharmacology USMLE Step 1 Practice Question
A 62-year-old man presents to his primary care physician with a 2-year history of progressive urinary symptoms including hesitancy, weak urinary stream, and nocturia (3-4 times per night). He denies dysuria, hematuria, or abdominal pain. Vital signs are stable. Digital rectal examination reveals a smooth, uniformly enlarged prostate without nodules or tenderness. Post-void residual is 120 mL on ultrasound. Serum PSA is 2.1 ng/mL (normal <4 ng/mL). A diagnosis of benign prostatic hyperplasia (BPH) is confirmed. He is started on tamsulosin, a selective alpha-1A adrenergic antagonist. Which of the following best explains the mechanism by which tamsulosin improves his obstructive urinary symptoms?
Answer choices
- ABlockade of alpha-1A adrenergic receptors on smooth muscle in the prostatic urethra and bladder neck, reducing urethral resistanceCorrect answer
- BInhibition of 5-alpha reductase, preventing conversion of testosterone to dihydrotestosterone and reducing prostate volume
- CCompetitive antagonism at muscarinic receptors in the detrusor muscle, increasing bladder compliance
- DActivation of beta-2 adrenergic receptors on bladder smooth muscle, promoting relaxation
- ECompetitive inhibition of angiotensin II type 1 receptors, reducing prostate inflammation
- FNonselective alpha blockade leading to decreased vascular tone and improved tissue perfusion throughout the prostate
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