**Core Concept**
Fenoldopam is a dopamine D1 receptor agonist used in clinical settings to manage hypertension and reduce intracranial pressure. It selectively binds to dopamine D1 receptors in the renal, mesenteric, and cerebral blood vessels, leading to vasodilation.

**Why the Correct Answer is Right**
Fenoldopam's mechanism of action involves the activation of dopamine D1 receptors, which are coupled to Gs protein. This activation increases cAMP levels, leading to vasodilation and a subsequent decrease in blood pressure. Fenoldopam's selective action on D1 receptors minimizes its effects on peripheral dopamine receptors, reducing the risk of adverse effects such as tachycardia and hypotension.

**Why Each Wrong Option is Incorrect**
**Option A:** Not a dopamine receptor agonist, as it does not selectively bind to dopamine receptors.
**Option B:** Fenoldopam is not a dopamine D2 receptor antagonist, as its primary action is on D1 receptors.
**Option C:** Fenoldopam is not a non-selective dopamine receptor agonist, as it selectively binds to D1 receptors.

**Clinical Pearl / High-Yield Fact**
Fenoldopam's use in clinical settings is limited due to its short duration of action and potential for tachyphylaxis, making it a less preferred option for managing hypertension.

**Correct Answer: D. Dopamine D1 receptor agonist.**