24. (2.0分) A 66-year-old man with chronic hypertension is treated with prazosin by his physician. The treatment successfully decreases his blood pressure to within the normal range. What is the mechanism of the drug's action?A. Inhibition of α1 receptors on vascular smooth muscleB. Inhibition of β1 receptors in the sinoatrial (SA) nodeC. Stimulation of muscarinic receptors in the SA nodeD. Stimulation of β1 receptors in ventricular muscle

本题考查药物作用机制，核心在于识别哌唑嗪（Prazosin）的药理作用及其作用靶点。

• 关键知识点：哌唑嗪属于α₁受体拮抗剂，通过阻断血管平滑肌上的α₁受体，引起血管舒张，从而降低血压。
• 解题思路：需明确各选项中受体类型与药物作用的关系，排除干扰项（如β₁受体、毒蕈碱受体等），锁定正确机制。

选项分析

A. Inhibition of α₁ receptors on vascular smooth muscle

• 正确。哌唑嗪通过竞争性阻断血管平滑肌上的α₁受体，抑制去甲肾上腺素的缩血管作用，导致外周血管舒张，血压下降。

B. Inhibition of β₁ receptors in the SA node

• 错误。β₁受体主要分布在心脏，抑制其功能会减慢心率、降低心肌收缩力，但与哌唑嗪的血管舒张作用无关。

C. Stimulation of muscarinic receptors in the SA node

• 错误。毒蕈碱受体（M受体）属于胆碱能受体，刺激其会导致心率减慢，但与哌唑嗪的机制无关。

D. Stimulation of β₁ receptors in ventricular muscle

• 错误。刺激β₁受体会增强心肌收缩力和心率，这与降压作用相反。