Okay, let's tackle this question. The user is asking about an alpha-1 blocker that doesn't affect blood pressure. First, I need to recall what alpha-1 blockers do. They typically block alpha-1 adrenergic receptors, which are found in various places like the smooth muscles of blood vessels, the bladder neck, and the prostate. Blocking these receptors usually causes vasodilation, leading to a decrease in blood pressure. So, the question is tricky because most alpha-1 blockers do lower blood pressure.

Wait, the correct answer here is supposed to be an alpha-1 blocker without any effect on blood pressure. How is that possible? Maybe there's a specific drug that's selective for certain tissues. Let's think. Tamsulosin is a selective alpha-1 blocker used for benign prostatic hyperplasia (BPH). It targets the alpha-1A and alpha-1D receptors in the prostate and bladder neck, which are different from those in the blood vessels. Because of this selectivity, tamsulosin doesn't cause significant vasodilation or hypotension. So, tamsulosin would be the answer here.

Now, the other options. Let's consider typical alpha-1 blockers like doxazosin, prazosin, and terazosin. These are non-selective and block alpha-1 receptors in blood vessels, leading to decreased peripheral resistance and lower blood pressure. They're used for hypertension, so they definitely affect blood pressure.

So, the key here is the selectivity of the drug. Tamsulosin is selective for the prostate and bladder, avoiding the vascular effects. Other options are non-selective and thus lower blood pressure. The clinical pearl is that tamsulosin is used for BPH with minimal hypotensive effects because of its receptor selectivity.

**Core Concept**
Alpha-1 adrenergic receptors mediate vasoconstriction and smooth muscle contraction. Selective alpha-1 blockers like tamsulosin avoid systemic hypotension by targeting subtypes (α1A/D) in the prostate and bladder, sparing vascular α1B receptors.

**Why the Correct Answer is Right**
Tamsulosin is a high-selectivity α1A/α1D blocker. It relaxes prostate and bladder neck smooth muscles without significantly blocking vascular α1B receptors. This avoids systemic vasodilation, making it ideal for BPH with minimal hypotensive effects.

**Why Each Wrong Option is Incorrect**
**Option A:** Prazosin is a non-selective α1 blocker causing significant hypotension.
**Option B:** Doxazosin blocks all α1 subtypes, leading to vasodilation and blood pressure reduction.
**Option C:** Terazosin is non-selective, used for hypertension due to its systemic vasodilatory effects.

**Clinical Pearl / High-Yield Fact**
Tamsulosin’s selectivity for α1A/D receptors (vs. α1B) avoids hypotension, making it the preferred α-blocker for BPH. Remember: “Tamsu” for the prostate, “other α-blockers” for blood pressure.

**Correct Answer: C. Tamsulosin**

✓ Correct Answer: A. Tamsulosin