Autonomic Pharmacology USMLE Step 1 Practice Question
A 62-year-old man with benign prostatic hyperplasia presents with progressive urinary hesitancy, weak stream, and incomplete bladder emptying over 6 months. His blood pressure is 138/86 mmHg and heart rate is 64 beats per minute. Current medications include lisinopril 10 mg daily and atenolol 50 mg daily. Digital rectal examination reveals a uniformly enlarged prostate (45 grams). Post-void residual volume is 95 mL. The urologist prescribes an alpha-1A-selective antagonist (tamsulosin) rather than a non-selective alpha-1 antagonist (terazosin). Which of the following best explains the pharmacologic basis for preferring the alpha-1A-selective agent in this patient?
Answer choices
- AAlpha-1A receptors have greater tissue penetration due to higher lipophilicity in prostatic tissue compared to vascular endothelium
- BAlpha-1A receptors predominate in prostatic smooth muscle, whereas alpha-1B receptors mediate vasoconstriction in systemic blood vesselsCorrect answer
- CAlpha-1A-selective antagonists undergo hepatic metabolism that inactivates the drug preferentially in vascular beds through first-pass metabolism
- DThe prostate expresses alpha-1 receptors with higher affinity for antagonists than vascular smooth muscle, allowing selective blockade at lower doses
- EAlpha-1A receptors in the prostate have a lower threshold for activation, allowing therapeutic effects at doses that cause minimal vascular effects
- FNon-selective alpha-1 antagonists are extensively protein-bound in blood, reducing their availability to prostatic tissue while maintaining vascular effects
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